George Davidson
i RPR.TQVI
Professor of Geography
University of California
•50UTH KENSINGTON MUSEUM.
CONFERENCES.
SPECIAL LOAN COLLECTION OF
SCIENTIFIC APPARATUS,
1876.
SOUTH KENSINGTON MUS!
Jffo,
CONFERENCES
HELD IN CONNECTION WITH
THE
SPECIAL LOAN COLLECTION OF
SCIENTIFIC APPARATUS.
1876.
PHYSICS AND MECHANICS.
Published for the Lords of the Committee of Council on Education.
I5Y
CHAPMAN AND HALT,, 193, PICCADILLY.
LONDON:
FEINTED BY VINCENT BROOKS, DAY AND SOX,
GATE STREET, LINCOLN'S INN FIELDS.
CONTENTS.
SECTION—PHYSICS (including Astronomy). ^ ^
The President, W. SPOTTISWOODE, M.A., LL.D., F.R.S. : Opening Address . . t
W.M. HUGGINS, D.C.L., LL.D., F.R.S.: On Spectroscopy Applied to the
Heavenly Eodies other than the Sun .. ..
J. NORMAN LOCKYER, F.R.S
Professor SORET, of Geneva : On a Spectroscope with a Fluorescent Ocular Glass . .
H. C. SORCV, F.R.S., Prcs. R.M.S. : On Spectrum Microscopes and the Measuring
Apparatus used with them
M. RAOULPICTET : On Ice Making Machines
Sir W. THOMSON, LL.D., F.R.S. : The Principles of Compass Correction
Capt. EVANS •* " " ^5
M. ELIE WAKTMANN : On Experiments with the Radiometer .. 37
Mr, FLETCHER: On Anemometers 39
The PRESIDENT 4r
Professor TYNDALL, D.C.L., LL.D., F.R.S. : The Reflection of Sound .. .. 4*
Dr. STONE: On Just Intonation 49
Mr. BOSANQUET : On Instruments of Just Intonation 55
Dr. STONE: On the Limits of Audible Sound 5°
Mr. F. GALTON, F.R.S 6l
Mr. ALEXANDER J. ELLIS, F.R.S 64
Professor W. G. ADAMS, M.A., F.R.S. : On the late Sir Charles Wheatstone's
Acoustical Discoveries
Mr. W. CHAPPELL : Ancient Musical Science 72
Mr. J. BAILLIE HAMILTON : jEolian Instruments : •• -- 7*
M. TKESCA : Upon Objects Illustrating the History of Science and the means of
ensuring their conservation
The Earl of ROSSE. D.C.L., F.R.S.: On Thermopiles .. *
The Earl of ROSSE, D.C.L., F.R.S. : On Zullner's Astro-Photometer 9-
Mr. DE LA RUE, D.C.L., F.R.S. : On a New Form of Eattcry 94
Professor ANDREWS, M.A., F.R.S W
Professor DE ECCHER : The Italian Instruments at the Exhibition of Scientific
Apparatus •• •<•
Professor J. CLERK-MAXWELL, M.A., F.R.S. : On the Equilibrium of Heterogeneous
Substances .. .. •• •• *43
Professor ANDREWS, M.A., F.R.S. : On the Liquid and Gaseous States of Eodie . . 15°
Professor DEWAR : On the Charcoal Vacuum I55
>I. SARASIN-DIODATI : Upon Auguste De La Rive's Last Researches in Electricity 157
vi. CONTENTS.
PAGE.
M. LEMSTROM : On the Aurora Borealis ." .. .. '.+ •• 158
Mr. DE LA RUE, D.C.L., F.R.S.: Astronomical Photography 164
Professor BLASERNA, of Rome : On the Variable State of Electric Currents .. .. 173
Mr. BROOKE, M.A., F.R.S. : Magnetic Registration 177
Professor RIJKE : On the Historical Instruments from Leyden 184
Baron FERDINAND DE WRANGELL : On a New Form of Voltameter 189
Rev. ROBERT MAIN, M.A., F.R.S. : On a Newtoniaa Reflecting Telescope of Sir
W. Herschell 191
Professor DE ECCHER : Continuation of Remarks on the Italian Exhibits .. .. 195
The PRESIDENT : Closing Remarks .. ... »- 201
SECTION— MECHANICS (including Pure and Applied
Mathematics and Mechanical Drawing).
The President, Mr. C. W. SIEMENS, D.C.L., F.R.S.: Opening Address „ .. 204
Sir JOSEPH WHITWORTH, Bart., D.C.L., F.R.S. : On Linear Measurement .. .. 216
M. TRESCA 221
Mr. CHISHOLM 222
Sir JOSEPH WHITWORTH, Bart., D.C.L., F.R.S. : In Reply 226
Mr. C. W. MERRIFIELD, F.R.S. : On Solid Measurement 227
Professor Sir WM. THOMSON, LL.D., F.R.S. : Electrical Measurement .. .. 230
The PRESIDENT 251
M. TRESCA: On the Fluidity and Flow of Solid Bodies .. .. 252
M. TRESCA : The above Paper in the Original French .. .. ,. .. .. 25
The PRESIDENT 26
Mr. J. SCOTT-RUSSELL, F.R.S 2
The PRESIDENT: Remarks as to Explanation of Objects in Exhibition at Stated
Intervals . . 269
Professor ALEX. B. W. KENNEDY : On the Collection of Kinematic Models by
Professor Reuleaux, of Berlin 269
Mr. BARNABY : On Naval Architecture . . 284
The PRESIDENT .. 298
Mr. FROUDE, M.A., F.R.S. : On Experiments in Relation to Naval Architecture .. 298
Mr. THOMAS STEVENSON : On Lighthouse Apparatus 315
General MORI N: Isotes on Warming and Ventilation .. .. 329
Messrs. E. DENT & Co. : On Time Measurers 336
Mr. GLASGOW 344
F. J. BRAMWELL, M. Inst. C.E., F.R.S. : On Prime-Movers 348
The PRESIDENT 380
Mr. HACKNEY : On Furnaces 381
Mr. PREECE : Electric Telegraphs 4°6
The PRESIDENT : Closing Remarks 4*9
INTRODUCTION.
The Conferences in connection with the Special Loan Collection of
Scientific Apparatus at South Kensington Museum, of which these
volumes form a record, originated in a suggestion contained in a letter
addressed by the Right Hon. Viscount Sandon, M.P., Vice-President
of the Committee of Council on Education, to the Presidents of the
various Learned Societies. In this letter his lordship stated that it
had been represented to the Lords of the Committee of Council on
Education that the utility of the approaching Loan Collection of
Scientific Apparatus would be much enhanced, both to the English
and to the Foreign men of Science who might be expected to visit it, if
arrangements were made for explaining and demonstrating the method
of using the various instruments, as well as for reading papers on, and
discussing, scientific subjects ; and he added that their lordships
would be glad to afford every facility for earring out this proposal, and
they desired to suggest, that with this view the various learned
Societies should organise a series of Conferences similar to the
sectional meetings of the British Association for the Advancement
of Science.
In accordance with this suggestion a Sub-Committee was formed
consisting of the Presidents and Vice-Presidents of each of the
Learned Societies by whom the details of the scheme were considered,
and it was finally decided to recommend to their Lordships that the
Sub-Committees of the various sections should be requested to
undertake the organization 0*. the Conferences in those branches of
science which came within their cognizance. It was also proposed
that the Conferences should begin on the 1 6th of May, 1876, and last
till the end of the month, and that the subject of the Conferences
should be confined to the description and use of the instruments
exhibited. The following are the Sub-Committees to whose labours
the Lords of the Committee of Council on Education are so largely
indebted for the successful carrying out of this proposal.
Vlll.
INTRODUCTION
SECTION— PHYSICS (including Astronomy.)
President :
Mr. W. Spottiswoode, M.A., LL.D., F.R.S.
Vice-Presidents .-
II Commendatore Professore
Blaserna.
Mr. De La Rue, D.C.L., F.R.S.
Professor Carey Foster, B.A.,
F.R.S.
Professor Guthrie, F.R.S.
Herr Professor Dr. Hclmholtz.
Herr Professor Dr. Rijkc.
M. le Professeur Soret.
Professor Tyndall, D.C.L., LL.D.,
F.R.S.
Professor Sir W. Thomson,
LL.D., F.R.S.
M. le Professeur Wartmann.
SECTION — MECHANICS (including Pure and Applied
Mathematics and Mechanical Drawing.)
President :
Mr. C. W. Siemens, D.C.L., F.R.S.
Vice-Presidents :
Mr. F. J. Bramwell, F.R.S. I Dr. Werner Siemens
Mr. W. Froude, M.A., F.R.S. M. Tresca, Sous-Dirccteur du
M. le General Morin, Directcur
du Conservatoire
ct Metiers"
des Arts
Conservatoire des Arts et
Metiers.
Sir Joseph Whitworth, Bart.,
D.C.L.,F.R.S.
SECTION— CHEMISTRY.
President :
Professor E. Frankland, Ph.D., D.C.L., F.R.S.
Vice-Presidents :
Professor Abel, F.R.S.
Herr Professor Dr. Von Babo.
M. le Professeur Beilstein.
II Commendatore Professore
Blaserna.
M. le Professeur Fremy.
Dr. Gilbert, F.R.S.
Professor Gladstone, Ph.D.,
F.R.S.
Herr Professor Heintz.
Herr Professor Himly.
Herr Professor Dr. Ilofmann,
F.R.S.
Herr Professor Dr. de Loos.
The Right Hon. Lyon Playfair,
C.B., M.P., F.R.S.
Professor Roscoe, Ph.D., F.R.S.
Herr Professor Waage.
Professor Williamson, Ph.D.,
F.R.S.
Herr Professor Dr. Wolilcr.
F.R.S.
INTRODUCTION.
SECTION— BIOLOGY.
P? esident :
Professor J. Burdon Sanderson, M.D., LL.D., F.R.S.
Vice-Presidents :
Dr. G. J. Allman, F.R.S.
M. le Professeur Van Beneden,
F.R.S.
Herr Professor Cohn.
Herr Professor Dr. Donders,
F.R.S.
Professor Michael Foster, M.A.,
M.D., F.R.S.
Colonel Lane Fox.
Herr Professor Ewald Hering.
Dr. Hooker, C.B., P.R.S.
M. le Professeur Marey.
Professor Rolleston, M.D., F.RS.
SECTION-PHYSICAL GEOGRAPHY, GEOLOGY, MINING,
AND METEOROLOGY.
• President :
Mr. John Evans, F.R.S.
Vice- Presidents :
Herr Professor Dr. Beyrich.
M. Daubree, Directeur de 1'Ecole
des Mines, Paris.
His Excellency Dr. Von Dechen.
M. le Professeur Dewalque.
Mr. H. S. Eaton, President of
the Meteorological Society.
M. le Professeur Dr. Forel.
Mr. N. Story-Maskelync, M.A.,
F.R.S.
Professor Ramsey, LL.D., F.R.S.
Major-General Sir H. Rawlinson,
K.C.B., F.R.S.
Mr. W. Warington Smyth, M.A.,
F.R.S.
The Baron Ferdinand
Wransrell.
Von
A central room in the range of buildings in which the collections
were displayed was assigned for the purposes of the Conferences, and
the first, that on Physics, was held on the i6th May. The Right Hon.
Viscount Sandon, M.P., Vice-President of the Committee of Council
on Education, took the chair at the commencement of the opening
meeting.
His Lordship expressed his great regret that, owing to the special
pressure of official business which the Education Bill entailed upon him,
it would be impossible for him to attend the Conferences — and even on
that occasion, to do more than convey the assurance of his own gratitude
and that of Her Majesty's Government, to the men of science all over
x.^ u IN TROD UL TION.
the world, for their invaluable assistance to this unique undertaking,
which had made it, what he might now with confidence pronounce it
to be, a great success, of which not only this country but the civilized
world might be justly proud. He could not however refrain from
bearing his special testimony on this, the first public occasion which
presented itself, to the unwearied zeal which had been shown, and the
extraordinary sacrifices of time which had been made by the first men
of science in this country, working together as one brotherhood in
endeavouring to make this collection as complete, as useful, and as
widely instructive as possible. He would at the same time wish to
express the warm appreciation of Her Majesty's Government of the
exertions which had been made by gentlemen of the highest distinc-
tion in scientific pursuits on the Continent to promote the success
of this work to which their Governments have given a most cordial
and gratifying support. It was the earnest hope, both of the Lord
President and of himself, that this collection would not be a mere
gazing place where nothing but feelings of wonder and pride would
be excited by the past triumphs of science, but that much instruction
would be gained from it. With this view the preparation of hand-
books had been committed by the Education Department to gentle-
men of the highest capacity, and he had reason to believe that they
would be found invaluable aids to such instruction, and would be
considered to be in themselves of high intrinsic value. With this
same view they had given their cordial consent to the Conferences, of
which this was the opening meeting, and he trusted that at these
gatherings many an old friendship between the workers in the fields
of Science would be renewed, and many a new friendship between
those who were labouring in the same cause in the different countries
of the world would be formed, so that by the interchange of ideas and
the comparison of their various researches and labours, the seeds might
be sown on the occasion of this Loan Collection of Scientific
Apparatus, of fresh achievements, to the general advantage of the
human race.
Before they proceeded to the business of the day, he must be
allowed to call their attention to the high services which had been
rendered by the officers of the Science and Art Department, to the
undertaking, the success of which they were now celebrating : he had a
INTRODUCTION. xi
personal knowledge of the large extent to which that success was due
to their highly cultivated intelligence, their zeal, their resource, and
their ungrudging devotion of time, and, he feared he might say
health. He could only say that he was proud to serve the Queen in
his Department of the State, in concert with such officers.
In conclusion, he must express his disappointment that his special
Parliamentry duties this Session would prevent his deriving that
advantage from the Loan Collection which he would have wished,
and would rob him of the power of profiting by the opportunity to
make the acquaintance of the many eminent men who would be
gathered together by this exhibition, in the preparation for which he
had from the first taken a warm personal interest. It only remained
for him now to bid a hearty welcome on the part of Her Majesty's
Government to the men of Science who were, and who would be
gathered in these galleries from all parts of the world, and to renew
the expression of the hope that when these Conferences have come to
an end, and when this collection is dispersed, it might be found that
no unimportant assistance had been given to those who were labour-
ing in the noble cause of scientific investigations.
The Conferences were held on the following days : —
Physics (including Astronomy), i6th, igth, and 24th May ;
Mechanics (including Pure and Applied Mathematics and Measure-
ment), i;th, 22nd, and 2$th May; Chemistry, i8th and 23rd May;
Biology, 26th and 2Qth May ; Physical Geography, Geology,
Mineralogy, and Meteorology, 3oth May, ist, and 2nd June.
SECTION— PHYSICS (including Astronomy).
President: Mr. W. SPOTTISWOODE, M.A., LL.D., F.R.S.
Vice-Presidents :
II Commendatore Professore
BLASERNA.
Mr. DE LA RUE, D.C.L., F.R.S.
Professor CAREY FOSTER, B.A.,
F.R.S.
Professor GUTHRIE, F.R.S.
Herr Professor Dr. HELMHOLTZ.
Herr Professor Dr. RIJKE.
M. le Professeur SORET.
Professor TYNDALL, D.C.L.,
LL.D., F.R.S.
Professor SIR W. THOMSON,
LL.D., F.R.S.
M. le Professeur WARTMANN.
May i6//z, 1876.
MR. SPOTTISWOODE : The opening of this Exhibition may prove an
epoch in the science of Great Britain. We find here collected, for the
first time within the walls of one building, a large number of the most
remarkable instruments, gathered from all parts of the civilised world,
and from almost every period of scientific research. These instru-
ments, it must be remembered, are not merely masterpieces of con-
structive skill, but are the visible expression of the penetrative thought,
the mechanical equivalent of the intellectual processes of the great
minds whose outcome they are.
There have been in former years, both in this country and else-
where, exhibitions including some of the then newest inventions of
the day; but none have been so exclusively devoted to scientific
objects, nor any so extensive in their range as this. There exist in
most seats of learning museums of instruments accumulated from
the laboratories in which the professors have worked ; but these are,
by their very nature, confined to local traditions. The present one is,
I believe, the first serious, or at all events the first successful, attempt
at a cosmopolitan collection.
B
2 SECTION— PHYSICS.
To mention only a few among the many foreign institutions which
have contributed to this undertaking, we are specially indebted to the
authorities of the Conservatoire des Arts et Metiers of Paris, the
Physical Museum of Leyden, the Tayler Foundation of Haarlem, the
Royal Museum of Berlin, the Physical Observatory of St. Petersburg,
the Tribune of Florence, and the University of Rome.
Among those in our own country, we have to thank the Royal
Society, the Royal Institution, the Ordnance Survey, the Post Office,
the Royal Mint, the Kew Observatory, besides various other institu-
tions and colleges, which have freely contributed their quota.
To enumerate even the chief of the individual instruments of his-
torical interest would be a task beyond the limits both of my powers
and of your patience. But I cannot refrain from naming as especially
worth notice among the astronomical treasures, a quadrant of Tycho
Brahe', telescopes of Galileo, a telescope of Newton, some lenses by
Huygens, one of Sir W. Herschel's grinding machines for specula,
and a telescope made by himself in intervals between his music
lessons during his early days at Bath, at a time when, to use her own
words, his sister Caroline " was continually obliged to feed him by
putting victuals by bits into his mouth." This also is probably the
"mirror from which he did not take his hands for sixteen hours
together," and with which he may have seen for the first time the
Georgium Sidus. To come to later days, we have the original
siderostat of Foucault, lent from the Observatory of Paris, a com-
pound speculum by the late Lord Rosse, the photoheliograph from
Kew, and from still more recent times a complete transit of Venus
equipment, from the Royal Observatory at Woolwich.
Turning to other branches of physics, we have a " composed
microscope," now nearly three centuries old, constructed in 1 590 by one
Zacharias Janssen, a spectacle maker, possibly a connection, or at all
events a worthy predecessor, of M. Janssen, the celebrated astronomical
spectroscopist. We have an air-pump and two " Magdeburg hemi-
spheres," with the original rope traces by which horses were attached
in the presence of the Emperor Charles V., in order, if possible, to
tear them asunder, when exhausted by the air-pump. We have the
air-pump of Boyle, the compressor of Pappin, Regnault's apparatus
for determining the specific heat of gases, Dumas' lobe for the
OPENING ADDRESS. 3
determination of vapour densities, Fizeau and Foucault's original
revolving mirrors and toothed wheels, whereby the velocity of light
was first determined independently of astronomical aid, Daguerre's
first photograph on glass, and the earliest astronomical photographs
ever taken. To these may be added De la Rive's instruments for
statical electricity ; the actual table and appurtenances at which
Ampere worked ; and some contrivances as if fresh from the hands
of Faraday himself.
Yet rich as is this part of our collection, and interesting as it might
be made in the hands of one versed in the history and anecdote of the
past, we must not linger even about these pleasant places. Indeed, a
museum of only the past, venerable though it might be, would be also
grey with the melancholy of departing life. For science should be
living, instinct with vigour and organic growth. Without a con-
tinuance into the present, and a promise for the future, it would be
like a tree whose branches are broken, whose growth is stopped, and
whose sap is dried. And if I may carry the simile a stage further, an
exhibition of the present, with no elements of the past, would be like
the gathered fruits to be found in the market-place, ready to hand, it
is true, but artificially arranged. But when past and present are
represented in combination, as has been attempted here, the very
newest achievements will be found in their natural places as ripened
and ever-ripening fruit in the garden from whence they have sprung.
In reviewing the series of ancient, or at least now disused, instru-
ments, one thing can hardly fail to strike the attention of those who
are accustomed to the use of the modern forms. It is this — how much
our predecessors managed to achieve with the limited means at their
disposal. If we compare the magnificent telescopes, the exquisite
clockwork, the multiplicity of optical appliances, now to be found in
almost every private, and still more in every public, observatory, with
those of two centuries past ; or, again, if we look at the instruments
with which Arago and Brewster made their magnificent discoveries in
polarised light, in contrast to those with which the adjoining room is
literally teeming, we may well pause to reflect how much of their dis-
coveries was due to the men themselves, and how comparatively little
to the instruments at their command.
And yet we must not measure either the men or their results by this
4 ££C Tl ON— PHYSICS.
standard alone. The character of the problems which nature pro-
pounds, or which our predecessors leave as a legacy to our generation,
varies greatly from time to time. First, we have some great striking
question, the ver.y conception and statement of which demands the
very highest powers of the human mind ; unless indeed, the clear and
distinct statement of every problem may be regarded as the first and
most important step towards its solution. Next follow the first outlines
of the solution sketched in bold outline by some master hand ; after-
wards, the careful and often tedious working out of the details of the
problem, the numerical valuation of the constants involved, and the
reduction of all the quantities to strict measurement. It is in this
part of the business that the more elaborate instruments are especially
required. It is for bringing small differences to actual measurement,
for detecting quantities otherwise inappreciable, that the complex
refinements with which we are here surrounded become of the first
importance. But happily this somewhat overwhelming complication
is not of perennial growth, for, curiously enough, by a kind of natural
compensation, it relieves itself. In reviewing from time to time the
various aspects of a problem in connection with the instrumental
appliances designed for its solution, the essential features come out by
degrees more strongly in relief. One by one the unimportant parts
are cast aside, and the apparatus becomes reduced to its essential
elements. This simplification of parts, this cutting off of redun-
dancies, must not, however, be understood as detracting from the
merit of the original devisors of the instruments so simplified ; the
first grand requisite is to effect what is necessary for the solution of
the problem, then follows the question whether it can be done more
simply or by some better process.
And this leads me in the next place to advert for a moment to the
advantages which may accrue to the cultivators of science, and through
them to the nation at large, from a national collection of scientific
apparatus. Through the liberality of our foreign neighbours, and
through the exertions of our own countrymen, we have here a magni-
ficent specimen, an almost ideal exemplar, of what such a collection
may be. By bringing together in one place, and by rendering
accessible to men of science generally, the instrumental treasures
already accumulated, and constantly accumulating, we should not
OPENING ADDRESS. 5
only portray in, as it were, living colours the history of science, we
should not only be paying just tribute to the memory of the great
men who have gone before us, but we should afford opportunities of
reverting to old lines of thought, of repeating with the identical instru-
ments important but half-forgotten experiments, of weaving together
threads of scattered researches, which could otherwise be taken up
again only with difficulty, and after an expenditure of much and
irretrievable time.
Let me now turn for a moment to the other side of the picture. If
the collection in the midst of which we are here assembled is an
evidence of the valuable relics which still remain to us of the great
men who have passed away, the circumstances under which some of
them have found their way hither, and the vacant places due to the
absence of others, are no less evidence of how much the preservation
of such objects would be promoted by the establishment of a museum
such as I have ventured to suggest. Many circumstances contribute
to thrust into oblivion, or to put absolutely out of reach of future
recovery, original apparatus. First, the paramount importance and
immediate uses of an improved instrument or a new invention ; next,
in Government departments such as the Survey, the Post Office,
£c., the imperative demands of the public service, which leave little or
no time for a retrospect of the past ; and if I may add a word from
the experience of private individuals, the pressing calls of space and
expense lead the possessors to throw away, or to utilise, by conversion
of the materials to new purposes, apparatus which has done its work.
I venture to particularise one or two considerations, which will
probably have occurred to many of you, but which appear to me to
illustrate the above remarks. In the case of the Ordnance Survey it is
almost certain that the current work of the department would neverhave
required, and it is doubtful whether any private interposition would
have brought about the removal of the disused instruments, here
exhibited, from the cellars at Southampton. Again, the Post Office
would hardly have been justified in devoting valuable time to the
arrangement, or valuable space to the storage, of instruments no longer
on active service, except at the call of a public department, or for st
public purpose. And surely it would be a matter of serious regret
that the time already spent upon the collections now before us should
6 SECITON-PHYSICS.
have no issue beyond the purposes of the present exhibition. To tab.
another instance; we have here fragments, but only fragments, ot
Baily's apparatus for repeating Cavendish's experiments ; but of
Cavendish's own apparatus we have simply nothing. Again, Wheat-
stone's instrumental remains must inevitably have been broken up and
scattered or destroyed, if there had not been found at King's College
a resting-place, and authorities intelligent enough to appreciate and
willing to receive them. Of other individuals from whom apparatus,
now of historical interest, has been received, some from sheer lack of
space have been breaking up old instruments, while others, from a
modesty commendable in itself, were with difficulty persuaded of, and
even now are only beginning to perceive the value, in a national and
cosmopolitan point of view, of their own contributions. Lastly, there
is, I think, little doubt that, if the objects in question were to go
a-begging, they would be gladly received in some of the foreign
museums which have so liberally contributed on the present occasion.
To put the suggestion in a more tangible form I would venture to
suggest that, in the first instance, instruments whose immediate use
has gone by, but which are nevertheless of historical interest, lent
either by public departments or by private individuals, might remain
here on permanent loan ; further, that other instruments as they pass
out of active service — for example, from the Admiralty, from the
Board of Trade, from the Ordnance Survey, or from the other depart-
ments— should similarly find a place in this museum. In such a cate-
gory also might be included the scientific outfit of the " Challenger,"
and of the Arctic Expeditions, and likewise those of expeditions for
the observations of the transit of Venus or of solar eclipses. To these
might be added apparatus purchased for special investigations through
the parliamentary grant annually administered by the Royal Society.
And further if, as I would suggest, this deposit of instruments be
made without alienation of ownership, then private societies or even
individuals might be glad to avail themselves of such a depository of
instruments not actually in use.
In making such a suggestion, it must of course be assumed that the
custody of property so valuable in itself, and so delicate in its nature,
would be confided to a curator thoroughly competent for such a charge,
but I abstain from entering prematurely into further details.
ON SPECTROSCOPY. 7
And now let me turn in conclusion to one more aspect of this great
undertaking. We have here collected not only the instruments which
represent the most advanced posts of modern science, but we have
not a few of the men whose genius and perseverance have led the way
thither ; men who stand in the forefront of our battle against ignorance
and prejudice and against the host of evils which a better scientific
education must certainly dispel ; we have men whose powers are com-
petent for, and whose very presence is an inspiration to further progress.
But, while taking this first opportunity of offering them a hearty
welcome, I shall however best consult their feelings and your wishes
by abstaining from any panegyric upon them in their presence, and by
giving them an opportunity of speaking, and you of hearing them,
upon some of their own subjects in illustration of the remarkable
instruments which they have with so much pains and trouble brought
under our view.
Mr. WARREN DE LA RUE, in proposing thanks to the President,
strongly expressed a hope that the collection might be the nucleus of
a permanent one.
The addresses arranged for the day were then delivered as follows :
ON SPECTROSCOPY APPLIED TO THE HEAVENLY BODIES OTHER
THAN THE SUN. BY WILLIAM HUGGINS, D.C.L., LL.D., F.R.S.,
Corresponding Member of the Institute of France.
There is not much that is very new in the subject on which I have
been asked to speak. I will give, therefore, a short summary of the
methods and present state of this part of science. It is, too, not inap-
propriate in this great collection of instruments to say something of the
methods and instruments by which the results have been obtained.
When the spectroscope is to be applied to the heavenly bodies, the
first consideration which presents itself is as to the method by which
the image of the apparently moving heavenly body shall be made to
remain steadily under observation. This effect of the moving platform
on which the astronomer finds himself may be counteracted in two
ways, either by mounting the telescope on an axis parallel to the- earth's
axis of rotation, so that the telescope will follow the star by a uniform
8 SECTION-PHYSICS.
motion given to it by a driving clock, or by giving suitable motions by
clockwork to a large plane mirror placed in front of the telescope,
which may then be immoveable,so that the light of the star as it travels
from east to west will be always reflected in the same direction, and
the star's image consequently remain stationary at one place. This
latter instrument, called a heliostat or sidereostat according as it is
applied to the sun or to the stars, is well represented in this collection
by a beautiful apparatus designed by Colonel Campbell and constructed
for him by Mr. Hilger.
When by either of these methods we have obtained a brilliant and
stationary image of the heavenly body, it then becomes necessary to
interpose somewhere in the path of the light, a prism or prisms by
which it may be separated into the different kinds of light which come
to us bound up together in the star's light. A prism of small angle
may be placed before the object-glass of the telescope. This plan
possesses some advantages, but the size of the telescope is limited by
the size that can be given to the prism. The other and more usual
method consists in subjecting the light to the separating power of the
prism after it has been condensed by the object-glass or mirror. If a
cursory general examination of the spectra of stars only (the images of
which are points of light) is required, a very excellent form of apparatus
consists in placing a direct vision prism immediately in front of the
field lens of a negative eye-piece. When the eye-piece is withdrawn
for a short distance, the spectrum is seen well defined and of sufficient
width without the use of a cylindrical lens.
If measures, and especially comparisons with terrestrial spectra are
desired, and if the objects, as the nebulae and planets, have images of
sensible size, it is best to employ a complete spectroscope. Several
forms of this instrument by Mr. Browning are in the exhibition. The
slit of the instrument is placed exactly at the spot where the image of
the heavenly body is formed. The diverging rays are brought parallel
in the usual way and the spectrum is viewed in the small telescope
of the instrument.
Having by one of the above methods obtained the spectrum of a
heavenly body, we have to seek the best method of applying exact
measurement to the spectrum. This may be accomplished by some
"orm of micrometer, or by simultaneous comparison with a known
ON SPECTROSCOPY. 9
terrestrial spectrum. If the spectrum is sufficiently bright, webs or wires
may be moved along it by a screw, and the relative positions of the
lines obtained. If the spectra are faint, some method of illuminating
the wires may be employed, or the continental method of forming by
the side of the spectrum the image of an illuminated scale. Zollner
has applied the principle of the divided object-glass to the small
telescope, with the addition of a prism, by which one spectrum is in-
verted relatively to the other, and the distance to be measured doubled.
Perhaps the most convenient form of bright line micrometer is one
recently invented by Mr. Hilger.
For the purpose of accurate comparison with terrestrial spectra the
use of the ordinary little reflecting prism, before the slit, is not suf-
ficiently trustworthy, unless some special arrangements are adopted.
It is obvious that, unless the light from the terrestrial source comes upon
the slit in precisely the same direction as that from the stars, the
method fails in accuracy. Practically, the introduction of the spark
or vacuum tube in the axis of the telescope, at a distance of about
two feet from the slit, gives sufficient accuracy of identity of posi-
tion of the two spectra. The most perfect method consists in
causing the image of the spark, by a suitable arrangement of lenses,
to fall precisely at the spot where the image of the celestial body is
formed.
It is now time to state in a few words the principal results of spectrum
analysis applied to the heavenly bodies other than the sun.
We have learned that the planets Mars, Jupiter, and Saturn, have'
atmospheres not very dissimilar probably from our own. The spectra
of the more distant planets Uranus and Neptune indicate atmospheres
of a wholly different constitution.
This analysis has taught us that the fixed stars are truly suns after
the order of our own. The spectra of the stars are not precisely similar
to the solar spectrum. They differ too, greatly, from each other.
Roughly, the spectra of the stars may be arranged in some four or live
divisions from the brilliant Sirius to telescopic red stars. These dif-
ferences of the spectra point to different degrees of temperature, and it
may be, also, to some differences of chemical constitution. It is
evident that great differences of temperature would be sufficient to
give rise to different chemical conditions of the investing atmospheres
10
SECTION— PHYSICS.
of the stars, even on the supposition that the stars do not really differ
greatly as to the substances which compose them.
The spectroscope has revealed to us the true nature of the nebulce.
This diagram represents the latest results of a comparison of the lines
of the nebula with terrestrial spectra.
Of the four bright lines, the two more refrangible ones appear cer-
tainly to show the presence of hydrogen. The brightest line appears
In a small instrument to be coincident with the brightest line in the
spectrum of nitrogen. A more critical examination shows the nebular
line to be single, while the nitrogen line is double. The line of the
nebula is sensibly coincident with the less refrangible of the components
of the double line of nitrogen.
Spectrum of the Nebula in Orion.
Nebula
Hydrogen
Nitrogen
Hy H/3 N
The same method of research has told us, that, a part at least of the
light of comets is emitted by the cometary matter in a state of gas.
Further, that this matter contains carbon in some form, probably
combined with hydrogen.
Spectrum of
WinnecMs
Comet, 1868
Carbon Spark
taken in
Olefiant Gas.
When the presence of a terrestrial substance has been established in
a star, then it is possible by a more critical comparison with greater
dispersive power to find out whether the star is in motion relatively to
the earth in the line of sight.
If a small shift in the stellar lines is seen towards the more refrangible
u/V SPECTROSCOPY. n
end of the spectrum, then we know that the star is approaching the earth.
If the lines of the star are shifted towards the red, we learn that the
star and the earth are receding from each other. Further, an exact
determination of the amount of alteration of wave-length of the lines,
will tell us the velocity with which the star is moving in approach or
recession relatively to the earth.
The line F in Sirius compared with the line of hydrogen shows that
this star is receding with a velocity of 25 miles per second.
Solar Spectrum
line F
Spectrum oj
Sirius
Hydrogen in
Vacuum tube
In the case of Arcturus independent comparisons were made with
lines of magnesium, hydrogen and sodium. The lines in the star cor-
responding to "B," "F" and "D" of the solar spectrum were all found
to have a small shift towards the blue end of the spectrum as compared
with the bright lines of the substances to which they are due. This
shift of the spectrum shows that the star has a motion of approach.
These comparisons are represented in the accompanying diagram.
F 6 E D
~~T~ ~~TT~
Solar Spectrum
Spectrum of
Arcturus
Hydrogen line
Magnesium line.
Sodium line
H M<7
In a similar \vay, the motions in the line of sight of about 21 stars
were ascertained. It is obvious that by combining these motions with
those at right angles to the line of sight obtained, by ordinary astro-
nomical observation, the true motions of the stars may be discovered.
The latest contribution to this part of science was made by Mr.
12
SECTION— PHYSICS.
Christie at the meeting of the Royal Astronomical Society on Friday,
May 1 2th. His paper contains the following table of comparison of
the recent application of this method at Greenwich.
A COMPARISON OF STAR MOTIONS IN LINE OF SIGHT.
+ == RECESSION. — = APPROACH.
STAR.
HUGGINS.
GREEN-
WICH.
STAR. HUGGINS.
GREEN-
WICH.
a Andromedce
a Urstz Majoris \ — 46-60
— 40
Aldebaran
+ ?
j3 Leonis
+ ?
Capella
+
+ 20
Spica
+
+
Rigel
+
+
7 Urstz Majoris
+ ?
Betelgeuze
+ 22
+
Arcturus
— 55
31)
Sirius
+ 18-22
425
Bootes
p
— 8
Castor
+ 23-28
+ 25
a Coronce
+
+ ?
Procyon
Pollux
—49
+43
Vega
a Cygni
—44-54
—39
—37
—50
Regulus
+ 12-17
+30
a Pegasi
— -7
j3 Ursa Majoris
+ 17-21
+ 20
Mr. Christie concludes his paper by saying — " Notwithstanding the
difficulties (connected with the methods of observation) it is gratifying
to find that out of the list of 21 stars, which have been observed both
by Dr. Huggins and Mr. Maunder (the observer at Greenwich), there
are only two cases of discordance, as will be seen in the table ; and for
both of these stars Dr. Huggins has expressed himself dissatisfied with
his observations, whilst the Greenwich results rest on too few observa-
tions at present."
Mr. Christie informs me that since his paper was written, the motion
of the planet Venus has been observed by means of a small displace-
ment of the Fraunhofer lines of the sun's light reflected from that planet.
I am now engaged in applying photography to the spectra of the
stars. This investigation may throw much light on the relative tempe-
rature of the suns and stars, and on some other important points of
astronomical physics. The investigation is at present too incomplete
for me to give any statement of the methods, and of the results obtained.
Mr. J. NORMAN LOCKYER, F.R.S.,gave some account of the present
state of spectroscopic research as applied to Solar and Molecular
Physics. He confined his remarks to a few points in connection with
the instruments exhibited relating to the construction of a new Normal
map of the solar spectrum, together with a perfectly purified map of
ON SPECTR OS COP Y. 13
the metallic spectra, showing which lines of these latter are coincident
with dark lines in the solar spectrum and which are not, and thus
confirming the presence of elements suspected to exist in the sun's
reversing layer by previous observers, and proving the presence of
numerous others. Moreover, there are considerations which point to the
existence of solar elements which are quiteforeign to, or have not yet been
discovered in this world. Mr. Lockyer exhibited the maps which have
been constructed for this purpose, and, up to the present time new maps
have been constructed for the region of the solar spectrum comprised
between wave-lengths 39.000 and 43.000. The metallic spectra
for the whole of this region are not yet completed, as the amount of
labour involved in their production is very considerable. However,
the spectra of about one-half of the metals for the first two sections,
viz., wave-lengths 39.00-40.00 and 40.00-41.00, are nearly completed,
and these are, in all probability, absolutely pure. The method of
purification was then stated. Here the lecturer observed that he
was glad to have that opportunity of expressing his obligations
to Corporal Murray of the Royal Engineers, who had most efficiently
prepared the enlarged maps, which were finally photographed
down to the size desired. The enlarged maps are drawn on twelve
O
times the scale of Angstrom, and the final photograph will be re-
duced to four times, this being none too large to ensure the
necessary amount of detail. To show how vast an improvement the
photographic map exhibits over that of Angstrom's, Mr. Lockyer stated
that whereas in Angstrom's map there were only three lines between
the H i and H 2 lines (of the solar spectrum), the present maps showed
ninety-nine. The lecturer proceeded to give some details of the
manner in which photography had been utilized in the research. The
instrument used consists of a spectroscope constructed on the model of
Bunsen and KirchofF s, with a train of four flint-glass prisms, 3 of 45°
and i of 60°. The observing telescope is replaced by a camera pro-
vided with a simple quartz lens of about 6 feet focus. By these means
the image of a tolerably large portion of the spectrum is thrown upon
the photographic plate at the end of the camera, and a good focus for
a part of the spectrum, at any rate, ensured. The novel feature of
Shis spectroscope consists in the adaptation of a sliding shutter to the
slit. It is well known that the width of a spectrum depends upon
14 SECTION— PHYSICS.
the extent of the slit exposed to the light, and this shutter admits
light only through a very small portion of the whole slit. By
successively exposing adjoining portions of the slit to the light
emitted from the incandescent vapours of metals whose spectra it
is necessary to confront with one another fcr the purpose of purification,
the final effect on the sensidizcd plate is that two or more spectra suc-
cessively record themselves thereon. All superposition of spectra and
gaps between them are guarded against by the following means. The
brass shutter with the square opening, slides in grooves in front of, and
up and down the slit. On one side of the shutter in one of the grooves,
holes are bored, the distance between each hole being the same as the
height in the opening of the shutter. A short pin fixed to a spring
falls into each hole in succession. The scale of measurement adopted
is a wave-length scale. In the first instance the solar spectrum as
obtained by the means here employed, being a refraction spectrum, is
reduced to a wave-length spectrum by means of curves of graphical
interpolation ; then the spectra of the metals being photographed side
by side with that of the solar spectrum, the measurements of the metallic
lines may be deduced from their position in relation to the dark lines
of the solar spectrum. Mr. Lockyer then mentioned that observations
made during his investigations led him to the conclusion that different
molecular aggregations produce five different kinds of spectra, viz. :
1. Line spectrum.
2. Channelled-space spectrum.
3. Continuous absorption at the blue end.
4. Continuous absorption at the red end.
5. Continuous absorption.
In fact modifications in the molecular construction of bodies would
produce a corresponding modification in the spectra themselves. Mr.
Lockyer also referred to some interesting experiments which he has made
in connection with the spectrum of calcium. When, for instance, the
chloride of calcium is subjected to a low temperature, we obtain
a line in the blue part of the spectrum, together with a nearly
complete spectrum of the chloride. This blue line is the blue line of
calcium. As the dissociation of the chloride progresses, the blue ray
becomes more brilliant and the chloride spectrum gradually disappears.
If, instead of the comparatively low temperature hitherto employed, we
ON SPECTROSCOP Y. 1 5
now make use of that of the electric arc, the [result is that this blue
line becomes extremely developed, and two additional lines in the
violet make their appearance, corresponding in position with the
two H lines in the solar spectrum. Now, in the sun, these two H lines
are the thickest in the whole spectrum, and the blue calcium line before
named is comparatively thin. The conditions in the spectrum of calcium
in the arc are just the reverse of this, the blue line being very much
thicker than the two violet lines. These facts suggested to Mr.
Lockyer that between the temperature here employed and that of the
sun, there should be a difference which affects the spectrum of
calcium in a corresponding manner, as the difference in temperatures
at our command affects the spectrum of the chloride of calcium. To
verify this, Mr. Lockyer made direct experiments upon calcium at
different temperatures, using for this purpose a large induction coil
and interpolating Leyden jars of different sizes, and by these means he
obtained at the lowest temperature the blue line without any trace of
the two violet lines, whilst at the highest the two violet were present
and the blue entirely absent. From these results, Mr. Lockyer argues
that here we may have a dissociation of calcium itself, seeing that a
parallel exists between them and the changes taking place during the
dissociation ot the chlo/ide. In conclusion, Mr. Lockyer justly
observed that this work was one which would have taken a single
individual very many years to accompli sh,but as portions had been
taken up by other workers at Owens College, Manchester, and at
Potsdam, a completion of this important work will be brought about in,
much less time.
Professor SORET (of Geneva) recalled that he gave, two years ago,
the description of a spectroscope with a fluorescent ocular glass
(Bibliothcque Universelle Archives, Sc. phys. et nat. 1874 t. xlix.,
p. 338.) The essential disposition consists in placing at the focus of
the telescope of an ordinary spectroscope, a thin plate of a transparent
and fluorescent substance, such as glass of uranium or a layer of a
solution of esculine between two lamels of glass. The ultra-violet spec-
trum is formed upon this plate, as in the celebrated experiments of
Professor Stokes, and it can be perceived with an ordinary positive
ocular glass, inclined towards the axis of the telescope.
This ocular glass was first applied to a spectroscope of which the
1 6 SECTION— PHYSICS.
prisms and the lens were made of ordinary optical glasses. Under these
conditions it is hardly possible to perceive rays more refrangible than N.
It remained to be seen whether the apparatus would work satisfac-
torily if use were made of prisms and lenses of quartz or of Iceland spar,
neither of which absorb rays of great refrangibility.
In one first arrangement, M. Soret followed the system of direct
vision employed by Herschel and Browning, the two prisms made
of Iceland spar being so cut that the crystallographic axis should
be parallel to the edges. The lenses are made of quartz. By this
apparatus the ultra-violet solar spectrum can be seen to the line R ;
but as much light is diffused (proceeding partly from extraordinary
rays, which are not included in the field of the spectrum) diaphragms
must be adapted to the tube for the observation to be easy. And
besides this, combination is somewhat difficult to carry out practi-
cally: it is necessary that the prisms should be extremely well cut
and adjusted with the greatest precision.
The second arrangement simply consists in fitting a prism of Ice-
land spar, in which the edges are parallel to the axis, to an ordinary
spectroscope furnished with lenses of quartz.
By concentrating the light of the sun upon the slit of this spectroscope
by means of a quartz lens with a long focus, the solar spectrum can
easily be distinguished as far as S ; if use is made of the light of the
Voltaic arc between different metals, the very refrangible brilliant lines
can be most easily perceived in it. Thus with cadmium all the lines
pointed out by Mr. Mascart can be seen up to the 25th.
With regard to the nature of the fluorescent substance on which the
spectrum presents itself at the focus of the lens, a solution of esculine
in water seems to be the most favourable for the observation of the
part between H and O. For radiations of greater refrangibility, glass
of uranium is preferable.
The spectroscope with a fluorescent ocular glass, without having,
perhaps, the precision of the photographic method, has nevertheless
great advantages for rapid observations. It allows of angular measure-
ment being taken, if, beforehand, two lines, in the shape of a cross,
have been drawn on the fluorescent plate, which would fulfil the func-
tions of a reticule. It can be used for a great number of researches.
MM. Soret and Sarasin have employed it for measuring the rotatory
ON SPECTRUM MICROSCOPES. 17
power of quartz ; their observations — which are not yet ended— go as
far as the line R.
But it is chiefly to the use of this apparatus for astronomical obser-
vations that M. Soret wishes to draw attention : the study of the ultra-
violet spectrum, in the centre or on the edges of the solar disc, in the
protuberances and in the spots, would be most easy with this instru-
ment, especially by adapting it to reflecting telescopes ; it would no
doubt lead to interesting results.
ON SPECTRUM MICROSCOPES AND THE MEASURING APPARATUS
USED WITH THEM. By H. C. SORBY, F.R.S.; Pres. R.M.S., &c.
The object of the author was to exhibit and explain the various kinds
of apparatus shown in the Exhibition, that had been contrived to
examine and measure the spectra of small coloured objects seen under
the microscope. The first form was that described by the author in
the Quarterly Journal of Science for 1865, vol. ii., p. 198, in which the
slit was placed some distance from the microscope, and the prism
under the achromatic condenser, so that a small image of a spectrum
was seen in focus at the same time as the object on the stage. The
characteristic spectrum of the object was then shown by the absorp-
tion of particular rays. In this form of apparatus the measurement
of the spectra was effected by means of a micrometer placed in the
eye-piece. The original apparatus is exhibited. It served very well
to prove that a wide field for research would be opened out by the
further use of the instrument, but it was soon found to be very incon-
venient not to be able to observe the spectra of very imperfectly
transparent or opaque substances. This led to the adoption of a
spectrum eye-piece, in which the slit is placed in the focus of the eye
lens, and compound direct-vision prisms are placed over it. They can
thus be taken off, and the object seen through the opened slit, and
then on closing up the slit and placing on the prisms the spectrum of
the object can be seen. A reflecting prism and side stage enable the
observer to compare two spectra together. Eye-pieces of this kind are
exhibited by Mr. Browning and Messrs. Becks, and another by Mr.
C
1 8 SECTION— PHYSICS.
Pillischer, in which the prisms can be pushed on one side, and the
object seen through the slit without taking off the prisms. These
spectrum eye-pieces can be very conveniently used with a binocular
microscope, since the natural object can be found and examined by
means of one tube, and its spectrum seen by the other tube.
For the sake of compactness in a travelling microscope, a mov^able
slit fitting into the eye-piece like a micrometer may be used, as exhibited
by Messrs. R. and J. Beck.
All these eye-piece methods have the advantage of enabling us to
examine the spectra of very minute objects, but the author has found
that when they are of moderate size, it is more convenient and less
trying to the eyes to make use of the binocular spectrum apparatus,
described in his paper in the Proceedings of the Royal Society for 1867,
vol. xv., p. 433. The slit and small reflecting prism are placed at the focus
of a special object glass of low power, and the direct vision prisms are
fixed between the slit and the lens. With this arrangement, it is, how-
ever, necessary to insert a cylindrical lens to make the spectrum in
focus at the same time as the line of division between the two spectra
which are compared side by side. An apparatus of this kind is exhi-
bited by Messrs. R. and J. Beck.
For the measurement of the position of the absorption bands seen in
spectra, the author has contrived and regularly used for many years
a standard spectrum produced by means of a plate of quartz, cut
parallel to the principal axis, placed between two Nicol's prisms, as
exhibited by Messrs. Becks, which gives twelve well-defined bands,
spread regularly over the spectrum, as described in the paper in the
Proceedings of the Royal Society already named. For quick and
moderately accurate measurements this plan is very convenient. The
chief objection is the difficulty of so preparing the plate of quartz, as to
give the bands exactly in one uniform position in every scale. Mr.
Sorby, however, proposes that in all cases the position of bands should
be expressed in wave-lengths ; and if each observer made a table of
wave-lengths for the quartz scale used by him, perfect identity in the
position of the bands is of very little importance.
Mr. Browning exhibits the bright slit micrometer made by him to
measure the position of absorption bands, as described in the Montfily
Microscopical Journal for 1 870, vol. iii., p. 68. For certain purposes this
ON SPECTRUM MICROSCOPES. 19
is very convenient, and with some modifications suggested by the author
may probably be much improved. Each observer should construct a table
applicable to his own apparatus, and describe the results in wave-lengths.
The chief objection to such a form of instrument is the absence of a
fixed datum, and the necessity of verifying the adjustment by reference
to the sodium D-line, and also the fact that the measurements vary
with the focal adjustment. In order to overcome these difficulties, and
also to be able to measure with greater accuracy than is possible with
the above-named quartz scale, in which the bands are fixed, the author
has contrived an instrument, exhibited by Messrs. R. and J. Beck,
fully described in a paper in the Monthly Microscopical Journal for
1875, vol« xiv-> P- 269- This consists of a piece of quartz, i£ inch long,
cut and mounted so that the light passes in the line of the principal
axis ot the crystal, along which there is no double refraction, but
circular polarisation. This is mounted between two Nicol's prisms,
one of which can be rotated along with a graduated circle, and the
other turned for adjustment. This gives a spectrum with seven black
bands, each of which moves into exactly the position of the one
above or below for each half revolution of the circle, which is so
graduated that it can easily be read off to one one-hundredth of
this half revolution. The author has constructed a table of wave-
lengths, as ascertained by using a diffraction spectroscope. By means
of this new apparatus it is easy to measure the position of the centre
of well-marked absorption bands to within one-millionth of a mille-
metre. The chief objection to the apparatus is that it is somewhat
large, but by placing it under the stage in the fitting made for the con-
denser, using the binocular spectrum arrangement, and placing the
object in front of the reflecting prism, very excellent results can be
obtained. It must, however, be admitted that it will be of use more
for ascertaining the general laws of spectra and the value of minute
differences, than for carrying out the ordinary kind of qualitative
analysis of colouring matters for which the spectrum microscope is so
well adapted. For this kind of research various branches of biology
furnish an almost boundless field, and promise most valuable results.
Professor CLIFTON, F.R.S., after giving a sketch of the history of the
discovery of phenomena of interference of light, and of the progress
made in the investigation of this branch of optics, drew attention ta
20 SECTION- PHYSICS.
some of the instruments in the Exhibition, intended to facilitate the
^lustration of this class of phenomena, and to enable the conclusions
of the undulatory theory of light to be compared with the results of
observation. He further described the method of adjusting the optical
bench, as arranged by himself, for repeating accurately the investi-
gations of Fresnel, Young, and others, and mentioned some results
obtained with this instrument in illustration of the close agreement
between observation and the deductions from the undulatory theory.
He also drew attention to the assistance which photography may
render in the study of interference phenomena, and exhibited some
photographs in illustration of his remarks.
The PRESIDENT : I will now ask M. Pictet to give an account of
the Sulphurous Acid Ice-Machine upon R. Pictct's Anhydrous
System.
M. RAOUL PICTET : In order clearly to understand the working of ice-
making machines, it is first of all necessary to explain the theory upon
which they are founded. Cold is produced by the evaporation of a volatile
liquid ; all liquids — without a single exception — in passing from a liquid
to a gaseous state, absorb a considerable quantity of heat, which is con-
sumed by the molecular work ; the constituent particles of the liquid
are strongly drawn together by the attraction of cohesion, heat
separates them, and thus does a great work. If, on the other hand,
vapours be compressed in a receiver, these vapours will transform
themselves into liquid, and will give out, during the process of conden-
sation, the same quantity of heat as that absorbed in their first change
of state. Thus, in theory, all liquids indiscriminately can, by their
passage through liquid or gaseous forms, be used for the artificial pro-
duction of ice. It is merely necessary to cause a volatile liquid to boil
in a closed vessel, surrounded by the water which one wishes to freeze ;
a pump continually draws away the vapours which are formed and com-
presses them in a condenser, in which they are condensed by means of
the temperature of a stream of water, and of pressure.
The mechanical theory of heat allows the exact relation to be estab-
ICE-MAKING MACHINES. 21
lished which exists between the work expended by the compression-
pump and the cold produced in the shape of ice.
The great differences which exist in the products of various ice-
machines are due solely to the practical considerations of which we
will now mention the chief.
Ether machines have to exhaust very rarified vapours, which have a
tension of but a few centimetres of mercury. They consequently
require immense cylinders for the pump. And, moreover, the relative
vacuum of the refrigerator allows the exterior air to penetrate, by the
slightest opening, into the interior of the apparatus, and thus com-
pletely frustrates the work of the machine. It is necessary to grease
the piston of the pump, and this grease mingles thoroughly with the
ether ; this has the effect of diminishing the volatilizing power of this
liquid. Finally, after many volatilizations the chemical state of the
ether transforms itself into acid substances, which differ materially
from sulphuric ether.
Accordingly, these machines do not work regularly in the factories
where they are used.
The ammonia machine of Card avoids many of these defects, inas-
much as ammonia is much more volatile than ether, but there is a
greater difficulty in the use of the machine — namely, the great pressure
which exists in the condenser and in the boiler. This pressure can
reach from eighteen to twenty atmospheres in hot countries, and thus
renders escape of gas inevitable and explosions much to be feared.
The grease, also, saponifies itself with the ammonia, and quickly
transforms itself into soap.
It can be perceived from these few words that the practical manu-
facture of cold for industrial purposes requires certain particular
conditions, which are not satisfied either by the ammonia or by the
ether machines. •.
It was to fulfil the various requirements of this question that I intro-
duced anhydrous sulphurous acid into the manufacture of ice.
This liquid plainly satisfies all the conditions requisite for carrying
on the process of manufacture regularly.
1. This liquid boils, under atmospheric pressure, at a temperature
of 10° of cold 15° Fahrenheit.
2. It never gives — even in the tropics — pressure greater than three
22 SECTION— PHYSICS.
and a-half atmospheres. This is very feeble to that given by
the ammonia.
3. This liquid cannot be decomposed, and has no action on metals
or grease.
4. This liquid, in a gaseous form, is so good a lubricator that all
grease is unnecessary.
5. By using this liquid all danger of fire or explosion is avoided.
6. This liquid can be produced at a lower price than that of ethei
or ammonia.
7. The price of a ton of ice, when sulphurous acid is used, is about
seven shillings, all told.
These are the principal advantages gained by the use of anhydrous
sulphurous acid in the manufacture of cold. I thank the Committee of
the Exhibition for having allowed me to explain my process.
The PRESIDENT : It is perhaps already known to most present
that the machine, which has been so well described by M. Pictet, is
exhibited downstairs, and is frequently in operation, so that you can
all see not only the results, but the actual modus operandi. I believe
I may say M. Pictet will have much pleasure in explaining it again on
the spot to any who may be desirous of understanding it.
I will now call on Sir William Thomson to speak on
THE PRINCIPLES OF COMPASS CORRECTION IN IRON SHIPS.
Sir W. THOMSON, LL.D., F.R.S. : Mr, President, Ladies, and
Gentlemen, the principles by which a compass in an iron ship may be
corrected so that it shall point to the true magnetic north in every
position of the ship, were pointed out about forty years ago by the
Astronomer Royal. He then shewed that by the application of masses
of soft iron, and also of permanent magnets, in the neighbourhood of
the compass, the whole disturbance produced by the iron of the ship
could be annulled and the compass brought to indicate the true north
in whatever position the ship's head might lie. In the Astronomer
Royal's investigation, however, there was a certain assumption made
regarding the magnetic induction, which could only be approximately
true for substances of exceedingly small inductive capacity, and which
was very far from being true for iron. The nature of this assumption
ON COMPASS CORRECTION. 23
was such that according to it a long bar of iron would have the same
degree of magnetisation by induction whether its length is held along
or across the lines of magnetic force. It seems strange that the
widely divergent character of the actual phenomena from those which
would result from this assertion did not strike him, his sole ground for
making the assumption being that there were no means of calculating
the difference between the amounts of effect in the two cases, and
that, therefore, they might be taken, for the sake of the investigation,
as being the same. This theoretical error was pointed out by Mr.
Archibald Smith, and an exceedingly curious result as regards the
effect of ships magnetism on the compass was also pointed out, when
the deviation from Mr. Smith's theory was also taken into account.
One point as regards the accuracy of the Astronomer Royal's method
of calculation, which would touch on this very important theoretical
point noticed by Mr. Archibald Smith, was that whereas, according to
the Astronomer Royal's theory, the compass would point correctly on
every course if corrected by magnets and soft iron placed in a certain
manner, which he points out ; according to Archibald Smith's
theory there might be a constant deviation left uncorrected, so that for
positions of the ship all round, the compass would point at a certain
angle from the true north and always in the same direction. This is
an exceedingly interesting result, and the consequences have been
followed out with great care and worked out by an exceedingly curious
and beautiful analysis, the method of doing which was pointed out by
Mr. Archibald Smith, which has been followed now most ably for
about thirty years in the Hydrographic Department of the Admiralty.
The nature of the disposition of iron which should produce that pecu-
liar effect discovered by Archibald Smith is essentially one in which
the masses of iron shall have a certain skewness or want of symmetry
in relation to the compass, so that when the compass is placed amid-
ships, and when the iron of the ship is symmetrical, as it usually is,
this peculiar term does not exist. Practically, as the compass is
placed in most ordinary ships, the amount of this effect is so small
that it may be regarded as practically insensible, and the indications
of it, which are found in the records of the Hydrographic Depart-
ment, may be considered as being in some degree due to inevitable
errors of observation. Still, I think I may be borne out in saying
24 SECTION— PHYSICS.
that there is perfectly distinct evidence in the Hydrographic Office
of the existence of this very remarkable result.
Having said so much, and having pointed out that, in the theoretical
point of view, an exceedingly important correction was required in
the' Astronomer Royal's theory, I must also point out distinctly that
the Astronomer Royal himself was conscious of the fact that his
theory made an assumption which was not rigorously true. He
justified it by the consideration that the results did not produce effects
of considerable importance with respect to the practical problem.
But there is just one thing in which this way of putting the Astro-
nomer Royal's case must be accepted with considerable reserve.
That is, that if any attempt were made on his theory to calculate
beforehand what would be the effect of particular masses of iron, such
as bars or globes, the theory would be found to be greatly at fault.
But if we merely take the integral result of the whole iron of the ship,
then we get precisely the same effect when the iron is distributed
almost symmetrically, as it is in all ordinary ships, as if the particular
assumption referred to had not been made. So that unless we wish
to calculate beforehand the effect of particular masses such as bars
and spheres, we may accept the Astronomer Royal's conclusion with-
out reserve. In respect to the estimation of the nature of the
effects produced by particular masses of iron in the ship, Archibald
Smith's more complete theory has been very valuable. The Astro-
nomer Royal's theory for instance could not have accounted for the
great effects that may be due to magnetic induction upon a vertical
mass of iron such as the stern post of a ship or a vertical staunchion.
But setting that aside altogether, and leaving what no doubt the
Astronomer Royal was ready to admit was a subject for special
investigation, the effect of bars and so on, and the fact that they
differ enormously in virtue of the mutual action of the different
portions of the iron from what they would be were such mutual action
insensible, then I have no more to say, but that the Astronomer Royal
has given a complete and practical method for correcting the compass.
When we come to some of the modern ironclads, such as the
Inflexible, in which I believe there are turrets unsymmetrically
distributed, that is to say a forward turret on one side, say the star-
board, and an after turret on the port side, then the want of symmetry
ON COMPASS CORRECTION. 25
must produce considerable effects, and may even produce that
remarkably curious effect, discovered by Archibald Smith. I need
not say any more on this point, but I would remind those who have
followed the investigations on this subject that the coefficient called by
the letter A. in Mr. Smith's theory may be looked for as being of
more practical importance in some of the modern ironclads with an
unsymmetrical disposition of iron than it ever has been in any other
ships hitherto. Before leaving the subject of this particular result,
I may say it would be altogether corrected, and permanently, on the
same ship, by shifting the needles round a little in the compass card,
so that the magnetic axis of the needles should be i?, i£°, or 2°, or
whatever it might be on one side or other of the true north. Then
that same compass card would always shew precisely the same result
as if this peculiar term called A. in Smith's theory did not exist. It
has sometimes been supposed that correction in the lubber line would
correct this error, but that is a mistake, it can only be done by a cor-
rection of the position of the needles in the compass card.
In respect to the principles of correction pointed out by the
Astronomer Royal, in the first place, the actual magnetism of the
ship's iron at any moment depends on two influences, the first being
the magnetisation which the iron has acquired somehow or other in
the process of manufacture. The hammering of bars of iron, if their
lengths be in any other direction than perpendicular to the lines of
magnetic north, tends to make them magnetic ; hammering masses of
iron when they are red-hot, and allowing them to become cold under
the hammer, produces this effect to a very marked degree, but it is
also produced even in hammering cold iron. The very hammering in
of the rivets in fastening the cold plates of the ship's sides shakes the
plates themselves in such a manner as to shake in a great deal of
magnetism. It shakes up the molecular structure, and causes them
to take magnetism due to the position in which they are when the
rivets are being hammered in. It appears that there is a great deal
of evidence of a very curious kind which has been collected by various
writers on this subject, to which I shall refer presently, shewing the
influence of the position in which the ship's head was when being
built upon the magnetism which she is found to have when launched.
Part of the magnetism thus hammered into the ship, as it were, is
c6 SECTION— PHYSICS.
held loosely, and is shaken out again, but part of it remains as long as
the plates remain attached to the frames, and the ship for twenty,
thirty, or fifty years, or whatever may be the life of an iron ship,
retains a very large part of the magnetism originally imparted to her
by terrestrial magnetic influence under the blows and shocks which
the metal experienced in the building. But besides the magnetism
which I have thus referred to, and which has been called by the
Astronomer Royal permanent magnetism and sub-permanent mag-
netism, and which has been called by Dr. Scoresby retentive magnet-
ism, which differs from induced magnetism which comes and goes
with the inducing force, there is a certain amount of magnetism
depending upon the position of the ship at the moment. The mag-
netic influence of the earth may be resolved into two components, a
vertical and a horizontal component. Whichever way the ship turns
the vertical component remains unchanged, and hence, as long as she
remains in one neighbourhood, or does not go to a different part of
the world, she experiences a magnetisation due to the constant vertical
component of the earth's magnetism. But, besides that, there is a
variable magnetism due to the horizontal component which differs
according to the position of the ship. Thus, when the ship's bow is
pointing to the magnetic north, magnetism becomes induced through-
out the whole of the ship, which makes the bow become a true south
pole and the stern a true north pole. When she is turned broadside
to the magnetic north, so as to point east and west, she experiences
magnetism in which the side next the magnetic north has a true south
magnetic polarity. Whatever permanent and sub-permanent mag-
netism there may be, this inductive magnetism comes and goes so far
as we know independently of it, so that the change of magnetism due
to turning the ship round is sensibly the same as if she had no per-
manent magnetism. It seems to me this is a subject which wants
experimenting upon, and one reason for my wishing to bring this
question before you is, that it seems to be one in which an impulse is
just now wanting for experimental investigation. Among other points,
it is very important to find whether the inductive magnetism is quite
independent of the permanent magnetism retained by the position of
the metal in question — to find whether a compass will, for instance,
experience the same inductive magnetism when it is turned into
ON COMPASS CORRECTION. 27
different positions relatively to the earth's magnetising forces as it
would if unmagnetised. We are almost without experimental infor-
mation upon this subject. Some most valuable experiments are being
made, and were communicated to the British Association Meeting at
Bristol last September, and they are still being continued by Rowland
in the New John Hopkins University at Baltimore, which promises to
be the greatest institution for experimental investigation the world has
ever seen. He is making exceedingly valuable investigations, the
result of which will be most important with respect to the problem of
correcting compasses at sea. In the meantime, so far as we know,
inductive magnetism takes place quite independently of any permanent
or sub-permanent magnetism of the ship.
The Astronomer Royal shewed that placing steel magnets in proper
positions in the neighbourhood of the compass corrects perfectly the
effect of the permanent and sub-permanent magnetism of the ship.
You will readily understand how that happens. Suppose the ship
itself to be a permanent magnet without change of magnetism, then as
the ship turns round it carries, so to speak, its magnetic force with it,
and if you apply a steel magnet, or set of steel magnets in the neigh-
bourhood of the compass whose magnetic force is equal and opposite
to the ship, the position beiug found by turning the ship round and
adjusting the distance until you find that the magnetic force of the
ship is exactly compensated by the steel magnets, then as you turn
the ship round into all positions the effect of the permament magnetism
of the ship will be annulled, and the compass will point just the same
as if the ship were non-magnetic. The ship and the magnets exercise, in
fact, a zero magnetic force upon the compass in its actual position.
But there remains the effect due to the induction. At first, let us
suppose that somehow the effect of the permament magnetism of the
ship has been annulled, and that we have nothing but the effect of the
magnetism induced according to the different positions of the ship to
deal with. Now, it appears, that if the ship is symmetrical, the effect
of the induced magnetism on the compass will be zero when the ship's
head is north or south, and when it is east or west. You will see that
readily. If you imagine the ship to be perfectly symmetrical, and the
Compass to be placed amidships, when the ship points due north it is
made magnetic by its inductive influence, with its true south pole
28 SECTION- PHYSICS.
towards the north, and its true north pole towards the south. That
magnet being perfectly symmetrical will exercise a force in the direc-
tion of the length of the ship, and will either augment or diminish the
force that the needle experiences from the earth, but it will not alter
the direction of that force. Consequently, the needle will point due
north, the magnetism induced in the ship notwithstanding. When
the ship's head is east and west, notwithstanding the inductive
magnetism of the ship, the perfect symmetry will still cause the needle
to point due north. This leads to the simple way of correcting the
errors in a symmetrical ship. We know that the error due to inductive
magnetism is zero when the ship's head is north or south, or when it is
due east or west ; then let the ship be placed north or south, and then
let the compass be made to point accurately by fixed magnets, then place
the ship east or west, and by another fixed magnet so arranged as not
to alter the effect of the first, let the compass be again made to point
correctly. Thus, by correcting the compass when the ship is north
and south, and again when it is east and west, we are perfectly sure
that we have annulled the effect of the permanent and sub-permanent
magnetism of the ship, provided always the iron of the ship is sym-
metrical.
It remains to correct the effect of the inductive magnetism of the
ship's iron. Now, I must introduce two names. The first is
"quadrantal error" — that name was introduced by the Astronomer
Royal when he brought forward the subject forty years ago — and
secondly : " semi-circular error," which was the name given by
Archibald Smith according to the analogy of that used by the
Astronomer Royal. The semi-circular error, is that due to the per-
manent and sub-permanent magnetism, whilst the quadrantal is that
due to the inductive magnetism of the ship by the horizontal com-
ponent of the earth's magnetism. It is called quadrantal, because it
has a maximum value in the middle of each of the four quadrants, from
north to east, east to south, south to west, and west to north. Thus,
the quadrantal error is at its maximum when the ship's head is north-
east, and is zero when the ship's head is east. Then it has a maximum
in the other direction when the ship's head is south-east, it is zero when
the ship's head is south, at the maximum again when the ship's head
is south-west, but in the same direction as when it was north-east.
ON COMPASS CORRECTION. 29
Then again, when the ship's head is north-west the quadrantal error
is at the maximum in the same direction as when the ship's head was
south-east. Let the quadrantal error be corrected in any one of the
maximum points, and the compass will point accurately for any
position of the ship. Get, first a north or south, then an east or west,
and then any one of the four quadrantal points correct by the
Astronomer Royal's method, and the compass will be correct for all
positions of the ship. This exceedingly beautiful and simple method
might seem at once to settle the whole of the problem of ship's
magnetism and allow us to send ships to sea with confidence that the
compass would always point correctly. But it would be a most
dangerous confidence, because there are a number of points which in a
short plausible statement such as that I have brought before you are
altogether overlooked, and points which are of paramount importance
in the practical problem.
First of all, can the correction be made perfect for any one place ot
the ship ? If the process I have indicated be carried out, and the
ship is sent to sea, will the compass be right within half-an-hour after
the correction is made ? It will not be right. It will be far wrong in
actual compasses and modes of adjustment to which the method has
been frequently applied, and is still very often applied. There is one
little assumption at the beginning of the Astronomer Royal's method in
his mathematical paper, which he makes in common with all mathema-
ticians—that is, that the needles are infinitely small. But what are
they in reality ? From about 7| inches long in the Admiralty standard
compass, to 14 or 15 in some of the compasses to which this method
has been applied. The consequence is, as discovered by Captain
Evans, that, although the compass is quite correct in the north and
north-east and east positions, and so on, there is an error amounting, if I
remember rightly, sometimes to about 5° in the intervening points.
In one of the compasses of the " Great Eastern," for instance, Captain
Evans found in turning the ship round to all points, that, although the
quadrantal error had been corrected perfectly enough for practical
purposes, for the north-east point there were errors in the intermediate
points having a maximum £ part of the way round from the earth
in one direction, and another error when another $. part of the way
round. These errors he called octantal errors. In conjunction with
3o SECTION— PHYSICS.
Mr. Archibald Smith, the theory of the octantal errors was worked
out and fully described in a paper communicated to the transactions
of the Royal Society of England, and published about the year 1861,
the title of the paper being Effect produced in the deviatiojts of the
compass by the length and arrangement of the compass needles ; and a
new mode of correcting the Quadrantal Deviation. This paper, by
Messrs. Smith and Evans, contains the mathematical investigation of
the theory of these octantal errors, and a very curious and interesting
result is arrived at, according to which these errors are very much
less with such a compass as the Admiralty standard, in which there arc
four needles instead of only two or one, as in many common compasses,
and with the needles arranged in a particular way, the two ends nearest
the north being 3oQ apart, and those on each side of them being, I
think, 30^ more, so that the four ends were placed at intervals ot 30?
from one another. With this particular disposition of the needles it
was proved that the octantal error was theoretically very much less,
and, by Captain Evans's experiments on the " Great Eastern," it
seems that, when an Admiralty compass was substituted for the great
compass with one needle which had been in the binnacle before, the
error was corrected nearly enough at all points by the correctors as
actually applied. That very dangerous kind of error then may be
considered as being rectifiable, and thus, although we cannot have
infinitely small needles, we can at all events have a correction which
will be perfect, or practically perfect, for the ship in all positions by
the correctors to which I have referred.
The quadrantal error has to be corrected by placing masses of soft
iron on each side of the compass, in such masses and in such positions
as shall, by the magnetism induced in them, counteract the effect of
the magnetism induced in the ship. The natural history of ships of
all classes, which has been worked out most admirably by the
Admiralty Compass Department, in respect of magnetism, worked by
the fullest development of the mathematical theory of Archibald
Smith, with the most thoroughly business-like perfection of detail,
and with great scientific accuracy of observation, and which has been
going on for thirty years, has given us knowledge which is of
inestimable value on this subject. Among other things it shows us
the amount of quadrantal error we have to meet with in different
ON COMPASS CORRECTION. 31
kinds of ships. One fact it brings out is, that the quadrantal error is
of such a kind that masses of soft iron placed not before and behind
the compass, but on the two sides of the binnacle (the starboard and
port side), will correct it. Where you have such an arrangement of
iron in such a ship, you could find a place (not the usual place for a
compass) in which the quadrantal error would be zero, or in which it
would be of the opposite kind, so that a mass of iron placed before it
and another behind it would be suitable for correcting it. But one
point brought out in the natural history of ships is, that the quad-
rantal correctors must be applied on each side for every ship in any
position of the compass.
There is one other point of considerable theoretical interest with
respect to quadrantal corrections which has hitherto escaped investi-
gation, and which has not yet been published. It is this, that even
with the Admiralty compass and its perfectness with respect to
escaping the danger of octantal errors there is another action which
vitiates the perfect completeness of that correctness, viz., that the
induction produced by the compass needles themselves upon the soft
iron correctors produces a very sensible disturbance. I will tell you
what I have in my mind about that. I found — to my surprise rather
— some years ago, that out of i2-£° of quadrantal error, corrected with
the Admiralty standard compass by cylinders of soft iron of the
dimensions recommended by the Compass Committee, only 6|°
were genuine, and 7° degrees depended on the influence of the
magnets of the compass card upon the correctors. That would not
in the slightest degree vitiate the correction as long as the same com-
pass is used and the ship remains in the same place. But if a
compass card with weaker magnets were used, then the correctors
would not be so efficacious, and if a compass card with more powerful
needles were introduced the correction would be overdone.
Now I have to refer to one most important and valuable
quality of the method of correcting quadrantal error, introduced
by the Astronomer Royal, and that is, that when once made for
a ship in any latitude, it remains perfect for that ship as long
as the iron of the ship remains unchanged, to whatever part of
the world she may go ; but that is on the assumption that the
needles are infinitely small, and of infinitely small magnetic moment,
32 SECTION— PHYSICS.
that last condition having never been stated. The state of the case
shortly would be this : with regard to quadrantal corrections with an
Admiralty compass, that, that which would be perfect and quite satis-
factory, and quite useful practically, as long as the ship remains about
the British Channel, or even about the British Islands ; if she goes
away to Labrador, where the horizontal component of the magnetic
force of the earth is much smaller, the quadrantal error would be
found to be greatly over-corrected ; or if she went to the magnetic
equator, where the horizontal force is much greater, the quadrantal
error would be under-corrected. Thus, the most valuable quality of
the quadrantal error is vitiated by the greatness of the magnetic
moment of the compass card in the best of the compasses hitherto
used at sea. Notwithstanding the fallacy in this respect, I should
say that the quadrantal error, if it were not possible to get compass
cards in which the defect would not exist, still the quadrantal error
ought to be corrected ; but there would be considerable awkwardness,
and the possibility of being liable to error, by being obliged to vary the
distance of the correctors according to the different latitudes. Thus,
the octantal corrector would want to be brought nearer the compass
at the equator, and moved farther away in high north or south mag-
netic latitudes. But, if we can get over the defect, and have the
quadrantal error, as has always been stated hitherto in books and
papers on the subject, perfect in all latitudes, it would be a very great
advantage. It was on this account, and also to avoid the octantal
errors that I was allowed a good many years ago to attempt to
produce practical working compasses with very small needles, and I
have now succeeded in obtaining an instrument which works well,
as I may say, from actual experience at sea with needles, the largest
of which is 3! inches, and of which the magnetic moment is utterly
inadequate to produce in any sensible degree the effect I have alluded
to. This is the largest kind of compass card that I have as yet made,
and it is really large enough for all practical purposes. I do not
think that any sailor could say that these divisions are not big enough
for him to see them, and certainly no navigating officer can say that he
cannot see them when he is using a sextant every day, and reading
the scale off to minutes. With this compass, correctors cannot be brought
nearer than within about 6 inches from the centre of the compass.
ON COMPASS CORRECTION. 33
The only reason for ever using a smaller compass than this,
provided this works well, except for purposes of convenience,
would be that if the quadrantal error to be corrected is very large, we
may want to bring the correctors nearer than the dimensions of the
compass card will allow. I have therefore, constructed a smaller one
with an 8-inch compass card, the length of the needle being rather
less than 3 inches. When there is a very great quadrantal error
to be corrected, as in some of the heavy ironclad ships, the masses of
iron required to correct it would be incoveniently great, and therefore,
I have taken as a convenient size for such correctors a globe of iron
6 inches diameter which weighs 31 Ibs. That is easily handled
and put in position, and does not sensibly increase the cum-
brousness of the binnacle. But if this is not sufficient I would rather
diminish the size of the compass then increase the size of the globe,
and therefore my practical rule would be this : if you want as large
a compass as this, use it, unless it requires more than a 6-inch globe
for quadrantal corrccton. If the quadrantal error does not exceed 5Q
a pair of 6-inch globes will correct it, and with a compass of this
size allows two such globes to be placed at the distance of 7 inches
on each side ; so that for any error less than 5° this sized compass is
perfectly convenient. When the quadrantal error is anything between
6° and n° I take a smaller size compass, allowing the correctors to be
brought within 7 inches of the centre of the card, and if the error
exceeds 11° and does not exceed 22Q then 6-inch correctors are stilt
perfectly available for a compass of this smaller size which has a
6-inch card. It really is not incoveniently small. It is as large as the
steering compass in many ships in the Navy, and therefore there is
not the slightest occasion for using incoveniently large correctors by
having a larger compass than that. If you imagine a ship with about
forty inches of iron sheathing such as the ships of the future will pro-
bably be, and with 200 tons guns, then perhaps even with this compass
you might want a ton or two of iron on each side, but in such a ship
perhaps even that would not be much thought of. It may be con-
sidered desirable however to have a somewhat smaller compass, and I
have therefore, made a miniature one. Although so small it can be
tossed about or rougly handled without being in the slightest degree
injured. I will now briefly explain the compass card. I have an.
D
34 SECTION— PHYSICS.
aluminium rim which is covered with a piece of paper gummed to it
in order that the compass card itself may be gummed on to that. The
card consists simply of a single thickness of paper, and I find it
necessary in the larger sizes to cut the paper radially, because when it
becomes heated by the sun it shrinks and tends to warp the rim into a
saddle shaped surface. That is obviated by radial slits in the paper.
The magnets are hung direct to the rim, and this specimen before you
is the first in which there is an arrangement for a perfect adjust-
ment of the magnets. I have got them out of position by throwing
it about, but I can adjust them in a quarter of a minute, and before
going to sea a little shellac could be applied to make the position
permanent. The magnets are placed in a row like a rope ladder,
being fastened by half hitches of silk thread around each magnet, like
the ratlins of a rope ladder. By the aid of a straight edge I can very
easily adjust the magnets exactly to the north and south line. The
magnets are hung on the rim by a silk thread and lastly the rim is
supported on the central boss by a silk thread also, that being put on
under equal tension in such a way as to secure exact and constant
centreing. The object is to get needles in a compass which will work
well at sea, and for this purpose it is found that a certain slowness of
period is necessary, accordingly I have a forty second period with
this, and this will be as steady at sea in air as any compass can be, so
that liquid compasses will be unnecessary. The other one has a
period of thirty three seconds, and the smallest has the same period
as the Admiralty compass, and therefore will have approximately the
same steadiness at sea.
With regard to the other correctors, I shall only say that a perfect
system of adjustment for different latitudes must be carried out. The
Astronomer Royal long ago pointed out this, and many patents have
been taken out for various methods of adjustment which have fulfilled
the conditions laid down by the Astronomer Royal with more or less
practical availability. I have endeavoured to introduce a system of
adjustment which would be more absolutely and perfectly simple and
ready in its use. I should have had great pleasure in shewing you a
binnacle with this compass in it, but by some mischance it is not
here. It is, however, in London, I believe, and you will have an
opportunity of seeing it from to-day forward. The variable effect clue
ON COMPASS CORRECTION. 35
to sub-permanent magnetism, varying, and to the different induction
produced by the different amount of the vertical component of the
earth's magnetic force in different parts of the world may also be
corrected. The rule will simply be to keep the compass correct on
whatever course you are steering, and once every three or four days,
or a week, or a month, according to circumstances, put the ship on
some other course, keep her on that course for a few minutes, correct
the error on that other course, and then the quadrantal error having
been once corrected originally, you may be perfectly certain that the
compass will be correct, and will remain correct until either the sub-
permanent magnetism of the ship changes or until she goes to. a
different magnetic latitude. It may be supposed that it is using too
strong a term to say it will be perfectly correct, and I admit that mathe-
matically there is no such thing as perfection. I mean as correct as
it is possible for a compass to be with the correctors which we have
in the ship. How small in fact can we get the practical error by
applying the table of corrections ? how near can we be sure of our
result ? Can we apply the table with any accuracy as supplied by the
Admiralty? Can we do it within a quarter of a degree, within i°, or
within 2° ? We can sometimes and sometimes we cannot, according
to circumstances. Then we can be neither more nor less near, and
neither more nor less sure, of the degree of nearness with which we
obtain our result by the application of the correctors on the
system which I am advocating, as by the application of the table of
errors on the principles laid down by Mr. Archibald Smith, and
practised thoroughly in the Admiralty, with the aid of the magnetic
correctors since introduced by Captain Evans. I must apologise for
having detained you so long, but* I thought the importance of the
subject warranted me in bringing it before you.
The PRESIDENT : 1 am sure we arc all much obliged to Professor
Thomson for the able manner in which he has brought this important
subject before us, and I have no doubt it is well known to many of you
that he is a bold British navigator himself, and therefore competent
to speak on both the theory and practice of the matter ; I beg to offer
our best thanks to Professor Thomson for his communication.
CAPTAIN EVANS : In case an erroneous impression should be left by
Sir \V. Thomson's very able remarks upon this new error which hc-hai
36 SECTION— PHYSICS.
found, arising from induction of the compass needle upon soft iion
correctors, amounting in some cases to 7° or 8°, I should wish it to be
understood that the Admiralty compass department have long recog-
nized the difficulty of applying these correctors for the quadrantal
deviation, and to avoid that source of error, or indeed any source of
error that may arise, they have inculcated the practice, and I think it
has been so far a very wholesome practice, of constantly observing the
amount of error of Ships' compasses. Sir W. Thomson rightly gave it
as a theoretical principle that when once this quadrantal deviation
was corrected it remained permanent in all parts of the world. That
which he described as the natural history of the ships of the navy we
have found very useful, and we know from it the quadrantal deviation
of every ship, and we also know this deviation remains constant in
all parts of the world. By not correcting the quadrantal deviation
we are enabled to see, knowing its constancy, that the compass has
been properly attended to. In attending to its values as given by the
officers in charge of the navigation from time to time as they progress
over the globe there is a great check upon them. We have found it
very useful in practice never to allow an officer to suppose that his
compass is correct, or that it can be practically accurately corrected.
Therefore from day to day they make careful observations, and it is
something like a man with his watch, if he knows it is five minutes in
error, he simply allows for the difference, and in the same way the quad-
rantal deviation is allowed for instead of being corrected. With reference
to these beautiful compass cards which Sir W. Thomson has brought
before us, I think I can see where they are likely to be of far greater
use than in the ordinary navigation to which he wishes apparently to
confine them. They appear to me to be likely to be of use in
those great iron-clads which he so well described, where there are
several apparently abnormal conditions, but which are in fact obedient
to law. I think they might be introduced there, and probably we
should have less trouble in correcting our compasses with the very
small needle that he employs than with the ordinary compass. That
leads me to another point. I consider Sir W. Thomson has done
good in calling attention to the advantage of using short needles.
When long ships were introduced both into the navy and the merchant
service, the idea prevailed that you should have large compasses, but
THE RADIOMETER. 37
really it should be just the reverse, and practically for accuracy the
larger the ship the smaller should be the compass. If I had my will
a ship like the Great Eastern instead of having, (as she originally had,)
a compass with a needle fourteen inches long, should have one of
three or four inches, as being more conducive to her safety. It would
take too long to enter upon either the theoretical or mathematical con-
siderations bearing on this subject ; but they are perfectly sound, and
my opinion is confirmed by the views that Sir W. Thomson has ex-
pressed in introducing these cards to your notice.
The PRESIDENT : Dr. Wartmann, Professor of Natural Philosophy
at the University of Geneva, will now give you an account of his expe-
riments with the Radiometer.
M. ELIE WARTMANN, Professor of Natural Philosophy in the Uni-
versity of Geneva : In the address which he delivered at the opening
of this conference, Mr. W. Spottiswoodc recalled to mind the invention
of the air-pump by Otto von Guericke. As soon as scientific men
knew how to produce a vacuum, they set to work to observe what
phenomena might manifest themselves in it. About the beginning of
the i Qth century, Sir Humphrey Davy proved that it is permeable to
heat, which influenced a thermometer placed in the middle of the
chamber of a barometer. Three years ago, Mr. W. Crookes, F.R.S.,
excited general attention by the curious instrument to which he has
given the name of the Radiometer. It is known that it consists of a
delicate mill, revolving freely in a glass vessel, in which the best
possible vacuum has been produced. This mill has four arms
supporting as many paddles (palettes), each one of which is painted
black on one side and white on the other.
This pretty instrument has, in England, often been called the " Light
Mill," and many persons are endeavouring to make use of it as a
photometer to determine the intensity of the light produced by gas
and by other means. This is the result of an erroneous impression which
ought to be removed. It is by no means light, as such, which cause3
the instrument to revolve, but solely heat, either luminous or obscure.
By exposing one of the blackened paddles to the focus of a large lens, or
of a concave mirror, the light of the full moon passing the meridian
may be concentrated on it without producing the slightest motion.
And it can likewise be proved that when revolving under the imluenco
38 SECTION- PHYSICS.
of heat, given out by a properly arranged Bunsen's burner, the mill
will keep up exactly the same rate of speed whether the flame be
rendered luminous or not.
There has been much difference of opinion as to the cause of the
rotation of the arms. To solve the difficulty I have made a great
number of experiments, of which I shall mention but a few. The
Radiometer is not affected by electrical sparks, produced outside and
quite close to the globe in which it stands, however intense or
often repeated they may be. But under a magnetic current its metallic
arms are influenced, and its motion is either partially or completely
arrested. If, by means of lenses of equal power (ouverture), the
radiation of exactly similar moderator lamps be concentrated on both
surfaces of the same paddle, a perfect equilibrium can be obtained by
placing the white surface always much closer than the blackened one.
This equilibrium is established when the intensity of the radiations on
each surface is in inverse ratio to their absorbing power. The slightest
change in the distance of, or in the degree ot power displayed by the
lamps, is sufficient to set the machine in motion.
In a horizontal plane, and concentrically to the axle of the radio-
meter, let an iron ring, thirty centimeters in diameter, and heated red
hot, be presented to the mill. The arms will immediately revolve with
a velocity which becomes very great indeed, when the plane of the
branches which support them is mingled with the plane of the ring.
The speed produced is the same, at equal distances from the ring, cither
above or below this plane.
The radiometer, placed either in the air or in water, does not move
when heat is applied equally in all directions. And this is the case
even at the most elevated temperatures.
If strong solar heat be concentrated on the paddles of the mill, the
mica, of which they are made, is partly split, and the instrument
pervaded by a grayish smoke; from that moment it loses a very great
part of its delicacy.
When the same radiometer is repeatedly exposed to the focus of
an optical instrument, which collects the rays of a powerful lamp, an
occasional deposit can be seen gradually forming inside, which is com-
posed of a material that has been vaporized, and which at times assumes
the appearance of sublimated crystals. I suppose it is produced by the
NEW FORM OF ANEMOMETER. 39
impurities contained in the smoke-black, or in the alcohol used to lay
it with a brush on the surfaces of the paddles ; and as pulverized coal
condenses vapours with an energy that is well-known, it is impossible
to avoid coming to the conclusion that the vacuum produced by
Sprengel's pump is by no means perfect. The pressure of the gases
which have not been removed varies according to circumstances, and
it is to the different degrees of this pressure that we must attribute the
various motions of the instrument invented by Mr. Crookes.
The PRESIDENT : I do not know whether Mr. Crookes is present,
but we should have been very happy to have heard anything from
him on this subject, which has excited so much interest both here and
on the Continent. If there is any other gentleman present who has
any remarks to offer we shall be very pleased for him to do so.
I am afraid Lord Rosse, who had promised to take a part in this
Conference, has been prevented by some means from coming, but Mr.
Fletcher is here, and he will give us an account of his Anemometers.
Mr. FLETCHER : When an effort was made to examine chemical
works with a view to carry out the provisions of the new Alkali Act it was
found necessary to measure the amount of vapour, gas or smoke which
was passing along the flues which entered the chimneys of the works, and
as a first step it was necessary to find out the speed at which the gases
were passing along. As there was corrosive vapour and soot, and in
many cases flame passing with the air, it was impossible to use the
ordinary Anemometer consisting of delicate mechanism of various
kinds, a light fan wheel passing round and the revolutions being
counted by delicately poised wheels. Of course, such an instrument
once introduced into a flue which was red hot would not shew any very
accurate indications when it came out again, therefore this Anemometer
was devised to answer the purpose which was wanted. It consists of
two tubes of ordinary gas piping which may be of any length.
One is bent at right angles, and the other is cut of short. They are
passed through a hole in the brick work and thus introduced in the
current of gas. If the vapour is passing upwards the bent one would
be turned down so as to receive the pressure into its open end, whilst
the other one is crossed by the current. The action in the open one
is to experience a slight vacuum or exhaustion, and a slight pressure
experienced in the bent one. By flexible tubing the other ends of
40 SECTION— PHYSICS.
these tubes are attached to a simple U tube, mounted with some little
care, such as you see here, by which the pressure is measured. As
the exhaustion of the chimney operates on each lime equally, the ether
in the U tube will not be moved by it, but as one is drawn by virtue of
the slight vacuum experienced, and the other pushed by virtue of the
slight pressure, they both act in the same direction, and so the ether
used in this U tube is moved, one limb being depressed and the other
elevated. Affixed to the flexible tubes is a small switch or button, by
reversing which, the limb which was first depressed is elevated, and
•vice versa. In using the instrument the operation will be to place the
scales level with the surface of the ether in the first instance, then to
reverse the button, and then move the scale to the new position and
read again, and by deducting the one from the other, you get a reading
which is double the amount of the elevation. Thus if the difference of level
is Toth of an inch you get iVhSj and this double reading of course halves
the error. The question then was to find out how this was to be con-
nected with the speed, and for that purpose I made a mathematical
calculation which gave this formula, V=N/pX28.55. I made a number
of experiments with currents of air of known x'elocity for the purpose
of checking this result. There was some difficulty to get currents of air
of known velocity, but I accomplished it by getting a flue of 100
feet in length, connected with a chimney letting off a small flash of gun-
powder at one end, and by means of a pane of glass, by which I could
see through the flue, I counted the number of seconds which the
smoke took in coming from the starting point to the place where I
stood at 100 feet distance. Estimating the exact speed in that way,
and testing it with the instrument, I got the constant 28.50., being
only 5 from the figure given by calculation. I then calculated a table
accordingly. I also made a table of corrections for temperatures.
The first table gives the speed, supposing the air to be at 60°, but as
the air in these flues is often as high as 500°, or 1000°, that also
required a careful calculation, which I have given. I take this
opportunity of shewing this instrument, thinking it may be useful
to those who have to measure gases where ordinary Anemometers of
the mechanical kind cannot be introduced. In this there is no friction
whatever, as there are no moving parts. The column of liquid in the
Anemometer attains its position, and is there kept by the constant
NEW FORM OF ANEMOMETER. 41
pressure of the current of air. There is nothing to move backwards
and forwards, and therefore friction is out of the question. I can
measure the rate of air, supposing it is going at the rate of 4 feet a
second, and can tell it is not going at the rate of 4 feet I inch a second.
When it gets down to a very low speed, below 12 inches a second, its
action is very feeble, and that is the weak part of the instrument, but
when it gets up to anything like 4 feet per second you can tell with
great accuracy.
THE PRESIDENT : I have now to convey the thanks of the meeting
to all those gentlemen who have favoured us with communications
this afternoon. It is remarkable to observe how subjects connected
with light have come forward. They were dealt with this morning
and have again reappeared for our consideration this afternoon. The
mode in which the different branches of optics which turned up this
morning, in the first place dispersion, then fluorescence, then inter-
ference and polarisation, keep cropping up here and there, shows how
very much all these different branches of the subject, notwithstanding
the care with which they are kept apart, as subjects of actual research,
do flow into one another, and by their mutual interference throw light
upon one another. The arrangement for our next Physical Conference,
which takes place on the iQth, are nearly complete, but I hope the
audience will always remember that we are indebted very much to
the voluntary assistance of those who are good enough to make
communications, and that our arrangements are, at all times, liable
to some kind of disturbance. Nevertheless, I feel quite sure that we
shall never lack for interesting matter during the Conferences.
SECTION— PHYSICS (including Astronomy).
May 19/7^, 1876.
The PRESIDENT : Ladies and Gentlemen, as it is now the hour of
commencement I think I need make no preface whatever in the case
of our first communication, but have only to mention the name of
Professor Tyndall to insure an attentive audience. I therefore call
upon Dr. Tyndall to give us his communication upon his remarkable
experiments upon the Reflection of Sound.
Professor TYNDALL, D.C.L., LL.D., F.R.S. : If gas be permitted to
issue from a nipple with a circular orifice, such as I now hold in my
hand, and if it issue under a very low pressure and in a very calm at-
mosphere the column of unignited gas will rise to a height, or can be
made to rise to a height of from eight inches to a foot or more. Great
calmness on the part of the atmosphere is required to accomplish this,
and if with the gas, smoke, or some other floating matter be associated
you can see the column rising through the air to this height. If you
augment the pressure a little very soon that column breaks up and you
have the gas issuing from the nipple thrown into tourbillons or vortices.
If you ignite that gas then those vortices instantly disappear, and a
flame more or less tall arises from the burner. You can then go on
augmenting your pressure, doubling it, trebling it, or even quadrupling
it, and it may be even more than this, the flame at the same time be-
coming taller and taller. You can in this way, with appropriate gas,
raise your flame to a height of eighteen inches or two feet. But if you
go on augmenting the pressure you come to a point where the ignited
jet also breaks up into those vortices, or tourbillonsj the gas flares,
to use a common term, but if, before the gas jet or flame reaches
this point, you bring it just to the verge of flaring, then by an
REFLECTION OF SOUND. 43
appropriate musical sound that gas is utterly broken up, and the
flame which would burn silently without the action of the musical
vibration at a height of two feet, will fall suddenly and break up
and roar at a height of only eight or nine inches. Here is a flame
issuing from a nipple such as I have described. The pressure is so
arranged as to bring it near the point of flaring, and a very slight
action of an appropriate sound upon the flame will bring it down,
abolishing the light altogether. Thus, when I take this bunch of
keys and shake them, the noise of the keys brings the flame down.
In such a flame we have a re-agent of extraordinary delicacy as
regards musical vibrations. We are indebted for the discovery of
this action of sound upon flame to one of the most remarkable men
in the United States, a man whom I am sorry to say was cut off
by the war from active work in science for some time, but he is
now engaged upon it again ; I mean Professor John Le Comte. He
observed this action of sound, and, moreover, he gave us the distinct
intimation that the flame required to be brought to the edge of flaring
in order to get this effect. You bring the flame to the edge of a
precipice as it were, and the musical sound pushes it over. Sub-
sequently, when I had the honour of his assistance at the Royal
Institution, Professor Barrett observed this effect also upon a flame,
and afterwards made various interesting experiments upon the subject.
It has also been experimented upon by Mr. Philip Barry and by my
present excellent assistant, and I have done something towards
exalting the sensitiveness of the flame myself. It is to be our
re-agent at the present time. Many of my continental friends who
desire to repeat these experiments find some difficulty in doing so,
because a full exposition of the proper conditions necessary to success
has never yet been given. Hence, my reason for introducing the
subject here. It is advisable to have a gas-holder that will enable
you to apply considerable pressure, and the gas-holder before you is
loaded in the manner you perceive, in order to bring the flame to the
required proximity to its point of flaring. It is also desirable that all
passages between the burner and the gas-holder should be fully open.
This is a point ot considerable importance. With regard to the seat
ot sensitiveness in this flame, the action is not caused by the im-
pinging of the sonorous waves upon the nipple, it is not caused by the
44 SECTION— PHYSICS.
impinging of the sonorous waves on the flame higher up. The action
occurs in the orifice. Converging the sonorous waves of a small
vibrating reed upon the nipple, a little below the orifice, they produce
no effect. Causing the waves to converge higher up, there is no
action upon the flame. Converging the waves on the orifice itself,
violent action occurs on the flame. We are to make this flame the
test of the reflection of sound. When my excellent friend, your
Chairman, mentioned the reflection of sound, he meant it to be from
the limiting surfaces of gaseous layers, not the ordinary reflection
of sound from the surfaces of solids or liquids. This is the pecu-
liar feature of the experiments that these echoes will take place at
the limiting surfaces of layers of gas. And here, I think, we may
confine ourselves, inasmuch as I know there are many gentlemen
coming after me, to one illustrative experiment. For the purpose of
making that experiment we have this apparatus devised, I may say,
by Mr. Cottcrell, and executed by Messrs. Tisley and Spiller. Through
a series of apertures, we might throw into this apparatus air saturated
with various vapours ; such, for example, as the vapour of ether. We
should, in this way, destroy the homogeneous character of the air in
this horizontal tube. But instead of making an experiment upon
vapours, I pass on to one .representative experiment which will enable
you to infer the character of all other experiments made with this
apparatus. Underneath this tube are apertures through which, when
this series of gas flames are turned on, the columns of heated air
from the gas flames will enter the tube. In that way, instead of
having a homogeneous horizontal column of air, we obtain a column
of air wherein heated layers alternate with cooler layers. The action
of this upon the sound will be made manifest to you. At every
passage of the sound wave, from the heated layer to the non-heated
layer, there is a slight echo, and those echoes occur even in that
short distance so frequently as entirely to waste the direct sound in
echoes. It is precisely analagous to the action of a cloud or of foam
upon light. You have there the mixture of two transparent sub-
stances— air and water — and in virtue of those repeated reflections
at the limiting surfaces of both, the mixture of those two transparent
substances becomes opaque. Foam becomes opaque, not in virtue
of absorption, but of these repeated internal reflections. My assistant
REFLECTION OF SOUND. 4S
will now start his reed and regulate the sensitiveness of his flame.
The flame, you observe, is steadied by the interposition of my hand
between it and the tube. And now, instead of my hand, my assistant
turns the series of gas flames round, the heated columns of air enter
the tube, and that moment the flame is stilled as effectually as when
I intercepted the waves with my solid hand. This experiment illus-
trates all of a similar class. We have operated with a great number
of gases. We have here, and can use, if necessary, carbonic acid gas,
hydrogen gas — anything, in fact, that will render the column of air
non-homogeneous. I said, subsequently, to my assistant that we
ought to be able, not only to shew the interposition of the sound
waves by these different layers of gaseous matter, but by proper
experiment to be able to make the echoes evident by their action
upon a flame. Mr. Cotterell, in an exceedingly ingenious and beau-
tiful manner, devised the means of doing so, and he will now make
his experiment himself. Two tubes are placed so as to form a V; at
the end of one of them is placed a vibrating reed, and opposite the
end of the other a sensitive flame. The two ends here referred to are
those widest apart. The sound from the reed passes down one tube,
impinges on the broad flame of a batswing burner, and is reflected
by it through the other tube to the sensitive flame, which is thrown
into violent agitation by the waves reflected from the hot gaseous
layer. As to the transmission of these sounds through different media,
it is very desirable that we should be clear upon this subject, inasmuch
as various theoretical notions have been entertained which had a very
important practical bearing as regards the establishment of sound
signals at sea. It was necessary to test these notions with the utmost
strictness, to examine the permeability of various kinds of air and
various states of the atmosphere for the waves of sound. Here is a
vibrating reed, from which the waves of sound will pass through the
tube, and act upon the flame. The interposition of my hand com-
pletely stops the action, and causes the flame to become quiescent.
I will next try a pocket-handkerchief. The sound waves go through
the handkerchief as if it were not there. I take a flannel, and you
will observe that it has hardly any influence on the sound. I double
it so as to make a thick blanket of four layers, and that is practi-
cally transparent to the waves of sound. Here is a thick woollen
46 SECTION— PHYSICS.
shawl, and you see that it has hardly any effect upon the waves of
sound, they go through it as if it were not there. I have here a piece
of close felt, impervious to the noonday sun ; it has hardly any effect
upon the waves of sound. They go through it almost as if it were
not there. Here are a hundred layers of cotton net all sewn together,
and you will see it has no sensible effect upon the waves of sound.
Here is another hundred which I add to them, and you see the thing is
sensibly transparent to the waves of sound. A piece of card-board,
on the contrary, immediately cuts off the sound. A piece of oilskin,
also, stops the waves of sound. Here is a piece of cambric, which
is really like nothing as regards its action upon the sound waves.
But the whole secret of it is, that these waves of sound possess the
power in a most astonishing manner of getting through any substance
in whose interstices the air is continuous. If you can suck the air
freely through a body, the waves of sound will go through it. This
piece of cambric, for example, has no sensible effect upon the waves
of sound. I dip it into water, so as to cause it to be thoroughly wetted
by the water, and when that is done you will find that its perviousness
to sound ceases. We have here a film of water filling up the inter-
stices of the cambric, and the result is that the sound waves are
entirely cut off. Let us repeat this experiment the converse way. I
put this cambric between bibulous paper and rub it, so as to take
away the water from the interstices, and you see its transparency to
sound is restored. I dip it again, and then it stops the sound. There-
fore, as long as there is no solution of continuity in the air, the waves
of sound possess this extraordinary power of permeation. You have
seen the action of these layers of differently heated air upon the waves
of sound. Sometimes the whole atmosphere is filled with these layers
of air of different densities produced in part by heat and in part by
different degrees of saturation ot aqueous vapour, so that you have
here what we may fairly call an acoustic fog in the air, uniformly
diffused through it. You can go beyond that. These masses of non-
homogeneous air sometimes drift through the air with definite bound-
aries, just as the clouds of the ordinary atmosphere drift over the
blue sky; and if you simply exercise the patience of observing a
bell or a clock strike with a certain definite force for a single week,
sometimes for a single day, you are able to see with the mind's eye,
REFLECTION OF SOUND. 47
those invisible accoustic clouds drifting through the atmosphere just
as certainly as the clouds that you see floating before your eyes
in the blue heavens. Standing, for instance at the end of the
Serpentine, and listening to Big Ben, let it be twelve o'clock in the
day, or twelve at night, you hear the first stroke of the clock with
powerful force — the second with power, the third absolutely quenched,
the fourth quenched, the fifth quenched, a feeble sound at the sixth,
the seventh comes out with sudden and extraordinary power, the eighth
with great power, the ninth and tenth are again silent ; and in this way
by observing a clock, or bell, struck with a definite mechanical power
you can realise to your minds the drifting of these acoustic clouds
through the atmosphere just as vividly as the clouds you see with your
eyes. Not only is this the case, but these accoustic clouds are also super-
posed upon ordinary clouds, and upon ordinary fog. You find this
action upon bells during foggy weather, the fog itself having no
sensible influence on the sound. Not by the most accurate measure-
ments can any sensible influence be established with regard to fog,
nor any sensible interception of the sound waves by the particles
of fog. To follow up the parallel a little further, you see a cloud
shone upon by the sun, and you sometimes receive dazzling white
light from the surfaces of that cloud ; those are the echoes, so to
say, of the light reflected back from the cloud. In precisely the
same way, with regard to these acoustic clouds, if you have your
source of sound strong enough, you get an echo of a most extra-
ordinary character. Put yourself in front of an acoustic cloud, and
you are able to detect by reflection the very sound that had been
refused transmission. I am sure you will find no difficulty in believing,
after having seen these experiments on bodies impervious to light,
but transmitting the waves of sound, that there is no connection
whatever between optical transparency and acoustical transparency.
What has been alleged regarding fog is also true of hail, rain, and
snow, and we find the same thing both by observation and by experi-
ment. I had a chamber at the Royal Institution, which I filled with
fumes, so dense that a layer of a couple of feet was sufficient entirely
to efface the strongest electric light. This fog was sometimes produced
by the combustion of gunpowder, sometimes by the combustion of
phosphorous, sometimes by the combustion of resin, and sometimes by
43 SECTION— PHYSICS.
the precipitation of a real cloud denser than any fog you have ever seen
in London, and still in no case did the fog or fumes exert any sensible
influence upon the waves of sound. The sensitive flame was as much
affected by the sound passing through these smoky media as when the
smoke was absent, whereas a couple of candles or a couple of gas
burners, placed within the chamber, in half a minute stilled the waves
of sound by virtue of a state of things perfectly invisible to the eye,
that is to say, layers of air of different densities produced by these
burning bodies. We have made artificial showers of snow, artificial
showers of hail, and artificial showers of rain. We have had showers
of bran, showers of grain of various kinds, and showers of sand ;
showers of real water and showers of pieces of paper to imitate flakes
of snow, and you will be prepared from what you have seen to
acknowledge the reasonableness of my statement — that none of them
had the slightest influence upon the waves of sound. You told me,
Mr. President, that I had half-an-hour, and I do not think I have
exceeded the time which you allotted to me.
The PRESIDENT : Ladies and Gentlemen, I will express once more
on your behalf our very sincere thanks to Professor Tyndall for his, in
the first place, extremely clear and interesting account of these remark-
able experiments, which he terminated some little time ago. We have
secondly to thank him for bringing the apparatus here and arranging
them so successfully as he has done, a thing certainly which could not
be done without great labour and great thought, especially at the dis-
tance which his usual laboratory and usual lecture room are from this
place. We have to thank him for filling this room with an atmosphere
of such intellectual transparency, that I feel there is not one trace of
fog, not one intellectually opaque cloud, if I may judge at all from the
intelligence and attention which has been shown by the audience, re-
maining in any corner of this room. Professor Tyndall has shown
himself to-day not only a successful experimental philosopher, but also
a great moral philosopher in restricting his remarks, of which we should
have been glad to have heard more if time had permitted ; to the time
which I had ventured to indicate to him, and thereby giving other gentle-
men who are kind enough to offer communications, an opportunity of
making them, and us hearing them. I beg to move our sincere thanks
to Professor Tyndall, and to call upon Dr. Stone for his communication
JUST 1NTONA TION. 49
ON JUST INTONATION.
Dr. STONE : Mr. President, Ladies and Gentlemen — In an interna-
tional exhibition of scientific instruments, the object of conferences
must necessarily be to draw the attention of persons present to those
particular points in that collection which deserve our study, and to this
I propose in the section which has been kindly committed to me, to
confine myself. We have in the acoustical department of the present
exhibition, an exceedingly fine collection of instruments brought to-
gether, illustrating the debatable point of just or tempered intonation.
Indeed I may say that we have, with one exception, a perfect collection
of such contrivances. In entering upon just intonation, I am aware
however, that incedo perignes and that I am liable to touch upon a little
warm controversial matter, which I shall endeavour to my utmost to
exclude. If we take for instance the written words of the father of
just intonation, Perronet Thomson, whose original instrument stands
in the corridor, we find him simply saying this — "The temptation to
the old systematic teaching to play out of tune was, that performers
might play with perfect freedom in all keys by playing in none. Hence
the rivalry in magnitude of organs, and the sleight of hand and foot
to conceal. But a reaction is setting in, and the world is finding out
that music is not a noise, but the concord of sweet sounds." This
was written in 1830 — the original edition. Yet in 1876 we find Dr.
Stainer, an equally able acoustician and musician saying, as regards
equal temperament — " When musical mathematicians shall have
agreed among themselves on the exact number of divisions necessary
in the octave, and when mathematicians shall have constructed in-
struments upon which the new scale can be played ; when the practical
musician shall have framed a new notation which shall point out to the
performer the ratio of the note he is to sound to the generator, — when
genius shall have used all this new material to the glory of art ; then "
— and here comes the bathos — " then it will be time enough to found a
new theory of harmony on a mathematical basis." I must confess,
that this putting off to the Greek Kalends, of scientific improve-
ment for practical purposes, does not seem to me, although I
generally agree with much that Dr. Stainer says— scientific, or indeed
E
50 SECTION— PHYSICS.
artistic — and the more so as the discrepancy and difficulty lie
not in the unfortunate mathematician whom he so sarcastically alludes
to, but in a law of nature. As well may the surveyor say, " when
mathematicians have made the diameter of the circle commensurate
with the circumference, when they have established a simple formula
for the circular measurement of an angle, then we will proceed to
mensuration and go into the art of surveying." In both instances
we might reply that there is no time but now ; and we must struggle
in spite of the difficulties which the accidental or possibly the
intended conformation of nature, at present hidden from us, puts in
our way, to produce as great an amount of perfection and as great
a union between science and practice, as we can possibly obtain.
This incommensurability of nature it would take too long to explain at
length, but it is so admirably given in a few words by Mr. Alexander
Ellis, in his translation of the great work of Helmholtz, that I may
venture to quote the single sentence which contains its exposition. " It
is impossible," says Mr. Ellis, in his appendix, " to form octaves by
just fifths or just thirds, or both combined, or to form just thirds by
just fifths, because it is impossible by multiplying any one of the
numbers %, or $, or -|, each by itself, or one by the other any number
of times, to produce the same result as by multiplying any other one of
these numbers by itself any number of times." Thus, having this initial
difficulty, how has it been met, and how may it be met ? The number
of plans brought forward for meeting it are numerous — almost number-
less. I will only venture to mention, on this occasion, one, two, or
three which stand out beyond the rest. The first is the old unequal
temperament. In former times players and composers of music were
content to restrict themselves to a certain number of keys. Modulation
was not so rapid nor so extensive as it has become of late years. The
early effects of music had to be developed before the more compli-
cated. Indeed, Handel's and Bach's music keep in one key. Even
Mozart in his early works keeps very much in one or two keys, but
with Mozart and Beethoven there came a time when equal tempera-
ment became known, and immediately these giants began to throw
their gigantic arms about and travel into all the irrelevant parts
of the scale. Thus the difficulty soon became manifest. But
the older composers, as I was saying, being content to keep to a
JUST IN TON A TION. 5 1
certain limited number of keys, were also content to exclude them-
selves voluntarily from certain other keys, and those keys were very
graphically called wolves, because they howled. They threw all the
howling into certain unfortunate keys, and they promised never to use
them. That was the first system. Then came the second, in which
the howling, instead of coming from a few individuals, was spread over
the whole community, and all the keys were allowed to howl to a
certain extent. The howling was distributed over all the keys, and it
became, some people say, so small that you do not notice it. Other
people think otherwise. That is the second system, termed the system
of equal temperament. Then there is a third, and this is the arrange-
ment of which I have to speak most, which was, that by increased
mechanism and by greater contrivance you might combine the two.
For this purpose there were obviously two ways open. You might
increase the number of the keys on the key- board; you might have
more digitals to put your fingers upon, each speaking to a more true
note, or you might increase the mechanism beyond the digitals in such
a way that by drawing combination stops, as they are termed, the
proper number of sounds for the particular scale should be brought
into action to the exclusion of the others. The first attempt of
this kind I have already noticed in speaking of Perronet Thomson's
organ. It is not only the first in that direction; it is also a very
admirable contrivance; and, I believe, it remains, as yet, without a
fellow. His idea was to complicate the key-board to any extent, so
that the true sounds were obtained. However, finding that this
would be almost impracticable, he limited himself to forty sounds;
these forty sounds are distributed, over three key-boards, each key-
board containing, besides the ordinary digitals, black and white red
ones, what he termed quarrels, what he termed flutals, and what he
termed buttons. There are three key-boards, therefore, furnished
with these various kinds of keys. No doubt the idea is very good.
Anybody can judge for himself who likes to play a simple melody
on those key-boards. But the fingering is extremely difficult ; and
I fear the difficulty is so great that it will not be very largely adopted
by practical musicians. They would have to re-learn all the mechanical
work of music, generally learned in childhood, and the work is too great.
Since then we have had several excellent contrivances, and the most
52 SECTION— PHYSICS.
perfect of all, perhaps, is the key-board of Mr. Bosanquct. Tie uses
fifty-three sounds to the octave, and I believe he has them all there
present for use. But he is here to-day, and has kindly undertaken to
explain the subject, in which he is much better informed than I am ; he
has also undertaken to mention to you the key-board of Colin Browne,
Ewing Professor in the Andcrsonian Institution of Glasgow, of which,
by Mr. Browne's kindness, I have a model. The real instrument is
only just patented, and is not completed. As soon as one is com-
pleted, Mr. Browne tells me he will kindly send it to this Exhibition
for inspection by visitors. Between these elaborate contrivances
of mechanism and the simple unaltered key-board there lie two
others. The first is that proposed by Professor Helmholtz, and
the second, which I hoped to be able to exhibit, but am unfor-
tunately prevented, is that of Mr. Ellis, the translator of Helmholtz,
whom I have just mentioned. He uses a combination stop system, and
it may be some consolation to us to know that the harmonium would
have shown very little ; that is to say, only the ordinary twelve notes. But
there are stops added, each of which draws out the proper com-
bination for the particular key. This, of course, lays you open to
the difficulty that the combination stops cannot be always drawn
rapidly during performance, and in extemporising or playing compli-
cated music you do not always know what key you are going to travel
into, and therefore what stop to draw. If the key-board is before you,
you can in a moment choose the right one, your very ear directs you
to it. Of this I have a specimen sent from Paris. It is termed Gueroult's
Harmonium, but it is practically, I believe, equivalent to the system
suggested by Helmholtz. There are twenty-four notes to the octave,
simply arranged on two key-boards, one above the other, like the key-
board of an organ, but close together so as to enable the finger of the
hand to touch the proper key of either range. The description of it I
have before me is as follows, if you will pardon a rough translation :
The' two key-boards are tuned each in true fifths ; but the posterior
key-board is tuned a comma lower than the anterior key-board, which
is, in the diapason normal, the French pitch. I need not go into the
account closely, but you can consider some notes as flats instead ol
sharps, and then considered as flats, the keys on the second key-board
represents the sharps on a third key-board, which would be tuned a
JUST INTONA TION. 53
comma still lower than the second. We have not time I fear to play
that harmonium ; but I think we can use it as a means of demonstrating
the fact that real just intonation is not inaudible. I think any-
body who tried that key-board would be able to tell without looking
at the keys whether I am using the common chord on the one
key-board, or putting in the more accurate note on the other. The
second is much more true than the first. I will take another chord.
I leave the exposition of the mathematical principle to Mr. Bosanquet.
But, as a practical conclusion, it seems to me that we have here to
strike the balance between mathematical and mechanical difficulty.
Absolute truth should be aimed at. Don't give it up as Dr. Stainer
says, because surely it is within hope that some mechanism may
simplify the contrivance so as to make it at any rate possible. It
seems to me, however, speaking as a medical man, that there is
a physiological condition involved, which has not been sufficiently
adverted to in these rather acrimonious debates about true and untrue
intonation. It appears that the ear gets deadened — spoilt, if you
like, as Perronet Thomson calls it. I confess that my ear is spoilt, to
some extent, by the habitual use of equal temperament. It has ceased
to give me pain — at least, in keyed instruments. And, singularly
enough, the real mathematical sixth seems to me what organists call
keen. Whether we have a right to call this a vitiation, which seems to
be a natural compensation for what we cannot help, I will not say. I
have only one other thing to speak about, and hope to imitate Professor
Tyndall's eloquent brevity. The question of intonation has hitherto
been entirely dealt with by persons playing on keyed instruments. It
is the more difficult problem, no doubt. There are many other instru-
ments which require intonation as much, or even more, but that question
has not been so much studied. Players generally trust in orchestral
instruments to the lip. The lip will do a great deal, but it is obviously
unfair to throw on nature's mechanism, beautiful as it is, what can be
made more simple by man's contrivance. As Helmholtz says in
another passage, in the whole question of equal temperament, too
much has been sacrificed to the instrument, and too little attention
paid to God's handiwork, which is the voice. That, I am sorry to
say, is a very pregnant truth. Merely taking your ordinary orchestral
instrument, there is still much to be done. This clarionet, which
54 SECTION— PHYSICS.
would not strike a musician as being different from others, has most
of the important quarter tones on it. Simply because, by doubling a
key in one place, and by utilising the different fingerings which are
upon the instrument, if they could only be attended to, you can get
nearly all the quarter tones. I shall be happy to show it afterwards to
anyone who knows the mechanism of a clarionet. Lastly, there comes
the large department of brass instruments. And here it seemed, for a
long time, to be rather a hopeless question, especially as to valve
instruments. They are very powerful, certainly a great addition to
our sum total of means for producing musical sounds. But they were
always considered to be very incorrect. This, which is a recent
invention of my friend, Mr. Bassett, is a trumpet which possesses, to
all intents and purposes, the ordinary mechanism of a trumpet, but not
quite the same. The third valve, instead of lowering the pitch, as it
does in the ordinary trumpet, has a separate function. The first valve
lowers the pitch a major tone ; the second valve lowers the pitch a
diatonic semitone. The third valve raises the pitch of any note, pro-
duced by the first by the interval of a comma ; therefore it has been
termed the comma trumpet. In other words, the first and third valves
together, lower the pitch a minor tone, and when the first is used
together with the second valve or alone, it gives, of course, other modi-
fied intervals, resulting in the production of a more correct musical scale
than has yet been obtained on any valve instrument, with very little
alteration of the usual fingering. It appears to me that this excellent
system, which has hardly yet attracted the notice of professional
musicians, ought to be applied to other instruments. Mr. Bassett is
here, and no doubt will, during the recess, play some notes and exhibit
the system. Here I beg to conclude for the moment, and can only
hope that the President will kindly allow Mr. Bosanquet to supplement
those parts which, as mathematician and acoustician, I am less com-
petent than he to undertake.
The PRESIDENT : I beg to return your thanks to Dr. Stone for his
communication, and I will now call on Mr. Bosanquet to give us a
short account of his instruments, on the theory and practice of which
lie has been for some time experimenting.
INSTRUMENTS OF JUST INTONATION. 55
ON INSTRUMENTS OF JUST INTONATION.
Mr. BOSANQUET : As the combinations which are to be dealt with
are complex, forms of arrangement have been employed which reduce
all the phenomena in practice and theory to a few simple types.
These I have called symmetrical arrangements. They were not
employed by General Thompson.
There are two forms of symmetrical arrangements. Those which I
employ I shall distinguish co-ordinate symmetrical arrangements;
other forms employed by Mr. Poole and Mr. Brown may be called
key-relationship symmetrical arrangements. Into these latter I shall
not enter, but only remark that those which depend on co-ordinates
possess all symmetrical properties in a more extended form than the
others ; i.e., they include the key-relationship and more besides.
Mr. Brown's position relations are exactly the same as Mr. Poole's,
with omission of the two series of sevenths.
In my co-orclinate symmetrical arrangements a number of equal
temperament semi-tones, or twelfth parts of an octave, is taken as
abscissa, and deviation or departure from the note thus arrived at as
ordinate. Thus, the exact pitch of notes can be expressed by reference
to co-ordinates in a plane.
To express a series of equal temperament (E.T.) fifths in this manner :
The E.T. fifth is TV of an octave. Taking twelve fifths up, we have
seven octaves exactly. The result is expressed by abscissce only.
To express a series of perfect fifths in this manner :
The perfect fifth is seven semi-tones and a departure = '01955 E.T.S.
= TrrsT ' '*• twelve fifths are seven octaves and a departure = '23460
E.T.S., the Pythagorean comma. The resulting notes have ordinates
which increase uniformly as we pass along the series of fifths ; and the
position arrived at after the twelve fifths has an ordinate which
represents the Pythagorean comma when the fifths are perfect, and
abscissa 7 X 12 = 84 or seven octaves.
The form of symmetrical arrangement employed in the generalized
key-board, is arrived at by arranging a series of notes in the order of
the scale as far as the abscissas are concerned, and taking for ordinates
distances proportional to those thus arrived at. That is to say, the
$6 SECTION— PHYSICS.
ordinate of any note is proportional to its distance from a fixed point
in the series of fifths.
The series of fifths is selected for the application of the conditions,
because it is the most convenient ; but the variations of all the concords
in any system are linked together in such a manner that it is indifferent
which is taken as independent variable, so to speak ; the results would
be always the same.
The generalized key-board, of which the harmonium exhibited offers
an example, may be conveniently described with reference to abscissae
from left to right, and horizontal ordinates on plan from back to front.
The vertical ordinates are one-third of the horizontal ones.
In the abscissae, half an inch corresponds to an E.T. semi-tone.
Twelve semi-tones make an octave. The octave measures 6 inches in
abscissa, and nothing in ordinate.
In the ordinates on plan, 3 inches correspond to the Pythagorean
comma or departure of twelve fifths. Thus the difference between the
ordinates of two notes on same abscissa, between which one series of
twelve fifths lies, is 3 inches.
The ordinates of the intermediate fifths are increased by £ inch at
each step upwards in the series of fifths, so that twelve steps upwards
in the series correspond to 3 inches.
I have described the key-board as connected with the system of
perfect fifths ; and it is so in this harmonium to all intents and pur-
poses. But it is clear that if each fifth have any departure from E.T.
whatever, this may be equally represented by the ordinates in ques-
tion, as no use has been made of the amount of the departure ; and we
can say that a key-board, constructed in the form of a co-ordinate sym-
metrical arrangement, forms a graphical representation of the interval
relations of any set of notes belonging to a regular succession of fifths.
Thirds can always be referred to fifths. In systems such as that of
perfect fifths — which we are dealing with here — by means of a theorem
brought into notice by Helmholtz : in other cases, in other ways.
The most important property of key arrangements which form
graphical representations of their intervals is, that any combination
of intervals has the same form to the finger on whatever notes or in
whatever key it may be taken. Thus a common chord always has
the same form.
INSTRUMENTS OF JUST INTONA TION. 57
Non- co-ordinate or key-relationship symmetrical arrangements,
such as those of Mr. Poole and Mr. Brown, possess a similar pro-
perty of more limited extent. In these it is, for instance, possible
that a common chord may assume different forms to the finger in
cases where the key relationship is differently assumed: not so in
co-ordinate arrangements.
I will only allude to one property of the division of the octave into
53 equal intervals, according to which the harmonium exhibited is
tuned.
The mode in which the number 53 is arrived at has been ex-
plained by me, as part of a general theory. But we can verify its
properties independently by noticing, that if we take 31 units for
the fifth of the system, then 12 X 31 =372 and 7 X 53 = 371 ; so that
we see directly without formulae, that the departure of twelve fifths
= -sV of an octave = if of a semi-tone; and departure of one fifth = -^
of a semitone. Now, the departure of a perfect fifth is ^rrsTj and the
difference is about atuu = TsVo of a semitone, which is the error of
the fifth of the system. Hence, we may say that the system of fifty-
three is sensibly identical with a system of perfect fifths.
In the enharmonic organ recently constructed, I have applied to a
generalized key-board of forty-eight notes per octave, Helmholtz's
approximately just intonation, and also the mean tone system, which
is of historical interest. Each system is brought on to the key-board
separately by a draw-stop. In the same way all systems of interest
are accessible ; it is this employment of the key-board that I would
at present commend to those who inquire into its utility.
Considering the facilities that we see about us for manipulating just
and approximately just systems, it is difficult to see why mere book
knowledge should continue to be alone regarded in the study of this
portion of the elements of music. When it is taught, for instance,
that certain vibration ratios correspond to certain musical effects, the
lesson should be taught experimentally; as it is, musicians for the
most part only know what consonances are from descriptions in
books. As illustrations, I may point out that we have, in the
harmonium now exhibited, the means of distinguishing three different
kinds of minor thirds, whose ratios are 6: 5, 32 -.27, 7 '•&'> and these
sound quite different to the ear. Again, Pythagorean thirds can be
58 SECTION— PHYSICS.
contrasted with exact thirds, the harmonic seventh compared with
other forms of minor seventh, and numerous other theoretical results
reduced to practical knowledge.
Of the applications of the various systems, I will only say that in
my opinion it is a mistake to apply ordinary music to them indis-
criminately. Just systems especially, which have both thirds and
fifths nearly perfect, must be studied and written for before they can
be used with advantage. I need hardly say that I think, when this is
done, the advantage will be great.
Dr. Guthrie here took the chair.
The CHAIRMAN : I am sure you will all thank Mr. Bosanquet for
his communication, and I am sure we are very glad to hear that there
is some practical prospect of this very desirable end being brought
about We have now the subject of the limits of audible sounds, and
if Dr. Stone will introduce the subject, I hope Mr. Galton will illus-
trate it by one or two practical results.
THE LIMITS OF AUDIBLE SOUND.
Dr. STONE : At the risk of the accusation of irrepressibility perhaps
you will allow me to occupy one or two minutes in the way of the Roman
nomenclator of old, to start a subject rather than to complete it. I
wish to mention the limits of audible and musical sound. Of course
we have them both above and below, at either extreme. We have, also,
I am proud to say, a very fine collection of illustrative instruments
in the exhibition, and I would name three at the upper limit and
three at the lower. The first is a curious instrument of Mr. Griesbnch's
which is interesting, not only on account of the perfect way in which
he illustrates the upper limits of audibility, but because he contrived
it so as to show many principles of musical sound which are con-
sidered to be of recent discovery. This is the instrument. It is to all
intents and purposes a small organ with a key-board, the pipes of
which are exceedingly small. They look rather long, but the greater
part of the pipe is foot, and the real acting part is very short indeed.
Here is a note which would astonish modern pianists to play. It is so
LIMITS OF AUDIBLE SOUND. 59
fine that I am afraid you will not hear it. Here is the semitone below
it on the same scale, and although many persons are not able to
hear these pipes separately, yet the resulting tone produced* by
blowing two together is perfectly audible to most people. This was
made many years ago, and it is historically interesting as being an
anticipation of modern research on the subject. Among the many
discoveries of Professor Wheatstone was one of this kind. He produced
the same effect by using two very small harmonium reeds ; reeds of the
same kind are here in this small box. These are made by Mr. Gries-
bach, but as to priority between the two I am unable to speak.
Unluckily, that is the condition of these small reeds also : they are
unable to speak, but there they are. Time has damaged them, but
the same things were certainly contrived as early, if not earlier, by
Professor Wheatstone. Then as to the lower limit of sound. Helm-
holtz may have erred from erroneous information given to him, and
perhaps the appreciation of musical sound might be rather different
in other persons than those he had to experiment with. I believe
he is a violin player, but I do not think he pretends to be a musician
of a practical kind. He says the deepest tone of musical character
which can be heard is about forty-one vibrations in the second, in
the upper half of the thirty-two feet octave he says the perception
of the separate pulse is clear, but practically he does not admit that
you can get any musical note below E or F on the common German
double bass. Now what seems to be wanting, if I may use the term,
in these investigations, is that the mass upon which he experimented
was rather small. He used pianoforte strings weighted with a kreutzer_
in the middle. That is a very feeble source of sound. If we are to
produce these low tones, the amplitude of the vibrations must be
enormously increased. Whether he has quite utilized the effect of a
consonant body or of a resonant case, on a vibrating string, to the
extent to which it might be done, is a point on which I have some
little doubt, because it has been done here. Here is Elliott's apparatus,
originally invented by Chladni, a sort of wand passed through a slit.
This Helmholtz alludes to, and declares it produces a false result,
because the upper partial tones are very strong compared with the
fundamental. No doubt they are. I should be delighted to find him
correct, and he is probably speaking only of simple pendular vibrations
60 SECTION— PHYSICS.
such as you get in the lowest stopped diapason pipes ot an organ ;
but if this is what he means by saying that you cannot hear simple
pendular vibrations below forty-one, he is simply saying that you
cannot carry the stopped diapason down below forty-one vibrations,
a much less extensive statement than to say that the ear cannot
distinguish sounds below that. As a matter of fact, all the extreme
bass instruments we make use of, perhaps unfortunately, have the
upper partials very strong ; strong compared to the foundation note,
but you can intensify the fundamental note by certain contrivances,
especially those of consonance. On this I have spent a great deal of
time myself. I have tried on a double bass. The double bass has
been often before made to produce very low notes, and there is one,
quite gigantic, on the other side of the building, which requires
giant to play it; the present race of pigmies had to stand on a
a table. It produces a very fine tone in the low notes, but it would
not suit this generation ; it needs sons of Anak to play upon it.
Other attempts have been made to produce the low tone, by making
the strings thicker ; but then you cannot get at the centre of gravity
of a cylindrical string ; you must strike at the outer circumference,
and these large strings rotate and produce false notes, not at all
the tone that is wanted. There remained one thing which had not
been clone, and that is to work by weight. By covering the string very
heavily with copper wire, and placing it on the double bass, I
succeeded in getting a sound which I thought satisfactory. The tone
contains a great predominance of 1 6-foot vibration. I had to
strengthen the double bass very considerably by what I term elliptical
tensicn bars, so as to give it, in the first place, force enough to resist
the enormous pull of this heavy string, and secondly to give it a
sound-conductor. There was already a bar from end to end which
tended to counteract the dumbing effect of the "S" holes, which are
necessary, however, for letting out tha air vibrations. If you will
permit me to add presently to my unmusical illustrations, I think I
can obtain a note from the double bass, which you will say is musical.
Another attempt was in the wind department. We have here an
instrument which some of you may know I habitually play, especially
with Sir Michael Costa's orchestra. I played it the other night at the
Albert Hall. It is a reed instrument of 16 feet in length, the octave
LIMITS OF AUDIBLE SOUND. 61
of a bassoon. It is not a new instrument, but it is on a new scale
This, as I hope to demonstrate afterwards, brings out the CCC, the
lowest note of the 16 feet octave, with a tone which you people may call
musical or not, but I think it is. At any rate it is not wanting in
power or in intensity. I have intentionally omitted to speak of one
excellent set of investigations on the upper limit of musical sound,
because Mr. Galton, the author, is here present himself, and will
explain them.
The CHAIRMAN : I have to ask you to again express your thanks
to Dr. Stone for these few supplementary remarks ; but I think before
we have any discussion on these communications, we had better
complete this branch of the subject, and I will therefore call on
Mr. F. Galton, F.R.S.
Mr. GALTON : I thought it would be of convenience to experi-
menters, that I should exhibit some little instruments I have combined
for ascertaining what the upper limits of audible sound may be in
different persons of the same race, and in individuals of different
races, and in different kinds of animals. It is, of course, a matter of
great interest to know whether insects and such small creatures can
hear sounds, and can in any sense of the word, converse in language
which to our ears is utterly inaudible. When I first devised to
make experiments, I was checked by the great difficulty of finding
instruments that vibrated with sufficient rapidity for the purpose in
question. Dr. Wollaston (to whom we are indebted for the first
experiments ever made on this subject, and for the fact that vibra-
tions exist which the ear is incompetent to seize and render into-
sound) found very great difficulty in making his small pipes. I tried
several plans for obtaining acute notes, and the one I finally adopted
was this : I made a very small whistle, whose internal diameter was
much less than one-tenth of an inch— I have many such here, made
for me by Massrs. Tisley and Spiller, Opticians, 172, Brompton-road,
— with a plug at the bottom, which plug is screwed up by a graduated
screw. The graduations are marked on the side, so that when you
use the instrument you know the depth of the tube, and knowing
what that is, it is a matter of calculation to learn the rate of vibration.
There is, however, a good deal of uncertainty in the matter, because
there must be some fair proportion between the length and width of
62 SECTION— PHYSICS.
the tube in order that the calculations should give a correct result.
A short whistle with a diameter exceeding two-thirds of its length,
will certainly not give a note whose shrillness is governed wholly by its
shortness. Therefore in some of my experiments I was driven to use
very fine tubes indeed, not wider than those little glass tubes that
hold the smallest leads for Mordan's pencils. It occurred to me, in
order to produce a note that should be both shrill and powerful, and
so correspond to a battery of small whistles, that a simple plan would
be to take a piece of brass tube and flatten it, and pass another sheet
of brass up it, and thus form a whistle the whole width of the sheet,
but of very small diameter from front to back. I have such a whistle
here, it makes a powerful note, but not a very pure one. I also made
an annular whistle by means of three cylinders, one sliding within the
other two, and graduated as before. I find that when the limits of
audibility are approached, the sound becomes much fainter, and when
that limit is reached, the sound usually gives place to a peculiar
sensation, which is not sound but more like dizziness, and which some
persons experience to a high degree. I am afraid it is of little use
attempting to make the audience hear these small instruments ; but I
will try, beginning by making rather a low note. It was found that
there was great variability in the audience, in their powers of hearing
high notes, some few persons who were in no way deaf in the ordinary
meaning of the word, being wholly insensible to shrill sounds that
were piercingly heard by others. I find that young people hear
shriller sounds than older people, and I am told there is a proverb in
Dorsetshire, that no agricultural labourer who is more than forty
years old, can hear a bat squeak. The power of hearing shrill
notes has nothing to do with sharpness of hearing, any more than
a wide range of the key-board of a piano has to do with the good-
ness of the sound of the individual strings. We all have our limits,
and that limit may be quickly found in every case. The facility of
hearing shrill sounds depends in some degree on the position of the
whistle, for it is highest when the whistle is held exactly opposite the
opening of the ear. Any roughness of the lining of the auditory canal
appears to have a marked effect in checking rapid vibrations of the ear.
For my part, I feel this in a marked degree, and I have long noted
the effects in respect to the buzz of a mosquito. I do not hear the
LIMITS OF A UDIBLE 'SOUND. 63
mosquito much as it flics about, but when it passes close by my car I
hear a sudden "ping," which is very striking. Mr. Dalby, the
aurist, to whom I gave one of these instruments, tells me he uses
it for diagnoses. When the power of hearing high notes is lost, the
loss is commonly owing to failure in the nerves. On the other hand
we may find very deaf people who can hear shrill notes, in which
case the nerves are usually all right, but the fault is in the auditory
canal. I have tried experiments with all kinds of animals on their
powers of hearing shrill notes. I have gone through the whole of
the Zoological Gardens using a machine of the kind that I hold in my
hand. It consists of one of my little whistles at the end of a walking
stick, that is in reality a long tube ; it has a bit of india-rubber pipe
under the handle, a sudden squeeze upon which forces a little air into
the whistle and makes it sound. I hold it, as near as is safe, to the ears
of the animals, and when they are quite accustomed to its presence
and heedless of it, I make it sound, then if they prick their ears it
shows that they hear the whistle, if they do not, it is probably inaudible
to them. Still, it is very possible that in some cases they may hear but
not heed the sound. Of all creatures, I have found none superior to
cats in the power of hearing sharp sounds. It is perfectly remarkable
what a faculty they have in this way. Cats, of course, have to deal
in the dark with mice, and to find them out by their squealing.
Many people cannot hear any notes in the squeal of a mouse. Some
time ago, singing mice were exhibited in London, and of the people
who went to hear them, some could hear nothing, whilst others could
hear a little, and others again could hear much. Cats are differen-
tiated by natural selection until they have a power of hearing all
the high notes made by mice and other little creatures that they
have to catch. You can make a cat, who is at a very considerable
distance, turn its ear round by sounding a note that is too shrill to be
audible by any human ear. Small dogs also hear very shrill notes,
but large ones do not. You may pass through the streets of a
town with an instrument like that which I used in the Zoological
Gardens, and make nearly all the little dogs turn round, but not the
large ones. At Berne, where there are more large dogs lying idly
about the streets than in any other town in Europe, I tried this method
for hours together, on a great many large dogs, but could not find one
64 SEC170N— PHYSICS.
that heard it. Ponies and cattle, too, are sometimes able to hear very
high notes — much more than horses ; I once frightened a pony with
one of these whistles in the middle of a large field. I can produce no
effect on ants, nor on the great majority of insects, though there are
some apparent exceptions about which, however. I am not yet prepared
to speak.
The CHAIRMAN : I am sure I need not ask you to thank Mr. Galton
for his very interesting remarks. Time is getting on, and I will now
invite those who have anything to say upon the general subject of
Just Intonation and the Limits of Audible Sound to do so. There was
only one remark which occurred to me specially during Dr. Stone's
last communication, and that was the able way in which he pointed
out the bearing which the mass of the air which is set in motion has
upon audibility. It has nothing to do with wave-length or wave
amplitude but with the quantity of air, which you may compare to the
end-length of sea waves. That seems to have great power and effect
on the auditory nerves. Perhaps the lowest audible note which we
have heard, at least, is that which you hear when you are outside a
tunnel, and you hear the actual throbbing of the piston of the engine.
You have an immense mass of air in the tunnel set in vibration. It
has nothing whatever to do with the length of the tunnel ; it does not
act as an organ pipe establishing stationary waves, but you have an
immense mass of air set in deliberate motion with slower vibrations even
than sixteen in a second, and the sound is perfectly audible.
Mr. ALEX. J. ELLIS, F.R.S. : I only wish to say a few words with
regard to the experiment of Helmholtz which was alluded to, for trying
to determine the lowest limit of tone. His object in operating on a
piano string loaded with a kreutzer was to render the upper partials
inharmonic to the fundamental, so that he should be quite sure that
he heard a simple pendular vibration. His object was to determine
the lowest audible limits of such vibrations. The subject is one which
has been very recently investigated, and accounts of the experiments
have been given by Professor Preyer, of Jena, one of the members of
the general committee. There are the pipes here which he experi-
mented upon. He found that the best way to hear these sounds, was
to obtain them first from a reed attached to a pipe, and then to shut oft
the air, and listen to the tone as it vanished, when he heard the funda-
LIMITS OF AUDIBLE SOUND. 6$
mental or lowest tone quite distinct from all the others, as a simple
pendular vibration. As the result of a great number of experiments he
found that ears differed very much as to what was really a musical
tone, defining that to be one in which we hear no throbs, but only a
continuity of sensation. He has also published a work on the limits
of sensational power, and. in fact, that was his great point, to deter-
mine the limit of continuity of sensation. He found that he himself
could hear continuous tone from as few as 14 vibrations to the second,
but that most ears perceived sensation to be continuous when the
number of vibrations reached 23. Therefore, somewhere between 14
and 23 vibrations must be fixed as the lowest limit of continuous
simple pendular vibrational tone produced in the human ear, as far
as it has yet been investigated. He also has gone very much into
the question of the upper limits of tone, but his especial investigations
were to determine the smallest amount of error in a melodic interval,
which the most practised ears could hear. For this purpose he made
use of some of these instruments of Herr Appun, of Hanau. There is
one which gives a complete series of partial tones up to the 32nd, and
there is another one in the next room which gives tones from 128 to
256 vibrations, proceeding by two beats at a time. With that instru-
ment Herr Preyer experimented, and the investigation has a very
important bearing on the method of representing just intonation by
means such as that of Mr. Bosanquet, who uses an approximative
scale, obtained by dividing the octave into 53 equal parts, which I
consider to be really perfect enough. I have not calculated all Herr
Preyer's results out completely, but I may state that no ear seems to
detect an error in an interval melodically — not in a chord— which
amounts to the hundredth part of an equal semitone, but that the
fiftieth part (double that) may be detected by very fine ears indeed.
With regard to just intonation and key-boards, I may say that key-
boards like Mr. Brown's and Mr. Poole's (which is very good if we
reject the natural sevenths), go upon the principle of carrying out
a series of tones proceeding by perfect fifths, in three columns,
so to speak, each column being a comma lower than the preceding.
Gueroult uses only two. Gudroult and Helmholtz's plan is the one
Dr. Stone said I wanted to simplify, using a single key-board by
means of compound stops, and that was the instrument which was to
P
66 SECTION- PHYSICS.
have been exhibited ; but he was a little in error. That instrument
was one with single, not compound, stops, and was intended to exhibit
the old organ tuning continued so as to play 21 notes to the octave.
It was invented by Mr. T. Saunders, who subsequently declined to
exhibit it. But the principle of Helmholtz's and Gue'roult's instru-
ments is to have two rows of 12 notes forming perfect fifths, one row
being a comma flatter than the other. This would give the full succes-
sion of major keys, but only five minor keys complete. The other
minor keys are quite imperfect, whereas with Mr. Bosanquet's instru-
ment which, although it has only 53 tones to the octave, has actually
84 finger-keys to the octave, so as to be able to go round and round,
all the keys, minor as well as major, are practically perfect. This
instrument is really almost as simple to play as an ordinary harmo-
nium when you understand that the major thirds are taken in a series
below, and the minor thirds in a series above ; whilst the oblique
arrangement of the finger-keys obviates the necessity of jumping from
one row to another and allows of playing each scale in one line. I con-
sider Mr. Bosanquet's arrangement to be the acme of perfection in this
respect, and I do not think that we are likely to arrive at anything
which is simpler. I hope Mr. Bosanquet will give us an opportunity
of hearing some of the effects of it afterwards, because until persons
have heard music played in just intonation they cannot at all appreciate
what it is that persons want to obtain as contra-distinguished from that
which we are generally obliged to hear. I had an opportunity only
last Christmas of hearing a well trained and educated choir of the
Tonic Sol-fa College, accustomed to sing in perfect intonation, and,
when they were singing unaccompanied, the chords in just intonation
were perfectly divine, but when they sang immediately afterwards to a
pianoforte which was almost inaudible, the chords were all torn to
pieces in such an extraordinary way by the accommodation of the
voices to the instrument that it was perfectly painful to listen to them.
With regard to the upper limits of audible tone, although I am rather
an old boy, I may say that I heard all the high tones produced by
Captain Douglas Galton perfectly.
ACOUSTICAL DISCOVERIES. 67
THE LATE SIR CHARLES WHEATSTONE'S ACOUSTICAL
DISCOVERIES.
Professor W. G. ADAMS, M.A., F.R.S.: If I were to speak of all the
instruments — or even of all the musical instruments — which may be
connected in some way or other with the name of Sir Charles Wheat-
stone, I am afraid I should occupy a very considerable time, weary
you, and shut out those who have to come after me; but I propose
to draw your attention to three classes of instruments with which Sir
Charles Wheatstone was specially connected. First of all, if we con-
sider the vibration of reeds, we may start from the very ancient
instrument the Marimba, which has iron rods fixed into a sounding
body in the same way as the iron fiddle, which consists of rods fixed at
one end to a sounding board, from the iron fiddle, by lengthen-
ing the rods, we get to the kalcidophone, which is so well known,
and the figures traced out by which are so familiar, that it will
not be necessary for me to describe them in detail. If we take
a cylindrical rod with one end fixed, and cause it to vibrate, being
cylindrical, it will vibrate transversely at tiie same rate in all direc-
tions, but it may be put in vibration so as to give not only a simple
figure, the ellipse, circle, or straight line, but by dividing it by nodes
or points of rest into separate vibrating segments we may get also the
super-position of the partial vibration figures combined with the
original simple figures.
The simple figures are obtained by causing the rod to vibrate as a
whole, and the partial vibrations are obtained by producing one or
more nodes on the rod. The ratio of the number of partial vibrations
to the number of fundamental vibrations is given by the number of
indentations produced in the original figure traced out by the free
end of the rod. The number of vibrations when there is one node
on the rod is about 6£- times the original number of vibrations of the
rod when it vibrates as a whole. With one, two, three or more nodes
the number of vibrations is as the squares of the second, third, or
higher odd numbers. No. of nodes, I, 2, 3, 4, &c. ; No. of vibrations, 9,
25, 49, 8 1, &c. With a rectangular rod. when its section is a square,
the curves traced out are the circle, the ellipse, or the straight line,
63 SECTION— PHYSICS.
exactly as in the case of cylindrical rods, and the partial vibrations
bear the same relation to the fundamental vibrations with rectangular
rods, which are not square in section, the number of vibrations will
depend on and be proportional to the thickness of the rod in the
direction in which the vibrations take place. If we increase that thick-
ness, we shall increase the number of vibrations in a given time ; if
we double the thickness, the number of vibrations will be twice as
many, and so, causing the rod to oscillate in one plane or in the other,
we shall get in the direction of the greatest thickness, the greatest
number of vibrations ; and if the length of the rod is such as would
produce musical tones, then the tone corresponding to the greatest
thickness will be the octave of the tone corresponding to the least
thickness, when the thickness in one direction is twice as great as in
the other.
We may pass on from an ordinary rod of this kind, gradually
thinning away in one direction, and if necessary, thickening a
little in the other, and we pass to a thin reed or vibrating strip of
metal fixed at one end, and placing that in an opening, we get the
" free reed." It is only necessary to mention the free reed to recall
again the name of Sir Charles Wheatstone, who developed it so
much, and applied it, or caused it to be applied, to so many instru-
ments. The figures traced out by these kaleidophones, when they
are of different diameter in different directions, are very well known,
and may be produced in various ways. There are many pieces of
apparatus in the Exhibition which will show this. If the point
of suspension of one pendulum be attached freely to the bob of another
pendulum, so that they can swing in planes at right angles to one
another, and the two are set in vibration, then the bob of the lower
pendulum will trace out a curve which results from the two motions :
the same curves may be traced out by Mr. Tisley's beautiful appara-
tus, having two pendulums vibrating in planes at right angles to one
another, which are placed at the corner of a table, one at the end and
one at the side, so that the oscillations take place in two planes,
at right angles to one another, a point connected with both pendulums
will trace out the curves. By altering the length of the pendulum
or the times of oscillation, we may get a variety of different curves, and
may make the times of oscillation so nearly coincident as to produce
ACOUSTICAL DISCOVERIES. 69
what corresponds to beats in music. Here is a very pretty instrument
for showing the same thing. In this case we may consider that we
have two free reeds, one attached to the end of the other, on the same
principle as the pendulums attached one to the end of the other.
There are two thin strips of metal soldered together end to end with
their planes at right angles to one another. Fastening one of these in
a vice, we may set them vibrating ; the motion of the free end will be
the result of the combination ot the motions of the two strips taken
separately. On lengthening the lower strip, it will make a smaller
number of vibrations in a given time, and in this way any combination
of two rectangular motions may be obtained.
I must also call your attention to another instrument invented by Sir
Charles Wheatstone for producing these figures by the motion of two
cranks, in two planes, at right angles to one another. The ends of the
cranks are fixed by a hinge to one end of a rod, the middle of the rod
turns in a fixed socket, so that the free end describes the same curves
as the end to which the crank arms are attached. There are several
points worthy of attention in this instrument, especially the arrange-
ment by which the number of revolutions of the two wheels which
drive the cranks may be made to bear any given ratio to one another.
I must now pass to another subject which is well illustrated by appa-
ratus in this exhibition, and which was worked at and developed by
Sir Charles Wheatstone, viz. : — The production of sound by exciting
vibrations in tubes by means of gas flames.
If a small gas-jet of suitable form be placed just within the lower end
of a tube open at both ends, vibrations will be excited in the tube, and
those vibrations which correspond to the length of the tube will be
reinforced by it, and a musical note will be heard. On raising the
flame into the tube the sound ceases, but on making the flame larger,
the sound is again produced and is louder than before. The sound
gets louder as the flame is raised, and the most intense sound is pro-
duced when the flame approaches to the position of the node.
Working at this subject, Sir Charles Wheatstone produced an instru-
ment which is called a chemical harmonicon or gas-jet organ. It
consists of a key-board, to the keys of which are attached small gas
burners coming from a tube containing hydrogen gas. Each burner
is placed just within the lower end of a gas tube, and the tubes are of
70 SECTION— PHYSICS.
such a length as to resound to the successive notes of the diatonic
scale, when a burning gas-jet is raised to the proper point of the
tube by pressing down the keys. This instrument is from the Wheat-
stone Collection of Physical Apparatus at King's College. A
photograph of a similar instrument is exhibited by Professor Oppcl
of Frankfort.
Wheatstone investigated experimentally the laws of vibration in
conical tubes, and showed the agreement between the calculations of
Bernouilli and experiment. For the first mode of vibration, i.e., for the
lowest note of a conical pipe, all the air in the pipe moves backwards
and forwards in the same direction at the same time. The particles
alternately approach to and recede from the apex of the cone. In the
second mode of vibration there is a ventral section in the middle of the
pipe, and the pipe is divided by it into two parts of equal length. In
the third mode of vibration there are three equal lengths separated by
two ventral sections.
Taking conical tubes, the different notes which may be produced
from them correspond precisely to those which maybe produced from
open cylindrical pipes of the same length. Taking this conical tube,
two feet long, the resonance corresponds to a middle C tuning fork,
and if from any cone I take a part of the same length and open at
both ends, I shall get the same note, so that with a conical pipe, either
closed at the apex or open at both ends, we get the same note as from
a cylindrical open pipe of the same length. The harmonics produced
in the conical pipe are the same as those in the open cylindrical pipe,
which are of course different f;om those produced by closed cylindrical
pipes ; the difference being seen in two musical instruments, the clarionet
and the oboe. The oboe being conical the harmonics are those of an
open cylindrical pipe. Cutting up the cone into equal lengths, we get
the same note from each, so that if these short pipes, which were Sir
Charles Wheatstone's, are sounded, the same musical note will be pro-
duced from each of them, but in each of these open pipes there is a
node which is not at the centre of the pipe. In a cylindrical pipe the
column of air will be divided equally into two vibrating parts at a node
in the centre, but in the conical tube the node is not in the centre but
will be nearer to the smaller end of the tube. As the pipe tapers more
moie, the distance of the node from the centre of it will be more
ACOUSTICAL DISCOVERIES. 71
and more increased. I have here two conical tubes each about
six inches long : one of them is open at both ends, the other I have
divided into two parts at the node. If I stop these two tubes
at the section where they have been divided by placing them on
the palm of the hand, and sound the note, we shall find that they
will produce the same note, and that this is the note given by the other
conical tube open at both ends. I have found by trial the position of the
node in these tubes, so that by stopping the tube at that point, the note
produced from that short pipe when closed shall be the same as from
the longer one open at both ends. If that is the case, we may expect
also that by stopping the small end of this pipe we shall get the same
note from it, which is the case, so that from those pipes, both closed,
one at the larger end and the other at the smaller end, we get the same
note produced, and this note is the same as that from an open cylin-
drical pipe equal in length to the sum of the two closed conical pipes.
Taking tubes of the same length, but with different degrees of
taper, we pass from a very low note, which is produced with
the tube of greatest taper when the largest end is closed, through
a succession of notes to the note of a closed cylindrical tube, then
by inverting the tubes, taking them in reverse order, and closing
the smaller ends, we may produce a succession of notes still increasing
in pitch up to the note of an open cylindrical tube of the same
length.
The CHAIRMAN : I will now ask you to record your indebtedness to
Professor Adams for his very able exposition of one of the chapters of
Sir Charles Wheatstone's great scientific career. It must have struck
all those who have been working in science, ever and anon, that when
they fancied they had found something new, they find it was done by
Sir Charles Wheatstone years ago. That has happened scores of times,
but I am happy to say there is every prospect soon of Sir Charles
Wheatstone's published and unpublished papers being collected and
presented to the public in a recognized form, so that that danger will
in future be avoided. I will now call on Mr. Chappell to give us an
account of ancient musical science.
72 SECTION— PHYSICS.
ANCIENT MUSICAL SCIENCE.
Mr. W. CHAPPELL : The limit of time imposed upon me makes
it necessary that I should say very few words indeed. In this
exhibition there are some models of ancient Egyptian pipes, and of a
Greek, or rather of an Egyptian, hydraulic organ. It was the custom
of the Egyptians, in the early dynasties of the empire to leave a pipe
in the tomb of a deceased person, and to lay by it a straw of barley,
by which the player might, as we assume, make fresh reeds when he
awoke. This was upon the assumption that, having been a very good
man, his soul would resume the human form. Here is an example of
the sort of pipe which was deposited. This pipe could only be played
with a double reed, such as that of the hautboy, the bassoon, or the
ancient shepherds' pipe, because there is no notch in it, as in the
flageolet or the diapason pipe of an organ, to excite the tone.
Through the kind assistance of my friend Dr. Stone these pipes are
fitted with reeds. The diameter of the pipe may not be exactly
copied, but that is of minor importance because increase of diameter
does but increase the volume of sound. It is the length of the pipe
and the distance between the holes which are essential. There is no
example of a bass pipe, thus deposited, but we have here two tenor
pipes and two treble pipes, and from these we ascertain at least some
of the scales of the ancient Egyptians. The Greeks constructed
their minor scale by joining together two tetrachords, which we call
fourths, but they are fourths with the semitone at the bottom, as in B,
C, D, E — not as in C, D, E, F, where the semitone comes at the top.
It was desirable to know how ancient that scale was in Egypt, and it
is evident that these pipes were anterior to it, for they are all on the
major scale. Greek writers upon music inform us that they joined
together two tetrachords of four notes each, by commencing the
upper tetrachord upon the highest note of the lower one, thus reducing
the eight notes to seven, because there were seven planets. There are
other associations connected with the number seven which might
have influenced them to do so. In these pipes we discover two
musical principles which we are not aware to have been known to
the Egyptians. One pipe has a hole bored through it within an inch of
ANCIENT MUSICAL SCIENCE. 73
the top, and it could not possibly have been sounded with those two
holes left open. This is copied from a pipe in the British Museum, and
it was necessary to cover the apertures with thin gutta percha to
elicit the sound. It proves to us that the ancient Egyptians knew the
principle of the famous pipe mentioned by Shakespeare, called the
Recorder, which differed only from the soft English flute, played at
the end, in having a little piece of bladder or something of that kind
fastened over openings of this sort, the object being to give »
tremulousness to the tone and to make it more like the human voice.
The tone of the pipe would otherwise be perfectly pure and steady, as
in an organ. In the case of a second Egyptian pipe we find it neces-
sary to sink the reed down three inches within the tube to elicit any
sound, and that is the principle of the drone of the bag-pipe. It
serves to protect the fragile reed from injury. There is no perfect
octave scale upon any of the four which have been tried. They are
very limited in compass, but we find that the Egyptians often played
in concert. There is a representation of three Egyptian pipers play-
ing in concert with pipes of about one, two, and four feet in length,
in the tomb of an Egyptian, named Tebhen in the hieroglyphics, and
this tomb is of the fourth dynasty, or about the time of building the
great pyramid. Three such pipes must necessarily be playing in
three different octaves — treble, tenor, and bass. One of these pipes
has six notes in the major scale, another has a diatesseron with the
semitone at the top, but no tetrachord — which is very curious. The
scale of two tetrachords which was borrowed by the Greeks must there-
fore be of later date. The tetrachord was the best possible arrange-
ment for recitations limited to four notes. Suppose the tetrachord to
be B C D E, C would be the reciting or key note, having B, the
semitone below as the true seventh for drawing to a close. The
chief part of the recitation would be upon the key note, and there
was the power of rising to a major third above it, which was quite
enough for eastern recitation. By joining two such tetrachords
together they reduced the eight to seven, thus B, C, D, E, and begin-
ning with E again, E, F, G, A, and then putting the octave A at the
bottom they made our minor scale A, B, C, D, E, F, G, A. We had
that minor scale earlier in England than in France, having received it
through the Greek organ. We had a Greek as archbishop about
74 SECTION— PHYSICS.
the year 668, when Theodore was made Archbishop of Canterbury,
and Adrian was sent with him to watch him, because he was a
Greek, and might introduce some practices of the Eastern church
which were not sanctioned in Rome. We find that Saint Aldhelm,
who died in 705, began his " Praise of Virginity " with these words :—
" Maxima millennis auscultans organa flabris."
(Listening to the greatest organs with a thousand bellows),
Wolstan fully describes an organ of the loth century in the cathedral of
Winchester, with 400 pipes, and it required many men to blow it. I
am indebted to Dr. Stone for having made this model of the action
of the hydraulic organ from my description in the History of Music.
Here are two glass vessels, one inverted inside the other, and when
we inject air into the inner one, water is expelled, and rises in the
outer ; and when we sound the pipe, the air escaping, the water
returns to seek its own level. There are many erroneous descrip-
tions of the hydraulic organ. Some say it was worked with boiling
water, but that idea arose from the bubbling of the water. Thus
when the cork which now floats sinks to the bottom, it shows that
the vessel is filled with air, and if we continue to blow, the surplus
air will ascend in bubbles outside, and thus give it the appearance
of boiling.
The object of this invention of the Egyptian Ctesibius was to prevent
the possibility of overblowing the instrument, to which the pneumatic
organ was then subject. It proves that he understood the law that
" Liquids transmit pressure equally in all directions, and the pressure
they produce by their own weight is proportionate to the depth."
The CHAIRMAN : I am sorry that we have not time to discuss this
interesting subject, but I must now call on Mr. Baillie Hamilton.
AEOLIAN INSTRUMENTS.
Mr. J. BAILLIE HAMILTON : I am going to bring before your notice
the last result of three years' work, and I select this particular one
because it to a great extent embodies all the rest. I hold in my hand
a small object, consisting of the following parts. There is a vibrator,
consisting of the tongue of a reed, and above it there is a double
AEOLIAN INSTRUMENTS. 75
circle, which can be made of any form to afford an elastic constraint.
There is here a rod which forms a prolongation of the vibrator, and
upon the reed a weight which can be turned upon a screw. By means
of this weight the pitch of the note can be regulated to the utmost
nicety, nor is there any chance of that being deranged ; and by the
constraint of this ring can be given any tone which I may desire.
This little object embodies all the capabilities and all the phenomena
characteristic of the asolian sounds ; and when I speak of an seolian
sound, I do not mean necessarily that of the seolian harp, but all that
class of phenomena which occur whenever wind is applied to strings
directly or indirectly. Here is a board illustrating the progress of
wind and string amongst civilized nations. First of all, there is the
earliest form of the asolian harp, in which the string was exposed to the
action of the wind. Then, next, Professor Robison used a flattened
reed, which was exposed to the wind along its whole length — a ribbon
lying in a long narrow slit, and by that means the fitful sound of the
asolian harp was reduced to one steady note. The next notable
change was that which took place under Sir Charles Wheatstone,
and I have here the original apparatus which was used by him, by
which the wind was concentrated on one part of the string's length.
There is another form in which the wire of a pianoforte was used, but
in other respects it did not vary. At least six names are connected
with those two forms, amongst whom I may mention Sir Charles
Wheatstone, Mr. Greene, and Isoard. Here for the first time is used
a reed in connection with a string, and that was used thirty years
ago by a man named Pape. It consists of a free reed as used in
harmoniums, and a string apart from it, the connection being effected
by means of silk thread, so that the reed acts only upon the string in
the backward motion. Then comes another form in which the string
could be played upon by hand. That was made by a man called
Julian twenty years ago. Here again is a string flattened at one
point to a tongue, which lay between flanges in a frame, and that
could be played upon as in a violin. The method upon which I
founded all my investigations is here shown. It consists of a reed-
tongue, instead of a flattened portion of a string attached to the end
of a string. That was first invented by Mr. Farmer, our organist at
Harrow. Here is the reed and string brought into direct and rigid
76 SECTION— PHYSICS.
connection, and here is the mode which I suggested, in which the
string is set apart from the reed, so that it can be used in its own
register as in a harmonium. When we get as far as this, and the
reed-tongue and string are used, there is no longer any room for
originality as regards either wind and string, or reed and string, but
there is plenty of room for improvement. When the reed-tongue is
put to the end of a string, you may make the string act, but the farther
you get from the reed the intervals get wider and wider, because the
amount of control exercised upon it gets less and less ; and if you go
as far as the sixth interval, it would be widened out immensely, but
you seldom even get as far as that, because the string would bring up
into new combinations of nodes and segments, or refuse to speak
altogether. After trying a whole year to make a wind violin on this
principle, I gave it up in despair, because I could not get enough
intervals, and because they were so irregular; also because the tone
varied. When you are close upon the reed, the reed is constrained in
its motion and the tone is pure, but as you get away it is less con-
trolled, and the tone becomes more loose, coarse, and reedy. It was
only within the last four months that it occurred to me to use a conical
form of string. The small end is applied to the reed, and as it
departed from it it got larger and larger in bulk, and accordingly
the intervals remained the same, and the tone remains the same,
because you encounter the firm resistance of the larger string. There
is another curious thing also, that whenever you timed the string the
intervals pulled out, because the relative intervals in the string did not
remain the same ; the tongue entered into its composition to such an
extent ; but when you tuned from the small end of this conical string,
instead of the diminishing bulk of the string, you are able to maintain
the same bulk, and accordingly this new form of string has recovered
to us an instrument which I once abandoned in despair. But although
I thought it impossible to do anything in the way of a wind violin,
there was still a chance of doing something with the organ. If you
use merely one string and one reed, you can take the best note they
afford, and these difficulties of the intervals do not arise. Accordingly,
I tried to make an organ with a separate reed and string to every
note, and I found that whenever the string broke up into three
segments, it gave a beauty of tone which I could not gain by the most
AEOLIAN INSTR UMENTS. 77
deliberate means. The reasons for this superiority of tone, when a
string is broken up, may be understood when one considers that
any body, whether it is a plate, or a reed, or a string, or glass, when
broken up into segments, and so made to sound, gives an intense
harmonic tone. Each of those segments which compose that body
are of course vibrating, with smaller amplitudes than the whole
body would, if vibrating in the fundamental note. This is especially
desirable when the string has to encounter the resistance of wind, and
when the vibrator meets wind the great thing to aim at is that the
vibrations should be close and small. Therefore, the smaller the
motion you obtain for the vibrator, the more intense and clean the
tone will be. That was the reason why I always endeavoured to gain
the presence of the node to ensure this harmonic tone. Nothing
better could be desired than the tone when you got it, so long as time
was no object; but you had to wait for it, because there was this
resolving of the string, and it was also desirable that space should
be no object, because if you got a structure about 8 feet high, it was
a mild and convenient form of making a string organ. However, these
difficulties of space have now been overcome, and the largest note
required with a string corresponding to the 20 feet pipe of an organ is
•contained in this small box. It is the section of the register of the
pedal stop of a string organ, and instead of the string being exposed,
and liable to be deranged, it is stowed away inside, the wind escaping
through a channel and pallet controlled by the ordinary harmonium
treatment. The string is in that little coil, only a foot long, and
instead of going out of tune, which it did when it depended on the
string, it now no longer depends on the elasticity of the string, but
•upon a sort of bow or crook which is placed at the end, on which the
tension depends, so that the tension now depends on a spring, instead
of on the string. These improvements have only taken place during
the last few months ; for about this time last year, when I spoke at
the Royal Institution, matters were in such an unsatisfactory state
that I felt the only thing to do was to retire home, and never emerge
until something satisfactory was done. Mr. Hermann Smith came
with me, who entertained a singular theory on organ pipes and
their functions, which has received a very remarkable verification.
He regards an organ pipe as containing reciprocating action of two
78 SECTION— PHYSICS.
forces — a reed and a column of air which acts upon it. The column
of air restrains, steadies, and purifies the vibrator, which would other-
wise be coarse, and not worth hearing. The theory may be summed
up in a few words, that an organ pipe is a spring cushion re-acting
upon a lamina or plate. When we have a reed pipe, that is easily
understood. Here is the reed, and here is the spring cushion of air,
its elasticity depending on its bulk and proportion, but when you
come to a flue pipe, in which the reed is not apparent, it is not so
obvious ; but Mr. Smith regards the reed as still existing, and con-
siders that the sheet of air which passes from the mouth of the pipe
acts in fact as a reed. Bearing this fully in mind, its application to
the reed is easily seen. It one day occurred to me to make a double
ring of wire, which I did ; and fixed the two ends into a board, bored
a hole in it, and applied an open reed, and I found there was the
same result as with the string. We then determined we would analyze
what were the real functions of the string and of the reed, and a long
series of experiments took place, and at length it was found that in
order to gain the asolian tone there were three things necessary : there
must be constraint ; there must be sympathetic resistance ; and there
must be transmission, in order to gain power ; and those were all
contained in the first object I had tried, namely, the ring. The ring
first adopted was that of the simple form of a watch-spring, namely, a
double ring ; but one day on looking at Lissajous's diagrams, showing
the different forms of vibration, an idea occurred to me that a different
tone might be gained by a different form of spring. At first I had
only a ring, and this afforded perfect constraining effect, but there
was still the danger that to get perfect purity of tone you had to go
on increasing the power of the ring, until there was so much resist-
ance that the reed would not sound. The question was, how to get
fulness of tone by getting that ring of a certain size and a certain
elasticity, and yet that you should have the power of changing the
quality of tone, without altering those favourable conditions? Accord-
ingly, I have here eight different type forms of constraints upon the
vibrator. Supposing I have a piece of wire, I begin with the frame
of the reed, turn it over, come round, and attach the reed to it, and
continue its course until it conies round on the other side of the frame,
so that it forms a circle. That gave perfect resistance, and a perfectly
AEOLIAN INSTRUMENTS. 79
pure tone, and was sufficiently elastic to allow it to speak at once, and
afforded sympathetic resistance. Then, if you wished to change the
tone, how could it be done ? The next deviation was to flatten out
the two circles, and a further development was to bring them to
almost the shape of an almond. In passing from the simple circle
to that form, you pass through all varieties of tone from the flute to
the horn. The simple ring makes the simplest tone, and as you
depart from that more harmonics are allowed to be introduced,
because more play is allowed to the vibrator. If a rectangular figure
is adopted, it allows more freedom than the circle, and that gives the
tone of an open diapason pipe ; and when that is changed into a more
acute form, you get all the phases between the open diapason and the
trumpet. I will sound two or three of these notes just to show you
that there has been something absolutely accomplished, and that you
may hear two or three qualities of tone. I will not detain you longer,
but I have one thing further to say which is to show you what is the
upshot of all this. It is not merely that one means is substituted for
another. It does not concern a scientific body that there should now
be success in place of a forlorn hope ; but it means that that which
has very naturally encountered ridicule has come true : that the natural
division of a string being broken up, and made to sound by a reed, is
a means of affording a more intense and more pure tone, and a tone
is at once afforded by this natural coincidence better than any scale
could arrange ; and that a vibrator can receive from solid objects that
reinforcement which has hitherto been considered peculiar to columns
of air. When you once come to use solid surfaces, we know that a
square yard of vibrating surface can afford to any amount of notes an
equally good reinforcement. The whole object of these experiments
is to show that we may use solid bodies, instead of columns of air, in
re-acting upon a vibrator. This is the result which has been reached
so far. The greatest progress has been made during the last year, but '
I think what I have said is enough to enable you to judge whether
that result is worth obtaining, and whether it has been honestly and
patiently worked for. *
* In the interval between this lecture, and the lecture delivered at South Kensington
Aug 26th, so many improvements have been made, that this lecture is chiefly interesting as
indicating the stage of progress then attained.
8o SECTION— PHYSICS.
The CHAIRMAN : I now ask you to pass a very hearty vote of
thanks to Mr. Hamilton for his very successful research, and for the
extremely lucid way in which he has brought it before us.
The Conference then adjourned until two o'clock.
On reassembling, Mr. DE LA RUE, D.C.L., F.R.S., took the chair.
He said : There has been a slight change in the programme this
afternoon in consequence of the modesty of M. Tresca, which prevents
him speaking twice on the same subject. He has already brought
before the Conference his wonderful researches "on the Fluidity of
Solids/' and he desires, being present this afternoon, and being
connected with the " Conservatoire des Arts et Metiers " in Paris, to
speak of the historical monuments of science and on the institutions
which ought to preserve them.
UPON OBJECTS ILLUSTRATING THE HISTORY OF SCIENCE, AND
THE MEANS OF ENSURING THEIR CONSERVATION.
M. TRESCA : Gentlemen, Mr. Spottiswoode informed me yesterday
that he had put my name down for a conference upon the Fluidity of
Solids. It would have been impossible for me to comply with his
wishes, since I have already touched upon that subject on Wednesday
last ; and, consequently, I can only show you my good will by offering
you another subject for discussion. I will accordingly replace a
question, which, on repetition, might be considered too personal, by a
few observations on the most advisable means of preserving the
historical apparatus collected in your exhibition, but which are yet far
from sufficient in number to satisfy, as fully as might be wished, our
scientific curiosity. In England, Newton's telescope, Newcomen's and
Watt's steam-engines ; in Italy the apparatus of Galileo, of Torricelli,
of Volta, of the Academy del Cimento; in Holland, the instruments by
which Huyghens made his discoveries, and the apparatus of
s'Gravesande and of Otto von Guericke, certainly form precious collec-
tions, but how many other important discoveries would not have been
likewise represented, if as much care had been bestowed upon
preserving the instruments, as in publishing their results. Without
OBJECTS ILLUSTRATING SCIENCE. 81
far back into the History of Science, how many instruments
have disappeared ? After having been kept for some generations in
families, with the respect they deserve, they are often passed over un-
noticed and are lost for science, because they, in a very short time, cease
to present any definite interest. If preserved in the laboratory of the
philosopher, they are often disfigured for other reasons ; professors,
•vho have them at their disposal, are often carried away by the love of
science, and cannot always resist altering an ancient instrument, in
order to adapt it to the purposes of some experiment at that moment
under consideration When once the modifications have been made,
the instrument is never brought back again to its former construction,
and often the new arrangement does not entirely answer the purposes
of the fresh researches. And many a time has the very author of the
first discovery mutilated his own instrument in order to follow up the
investigation of some matter of secondary importance, and the original
apparatus is for ever lost.
These observations are suggested by the difficulties which we have
met with in collecting, as far as we could have wished, all the historical
instruments connected with French discoveries in science, and if we
have succeeded in bringing a certain number together at this exhibition
it is owing to the readiness shown by the directors of our scientific
establishments in responding to the call made by England.
To speak here only of the apparatus included in the Physical
Section, the " Ecole polytechnique," the " Observatoire,'' the " College
de France," the " Faculte des Sciences," have united with the
" Conservatoire des Arts et Metiers " in order to call to mind, by a
few original instruments, the discoveries of most of the celebrated
French scientific men. This last institution, founded at the beginning
ol this century, and endowed with all the valuable objects found after
the great political events of the preceding years, has been able to save
from destruction many instruments interesting on more than one
account. Those of the i8th century, however, are few in number ;
and we can mention but one or two that date as far back as the I7th
century.
The immortal Pascal, whom we might place by the side of
Torricelii, is only represented by his calculating machine ; and if it
affords but slight scientific interest it is, at least, undoubtedly
G
82 SECTION— PHYSICS.
authentic. As you may see, Pascal wrote on it with his own hand this
inscription : —
" Esto probati symbolum hoc.
" Blasius Pascal Arvernus, inventor. 20 Mai, 1652."
How much it is to be regretted that the original instruments employed
to prove and to measure the effects of atmospheric pressure should
not likewise have been handed down to us. Let me also draw your
attention to these two globes with clock movement by Just Burg (1586)
and Jean Reinhold (1588), and which are, moreover, so remarkable for
their chasing, attributed to Jean Goujon. The names of the makers
are, no doubt, of less importance, but the inscriptions are contemporary
with the change in the calendar, and the mechanism within them
cannot but offer us curious problems which demand no little investiga-
tion to prove certain much controverted points in the history of clock-
making
On the other hand, our collection, from the last years of the i8th
century, is extremely rich, in spite of frequent gaps, and you may see
the proof of it in the number of instruments which I have placed
before you, and which — should you find the subject interesting — we
will examine in the order which has been so suitably chosen for the
classification of the objects sent to this exhibition.
But before entering into these divisions, let me call to your notice
this small cathetometer by Dulong, the first that was ever constructed,
and which was made under the direction of that celebrated man. It
has been used as a model for all similar instruments, by means of
which the numerical values of the differences observed in the principal
phenomena have been able to be computed with exactness.
In the Section of Sound we should have wished to renew Savart's
beautiful experiments on vibrations, but the plates on which he studied
them have not been able to be arranged as they were originall>, and
so we have been forced to be satisfied with his musical instruments,
near which you see the Register of Duhamel, who was the first to
succeed in inscribing with sufficient precision the vibrations of
sound. The determination of the velocity of sound is brought before
you by M. Regnault's original apparatus and also by the one of M. Le
Roux, who arrived, at about the same period, at a nearly identical
conclusion.
OBJECTS ILLUSTRATING SCIENCE. 83
To judge by the number and the perfection of the modern French
optical instruments sent to the exhibition, there would be reason to
believe that this branch of science is more attended to in France than
anywhere else.
It is true that we have been fortunate enough to secure, in the
various sub-divisions, historical instruments bearing well-known names.
Fresnel's first lens — a true landmark in the History of Science — is
accompanied by a large collection of models of the French light-
houses, from the first to those most recently constructed. And
thus all the improvements which have been effected in this powerful
means of averting loss of life at sea, can be seen at a glance. And
England is, indeed, the most appropriate place where we could have
exhibited such a collection which has been brought together, thanks
to the engineer who carries out, with so much skill, the administration
of our lighthouses.
Electric light has lately been applied to industrial purposes to an
extent that cannot but go on increasing. The machines made by the
" Compagnie 1'Alliance," and the Gramme instrument, can light up vast
workshops or timber-yards. And now M. Carre has succeeded in
making carbon artificially, which, used instead of crayons of coke,
gives a much greater regularity, although it burns faster. There is
every reason to hope that this manufacture will allow of the use of
sufficient compression, so as soon to get rid of the defect entirely.
The regulators used are those of M. Foucault, M. Dobosq, M.
Serrin, and of M. Carre himsc'f.
With regard to the determination of the velocity of light, here are
the two instruments made use of by M. Foucault and M. Fizeau ; it is
known that it was by means of the latter one that M. Cornu succeeded
last year, in his experiments between the Observatory and the Tower
of Montlhery, a distance of twenty kilometres. We have placed next
to them Wheatstone's revolving mirror, which belongs to the Paris
Observatory.
To this establishment we likewise owe Arago's interfcrential appa-
ratus, and the complete collection of his historical prisms ; I can
merely mention those of Biot, and Senarmont, and Jamin, and so
many others who have made themselves celebrated by their researches
in polarization, interference] and double refraction. M. Descloizeau
84 SECTION— PHYSICS.
must be named on account of the polarizing microscopes which he uses
for the investigation of crystals, and which complete, in another branch,
the series of goniometers of Charles, and Babinet, and Senarmont.
The spectroscope is now largely employed for industrial purposes.
Here is the whole collection of instruments of M. Dubosq and
Laurent, who have with such signal results followed in the steps
of M. Soleil.
You know M. E. Becquerel's phosphoroscope, but I advise you to ex-
amine the small tablet upon which one of our most skilful glass-blowers
has written in large letters this one word : Phosphorescence. If this little
plate be exposed for a few instants to the rays of the sun, it is affected
in such a way that all the letters appear luminous and assume different
colours. The phosphates, with which the tubes are filled, then vibrate,
each in its own fashion, conformably to the principles laid down by M.
Edmond Becquerel, and the light which it gives out is of such brilliancy
that it makes this phenomenon of phosphorescence one of the most
beautiful of optical experiments.
I will point out presently the heliostats of s'Gravcsande, of Silbcr-
mann, of Gambey, and of Foucault, which are in this exhibition. They
form an almost complete collection of these instruments so precious for
observations.
We have decided to entrust to you Daguerre's second proof. It
is with great satisfaction that we have noticed the precautions
you have taken — by placing it in a red glass frame — to preserve
in a fitting manner this first specimen of a great art. And we are most
happy to have been able to place by the side of the historical picture of
the Photographic Society of France, in addition to Daguerre's attempts,
those lent to us by M. Fizeau, and which represent the fixture by
chlorate of gold, and his process of photo-engraving which marks a
first and most important epoch in the annals of photographic repro-
ductions. The stone and the proof by Poitevin call to mind undoubtedly
the most important step which has been taken since then.
Daguerre's attempt carried out in red glass, without mercury, by
M. E. Becquerel, and especially his coloured spectrum, are also very
striking curiosities of photography. M. A. Girard's microscope is a
more practical object : it gives directly magnified impressions of
microscopic objects placed before the object glass.
OBJECTS ILLUSTRATING SCIENCE. *>$
The French cases exhibit, through the original apparatus of our
principal inventors, the most complete history of the studies and dis-
coveries in heat. The measurement of heat is represented by the
instruments of Lavoisier, of Dulong, of Regnault, of Favre and
Silbermann ; observations on sideral heat by the actinometer and the
pyrheliometer of Pouillet, and by the actinometer with thermo-electric
pile of M. Desains. The metallic bars of Despretz are those which he
used for his first experiments on the conductibility of solids ; Gay-
Lussac, Despretz, M. Dumas, and M. Regnault remind one of the
uninterruoted series of studies on the density of gases and vapours ;
the collection of M. Regnault's apparatus is a proof of the gigantic
labours which he has successfully undertaken to place upon a firm
basis the actual facts connected with the science of gases and
vapours.
With regard to the measurement of the expansion of bodies according
to the method of Newton's rings it has become, in the hands of M.
Fizeau, perhaps the most exact of all those connected with the science
of heat.
For the very reason that discoveries relative to magnetism are com-
paratively of recent date, we have been able to procure some historical
objects of great value.
M. Jamin has given us his great artificial magnet, made of thin plates
of steel, which can lift 200 kilogrammes, and which this skilful experi-
mentalist used as a starting point for his studies on the laws of magnetic
distribution, which had been, up to that time, so little understood.
We have placed next to it the model of Gambey's deflecting compass,
one of the finest instruments from the hands of that celebrated man.
In the collection of the Ecole Polytechnique, the small natural magnet
belonging to M. Obelliane is remarkable as being, with regard to its
weight, by far the most powerful magnet known ; it can lift forty times
its own weight.
With regard to electricity we are necessarily less rich in historical
models, but nevertheless the series of discoveries made by French
scientific men is tolerably complete.
Among the electrical piles may be noticed the fine collection of the
different models reproduced by M. Ruhmkorff and the considerable
effects of the secondary pile of M. Plantd ; among the thermo-electrical
86 SECTION— PHYSICS.
apparatus, the piles of Pouillet and of M. Becquerel, as well as his
thermometer and his pyrometer. Thermo-electrical needles have, for
some years, been put to a great number of different uses.
This support and this "solenoide" are particularly deserving of
your respect : They are those of Ampere, and the College de France
wished that this table which forms part of the apparatus, and by
means of which the celebrated philosopher varied his experiments
and proved the laws of the action of currents upon currents, should
be exhibited here. And thus, for the first time, the means of the
discoveries of Volta, of Faraday, and of Ampere are to be seen undei
one roof.
Ruhmkorff s great induction bobbin (bobine d' induction) represents
in itself alone a new conquest by science ; but, in the Telegraph
Division, in spite of the very interesting telegraphic apparatus of M.
Mayer, of M. D'Arlincourt, of M Deschiens, of the military system of
M. Trouve, and of our telegraphic administration, we cannot show a
collection at all comparable to fine English one, which commences
•with Wheatstone, and which forms a complete museum of this portion
of the History of Science in its relation to the every-day wants of
modern society.
On the other hand, you will no doubt have observed the models of
the first optical telegraphs by Chappe, Betancourt, and the last optical
telegraph of Colonel Laussedat. Galvano-plasticism is only repre-
sented by Jacobi's first work, already perfect, and which the inventor
presented to the Conservatoire in 1868.
With regard to modern astronomy, a few instruments only are to be
seen at this Exhibition, but they have been selected with the view of
interesting persons engaged in this science. Here is the siderostat, of
which the mirror has been improved by Foucault himself, and the photo-
graphic telescope which was used for observing the transit of Venus
from Campbell Island, one of the French stations in this astronomical
campaign in which all the learned nations took part. The proofs given
by these telescopes have allowed of tolerably numerous data being
obtained, which measured, at leisure, under the direction of M. Fizeau,
by micrometric means, already permit us to state the exactness of the
figures which may be deduced from them for the chief results of the
phenomenon.
OBJECTS ILL USTRA TING SCIENCE. 87
Nor have we failed to exhibit at Kensington the pendulum, by means
of which Foucault succeeded at the Panthdon in his first attempt to give
a direct demonstration of the rotation of the earth ; it is accompanied
by the plaster sphere on which he drew his preliminary figures, and
by the "entreteneur" which he had constructed afterwards in order to
make the demonstration continuous. The "entreteneur" is the one
which he sent to the Exhibition of 1855.
I will not speak at greater length on this subject, especially as M.
Le Verrier intends soon coming among you to praise the English
astronomers, and particularly Bradley, for whom I know him to enter-
tain the utmost veneration, in consequence of the methods he has
followed, and of the marvellously accurate results they have always
produced.
In calling your attention, Gentlemen, to a few of the historical ap-
paratus of French science, we have certainly not had the intention of
exciting competition. If it gives us pleasure to show our instruments,
we are also most happy to see yours ; and judging from what we have
already seen of your exhibition, there can be no doubt that if, under
the direction of my excellent friend Mr. Owen, whom I notice among
you, the idea was seriously entertained of devoting the great resources,
which you have at hand, to the foundation of an institution similar to
our Conservatoire, you would very soon obtain the most satisfactory
results.
If such is your intention, we would seize the opportunity offered us
of assuring you of our hearty co-operation and assistance.
We are, however, not generous enough to be careless ot any return
for our good wishes, and we are already thinking of asking your leave
to have copies made of some of your most precious documents : it is
good that it should be known everywhere with what a small instrument
great discoveries could be made in Newton's time, and it is also
necessary that our scientific men should have in their labora-
tories perfectly accurate copies of the apparatus of Wheatstone and
of Joule.
When we shall possess authentic specimens of all your historical
models, and when you have copies of all ours, the yet unsettled points
in the history of science will decide themselves ; the same discovery
will bear everywhere the same name ; indisputable dates will put an
S3 SECTION— PHYSICS.
end to all competition, and science will henceforth have acquired, in a
firmer manner, both with regard to the past and to the present time,
that cosmopolitan character which it is so important for it to
assume.
The CHAIRMAN : Ladies and Gentlemen, you have anticipated, as
I am sure you would do, the proposal I intended to make of inviting
you to thank M. Tresca for his very lucid review of the instruments
contributed by France, and connected with some of the grandest
discoveries of the French savans, but for the few words he has
been so good as to utter, they might pass unnoticed by a great number
of persons. The names of Biot, Arago, Becquerel, Ampere, Daguerre,
Fizeau, Pascal, Savart, Fresnel, Lavoisier, Dulong and Regnault are
all historical names in science, and we are very happy to have even a
small portion of the apparatus which they used. I need only refer to
this wonderfully simple piece of apparatus devised by Ampere for
the foundation of the electro-magnetic discoveries with which
science has been enriched by so many savans, not the least amongst
them our own Faraday. The ingenious instruments, which M.
Tresca has passed so rapidly in review, recall one's recollection to
one's reading and experience respecting the progress of science during
the last fifty years, and if the next fifty years are only as prolific in
discoveries as the last it will indeed be a privilege to live in the days
in which they occur. The last outcome of the work is the production
of magnets of great power by M. Jamin ; I possess one which is so
powerful that it will allow itself to be held out horizontally by its
armature. Many years ago the Dutch were considered to construct
the strongest magnets, but by this beautiful arrangement of magnetic
plates attached to each other far more power is obtained. M. Tresca
has also alluded to a photograph produced by the red rays by
Becquerel. We all know that the red rays and the ultra red rays
possess very little actinic power. Their study has been taken up
recently by Captain Abney, and we may hope some day to get the
whole spectrum, not only photographed but also fixed ; it was photo-
graphed some time back by M. Becquerel, and this case, which is
very properly locked, so that it cannot be opened except under proper
precautions, for exposure to strong daylight would spoil it, contains
his photograph of the whole spectrum in its natural colors : And the
ON THERMOPILES. 89
day may come when we may not only get portraits and delineations
merely in monochrome, as it were, but get photographs of natural
objects in their natural colors. The review, which M. Tresca has
been so good as to give of the progress of French science, illustrated
by a selection of the apparatus used by philosophers of the great
names he has enumerated, is highly important. He has alluded
also to the difficulty he has experienced in collecting such objects,
simply because they are very seldom taken care of when once they
have served the purpose of their authors ; and has also mentioned
the grand institution in Paris, the Conservatoire des Arts et Metiers,
with which he is intimately connected, in which are contained some
of the most valuable records of the progress not only of science
but of the mechanical arts. He has also alluded to a rumour he has
heard that something of the kind is contemplated in England. I
only hope that this may have effect, and that in this country we
shall not in future have to regret the loss of apparatus which he
has deplored on the part of the French ; and that, eventually, all
those pieces of apparatus which have served and will serve for
scientific discovereries may be preserved for future generations. I
point again to this very beautiful and simple apparatus of Ampere's to
show what very small means are required to effect the most grand
discoveries ; and I ask you, again, to repeat your thanks to M. Tresca.
Mr. Ranyard had promised to give us a description of the astro-
nomical instruments contributed by the Astronomical Society, but I am
informed that they are not yet sufficiently well arranged for him to give
you his intended discourse, and we will therefore defer that to next
week ; and I will now call on Lord Rosse.
ON THERMOPILES.
The EARL OF ROSSE, D.C.L., F.R.S. : I have been asked to describe
in as few words as I can the thermopiles which I use with the moon,
as I believe they are more successful than any other apparatus which
have been tried. I am happy to do my best to make my method of
observation intelligible to the public. There are very few points I
need refer to. Of course if I went into the whole subject, and into
90 SECTION— PHYSICS.
the results, it would take much more time than we have at our disposal.
This is the actual apparatus which was used in most of my experi-
ments. I may mention that the reflector of my telescope is three feet
diameter. The larger telescope, which is six feet, was not used for the
purpose, because it had only a very limited range of motion, only
about twenty minutes to half an hour on each side of the meridian,
and therefore there was only that length of time on any night on
which to make observations, and clearly, anywhere but especially
in an uncertain climate like ours, it is desirable to seize on every
moment when the moon may be sufficiently high in the sky. The focal
length is about twenty-seven feet, and this apparatus was presented to
the mirror, being fixed in the mouth of the tube, the small condensing
mirrors being fixed in the focus of the large mirror. These mirrors are
of about three inches focal length, and the thermopiles are placed in
their foci, so that the whole light that enters the tube of the telescope,
or falls on to a space of three feet in diameter is first concentrated by
the large mirror on to the surface of each reflector, and then by them
concentrated further on to the faces of the thermopiles -| inch diameter.
The reason why I used two reflectors was to destroy the disturbing
effects of the various strata of the atmosphere, the clouds which might
be over it and those arising from heat and cold acting unequal
on the thermopiles. The effect of using two mirrors is that they
neutralize in one another the differences produced by heat and cold
falling on the apparatus, as they act in opposite directions. If the
heat of the moon be turned alternately on this reflector and on that,
you pimply get the effect of the moon doubled, but by throwing it on
one and then off it, you get the single effect. Many of the details of
the apparatus are hardly of general importance, because it is adapted
to the instrument for which it is used. The mounting of the instrument
was at that time an altazimuth which, as all astronomers know, is an
inconvenient one to use for this purpose, as it is necessary constantly
to work both the altitude and azimuth motions in following the
motions of the heavenly bodies. The image being seen by the attendant
on each mirror alternately, he swings the tube of the telescope which is
suspended by a rope until he sees the moon's image on the reflector
where the slight dust or tarnish allows it to be seen. There is only one
point I think I need allude to further, and that is the construction of
ON THERMOPILES. 91
the thermopiles. I am not aware that anyone has brought this
principle to bear either before or since. In the ordinary thermopiles
the number of elements is very great ; a plate of bismuth is soldered
to one of antimony, and you have as many as you please, and the
solderings all side by side form the surface on which the heat acts. If
you applied this to the moon the moon's light would shine on each of
the solderings and you would have some of the effects on all the
separate solderings. I found some difficulty in getting thermopiles of
sufficiently equal parts to use in the apparatus, and therefore I thought
of a simpler form which was within my own powers of manufacture.
I tried to make thermopiles with several alternations, but the matter
is one of great delicacy ; the bars are so thin and have to be handled
with such a care that a maker told me that after making them for
some years his sense of touch became so delicate, and he handled
everything so lightly, that he frequently, without intending it, let fall
heavier things. I adopted the plan of having one bar of bismuth and
one of antimony soldered to a copper disk. I made the bars finer
and finer every time, and the finer I made them the stronger was the
effect, because the cross section to carry away the heat and the mass to
be heated were smaller, and the limit of the thickness really was the
difficulty of manufacture. By having a thin disk of copper I was able
to work with much finer bars. I think this construction of a thermopile
is worthy the attention of instrument makers, because it so much simpler
to make. I do not see any reason a priori why as great an effect
should not be obtained from that construction as from fifty or sixty
pairs. The heat falls on the face of the copper which is a good con-
ductor, and if it is perfect I see no reason why there should not be nearly
as much power obtained from a single pair as from a great many. I do
not think there is anything else I need say on this subject, unless it is
to state the amount of heat obtained which I compared with that
obtained from a vessel filled with boiling water. The heat derived
from the moon would lead one to infer that the radiation was equal to
what it would be if the moon's surface at full moon was at about the
temperature of boiling water, or something like 200° Fahrenheit. Ot
course the assumption must be made that the moon has the same
radiant power as a lamp-blacked surface of a tin vessel of boiling
water, and that we have no right to assume at all. In fact I ought
92 SECTION— PHYSICS.
simply to say that that assumption is made in order to enable another
hereafter to calculate what is the probable radiating power of the moon.
I placed a sheet of glass so as to intercept the rays of the moon, and
then I found the heat was all intercepted except ten or twenty per
cent, showing that the moon's heat was of a different quality and lower
refrangibility than the sun's heat, because the sun's heat on an average
gives eighty per cent, of the power through a glass against ten to twenty
per cent, of the moon's rays. I might also add that the concentration
obtained by this apparatus is very large. The moon's light spread on
a three feet diameter is concentrated on a third of an inch, which would
represent a concentration of the moon's light of about 1 1000 times, and
allowing for loss by reflection by the large mirror it would be about
4 $00 times.
The CHAIRMAN : I believe Lord Rosse will also describe to us a
photometer, which is also on the table.
ZOLLNER'S ASTRO-PHOTOMETER.
LORD ROSSE : This is not a piece of apparatus with which I am
particularly connected, but I have brought it for description, because
it appears to be very little known in the British Isles. It is a German
instrument, devised by Professor Zollner. Our climate is not at all
well suited for photometric observations, because of the variability
of the transparency of the atmosphere, and the number ot clouds
which perpetually interfere with the observations. But this instru-
ment has been used in the German climate very generally, and
appears to rank very highly. Its primary object was to compare the
light of various stars. There is one considerable difficulty in com-
paring the light of stars, which does not occur in some other
photometrical experiments, viz., that you have to compare them as
accurately as possible when they are of different colours, and it is a
problem, therefore, to which only an approximate solution can be
given. In comparing two stars, you have simply to equalize the
colour as far as you can of the lamp which is used, and then, by
trying backwards and forwards, to seek to get the mean result as
accurately as you can. There is a small pin-hole which admits the
light of the lamp. It passes first through a double concave lens, then
ZOLLNERS ASTRO-PHO TOME TER 93
through a Nicol prism, then through a quartz plate, by means of
which the colour is varied, and then through two more Nicol prisms.
The pin-hole forms a minute point of light, and there is also a double
concave lens which brings the light to a focus. The light from the
natural star comes through an object glass, and is seen by the
side of the artificial star, reflected by a diagonal clear plate of
glass, whilst that of the star passes through the glass with very little
diminished brilliancy. The size of the pin-hole may be varied, there
being six different sizes attached to the instrument. There are various
telescopes used with it; this is the smallest size, a very small one
being used for very brilliant objects. For observing Venus you require
a very small aperture, or else you never get an image faint enough to
compare. The concave lens is to make the light smaller and more
like the light of a star. Passing through the first Nicol, by turning it,
in combination with the quartz, you are able to vary the colour. It
then passes through the other prisms, which can be turned round,
and you can thus vary the intensity according to the well-known law.
It is usual to take four readings, and then find the average. Professor
Seidell, of Munich, who worked at the stars with this instrument,
obtained complete observations by four readings within the limits
of probable error of about 8f per cent. I may mention that the error
of one night's observation of the moon's heat by the thermopile was
about 10 per cent, on an average. It is rather less accurate than this
instrument was in Professor Seidell's hands, but I do not think, with
the practice I have had with this, I could get quite as good a result
as with the thermopile. Here is another piece of apparatus attached
to it, which is used for measuring the moon's light. It is similar to
that described above for forming the artificial star, except that there
is no quartz plate. In using it you see in the focus of the eye-piece
three stars, two from the lamp — one coming from the back surface
of the lamp, and the other from the front, and one of the moon;
and a very practised eye would be able by changing the position of
the Nicol to make the image of the moon intermediate between the
brilliancy of the two, the difference in their light being due simply to
the absorption in passing twice through the thickness of the glass.
The CHAIRMAN : Lord Rosse, who is a most worthy successor to
his illustrious father, has been good enough to explain to us some of
94 SECTION— PHYSICS.
the improvements which he has been making in the great telescopes
which he inherited from their constructor. It will be in the recol-
lection, I daresay, of many of you, that in all instruments at that time
you had to get two movements, and it is no easy task to mount them
on an axis inclined parallel with the earth's axis. That, Lord Rosse
has now effected, and is now improving the equatorial mounting, and
also the means for the observer to reach the telescope, which is not
very easy with either of those enormous instruments. He has nearly
completed the mounting of the three feet, and if that is farther carried
on to the six feet telescope, we may expect far greater results than it
has hitherto yielded, inasmuch as the objects which have to be
observed are, of course, carried round by the diurnal motion of the
earth, and the large telescope being mounted only with an hour's
range on each side of the meridian, you perhaps can only catch them
very occasionally. If, however, he mounts the six feet telescope to
reach any part of the heavens, undoubtedly new features will ccme
out. It is a very beautiful investigation he has carried out with
respect to the heat radiation of the moon. It was thought at one
time that no heat reflected from the moon reached us, but he has
shown in the most effectual manner, eliminating all radiation from the
atmosphere near the moon, that there is a positive amount of heat
reaching us from the moon.
I ought not to omit calling your attention again to this beautiful
apparatus, the thermopile — the application, as he has said, of an
ordinary thermopile. The difficulty of getting two exactly alike in
their indications is extremely great, but by this beautiful contrivance
of receiving the image of the moon on a large plate, and allowing it to
conduct the whole effect to one joint, was a very happy thought, and
it has been most admirably carried out. I beg you to offer your
thanks to Lord Rosse.
Lord Rosse here took the chair, whilst Mr. De La Rue gave the
following account of his new battery: —
Mr. DE LA RUE : I have ventured to take somewhat out of order
'the description of a piece of apparatus which may have some interest
for you. It is a galvanic or voltaic battery, particularly applicable to
those cases where a very large number of elements is required. It
is extremely. -simple, and. consists essentially of a flattened wire of
MR. DE LA RUE'S BATTERY. 95
silver and a rod of zinc. At one end of the silver D is a cylinder of
chloride of silver cast upon it. In order to prevent contact between
the rods of zinc and chloride of silver, the chloride of silver is
surrounded with a cylinder A, open at the top and bottom, made of
vegetable parchment. B shows the rod of chloride of silver surrounded
by the cylinder.
Figure I.
Ag.CL
The cell is a glass tube ; the stopper is a cork, made of paraffin,
and a rod of non-amalgamated zinc is inserted through a hole in it ;
and then there is a second aperture, closed with a small paraffin
plug, to enable one to fill the tube with a solution of twenty-three
grammes of chloride of ammonium to one litre of water. I could
not send the whole of my battery here ; first of all, it is not easily
conveyed ; and, in the next place, it would be difficult to show its
effects without special preparation ; but I can show you one of this
96 SECTIOK-PI1 YSICS.
Figure 2, showing ten cells of a rod — chloride of silver batUry in
their tray.
kind composed of forty cells. When I connect it with a Voltameter,
which is a piece of apparatus for the decomposition of water and the
collection of the products of decomposition, you will see that there
is a rapid decomposition for the size of the battery, and that a
certain accumulation of gases will take place. The object of this
battery is to follow on the lines already laid down by our excellent
and distinguished friend, Mr. Gassiot, who was the first, I believe,
to construct batteries with any very large number of cells. I recollect
he began with a water battery, in which there was a plate of zinc, one
of copper, and distilled water as the electrolyte. With this he made
some very interesting experiments, and showed that which was
doubted at one time, that the voltaic spark will jump some distance
MR. DE LA RUE'S BATTERY. 97
before actual contact is made between the poles. We all know that
when once contact is made, and the poles are afterwards parted,
a beautiful arc of light, the voltaic arc, passes between the terminals,
and the action is then continuous. He obtained some very beautitul
results, with the discharge of the voltaic battery in residual vacua in
tubes pretty nearly exhausted of the gases which they contained, and
was one of the first, I beleive, to observe the stratification which
takes place in these discharges. In a tube connected with the poles
of a battery, or with the secondary wire of a Ruhmkorff coil, the
discharge is sometimes continuous as a sheet of nebulous light,
but mostly is beautifully stratified, and these stratifications we find to
be different for different tubes. There has been no incontestable
explanation yet given of the cause why we should have intervals
of light and dark in the electric discharge in vacuum tubes. Mr.
Gassiot carried on for many years a number of experiments, latterly
with 3500 Icelandic cells, with a view to elucidate the theory, and
.since he has in a manner relinquished them, I have taken up the
.subject in conjunction with my friend Dr. H. W. Miiller. We have
now 5,640 cells at work, and are adding 2,400 more, which will be
at work in a few days.* If I could have had wires laid here from my
laboratory, I could have repeated many instructive experiments. We
have obtained some very curious results, which will form the subject
of a communication to the Royal Society. The number and form of
the strata varies, depending first of all on the individual tube, and the
nature and tensions of the gases it contains, and also on the electro
motive force of the battery and resistance interposed in the circuit'
One may make the number of strata greater or less. Generally, if one
introduces very great resistance their number augments, and as one
takes out the resistance they diminish in number, and their width
becomes greater, but this law does not always hold good, for there are
.some tubes which behave in exactly the contrary manner. But there
is one point that I wish to bring particularly under your notice, and it
* 8,040 cells have been completed since this discourse, part of them, 3,240, have the
•chloride of silver in the form of powder, and are not so energetic as when it is in the form of
a rod fused on to the silver wire. The striking distance of 8040 cells between a point (positive),
-and a plate one inch in diameter (negative), is 0.345 inch rather greater than one third of an
inch.
H
98 SECTION— PHYSICS.
is this : — formerly it was a point of doubt whether the spark would
jump any appreciable distance before the circuit is closed. We have
found the length of the discharge to be in the direct ratio of the square
of the number of elements, and that leads to some very curious
conclusions. For instance, in the paper, from the Proceedings of the
Royal Society r, I have before me the results given as follows :
Cells. Rod chloride of silver. Striking distance.
600 '0033 inch.
1200 -0130 „
1800 -0345 „
2400 ... -0535 „
which is very nearly the square of the number of cells. But as we have
carried the number of experiments further we find that the striking dis-
tance increases in a far greater ratio. But even if the striking distance
does not increase in a greater ratio than that and looking upon 1000
cells as unit — because with this high intensity we must have a larger
unit than one cell — if we carry the battery up to 1000 units, or one
million cells, the striking distance would be 764 feet, a true flash of
lightning not only in distance but in quantity. I think it is not likely
that a million cells will ever be made, but it is quite possible to carry
up the number to 20,000 or 30,000 cells, and it is almost impossible to
foresee the results one will obtain as the number increases. The
advantage of this battery is that one can have it in one's laboratory
always ready, walk in and make experiments at any time. Most
other batteries from efflorescence or other causes continually get out
of order, but with this one the first thousand was charged up in
November, 1874, and to-day I was working with it and had the
honour of showing some experiments to some of our foreign visitors.
The acting electrolyte is the solid chloride of silver, which is insoluble
in the weak solution of chloride of ammonium, with which the cells are
charged, and yields up its chlorine only when the circuit is closed ; at
other times no action takes place, and consequently no consumption
of material occurs ; indeed, the battery remains always in action,
and is very nearly constant. You notice figure 2 that the stoppers
are made with paraffin, the feet are of ebonite, and the connectors
are mounted on ebonite, so that the insulation is very perfect, and
very little leakage takes place. It is most agreeable to be able to
MR. DE LA RUE'S BATTERY. g9
walk into one's laboratory and to find the battery always ready for
work, and I am only sorry that the effects of 8,040 cells cannot be
shown to you.
Lord ROSSE : I am sure you will all return thanks to Mr. De La Rue
for his very interesting communication. The subject of batteries is one
of very great importance, not only in experimental physics, in which
a battery is a constant piece of apparatus, but in the telegraphic service
and other applications to the arts. A constant battery which will not
lose power by polarisation, or by working, or when it is not in work,
which many batteries do, is a most invaluable thing.
Professor ANDREWS : I have one single observation to make. I
must express my great admiration and delight at the fact that Mr.
DeLaRue is continuing thoseresearches which Mr. Gassiot commenced,
and I wish merely to correct one historical fact of which I happen to
have an intimate personal knowledge. It was not Mr. Gassiot in this
country but Sir Wm. Grove who observed these stratifications first. I
should have been unwilling to make the statement but that the correc-
tion I think is better to be made at the time, and I should add that
these stratifications were discovered about the same time in France.
It has been a matter of some little doubt whether a Frenchman, whose
name I forget, or Sir Wm. Grove was the first discoverer, but I believe
Sir Wm. Grove was actually the first. I am quite sure if Mr. Gassiot
were here, he would confirm what I say, that he does not claim the
discovery.
Mr. DE LA RUE : I am much obliged to Professor Andrews for the
correction, but as Mr. Justice Grove and Mr. Gassiot so frequently
interchanged their thoughts the confusion was natural, and I qualified
the statement by the saying I believed that was the fact.
Mr. DE LA. RUE again took the chair, and called upon Cavalierc
Professore de Eccher to read a communication on the instruments from
Italy, especially those of Gallileo.
ioo SECTION— PHYSICS.
ITALIAN INSTRUMENTS AT THE EXHIBITION OF SCIENTIFIC
APPARATUS.
Professor DE ECCHER : Your Queen was graciously pleased per-
sonally to thank the city of Florence and Italy for having sent the
precious relics of Galileo and of the Accademia del Cimento to this
first great International Exhibition of Scientific Instruments. Allow
me, once more, to express here our most heartfelt and respectful
thanks for such high condescension ; which clearly shows how much
importance England attaches to the historical instruments which you
see before you. But with this accession to their value, I feel a pro-
portional increase in the difficulty I have of speaking of them briefly,
when thick volumes might easily be written upon them. I, therefore,
humbly beg of you to excuse me if I fall short of your expectations.
Having done my utmost in order that Florence should contribute her
most precious relics to this solemn exhibition, I felt it my duty to
accept the honourable, but at the same time onerous, task entrusted to
me of explaining to you something of the principal instruments
exhibited here. I am now present to discharge this duty.
I will naturally begin with those of Galileo.
This great man, born at Pisa on the i8th of February, 1564, was
destined by his father for the medical profession ; but in the year 1589,
we find him mathematical lecturer at the university of his native town.
His powerful intellect, adapting itself badly to the uncertainties of the
art of medicine, had succeeded, almost unassisted, in mastering the
exact sciences — the only ones which could satisfy his craving to scruti-
nize and become acquainted with Nature. When he was yet but a
student at Pisa, he made the celebrated observation of the oscillations
of the lamp, equable through different arcs, from which he afterwards
deduced the theory of the pendulum and of the fall of weights. Here
are two photographs of portions of Galileo's gallery. This third one
shows the whole of the monument raised by grateful Tuscany to the
memory of the creator of modern science. In the first one you see the
student Galileo watching the oscillation of the lamp in the famous
cathedral of Pisa ; in the second, Galileo, as -mathematical lecturer,
repeating the experiments on the fall of bodies on inclined planes ;
ON INSTRUMENTS FROM ITAL Y. 101
and in the distance the Tower of Pisa, from which, by letting fall
bodies of different substances, he first showed how, but for the resis-
tance of the medium through which they pass, they would all fall in the
same time. Partly, perhaps, on account of being badly requited,
Galileo left the University of Pisa, and in 1592 we find him mathe-
matical lecturer at the University of Padua.
It was here that for the convenience of the youth whom he had to
instruct in the arts of fortification and mechanics, he invented his pro-
portional compass, also called military compass. This is one of the
many which he himself made. On one side may be seen four sets of
lines, they are : —
Arithmetical lines, which serve for the division of lines, the solution
of the Rule of Three, the equalization of money, the calculation of
interest.
Geometrical lines, for reducing proportionally superficial figures,
extracting the square root, regulating the front and flank formations
of armies, and finding the mean proportional.
Stereometrical lines, for the proportional reduction of similar solids,
the extraction of the cube root, the finding of two mean proportionals,
and for the transformation of a parallelepiped into a cube.
Metallic lines, for finding the proportional weights of metals, and
other substances, for transforming a given body into one of another
material and of a given weight.
On the other side of the instrument are :
Poly graphic lines, for describing regular polygons, and dividing the
circumference into equal parts.
Tetragonical lines, for squaring the circle or any other regular
figure, for reducing several regular figures to one figure, and for
transforming an irregular rectilineal figure into a regular one.
Joined lines, used in the squaring of the various portions of the
circle and of other figures contained by parts of the circumference, or
by straight and curved lines together.
There is joined to the compass, as you see, a quadrant, which,
besides the usual divisions of the astronomical compass, has engraved
on it a squadron of bombardiers, and in addition, these transversal
lines, used for taking the inclination of the scarp of a wall.
From Galileo's own correspondence we gather that in 1598 he had
102 SECTION— PHYSICS.
already presented his compass to the Prince of Holstein, and shortly
afterwards he sent two others in silver, the one to the Archduke
Ferdinand of Austria, the other to the Landgrave of Hesse ; and he
mentions besides that he had had 100 made in Padua by Antonio
Mazzoleni, which he distributed among his patrons and admirers.
Here is the thermometer, or rather the thermoscope, as it first
appeared from the hands of Galileo.
As far as my knowledge goes, the invention of the thermometer has
been attributed to several philosophers ; among the principal are
Bacon, Robert Fludd, Cornelis van Drebbel, and Sanctorio.
In the first work of Bacon, " De Augmentis Scientiarum," the ther-
mometer is not mentioned, nor is there any allusion to it in his second
work, " De Sapientia Veterum ;" but in the " Novum Organum,"
published in 1620, he describes a thermometer similar to the one you
see before you without, however, declaring himself its inventor. With
regard to Fludd, he published a description of a thermometer about
the year 1603, after having visited Italy and spent some time at
Paclua. Sanctorio, without giving himself out as the inventor,
describes a thermometer in his works published in 1625. In favour
of Galileo, however, we have the testimony of Padre Benedetto
Castelli, who in a letter written in 1638 to Dr. Ferdinando Cesarini,
relates as follows : " I now call to mind an experiment shown me, more
than thirty-five years ago, by Signer Galileo. It was this : a little
glass bottle was taken of about the size of an egg, having a neck thin
as a stalk of corn and about two spans long, and it was well warmed
with the hands [you see that the instrument I am holding corresponds
perfectly with this description, so that I am able to repeat the experi-
ment before you] ; then, the mouth of the bottle being turned upside
down into a vessel placed underneath, in which was a little water,
and the warmth of the hands being removed, the water immediately
began to rise in the neck, and continued to do so until it was more
than a span higher than the level of the water in the vessel. Signor
Galileo had made use of this effect to construct an instrument for
investigating the degrees of heat and cold/'
With regard to this instrument we might well say that Galileo
would thus have invented the thermometer even before the year 1603.
We have, moreover, the evidence of Signor Giov. Francesco Sagredo,
ON INSTRUMENTS FROM ITAL Y. 103
a noble Venetian, who, writing to Galileo on the 9th of May, 1613,
says : " The instrument you invented for measuring heat, has been
reduced by me into several very convenient and excellent shapes, so
much so, that the difference of the temperature from one room to
another can be seen up to 100 degrees. By the help of it I have
observed several marvellous things, for example, that in winter, the
air is colder than ice and snow ; that at this season water appears
colder than the air ; that very little water is colder than a great
quantity, etc.," adding that some peripatetics believe, " that the con-
trary effect ought to ensue, because heat having, as they say, an
attractive power, the vessel in becoming warm ought to draw the
water to itself. Then Vincenzo Viviani, in his life of Galileo, affirms
that between 1593 and 1597 he invented the thermometer. Galileo's
not having made any mention of his works ought not to create
surprise ; for the fact is that he undoubtedly communicated all his
discoveries to his friends and disciples long before he made up his
mind to write about them.
But in any case it is well known that the thermometer was for a long
time called the Florentine Instrument ; and this indeed is accounted
for, since it was in Florence that it received its most important im-
provements, thanks especially to Ferdinand II. Sagredo, however,
was the first to divide it into degrees (in 1612), and it was he also that
closed it hermetically about the year 1615. The improvements effected
by Ferdinand were described by Padre Urbano Daviso, who, after
having mentioned that he gave it a special shape (corresponding to
the one we now see), and that he filled it with coloured spirits of
Avine instead of with water, which, by freezing, breaks the glass, adds :
*' Hence it may be seen which of two liquids gives out the more or less
heat or cold ; and it will be possible to warm water, or a room, or a
furnace to any degree ; to keep it at that temperature, or raise it ; to
know when a thing has reached that state of heat necessary for cooking
it properly ; all operations from which it may be said that the chemical
art has received its finishing touch ; and in the same way it will be
possible, with instruments made on the same principle, to find out the
heat and coldness of any province, due observations having been taken
beforehand, £c. And by this means it has been discovered that
spring-water and also caves, cellars, grottoes, and other deep subter-
104 SECTION— PHYSICS.
ranean places, that in winter seem to our senses warmer than in
summer, are at all times at the same temperature. And we are, there-
fore, compelled to say that the apparent difference comes from the way
in which the air which circulates there affects our senses, and not from
any variation in the degree of heat or of cold in the place.
Fra Paolo Sarpi, in a letter to Galileo Galilei, dated the nth of
September, 1602, says, that the same year Galileo had carefully ex-
amined the work of Guglielmo Gilberto, published in 1600 : " De
Magnete, &c.," and had repeated the experiments mentioned in it, and
also made many new ones. The principal result to which he came
was that of discovering the way to multiply the attractive power of
magnets by arming them in a special manner. From a letter of
Galileo himself, addressed to the Secretary of State, Curzio Pichena,
we learn that he (Galileo) considered it probable that the same piece
of loadstone did not preserve an equal power in all places on our
globe. He states, moreover, that he was engaged in making the
magnet bear three times its own weight ; and that by dividing it into-
pieces, he could render it capable of raising thirty or forty times its
own weight ; finally he observes that the longer a magnet sustains a
weight, the more it gains in strength. In another letter, to Marsili,
Galileo announces that he had succeeded in making a magnet six
ounces in weight bear 150 ounces. And the Abbot Castelli, in his
lecture on the magnet, says : " I have seen a loadstone, only six ounces
in weight, armed with iron by the untiring industry of Sig. Galileo
and presented to his Serene Highness the Grand Duke Ferdinand,
which lifts fifteen pounds of iron, worked into the shape of a sepulchre."1
Here is this historical magnet. As to the form of a sepulchre, this
shape was probably given to illustrate the legend of Mahomet's tomb
remaining suspended in the air.
And now, approaching the subject of Galileo's telescope, I cannot
pass over in silence the fact that the invention of spectacles is likewise
due to a Florentine. Ferdinando Leopoldo del Migliore, in his work
printed in 1684, and entitled " Firenze citta Nobilissima Illustrata,"
writes as follows : " There was a memorial (in Santa Maria del Fiore)
which came to grief at the restoration of that church ; it was, however,
duly inscribed in our ancient register of burials, and is all the more
dear to us, as it is, thanks to it, that we are made acquainted with the
ON INSTRUMENTS FROM ITALY. 105
original inventor of spectacles. This was Messer Salvino degli
Armati, «S:c. A figure of this man was to be seen, lying at full length
on a stone slab, in civil costume, with an inscription around it, which
ran thus —
*' Qui giace Salvino d'Armato degli Armati di Fir.
Inventor degli occhiali.
Dio gli perdoni le peccatx.
Anno D. MCCCXVII."
[Here lies Salvino, etc., of Florence. The Inventor of Spectacles.
May God forgive his sins. A.D. 1317.]
Redi, in a letter on the invention of spectacles, quotes Frate Ales-
sandro Spina, a Dominican, as their inventor ; speaking of whom,
Frate Bartolommeo da San Concordio wrote in 1313: "Frater
Alexander Spina vir modestus et bonus, quaecumque vidit, aut audivit
facta, scivit et facere. Ocularia ab aliquo primo facta, et comunicare
nolente, ipse fecit, et comunicavit corde ilari, et volente." From
which it would appear that as Armati would not explain his method of
making spectacles, Spina had found it out for himself. With regard
to the date of their invention, Redi quotes a passage from the papers
of the family of Sandro di Pippozzo, a Florentine, written about 1299,
in which may be read : " I find myself oppressed with age and should
not be able to read or write, without glasses called spectacles, in-
vented lately for the comfort of old people when their eye-sight grows
weak." These various quotations agree in establishing the fact that
spectacles were invented shortly before the year 1299, by a native of
Florence called Armati. Let us now return to Galileo.
In June, 1609, it was rumoured in Venice that an artificer in
Flanders had presented to Count Maurice of "Nassau an eyeglass so-
cunningly contrived that it made objects far off appear as if they were
close at hand. When Galileo heard this he immediately returned to
Padua, and after having thought over the matter for a day and a night,
he set to work to make his telescope. When it was known in Venice
that he had succeeded in constructing the enigmatical machine, he
was invited by the Venetian Republic to present them with his tele-
scope ; he complied with this request on the 23rd of August, 1609,
and dedicated it to the Doge. This solemn presentation you see re-
presented in the photograph of the Gallery. Then the Senate, as a
mark of appreciation, by a decree of the 25th of August, 1609, elected
ic6 SECTION— PHYSICS.
him a life lecturer of the Studio of Padua, at the same time granting
him a provision of 1000 florins per annum.
As on several occasions Galileo was accused of passing himself off
as the inventor of the telescope, and at the same time the great merit
which is his due for having made it upon the very vague indications
which he possessed, ought not to be ignored, it will, I hope, not be irre-
levant if I quote a portion of what he wrote in answer to Padre Orazio
Grassi, a Jesuit.
" What share of credit may be due to me in the invention of this
instrument (the telescope), and whether I can reasonably claim it as
my offspring, I expressed some time ago in my ' Avviso Sidereo/ which
I wrote in Venice. I happened to be there when the news reached
that a Dutchman had presented Count Maurice with a glass, by means
of which things far away appeared just as clearly as if they were quite
close at hand — nor was any detail whatever added. Upon hearing
this I returned to Padua, where I was at that time living, and pondered
over this problem ; and the first night after my return I found it out.
The following day I made the instrument. After that I immediately set
to work to construct a more perfect one, which, when it was completed
six days afterwards, I took to Venice ; and there so great a marvel
attracted the attention of almost all the principal gentlemen of that
Republic. Finally, by the advice of one of my dearest patrons, I pre-
sented it to the Prince in full college. The gratitude with which it
was received and the esteem in which it was held are proved by
the ducal letters, which I have yet by me, since they contain
the expression if his Serene Highness's generosity in confirm-
ing me for life in my lectureship in the Studio of Padua,
with double the payment of that which I had previously received,
which, in its turn, was more than three times what any of my
predecessors had enjoyed. These facts, Signer Sarsi, did not take
place in a forest or desert, they occurred at Venice ; and if you had
then been there, you would not have simply put me down as a foster-
parent of the invention. But, perhaps, some one may tell me that it is
no small help towards the discovery or solution of any problem to be
first of all apprised, in one way or another, of the truth of its conclu-
sion, and to know for certain, that it is not an impossibility that is
being sought after ; and that, therefore, the information and the cer-
ON INSTRUMENTS FROM ITAL V. 107
tainty that the telescope had already been made, were of such use, that,
without them, I should in all probability never have made the dis-
covery. To this I answer, that the help given me by the information
I received undoubtedly awoke in me the determination to apply my
mind to this subject, and without it I should very likely never have
turned my thoughts in that direction ; but besides this, that I cannot
believe that the notice I had had could in any way render the invention
easier. I say, moreover, that to find the solution of a problem already
thought out and expressed, requires far greater genius than to discover
one not previously thought of ; for in the latter, chance can play a great
part, whilst the former is entirely the work of reasoning. We know
that the Dutchman, the first inventor of telescopes, was simply a
common spectacle-maker, who handling by chance glasses of various
kinds, happened, at the same moment, to look through two, the one
concave, the other convex, placed at different distances from his eyes ;
and in this wise observed the effect which followed, and thus invented
the instrument ; but I, warned by the aforesaid notice, came to the
same conclusion by dint of reasoning ; and since the reasoning is by
no means difficult I should much like to lay it before you.
" This, then, was my reasoning : this instrument must either consist
of one glass, or of more than one ; it cannot be of one alone, because
its figure must be either concave or convex or comprised within two
parallel superficies, but neither of these shapes alter in the least the
objects seen, although increasing or diminishing them ; for it is true
that the concave glass diminishes, and that the convex one increases
them ; but both show them very indistinctly, and hence one glass is
not sufficient to produce the effect. Passing en to two glasses, and
knowing that the glass of parallel superficies has no effect at all, I
concluded that the desired result could not possibly follow by adding
this one to the other two. I therefore restricted my experiments to
combinations of the other two glasses ; and I saw how this brought
me to the result I desired. Such was the progress of my discovery, in
which you see of how much avail was the knowledge of the truth of
the conclusion. But Signor Sarsi, or others, believe that the certainty
of the result affords great help in producing it and carrying it into
effect. Let them read history, and they will find that Archites made a
dove that could fly, and that Archimedes made a mirror that burned
loS SECTION— PHYSICS.
at great distances, and many other admirable machines. Now, by
reasoning on these things, they will be able with very little trouble,
and with very great honour and advantage, to discover their construc-
tion ; but even if they do not succeed they will derive the benefit of
being able to certify, for their own satisfaction, that that ease of fabri-
cation which they had promised themselves from the pre-knowiedge
of the true result, is very much less than what they had imagined."
From the above-mentioned statements it is evident that if we have
to thank Holland for having by chance discovered the principle of the
telescope, we cannot but render due homage to the genius of the man
who thought it out and constructed the instrument with full knowledge
of what he was doing. And I may mention that very great was the
number of telescopes made by Galileo, and that he himself gave away
many, chiefly in compliance with demands for them, to distinguished
persons, among whom were : — The Grand Duke of Tuscany, Prince
D. Antonio de' Medici, the Elector of Bavaria, the Emperor Mathias,
Cardinal Borghese, the Queen of France, the Landgrave of Hesse-
Cassel, the King of Spain, the King of Poland, Giuliano de' Medici,
Cardinal Dal Monte, the Dukes of Acerenza, Professor Wallis [Valseo]
of London, and many others. And he, moreover, got reports from
Holland, in which it was stated, on the authority of Signer Danielle*
Antonini, and of Spinola, that in that country, no one, not even the
inventor, could make a telescope that would enlarge an object more
than five times. And Constantine Huygens writes to Elia Diodati, in
1637, that in Holland magnifying glasses were not yet made with
which Jupiter's satellites could be observed distinctly.
In the meantime, by dint of industry and perseverance, Galileo had
succeeded in perfecting his telescopes, so that for some time he
obstinately refused to impart to any one the manner in which he made
them ; and it was not until his eyesight began to fail him, that he
consented to create a manufacturer in the person of Ippolito Mariani,
commonly called II Tordo ; whose only authentic telescope now in
existence, I am pleased to be able to place before you. It was only
about the year 1637 that Francesco Fontana, a Neapolitan, began to
make good telescopes. And since I am on the subject of telescopes, I
must mention Torricelli, who, after the death of Galileo, having been
made mathematician to the Grand Duke, set to work to construct
ON INSTRUMENTS FROM ITAL Y. 109
telescopes of rare perfection. He had devised a more applicable
method for whetting and cleaning the lens, of which he was the first to
calculate the curve previously. Here is one of Torricelli's telescopes.
This other one was made by Eustachio Divini di S. Severino, who,
between 1646 and 1668, constructed telescopes of the extraordinary
length of seventy-two " palmi romani." And Viviani, likewise, made
telescopes in a masterly fashion. It is important to remember also
that Cesare Marsilli, a member of the Accademia de' Lincei, devised a
method of making telescopes by substituting a concave mirror, for the
objective — an idea to which he alluded in a letter to Galileo in July,
1626 ; but which he never carried out, probably in consequence of the
difficulty in obtaining the necessary mirrors. In his time, no man
made more excellent telescopes than Giuseppe Campani, a Roman ;
there exist in many places in Europe beautiful ones made by him, some
of which were even of the length of 210 palmi romani. This one of
medium size is by Campani.
To return, once more, to Galileo. I am able to offer for your admira-
tion all that remain of his venerable optical instruments, the two
telescopes, and the broken objective, with which he made his most
important astronomical discoveries ; and these were described in a
masterly way in his " Nuncius Sidereus," and in his letters and
dialogues on the systems of the universe. Before all comes the dis-
covery of the mountains in the moon ; he showed the manner of calcu-
lating their heights, and proved that some of them are higher than
some of our terrestrial ones. Then he explained that the lunar disc
appears to us to shine but feebly in the various phases of the new moon,
in consequence of the reflection of the earth, and how the movements
of the moon influence the flux and reflux of the sea. He was the first
to show that the milky way consists of a mass of innumerable stars ;
and, on the 7th of January, 1610, having his telescope fixed on Jupiter,
he made the discovery that three small planets revolve round it ; and
on the 1 3th of the same month he observed the fourth satellite.
Following up these researches in Rome, he determined the times of
their conversions, described a figure of their movements, certified that
they undergo eclipses, like the moon, and discovered that their progress
is extremely fast, inasmuch as the slowest completes a revolution round
Jupiter in little more than sixteen days ; and that by their means, more
i io SECTION— PHYSICS.
than 1000 eclipses can be observed in the year, a matter of great
importance for finding the longitude of any place. He dedicated these
satellites to the Tuscan princes, calling them the " Stelle Medicee."
In August, 1 6 io, while examining Saturn, he was struck by its tri-
corporeal appearance — as he himself expresses it. On the 3oth of
September, 1 6 io, he discovered that Venus changes form, just as the
moon does. In truth, whoever thinks over these most noble discoveries
of Galileo, cannot but feel both heart and mind exalted and invaded
by a sacred respect and veneration for the simple instruments that
revealed to us so great a part of the heavens.
We are now approaching the moment when Galileo, urged by an
ardent desire to return to his native city, and wishing to attend — un-
fettered by the trammels of public duties — to the publication of his
works, is about to abandon the University of Padua, and establish
himself in Florence, under the patronage of, and in the receipt of a
stipend from the grand duke. Poor Galileo ! Forgetting for a moment
the uncompromising lealty to the Papacy, which thy future masters
necessarily owed, since they had been re-installed in their dominions
by Clement VII. — that head of Christianity and citizen of Florence,
who did not hesitate to extinguish, by means of blood and treachery,
the liberty of the Republic ; dreaming of solitude, and tranquillity and
study, thou foundest, on the contrary, agitation and persecution, and
even torture ! To which thou wast abandoned by thy princes, more
through indolence and fear than from any ill-will against thee. How
much more nobly would not the valiant lion of Saint Mark have pro-
tected thee ! and alas ! how prophetic was Sagredo in the affectionate,
frank letter which he sent to thee as soon as he heard of thy departure !
Towards September, 1610, Galileo had already settled down in
Florence.
Viviani, in the inscriptions which he placed on his own house in the
Via dell' Amore in Florence, states that the first microscope invented
and made by Galileo was presented by him in the year 1612 to the
King of Poland ; nay, in the Life of Galileo, which he was com-
missioned to write for Prince Leopoldo de' Medici, Viviani attributes
the invention of the microscope to Galileo. On the 26th of October,
1624, Prince Cesi, the founder of the Accademia de? Lincei at Rome,
says in answer to Galileo, who had sent him one of his microscopes,
ON INSTR UMENTS FROM ITAL Y. 1 1 1
that he had received the instrument which he (Galileo) had lately
constructed for minute objects, but that as he had merely begun to
taste it, so to speak, he would reserve an account of so admirable an
instrument till he had had time to relish its merits more fully. And
under similar circumstances (having likewise received the present of
a microscope from Galileo), Imperial! writes on the 5th of September,
1624 : " I have not words enough to thank you for the microscope
which you have been so kind as to send me ; it is very perfect in
every respect, and is most admirable, as indeed are all your inven-
tions." At the same period Bartolomeo Baldi, asking Galileo to give
him one of these instruments, calls it the little newly invented micro-
scope (occhialino). Hence we may conclude that Galileo invented the
microscope, either about the year 1612, according to Viviani, or about
1624 according to the others. Christian Huygens in his work on
dioptrics, written in 1678, remarks that he had heard say that about
the year 1621 microscopes were seen in the hands of Drebbel.
But there exists no document in proof of this. And besides,
numerous were the inventions attributed to Drebbel, but the greater
number of them belong more to witchcraft than to science.
Hence we Italians maintain, and I hope that others will agree with
us, that Galileo is the inventor and first maker of the microscope.
Unfortunately none of his instruments have been handed down to us.
The one that I am now placing before you was found among the
remains of the Accademia del Cimento ; it is merely a simple tube —
the lens is wanting. We may mention here that at a later date
Galileo effected many improvements in his microscope.
To my great surprise, hovi ever, I found among the objects in this
exhibition a microscope described as follows : Microscope invented
and constructed by Zacharias Janssen, telescope maker, at Middle-
burg in the Netherlands. I cannot explain to myself how it is that
Huygens, who was so bent on bringing under notice the works of his
own country, should not have known of this microscope, which has
been handed down even to us. But while acknowledging how
difficult it is to obtain information regarding all these different
discoveries, allow me te observe that I have never seen any document
in which mention is made of a microscope before 1624.
And this is a suitable place to mention the binocular telescope,
1 1 2 SECTION— PHYSICS.
made by Galileo for observing with greater ease the satellites of
Jupiter, and called by him the " Celatonc" or " Testiera" (for the
apparatus resembled a diving-helmet, having telescopes fixed in the
apertures for the eyes). It was intended for use on board ship. And
speaking of this same instrument, let me mention that towards the
end of his life he offered it to Spain — at that time an important
maritime power, in order that it should be of use for observing the
eclipses of Jupiter's satellites, and hence, by knowing the ephemeris,
to determine the longitude of any place even in a rough sea. The
negotiations, however, with Spain having failed about the year 1636,
Galileo offered the same instrument to the States-General of Holland,
at the same time stating distinctly the four conditions on which the
value of his instrument depended — namely, to know the theory and
the tables of the " Stelle Medicee," to have perfect telescopes, to
overcome the difficulties of the ship's motion, to have a perfect
instrument for the measurement of time : all of which conditions he
affirmed to be able completely to satisfy, for he had indeed invented
a perfect measurer of time ; and as to the motion of the ship, after
having devised several other ingenious methods to protect the observer,
the idea struck him of placing him in a boat floating in another boat
filled with water, a spring being placed between them so that the two
boats should not dash against one another. When the transaction
which had been delayed through the death of the appointed agents,
seemed, at last, to be coming to an agreement, Galileo himself died.
Allow me, after having spoken of these instruments of Galileo, tho
only ones which remain to us, and which I have the good fortune to
be able to show you, to call to mind the principal discoveries which
he made and afterwards published. And first of all the observation
of the spots on the sun. Before he had given up his professorship at
Padua, he had occasion while at Venice to point them out to Fra
Paolo Sarpi, the celebrated Venetian theologian, and also to Fra
Fulgenzio, his disciple and successor. Here is what the latter writes
to Galileo, in a letter of the 27th of September, 1621, with reference
to the Jesuit, Father Scheiner, who gave himself out as the discoverer
of the solar spots : " It seems to me that that German Jesuit is a man
of good judgment and deserves high praise ; for as it is their
peculiarity to make themselves a name by evil speaking, he could
ON INSTRUMENTS FROM ITAL Y. 113
not, in his profession, have taken up a higher or more distinguished
subject, or one that could bring his name in greater evidence ; for
even to be known as a slanderer is to have a certain reputation. But
to return from this digression.
" I have the most distinct recollection that when you had constructed
here the first telescope, among the first things which you discovered
were the spots on the sun ; and I should be able to point out the
exact place, where you, by means of the telescope, showed them on a
sheet of white paper to that father of glorious memory. I well
remember the discussions which took place, first as to whether it
were a deception of the telescope, or vapours in the interposed air,
and then having repeated our observations, we concluded that the
fact was such as it appeared and that it was deserving of serious
thought. And that afterwards you left us. The recollection of all
this is as fresh in my memory as if it were taking place at this very
moment. But what beasts are to be met with ! Truth conquers."
Thus it clearly appears that even in August, 1610, Galileo had dis-
covered the spots on the sun. The following year he had occasion in
Rome, to draw the attention of several dignitaries to them, as may
be1 seen from what Angelo de Filiis wrote in 1613 : " Besides this, he
(Galileo) did not leave Rome until he .... not merely mentioned
with words that he had found that the sun was spotted, but actually
proved it. He pointed out the spots on several occasions, and once
in particular in the garden of the Quirinal, in the presence of the
most Illustrious Cardinal Bandini, and of the most Reverend
Monsignori Corsini, Dini, Abbate Cavalcanti, Signer Giulio Strozzi,
and many other gentlemen."
Nevertheless, the above-mentioned Father Scheiner did not hesitate
to assume as his own this great discovery, when it was already known
to most people. His brother monk, however, Padre Galdino wrote :
" That he warned Father Scheiner that the spots which were to be
seen on the sun, had been observed before any one else by Galileo ;
and Padre Adamo Tannero, who was not only a Jesuit, but also
Schemer's colleague in the college of Ingolstadt, in his "Astrologia
Sacra," not only leaves him (Scheiner) unmentioned, but alluding to
the solar spots expresses himselt as follows : " Certe magnus astrono-
mus Galileus horum Sydereonun ostentorum proecipuus inventor
I
ii4 SECTION— PHYSICS.
maculas. Solem incumbrantes aliud non vtilt esse, etc." Hero it is
beyond all doubt that Galileo was the first to discover the solar
spots, upon which he afterwards wrote his " Lettere Solari," in 1613,
in which he rebuffs, with solid arguments, all the objections raised
against him ; gives an account of the spots, teaches the way to draw
them on paper, and, with happy intuition, compares them to terres-
trial clouds ; speaks of the rotation of the sun on its own axis, and
admits that that luminary, to maintain its own heat, must be con-
tinually requiring fresh aliment (pabulo).
Another important work of Galileo is the one entitled, " Concerning
the Things that Float on the Water, or that Move in it," in which, for
the first time, light is thrown upon the principle of potential velo-
cities. Most important, then, is his " Saggiatore," which was pub-
lished in 1623, in answer to an astronomical work of the Jesuit
Grassi, chiefly on the subject of comets. Among the many treatises
which Galileo wrote, are some in which may be discerned the founda-
tions of the sciences of hydrostatics and hydraulics ; and it is certain
that he conceived and made use of the theory of indivisibles before
his disciple the celebrated Cavalicri. Coming to the " Dialogue on
the Great Systems of the Universe," which brought such persecution
on Galileo's head, it will not be out of place to recall how his incom-
parable knowledge and honesty and frankness brought clown upon
him the envy and hatred of the greater part of the clergy. That body
knew full well that they could not for long battle against the light of
truth, by means of the dark mist in which they had sought to en-
velop the minds of men, in order that every appearance of knowledge
should belong to them alone, the absolute masters of the human con-
science. At each new publication or discovery by Galileo there
never failed a most bitter storm of reproof, incited by that caste which
most of all hated and feared him, and which was often most disgrace-
fully supported by some peripatetic, who, measuring Aristotle's vast
mind by his own most limited intelligence in interpreting him, could
not conceive that if that great philosopher were now to know of one
of Galileo's sublime conjectures, very different would be his reasoning
on the nature of things. It is enough to mention, that to such an
extent was the hostility towards Galileo carried, mainly through the
agency of the Dominicans, that one of them, Fra Tommaso Caccini.
ON INSTRUMENTS FROM ITAL Y. 115
lowered himself so far as to inveigh against him, in low and insolent
language, in the Duomo of Florence, and did not blush to conclude
with his opinion that " mathematicians, as the authors of all heresies,
ought to be driven from every State." The narrow-minded monk
ignoring the while, that of all the heresies which he so deeply lamented,
not one was originated by a mathematician, while many had monks
for their founders. Even the Bishop of Fiesole thought it his duty
to allude to Galileo in his sermons.
So that when Galileo, who, it was well known, had, when yet but a
student at Pisa, embraced the system of Copernicus, and both in that
celebrated university and afterwards at Padua, had explained it with
the greatest clearness, and with the addition of new arguments in its
support to his scholars — when Galileo, I say, went to Florence, and
began there, beyond the reach of the dreaded protection of the Lion
of St. Mark, to publish the arguments which he was in the habit of
communicating by letter to his friends, there was let loose against him
a torrent of abuse and insinuations and subterfuges, for the purpose
of obtaining his condemnation by the Inquisition. In fact, it was
unavoidable necessity that compelled him to go to Rome to defend his
views, and attempt to persuade the most obstinate that, as a matter
of fact, the Bible was not opposed to the opinions of Copernicus,
who, indeed, more than seventy years ago, had published his works,
with a dedication to Paul III. Nor had there ever been any thought
of prohibiting them. For all that, he could count it as a great piece
of good fortune that he was able to return to Florence without any
serious inconvenience, but with the sad annoyance, however, of having
seen the book of Copernicus condemned by a band of ignorant and
fanatical monks, by a decree of the 5th of March, 1616.
And for the moment everything seemed quiet ; the fire, however,
was but smouldering. In September, 1623, there succeeded to the pon-
tificate, tinder the name of Urban VIII., Cardinal Maffeo Barbcrini,
the friend of Galileo ; and the latter went to Rome to do him homage,
and received such honours and recompenses, that he was convinced
that the time was come when he should be able to publish his " Dia-
logues on the Great Systems," a masterpiece both of language and
science, in which he represents Signor Sagredo and Salviati, of Venice,
ks speaking in favour of the opinions of Copernicus, as well as Signor
ii6 SECTION—PHYSICS.
Shnplicio, a learned and sincere peripatetic. After many and gieat
difficulties, the Dialogues, having been revised and approved, were
finally published at Florence in 1632. But no sooner had they
appeared, than his enemies decided to bring into play eveiy evil art
in their power in order to effect his ruin ; and knowing that the
Pope favoured him, and had even corrected, with his own hand, the
introduction to the Dialogues, they quickly understood that, to carry
out their purpose, they must turn Urban's friendship for Galileo into
enmity. They therefore insinuated themselves hypocritically into the
councils of the Pontiff, whom they made believe that Galileo, in his
Dialogues, had meant to represent in the person of Simplicio no other
than his own sacred person. At this suggestion anger and perse-
cution straightway took the place of friendship in the mind of the Father
of the Faithful. Of no avail was the protection, which indeed was but
timidly proffered by the Grand Duke ; nor yet the intercession of
persons in high authority, nor even that of some ecclesiastics, in whom
the feelings of religion were undoubtedly sincere, being inseparably
bound up with those of truth. All was in vain ; and although a pesti-
lence was raging at the time, poor Galileo, old, in bad health, and
sorely afflicted, was forced to leave .Florence in the very middle of
winter and proceed to Rome. At the Bridge of Centino, on the
frontier, he was compelled to undergo twenty days' quarantine in a
miserable old house, totally denuded of comfort. And in the mean-
time the Pope was revenging himself on all those who had had com-
passion on the unfortunate old man.
On the 1 3th of February, 1633, Galileo reached Rome, and was at
first lodged at the Villa Medici, from which he was afterwards taken
to the dungeons of the Holy Office, where he remained seventeen days,
and was only released on account of his increasing ill health. Finally,
after six months' distress and suffering, having once more passed four
days in the dungeons of the Holy Office, he was conducted to the Church
della Minerva, where, in the presence of the Inquisitors, he was obliged^
on the 20th of June, 1633, to pronounce the famous recantation, which
did not prevent him from uttering the now historical "Eppur s
muove," which, while summing up in a word the most severe martyr-
dom to which a man outraged in his convictions could be subjected,
expressed at the same time the boldest challenge that knowledge
ON INSTRUMENTS FROM ITAL Y. 117
conscious of itself could possibly throw down to Ignorance. Endea-
vours have been made to ascertain whether Galileo underwent
torture ; in truth, there is reason to believe that he did, although not a
word ever escaped from him on the subject of his treatment. He was
held back, perhaps, by the threats and oaths, by means of which the
Inquisition knew how to secure the silence of its victims. He was
allowed, it is true, as a high favour, to have the Villa di Arcetri for a
prison ; but the state of his health after his condemnation, and the
indignity with which he was treated, up to the time of his death, by
the Court of Rome, lead one to believe that those barbarians must have
vented their insolent wrath even on the body of so great a martyr for
progress. But who can picture the heart-rending anguish inflicted on
him when he was obliged to recant that which was the fruit of the
great labours of his whole life ? and he, who had risen higher than any
one in the comprehension of Truth and of God, was forced to bow his
head to a power — the direct denial of the Divine Essence — which, in
order to rule more absolutely over the ignorant, has been compelled
to have recourse to the monstrous Proclamation of Infallibility !
Pardon me if I have needlessly digressed from the duty entrusted to
me of speaking only of what appertains to the instruments exhibited
here ; but in speaking of Galileo my inclination to discuss his merits
in enthusiastic language is very strong indeed. Hence I will omit
mentioning the principal thoughts contained in the Dialogues on the
great system and the new sciences, and shall briefly relate what regards
the application of the pendulum to clocks.
Galileo's observation on the oscillations of the lamp in the Duomo
of Pisa is known ; from that moment he thought of availing himself of
the pendulum to determine the number of beatings in the pulse of a
sick person ; being then obliged, against his inclination, to occupy him-
self with medicine. Some time afterwards, reflecting on the means of
obtaining in astronomy a more perfect measurer of time in order to
determine longitudes with certainty, he returned with greater diligence
to the subject. On the occasion of his offering his method for finding
longitudes to the States-General of Holland, he wrote to Lorenzo
Realio, under date of the 5th of June, 1637, as follows : " I come now to
the second contrivance to increase to a vast extent the accuracy of
astronomical observations. I am alluding to my time-measurer of
Ji8 SECTION— PHYSICS.
which the precision is so great, that not only will it register the exact
amount of hours, but minutes, primes, and seconds, and even thirds if
their frequency could be numerated by us ; and its punctuality is such,,
that if two, four, or six of these instruments be taken, they will keep so
well together, that there will be no variation between them- — not even
as much as the beat of a pulse — at the end, not merely of an hour, but
of a day, or even of a month. I derived the fundamental principle of
this machine from an admirable proposition which I demonstrate in
my book ' De Motu.' " And then, unfolding the theory of the oscillations
of the pendulum, he continues : " The tediousness, however, of being
obliged incessantly to count the vibrations can very conveniently be
provided against in this wise — viz., by arranging that there should pro-
ject from the middle of the circumference of the sector, a small, fine,
thin pin, that in passing hits on a boar's bristle fixed at one of
its extremities, which bristle rests upon the teeth of a wheel, as light as
paper, which must be placed on a horizontal plane near the pendulum and
having around it teeth like those of a saw, that is, with one of the sides
placed at right angles on the plane of the wheel, and the other inclined
obliquely ; thus, it will serve this purpose, that when the bristle hits
against the perpendicular side of the tooth, it will move it ; but on the
return of the same bristle on the oblique side of the tooth it does not
move it, but bending over it, slides past and falls at the foot of the
following tooth. In this manner, in the passage of the pendulum, the
wheel will move for the space of one of its teeth, but at the return of
the pendulum, the wheel will not move in the least. Hence its move-
ment will be circular, and always in the same direction ; and having
marked the teeth with numbers, it will be easy to know the quantity
that have passed and consequently the number of vibrations, and the
particles of time run. Around the centre of the first wheel another
wheel can be adjusted having a smaller number of teeth; which
in its turn touches a third larger one ; from the motion of which
we shall be able to know the number of complete revolutions of
the first wheel, by so disposing the teeth that, for example, when
the second wheel shall have made one turn, the first shall have
accomplished twenty, thirty, or forty, or as many as you like ; but
to explain this to you, who have men most exact and ingenious in
the making of clocks and other admirable machines, is quite super-
ON INSTRUMENTS FROM ITAL Y. 119
fluous, since you yourselves, starting from this new principle that
the pendulum, moving through greater or lesser spaces, always makes
its reciprocating motions perfectly equal; you, I say, will deduce
much more ingenious and sublime consequences than I can possibly
imagine."
From this we gather that the first clock with a pendulum made by
Galileo differed essentially from ours, inasmuch as the wheelworks
were moved by the pendulum, which made it necessary for some one
to impart a new impulse to it as soon as it was about to stop. If no
olher document existed in favour of Galileo, it would seem to me to
be more than enough to secure the first place for him, with regard
likewise to the application of the pendulum to clocks. The essence
of the invention lies, of course, in the first idea, and we have here,
moreover, an instrument that works very well.
But in Galileo's lofty mind it was impossible but that the thought
should flash of making the motion itself of the clock maintain that of
the pendulum, which would thus be reduced to a simple regulator.
Not to draw out this lecture to 'too great a length, I shall only quote
what Viviani wrote upon this subject for Prince Leopoldo de' Medici.
In that account, after having described Galileo's experiments on the
pendulum and the manner in which he applied it to the measurement
of time, he proceeds thus :
" But as Galileo was most liberal in communicating his inexhaustible
speculations, it frequently happened that the uses and newly dis-
covered properties of his pendulum, spreading little by little, fell into
the hands of persons who adopted them for their own purposes, or
inserted them into publications, and by artfully passing in silence over
the name of their true author, made such use of them that it was
believed — at least by those who knew nothing of the origin of the dis-
coveries— that the writers were the real authors of them." He next
speaks of the observations of the " Stelle Medicee," of the tables rela-
ting to them prepared by the Padre Renieri, of the offering made by
Galileo to the States-General of Holland of his method for determining
longitudes by means of the eclipses of Jupiter's satellites, and of
Galileo's determination to send his son Vincenzo and the aforesaid
Padre to Holland, since he himself, being old and blind, was unable
to travel thither. He then continues : " While, therefore, Padre
120 SECTION— PHYSICS.
Renieri was employed on the composition of the tables, Galileo gave
himself up to meditations on his time-measurer, and I remember one
day in the year 1641, when I lived near him in the Villa d'Arcetri,
that the idea struck him that it would be possible to adapt the pen-
dulum to clocks with weights or springs, and avail himself of it
instead of the usual regulator, hoping that the perfectly equable and
natural motion of the pendulum would correct all the defects in
the mechanism of the clocks. But as his blindness deprived him
of the power of making designs and models which would answer
to the designs which he had formed in his brain, his son Vincenzo
having arrived one day at Arcctri from Florence, Galileo con-
fided his idea to him, and many times afterwards did they reason
over the matter, and at last they settled upon the method which
is shown in the accompanying drawing, and they set at once to work,
in order practically to overcome those difficulties which it is for the
most part impossible to foresee. But Signer Vincenzo intended to
construct the instrument with his own hand, in order that by this
means the secret of the invention should not be reported by tlio
artificers, before it had been presented to his Serene Highness the
Grand Duke, his master, and the States-General (to be used for ob-
serving the longitude), but he put off the execution of his work so fre-
quently, that a few months later, Galileo, the author of all these
admirable inventions, fell sick, and on the 8th of January, 1641, ' ab
Incarnazione,' according to the Roman style, he died. And conse-
quently Signer Vincenzo's energies so cooled down that it was not
until the month of April, 1649, that he actually began to make the
present clock upon the idea explained to him by his father, Galileo.
He then managed to obtain the services of a young man — who is
yet living — named Domenico Balestri, a locksmith who had had
some experience in making large wail clocks, and he made him
construct the iron frame, the wheels with their axes and pinions,
without cutting (intagliare) ^ and the remainder he made with his own
hand, constructing on the highest wheel, called the wheel of notches
(tacche), No. 12 teeth, with as many cogs, divided between each
tooth, and with the pinion in the axis of No. 6 ; and another wheel
which moves the above-mentioned of No. 90. He then fixed on one
side of the support which is at right angles to the frame, the key
ON INSTRUMENTS FROM ITALY. 121
or trigger (scatto\ which rests on the above-mentioned higher wheel ;
and on the other side he fixed the pendulum, which was made
of an iron wire, in which was threaded a ball of lead, which could be
loosened by a screw, so that it could be lengthened or shortened ac-
cording as it was necessary to regulate it with the weight. When this
much had been done Signer Vincenzo wished me (as one who was in
the secret of this invention, and who indeed had urged him on to com-
plete it), to see, by way of trial, the combined working of the weight
and the pendulum. I observed the mechanism in operation more than
once, and his workman was likewise present. When the pendulum
was at rest, it prevented the descent of the weight. But when it was
raised and then let go, in passing beyond its perpendicular with the
longer of the two cords attached to the pivot of the pendulum, it raised
the key, which fits into the wheel of the notches ; which wheel drawn
by the weight in turning round with its higher parts towards the pen-
dulum, pressed with one of its levers on the other shorter cord, and
gave it at the beginning of its return such an impulse that it served as
a kind of accompaniment to the pendulum, which lifted it to the height
from which it had started ; so that when it fell back naturally and had
passed the perpendicular, it returned once more to lift the key and im-
mediately the wheel of the notches was set in motion and continued to
revolve and push with the following lever the pendulum, and thus in a
certain way, the swinging of the pendulum was rendered continual
until the weigh I had reached the ground. We examined together the
operation, connected with which, however, many difficulties arose;
but Signer Vincenzo did not doubt but that he would be able to over-
come all of them ; indeed he fancied that he would be able to apply
the pendulum to clocks, in a different manner and by means of other
inventions ; but since he had got so far, he wished to finish it on this
plan, as the drawing shows it, with the addition of hands to show the
hours and even minutes : for this purpose he set to work to notch
(intagliare) another cog-wheel. But whilst engaged in this work, to
which he was unaccustomed, he was overtaken by a very acute attack
of fever, and he was obliged to leave it unfinished at this point ; and
on the twenty-second day of his illness, on the i6th of May, 1649, all
his thoughts and aspirations, together with this most exact measurer
of time, were lor ever lost to him. He their author passed away to
122 SECTION— PHYSICS.
measure, in the enjoyment, let us hope, of the Divine Essence, the in-
comprehensible moments of eternity."
I think it is useless to occupy your time in further comments ; the
facts and evidence are clear, and you have moreover before your eyes
the design for the application of the pendulum to clocks. You must
not be surprised therefore if, without wishing to quarrel with the
Dutch, fully recognising as I do Huygens's merits, I maintain and hope
that all impartial thinkers will agree with me that Galileo must be
considered the inventor of the system for the application of the pen-
dulum for regulating the time of clocks, as he was likewise the author
of many other useful discoveries.
And who knows how many others might not have sprung from that
energetic and fruitful mind had his more mature years been less
oppressed by bodily and mental cares, had the war carried on against
him by the ignorant been less implacable ?
He expired in the arms of his friends, Torricelli and Viviani, and
returned immortalized in God that gigantic intelligence that had ani-
mated him. .Let us venerate in him the father of modern philosophy,
the leader of true progress, the redeemer of science.
In the meantime the number of the followers of his doctrines went
on increasing every day. In Pisa, Castelli — who had been called to
Rome by Urban VIII., while Galileo was yet living there — was suc-
ceeded by Niccolo Aggiunti del Borgo San Sepolcro, a man distin-
guished in geometry and physical science. To him are due many
important observations on the resistance encountered by the pendulum
moving in various liquids or in the air ; and the discovery of the
ascent of liquids in capillary tubes, which was applied by him to
explain various phenomena, such as the ascent of chyle in the milky
veins, the nutriment of plants, the preservation of flowers in moisture,
the method of feeding peculiar to certain small animals, the rapid rise
of water in sponges and wood, and the sperical shape of drops of water,
attributed by him to what he called the occult motion of water, and
which, from the general character of his works, may be set down as
merely molecular affinity.
At Rome, Castelli, following in the footsteps of his great master,
established the laws of hydrodynamics, explained the phenomena de-
pending on the duration of luminous impressions on the retina ; the
ON INSTRUMENTS FROM ITALY. 123
apparently larger appearance of stars on the horizon ; and found the
ingenious manner of making sight more distinct without employing
lenses, by making use of a little hole, and thus clearly demonstrating the
utility of diaphragms in optical instruments. Then, forestalling the
modern theories of heat, he clearly pointed out how different the
warming of bodies is according to their nature and to the state of their
surfaces ; and in his publication on the magnet, he was the first to
explain the arrangement which iron filings make on paper spread over
the poles of a magnet according to lines, which were afterwards named
" lines of strength." Castelli, who had made Torricelli's acquaintance
in Rome, and who was convinced of his genius, introduced him to
Galileo, who was at once eager to know him ; but it did not fall to
Torricelli's lot to spend in the society of that great man more than the
last three months of his laborious existence.
Torricelli extended the mechanical discoveries of Galileo, ingeniously
applied the method of indivisibles, conceived by Galileo, to the squaring
of the circloide, which he was the first to demonstrate, and to the
measurement of hyperbolic solids. Being appointed mathematician
to the Grand Duke, he established himself in Tuscany, occupying
himself, among many other things, some of which we have mentioned
above, in the perfecting of telescopes. We also owe him a microscope
simpler than Galileo's, being made of only one lens, or rather of a little
glass ball, which he fashioned by the flame of a lamp. But the in-
vention which contributed the most to his celebrity was, as every one
knows, that of the barometer.
Galileo, by condensing air, had demonstrated its weight, and in his
Dialogue on the resistance of solids, he says of water, that in suction-
pumps, it does not rise higher than about eighteen " braccia," leaving
the space above empty. Torricelli, pondering over this fact, was led to
think of what would happen if in the place of water, mercury, which is
so much heavier, were used ; for he argued that by its means there
would be much greater ease in obtaining a vacuum, in a much shorter
space, than that necessary for water. And he then made a long tube
of glass of the length of about two braccia which terminated at one end
in a ball, likewise of glass, and remained open at the other ; through
this aperture he proposed to fill the tube and the ball completely with
mercury ; and then holding it with his finger and turning it upside-
124 SECTION— PHYSICS.
down, submerge the orifice of the tube below the level of more mercury
in a large vessel ; and that being done, take away his finger and open
the tube, thinking that the quicksilver would detach itself from the ball,
and having glided down, and remained suspended, according to the
various calculations, at about the height of one and a quarter braccia,
would, in all probability, leave a vacuum in the ball above and in part
of the tube. He communicated this thought to his great friend,
Viviani, who, most anxious to see the result, agreed to the experiment,
which he himself carried out, and was, hence, the first, about a year after
Galileo's death, to see Torricelli's ingenious idea confirmed by the fact.
He hastened to his friend, who, most joyful at the news of this evidence,
was all the more persuaded that the weight of the air was really that
which was in equilibrium with the column of water or mercury. Indeed,
being asked by Viviani what would have happened if the experiment
had been made in closed space, Torricelli, after having reflected for a
short time, answered : The same thing ; since the air is already com-
pressed in it. This most important discovery was communicated by
the author himself to Ricci in Rome, and by Ricci to Signer de Verdus»
who, in his turn, made Padre Mersenne acquainted with it, from whom
Pascal learnt it and made it famous, as every one knows, in his cele-
brated Puy-de-D6me experiment. It is very probable, however, that,
v/ithout detracting in the least from the great merit due to Pascal, the
experiment of the sinking of the mercury in the barometrical tube in
proportion to the increase of the height to which it is carried, was made
for the first time in Italy. Carlo Beriguardi, in his " Circolo Pisano,"
published in 1643, while endeavouring to clothe in an Aristotelian dress,
both this and other experiments, says : — That the tube of quicksilver
leaves more space empty when placed at the top of a tower or of a
mountain, than at the foot. And in a letter to Ricci, Torricelli himself
observes : — That it would be possible, by means of his instrument, to
get to know when the air was lighter or heavier ; and that it might be
the case that this air, which is most heavy upon the surface of the
earth, becomes more and more light and pure as we rise higher and
higher to the tops of the loftiest mountains. There is, accordingly,
reason to believe that he himself, or others following up his indications,
really made the experiment and saw the mercury sink as the height
ON INSTRUMENTS FROM ITAL Y. 12;
increased, Here are two tubes which Torricelli used in his firct
experiments.
Before speaking of the Accademia del Cimento, it will not be out of
place if I allude here to certain measuring instruments, which were
made use of in its researches, and which are to be found described in
the " Libro de Saggi " as belonging to the academy ; but some of
which, however, were made before its foundation, according to the
directions chiefly of the Grand Duke Ferdinand II. And beginning
with thermometers, it is useful to notice how even Galileo had sub-
stituted wine for water, which by freezing easily broke the thermo-
metrical bulb ; while the Grand Duke had replaced wine, first of all by
coloured alcohol; and afterwards, in order that the deposit thrown
down by the colouring matter on the inside of the bulb should not render
the reading less clear, he substituted natural alcohol ; which they call
" acquarzente." Here is a series of thermometers of that period. But
I must tell you that I have only brought to London a very small part
of the ancient instruments existing in Florence. This is the thermo-
meter, which we owe to the Grand Duke, it is called the " cinquanti-
grado," because it was divided into fifty parts in a masterly manner by
means of these little grains of enamel or glass ; and it is exceedingly
interesting to observe how the thermomelrical bulb was constructed,
not merely in a spherical shape, but even in the cylindrical one which
has now come into generalise ; as you may see in this second thermo-
meter, which is also a " cinquantigrado." As to the way of dividing
them into degrees, this is the method they employed : — They immerged
the thermometer, just as we do, into melting ice or snow, and they
marked the point to which the alcohol .descended — which in
thermometers of 50° was about I3°'5 ; while they remarked that the
greatest cold of Florence could reduce it on some occasions even to 7°*
Then they exposed it to the rays of the sun at midsummer, in the open
air, without any object of reflection whatever ; in this case the
" cinquantigrado " rose, in Florence, to 43° at the highest, and in the
shade, at the same season, to 34° ; so that the difference between
melting ice and the extreme heat was divided into 30° ; and these were
the points of comparison for their thermometers. Other thermometers,
were then constructed with arbitrary scales of 60, 70, 100, 200, or evea
j-5 SECTION-PHYSICS.
400°, chiefly by Giuseppe Moriani, called on account of his art, " il
Gonna," who was famous for making thermometers of 50° perfectly-
similar to one another. And such do some of those existing in the
Royal Museum of Florence still remain. Here is a thermometer
divided into 470° ; and in this other one the bulb is exquisitely worked
so as to form a hollow branched stand full of alcohol. To render these
delicate thermometers less fragile here is another shape that they some-
times gave to the tube, by twisting it, as you see, spirally. The tube of
this thermometer is 230 centimetres long, and yet the total height of
the instrument is but 32 centimetres. Here is a thermometer on which
is marked the exact temperature which the water should reach in order
to be fit for bathing in. This one is rather a curiously shaped
thermometer, or thermoscope ; we owe it, also, to the Grand
Duke Ferdinand II.; it is described in the " Saggi dell' Accademia
del Cimento" as a "thermometer lazier, or more slothful than
the others" The tube contains alcohol, besides six little coloured
glass balls. At the temperature of melting ice these little balls
float. At 10° of their yo-grade thermometer one of the balls falls
to the bottom, at 20° a second one sinks, and so on. At 70° they
are all at the bottom. This other shape, like a small frog, used to
be given to similar thermoscopes, in which cases the little balls were
regulated so as to mark certain degrees of temperature nearer to one
another. The thermoscope was tied as .you see to the pulse of a
sick person, and served to show the intensity of the fever. In certain
€xperiments upon the amount of heat transmitted by different sub-
stances which were first warmed and then plunged into water, it is
mentioned that of two thermometers used, the one of alcohol, the
other of mercury, the first to show any sign was the one with mercury.
It is nevertheless difficult to establish the precise date at which
mercury thermometers were first made. And before finishing what I
have to say on the subject of thermometers, I shall call to mind a
most useful application that was made of them even at that time by
the Grand Duke, that is to say, for meteorological observations. He
thought of availing himself for this purpose of the monks, who,
scattered as they were in every direction, could on account of their
manner of life, apply themselves better than any one else to such
observations. It is said that such a duty was entrusted to Padre
ON INSTRUMENTS FROM ITALY. 127
Luigi Antinori. The observations used to be taken at Florence, at
the Palazzo Pitti and at the Boboli Gardens, and in the Convento
degli Angeli ; and as far back as the year 1654 they were regularly
established at Vallombrosa, Cutigliano, Bologna, Parma, Milan, War-
saw, and Innsbruck. Observations were usually made at different
hours of the day, of the state of the thermometers exposed to the
north and to the south, the state of the sky, and the direction of the
wind. From a manuscript of Viviani, however, we learn that in
some places were noted the date, the hour, the temperature, the state
of the barometer, the wind, the sky, and the humidity of the air. In this
volume, entitled " Archivio Metereologico Ccntrale Italiano," you will
see registered the observations of those days, and besides others made
in this century. Now if the observations taken so long ago be
compared to recent ones, it will be seen that after the due corrections
have been made, or if observations be taken now with some of the
best instruments of the Accademia del Cimento, the meteorological
conditions of Tuscany have not changed.
Passing on to the subject of hygrometers, besides the one imagined
by the great Leonardo da Vinci, and which is founded on the increase
in the weight of certain substances through the action of moisture,
others were used in which lengthening out or contraction of a given
substance served to determine the humidity of the atmosphere in
which it happened to be situated. Torricelli had already used oats.
In 1664, Dr. Folli da Poppi constructed a new hygrometer founded on
the expansion of paper with the variation of moisture, which, having
been perfected by the Accademia del Cimento, was reduced to the
shape in which you see it now. The movement of the hand to the
right or to the left, according as the paper expanded or contracted,
pointed out on the quadrant the relative quantity of moisture. Most
interesting likewise is this other one, which has been called the
condensing hygrometer. We owe it to the Grand Duke Ferdinand II.
It consists of a truncated cone made of a tinned sheet of iron,
covered on the inside with a layer of cork, and is supported on
a tripod. Below the smaller aperture, turned downwards, there is
suspended a hollow glass cone ending in a closed point, likewise
turned downwards, and provided towards the upper portion with an
escape-pipe. The superior cone is then filled with snow or ice, which
128 SECTION— PHYSICS.
in melting, runs into the glass cone which remains at the temperature
of o°, whilst the excess of water runs through the pipe into an
appointed recipient. The moisture of the air in contact with the cold'
side condenses itself and covers it with dew, which collecting by
degrees into drops, runs towards the point, whence it falls into a
graduated vessel. If the time the experiment has lasted be taken
into consideration, the quantity of water collected will be found to be-
in proportion to the humidity of the air. Experimenting in this wise,
the members of the Accademia del Cimento found that the south
winds are so charged with moisture that in one minute the hygro-
meter has given as much as thirty-five, fifty, and even eighty drops of
water, whilst the north wind leaves the glass perfectly dry.
Here are various examples of the so-called Hydrostamms for
liquids, used by the Accademia del Cimento, and some of which we
owe to the Grand Duke Ferdinand II. This one with the ballast of
mercury is employed for liquids lighter than water ; this other one
with the ballast composed of little balls of lead, is for those heavier
than water. Just as is usually the case with thermometers, the divi-
sions are marked with little balls of glass or enamel soldered to the
pipe. Docs not this other hydrostamm, provided with a kind of
balancing plate, remind one of Nicholson's aerometer ? It was used
for determining the specific gravity of precious stones, by observing
to what degree it sank without the precious stone, and with the pre-
cious stone placed upon the little metallic disc suspended by the
three little chains. This is also a fitting place to draw attention to the
so-called " Palla d'Oncia" (ounce-ball) of the Grand Duke Ferdinand,
a ball of glass which displaces very nearly an ounce of water ; into its
pipe several rings were strung in order to make it sink, and then by
the number of these rings it was known what the specific gravity of
the liquid was in which it had been immersed. Other hydrostamms
were afterwards constructed on the principle of the thermometer
with the little balls, which has already been described ; they were
called " a gabietta" (like a small cage) ; because the little balls were
placed in a sort of cage made of fine brass wirework. When it was
immerged into the liquid which was to be experimented on, the
number and colour of the balls that sank determined the specific
gravity required. And it being known, even at that time, that the-
ON INSTRUMENTS FROM ITAL Y. 129
specific gravity varied with the temperature, it was thought that one
experiment would suffice to give both the data necessary in order to
determine it with precision. In this photograph you can see one of
the methods employed — viz., by fixing a thermometer in a hydro-
stamm ; but other ones of the Accademia del Cimento exist, which are
true thermometers, having, in addition, the graduation of the hydro-
stamm.
The Grand Duke also occupied himself in perfecting a certain
pendulum, in order to obtain equable intervals of time of greater or
less duration ; and from the figure which you see here in the t( Libra
de' Saggi di Naturali Esperienze," you can understand how for the
oscillating ball always to remain in the same plane, it was suspended
by two threads, which thus formed the two sides of an isosceles tri-
angle, and of which it was possible to alter the length, at pleasure, by
means of a convenient pincers. This pendulum was also used in the
experiments made upon the velocity of propagation of light and
sound. Indeed concerning the latter, which were afterwards repeated
by the Accademia del Cimento, I cannot but say a few words, as in
the usual works on physical science mention is only made of the
experiments carried out by the French academicians, while those
made so many years before, upon the same plan and with the same
results, are omitted.
Here is an extract from one of Viviani's letters, in which he gives
an account of these experiments. After having related certain dis-
cussions upon sound which had taken place with Signer Rinaldini and
Signer Borelli, and had spoken of some bomb-shots that had been
fired from the Petraja, he having been with the Grand Duke when
they were determining its distance from Florence, he continues : —
" His Highness asked me the following questions — Which of the two
sounds, the greater or the less, reached the ear in the shortest time ?
To this I answered that both would reach exactly in the same time.
Secondly, of what impediment the wind could be to the propagation
of sound ? I answered : None. He then proceeded with his inquiries,
and asked me what difference of time I thought there would be in the
rate of the sound, between the discharge of the piece with the mouth
turned towards the ear of the observer, or turned up perpendicularly,
or turned the other way ? To which I answered immediately, although
K
1 30 ~ SECTION— PHYSICS.
the question was perfectly new to me, that I should have thought these
periods perfectly equal to one another. His Highness did not tell
me whether I had answered these questions rightly or not; but
in the evening, when he came up to see the experiments, he assured
me that in those which had already been made, and had been repeated
two evenings before with a large arquebuse from the Petraja, it had
been found to be actually the case that the rate of the lesser sound
was equal to that of the greater ; that the wind, which on the second
evening was blowing from the south-east, did not affect it in any way
whatever ; and that the difference in the direction of the discharge
made no variation in the rate of progress of the said sounds. Nor did
his Highness's demands end here, for before I had left him, in order
to ascend the terrace to make the observationSj he finally asked me
what I should think would be the rate of two sounds, the one made
at a distance of two miles and the other at double that distance ? I
answered that I had also had a great curiosity to satisfy myself
whether the motion of sound was in itself of a continually slackening
velocity, or whether it were equable, because if it were found to be
such, it seemed to me that more curious consequences might be
drawn from it, and which might prove to be of great use. Upon this
he urged me to say what I thought, as he wished afterwards to make
the experiment. I answered — and indeed too boldly — that at double
the distance the time would be exactly double, for I held that the
progress of sound was in itself uniform — that is to say, that in any
given equal spaces of time it will traverse equal distances. As I had
reasoned on this particular point the day before, and I seemed to
have greater reason to be convinced of this than of the contrary, I
therefore threw no doubt in my answer, and for the time being our
conversation stopped there."
Then after having related how the following day he had determined
the required distance between the Petraja and Florence, about 9500
braccia, he continues : " Whilst conversing with his Highness and
Prince Leopold about the experiments which had been made, and
others which were to be made upon the subject of sound, I took occa-
sion to let their Highnesses hear the contents of the enclosed writing,
in which I had, the previous evening, noted down, more for my own
remembrance than for any other purpose, all that had once suddenly
ON INSTRUMENTS FROM ITALY. 131
struck me, and which would be able to be obtained, in case the pro-
gress of sound were always equable, or at least if the proportional rate
at which it advanced were known.
" Serenissimo Granduca, — If the velocity of the motions of all
sounds, both loud and soft, powerful and weak, are perfectly equal, as I
am convinced they are, and are likewise unaffected by any change of the
air or gust of wind, either favourable or unfavourable ; and if moreover
the progress of any sound is equable, as I believe to be the case— that
is, that in any given equal spaces of time the distances traversed are
the same (as the Discussion has persuaded me must follow), most
useful and most curious consequences can be drawn.
" Let a most exact experiment be made of the time which the sound
of a bomb (exploded, say, at the precise distance of three miles) takes
to reach our ears, and having accurately found by measurement the
time which it takes, we can say a third of a minute prime of an hour ;
or without caring to know what part, of an hour the time may be, we
can say that it took forty vibrations of such a pendulum ; and from
this observation alone we shall obtain the following, and many other
results. And first of all, we shall be able expeditiously to know how
far from us anything making a sound is, provided we can see the blow
given and that the sound reaches our ear.
" It will be possible, without using any instruments (which for the
most part prove incorrect), without moving from one spot, to know the
distances of towns, villages, castles, £c., provided they be seen, and
that the sound of a blow or a shot be heard at such a distance. Plans
of great countries can thus be made, by merely' knowing the angles,
and with very great saving of positions ; it will be equally effective
in plains as on mountains, where great difficulty is experienced on
account of the imperfections of the instruments, £c.
" It will be possible to ascertain the distance of an army from any
place, to know how far off batteries are stationed, and obtain many
other similar advantages in time of war.
" Moreover, we shall be able to know how far distant from any place
on land or at sea an island may be, or a ship, or a fleet, or how far
off a naval battle is taking place ; we shall be able to measure the
distance bct\vecn two ships, or two islands, or two rocks, when they
1 32 SECTION— PHYSICS.
are in the open sea and there is no place to stop in order to take up
the two stations, a thing which it is impossible to do by any other
means, or at least has never yet been done, as the sailors tell me.
" Finally, we shall know with perfect accuracy the distance from us
of the clouds from which issues the thunder, and this by measuring with
the same pendulum the time which escapes from the moment when
the flame of the discharge or the beginning of the lightning is first
seen to the instant when the sound reaches the ear ; for, by the Rule
of Three, we shall say that if in forty vibrations exactly three miles
(that is, 9000 braccia) are traversed by sound, how many miles or
braccia will be traversed in ten, twelve, or thirty vibrations ; for the
fourth number given will show the distance required.
" It is well to notice that the measurements of very great distances
will prove more accurate than those of the nearer ones, and this be-
cause the interposition of time between the flash and the arrival of the
sound is so short that there is but little time to measure the vibrations
even of the shortest and therefore quickest pendulum, which would be
the one it would be necessary to use in similar operations, &c.
"VlNCENZO VlVIANI.
" October 10, 1656."
" It so happened that their Highnesses thoroughly approved of these
ideas and became all the more anxious to endeavour to find by means of
experiments the proportion of these velocities. Shortly afterwards Signer
Borelli appeared, and his Highness commanded that the next evening we
should go to make the trial on the high road of the wood of St. Moro
dalle Mulina, and appointed Ricci and Monsu Filippo to aid us. We
went on the appointed day at 20 o'clock, having with us the same
bombardier, who was the lame De Neri who had fired the shots at the
Petraja, carrying with him powder, rockets, and a cannon (maschid).
We employed the hours of the day in accurately measuring the length
of the road, and we found that from the old wood to the Arno it was a
little more than a mile and one-fifth ; but in order that the experiment
should be accurate we measured out exactly one and one-fifth mile,
and at that spot we made the cart stop with the maschio on it. We
then placed two pendulums, one at the very end of the above-mentioned
road, the other at the precise middle ; they were instruments the
ON INSTRUMENTS FROM ITAL V. 133
vibrations of which were perfectly equal. Signer Borelli and Signer
Ricci stood at the end, with the youth De' Galilei, who seemed to
behave well ; and I was placed in the middle, together with Monsu
Filippo d' Augusta, clockmaker to his Highness. When night had
come on Signer Borelli made the first sign to the bombardier with the
rocket, and then the firing began, but no shot was fired without a sign
being given from another rocket. Each one of us was consequently
previously warned on each occasion to watch the movement of the flame
of the maschio, and we immediately set to work to count the vibrations
of our pendulum ; and the others further off did likewise. As many as
fifteen shots were fired, and we always found, to my very great satis-
faction, the same number of vibrations from the appearance of the light
to the arrival of the sound, and ours were always less than eight, and
we settled among ourselves that it might be called seven and a half.
We finished the experiment at about two and a half o'clock in the
night ; and we, who were nearer Florence, remained waiting with the
greatest anxiety for the others with the carriage, in order to hear their
number of vibrations ; and finally, not to keep you- any longer in sus-
pense, they, without knowing what ours had been, told us that they had
always counted fifteen and a half ; which was exactly double our time,
just as one and one-fifth of a mile is double three-fifths of a mile ; and
so we all got into the carriage with the utmost satisfaction and entered
Florence about four o'clock at night, and we immediately informed his
Highness, who was awake, and expecting the news of the result of our
experiment ; and you can imagine with what pleasure he heard our
communications. The following evening we repeated the firing from
the Petraja, when there was a strong north wind blowing, and yet we
found the same result as the previous evenings, which had been
forty-one vibrations of the same pendulum. And to put a seal to this
story, I must add that I have made the following calculation : If
sound traverses 3600 braccia in fifteen-and-a-half vibrations, how
many braccia will it have traversed in forty-one vibrations — the num-
ber between the Palace and the Petraja ? and the fourth number is
9522 braccia, which is about the figure given by the greater number of
instruments."
When the Accademia del Cimento afterwards repeated these same
experiments, it was found that in five seconds sound traverses one
134 SECT10A7— PHYSICS.
Tuscan mile=to kil. i '65666, that is to say, it travels at the rate of
332 metres per second.
And at this place, I cannot but call your attention to the fact that
it was Prince Leopold who was the life and soul of the Accademia del
Cimento. This Macsenas of science facilitated the publication of the
most useful and distinguished works, he gave his advice and assistance
towards the reprinting of the old works on geometry ; he arranged and
watched over the collection of Galileo's works and of the scientific
essays of Padre Castelli ; he urged Torricelli to make public the
mathematical definitions of inertia ; he encouraged Rinieri to bring
to a conclusion the laborious charge, which he had undertaken, of
finding the constitution of the Stelle Medicee ; but in 1647 when the
latter was giving daily information regarding Jupiter's satellites, and
was on the point of publishing the tables, he suddenly died, and his
valuable papers were, alas ! very quickly scattered. It was. indeed, a
year of ill-omen, for in it Rinieri, Torricelli, and Cavalieri descended,
one after another, into the tomb. But their works, the germs of future
disciples, outlived them. In fact, ten years afterwards, we find our-
selves face to face with a great event in the annals of science, and one
most auspicious for Italy, and particularly for Florence — namely, the
foundation of the first scientific Academy. We are chiefly indebted
to Prince Leopold for the great idea of establishing an academy which
should be destined expressly to the study of experimental philosophy.
That distinguished man, who was accustomed to gather round him
for useful conversation the most illustrious persons of his time, thought
that researches would be more systematically pursued, and the gather-
ings of many men would benefit to a much greater extent the progress
of science, if meetings were held regularly and some rules and regu-
lations laid down. Ferdinand joyfully agreed to his brother's pro-
posal, and showed the greatest generosity towards the new institution ;
he presented all his own valuable instruments to it, and even endowed
it with the results of his former experiments, several of which have been
regarded as the work of the Academy, which was certainly not the
case. On the iSth of June, 1657, there was held in the Pitti Palace,
the first sitting of the first scientific Academy ; it justly chose to name
itself the " Accademia del Cimento" (Attempt, trial, essay), and it
selected as its device the now celebrated motto : " Provando e Ripro-
ON INSTRUMENTS FROM ITALY. 135
vando" (By trying, and trying again). The members present at this
celebrated meeting were : Vincenzo Viviani, Alfonso Borelli, Carlo
Rinaldini, Alessandro Marsili, the brothers Paolo and Candido del
Buono, Antonio Oliva, Lorenzo Magalotti, Francesco Redi, and Carlo
Dati. Among the Italian correspondents, Ricci, Cassini, Montanari,
Rossetti, and Falconieri must be mentioned ; and among foreigners,
Stenone, Tevenot, and Fabbri.
It is not my intention to speak individually of each of these
academicians ; the limited time at my disposal would not permit of
it ; nevertheless, before speaking of the labours of the Academy, I
cannot but add a few words more respecting one or two of them.
And above all I must mention Viviani, Galileo's only disciple, a subtle
and industrious academician, to whom we are indebted for many
experiments which led the way to the discovery of the theory of undu-
lations, the general idea of which, he even at that time, suspected.
We owe him likewise a barometer, without a small well (pozzetto) ;
experiments on capillary phenomena, independent of pressure ; the pro-
position for finding the weight of ice compared with that of water ; the
experiments on the swim-bladder of fishes ; but, above all, the machine
for making a great vacuum, to which primitive shape of a pneumatic
instrument we have at present returned, giving it the name of mer-
curial ; and many persons dispute the invention of such a machine,
forgetting all the while that the first instrument of the kind was made
by Viviani.
From the explanatory figures of this machine, which are in the
41 Libro de Saggi," published by the Academy, and which you see
before you, you will be able to understand how. it was in reality a true
mercurial machine, with which the academicians made a great number
of experiments, to which I shall allude further on.
A no less powerful intellect was that of Borelli, a Neapolitan. A
mathematician, a physician, an astronomer, he occupied himself with
all subjects, and thus supplied himself with ample materials for future
discoveries. He studied the reciprocal attraction of floating bodies
(galleggianti\ and discovered its theory ; he was the first to observe the
variations of the barometer with the changes in the atmosphere ; he
considered the question of the freezing of water ; he planned the ex-
periments which were decisive against the idea of the positive light-
136 SECTION— PHYSICS.
ness (leggerezza positive?) ; he measured the greatest expansion of air,
freed from the surrounding pressure ; he determined the weight of air
compared to that of water ; he suggested the famous experiment with
the silver ball, to test the compressibility of water ; and another experi-
ment on the propagation of sound in vacuo ; he studied the con-
traction of various liquids in cooling ; and in the researches on the
velocity of propagation of light, he was the first to construct the
Heliostat (Eliostata) ; he published, whilst lecturer in Pisa, the
"Euclides restitutus," in which he reduces to 230 propositions the
elements of ancient geometry ; and afterwards the treatise on the force
of the blow, which together with that on the natural motions depend-
ing on will, serve as an introduction to his great work " Del moto
degli Animali ;" he studied the optic nerve, and the organs of respira-
tion in fishes, and was the first to occupy himself with the anatomy of
the torpedo ; he observed the comet of 1664, declaring that it was not
an accidental meteor, or vapour, but a solid body moving, not round
the earth, but round the sun, in a line resembling a parabola, and thus
laid the foundations of the theory of the comets ; he published the
theory of the " Stelle Medicee," in which he clearly proved that the
orbit of the satellites is not in the same plane as that of Jupiter, and
he compared these satellites to the moon, and thus alluded to the
principle of universal attraction ; he was the first to make known that
Venus can be seen two days running, as a morning and as an evening
star ; he wrote an account of the eruption of Mount Etna which took
place in 1669 ; he studied the constitution of liquids, and was the first to
point out the phenomenon of the contraction of the liquid vein;
and he illustrated by new experiments Galileo's idea of the fall of
weights in vacuo.
But we must now turn, for a short time, to the principal works of the
Academy, although very much must necessarily remain unsaid of the
individual academicians, and especially of Redi and Stenone and
Cassini.
And coming now to the experiments, the first series refers to the
natural pressure of the air. In a discussion on Torricelli's experi-
ment, and on the reason why solid bodies do not lend themselves to
it, and among liquids, mercury should adapt itself the best, there is to
befound noted down,with regard to liquids, a most important hypothesis
ON INSTRUMENTS FROM ITALY. 137
on their constitution : " Either on account of their slippery smoothness,
or on account of the rotundity of their extremely small bodies or for
some other figure which they may take, particularly inclined to motion,
being just equilibrated, as soon as they are pressed they immediately
give way on all sides and scatter themselves . . ." so that it would
not be possible in our days to discuss their fundamental property
any better. And another important law is added further on : " In all
liquids this force of the pressure of the air is admirably shown, par-
ticularly when they are caught in some place where they have on one
portion of their superficies an empty, or nearly empty, space into
which they can withdraw. Since, in this case, being pressed on one
side by contiguous air, which in its turn is pressed down by so many
miles of amassed atmosphere, and on the other side, where there is
no obstacle, are confined by the void which has no weight at all, they
rise until the weight of the liquid raised up is equal to the weight of
the air pressing on the other side." It is afterwards observed that by
vacuum or void is meant that the air alone should be excluded, and
not light, or heat, or ether.
We are indebted to the Accademia del Cimento for the usual ex-
periment which is made under the bell of the pneumatic machine, with
the bladder that swells by exhausting the air, and also swells when it
is forced back into it ; the second of those two barometers, the one
with the little well (pozzetto] outside, the other shut up in a bell in
which the vacuum is obtained, and which was invented to prove that
it is really the pressure of the air that holds up the mercury, and which
was afterwards altered by immerging the barometer in a vessel full of
water, so that the mercury was found to rise above the usual braccio
and ^ by T\ of the height of the water in the vessel, the level being
taken from that of the mercury in the little well (pozzetto).
Then availing themselves of Vivianf s mercurial pneumatic machine,
they instituted a number of experiments in vacuo, to see whether their
operations prove contrary to, or in any way different from, those which
manifest themselves when surrounded by air. They accordingly experi-
mented on the spherical shape of the drops independent of the pressure
of the air ; on the heat and the cold which cause the rise or fall of the
barometrical column ; on the reflection of images in lenses, attributed
by Kepler to the air ; on the attraction of amber in vacuo ; on the
138 SECTION— PHYSICS.
propagation of heat ; on the propagation of sound in vacuo, v.-hcn it
was wisely remarked that the sound generated could be communicated
to the exterior air, by the very partitions of the recipient in which the
sonorous body was closed ; on the attraction of the loadstone ; en.
capillary phenomena, independent of atmospherical pressure ; on the
boiling o£ water in vacuo ; on the bursting of air-bubbles by cold ;
and, finally, on the various ways in which many animals are afTected
when placed in vacuo, or in very rarefied air, such as leeches, snails,
grasshoppers, butterflies, lizards, flies, little birds, crabs, frogs, and
different kinds of fish, and they paid particular attention to the effects
produced on the swim-bladders of the latter. With regard to these last-
mentioned experiments, and especially to those which refer to little
birds that die immediately, and even when succoured in time do
not fly away, it is well known that in one of Boyle's experiments a
lark lived ten minutes in vacuo, and a goose seven minutes. But, it
is added, that whoever reflects upon the different ways of producing
the void in these two cases will perceive that the experiments, far from
proving contradictory to one another, agree most admirably; inas-
much as where in the one case (Boyle's) the air is thinned by succeed-
ing attractions with very slow and little less than insensible acquisi-
tions ; in the other, by the extremely rapid descent of the quicksilver, it
is immediately reduced to that last degree of rarity and thinness, which
cannot be of any avail for respiration. And from this we can gather
that even at that time the superiority of the mercurial pneumatic
machine over all others was perfectly well known.
As an introduction to the experiments on the compression of water,
Magalotti writes — " Although the truth is not always arrived at by the
first experiment, that is not the case because the first idea cf the ex-
periment is not very often quite adequate to obtain the truth ; but it
may sometimes happen because the materials and means which are
used to carry it out practically are not adapted to that purpose ; and
although these experiments cannot contaminate the purity of the
theoretical speculations, they are nevertheless unfitted to second them,
on account of the materials employed. But not for this reason must
these experimental inquiries into natural phenomena be deemed to
have failed ; because, although at times we do not succeed, by means
of them, in coming to the bottom of the truth, which was first of all
ON INSTRUMENTS FROM ITALY. 139
sought after, it is indeed rare, if some glimmering of the fact be not
derived from them, or the falsity of some other contrary supposition
discovered by their means."
Of the three ingenious experiments that were made to compress
water — viz., by the force of rarefaction, by the pressure of mercury,
and by the force of a blow — the last has remained the most universally
known. It was made with a subtle ball of silver containing the water,
which, when the ball was beaten with a hammer, sweated through all
the pores of the metal, and looked like quicksilver coming out drop by
drop through some skin in which it was squeezed. Here is the ball
which was used for this celebrated experiment, and it still contains
some water. This other one, which likewise has water in it, was pre-
pared by the academicians for a repetition of the experiment, which
did not, however, take place. Other most ingenious and conclusive
experiments were made by the academicians on the question of posi-
tive lightness — namely, " whether those things which are commonly
called light are so by their own nature, and whether they float upwards
of their own accord, or whether their rising be merely the effect of
heavier bodies driving them away ; these weightier bodies having
more vigour and greater power to descend and place themselves lower,
squeeze the lighter ones away (so to speak), and compel them to rise."
Nor did they forget the marvellous operations of the magnet, a vast
field, in which though much be already discovered, there undoubtedly
remains a great deal more to be found out. They clearly showed
that iron and steel are essentially magnetic ; that attraction and re-
pulsion can take place, even through solids and liquids ; that the poles
of the magnetic needle are much enfeebled wlien held in the position
of the magnetic equator. With regard to the electrical action, the
academicians merely explained which substances possessed such a
property, and which not, and concluded that it was common to all
transparent stones and not to opaque ones, but that it was more
especially a property of amber, which, even attracts smoke.
With regard to the experiments on sound, we have already spoken
of them at sufficient length ; those on projectiles are but experimental
proofs of three propositions of Galileo. The first, that a ball dis-
charged horizontally from a tower always takes precisely the same
time in reaching the earth as it would take had it been let fall freely
140 SECTION— PHYSICS.
from the same height ; and that would always be the result whatever
the force of the discharge. The second, that, on account of the
resistance of the air, there is a maximum limit of the velocity with
which a body falling from any height can reach the earth. The third,
that a motion cannot be destroyed by another motion coming upon it
afterwards ; and this was illustrated by the well-known experiment of
a cannon mounted on a waggon drawn by six horses ; when the ball
was discharged upwards, it always fell close to the mouth of the
cannon, whether the waggon was at a standstill, or whether it
was going at full speed. Other experiments refer to the relative
weight of air and water ; others to the impermeability of glass to
moisture and smells ; some are directed, in accordance with one of
Galileo's ideas, in determining whether light takes any time in pro-
pagating itself; others again clearly demonstrate that even white
substances can be set on fire by means of a powerful burning-glass j
nor did theyfail to observe thephenomena called byus phosphorescence
in sugar, in rock salt, rock-crystal, in agates, in jasper, &c.
Chemistry, likewise, was included in the field of their researches :
they observed that waters distilled in lead, render turbid all natural
waters, which are afterwards made clear by means of strong vinegar
(acetoforte) ; that oil of tartar and oil of aniseed infused in water
occasion the formation of a little cloud, which disappears on the
addition of spirits of sulphur ; and they insist strongly on the fact that
the thickness is less with purer and lighter waters, and hence point
out the above-mentioned liquids for the analysis of waters ; that the
tincture of roses, extracted with oil of vitriol, becomes green when oil
of tartar is poured upon it, and returns to its original colour by means
of spirits of sulphur ; that citric acid, spirits of vitriol, and spirits of
sulphur change lac into violet, and the tincture of violets into ver-
milion, which can be made violet by the addition of oil of tartar, &c.
But there remains to tell of more interesting experiments — namely, of
those made on artificial freezing, and on the dilation of bodies by
heat. It was Galileo's opinion that ice was rather rarefied water than
condensed water; since condensation brings about diminution of
bulk and increase of weight, whilst rarefaction, on the other hand,
causes greater lightness and enlarges the bulk. But water, in freezing,
augments in bulk, and ice already made, is lighter than the water
ON INSTRUMENTS FROM ITAL Y. 141
on which it floats. Now the academicians by means of intelligent
and varied experiments, clearly set forth, that as a matter of fact
water by freezing increases in volume, so as to rend in pieces the
vessels in which it 'is contained, and they proved, at the same time,
that the bursting of the vessels is not to be attributed to the formation
of a vacuum, but solely to the dilation of the contents. In this way
they caused the bursting of balls of the thickest glass, and of brass,
and of copper, and of silver, and of gold. They also determined the
relative expansion of ice and water, which they established as 9 : 8.
Then the experiments made to investigate even in its most minute
details the act of freezing are marvellously interesting, clear, and
precise.
Here are these subtle observations and their classification ; and I
leave you to judge whether at that time, or even in our days, I was
about to add, more could be done. They used for these experiments
balls of glass ending in long tubes ; they were filled with water and
then immersed into a freezing mixture of salt and ice, to which they at
times added a sprinkling of alcohol (aquarzente). The natural state
means the degree of temperature of the water or other liquid in the
tube of the vessel before it was placed in ice. " Salto dell' immersione"
is that first rebound which the water is seen to make the moment
the ball touches the ice. This does not come from any intrinsic
alteration of the water, but from extrinsic reasons of the vessel.
Hence it is that it sometimes varies slightly, and thus brings about
some change in the other conditions through which the liquid passes
before freezing. But as that leap altogether is but very little, so ar
its variations but very slight, and infinitesimal are the effects which it
produces in the subsequent changes. "Abbassamento" denotes the
degree to which the water, after the above-mentioned salto dell* im-
mersione, descends when the cold is beginning to affect it.
" Quiete" is the state in which the water remains for some time after
the dbbassamentOy without showing any apparent signs of motion.
" Sollevamento" is similarly the state which the water from the
lowest point of abbassamento attains by means of rarefaction, with a
very slow and apparently equable motion (in all respects like the first),
with which it contracts itself.
" Salto delP agghiacciamento" means the state into which the water
142 SECTION— PHYSICS.
is thrown with the utmost velocity, at the moment of freezing. So
that in quoting the terms by which they signified the different con-
ditions which they observed, and in telling you what they meant to
define by each one of them I have already informed you of the im-
portant observations which they succeeded in making. They proved
the salto dell' immersione, not only by thrusting the ball into ice,
but into hot water. The quiete corresponds to our maximum of
density of water, which was indicated in their thermometers by 119°.
Sollevamento is the expansion which the water undergoes from 4°
down to the point at which it freezes. Then the word salto (leap,
jump) shows us how the phenomenon of freezing takes place rapidly ;
in fact the academicians well observe the almost instantaneous freezing
of water in certain cases — namely, when left to itself, its temperature
descends to below o°, and being then shaken (the ball having been
taken from the snow, as they were accustomed to do, to see the salto
del? agghiactiamento) all of a sudden the whole of its mass became solid.
And conditions similar to these they observed in spring water, and in
water distilled from various substances, in wines, in vinegar, in spirits of
vitriol, in oil, in which, however, they found no rarefaction, so that
frozen oil sinks to the bottom of fluid oil, and in brandy, which con-
tracts itself regularly but does not freeze. As to natural freezing it
was so minutely observed and described that it fills one with astonish-
ment and admiration. They proved that ice produced in vacuo is
more compact and weighs more than in the air ; and that when water
freezes slowly in a glass it makes first of all a crust, which, being
pressed, in some place or other, by the expansion of the remainder of
the water affected little by little by the cold, breaks open, so that from
the aperture there issues a certain amount of water, which, freezing in
its turn, renders the surface of the ice convex ; and sometimes if the
cold be intense, wrinkled, or rather forms an excrescence of ice, which
can even reach the height of a finger. And this observation recalls to
my mind the experiments of the illustrious Gorini, and his theory on
the origin of volcanoes and mountains. But if the crust be too thick
and the expansion underneath be not able to break it, it generally
happens that the vessel bursts. Then they pointed out the difference
between the ice of ordinary water, of distilled water, of sea water, and
the congealing action of common salt, and of the more efficacious salts
ON INSTRUMENTS FROM ITALY. 143
of ammonia ; and even the vapour which rises from ice, and which
they with happy intuition compared to clouds ; and finally all that you
see illustrated here in the photograph of a part of Galileo's Tribune —
namely, the reflection of cold by means of a burning-glass, which thus
outstrips the modern theories of radiating caloric and its tendency
towards equilibrium. To clear up the phenomenon of the salto dell'
immersione, they were led to make other and no less important experi-
ments on the expansion of bodies by heat, and their contraction by
cold, using glass and many metals ; and they were the first to make
the well-known experiment with a bronze armlet in which when heated
moves sensibly a cylinder made expressly, but when it has cooled
down this last does not fit in to it.
And this Academy, the first, and one so rich in most important dis-
coveries in every branch of science, after a duration of only ten years,
ceased to exist. Its founder was made a cardinal ; reasons of State
required it ; and truly for a cardinal to be the head of an Academy
which was named Del Cimento, would have been too much for those
times. And indeed the disestablishment of the Academy was but a
corollary to Galileo's trial.
Instituted in the year 1657, it was the first scientific academy ; the
one of Vienna, begun by Doctor Bausch was not fully established
till the year 1670. The Royal Society of London had its true origin
in 1663, and in the first volumes of its reports it relates the experi-
ments of the Accademia del Cimento. The Academy of Sciences of
Paris dates from 1666.
The CHAIRMAN : Ladies and Gentlemen, I have no doubt a great
number of the audience were able to follow the Cavaliere de Eccher
better than I have been able to do in the interesting history of the
instruments he has described, but we cannot too much . thank the
Italian Government for permitting them to leave Italy. As I might miss
much in giving you a summary, from my imperfect knowledge of Italian,
I have asked my distinguished friend the Rev. S. J. Perry, whom you
have all heard of as being at the head of the expedition to Kerguelen
Island to observe the transit of Venus, to run briefly over the princi-
pal topics of the paper.
The Rev. S. J. PERRY having given a resume of the paper above
printed —
144 SECTION— PHYSICS.
The CHAIRMAN said : I must thank Mr. Perry for having helped
me out of the difficulty in giving you this very interesting review of
science developed in the Florentine Academy, and I hope we shall
have the full document preserved and translated into English, for it
will be a great pity if such an excellent expose should be lost to the
English public. I imagine that in the review which Father Perry has
been so good as to give, he omitted to state that a claim was made also for
the determination of the maximum density of water, which I fancy was
among the matters which the Florentine Academicians undertook.
The experiments upon the supposed non-compressibility of fluids were
very remarkable. Several attempts were made to compress different
liquids, but in all cases they escaped and no appreciable compression
was observed. I must say again that we are deeply indebted, not only
to the learned Professor who has given us this excellent discourse,
but also to the Italian Government, and I believe also to the
municipality of Florence, to whom many of these invaluable records
of the past belong. I ask you, therefore, to return by acclamation your
thanks, not only to Professore de Eccher, but also to the Italian Govern-
ment, and to the municipality.
The Conference then adjourned.
SECTION— PHYSICS (including Astronomy).
May 24/7*, 1876.
The PRESIDENT : The first paper on our list to-day is that by Pro-
fessor Clerk-Maxwell, on the Equilibrium of Heterogeneous Bodies.
He is here now to speak for himself, and I beg to call upon him to
give us his communication.
ON THE EQUILIBRIUM OF HETEROGENEOUS SUBSTANCES.
Professor J. CLERK-MAXWELL, M.A., F.R.S. : The warning which
Cointe addressed to his disciples, not to apply dynamical or physical
ideas to chemical phenomena, may be taken, like several other warn-
ings of his, as an indication of the direction in which science was
threatening to advance.
We can already distinguish two lines along which dynamical science
is working its way to undermine at least the outworks of Chemistry,
and the chemists of the present day, instead of upholding the mystery
of their craft, are doing all they can to open their gates to the enemy.
Of these two lines of advance one is conducted by the help of the
hypothesis that bodies consist of molecules in motion, and it seeks to
determine the structure of the molecules and the nature of their motion
from the phenomena of portions of matter of sensible size.
The other line of advance, that of Thermodynamics, makes no
hypothesis about the ultimate structure of bodies, but deduces relations
among observed phenomena by means of two general principles — the
conservation of energy and its tendency towards diffusion. The ther-
rnodynamical problem of the equilibrium of heterogeneous substances
was attacked by Kirchhoff in 1855, when the science was yet in its in-
145 SECTION— PHYSICS.
fancy, and his method has been lately followed by C. Neumann. But
the methods introduced by Professor J. Willard Gibbs, of Yale College,
Connecticut,* seem to me to be more likely than any others to enable
us, without any lengthy calculations, to comprehend the relations be-
tween the different physical and chemical states of bodies, and it is to
these that I now wish to direct your attention.
In studying the properties of a homogeneous mass of fluid, consisting
of 11 component substances, Professor Gibbs takes as his principal func-
tion the energy of the fluid, as depending on its volume and entropy
together with the masses, mv mz .... mn, of its n components, these
11+2 variables being regarded as independent. Each of these vari-
ables is such that its value for any material system is the sum of its
values for the different parts of the system.
By differentiating the energy with respect to each of these variables
we obtain ?/ + 2 other quantities, each of which has a physical signifi-
cance which is related to that of the variable to which it corresponds.
Thus, by differentiating with respect to the volume, we obtain the
pressure of the fluid with its sign reversed ; by differentiating with
respect to the entropy, we obtain the temperature on the thermo-
dynamic scale ; and by differentiating with respect to the mass of any
one of the component substances, we obtain what Professor Gibbs
calls the potential of that substance in the mass considered.
As-this conception of the potential of a substance in a given homo-
geneous mass is a new one, and likely to become very important in the
theory of chemistry, I shall give Professor Gibbs's definition of it.
" If to any homogeneous mass we suppose an infinitesimal quantity
of any substance added, the mass remaining homogeneous and its
entropy and volume remaining unchanged, the increase of the energy
of the mass, divided by the mass of the substance added, is the poten-
tial of that substance in the mass considered."
These ;z + 2 new quantities, the pressure, the temperature, and the
# potentials of the component substances, form a class differing in
kind from the first set of variables. They are not quantities capable
of combination by addition, but denote the intensity of certain physical
properties of the substance. Thus the pressure is the intensity of the
* Transactions of the Academy of Sciences of Connecticut, vol. ili.
•* •
HETEROGENEOUS SUBSTANCES. 147
tendency of the body to expand, the temperature is the intensity of its
tendency to part with heat ; and the potential of any component sub-
stance is the intensity with which it tends to expel that substance from
its mass.
We may therefore distinguish these two classes of variables by
calling the volume the entropy, and the component masses the magni-
tudes, and the pressure, the temperature, and the potentials the in-
tensities of the system.
The problem before us may be stated thus : — Given a homogeneous
mass in a certain phase, will it remain in that phase, or will the whole
or part of it pass into some other phase ?
The criterion of stability may be expressed thus in Professor Gibbs's
words — " For the equilibrium of any isolated system it is necessary
and sufficient that in all possible variations of the state of the system
which do not alter its energy, the variation of its entropy shall either
vanish or be negative.
" The condition may also be expressed by saying that for all possible
variations of the state of the system which do not alter its entropy, the
variation of its energy shall either vanish or be negative."
Professor Gibbs has made a most important contribution to science
by giving us a mathematical expression for the stability of any given
phase (A) of matter with respect to any other phase (B).
If this expression for the stability (which we may denote by the letter
K) is positive, the phase A will not of itself pass into the phase B, but
if it is negative the phase A will of itself pass into the phase B, unless
prevented by passive resistances.
The stability (K) of any given phase (A) with respect to any other
phase (B), is expressed in the following form : —
K = e - v p + rj t — m, \L, — £c. — ;;zn ^
where e is the energy, v the volume, 77 the entropy, and mu m2, £c. the
components corresponding to the second phase (B), while p is the
pressure, t the temperature, and /z1? /u2, &c. the potentials corresponding
to the given phase (A). The intensities therefore are those belonging
to the given phase (A), while the magnitudes are those corresponding
to the other phase (B).
We may interpret this expression for the stability by saying that it is
148 SECTION— PHYSICS.
measured by the excess of the energy in the phase (B), above what it
would have been if the magnitudes had increased from zero to the
values corresponding to the phase B, while the values of the intensi-
ties were those belonging to the phase (A).
If the phase (B) is in all respects except that of absolute quantity of
matter the same as the phase (A), K is zero ; but when the phase (B)
differs from the phase (A), a portion of the matter in the phase (A)
will tend to pass into the phase (B) if K is negative, but not if it is
zero or positive.
If the given phase (A) of the mass is such that the value of K is
positive or zero with respect to every other phase (B), then the phase
(A) is absolutely stable, and will not of itself pass into any other
phase.
If, however, K is positive with respect to all phases which differ from
the phase (A) only by infinitesimal variations of the magnitudes, while
for a certain other phase, B, in which the magnitudes differ by finite
quantities from those of the phase (A), K is negative, then the question
whether the mass will pass from the phase (A) to the phase (B) will
depend on whether it can do so without any transportation of matter
through a finite distance, or, in other words, on whether matter in the
phase B is or is not in contact with the mass.
In this case the phase (A) is stable in itself, but is liable to have its
stability destroyed by contact with the smallest portion of matter in
certain other phases.
Finally, if K can be made negative by any infinitesimal variations
of the magnitudes of the system (A), the mass will be in unstable
equilibrium, and will of itself pass into some other phase.
As no such unstable phase can continue in any finite mass for any
finite time, it can never become the subject of experiment ; but it is
of great importance in the theory of chemistry to know how these
unstable phases are related to those which are relatively or absolutely
stable.
The absolutely stable phases are divided from the relatively stable
phases by a series of pairs of coexistent phases, for which the intensi-
ties p, t, p, £c. are equal and K is zero. Thus water and steam at the
same temperature and pressure are coexistent phases.
As one of the two coexistent phases is made to vary in a continuous
HETEROGENEOUS SUBSTANCES. 149
manner, the other may approach it and ultimately coincide with it.
The phase in which this coincidence takes place is called the Critical
Phase.
The region of absolutely unstable phases is in contact with that of
absolutely stable phases at the critical point. Hence, though it may
be possible by preventing the body from coming in contact with certain
substances to bring it into a phase far beyond the limits of absolute
stability, this process cannot be indefinitely continued, for before the
substance can enter a new region of stability it must pass out of the
region of relative stability into one of absolute instability, when it
will at once break up into a system of stable phases.
Thus in water for any given pressure there is a corresponding tem-
perature at which it is in equilibrium with its vapour, and beyond
which it cannot be raised when in contact with any gas. But if, as
in the experiment of Dufour, a drop of water is carefully freed from air
and entirely surrounded by liquid which has a high boiling point, it
may remain in the liquid state at a temperature far above the boiling
point corresponding to the pressure, though if it comes in contact with
the smallest portion of any gas it instantly explodes.
But it is certain that if the temperature were raised high enough the
water would enter a phase of absolutely unstable equilibrium, and that
it would then explode without requiring the contact of any other sub-
stance.
Water may also be cooled below the temperature at which it
generally freezes, and if the water is surrounded by another liquid of
the same density the pressure may also be reduced below that of the
vapour of water at that temperature. If the water when in this phase
is brought in contact with ice it will freeze, but if brought in contact
with a gas it will evaporate.
Professor Guthrie has recently discovered a very remarkable case of
equilibrium of a liquid which may be solidified in three different ways
by contact with three different substances. This is a solution of
chloride of calcium in water containing 37 per cent, of the salt. This
solution is capable of solidification at — 37° C., when it forms the solid
cryohydrate having the same composition as itself. But it may be cooled
somewhat below this temperature, and then if it is touched with a bit
of ice it throws up ice, if it is touched with the anhydrous salt it throws
ISO SECTION— PHYSICS.
down anhydrous salt, and if it is touched with the cryohydratc it
solidifies into cryohydrate.
The PRESIDENT : We must return our best thanks to Professor
Clerk-Maxwell for his very curious communication illustrating the
unexpected condition in which matter may be found and its unexpected
tendency to change in various ways. To myself it has been par-
ticularly interesting to see how all these conditions of matter and their
tendency may be represented by a model of some tolerable simplicity
and how the geometrical properties of that model are capable of
illustrating and expressing the laws of these peculiar conditions of
matter.
I believe Dr. Andrews, who has paid great attention to the molecular
condition of matter, is present, and we shall be glad to hear any com-
munication which he has to make.
ON THE LIQUID AND GASEOUS STATES OF BODIES.
Professor ANDREWS, M.D., F.R.S. : It is with some difficulty, not
being accustomed to address meetings of this kind, that I attempt to
speak on the subject of which I have given notice, more particularly as
it is a very wide subject and represents the work of nearly ten years.
The facts are so numerous that I am afraid in attempting to give even
a sketch of the entire subject I may end in being partially unintelli-
gible. At the commencement I wish to say that researches of this
kind are not researches on conditions of matter which cannot be
realized in Nature. It is highly probable that in the stellar regions,
and also in many of the larger planets of our own system, all the
conditions of matter to which I shall refer may actually exist.
Certain it is that we could produce them without any artificial means,
if it were possible to descend to the depths of our existing ocean,
and there to establish at certain intervals experimental laboratories.
Many years ago, as some of you will remember, Professor Leslie, of
Edinburgh, imagined that at the bottom of the ocean there was a
layer of condensed air heavier than water, and that there might be
inhabitants in that condensed atmosphere. Certain it is we can
reduce the gases to very nearly the same density as water — to a
density at which, as I have seen myself, they barely rise in that
ON LIQUID AND GASEOUS STATES. 151
liquid. I may perhaps just mention, to give a popular idea
of the question— I am speaking roughly— that if you descend to
1200 feet below the level of the sea, and there examine the properties
of carbonic acid, it would exist, at the pressure there produced and
at the temperature of o° C. (the freezing point of water), in the state of
a liquid. If you descend 1700 feet, not a great depth in the sea, you
would find that this body would remain a liquid at the temperature of
15° C., and if you heated it above that point, it would boil ; it would
resemble in this respect the chemical compound hydrochloric ether
which boils at the ordinary temperature of the atmosphere. If you
descend to a depth of about 2500 feet, and there make your obser-
vations, you will find that the carbonic acid would cease to show the
properties of an ordinary liquid at all temperatures above 31° C. At
the temperature of 15° C. and at a depth of 2500 feet, carbonic acid
would be a liquid. If you heated it, instead of boiling, it would
change in a most remarkable manner, the surface would lose its
curvature, the concave surface with which every one is familiar in an
ordinary liquid would gradually become flattened and disappear, and
at last the liquid would change, not into the gaseous state, but into
one of those intermediate conditions which I have described as con-
necting the liquid and gaseous states together. At this depth of 2500
feet and at 31° C., which I have designated the "critical temperature
of carbonic acid," new conditions of matter supervene, which cannot
be referred either to the liquid or gaseous states, but connect those
states by an unbroken continuity with one another. If the temperature
or pressure be varied by i° or 2° when the carbonic acid is at the
critical point, you will have flickering movements of the same kind as
those which every one has seen on a fine summer's day, or still
better in a telescope, produced by the changing densities of the air, but
here those conditions are so intense and extraordinary that you
would not be able, I believe, to see one foot before you. You would
be in a transparent atmosphere, but at the same time it would be
rendered useless for all ordinary purposes by the intensity of these
conditions. I may just further mention that the experiments of which
you see a representation on the diagram, are experiments which have
been carried on with exact measurements to pressures corresponding
to the depth of 9000 feet below the level of the sea ; and in the same
152 SECTION— PHYSICS.
apparatus I have without measurement gone as far as pressures of 500
atmospheres, which correspond to a depth of 16,500 feet below
the sea. I mention the subject in this popular way so as to
give an idea of the general conditions corresponding to those which
can be seen in a few moments with the apparatus before you. With
regard to that apparatus itself I will very shortly describe it (Professor
Andrews then explained the apparatus by means of a diagram). The
lower ends of the glass tubes containing the gases dip into small
mercurial reservoirs formed of thin glass tubes, which rest on ledges
within the apparatus. This arrangement has prevented many failures
in screwing up the apparatus, and has given more precision to the
measurements. A great improvement has also been made in the
method of preparing the leather-washers used in the packing for the
fine screws, by means of which the pressure is obtained. It consists
in saturating the leather with grease by heating it in vacua under
melted lard. In this way the air enclosed within the pores of the
leather is removed without the use of water, and a packing is obtained
so perfect that it appears, as far as my experience goes, never to fail,
provided it is used in a vessel filled with water. It is remarkable,
however, that the same packing, when an apparatus specially con-
structed for the purpose of forged iron was filled with mercury, always
yielded, even at a pressure of 40 atmospheres, in the course of a few
days. The carbonic acid gas, which is now under a pressure of
about 40 atmospheres, can be liquefied by a few turns of the screw,
and then you can go on visibly compressing the liquid, because liquid
carbonic acid is much more compressible than water. Here is a single
apparatus, but the diagram shows a double one — a communication
being made between the two tubes, so that although we have two
screws we can operate with either or with both. One tube is filled with
air and serves as a manometer, and the other is filled with the gas to
be examined. In making observations of this kind it is necessary not
merely to make them at ordinary temperatures, but to examine the
properties of the gases under different temperatures, and for that
purpose there are two modes. You may work with ordinary glass
cylinders, but experiments of great accuracy can never be made in this
way, because the inequalities in the glass produce an error of some-
times half a millimetre, and therefore it is necessary to make observa-
ON LIQUID AND GASEOUS STATES. 153
tions through plate glass. Accordingly this arrangement has been
made which I described the other day. I should mention that some
of these instruments are in the hands of different Professors, amongst
others of Professor Rijke of Leyden. I have sometimes found diffi-
culty in operating at the temperature of 100° from the tendency of the
tube to become greasy, and drops of water collecting upon it. This
for a long time gave me a great deal of trouble, but at last I found a
remedy, which was to pour boiling water over the tube, — an operation
which even under a pressure of 300 atmospheres is unattended by any
danger provided the apparatus be at exactly the same heat as the
steam — namely, 100° C. I should have further mentioned that in
order to make experiments above 100°, you must bend the tube, and
introduce the end of it into a suitable medium, such as sulphuric acid
or melted spermaceti, or heated air ; the only limit to the temperature
being the softening of the glass. In all these cases so perfect is the
apparatus as regards pressure that all our difficulty is with the tem-
perature. I should mention another matter of importance. If you
run up the apparatus suddenly to a pressure of 200 atmospheres or
more, it will appear to leak ; this is caused by the compression of the
leathers. It requires some little time, in short, before everything be-
comes steady. Therefore, in some experiments, it is desirable to run
up the pressure a little above what you want for a few minutes, and
then bring it down to the proper point.
Now, having given a general account of the apparatus, I will very
briefly refer to the results, and in order to make the subject as intel-
ligible as possible, I shall refer for a moment to a series of effects
which I think establish pretty clearly the remarkable fact, that between
water or any other liquid — for it is not confined to one liquid more
than to another — between any body in the liquid state and the same
body in the gaseous or vaporous state, not only is continuity pos-
sible, but we have been able to establish it by experiment. This
continuity has not been extended to the solid state, nor do I believe
that the ordinary plastic condition of the solid is a passage between
the solid and the liquid condition. That such a passage may be
hereafter effected is possible ; but as far as I can see my way at
present, it is a question which will involve an apparatus capable
of bearing a pressure of many thousands of atmospheres. I may be
154 SECTION— PHYSICS.
wrong on that point, but it is the view which I have taken for many
years, and I believe it is the true view.
Here is a tube which illustrates some of these conditions. It is a
sulphurous acid tube, and when you heat the liquid it first boils, and
then changes into the intermediate conditions to which I have already
referred. Here is another tube, which I am almost afraid to open, not
because it contains carbonic acid, but because it is not so strong. It
was made by Professor Dewar, and contains liquid carbonic acid.
I will very briefly refer to the recent investigations I have made on
the properties of matter in the gaseous state. There are three impor-
tant laws which are known with regard to the gaseous state : the law
of Boyle, according to which gases vary inversely in volume accord-
ing to pressure ; the law of Gay-Lussac, according to which they vary
in volume by a definite amount of their volume at zero, or any other
fixed temperature ; and the law of Dalton, according to which gases
in mixture act as if the other gas were not present, as if each gas
occupied the whole space. At high pressures these laws fail. They
are true in the ordinary conditions of gaseous matter approximately,
very closely indeed in the case of some of the gases, but when you
operate under these great pressures all these laws fail. The failure of
the law of Boyle has been known to some extent, but that of the law
of Gay-Lussac, I believe, has not been observed till my last commu-
nication to the Royal Society.
I will conclude by writing down three formulas which express
ascertained facts. The expansion by heat of a body in the ordinary
gaseous state, whether measured by its expansion at constant
pressure, or by the increase of elastic force under constant volume, is
not a simple function of the initial volume or initial elastic force but a
complex function changing with the temperature. There are certain
points to which I have given the name of homologues. The following
are the formulae p, = •*> If you take any two isothermals, the value
of \i is the same throughout the whole range of isothermals.
(l — p V] V = C.
ON THE CHARCOAL VACUUM. 155
The PRESIDENT : I am sure our thanks are due to Professor
Andrews for the account he has given us, and for the very interesting
and delicate experiments which he has performed. I am sure you will
with me regret that we, like himself, are working under such extreme
pressure that we were obliged to ask him to make his communication
very short.
Before calling on M. Sarasin-Diodati I will venture to ask Mr.
Dewar to give us a short communication on charcoal vacua. We
are fortunate in having him here this morning, and his communi-
cation may be properly and naturally placed between the two you have
already had and the lecture which is to follow. I have no doubt it
will come in very well between the two other subjects best, and he will
further imitate nature in allowing that state of transition to be one of
extreme brevity in point of time.
Professor DEWAR : Especially since the recent experiments of
extraordinary interest of Mr. Crookes on motion in vacua, a method
of readily getting a very perfect vacuum has been one of considerable
importance ; and my friend, Professor Clerk-Maxwell, has mentioned
my name in his report in the department of physics, dealing with a
method of effecting this result. All I have to say is that this plan
was originally used by Professor Tait and myself, to improve on the
mercurial vacuum. Of course, Sprengel's method may be carried to
a very great extent, and will produce a very perfect vacuum as com-
pared with an ordinary air-pump. The plan we adopted at that time
was as follows : — Suppose this tube is to be made a very perfect
vacuum. Charcoal is placed in the tube, and the whole exhausted
by means of a mercurial air-pump at a red heat ; it is then sealed
up, and the last traces of gas, the vapour of mercury, sulphuric
acid, and other traces of impurity are absorbed by the charcoal, and
in a very short time we found that an electric spark could not
pass. That has been shown very often at the Royal Institution. The
advantage of this method was that by heating the charcoal again you
could at once produce stria; it goes backwards and forwards as often
as you like. The improvement which I have made on this within the
last two or three days, is one which, I daresay, may interest Mr.
Spottiswoode, in connexion with his experiments on stricz. This
vacuum is made by charcoal without the use of any mercurial pump
156 SECTION— PHYSICS.
whatever. The secret is a very simple one. Unless I wanted to use
the charcoal tube it would be sealed off, and there is virtually no loss
of matter nor of charcoal, because, if I seal this off, the same charcoal
can be used for another tube, and then the matter which is left in
the tube is so excessively small that the original matter I put in is
virtually recovered. I will show you first that it is a tolerable vacuum,
and then I will show you that the charcoal does contain a very large
quantity of matter by heating it. I will attach a coil to it, and Mr.
Spottiswoode will be the best judge if it is a tolerable vacuum, and you
will see by the strice when I heat it, that it contains a very large
quantity of matter. The stria are very wide at first, and by this
simple method you can study them in all stages of their formation,
from an innumerable number there is a gradual widening until they
nearly disappear altogether. You see at once it is a tolerable
vacuum from the enormous width of the stria ^ and the condition
of the negative pole, which is always the best evidence of a good
vacuum, being isolated altogether from the other portion. I will
now heat the charcoal in a spirit lamp, and you will see that it
holds a large quantity of matter. As I heat it gradually, the gas comes
out of the charcoal, and I may tell you at once the substance is bromine.
I place a little fluid bromine in this tube, then place it in a water bath,
the bromine distils over. The charcoal is heated during the process
to drive out all gases, and it absorbs the bromine vapour and
creates the vacuum. In this way you can produce a very good vacuum
without any machine at all. You see at once the alteration in
appearance, as the heat acts on the charcoal, and in a few moments the
spark will not pass, the tube getting quite full of bromine vapour.
If I had a Bunsen flame I could make it give up all the bromine.
There is no special care required in this process ; this is cocoa-nut
charcoal, but any charcoal will do. The quantity of bromine used
was about a cubic centimetre. You can now see quite plainly the
colour of the bromine vapour, but on cooling it will be ail again
absorbed by the charcoal.
The PRESIDENT : Our thanks are due to Professor Dewar for his
account of this remarkable instance of the simplification of processes
which only those who have been engaged in these matters know how
to appreciate. We sometimes get a vacuum by air-pumps and so on.
DE LA RIVES RESEARCHES. 157
and here we have seen a way of getting it without any pump at
all.
I now beg to call upon M. Sarasin-Diodati to give his communi-
cation on " M. de la Rive's Experiments in Statical Electricity."
M. SARASIN-DIOD ATI'S ADDRESS UPON AUGUSTE DE LA RIVE'S
LAST RESEARCHES IN ELECTRICITY.
M. SARASIN gave an account of the last works of Auguste de la
Rive, conjointly with whom he had often worked, and he described
some of his instruments, which were sent to the exhibition, from
Geneva.
He stated that M. dc la Rive and he himself had repeated — in order
to study them more accurately — the observations previously made by
Pliicker, by De la Rive himself and by others, upon the modifications
which the electric discharge undergoes, in rarefied gases, under the action
of magnetism. They first of all considered the case in which the spark
is produced perpendicularly to the line of the poles of the magnet, work-
ing for that at pressures included between imoiland iomou. In this case
the discharge is deviated and tends to describe a circular curve around
the axis of the magnet ; moreover the luminous jet is more condensed
and has all the characteristics which it shows at a higher pressure.
MM. de la Rive and Sarasin have verified the fact that the resistance
offered to the passage of the discharge then increases in a considerable
degree, different for every gas and greater in proportion as the con-
ductibility of the gas is weaker. They have besides, observed that
the condensation of the luminous jet is accompanied by a real
condensation of the gas in the part in which the magnet acts. This
can explain, to a certain extent at least, the observations made by M.
Chautard upon the modifications of the spectrum of gases under the
action of magnetism. This fact is easily proved by means of a special
Geissler's tube, divided into two chambers, both traversed by the same
discharge, one of which is placed under the influence of the magnet,
the other not. These two compartments being separated by the
turning of a cock whilst the discharge is passing, it will be afterwards
found that there is a greater pressure in the compartment placed
between the two poles of the magnet than in the other.
A very brilliant experiment made about thirty years ago by A. de la
153 SECTION—PHYSICS.
Rive shows the action of the magnet upon the electric discharge when
the latter radiates round the pole of the magnet which then forms one
of the electrodes, the other electrode being a concentric ring at the
pole. The electric discharge revolves, in this case, round the magnet,
like a needle on a dial, and with a velocity which varies considerably
according to the nature of the gas, and which is nearly in an inverse
ratio to its density. MM. de la Rive and Sarasin have, moreover,
satisfied themselves with regard to the fact that the electric spark
carries along with it, in its rotation, the gas itself which transmits it
and any sufficiently light movable body, such as a little pendulum, or,
still better, a small mill having its fulciment concentric to the annular
electrode. In hydrogen at a pressure of imoa the discharge, revolving
under the action of the magnet, has imparted to this mill a velocity of
120 and even 140 revolutions per minute. If the direction of the
rotation be changed, the discharge very quickly stops the mill, and
then causes it to revolve in the opposite direction at a speed which
very soon equals the former.
Finally, M. Sarasin drew attention to the fact, that this experiment
of De la Rive, upon the rotation of the electric spark around the pole
of a magnet, has given him new and important evidence in support of
the electric theory of the aurora borealis, of which he has been one of
the most earnest defenders. Indeed this experiment can perfectly be
compared to the well-known fact of the rotation of the arcs of the
aurora round the poles of the earth. M. Sarasin gave a rapid sketch
of the theory of the aurora borealis such as De la Rive had stated it,
and explained the apparatus which he devised in order to reproduce the
phenomenon, for the sake of experiment.
The PRESIDENT : We must now convey our thanks to M. Sarasin-
Diodati for his interesting communication. He has explained very
•clearly the origin of the pieces of the apparatus which are happily now
well-known to us ; thanks to Professor de la Rive and himself.
I will now call on M. Lemstrom to read his paper on " The
Aurora Borealis."
Professor Lemstrom, of Helsingfors, Finland, then delivered the
following Address on his Polar-light Apparatus, and on the Theory
of the Polar Light.
Professor LEMSTROM: This apparatus serves to prove that the
POLAR-LIGHT AS PAR A TUS. 1 59
polar light or aurora borealis is an electric current flowing from
the higher regions of the atmosphere down to the earth.
A sphere of brass, fixed on a bar of india-rubber or ebonite o-6
metre long, is screwed in the board of the cross-shaped foot. A
cylinder of india-rubber, 3 metres long, is fixed to the same board at
about 07 metre from the sphere. From the cylinder comes out a
branch with a bow, both of india-rubber. On the bow are fixed sixteen
Geissler's tubes, wherein the air has a pressure of about 0*5 millimetre.
The lower ends of the tubes are pierced by platinum wires, which are
directed towards the sphere, whilst at the upper end the platinum
wires are, by means of their copper wires, in a metallic union with a
button, and also in metallic union with the earth. From underneath
the sphere a copper wire, well insulated with india-rubber, leads to the
negative pole of a Holtz's electric machine (a machine of Carre' (Paris)
was employed with great advantage), of which the positive pole is in
metallic connexion with the earth. As soon as the machine is put in
movement, the sphere being charged, becomes negative-electric, and
at the same time there goes through all the tubes a current of reddish-
lilac light, so that they altogether form a shining bow-shaped belt.
With an ordinary machine this phenomenon may still be observed
when the lower ends of the tubes are at a distance of two metres from
the sphere. This proves evidently that the electricity flowing out
from (or into) the sphere not only traverses the layer of air that is
between, but goes also with such power through the tubes that the
gas therein becomes glowing by the heat that the electric current
produces, as is well known. In order that the electricity might more
easily flow out in the air from the sphere, this latter is furnished with
points. These points, as well as the metallic union between the upper
end of the tubes and the earth, are of no absolute necessity, for the
phenomenon may be produced without them, the distance between
the sphere and the tube must, however, then be considerably reduced.
The described light-phenomenon produced by the apparatus proves
clearly that a current of electricity may go through a layer of air of
ordinary pressure 76omm without producing the light-phenomenon, but
if it meets in its way a space of rarefied air of low pressure (from o to
3on;m to 4omm) there arises immediately a light-phenomenon, caused by
the fact that the current makes the molecules of gas glovr.
i6o SECTION— PHYSICS.
As regards the theory of polar light, the knowledge we have
acquired of the electric state of the earth proves that it is a conducting
body, charged with a small quantity of negative electricity, and
surrounded by the atmosphere, in general charged with positive
electricity. Though this latter might be produced by an influence
from the earth, it is still very probable that it proceeds from the-
process of evaporation, either directly by this phenomenon itself, or
by the friction of vapour against particles of air. The atmospheric
air possesses a very small conducting power for electricity when dry
and of ordinary pressure, but the conducting power increases con-
siderably as soon as the air becomes moist and rarefied. It has been
proved by experiments that the conducting power is highest at a
pressure between 5mw and ioram, and goes then 10,000 times beyond
the conducting power at a pressure of 760""". If the rarefaction of
the air is carried further than 5mm, the conducting power diminishes
again, but very slowly. It is known that in proportion to its elevation
over the surface of the earth the air becomes more and more rarefied
according to an irrefragable law, which finds its expression in the
formula given by Laplace, and that consequently, at a certain elevation
the earth is surrounded by a layer of air that has a pressure of only
5ram ; the conducting power for electricity in this layer is sufficiently
great to allow of its being regarded as a conductor in comparison to
the air in lower regions, and even in the highest. The negative
electric earth is thus surrounded by a conductor for electricity con-
centric with it. All the positive electricity that attains the space of
rarefied air of about 5mm, or, as it might be called, this conductor of
air, submits almost to the same laws as if it were in a real conductor,
and must thus set in a restricted manner according to the influence of
the electro-negative earth. Part of the electricity, conducted by the
vapours, remains on the clouds in the atmosphere and discharges in
form of lightning and thunder ; another part attains the space of
rarefied air or conductor of air, by the fact that the vapour itself, sub-
mitting to well-known physical laws, rises to this elevation, and also
because electricity, according to its nature, endeavours always to set
on something.
The manner in which the electricity divides itself on the two
conductors depends on their reciprocal position to each other as well
POLAR-LIGHT APPARA TUS. 161
as on their form. The earth might, without a remarkable difference,
be considered as a sphere, and likewise the conductor of air, but in
their reciprocal position to each other it appears that the space of
rarefied air of 5mm approaches much nearer to the earth at the poles
than at the equator, principally in consequence of the inequality of
the temperature of the air in the two places. If we assume the mean
temperature of the air round the equator to be 25°, at the poles — 12°,
and everywhere on the conductor of air —60°, and we suppose at the
same time the air everywhere half saturated with moisture, and that
the temperature is reduced in proportion to the elevation, we find,
if the above-mentioned formula of Laplace* is applied, that the
conductor of air, at the equator, must be at an elevation of 37*47
kilometres, and at the poles but 34*25.
In consequence of this relative position, and if the two conductors
are regarded as conducting surfaces, the electric density on them both
becomes about 9 per cent, greater at the poles than at the equator, and
the power, by which the two electricities endeavour to join again, at
least 20 per cent., but probably 30 or 40 per cent, greater, if all the
circumstances are considered, at the poles than at the equator. It is
in these facts we have to seek the principal cause of the accumulation
•of electricity at the poles of the earth and of the phenomenon that
•occurs there, and is called polar light or aurora borealis.
It is a remarkable fact that thunderstorms diminish as well in
number as in intensity in proportion as we remove from the equator,
and that at the 7oth degree of latitude they cease completely, after
having shown once more in the highest north vestiges of their primitive
intensity. In Finnish Lapland, for instance, thunderstorms are very
uncommon, but when they occur they are extremely severe, and are
almost always accompanied by thunderbolts. This peculiarity has
probably its cause in the fact that the region of thunderclouds lowers
towards the earth in accordance with the same rule as the before-
mentioned conductor of air. The reduced number of thunderstorms
* X= 18-393 metres (1+0-002837 Cos. 2 <f>) (i+°'o<>4T+*) /H where x s5gn;fies the eleva.
2 A
tion, <j) the latitude, T the temperature at the surface of the earth, t at the upper point H,
and h the stand of the barometer for the same points, but duly reduced.
M
162 SECTION— PHYSICS.
is caused by the fact that the very source of electricity in the atmo-
sphere, that is to say, the evaporation, is very much reduced ; however,
another important cause is here active — namely, the heightened con-
ductive power that the air possesses in consequence of its greater
quantity of moisture, whereby the electricity becomes unable to keep
itself, beyond a certain latitude, upon the clouds, until it has attained
a greater tension, but is conducted down to the earth in form of a slow
current, visible in the polar light.
It results from experience, with a high degree of probability, that
the polar light is an electric phenomenon, for its effects are of the
same nature as those of the electric currents. Thus the polar light
causes disturbances in terrestrial magnetism, induces currents in the
telegraphic wires, and furnishes a spectrum of nine bands, which
coincide, except one, with the spectral lines produced if an electric
current goes through a rarefied space of air. Thus there is no doubt
that the polar light is caused by an electric current going down from
the upper rarefied layers of air to the earth ; this current, during its
passage through the rarefied air, produces light phenomena that cannot
arise in denser layers of air.
The polar-light apparatus now exhibited shows that an electric
current flowing out from an insulated body does not produce any light
phenomena in air of normal pressure, but as soon as it rises to the
rarefied air in the Geissler's tubes, there is directly produced a light
phenomenon very like the real polar light. In the apparatus the
upper end of the tubes is in union with the earth ; this is by no means
necessary, for the light phenomenon is also produced if this union be
removed, provided that in such case the tubes be brought a little
nearer to the insulated sphere. For the rest, the earth represents here
the wide space of rarefied air that we find beyond the limits of the
conductor of air, and which serves here as an electric reservoir.
Let us now consider how the polar light on a large scale is formed
in nature. As before said, the earth, and the conductor of air, hold
to each other the position above-mentioned, and the two electricities,
the negative electricity of the earth and the positive electricity of the
conductor of air, endeavour with a certain force to unite in a belt
around the north pole. The insulating power of the denser air
prevents this reunion ; but if we assume that perfect equilibrium is
POLAR-LIGHT APPARA TUS. 163
attained, the reunion will take place as soon as this equilibrium
is disturbed, either by the insulating power being diminished or
the electricity of the conductor augmented. The first case, which
probably is the most ordinary, happens if a southerly wind carrying a
quantity of vapour attains the polar regions : for instance, the belt,
where the vapour, in consequence of the cold, is condensed into a fluid
form, reduces thereby considerably the insulating power of the air and
enables the electric current to flow through it. The same thing would
occur if a layer of clouds happened to enter into this belt ; the upper
end of the cloud would become negatively electric, the lower one
positive, and thus the distance between the two conductors would in
fact be diminished. The electric current would go from the conductor
of air to the cloud, and through this latter to the earth. Similar
phenomena are observed in the polar regions, or the upper edges of
the clouds are not unfrequently seen shining with a yellowish light
stretching considerably upwards, whilst no light is discernible under
the cloud because of the air there having attained a density sufficient
to prevent the current from producing light.
For special knowledge of the polar light and its theory, we refer to
essays inserted in the Archives des Sciences Phys. et Natur. de
Geneve, 1875 (Sept. and Oct.), and in January, 1876, as well as to two
essays published in the years 1869 and 1873, in the same scientific
journal, all which articles are more or less the result of observations
made in the arctic regions. Besides these we may refer also to the
works upon polar light of the American natural philosopher Loomis,
Eep. of Smithsonian Inst., 1865, &c.
The PRESIDENT : We must return our best tharks to Mr. Lem-
strom for his elaborate paper, and express a hope that he may some
day publish it, when we shall be better able to do justice to it than we
can to-day.
In consequence of the lateness of the hour Baron Ferdinand de
Wrangell and II Commendatore Professore Blaserna will give their
communications in the afternoon.
(The Conference then adjourned for luncheon.)
The PRESIDENT : The clock having struck two, I will call on
Mr. De La Rue for his communication on astronomical photo-
graphy.
164 SECTION— PHYSICS.
ASTRONOMICAL PHOTOGRAPHY.
Mr. DE LA RUE : In the Loan Exhibition there are, as you know
several astronomical photographs, and some apparatus with which
these photographs were taken. There is one telescope which is
absent necessarily on account of its enormous size ; but I have a
small model of it, the Melbourne telescope, to which I shall presently
allude. In speaking of astronomical photography, I wish my audience
to understand that it is not merely the pictorial representation of
celestial objects that astronomical photography concerns itself with
mainly ; it is the production of records which can afterwards be
measured, and which afford data for astronomical investigations.
I had better, in the first instance, just state what happens. Suppose,
for example, we have a lens or a mirror directed on to a celestial
object and that the image is received on a sensitive plate. I will
imagine we have a fixed star in focus whose image is a very small
point indeed, scarcely to be distinguished from specks in the col-
lodion. But the lens or mirror not being provided with any movement
to follow the star, it would happen that in consequence of the star's
apparent path in the heavens, if the atmosphere were perfectly quiet,
we should have a straight line impressed on the plate instead of a
spot, the line being longer or shorter in proportion to the duration of
the exposure ; but what does really happen is that we get an irregular
wavy line on account of atmospheric disturbances. Now I will sup-
pose we use a telescope mounted equatorially, that is to say, on an
axis parallel with the earth's axis, and that we drive it by means of
clockwork machinery in order to follow the apparent path of the star
perfectly. Then the star would, if undisturbed, stand still in the
centre of the field, if it weue placed in the centre to start with, but
instead of its being depicted as a single spot, we get a series of dots,
in consequence of the agitation of the image arising from the cur-
rents of air differently heated and differently refracting, if it were a
double star we should get a conglomeration of each of the two pictures,
for the same reason. The eye looking at a star sees it sometimes
steady and well defined, at others blurred and moving about in diffe-
rent positions of the field, but the mind selects the best images, and in
ASTRONOMICAL PHOTOGRAPHY. 165
all astronomical drawings the disturbances are eliminated ; the
memory discards those, and the hand only draws the appearances at
moments of finest definition. A photographic plate, however, retains
all the impressions ; it is a retina on which all the disturbances are
permanently recorded, and consequently no photograph yet obtained
in any way conveys the sharpness of outline of the finest definitions
of the telescope, it is always more or less blurred. Nevertheless very
valuable results, as you will presently see, are obtainable. For
example, if we want to ascertain the position angle and the angular dis-
tance of two double stars, the disturbances do not prevent our finding
accurately the centres, and we can get, by means of a micrometer, these
data just the same as though there were no blur.
The size of the focal image of any celestial object, other than a fixed
star, which is always a mere point, I need scarcely tell you, depends on
the length of the telescope ; in my own telescope the focal length is
ten feet, and the image of the moon is about an inch ; I say " about
an inch," because it varies in consequence of the nearer approach of
the moon to the earth at one time than at another. I have here a
group of original negatives of the moon, showing the sizes they are
obtained by my telescope when she is in different positions in her
orbit. The time of the exposure of these photographs is marked on
them, — it varies generally from about one second or less than a
second, for a full moon, to about eight or ten seconds when at the
crescent. The duration of exposure to produce an image depends,
with equally sensitive chemicals, mainly on the relation of the aperture
to focal length, and hence it is very desirable to get as large an aper-
ture as possible with respect to the focal length — or, in other words, to
make the focus of the telescope as short as is consistent with good defi-
nition. It is quite possible, by means of clockwork, to follow a star
almost perfectly, that is to say, if a telescope is put on a star and
adjusted so that its image falls on the cross wires in the field, one may
leave the telescope and come back again after an hour, and find the
star there still ; so that that mechanical difficulty to obtaining good
photographs is quite overcome. The great enemy, however, is always
the atmospheric disturbance ; but with regard to the moon there is
another difficulty : the equatorial telescope moves simply in a circle
parallel with the earth's equator ; but you all know that the moon's
166 SECTION— PHYSICS.
orbit is inclined to the earth's equator ; and, consequently, if we have
placed the moon centrally in the telescope adjusted to follow her in
right ascension, after a time she will have moved up or down (in
declination) some distance, in consequence of her orbital motion.
The motion of the moon in declination, as it is called, is greatest
when she is near her nodes, and then in one minute she may move
as much as 16 seconds of arc, consequently in 10 seconds she may
have moved 2*7 in arc, or nearly 3 seconds of arc ; and as we can
depict on the moon objects whose diameter is not greater than
i second, which is equal to about a mile, it is very clear that when
the moon has the greatest motion in declination, the lunar pictures
cannot be as perfect as when she is at a greater distance from her
nodes. The Astronomer Royal, Sir George B. Airy, whose name is
not only connected with mathematical astronomy, but also with astro-
nomy as a great mechanist, has proposed to add to the ordinary
equatorial a second axis, which would be carried round so as to remain
parallel with the axis of the moon's orbit in its diurnal path, and pro-
vided with an independent clockwork driver carrying the telescope
in a direction inclined to the equator, so as to follow the moon in her
orbit from west to east. I need scarcely say that this appliance
would complicate a large telescope so much that it would be almost
impossible to adopt it ; still it is conceivable that we may, besides the
motion in right ascension, give an adjustable motion to the declina-
tion axis, varying from nothing up to 16 seconds of arc either in
north or south declination in a minute. But this has not yet been
done, and consequently it has to be accomplished in order to make it
possible to photograph the moon perfectly at all times. However,
the first photograph I ever obtained I took with the piece of apparatus
I hold in my hand, by which I followed the motion of the moon both
in right ascension and declination. It is unfortunately now getting
broken. It was put on to the eye end of the telescope which was
allowed to remain at rest, and by means of this milled head, the
sliding piece carrying the sensitive plate having been placed so as to
move in the direction of the motion of the moon in her orbit and in
right ascension, I was able for a short time, by making three quarters
of a turn, to follow the moon by hand ; and here is a picture which
was obtained in 1853 in that way. But I was not the first to photograph
ASTRONOMICAL PHOTOGRAPHY. 167
the moon. I have here a daguerreotype, copied from one which was
exhibited by the late Mr. Bond, of Cambridge, Massachusetts, in the
International Exhibition of 1851.
You are aware that the moon does not always present precisely the
same hemisphere towards us in consequence of her unequal angular
motion in her orbit, while her axial motion, her rotation on her axis, is
perfectly equable. Although they coincide for a whole revolution, and
bring a crater of the moon exactly again to the same place — at other
times we see a little on one side and a little on the other side of the
hemisphere which is turned away from us. Moreover, the moon's axis
is inclined to the earth's equator, and, consequently, sometimes we see
a little more to the north, and sometimes a little more to the south,
of the moon's equator as she moves round in her orbit. These effects
are called libration in longitude and libration in latitude, and we also
have the diurnal or parallactic libration dependent on the position of
the observer. The moon may be in the horizon or overhead, at one time
or the other, and in consequence of parallax, which is quite sensible,
being rather more than a degree, we sometimes see a little on one side
or the other of the moon in varying directions. We have here those
conditions which enable us to obtain a stereoscopic view of the moon,
by combining two pictures taken at different times, showing the moon
as a globe. But besides these three librations, it has been suggested
that the moon has a real or physical libration, in consequence, as
it is supposed, of a protuberance of matter on that hemisphere which
is turned towards the earth which would tend to follow the redundance
of matter about the earth's equator, and to adjust itself towards it with
a sort of balancing or wobbling motion. Whether there is or not a
physical libration of the moon, is a problem which astronomical photo-
graphy can solve, and I do not know that there is any other method
by which it could be done so perfectly. For this object the original
negatives may be placed on an instrument called a micrometer, and
adjusted concentrically with it ; then by bringing any object, a selected
crater for example, under the microscope, which is effected by turning
the divided circle, and then drawing out the slide, we can measure the
angular position and the distance from the centre or periphery of the
moon of that object, and obtain data for ascertaining whether there is
a physical libration of the moon or not, after taking into account the
168 SECTION— PHYSICS.
effects due to libration in longitude and latitude, and to parallactic
libration in shifting the crater in question from the position it occupies
in reference to the lunar disc at the period of mean libration. The
telescope with which these negatives were taken is now at Oxford, and,
I believe, Professor Pritchard, the Director of the University Obser-
vatory at Oxford, intends to devote the telescope to determining this
problem, and a very interesting one it is. I said that the size of the
negative depends essentially on the length of the telescope and the
position of the moon in her orbit. I have here a model of the very
splendid instrument, constructed for Melbourne by Messrs. Grubb,
of Dublin, under the superintendence of a Committee of the Royal
Society. In that colony they are more public spirited than we are here,
and they have found the money for constructing this very large and
perfect equatorial telescope, the mirror of which is four feet in diame-
ter, whereas the telescope, with which my photographs were obtained,
is only thirteen inches. Here, through the kindness of Mr. Ellery,
the Melbourne Astronomer, are some negatives of the moon three
inches in diameter, made with the Melbourne telescope, and very
beautiful productions they are. These especially would be particularly
well adapted for measurement with the micrometer for determining
the question of the libration, but even pictures so small as those
obtained with a thirteen inch reflector may be magnified to a suit-
able size. There is one on the wall thirty-eight inches in diameter
obtained in a negative taken at Cranford, and here is another, about
eighteen inches from diameter, a very beautiful one, taken by a Mr.
Rutherfurd, an American gentleman, in his private observatory. I do
not know whether that is his best, but there is one he has taken
under particularly fine conditions of the atmosphere, which is the
finest in existence.
It may be interesting to you to know, as all the necessary apparatus
is before you, in what way the enlarged photographs are obtained.
One of these original negatives is placed in the focus of this long
camera. Lenses, specially made by Mr. Dallmeyer, are used for
projecting the image along the axis of the camera on to plates about
one-foot square, and then the first enlargement takes place. Here are
specimens taken from downstairs, this is a first enlargement to nine
inches in diameter, and is a transparent positive on glass ; by a second
ASTRONOMICAL PHOTOGRAPHY. 169
enlargement it furnishes the negative which is used to print the paper
positives. There are a great number of such along the wall of different
phases of the moon enlarged to about eighteen inches. The largest
here is nearly one metre or rather over three feet two inches diameter ;
and at the time this was made, some years back, we did not possess
cameras large enough to produce so large a photograph at one opera-
tion, so that it was done on four plates. You will notice that in the
successive enlargements there is always a loss of definition, and that
more details are to be seen in the original negative, to which recourse
must be had for exact measurements.
I now come to solar photography. There are some early French
photographs downstairs ; but solar photography was first systemati-
cally followed up at the Kew Observatory, in consequence of a
suggestion of the desirability of photographic sun observations having
been made by the late eminent astronomer, Sir John Herschel, to the
Royal Society. The Kew photo-heliograph is before you. This
instrument was in use about 1854 at Kew, but was not systemati-
cally worked. It was taken to Spain in 1860, and there used for
photographing the solar eclipse. It was afterwards worked from
1862 to 1872 systematically in observing the sun's spots. Eleven
instruments on the Kew model, but improved, have since been con-
structed by Mr. Dallmeyer under my direction, and took part in
the observations of the transit of Venus. The more recent photo-
heliographs have the object glass four inches in diameter ; this is
about three and a half. The image is not allowed, as in the case
of lunar photography, to fall directly on the sensitive plate, but
passes through a secondary magnifier, and is thus enlarged to four
inches. In the common focus of the object glass and the magnifier
are cross wires, most conveniently placed at the angle of 45° to a
terrestrial meridian passing through the sun's centre, and a negative of
the sun like that I show you has the cross wires depicted upon it.
They are of great use in the subsequent measurements for obtaining
the position angle from the north of any spots that may be depicted.
The pictures obtained during ten years are now undergoing measure-
ment by this micrometer, which I will describe. It has a divided
circle, on which the photograph to be measured is placed and fixed ;
with the aid of the microscope it is then adjusted so that the centre of
i;o SECTION—PHYSICS.
the sun exactly coincides with the centre of the divided circle whose
axis is a hollow cylinder, and the north point made to correspond
with the zero of the circle. By drawing out a slide we can bring
the periphery of the sun under the cross wires of the microscope, and
by reading off on a vernier can see the distance'passed over, and obtain
the value of the radius of the sun in inches and decimal divisions.
The photograph is then crossed over to the other side so as to eliminate
any error of centring, and then we have the measure of the whole
diameter on the arbitrary scale. We then bring any sun spot under-
neath the microscope by turning the circle and drawing out the slide,
and we read on the circle its angle of position and on the slide its
distance from the centre. With these measurements after they are
reduced we are enabled to ascertain the helioscopic position in
latitude and longitude. But there is another disturbing cause to the
application of photography to exact measurements in astronomy.
There is always some optical distortion. In order to ascertain its
amount, a scale, of which this is a model, was fixed on the Pagoda
at Kew, distant 4398*24 feet from the Observatory, and photo-
graphed. Each of these plates of the scale, one foot wide, is
depicted in the photograph, and occupies rather a large space in the
picture the further it is from the optical centre. We were able to
measure, by means of the micrometer, the width of the image at the
centre, and the width at other parts of the field up to the edge. That
gives us the means of ascertaining what allowance ought to be made
for distortion, and we can apply this correction and obtain most
accurate measurements of the sun.
I ought to say that the Kevv photo-heliograph had the honour, by
its observations in 1 860, of first proving that the luminous prominences
which are depicted in this photograph, and which were only to be seen
at the period of a total eclipse, absolutely belong to the sun. We do
not want that proof now, because we can see them at any time under
favourable atmospheric conditions, whether there is an eclipse or not.
I have already alluded to the transit of Venus. The English, the
Russians, and our colonies employed the eleven instruments of the Kew
model, before spoken of, but the Americans made use of a long tele-
scope, I think nearly forty feet in focal length placed horizontally in the
direction of the meridian, and the image was thrown into it by the
ASTRONOMICAL PHOTOGRAPHY. 171
optical instrument which you will see in the lower gallery called a
siderostat or heliostat, which was adjusted to reflect the image of the
sun constantly in the axial direction of the telescope. This has some
advantages and some disadvantages — the advantage is that distortion
is reduced to a minimum. Our Chairman reminds me that I ought
not to forget to call attention to a set of instruments for the optical
and photographic observation of the transit of Venus, kindly con-
tributed by the Astronomer Royal, which will be found on the
balcony. It is a complete equipment, and it is well worth inspecting
because it shows how very much had to be done for eveiy fully
equipped station in order to secure accurate results. In the Kew
photo-heliograph the diameter of the sun on the occasion of the late
transit of Venus would be nearly four inches ; — the diameter of Venus
is i '26 of an inch, and the maximum displacement of Venus nearly
one-tenth of an inch. Measurements can be made accurately within
o'2 of a second of arc, by means of the micrometer which I have
described, but an error to that extent would only produce an error of
less than 0^04 second of arc in the deduced solar parallax. It is to be
hoped, thereiore, with what has been secured in these observations
that we shall obtain the solar parallax — in other words the earth's
distance from the sun — to a very great degree of accuracy ; more-
over we have another eclipse coming off in 1882, and the same
instruments or similar ones will be ample to obtain the observations
requisite for a still closer approximation to the true parallax.
I now wish to call your attention to some photographs of the sun
on a scale of four feet for the sun's diameter. They were obtained
with the Cranford instrument, which is only thirteen inches in diameter,
the image passing through a secondary magnifier, by which it was
magnified, before it fell on the sensitive plate. Not only is it possible
to photograph the sun directly on this large scale, but it is also
possible, as you will see by this print, made in 1862, to obtain solely
by the action of light and electro-metallurgic processes, printing
blocks without the touch of a graver which will print the sun spots.
This appeared in the monthly notes of the Astronomical Society in
1862, but unfortunately it was very badly printed.
You are all aware that many attempts have been made to connect
solar phenomena with meteorological phenomena, and there can be no
172 SECTION— PHYSICS.
question whatever that as solar radiation varies so must vary also the
whole atmospheric conditions of moisture and rainfall ; hence it is
most desirable that sun pictures should be obtained in a sufficient
number of places, in order that we may have a solar picture at least
every day, not only on a small scale for the position and area of the
spots, but on a large scale, so that we may study special phenomena
of the sun intimately on a large scale. Solar photography has this
advantage, that it can be pursued in a town ; — the sun has so much
actinic power that it matters very little where we are placed so that the
sun shines. I am happy to say that in Austria they think of making
such observations. In Paris there seems to be a chance also, and I
trust that through the action of the Royal Society and the Astronomical
Society we shall get the Indian Government to take it up, and I
certainly do hope that in England we shall have a solar physical
observatory.
The PRESIDENT : I am sure you will all join with me in offering
our best thanks to Mr. De La Rue for so complete an exposition in
most respects and so lucid in all, of this important subject of
astronomical photography. I say emphatically complete in most
respects because there is one point in which it is decidedly incomplete.
He has given us a very clear and fair idea of how these processes
were brought successfully into action, and how it has been managed
to bring out of them these great results of which he has given us
specimens, but he has by no means conveyed to the minds of his
audience how much these results are due to his own individual efforts
and contributions. I think I shall not say too much if I speak of
astronomical photography in this country at all events, and through
this country to most parts of the civilized world, as being indebted
more to him than to any one individual from its commencement to
the present time.
[Mr. De La Rue here took the chair.]
ON THE VARIABLE STATE OF ELECTRIC CURRENTS. By Professor
BLASERNA, of the Royal University, Rome.
Gentlemen, —
I regret much not being able to address you in English, and
I must therefore ask your indulgence for speaking to you in a language
which is neither yours nor mine.
The question of the Variable State of Currents was originated and
has been treated by Ohm.
By following up the ideas which lead him to the discovery of one of
the most important laws of physical science, he arrived at the con-
clusion, with regard to the origin of the current, that the fixed normal
state, from which the current derives its permanent intensity, is pre-
ceded by a variable state, in which, from the moment of interruption,
begins at zero, and reaches, in a very short space of time, its permanent
intensity.
Ohm endeavoured also to establish the law of this movement, which
may be represented by a curve, at first convex, and then concave
towards the axel of the abscisses, and which has consequently a point
of inflexion.
We can understand that the variable state should exist. There are
no phenomena in Nature which do not require a certain time for their
formation and development, and the question is merely to find out
whether this time is sufficiently long to be indicated or measured by
instruments of the most delicate make, and the most perfectly adapted
for the object to which they are to be applied.
Faraday's great discoveries of inducted currents and extra currents
gave to this question a new and wider aspect. The question may be
asked, What are the nature and duration of the extra current ? either of
cessation or interruption ; and as the extra current is nothing but the
current inducted on itself, the general laws of inducted currents may
be looked for in wires and in fixed helices.
These different questions have been discussed by a great number Of
scientific men. I will mention, among others, M. Helmholtz, who, by
calculations and by experiments, has succeeded in representing the
174 SECTION— PHYSICS.
variable state of currents by an exponential curve, differing from that
of Ohm, and without a point of inflexion; M. Rijke, who, by an
ingenious, but, as he himself confesses, not sufficiently accurate pro-
cess, tried to determine the duration of extra currents ; M. Guillemin,
who confirmed Ohm's theory with regard to long telegraphic lines;
and finally Sir W. Thomson, who arrived at far different conclusions
from the others.
This was the state of the question when I began to interest myself
in it. After me, it occupied the attention of many scientific men,
among them MM. Helmholtz, Lemstrom, Bernstein, Felici, Donati,
Cazin, and others.
A certain number of instruments have been made, of which I shall
mention the most important : The apparatus of M. Helmholtz upon a
system of levers ; it has also been employed by M. Lemstrom. My
apparatus, with a revolving cylinder, and with metallic contacts, after
the idea of MM. Wartmann and Dove. The second apparatus of
M. Helmholtz, in the form of a pendulum, with metallic contacts. The
apparatus of M. Bernstein, revolving, with contacts of mercury. The
apparatus of M. Cazin, a weight, which in falling forms a current.
Finally, the apparatus of M. Felici, revolving, with an inscribing
diapason for the measurement of time.
The principal fact which resulted from my researches, and which has
been confirmed and amplified by other scientific men, is that the
variable state of currents is occasioned by a phenomenon far more
complex than it was supposed to be. The intensity of the current,
which is at first zero, reaches a degree nearly double that of its normal
value ; then descends nearly as far as zero — but without quite reaching
it ; then attains a second maximum, rather less than the first ; then
descends to a second minimum, less marked than the first. Thus the
current makes a series of fluctuations around its final value. The
duration of an oscillation does not appear to be always the same. The
conditions, on which it depends, are not yet known ; but it seems that
it can vary from a half to four ten-thousandth part of a second. The
number of these oscillations is very great. I have found traces of them
to the hundredth parts of a second. The number which can be
observed depends evidently upon the delicacy of the galvanometer used
It depends also upon the shape of. the circuit. When in the circuit
VARIATIONS OF ELECTRIC CURRENTS. 175
there are helices, capable of giving strong extra currents, the oscilla-
tions are strong, and consequently more numerous. They may be
expressed by a formula which contains an exponential and, at the same
time, a periodical function. In rectilineal circuits they are very feeble,
and perhaps they do not exist at all. So much for the variable state.
If the extra current be separated from the principal current, and be
considered as an independent thing, it may be said that the inverse
extra current is formed of a series of alternate currents, which begin
by being very strong and become gradually very weak. They are
oscillations positive and negative.
As to the direct extra current, it is also formed of oscillations, which
are even more energetic and rapid.
Sir W. Thomson had arrived, by analysis, at the conclusion, that,
under certain circumstances, the current may become oscillatory. The
oscillations, which he discovers, have a different character from those
which experiment has, up to the present time, revealed. According to
what has as yet been experienced the fluctuations of the current, in its
variable period, never reach zero, whilst Sir W. Thomson proves that the
oscillations are positive and negative— that is to say, there are contrary
currents. It would be very difficult to say whether the conditions,
under which Sir W. Thomson's beautiful analysis brings about this result,
could ever be practically realized, for it becomes most difficult to turn
these mathematical conditions into experimental ones. In any case, it
is interesting to see how calculation had, to a certain extent, foreseen
these phenomena.
With regard to inducted currents, judging by all the results obtained
by experiment up to the present moment, it may be said that they are,
like the extra currents, formed of very numerous oscillations. The
exact conditions on which they depend are as yet unknown, and many
questions relative to them must yet be studied. It is indeed a broad
field that has still to be gone over. You will permit me not to enter
into the details of this question, regarding which there exists still much
difference of opinion, which will, however, disappear under the in-
fluence of time and research.
I prefer rather to call your attention to an idea which readily
suggests itself to the mind, and which, according to my opinion,
deserves to be considered. It has been somewhat difficult to prove the
176 SECTION— PHYSICS.
existence of the oscillations of the current, but they cannot be con-
sidered very rapid. They occur at the rate of about 5000 a second.
In the vibrations of sound far higher figures than this are attained.
And thus the molecules might yet undergo vibrations.
Now, all phenomena can be divided into two perfectly distinct
classes : into phenomena which propagate quickly and into those that
propagate slowly. To the first division belong light and radiating
heat, which are formed by the oscillations of ether, and which have a
propagating velocity of several hundred thousand kilometres a second.
Sound, communicated heat, &c., belong to the second class. They
attain a speed of some hundreds of metres, or, at the most, some kilo-
metres a second, and this speed is produced by the motion of the
molecules. The difference is immense between the first and the
second category.
As to electricity, it propagates itself, in good conductors, at a rate
which can be compared to that of light. But the oscillations of the
current belong to the second division : they are slow. The conclusion
might be drawn that the motion of electricity in metals is caused by
ether or by another fluid of about the same elasticity and delicacy,
whilst in the oscillations of the current the molecules themselves
vibrate, or else they acquire in it a predominant influence. The oscil-
lations of the current are the result of a reaction of the helices on
themselves. They are phenomena of induction through bodies which
are bad conductors. They are consequently slow, and must not be
confounded with the vibrations, which the ether probably makes in
vibrating electrically in bodies, which are good conductors. They
stand in the same relation to these latter as the great waves of the sea
do to the small calorific vibrations, which the molecules of the sea can,
at the same time, produce.
The CHAIRMAN : You have anticipated me by your applause in
asking you to pass a vote of thanks to Professor Blaserna for his most
interesting and lucid account of these most remarkable experiments.
In confirmation of what he has been stating, with respect to the
induced currents and the principal currents in an induction coil, I
may state that your President, in his way of experimenting, and I
and my colleague, Dr. W. H. Miiller, in ours, with a voltaic battery
consisting of several thousand cells, have come very much to the same
MA GNETIC REGISTRA TION. 1 77
conclusion — that there is no such thing as a perfectly continuous
uniform electric current. There is what appears to be a continuous
flow, but at certain periods this flow is very much increased ; and I
think that the more we experiment the more we shall see that the
electric current passing through any medium — metallic wires and
other solids, fluids, or gases — does take up certain pulsations, and
there is a maximum and a minimum of transmission — there are starts
as it were in the current. Mr. Spottiswoode has been pursuing for a
long time some most interesting experiments on electric discharges in
vacuo. A portion of his researches was communicated the other day
to the Royal Society, and I and Dr. Miiller had the honour of com-
municating one with him, in which we believe we detected that when
stratification took place in vacuum tubes there was a fluctuation of the
current. We are still pursuing our experiments, and he is pursuing
his, and they all go to confirm that which Professor Blaserna has
stated. Professor Blaserna wishes me to say also, that Sir William
Thomson mentioned to him that, on mathematical grounds, he con-
sidered it was quite possible — in fact probable — that there were
oscillations in the electric current.
MAGNETIC REGISTRATION.
Mr. BROOKE, M.A., F.RS. : The subject to which I am desirous of
directing your attention is that of the instruments connected with the
automatic registration of the variations of the magnetometers, which
are exhibited in this building. In order that it should be better
understood by those who have not paid any particular attention to the
subject of magnetism, I may state that the magnetometers are in-
struments which have now for many years past been subjected to con-
tinuous registration by the photographic method, and those I may
briefly describe are three in number. The first is the declinometer,
a magnet suspended by a single skein, which takes up its position
according to the direction in which the magnetism of the earth
acts upon it, and if the direction of the action of the earth's mag-
netism varies, it will vary the position of this magnet, just the
same as it would that of a compass needle : the declinometer is
N
1 78 SECTION— PHYSICS.
intended, therefore, to record changes in the direction in which the
earth's magnetism is acting. The second instrument is called a bifilar
magnetometer : it is a magnet suspended by two parallel or nearly
parallel threads, and the upper attachment of those threads is twisted,
so as to bring the magnet round exactly into the position of magnetic
east and west, that is, at right angles to the magnetic meridian. In
that position the tendency of the suspended weight to untwist is
balanced by the pull of the earth ; and supposing its tendency were
to untwist towards the south, the magnetism of the earth tends to pull
the marked end of the magnet towards the north, and it is so
arranged that the torsion force is exactly balanced by the magnetic
force. Now if any increase of magnetic force takes place, it would
tend to overcome the torsion force, and to pull the marked end of
the magnet further towards the north ; but if the magnetic force of
the earth diminishes, the torsion force will preponderate and the
magnet will untwist a little, and it will move slightly in the contrary
direction. The third instrument is what is called the balanced mag-
netometer, which I hold in my hand. For that purpose a magnet is
balanced on a knife-edge resting on an agate plane, and placed at right
angles to the magnetic meridian, so that while the weight of the magnet
tends to elevate the marked end, the vertical force of the earth draws
the marked end downwards, and that force will deflect a dipping-needle
about 70° to the horizon. The vertical force of the earth tends to
draw the marked end down, and if it diminishes, the weight would
cause that end to move in the other direction and rise a little upwards ;
consequently the movements of this magnet in a vertical plane indicate
the changes which take place in the earth's vertical force.
For many years observations were made with these instruments
solely by means of the eye with the aid of a telescope ; and they
were made by attaching a small mirror to the magnet, which was viewed
by a fixed telescope with cross-wires in it, and by the telescope a fixed
scale placed at a certain distance was seen by reflection from this mirror ;
and as the magnet moved, and, consequently, the mirror moved with it,
it is clear that if the cross-wire in the telescope were adjusted so as to
fall on the scale, as the mirror moved, the cross-wire would appear to
rise or fall upon the scale, and by that means the position of the
magnet at the time was recorded simply by eye observation. But in
MA GNETIC REGISTRA TION. 179
the Magnetic Conference, which was held at a meeting of the British
Association at Cambridge in 1845, there was a general expression of
opinion that it was a great drawback that no means had been hitherto
found for making the magnetic instruments record their own changes
of position. Attempts had been made to effect this by means of an
attached needle-point which was periodically impressed upon a surface
so as to mark it; so that by that alteration in the position of the mark of
the needle, an indication of magnetic change would be obtained ; but it
was found totally impracticable. In point of fact, the amount of actual
force that is exerted is so very minute that it was quite clear that it
could actuate no pencil but one which moves without friction or
any mechanical resistance — viz., a pencil of light. The desirability of
accomplishing this object attracted the attention of many persons to
it — amongst others that of the late Sir Francis Ronalds and myself,
and the instruments which were devised for this purpose by both of
us are to be seen downstairs. In the apparatus of Mr. Ronalds the
plan pursued was to attach a screen with a slit in it to the magnet. A
light was burnt behind the screen, and as the magnet moved, of course
the screen would move by minute quantities, and the light transmitted
through the slit was allowed to fall upon a sensitive photographic
surface. But for various reasons which I need not go into now, this
system was found impracticable. The idea that suggested itself to my
mind was that of attaching a concave elliptical mirror, as you see here,
to the magnet. The same system is applied to all three instruments
such as I have described. A concave elliptic speculum is attached
which has its conjugate foci at about two and seven feet from the
surface of the mirror. A light, either a lamp or jet of gas, is placed at
a distance of two feet from this mirror. The light passing through the
small slit in the opaque chimney of the lamp or gas burner, as the case
may be, falls upon the mirror, and an image of that slit is formed at
a distance of about seven feet. The reason for using a slit, and not a
point, is that the image of the line of light is received upon cylindrical
lenses which contract an image which is about one inch and a half
long, into a narrow point not exceeding one-sixteenth of an inch in
width, and consequently the whole of the light is accumulated into a
very narrow space. That point of light falls upon a sheet of photo-
graphic paper which is placed round a cylinder, and the cylinder is
i8o SECTION— PHYSICS.
carried round by clockwork once in twelve hours. For the balanced
magnetometer the axis of the cylinder is placed vertically, but for the
other two instruments, horizontally ; so that the combination of the
motion of the point of light on the paper, with the motion of the paper
in a perpendicular direction presents a means of tracing out the
magnetic curve. Here I have an actual photograph of a magnetic
disturbance which took place in the observatory at Toronto, where,
for many years, as at other places, these instruments had been,
in action. The cylinder goes twice round in the twenty-four hoursy
and therefore there will be two photographic traces on the paper. In
one of these you will see the changes are very small, while in the
other they are very large, and there is a constant vibratory distur-
bance of the magnet which has been maintained through nearly the
whole period of twelve hours. It is quite impossible that any eye
observations could ever have made us acquainted with the details of
magnetic disturbance which are shown by photographs of this kind.
With regard to the amount of movement, I would state to you that the
distance is about seven feet one inch to seven feet six inches from the
mirror to the point of light which falls on the photographic paper, and
inasmuch as the angular motion of the magnet is doubled in the
angular motion of the point of light upon the paper, this would
represent the actual amount of change which would take place in a
magnet of about thirty feet in length, that is, the end of it would
move to the extent here indicated. That is the general system of
photographic registration which has been adopted at Greenwich, at
Lisbon, in America, in Canada, and many other places.
There is one further point to which I wish to draw your attention,
and that is to the mode of correcting these instruments for changes
of temperature. It is perfectly well known that as the temperature
of a magnet rises, it loses its magnetic force, and where the changes
are not beyond a certain amount, as it cools down again it regains
its power when it arrives at the same temperature from which it
started. It is therefore evident that the movements noticed would be
due to two causes, to changes in the earth's magnetism and therefore
to the induction upon the magnet, and also to alterations in the force
of the bar itself, because the position which the bar takes is the joint
action of the earth on the magnet, and of the magnet on the earth.
MAGNETIC REGISTRA TZOZV. 181
For this reason it became necessary either so to place the magnet
that it is not liable to changes of temperature, or else to provide
it with some means by which those changes can be compensated.
Unquestionably the best course is to place the magnets as is now done
in the Observatory at Greenwich, in an underground apartment,
which is liable to very small changes of temperature ; but if it be not
convenient to do that, it is then desirable to employ some means by
which the change of temperature can be compensated. In the bifilar
magnetometer that is accomplished by attaching to the magnet a rod
of glass to the ends of which two zinc tubes are clamped, and at the ends
of these near each other two hooks are placed to which the double
skein is attached. It is quite clear that owing to the greater expansion
of zinc over glass, heat will have the effect of approximating the hooks
by which the magnet is suspended by a minute quantity, and if they are
made to approach each other the torsion force is diminished. If the
interval between the hooks be diminished so as to diminish the torsion
force proportionate to the diminution of magnetic force by change of
temperature, it is quite clear that in that case the indications will be
unaffected by temperature : that is shown in the bifilar instrument
downstairs. In the balanced magnetometer the compensation is
effected in a different way : a thermometer tube is clamped to the
magnet, the bulb being on one side of the point of support and the end
of the thread of mercury in the closed tube somewhere on the other
side. It is quite clear that as the temperature rises and consequently
the thread of mercury travels along the tube, a minute quantity will be
transferred from one side of the balance to the other ; as the energy
of the bar diminishes a little additional mercury would be thrown over
from one side to the other, and the weight of mercury in the tube is
such that it just counteracts the diminishing force of the bar, so that in
spite of change of temperature, supposing the earth's magnetism
remained constant, the magnet will retain the same position. There
is a further advantage in this mode of compensation, which is this :
the amount of the temperature correction may be represented by a
formula of this kind (A t + B /2), supposing / to be the number of
degrees of temperature at the time above the freezing point, and A and
B are coefficients which have to be determined. Those I have
determined in the instrument to which this correction has been applied
182 SECTION— PHYSICS.
by suspending the bar-magnet as a bifilar magnetometer without any
correction, the zinc tubes being clamped at their proximate ends so as
to prevent any alteration in distance. Then, while the registration
is going on, the temperature on the magnet is gradually raised by a
water envelope, the water in which is gradually heated by a jet of gas
burnt outside the apparatus. This goes on for a period of about six
hours, and the heat is so arranged that the temperature of the water
should be raised gradually from that of the atmosphere up to about
90°, which is as high as is necessary. The jet is then extinguished,
and the water allowed to cool down again, in about the same period
of time. It is found that the line which would represent the actual
magnetic variation during twelve hours is deflected in the direction of
diminished force as the temperature rises, and goes back again as it
cools down, and thus it is found that the register line will again return
to its normal position. It is quite clear, therefore, that these changes
are due entirely to temperature. The temperature having been
recorded at intervals of a quarter of an hour or any convenient time,
there are means of identifying these epochs with the register line when
removed from the cylinder and developed, by shutting out the light
for a very brief period, and then letting it in again, when you have
a little interruption in the line which identifies the line with the
particular time when you have produced that spot. By equating the
formula A t+ B t° with the differences of the ordinates of the normal
and displaced register lines, at the times at which the temperatures
have been recorded, and reducing these equations by the method of
least squares, the values of the coefficients A and B may be obtained.
With regard to the bifilar magnetometer the coefficient A only is taken
account of. In the balanced magnetometer B is also given by the
relation of the bore of the thermometer to the weight of the mercury
in it, because it is evident that the finer the bore the further the
minute quantity of mercury will travel for each degree of temperature,
the more will it affect the balance, and that will determine the
coefficient of t\
The set of instruments constructed by the authorities at Kew is not
yet arranged, but it will be shortly ; the principle is exactly the same,
the registration being obtained by reflected light. There is, however,
one deviation from the system which I adopted which I am free to
MAGNETIC REGISTRATION. 183
confess is an improvement, that is, instead of having a concave mirror
attached to the magnet, there is a plane glass mirror, and the light
is collected into a focus by means of a fixed combination of lenses.
The advantage is that the mirror is much lighter, the magnet is not so
much loaded, and you then get a direct image in which the axis of the
pencil of light falls centrally on the paper ; whereas by the system I have
adopted you get to a certain extent an oblique reflection, and the image
so obtained is not so distinct as that obtained by direct reflection
or refraction.
There is a little additional apparatus here for the purpose of
testing the scale coefficient, or value of the displacement of the in-
dication on the paper, by adding a minute weight of '01 of a grain in
this scale. You will observe how much that displaces the bar, and
thence obtain the value of the ordinates of the curve. I have only
further to say that the magnets in some cases are flat bars ; but as
set up by myself at the Paris Observatory, they are of this form — a
hollow magnet, with a lens at one end and a collimater scale at the
other, so that the photographic records may always be checked by
observations with the telescope of the magnet itself. To each in-
strument a small plane mirror is also attached, so that the indicated
amounts of variation may be checked by a fixed telescope and a scale.
The CHAIRMAN : I am sure you will all agree with me that we are
much obliged to Mr. Brooke for his very able description of the
photographic recording instruments, to which he has so largely con-
tributed. Mr. Ronalds, formerly director at Kew, he has already
alluded to, but since Mr. Ronalds' time the directors of Kew have not
been idle ; the late Mr. Welch contrived the above-mentioned modifi-
cation of this very beautiful instrument of Mr. Brooke's, and a complete
set will be shortly erected in the grounds of the observatory. The Kew
instrument is now being worked under the direction of Mr. Whitwell ;
and beside that there are instruments at St. Petersburg, Lisbon, Coimbra,
Florence, Toronto, and in many other places. It is extremely important
that simultaneous and continuous records of magnetic changes should
take place at a great number of points on the earth's surface. We have
the curves recorded at Lisbon and at Kew, and the disturbances are
found to take place at the same time, and prove that magnetic changes
are cosmical and that they are synchronous — that is to say, the instru-
184 SECTION— PHYSICS.
ment at Kew was disturbed at the same time as the one at Lisbon.
Moreover, two astronomers, both now dead — Mr. Carrington and Mr.
Hodgson — were looking at the sun at the same time, and happened to
observe a sudden outburst of light. Mr. Chambers, who was then at
the Kew Observatory, observed a simultaneous disturbance of the
magnet. You are aware that the period of sun spots and magnetism
appear to be closely connected ; and it is extremely important that
these observations, which have been going on now with the same in-
strument for sixteen years, should be continued for a great number of
years still, and then we may have some light thrown possibly on the
cause of magnetism. I beg to return your thanks to Mr. Brooke, not only
for the account he has given us, but for what he has done for science.
I now call on Professor Rijke, on the Historical Instruments from
Leyden.
Professor RIJKE : Ladies and gentlemen, — The first thing I have to
do is to implore your indulgence for the bad English which I am about
to speak, but I hope that you will remember that, if you were obliged
to lecture in Dutch, your Dutch would not perhaps be much better
than my English. I hope also that you will forgive me if I use a foreign
word when I cannot find the English one. I shall not lecture on the
services which my countrymen have rendered to science, but I intend
only to speak a few words on the most interesting Dutch instruments
of the seventeenth and eighteenth centuries which have been here ex-
hibited. The first instrument to wlAch I wish to draw your attention
is the first compound microscope which was made in Middleburg, and
which you see here. It consists only of two convex lenses, and was
made by Hans and Zacharias Janssen. There is a letter written by
William Boreel, Dutch ambassador in France, stating that Hans and
Zacharias Janssen, whom he knew perfectly well, having been their
neighbour at Middleburg, and having often played with them when
they were young, — he says in that letter that compound microscopes
were made by the Janssens long before the year 1610. The art of
making compound microscopes made hardly any progress at all during
the 150 years which followed upon the invention of the Janssens ; and
indeed no progress could be made until their theory was further com-
pleted. It was for this reason that the great discoveries in the micro-
scopical^world were made by single lenses, and the man who was fore-
ON THE INSTRUMENTS FROM LEYDEN. 185
most in the field of science was an usher to the sage magistrates of a
little town in Holland called Delft. His name was Van Leuwenhoek,
a name which is now known throughout the whole world. Last year
we had not only a festival in Holland, but also in different parts of
Europe, to commemorate one of Van Leuwenhoek's greatest discoveries
of which I am to speak, and all these discoveries were made with the
little instrument I am showing you, of which every part was made
by himself. It consists only of a little lens, which is not as large as
the head of an ordinary pin, and the objects which had to be observed
were placed on a pin underneath. When we remember how well and
carefully arranged are the microscopes which we use now, we cannot
too much wonder how it was possible to make with such an apparatus
the discoveries which he made. The most important discovery was
that of the Infusoria — those little microscopical animals which are to
be found nearly everywhere, and which give so much trouble to
modern science. In order to observe those infusoria he was obliged
to change the form of his apparatus a little, and constructed a micro-
scope of this form. His whole life was devoted to microscopical
researches, and you will understand this when I tell you that at
his death 247 microscopes with their frames were found, and also
172 lenses without frames. As often happens, his merits were
much sooner acknowledged by foreigners than in his own country,
and I am happy to say that it was Englishmen who were the first
to declare how great a man he was. He was made a Fellow of
the Royal Society, and that was, as he often declared, the greatest
blessing he ever received. I will now speak of another scientific man,
who lived quite another life — namely, Christian Huygens, who was not
a man of humble extraction, for his grandfather had been Secretary
to the first Prince of Orange, and his father held the same office
under the following stadtholders, even under William the Third, who
was as much yours as ours. He at once saw that if astronomers were
to make greater discoveries it was necessary to have lenses of greater
focal length, and as these lenses could not be found in any part of
Europe, he, with his brother Constantine, made them himself. After
some trials he succeeded very well, and two or three days after his
first lens had been made, he was fortunate enough to discover a
satellite of Saturn, and afterwards he was able to solve a problem
1 86 SECTION— PHYSICS.
which had not yet been solved — namely, to say what was the true
nature of those little bodies which Galileo discovered near Saturn.
He first discovered that they were not two, but one body only, and
that that one body was a ring. He made that discovery, not with the
telescope which is here exhibited, but with one nearly the same. He
made more lenses, but not as many as his brother Constantine. The
object lens of this old telescope has been made by Christian Huygens,
and here is another one. Here also is a lens on which is written the
name of Christian Huygens, but it is not genuine. The lenses of
the greatest focal length are here in England, and belong to the Royal
Society. There is one of 210, another of 170, and one of 120 feet,
those lenses however were not made by Christian Huygens, but by
Constantine ; but I am happy to add that the lenses of Constantine
were as good as those which Christian himself made. We have sent
to the Exhibition this planetary, because it was invented by Huygens,
and was in fact the first instrument of that kind ever made.
We have exhibited several instruments invented by 'sGravcsande,
not because great discoveries have been made by each of them, but
because you find amongst them the first specimens of instruments
which were devised to illustrate by experiment discoveries which had
been made by mathematical research. It was his object in the first
instance to make popular on the Continent the great discoveries of
Newton, and he succeeded in fact very well. I think I do not say too
much when I say that in his time he was the first lecturer on the
Continent. Unfortunately he had to deliver lectures not only on
natural philosophy, but on mathematics and on moral philosophy,
and that is the reason why he did not make a great number of disco-
veries. Some of those instruments have been brought upstairs. For
instance, this is an instrument to show that the velocities acquired by
falling bodies are to one another as the square roots of the heights.
Two little balls are made to roll down a curve, called cycloide, side
by side, and one being placed at the height marked 4 and the other at
the height marked 16, it is seen that the velocity of the body which
has fallen the height of 16 is twice as great as that which has fallen
from the height of 4.
Here is an apparatus which was made to show the properties of
centrifugal forces, and it was so good that it is still used every year in
•Jfe
ON THE INSTRUMENTS FROM LEYDEN. 187
our Lectures. Here is also a little apparatus for demonstrating the
properties of the wedge. If 'sGravesande did not make a great deal
of important discoveries, he at all events invented an instrument which
has rendered great services to science — viz., the Heliostat. This is
the first which has been constructed. You all know that when a
physicist is experimenting upon light he desires that the pencil of
light with which he is experimenting should always keep the same
direction. Now a pencil of light which comes directly from the
sun changes its direction at each moment, and therefore 'sGravesande
contrived an apparatus through which the pencils of light fall upon
this mirror and are always reflected in the same direction. He also
made some experiments which had at that time a very great impor-
tance. Scientific men were divided on the question in what manner
the power of a body, which has received a certain quantity of velocity,
should be calculated. They all agreed on one point, that the power
was in the ratio of the masses of the two bodies, but did not agree on
the question if the power was in the ratio of the velocity or whether it
was in the ratio of the squares of the velocities. 'sGravesande thought
that the powers were in proportion to the ratio of the velocities, but he
thought it would be very useful to solve the question by direct experi-
ment, and the experiments he made were the following. He took two
pieces of wet clay and two bodies whose masses were different and
those bodies he made fall from different heights on to the clay.
Falling on the clay they made holes, and if the power of the two bodies
were the same the holes must be the same too. He began by making
such arrangements that the mass of each body multiplied by its
velocity was the same, and that he could do by allowing them to fall
from different heights. They made holes which were different. Then
he made them fall from such heights that the mass of the bodies multi-
plied by the squares of the velocities were the same and then the holes
were the same in each piece of clay. He found thus that he was
wrong. But look what a man he was ! His brother-in-law was in the
same room in which he was experimenting, and after 'sGravesande
had ascertained that in the last experiment the two holes were the
same, a shout escaped him so that his brother-in-law came to ask
what was the matter. " What is the matter, my dear fellow !" he
said, " the matter is, I am quite in the wrong, and Leibnitz is quite in
1 88 SECTION— PHYSICS.
the right." He was as joyous, his relative relates, as if he had just dis-
covered that he was in the right. It was by that experiment that the
matter was settled for ever. You will also find downstairs a very in-
genious apparatus invented by ;sGravesande, by which he has been
able to prove by experiments that the same quantity of labour pro-
duces always the same quantity of vis viva. I should certainly have
some more things to add, but I have already spoken, I fear, too long.
The CHAIRMAN : I do not think that Dr. Rijke need have made
any apology for his want of fluency in speaking English, for he has
given a most lucid description of these wonderful contributions to
science of his countrymen. The compound microscope of the Janssens,
but more remarkable still, the simple microscope of Leuwenhoek,
whose name every microscopist is well acquainted with, certainly
performed wonders. These simple lenses showed an amount of
detail in the objects he examined which for a long time was unre-
vealed, and certainly was not revealed for a long time by the com-
pound microscope. Of course it is not to be compared with the
microscopes of the present day, but in its day it was a remarkable
instrument. Dr. Rijke has also alluded to the two Huygens, and
these lenses upon which I place my hand belong to the Royal
Society, and as you are aware they were mounted with a ball and
socket and a balance, and placed at the top of a high pole. The
eyepiece was held in the hand, and the object glass was controlled
by a long rod and a string. The observer had first to find his object
glass with a lantern, and when he found it, turn it on to a star and
seize the blaze of light in the object glass, and then he went on
observing. In the lower room is a tower constructed on piles, which
was intended by the Royal Society for mounting, at the suggestion of
Mr. Struve, the celebrated Russian astronomer, these object glasses
of Hugyens, with a view of ascertaining whether there was any change
in Saturn's rings. A theory had been started that the rings were
altering and collapsing. It was found to be rather expensive, and
Mr. Struve on reconsideration did not press for the expenditure of
400/. or 5007. for mounting them. I have myself looked through these
object glasses and can attest that they are very good ones. I did not
look at a celestial object, but at a test object on the Pagoda at Kew.
Now I believe Mr. Lockyer has employed them with a siderostat for
NEW FORM OF VOLTAMETER. 189
making investigations on the solar phenomena. These experiments
of Dr. 'sGravesande's are very remarkable, and show what a great
philosopher he was. At all events, when he found himself in error,
he was only rejoiced to have discovered the cause and to give credit
to Leibnitz for the correctness of his theory. I have now only to ask
you to return your thanks again to Dr. Rijke.
ON A NEW FORM OF VOLTAMETER.
Baron FERDINAND DE WRANGELL : The instrument to which I
have the honour to draw your attention has been devised by my
friend Professor Robert Lenz of St. Petersburg, and as he is unable
to attend he has requested me to explain the principle on which it is
founded. I will not go into the details now, but if any one is interested
in the subject I shall be very glad to explain the construction of the
instrument in its details at any time. The instrument is intended for
volta-metric measurement of the strength of a current, and it is based
upon the principle that the quantity of matter decomposed by the
current which flows through it is proportional to the strength of the
current, all other conditions remaining equal. This assumption that
all other conditions remain equal is the most important point and
the most difficult to attain in a voltameter. Besides this first con-
dition of equality of conditions from one measurement to another, in
order to compare the two currents, of course brevity of time and ease
of management are very important conditions, and I think that this
mercury voltameter fulfils all these conditions in a much higher
degree than those which are generally used. The best mode of
which I am aware consists in measuring the decomposition of a salt
of silver solution by a current. The solution is contained in a
platinum vessel, and after the decomposition has taken place for a
certain time, the vessel is washed out, then dried perfectly, and the
amount of silver which has been decomposed by the current in a
certain period of time is ascertained by weighing. This process of
washing out the silver, secondly, of drying it, and thirdly, of weighing
it by a chemical balance, takes a great deal of time, is very trouble-
some, and is liable to some errors, of which the most important is
190 SECI10N— PHYSICS.
that in washing out the silver contained in the vessel some parts of it
are easily broken off, because it covers the black platinum vessel with
a rough surface, and so some particles are lost. Then if it is not well
washed, foreign matters remain in it, and thirdly, if it is not well
dried, a great deal of water may adhere to it ; for instance, upon a
square centimetre of a plate covered with silver by this process, eight
milligrammes of water will adhere under ordinary circumstances.
This instrument, devised by Professor Lenz, measures the decompo-
sition of mercury not by weighing it but by volumetric measurement.
There are two vessels connected by an inclined tube, and in the bottom
of the upper one a little mercury is put ; the lower vessel ends in a
glass tube which dips into a cylindrical iron vessel, which forms the
chief part of the measuring apparatus. Some mercury is poured into
the upper vessel and drips into the lower one, and goes through the
glass tube and into the measuring apparatus. Platinum wires, enclosed
in glass tubes, are immersed into both vessels, and they form the
electrodes. The platinum wire is quite immersed into the mercury, so
that the mercury really forms the electrode. Over the surface of the
mercury in both vessels a solution of mercury salt is poured. There
is a micrometer screw which works an inner cylinder which fits into
the iron vessel quite tightly, and which is carefully calibrated so that
the value of one division of the micrometer screw is easily ascertained ;
and by this screw one can lift the mercury in the tube or let it fall.
Before the commencement of the experiment, when the solution is
poured in, the mercury contained in the tube is lowered to a standard
point, which can be read off by means of a lens, and it is then lifted
again so that it forms a bead at the bottom of the vessel, which is
sufficient to cover the end of the platinum wire. The experiment then
begins ; the current flows through one wire to the other ; the decom-
position begins, and the mercury is evolved at the lower electrode, and
just as much as is evolved there would enter into combination from
the acid solution contained in the other vessel. By the decomposition
of the mercury in the lower vessel the fluid becomes lighter, but that
is prevented by the slanting tube, which allows it to flow from the
upper vessel, and it can also be stirred. After a certain lapse of time
the current is broken, the screw is lowered down, which brings the
mercury again to the standard point ; and then, by means of the
NEWTONIAN REFLECTING TELESCOPE. 191
micrometer, you can ascertain the exact volume of mercury which has
been decomposed by a given current in a given lapse of time. That
is easily converted into weights, and so you have an exact measure of
the effect produced by the current in a certain time. You can perform
the whole measurement in five minutes with great facility and great
precision, for by a series of experiments it has been proved that the
error is not more than "04 per cent, of the quantity measured. If the
current is not strong enough crystals may be formed on the surface of
the mercury, but that is prevented by heating it a little. The correc-
tion for temperature is very small indeed, because the bore being so
very small it is scarcely noticeable; but still it can be taken into
account, because all the dimensions are known.
The CHAIRMAN : This ingenious instrument for measuring electrical
currents is, I think, likely to prove of great value ; and it is interesting
as having been contributed by Mr. Lenz of St. Petersburg, the son of
the great physical philosopher of that name. We are very much in-
debted to the Baron de Wrangell for his description of it.
I will now call upon the Rev. Robert Main, the Radcliffe Observer.
ON A NEWTONIAN REFLECTING TELESCOPE OF SIR W. HERSCHEL.
The Rev. R. MAIN, M.A., F.R.S. : I am rather taken by surprise in
being asked to say anything about this telescope, which I sent from the
Radcliffe Observatory, but it may perhaps give me an opportunity of
saying a few words to those not accustomed to the instruments in an
observatory. The telescope in question is a ten-foot Newtonian re-
flecting telescope, and almost the only interest it can have here is that
it was prepared and brought down to the Radcliffe Observatory by Sir
William Herschel himself, and his correspondence is preserved there.
It was made in the year 1812, and was received by the Observatory in
1813. I wish I could assure you that there was any series of observa-
tions made with it worthy of the telescope. I fancy there were a few
casual observations, but nothing much was done with it.
It will be well perhaps to say a few words about the Observatory itself,
and the way in which observatories at that period were furnished with
instruments. The want of some such institution in Oxford had- been
192 SECTION— PHYSICS.
much felt near the end of the last century, about 1770, and the Univer-
sity not being able to furnish anything, the Radcliffe Trustees under-
took it and built that magnificent erection with which most of you are
no doubt familiar. But the instruments were servilely copied from
those at Greenwich, which was a very great misfortune for astronomy.
Here was an opportunity for bettering a very bad class of instrument
which had been used for the determination of the absolute places of
bodies, by a due consideration of what could be done in this new ob-
servatory ; but unfortunately Bird, who at that time was a great instru-
ment maker, had a reputation for his quadrants, and two quadrants
were ordered ; and a transit instrument of the character usual in those
days, with a small object glass, was also furnished, and that was the
equipment of the Observatory. It was thought by Dr. Robertson that
some instrument for observing casual phenomena would also be de-
sirable, and Sir William Herschel gave a good deal of consideration
to it, and recommended him to have this Newtonian reflecting tele-
scope. It is very similar to the one you see here on the table. It has
a small mirror of eight and a half inches, which was not considered
small then, and the focal length is ten feet. The epoch at which this
telescope was given is an important one and an interesting one. The
first mural circle had just been established at Greenwich, and then
began that series of observations which have only been improved upon
very recently, and which totally superseded all observations of zenith-
distances of bodies which before had been obtained by the quadrant.
You may consider that as an epoch in the new astronomy. The
Radcliffe Observer did not for a long time get any new instruments ; he
had not the power, in fact, of getting out of the groove in which things
then were. The quadrants continued in use up to almost the termina-
tion of the Directorship of Professor Rigaud, and it was only just
before the time when Mr. Johnson became Radcliffe Observer that a
meridian circle, based on that of Dr. Robinson of Armagh, was
established, and this you may consider another epoch in the astro-
nomy of the age. From this time began an uninterrupted series of
star-observations, rivalling those of Greenwich in the continuity and
the value of the definite series of observations which were made.
Similar observations have been kept up to the present time.
These things may not seem to have much connexion with the par-
NEWTONIAN REFLECTING TELESCOPE. 193
tkular subject I have before me — namely, this telescope, but you
may consider that the same kind of improvement has gone on in
everything else ; and yet if we were to observe one thing more than
another, we are not so much astonished at the improvements which
have been made in this long interval of time, but rather at the tenacity
•with which old methods utterly unsuited to the purpose for which they
were intended have been kept to. Nothing could be more clumsy or
ill devised for the object in view than the old quadrants, but they were
kept up on the Continent of Europe long after they were given up
in England, and long after Pond had superseded them by the mural
circle at Greenwich. In the same way it was through an unfortunate
mistake of Newton that the reflecting telescope, without those im-
provements and the mode of mounting which have made it a very apt
and proper instrument at the present day, was kept up in contra-
distinction to the refracting telescope. It was supposed that the
want of achromatism was hopelessly insuperable. Newton laid down
the principle, and others servilely followed it, and thus was delayed
the making of large object glasses for the greater part of a century.
The tax on glass also, in England at least, was another reason why
great object glasses could not be made. It is only within the last few
years since the tax has been taken off and that glass has become an
article of commerce which could be used freely, that we have been
able to reap the full advantage of the scientific improvements which
have been made in the construction of glasses, the shortness of focal
length, and everything of that sort which renders telescopes of very
considerable apertures as manageable as small ones used to be. I
make these few rambling and cursory observations with respect to
these things to show in some degree the way in which we have got to
our present position. The wonder is not so much that, when the
human mind is bent on any particular discovery, improvements are
so rapid, but that in the preceding century they were so slow. It is to
be hoped that, as time goes on, the rate of discovery, rapid as it is at
present, will be still further increased. There is no want of genius,
no want of scientific means for improvement in material things ; it was
want of opportunity and want of interest in the general public which
stood in the way. That want of interest has now vanished ; — all classes
and both sexes, in fact the world at large, take interest now in what
O
194 SECTION— PHYSICS.
would have been formerly considered very recondite researches. All
are eager and anxious to learn something, if but little, of various
sciences, and to learn that little well. The fervour with which the
public take up these things react on scientific men themselves. Each
is anxious to do something in his vocation, and is only baffled
by finding that, however early he may have been in the field, some-
one else, either at home or abroad, has forestalled him. At this hour
it is not desirable to keep you any longer, but I would call your
attention when you go below to those four telescopes of the class I
have been mentioning as being so materially connected with the history
of astronomy. There is first Newton's original telescope in a paste-
board case, very likely the cover of an old copy-book ; there is a
telescope of Sir William Herschel's with which he began his re-
searches ; there is another of seven feet, although in rather an imperfect
condition ; and finally there is this ten-foot one, which is a very good
representative of the telescopes which he made when they became
with him an article of commerce. They will amply repay you for the
little attention you may bestow upon them, though they form such a
very sir^H portion of even the astronomical instruments in this grand
collection, which contains so vast a variety of interesting objects.
There :s the learning of a whole life here ; in fact the ordinary
Sp>in .rc'human ]'"e would hardly suffice for the study of all one sees ;
but in this one particular I am glad to have been enabled to say a few
words to show how improvement has gone on, and by what means?
and what are our hopes for the future.
The President here again took the Chair.
Mr. DE LA RUE : The President wishes me to ask you to return
your thanks to Mr. Main, as he has not been here during the whole of
his address, which has dealt with some very important things. I may
say that I am intimately acquainted with the work which the Radcliffe
Observer is doing, and can attest that the observatory in his hands is
doing as good work, and that that work is as rapidly brought before
the public on the reduction of the observations as ever it was before —
perhaps faster. He has alluded to Sir William Herschel taking down
to the observatory part of its first equipment— namely, an eight or
nine inch reflector, and has alluded to the very inadequate instruments
which were for a long time employed when the observatory servilely
ON THE ITALIAN EXHIBITS. 195
copied what existed in another. But he has also shown that in recent
times invention has proceeded so fast that there has been no necessity
to continue the use of those old instruments. He himself has acquired
a transit circle designed by the late Mr. Carrington, and has continued
that very important series of star observations- which his predecessor
commenced. He has also alluded to the first reflecting telescope of
Newton. I had recently to allude to the four-foot reflecting telescope
made by Messrs. Grubb, of Dublin, mounted equatorially, and I may
say that I recollect when first a four-foot equatorial was spoken of, it
was thought to be impossible to mount it on a polar axis, and a con-
trivance to guide such telescope temporarily in the diurnal path was
proposed. We are very much obliged to Mr. Main for having alluded
to the older form of instruments in this interesting historical account
which he has given.
The PRESIDENT : Professor Eccher now wishes to address a few
words to the meeting in addition to what he said on a former occasion,
with reference to the instruments from Italy.
Professor DE ECCHER : Your celebrated Faraday, in a letter to his
mother, giving an account of his journey on the Continent, thus
expresses himself with regard to Florence : " Florence, too, was not
destitute of its attractions for me, and in the Academy del Cimento,
and the Museum attached to it, is contained an inexhaustible fund of
entertainment and improvement ; indeed, during the whole journey,
new and instructive things have been continually presented to me. Tell
B. I have crossed the Alps and the Apennines ; I have been at the Jardin
des Plantes, at the Museum arranged by Buffon, at the Louvre, among
the chefs-d'oeuvre of sculpture and the masterpieces of painting, at the
Luxembourg Palace, among Rubens' works ; that I have seen a GLOW-
WORM ! ! ! waterspouts, a torpedo, the Museum of the Accademia del
Cimento, as well as St. Peter's, and some of the antiquities here, and
a vast variety of things far too numerous to enumerate."
And those among you who have visited Florence can bear witness
to the great number of celebrated scientific instruments which that
city is fortunate enough to possess. It was, I can assure you, no easy
task to choose trom the midst of such abundance, a few objects only,
to bring to this Exhibition. All are worthy of such a distinction.
But it having been decided that the selection should be- of Italian
196 SECTION— PHYSICS.
instruments, there was chosen from among them a small number, that
would give an adequate idea of the History of Science in Italy, and
especially in Tuscany.
Two instruments, however, although not Italian ones, were chosen
as a mark of homage to your noble country : the one was the invention
of a countryman of yours ; the other was made use of, in many cele-
brated experiments, by another Englishman. In the Times of the
2oth of this month, there is this statement : " Besides this, there are
other astrolabes of different countries — French, German, Arabic,
and Persian, but unfortunately no English specimen." Now you
have before you here the astrolabe of Lord Dudley, and in return for
having placed before his eyes an English astrolabe, I would ask the
Times' reporter to be good enough to notice, also, the Italian astrolabes,
which are exhibited in our cases.
But not only these astrolabes, but these astronomical quadrants,
these sundials, this series of instruments, in a word, will be able to
give an idea of the manner in which, during the i6th and I7th
centuries, mathematical and astronomical science was cultivated in
Italy ; and how numerous and renowned were the artificers of such
apparatus.
Here is the great lens, made by Benedetto Bregans, of Dresden, and
presented by him, about the year 1690, to the Grand Duke Cosimo III.
About the beginning of this century it was made use of by your
celebrated philosopher, Sir Humphry Davy, in the researches which
he made in Florence, together with Faraday, who was at that time his
assistant, on the chemical constitution of the diamond.
I must, however, tell you that Averani and Targioni had already
succeeded, by means of the aforesaid lens, in vaporizing the diamond.
We now come to the barometrograph of Felice Fontana, a well-known
scientific man, born in Rovereto, and who was Director of the Royal
Physical and Natural History Museum of Florence, founded by Peter
Leopoldo. Not to impose upon the indulgence which you have so
kindly granted me, I will omit describing to you the other experiments
made by Fontana, who, in order to push forward meteorological
science, constructed, upon the principle which you see here before you,
a barometrograph, a thermometrograph, and other self-registering
instruments. You will be able by the help of photography to under-
ON THE ITALIAN EXHIBITS. 197
stand how these instruments register themselves. The wooden stopper
floating on mercury rises and falls with it, and transmits its motion to
this pendulum, which in its upper portion has an arc covered with
paper, on which at every hour, this needle, set in motion by clock-
work, makes a mark. This same needle advances a little after every
impression, and thus these marks form a curve upon the paper.
I come now to speak of Nobili, and shall, for the sake of brevity,
mention only those objects which you see before you. Here is his
first astatic galvanometer, made in the year 1825. And this is
another instrument for hydro-electrical currents. Here is Nobili's
magnetoscope for proving the presence of the very slightest magnetic
influences ; it is composed, as you see, of a system of astatic needles
suspended to a thin thread of silk inside this crystal bell, surmounted
by a tube which has on its upper part a graduated circle, with an
index such as is used in scales " di torsione."
Here are three different models of thermo-electrical piles. In the
construction of such instruments he attained great excellence. But I
want particularly to draw your attention to this one, which is com-
posed of thirty-six elements, bismuth antimony, and is provided
with a conical reflector ; it was of the greatest possible use to him in
the experiments which he carried on, partly in collaboration with the
celebrated Melloni, on the radiation of heat. All have heard of
Nobili's coloured rings, obtained by means of the chemical action of
the electric current ; this " rosettone" was obtained by him in this
wise. We have in Florence the complete chromatic scale constructed
by him, and who has read his memoirs on the subject knows with
what profundity he has treated this attractive argument.
And, although I cannot put the instrument itself before your eyes,
allow me to remind you of his globe, round which there circulates an
electrical current for imitating the magnetical phenomena of the earth.
It was made by him in 1822, whilst it was only in 1824 that Dr. Birk-
beck presented a similar one to the Royal Institution (of London) ;
and, as he got his first idea from Barlow, it was henceforth known as
Barlow's Globe.
With regard to the magneto-electrical machines of Nobili and
Antinori, and to their publications on the phenomena of induction, I
feel it my duty to add a few words. It is certain that your celebrated
193 SECTION— PHYSICS.
Faraday, in whatever direction he investigated the mysteries of nature,
he compelled her to disclose her secrets. He was the first likewise in
this most important branch of science. But nevertheless, Nobili and
Antinori, starting from an imperfect report of Faraday's works, which
was communicated to the Academy of Sciences of Paris by M.
Hachette, by dint of repeating Faraday's experiments, they not only
succeeded in obtaining results equal to Faraday's, but, in some cases,
produced effects that had never before been observed.
I well know that the English philosopher was somewhat displeased
at Nobili's intrusion into the wide field of science which he had just
thrown open ; indeed, the illustrious Tyndall mentions this fact as
characteristic of Faraday. I can perfectly understand his annoyance.
But at the same time I hope that you will agree with me that the field
of science is not merely open to all, but that it invites all to enter ;
that Faraday's renown is too firmly established for there to be any
reason why some distinction should not be allowed to others ; and
that it was impossible for an investigator like Nobili not to throv--
himself eagerly into this new field of such marvellous and profound
investigations. I beg you, therefore, to admit the fact that the first
magneto-electrical machine was made by Nobili and Antinori. Here
it is. If I quickly remove the keeper, armed, as you see, with this
" rocchctto" of thread, of which one extremity is in contact with the
magnet itself, the other with this spring (molla), afterwards also in
contact with the magnet ; this second contact is immediately inter-
rupted, and thus the inducted electrical current occasions, as you see,
a spark. This instrument gave forth its first spark on the 3oth of
January, 1832.
Under No. 1298^ of the Catalogue you may observe another example
of a magneto-electrical machine made by Nobili and Antinori. It is
exhibited by the illustrious Professor Dove of Berlin.
Latterly this same form of a magnetico-electrical machine has been
returned to, for use in the lighting of mines (accensione delle mine}
Then in order to get a more' intense current, and a greater number of
interruptions in a given time, Nobili and Antinori constructed their
so-called " united magnets machine" (macchina a catamite conjugate] ;
made up, in fact, of permanent magnets, among which, by means of a
handle, or lever (manubrio], and of an eccentric, the keeper with its
ON THE ITALIAN EXHIBITS. 199
"rocchetto," swings, passing successively from the contact of the
first magnet, to that of the second, and then back to the first again,
and so on.
Then, by making use of the great natural magnet of the Regio
Istituto Superiore di Firenze, a very large parallelepiped of about
50 x 65 X 78 centimetres in dimension, and fastening the keeper with
isolated thread, they were easily able by detaching it, interrupting at
the same time the inducted current, to obtain the spark and every
other effect peculiar to electricity.
And with regard to Nobili, allow me to remind you that, besides his
important researches in electro-physiology ; on rotary magnetism (di
rotazione) ; on electric-dynamical phenomena, &c., he founded his
electrical condensator upon the principle of the extra current, upon
-which, shortly afterwards, so much light was thrown by your illustrious
Faraday. It consisted of a " rocchetto" of thread interposed in the
circuit of the electrical current, which acted in such a manner that the
spark of opening (d'aperturd) was greatly increased in intensity.
And now turning to Amici, I am sure that all will recognise in him
a remarkable scientific man, of very remarkable mechanical genius,
and one who has bestowed his name on many valuable and useful in-
struments. He was especially noted for his microscopes and tele-
scopes, two of which are among the most honoured objects in the
observatory of Arcetri. One of the objectives has a diameter of
twenty-nine centimetres. The two microscopes which you now see
before you, although not among the best of those made by Amici,
are, however, the oldest In one of them you may observe how the
objective is made by means of a concave glass ; among the acces-
sories you will find various systems of camera lucida, some of them
were imagined by him ; and you can likewise see ingenious methods
for concentrating light, especially on opaque bodies.
I cannot conclude this hasty review without reminding you of
Matteucci, of whom science was, alas ! too quickly robbed. The
greater number of us have constantly present in our minds the weighty
judgment pronounced upon his works by the most illustrious scientific
men of Europe ; and many venerable institutions inscribed his name
?n their lists of members. The fact that your Royal Society for the
Advancement of Science granted him the Copley Medal frees me
200 SECTION— PHYSICS.
from the necessity of vindicating his claims to certain important dis-
coveries, the originality of which have been contested by one who,
from the perusal of Matteucci's writings, was imbued with the impulse
to prosecute those researches upon which was afterwards founded his
own fame. This is the galvanometer which he used in his principal
experiments, and by means of which he discovered the muscular
current, in the year 1844. It was rewarded by your Society with the
Copley Medal.
And under No. 1742^ of the Catalogue you will find another appa-
ratus sent by France, which Matteucci and Arago used in their
researches on the distribution of currents, inducted by magnetism in a
revolving disc of copper.
I have the good fortune to be able to place before you the spectro-
scope made by Professor Donati, an astronomer of Arcetri ; and it
was by means of this instrument that in 1870, on the occasion of the
total eclipse of the sun, he observed the luminous lines of hydrogen.
In the last years of his too short career he constructed a new spectro-
scope for solar analysis, composed of twenty-five prisms, some of
which were placed in the very tubes which have the fissure and the
lenses of the telescope.
Finally, allow me to place before you the galvanic chronographic in-
terrupter of Professor Felici, about which you have already heard
something in the conference held by my excellent colleague, Professor
Blaserna.
Before ending, allow me to express my regret at Italy being so
inadequately represented at this great exhibition. A country in which,
little more than ten years ago, youth was prohibited from tasting of
the fountains of science or reading the works of the greatest of its
citizens— of Dante, of Galileo — such a country is too new to compre-
hend suddenly the high importance of scientific rivalry, of these
Olympiads of science. And yet it might have sent various objects
of Galvani, Volta's piles, Brugnatelli's gilding, the electro-magnetic
movers of Dal Negro, Melloni's apparatus, Belli's electrostatic in-
duction machine, and many other ancient and modern instruments,
to compete for the prize of merit with those of more fortunate nations.
Florence alone, the birthplace of physical science, and which has
at all times cultivated it, has contributed largely with its treasures.
PRESIDENTS CLOSING REMARKS. 201
Let this be a proof of the existence of the spirit of science which
has at all times inspired it, and of the goodwill of the directing
Council of its Institution, which following in the wake of Galileo and
of the Accademia del Cimento, places its trust in science and progress
alone.
The PRESIDENT : In rising, as I now do, to offer our best thanks to
our foreign friends who have just given us this account of these remark-
able instruments, I wish to add, that it seems not without significance
or happiness of accident that the last contribution to this Physical
Section of the Conference should have been made by a foreigner. We
are indebted very materially to our foreign friends for the success
which, at all events up to this point, has attended this exhibition. We
are indebted in the first place to the Governments who have given an
impetus throughout all Europe to this undertaking. We are indebted
to the foreign Academies who have taken up the movement on the part
of the Governments ; we are indebted, further, to the curators and
the authorities connected with the museums who have so largely con-
tributed to our collection ; and we are indebted still further to the
individual men of science who have been permitted to transport the
collections of these instruments, and have put the crowning stroke
upon their efforts by giving us the favour and instruction of their pre-
sence here. While, however, I am speaking of foreigners (and I cannot
say too much on that score), we must not forget the efforts which have
been made, and which originated in this country. We are indebted in
the first place to the heads of the department under whose auspices
this exhibition has been brought together. We are indebted also to
the various men of science throughout the country who co-operated ;
but we must not forget those who have so largely contributed to re-
moving the preliminary difficulties. I mean those few energetic and
self-devoted individuals who have done perhaps more than any one
else to insure the success of the undertaking. Many names might be
mentioned, but I must not omit to name particularly Major Donelly,
Major Testing, and Mr. Lockyer. To-day is, I am sorry to say, the
last of the conferences in the Physical department, but I have no doubt
that the success which has attended our meetings in this department
will attend all the others to the close of the Conference. We have in
these meetings, and in the collection which is covered in this building,
202 SECTION— PHYSICS.
a fresh illustration of the very old saying, that science is of no time
and of no country. Science, it is true, is concerned with time and
space, but within the range of those quantities it admits of and it will
tolerate no distinctions. Science is the same whether it be pursued in
these pleasant climes of Europe, whether it be followed out in the
torrid zones of Central Airica, as Cameron and Livingstone and a host
of others have done ; whether it be studied in the deserts of Australia
or in the forests of New Guinea ; or whether it be followed out again
as it has been done by foreign countries over and over again, and is
now being by this country in the Arctic Expedition, of which we hope
soon to hear tidings. Science is the same through all time — from the
earliest dawn of intelligence, when the patriarchs went out to meditate
in the fields at eventide, or when they studied in their fashion the moon
and stars and the host of heaven. It is the same through all these
days of which we have records in this museum, and it will be the same,
I doubt not, until all feelings of wonderment and the like have been
not superseded, but swallowed up by perfect knowledge. I beg now to
congratulate the Section on the success which I have reason to hope
has attended it.
Mr. DE LA RUE : Our Chairman has very briefly gone over the
ground and described the commencement of this Exhibition, and also
the valuable co-operation of the scientific gentlemen who have joined
Yvdth the English philosophers in making these meetings interesting :
but not only was the Loan Exhibition a bold undertaking, but so much
of novelty attached to these Conferences that we were doubtful, even on
the first day, whether they would be successful. That they have been
eminently so is decided by the presence of so many ladies and gentle-
men at our meetings ; but the success does not come of itself. It re-
quired organization : it required a great deal of thought on the part of
those who took part in the management, and to no one are our thanks
more due than to Mr. Spottiswoode, who opened the seance. Throughout
the whole of our meetings he has been daily employed in grouping
subjects together, and in asking gentlemen to come forward to render
them not only interesting but instructive. I ask you, therefore, to
give your best thanks to the President of the Physical Section, Mr.
Spottiswoode.
CLOSE OF THE SECTION. 203
The PRESIDENT : I am much obliged to you for the vote of thanks
which you have given to me for the very small part which I have
taken. It has been a labour entirely of love, for the great readiness
with which the gentlemen who have made communications have fallen
in with such arrangements as I have thought it best to suggest
has been very pleasing, and has made the whole thing a very easy
business.
SECTION— MECHANICS (including Pure and Applied
Mathematics and Mechanical Drawing).
President: Mr. C. W. SIEMENS, D.C.L., F.R.S.
Vice-P residents :
Mr. F. J. BRAMWELL, F.R.S.
Mr. W. FROUDE, M.A., F.R.S.
M. le General MORIN, Directeur
du Conservatoire des Arts et
Dr. WERNER SIEMENS.
M. TRESCA, Sous-Directeur da
Conservatoire des Arts et
Metiers.
Sir JOSEPH WHITWORTH, Bart.,
D.C.L., F.R.S.
May ilth, 1876.
Metiers.
DR. C. W. SIEMENS' OPENING ADDRESS.
In opening the proceedings of the Conferences regarding me-
chanical science, it behoves me to draw attention to the lines of
demarcation which separate us from other branches of natural
science represented in this Exhibition.
In the department of applied science we have collected here
apparatus of vast historical interest, including the original steam
cylinder constructed by Papin in 1690, the earliest steam-engines by
Savery and by James Watt, the famous locomotive engine the
" Rocket," by which George Stephenson achieved his early triumphs,
as well as Bell's original marine engine, and a variety of models
illustrative of the progress of hydraulic engineering and of machinery
for the production of textile fabrics. In close proximity to these we
find a collection of models illustrative of the remarkable advance in
naval architecture which distinguishes the present day.
It would be impossible to deny the intrinsic interest attaching to
such a collection or its intimate connection with the progress of pure
science ; for how could science have progressed at the rate evidenced
DR. C. W. SIEMENS* ADDRESS. 205
in every branch of this Exhibition but for the great power given to
man through the mechanical inventions just referred to. Yet, were
mechanical science at these Conferences to be limited to the objects
exhibited in the South Gallery (and separated unfortunately from
apparatus representing physical science by lengthy corridors filled
with objects of natural history), we should hardly find material worthy
to occupy the time set apart for us. But, thanks to the progress of
opinion in recent days, the barrier between pure and applied science
may be considered as having no longer any existence in fact. We see
around us practitioners, to whom seats of honour in the great
academies and associations for the advancement of pure science are
not withheld, and men who, having commenced with the cultivation of
pure science, think it no longer a degradation to follow up its applica-
tion to useful ends.
The geographical separation between applied science and physical
science just referred to, must therefore be regarded only as accidental,
and the subjects to be discussed in our section comprise a large pro-
portion of the objects to be found within the rooms assigned more
particularly to physics and chemistry. Thus, all measuring instru-
ments, geometric and kinematic apparatus, have been specially
included within our range, and other objects such as telegraphic
instruments, belong naturally to our domain.
With these accessions, mechanical science represents a vast field
for discussion at these Conferences, a field so vast indeed that it would
have been impossible to discuss separately the merits of even the
more remarkable of the exhibits belonging to it. It was necessary
to combine exhibits of similar nature into subdivisions, and the Com-
mittee have asked gentlemen eminently acquainted with these branches
to address you upon them in a comprehensive manner.
Thus they have secured the co-operation of Mr. Barnaby, the
Director of Construction of the Navy, to address you on the subject
of Naval Architecture, and of Mr. Froude to enlarge upon the subject
of fluid resistance, upon which he has such an undoubted right to
speak authoritatively, Mr. Thomas Stevenson, the Engineer of the
Northern Lighthouses, will describe the modern arrangements of
Dioptric lights, which mark a great progress in the art of lighting up
our coasts. Mr. Bramwell has undertaken the important task of
206 SECTION— MECHANICS.
addressing you on the subject of Prime Movers, and Professor
Kennedy upon the kinematic apparatus forwarded by Professor
Reuleaux, of Berlin. M. Tresca will bring before us his interesting
subject, the flow of solids. Mr. William Hackney will address you
upon the application of heat to furnaces, for which he is well qualified
both by his theoretical and practical knowledge. Mr. R. S. Culley,
Chief Engineer of the Postal Telegraphs, will refer you to a most
complete and interesting historical collection of instruments, revealing
the rapid and surprising growth of the electric telegraph.
Measurement. — Regarding the question of measurement, this con-
stitutes perhaps the largest and most varied subject in connection
with the present Loan Exhibition. In mechanical science, accurate
measurement is of such obvious importance, that no argument is
needed to recommend the subject to your careful consideration. But it is
not perhaps so generally admitted, that accurate measurement occupies
a very important position with regard to science itself, and that many
of the most brilliant discoveries may be traced back to the mechanical
art of measuring. In support of this view I may here quote some
pregnant remarks made by Sir William Thomson in his inaugural
address, delivered in 1871 to the members of the British Association,
in which he says, " Accurate and minute measurement seems to the
non-scientific imagination, a less lofty and dignified work than looking
for something new. But nearly all the grandest discoveries of science
have been but the rewards of accurate measurement and patient long-
continued labour in the minute sifting of numerical results. The
popular idea of Newton's grand discovery is that the theory of
gravitation flashed upon his mind, and so the discovery was made.
It was by a long train of mathemetical calculation, founded on results
accumulated through prodigious toil of practical astronomers that
Newton first demonstrated the forces urging the planets towards the
sun, determined the magnitude of those forces, and discovered that a
force following the same law of variation with distance, urges the nx)on
towards the earth. Then first, we may suppose, came to him the idea
of the universality of gravitation j but when he attempted to compare
the magnitude of the force on the moon with the magnitude of the
force of gravitation of a heavy body of equal mass at the earth's sur-
face, he did not find the agreement which the law he was discovering
DR. C. W. SIEMENS' ADDRESS. 207
required. Not for years after would he publish his discovery as made.
It is recounted that, being present at a meeting of the Royal Society,
he heard a paper read, describing geodesic measurement by Picard,
which led to a serious correction of the previously accepted estimate of
the earth's radius. This was what Newton required ; he went home
with the result, and commenced his calculations, but felt so much
agitated, that he handed over the arithmetical work to a friend ; then
(and not when sitting in a garden he saw an apple fall) did he ascertain
that gravitation keeps the moon in her orbit.
" Faraday's discovery of specific inductive capacity, which inaugu-
rated the new philosophy, tending to discard action at a distance, was
the result of minute and accurate measurement of electric forces.
" Joule's discovery of thermo-dynamic law, through the regions of
electro-chemistry, electro-magnetism, and elasticity of gases, was based
on a delicacy of thermometry which seemed impossible to some of
the most distinguished chemists of the day.
" Andrews' discovery of the continuity between the gaseous and
liquid states was worked out by many years of laborious and minute
measurement of phenomena scarcely sensible to the naked eye."
Here, then, we have a very full recognition of the importance of
accurate measurement, by one who has a perfect right to speak
authoritatively on such a subject. It may indeed be maintained that
no accurate knowledge of any thing or any law in nature is possible,
unless we possess a faculty of referring our results to some unit of
measure, and that it might truly be said — to know is to measure.
To resort to a homely illustration of this proposition, let us suppose
a traveller in the unknown wilds of the interior of Africa, observing
before him a number of elevations of the ground, not differing
materially from one another in apparent magnitude. Without
measuring apparatus the traveller could form no conclusion regarding
the geographical importance of those visible objects, which might be
mere hillocks at a moderate distance, or the domes of an elevated
mountain range. In stepping his base line, however, and mounting
his distance-measurer he soon ascertains his distances, and observations
with the sextant and compass give the angles of elevation and
position of the objects. He now knows that a mighty mountain
chain stands before him, which must determine the direction of
2o8 SECTION— MECHANICS.
the watercourses and important climatic results. In short, through
measurement he has achieved perhaps an important addition to our
geographical knowledge. As regards modern astronomy, this may
almost be defined as the art of measuring very distant objects, and
this art has progressed proportionately with the perfection attained in
the telescopes and recording instruments employed in its pursuit.
By the ancients the art of measuring length and volume was tolerably
-well understood,hence their relatively extraordinary advance in architec-
ture and the plastic arts. We hear also of powerful mechanical contri-
vances which Archimedes employed for lifting and hurling heavy
masses; and the books of Euclid constitute a lasting proof of their
powers of grappling with the laws regulating the proportion of plane and
linear measurement. But with all the mental and mechanical power dis-
played in those works, it would seem strange that no attempt should
have been made on the part of the ancients to utilise those subtle
forces in nature, heat and electricity, by which modern civilisation has
been distinguished, were it not for their want of means of measuring
these forces.
Hero, of Alexandria, tells us that the power of steam was known to
the Egyptians, and was employed by their priesthood to work such
pretended miracles as that of the spontaneous opening of the doors
of the temple whenever the burnt offering was accepted by the gods,
or, as we moderns would put it, whenever the heat generated by com-
bustion was sufficient to produce steam in the hollow body of the
altar, and thus force water into buckets whose increasing weight, in
descending, caused the gates in question to open.
Unfortunately for them, the Academia de Cimento of Florence had
not yet presented the world with the thermometer, nor had Toricelli
shown how to measure elastic pressures, or there would, at any rate,
have been a probability of those clear-headed ancients applying the
power of steam for preparing and transporting the materials which
they used in the erection of their stupendous monuments, and for
raising and directing the water used in their elaborate works of
irrigation.
The Art of Measuring may be divided into the folowing principal
groups : —
ist. That of linear measurement, the measurement of area within
DR. C. W. SIEMENS' ADDRESS. 209
a plane, and of plane angles ; comprising geometry, trigonometry,
surveying, and the construction of linear measures, distance meters,
sextants and planimeters, of which a great variety will be found
within this building.
The subject of linear measurement will, I am happy to state, be
brought before you by one whose name will ever be remembered as
the introducer into applied mechanics of the absolute plane, and of
accurate measure, I mean Sir Joseph Whitworth. It is to be re-
gretted, I consider, that Sir Joseph Whitworth adopted as the unit of
measure, the decimalized inch, instead of employing the centimetre,
and I hope that he will see reason to adapt his admirable system of
gauges, also to metrical measure, which, notwithstanding any objec-
tions that could be raised against it on theoretical grounds — that,
namely, of not representing accurately the ten millionth part of the
distance from one of the earth's poles to its equator — is, nevertheless,
the only measure that has been thoroughly decimalized, and which
establishes a simple relationship between measures of length, of area
and of capacity. It possesses, moreover, the great practical advantage of
having been adopted by nearly all the civilized nations of Europe,
and by scientific workers throughout the world. Sir Joseph Whit-
worth's gauges, based upon the decimalized inch, are calculated to
maintain their position for many years, owing to the intrinsic mechan-
ical perfection which they represent, but the boon conferred by their
author would be still greater than it is, if, by adopting the metre he
would remove the last and only serious impediment in the way of the
unification of linear measurement throughout the world. A discussion
will probably arise regarding the relative merits of measurement a but,
of which Sir Joseph Whitworth is the representative, and of measure-
ment a trait, which is the older method, but is still maintained by the
Standard Commissioners, both in this country and in France.
The second group includes the measure of volume or the cubical
contents of solids, liquids, and gases, comprising stereometric methods
of measurement, the standard measures for liquids, and the apparatus
for measuring liquid and gaseous bodies flowing through pipes, such
as gas meters, water meters, spirit meters, of which, likewise, a great
variety, of ancient and modern date, will meet your eye, and upon
which Mr. Merrifield will address you.
210 SECTION— MECHANICS.
Another method of measuring matter is by its attraction towards
the earth, or, thirdly, the measurement of weight, represented by a
great variety of balances of ancient and modern construction. These
may be divided into beam weighing machines, which appears to be at
the same time the most ancient and the most accurate, into spring
balances and torsion balances. The accuracy obtained in 'weighing
is truly surprising, when we see that a mass of one ten-millionth part
of a gramme suffices to turn the scale of a well-constructed chemical
balance. Perfect weighing, however, could only be accomplished in a
vacuum, and, in accurate weighing, allowance has to be made for the
weight of air displaced by the object under consideration. The general
result is that the mass of light substances is really greater than their
nominal weight implies, and this difference between true and nominal
weight must vary sensibly with varying atmospheric density.
Weighing in a denser medium than atmospheric air, namely, in
water, leads us, fourthly, to the measurement of specific gravity, which
was originated by Archimedes when he determined the composition
of King Hiero's crown by weighing it in water and in air.
Among measures of weight may be noted a balance, which weighs
to the five-millionth part of the body weighed, sent by Beckers Sons,
of Rotterdam ; another from Brussels, weighing to within a fourteenth-
millionth part of the weight, in weighing small quantities ; a balance
formerly used by Dr. Priestly ; and Professor Hennessy's standards,
derived from the earth's polar axis, as Common to all terrestrial
meridians.
Next comes, fifthly, the Measurement of Time, which, although of
ancient conception, has been reduced to mathematical precision only
in modern times. This has taken place through the discovery, by
Galileo, of the pendulum, and its application, by Huygens, to time-
pieces in the i7th century. The most interesting exhibits in this
branch of measurement are, from an historical point of view, the
Italian, German, and English clocks of the iyth century; the time-
keeper which was twice carried out by Captain Cook, first in 1776
and which, after passing through a number of hands, was brought
back to this country in 1843 ; and an ancient striking clock, supposed
to have been made in 1348 — it has the verge escapement, which is
said to have been in use before the pendulum. The methods em-
DR. C. W. SIEMENS* ADDRESS. 211
ployed in modern clocks and watches for compensating for variation
of the thermometer and barometer, are illustrated by numerous
exhibits, notably the astronomical clock, with Sir George Airy's
compensation, which will form the subject of a special demonstration
by Messrs. Dent and Co.
The measurement of small increments of time has been rendered
possible only in our own days by the introduction of the conical
pendulum, and other apparatus of uniform rotation, which alone
convey to our minds the true conception of the continuity of time.
Among the exhibits belonging to this class must be mentioned Sir
Charles Wheatstone's rotating mirror, moved by a constant falling
weight, by which he made his early determination of the velocity of
electricity through metallic conductors ; the rotative cylindrical
mirror, marked by successive electrical discharges, which was em-
ployed by Dr. Werner Siemens in 1846, to measure the velocity of
projectiles, and has been lately applied by him for the measurement
of the velocity of the electric current itself, and the chronometric
governor, introduced by him in conjunction with myself, for regu-
lating chronographs, as also the velocity of steam engines under their
varying loads ; Foucault's governor, and a considerable variety
involving similar principles of action.
Another entity which presents itself for measurement is, sixthly,
that of Velocity, or distance traversed in a unit of time, which may
either be uniform or one influenced by a continuance of the cause of
motion, resulting in acceleration, subject to laws and measurements
applicable both in relation to celestial and terrestrial bodies. I may
here mention the instruments latterly devised for measuring the
acceleration of a cannon ball before and after leaving the mouth of
the gun, of which an early example has been placed within these
galleries. Other measurers of velocity are to be found here, ships'
logs, current meters, and anemometers.
In combining the ideas of weight or pressure with space, we arrive
at, seventhly, the conception of work, the unit of which is the foot-
pound or kilogrammetre, and which, when combined with time, leads
us to the further conception of the performance of duty, the horse-
power, as denned by Watt. The machines for the measurement of
work, here exhibited, are not numerous, but are interesting. Among
212 SECTION— MECHANICS.
these may be mentioned Professor Colladon's dynamometrical
apparatus, constructed in 1844; Richard's patent steam engine
indicator, an improvement on Watt's, and Mr. G. A. Hirn's flexion
and torsion pandynamometers.
Eighth. — The measurement of Electrical 'Units— of electrical capacity
of potential — and resistance, forms a subject of vast research, and
of practical importance, such as few men are capable of doing justice
to. It may be questioned, indeed, whether Electrical Measurement
belongs to the province of mechanical science, involving, as it does
problems in physical science of the highest order ; but it may be con-
tended on the other hand, that at least one branch of Applied Science,
that of Telegraphy, could not be carried on without its aid. I am happy
to say that this branch of the general subject will be brought before
you by my esteemed friend Sir William Thomson, than whom there is
no one more eminently qualified to deal with it. I may, therefore, pass
on to the next great branch of our general subject, the ninth : Thermal
Measurement. — The principal instrument here employed is the ther-
mometer, based in its construction, either upon the difference of expan-
sion between two solids, or on the expansion of fluids such as mercury
or alcohol — (the common thermometer) or upon gaseous expansion (the
air thermometer) ; or again, it may be based upon certain changes of
electrical resistance, which solids and liquids experience when sub-
jected to various intensities of heat. With reference to these, the air
thermometer represents most completely the molecular action of matter
which is the equivalent of the expansibility. I shall not speak of the
different scales that have been adopted by Rdaumur, Celsuis and
Fahrenheit, which are based upon no natural laws or zero points in
nature, and which are therefore equally objectionable upon theoretical
grounds. Would it not be possible to substitute for these a natural
thermometric scale ? One commencing from the absolute zero, of the
possible existence of which we have many irrefutable proofs, although
we may never be able to reach it by actual experiment. A scale com-
mencing in numeration from this hypothetical point would possess the
advantage of being in unison throughout with the physical effects due
to the nominal degree, and would aid us in appreciating correctly the
relative dynamical value of any two degrees of heat which could be
named. Such a scale would also fall in with the readings of an elec-
DR. C. W. SIEMENS' ADDRESS. 213
trical resistance thermometer or pyrometer, of which a specimen has
been added to this collection by myself.
When temperature or intensity of heat is coupled with mass, we
obtain the conception of quantity of heat, and if this again is referred
to a standard material, usually water, the unit weight of each being
taken, we obtain what is known as specific heat. The standard to
which measurements of quantity of heat are usually referred is the heat
required to raise a pound of water one degree fahrenheit, or the cubic
•centimetre of water one degree centigrade.
The most interesting exhibits in this branch of measurement, are,
from an historical point of view, the original spirit thermometer of the
Florentine Academia del Cimento, and the photographs of old ther-
mometers ; the original Lavoisier Calorimeter for measuring the heat
disengaged in combustion, Wedgwood's and Daniell's Pyrometers.
As illustrating modern improvement, may be instanced a long brass-
cased thermometer showing the variation in the readings, when the
bulb and when the whole thermometer is immersed ; a thermometer
with flat bulb to improve sensitiveness ; a thermo-electric alarum, for
giving notice when a given temperature is reached ; an instrument for
measuring the temperature of fusion by means of electric contact
invented by Professor Himly ; Dr. Andrews' apparatus for measuring
the quantity of heat disengaged in combustion ; Dr Guthrie's diacalo-
rimeter for measuring the conductivity of liquids for heat, and a ther-
mometric tube by Professor Wartmann for determining the calorific
capacities of different liquids by the process of cooling.
Finally, Joule has taught us how to measure the unit of heat dyna-
mically, and the interesting apparatus employed by him from time to
time in the various stages of the determination of this most important
constant in applied mechanics, are to be found, rightly placed, not
iimong thermometers, and other instruments placed in the physical
sections, but among the instruments required in the determination of
three great natural standards— of length, time, and mass, and their
combinations.
Another branch of the general subject is the Measurement of Light,
which may be divided into two principal sections, that including the
measurement of the wave-length of light, of different colours, and the
angle of polarization, which belongs purely and entirely to physical
214 SECTION— MECHANICS.
science ; and the measurement of the intensity of light by photo-
metry, which, while involving also physical problems of the highest
order, has an important bearing also upon applied science. The
principal methods that have been hitherto employed in photometry
are by the comparison of shadows, that of Rumford and Bouguer ; by
employing a screen of paper with a grease-spot, the lights to be com-
pared being so adjusted that the spot does not differ in appearance
from the rest of the paper, Bunsen's method ; Elster's, by determining
in combustion the amount of carbon contained in a given volume of a
gas ; and the one lately introduced by Professor Adams and Dr.
Werner Siemens, by measuring the variation in the electrical resistance
of selenium, under varying intensities of light.
Before concluding, I wish to call your attention to two measuring instru-
ments which do not fall within the range of any of the divisions before
indicated. The first is an apparatus designed chiefly by my brother,
Dr. Werner Siemens, by which a stream composed of alcohol and
water, mixed in any proportion, is measured in such a manner that
one train of counter wheels records the volume of the mixed liquid ;
whilst a second counter gives a true record of the amount of absolute
alcohol contained in it. The principle upon which this measuring
apparatus acts may be shortly described thus : — The volume of liquid
is passed through a revolving drum, divided into three compartments
by radial divisions, and not dissimilar in appearance to an ordinary
wet gas-meter ; the revolutions of this drum produce the record of
the total volume of passing liquid. The liquid on its way to the
measuring drum passes through a receiver containing a float of thin
metal filled with proof spirit, which float is partially supported by
means of a carefully-adjusted spring, and its position determines that
of a lever, the angular position of which causes the alcohol counter to
rotate more or less for every revolution of the measuring drum. Thus,
if water only passes through the apparatus, the lever in question
stands at its lowest position, when the rotative motion of the drum
will not be communicated to the alcohol counter, but in proportion as
the lever ascends a greater proportion of the motion of the drum will
be communicated to the alcohol counter, and this motion is rendered
strictly proportionate to the alcohol contained in the liquid, allowance
being made in the instrument for the change of volume due to
DR. C. IV. SIEMENS' ADDRESS. 215
chemical affinity between the two liquids. Several thousand instru-
ments of this description are employed by the Russian Government
in controlling the production of spirits in. that empire, whereby a
large staff of officials is saved, and a perfectly just and technically
unobjectionable method is established for levying the excise dues.
Another instrument, not belonging to any of the classes enume-
rated, is one for measuring the depth of the sea without asounding
line, which has recently been designed by me, and described in a
paper communicated to the Royal Society. Advantage is taken in the
construction of this instrument, of certain variations in the total
attraction of the earth, which must be attributable to a depth of
water intervening between the instrument and the solid constituents
of the earth. It can be proved mathematically that the total gravita-
tion of the earth diminishes proportionately with the depth of water,
and that if an instrument could be devised to indicate such minute
changes in the total attraction upon a scale, the equal divisions on
that scale would represent equal units of depth.
Gravitation is represented in this instrument by a column of mercury
resting upon a corrugated diaphragm of thin steel plate, which in its
turn is supported by the elastic force of carefully tempered springs
representing a force independent of gravitation. Any change in the
force of gravitation must affect the position of this diaphragm and the
upper level of the mercury, which causes an air-bubble to travel in a
convolute horizontal tube of glass placed upon a graduated scale, the
divisions of which are made to signify fathoms of depth. Special
arrangements were necessary in order to make this instrument
parathermal, or independent of change of temperature, as also
independent of atmospheric density, which need not be here de-
scribed. Suffice it to say that the instrument, which has been placed
on board the S. S. "Faraday" during several of her trips across the
Atlantic, has given evidence of a remarkable accordance in its indica-
tions with measurements taken by means of Sir William Thomson's
excellent pianoforte wire-sounding machine ; and we confidently
expect that it will prove a useful instrument for warning mariners of
the approach of danger, and for determining their position on seas,
the soundings of which are known.
Another variety of this instrument is the horizontal attraction
2 1 6 SECTION— ME CHANICS.
meter, by which it will be possible to obtain continuous records of
the diurnal changes in the attraction of the sun and moon as in-
fluencing the tides. This instrument belongs, however, rather to the
domain of physics than to that of mechanical science.
These general remarks upon the subject of measurement may suffice
to call your attention to its importance, several branches of which, those
of Linear, C^lbical, and Electrical Measurement, will now be dealt with.
The discussions which will follow these addresses will be carried on
under circumstances such as have never before co-operated, namely,
the presence of leading men of science of all civilised nations, who
will take part in them, and the easy reference which can be had to
the most comprehensive collection of models of scientific apparatus —
both of modern and ancient— which has ever been brought together.
Mr. BRAMWELL, C.E. : I think it is our duty to move a vote of
thanks to Dr. Siemens, our President, for his interesting and valuable
address to our conference to-day. He has foreshadowed a large
amount of work, which I hope will be faithfully fulfilled, and if so I
am sure these meetings will be most useful to mechanical science.
Sir JOSEPH WHITWOE^TH : I shall be most happy to second that.
The motion was carried unanimously.
The PRESIDENT : I thank you very much for your expression of
approval with regard to the address that I have just delivered. I
found the subject was a very vast one, and that it was impossible to
do full justice to it, but I hope that this address may be followed now
by communications of a more specific kind, which will be both
interesting and useful. I will now call on Sir Joseph Whitworth to
read his communication
ON LINEAR MEASUREMENT.
Sir JOSEPH WHITWORTH : The two great elements in mechanics
are the power of measurement and the true plane. The measuring
machines which I have constructed are based upon the production of
the true plane.
Measures of length are obtained either by line or end-measurement.
The English standard yard is represented by two lines drawn across
two gold studs sunk in a bronze bar about 38 inches long, the
temperature being at 62° fah.
LINEAR MEASUREMENT. 217
There is an insurmountable difficulty in converting line-measure to
end-measure, and therefore it is most desirable for all standards of
linear-measure to be end-measure.
Line-measure depends on sight aided by magnifying glasses ; but
the accuracy of end-measure is due to the sense of touch, and the
delicacy of that sense is indicated by means of a mechanical
multiplier.
In the case of the workshop measuring machine, the divisions on
the micrometer wheel represent ten-thousandths of an inch. The
screw has twenty threads to an inch, and the wheel is divided into
500, which multiplied by twenty gives for each division the ten-
thousandth of an inch.
We find in practice that the movement of the fourth part of a divi-
sion, being the forty-thousandth of an inch, is distinctly felt and gauged.
In the case of the millionth machine, we introduce a feeling-piece
between one end of the bar to be measured and one end of the
machine, and the movement of the micrometer wheel through one
division, which is the millionth of an inch, is sufficient to cause the
feeling-piece to be suspended or to fall by its gravity.
The screw in the machine has twenty threads, which number multiplied
by 200— the number of teeth in the screw wheel — gives for one turn of
the micrometer wheel the four-thousandth of an inch, which multiplied by
250— the number of divisions on the micrometer wheel — gives for each
division one-millionth of an inch. The sides of this feeling-piece are
true planes parallel to each other, and the ends both of the bars and
the machine are true planes parallel to each other, and at right angles
to the axis of the bar ; thus four true planes act in concert. In
practice we find that the temperature of the body exercises an
important influence when dealing with such minute differences, and,
practically, it is impossible to handle the pieces of metal without
raising the temperature beyond 62°. I am of opinion that the
proper temperature should be approaching that of the human body,
and I propose that S$Q fahr. should be adopted, and that the
standards and measuring appliances should be made and kept in a
room at a uniform temperature of 85° fahr.
In many workshops we hear the workmen speak in such vague
terms as a bare sixteenth or full thirty-second, but minute and
218 SECTION— MECHANICS.
accurate measurement requires to be expressed in decimals of an inch.
In 1857, when President of the Institution of Mechanical Engineers,
I read a paper on standard decimal measures of length, and I am
happy to say that since that period the decimal system has been
introduced to a certain extent in many engineers' works, but it is still
far from being universal.
In the manufacture of our standard gauges, the workmen measure
to the one twenty-thousandth of an inch, and these measures are as
familiar and appreciable as those of larger dimensions.
As an illustration of the importance of very small differences of
size, I have here cylindrical standards with a difference of the ten-
thousandth of an inch. It is therefore obvious that a difference of
one ten-thousandth of an inch is an appreciable and important
quantity.
It will be at once conceded that the only scale of measurement
which can be used for such small differences must be a decimal one.
For many years the decimal system has been in use at our works,
taking the inch as the unit, and the workmen think and speak in
tenths, hundredths, and thousandths of an inch.
It is of great importance to the manufacturer to have the means of
referring to an accurate fixed measure, as it will enable him, at any
time, to reproduce a facsimile of what he has once made, and so
preserve a system of sizes of the fitting parts unaltered.
The great value of the workshop measuring machine is making
difference gauges.
Every external diameter having to work in an internal diameter
should have a certain difference of size ; and close observation and
experience can alone determine what this difference of size ought
to be.
Take, for instance, a railway axle ; if the bearing in which it has to
work be too small the heating of the axle by rapid rotation will be the
consequence ; if, on the other hand, the bearing be too large, it will be
sooner worn out.
It is therefore most important when rapid revolutions and great
strains have to be undergone, that the proper difference of size, when
once ascertained by experience, should be strictly adhered to.
In the manufacture of axles there should be two gauges used, the
LINEAR MEASUREMENT. 219
axle being made to the standard gauge, and the bearing bored out to
fit a different gauge, which has to be as much larger as experience
has found to be necessary, according to the conditions under which
the axle has to work. Hence every manufacturer should be in a
position to manufacture his own difference gauges.
Fifty years ago the thousands of spindles in a cotton factory had
each to be separately fitted into the bolster in which it had to work.
At the present time all these spindles are made to gauge, and are
interchangeable.
It cannot be impressed too forcibly, both upon the student in
mechanics and upon the workman, that accuracy of measurement is
essential for good and efficient workmanship and that it tends to
economy in all branches of manufacture, so as to have the parts inter-
changeable.
I will now endeavour to explain two or three things which I have on
the table. I have said that the measuring machines are based on the
production of a true plane. I have here a true plane of ten inches
square. I will not go into the method by which these true planes
were produced, which would take too long, but I may mention that in
getting one true plane we have to get three, because if we had only
two, one might be a little concave and the other a little convex, and
still they might be made to fit, but if the third will fit the two, it must
be a true plane. You will see that when I put this plane down on the
other, they do not touch each other, but float on the air between them
for a short time ; and if I let one fall upon the other, you perceive the
metals do not come in contact — there is a muffled sound. The plane
is equally true when it is suspended as when it is supported. It is
suspended by three points, and we also now lift them from those three
points, so that when applied to a piece of work it remains true.
I will now refer to the workshop measuring machine. The divisions
on the micrometer wheel represent ten-thousandths of an inch — that is
if you move this wheel one division, the end of the machine is moved
forwards one ten-thousandth of an inch. We find in practice that the
movement of a fourth part of a division, being one forty-thousandth
of an inch, is distinctly felt and gauged. I have here a small gauge
one-fourth of an inch in diameter, and on setting this wheel to zero, I
then regulate the machine with the small wheel at the other end, so
220 SECTION— MECHANICS.
that I can just feel this gauge go through. Now, if I move this wheel
half a division, the gauge will not pass through. We get thus half a
•division, which would be one twenty-thousandth of an inch. No one
would believe that so small a difference would produce such an effect
as that. When everything is in nice order I can feel perfectly well
the fifty-thousandth of an inch. In the case of the millionth machine
we introduce a feeling-piece between one end of the bar to be
measured, and one end of the machine, and the movement of the
micrometer wheel through one division, which is the one-millionth, is
sufficient to cause the feeling-piece to be suspended or to fall by its
own gravity. This is a standard inch to be measured. We bring the
inch bar up to one end, and introduce the feeling-piece. When the
machine is adjusted, we find that moving the end one-millionth of an
inch is sufficient to cause that feeling-piece to be suspended or to fall.
As an illustration of the importance of very small differences of size,
I have here cylindrical standards with the difference of ten-thousandths
of an inch. This is a standard inch measure, and this is the cor-
responding one — internal gauge. You see that it is what we call a nice
fit. These gauges are made of steel and case-hardened, so that they
will last a longtime, and nothing will cut the surface except a diamond
or the grinding process by which they are made. This other gauge is
one ten-thousandth part of an inch less, and you see the difference
which it makes. The internal gauge slides down of its own gravity,
and it is therefore obvious that the difference of a ten-thousandth part
of an inch is an appreciable and important quantity. I have said that
the great value of the workshop measuring machine is making
difference gauges. These are a set of gauges which I made for
Lord Hardinge in 1855 for the improvement of the Enfield rifle.
The size is -577. Each of these gauges are one five-thousandth
of an inch less than the other, and you see how much more loosely
one fits than the other. The value of these difference gauges is this :
If you tell a man to bore a barrel to that size he is sure to make it
wrong, he will get it too large ; but if you give him this set of
difference gauges he gets the bore first of all to the one-thousandth of
an inch less than the standard, and then feels his way up to the
standard. In making rifles we never made any allowance. We gave
the men these difference gauges, and every barrel was made the same,
LINEAR MEASUREMENT. 221
so that all shot alike. There was no high gauge and low gauge as it
is termed at Enfield. By the use of these difference gauges we were
able to work up to a certain point, and they were all made alike.
Then I have said that every external diameter having to work in an
internal diameter should have a certain difference of size, and close
observation and experience can alone determine what this difference
of size ought to be. I may mention that in making these cylindrical
gauges we do not go below one-tenth of an inch, and when we want a
gauge less than that we make this class of gauge — flat gauges ; they
are made with a tolerably good surface on each side, of steel and
tempered, and they last pretty well. This is one-hundredth of an
inch, and we can easily make this from the measuring machine. The
largest of these gauges is one-tenth and the smallest is one-hundredth,
and there are regular differences of sizes between. They serve the
purpose of wire gauges. It is very important when you get so smalt
a size that it should represent accurately what it professes to be.
This is a little apparatus by which it is demonstrable that we can
make the ends of this bar at right angles. It was once objected
that we could not make the end of the bar at right angles to the faces.
It is done by placing the standard in a solid block, with a V shaped
channel to receive it, and the end of the standard and of the block is
made a trueplane. The standard is then turned round in its resting place,
and again tried with the true plane. If it is not true it is again faced
up until it becomes so, and when it corresponds to the true plane in
each of the four positions it is evident that the end is at right angles
to the four sides. This is a rod which is another application showing
the sense of touch. It was made for ascertaining after a gun had
been proved or fired a certain number of times whether there was any
appreciable wear or whether one part expanded more than another.
At one end there is an inclined plane, which moves out three little
feeling-pieces. The bar is introduced into the bore of the gun and is
moved endways, and there is no difficulty at all in feeling the ten-
thousandth part of an inch. There is a little roller fixed on the
muzzle of the gun on which it works, and the attendant can feel quite
easily a difference of the ten-thousandth part of an inch.
M. TRESCA recognised the fact, that, in the actual state of things,
the exactness of one-millionth of an inch is the utmost limit which it is
222 SECTION— MECHANICS.
possible to appreciate : and that Sir J. Whitworth's process is the only
one which allows of this appreciation of small quantities.
In the proceedings which are being carried on by the members of the
International Commission on the Metre, it will be as much as they can
<io if they succeed in appreciating, by the most delicate optical means,
a quantity four times as great, viz., the ten-thousandth part of a milli-
metre (miilimetre=*o3,937 inch).
Sir J. Whitworth's process is then the most exact which is as yet
known, and whenever short distances are concerned, it can be adopted
with perfect security.
The " Metre " Commission has nevertheless adopted the " metre a
traits " as being more easily comparable. In it the true length is in
reality merely defined by the medium of the thickness of a line, which
is not to be less tha five-thousandths of a millimetre in breadth.
The fact is, that for long distances, the direct measurement between
two trials (touches) is much less precise, unless recourse is had to a
complemental standard of the same perfection as those of Sir J.
Whitworth ; but then the true measurement is further complicated by
two contacts, and it is absolutely necessary, in measures of precision,
to take particular precautions with regard to all that concerns the
influence of the temperature and of flexion.
In order to satisfy these two conditions in the best way possible, a
proposal of mine has recently been adopted. It consists of a form of
set section ruler having the shape of an X, in which the neutral fibre is
apparent. As the international metres must be "mesures a traits,"
recourse will exclusively be had to optical processes, in order to
compare them ; proceedings which alone can guard against contacts
and the wear of the faces, which might result rom frequent use.
We could not, however, in any case, hops to reach the degree of
exactness attained by Sir J. Whitworth's English inch standard, which
he has made with so much care and trouble, and which must be
considered, until the definitive adoption of the metrical system, as
the type of the most perfect precision, which mechanical means permit
of attaining.
Mr. CHISHOLM : The question whether a measure of length was
best defined by the whole length of a bar, or oy the distance between
two points or lines marked upon it, was carefully considered by the
LINEAR MEASUREMENT. 223
Standards Commission for restoring the British Standards destroyed
in 1834.
The ancient standards of length, the yard of Henry VII. and the
yard of Queen Elizabeth, were both end-standards.
The Parliamentary standard yard, legalised in 1824, and destroyed
in 1834, was defined by two dots marked on a brass bar.
The ancient Prussian standard of length was a line-standard, but in
1838 there was substituted for it an end-standard, constructed by
Bessel. He gave as his reasons —
1. That if a flexible bar be supported on two points, the extreme
length of the bar from the centre of one end to the centre of the other
end is not sensibly altered by its flexure, whilst the distance between
two points or lines upon the upper surface may be sensibly altered.
2. That the principle of end-measure is more convenient than that
of line-measure for the production of copies, in other words, for
comparisons.
As to the first of these points, the Standards Commission remarked
in their report, that Bessel himself admitted this objection would be
removed if the lines were engraved on surfaces depressed to the middle
of the thickness of the bar. And they stated, moreover, that the ten-
dency to an alteration of the apparent length, either at the surface or
mid-depth of the bar, might be obviated by proper adjustment of the
points of support, and still more surely by supporting the bars at
numerous points on lever frames, with equal supporting forces at all
the points, or by floating the bar in quicksilver.
As to the second point, the Commission considered that line-
measures had been invariably adopted for measuring British geodetic
bases ; and their use led the Commission to form a high estimate of
the convenience of the line principle, and to consider that a standard
which was intended to apply to them should be constructed on the
same principle. They considered, also, that the construction of defining
lines on a standard bar was more simple and easy than that of defining
ends ; and that the tendency of an end-standard to an alteration of
length was by wear in only one direction, whilst a line-standard was
practically invariable.
The end-standards are connected with spherical ends, the radius oi
the spherical curve being half the length of the bar.
224 SECTION—MECHANICS.
That although a single comparison by end-measure was, perhaps,
more accurate than a single comparison by line-measure, yet there was
no doubt that by repeating the comparisons, unexceptionable accuracy
might be given to observations of line measures.
Upon full consideration, the Commission unanimously preferred to
adopt a line-measure for the new standard of length, the defining line
to be marked at the mid-depth of the bar. ^ <H**U\*v(^ <*«J*s)
Specimens of both the line-standard and end-standard yards, con-
structed under the superintendance of the Standards Commission, and
of the lever-supports, are now exhibited.
The same question was also fully considered by the International
Metric Commission at Paris, and a similar conclusion was arrived at
for the construction of the international standard metres.
There can be no question of the advantages of the form of end-
measures, adopted by Sir Joseph Whitworth, with the defining ends
constructed as true planes normal to the measuring axis; and more
particularly to his application of the principle to guages, to which,
indeed, the principle of line-measure is clearly inapplicable. But this
mode of application of the principle of end-measure is no.t so well
adapted to a standard unit of length, such as our standard yard, from
which secondary standards of multiples and parts of this unit are to be
derived. If a measure of length, whether an end-standard or a line-
standard, is to be subdivided into parts, these parts can only be marked
upon it by defining lines.
f There are now in existence no less than ten standard Egyptian
/ measures of the home of the Pharaohs. These are standard cubits,
\ end measures, divided by lines into palms and digits. A model of the-
\ Jbest specimen of these ancient standard cubits~is~now exhibited.
It appears to me, however, that one great practical objection to an
end-measure, as used by Sir Joseph Whitworth, with a contact or
feeling apparatus, consists in alterations of its length by variations of
temperature, and in the difficulty, if not impossibility, of determining
the extent of this influence. In comparisons made with a micrometer
microscope, on the other hand, whether of line-measures or of end-
measures, the actual temperature of the measuring axis of the bar may
be maintained nearly constant, and may be ascertained, and allowance
made for its effect. There is really no practical difficulty in the accurate
LINEAR MEASUREMENT.
225
comparison of line-measures with end-measures, and could easily be
shown if time allowed.
It is also of the utmost importance to determine with precision the
rate of dilatution by heat of a standard bar, and such determination
can be practically made more easily and accurately from observations
of the defining lines of a standard bar.
It may be desirable here to examine the extent of alteration of a
measure of length arising from variations of temperature and to show
it in the following tabular form, in regard to the materials of which
standards of length are ordinarily made : —
Material.
Co-efficient of line.
Expansion
For i° Fahrenheit.
Variation of length
of 36 in.
For i9 Fahrenheit.
Brass
o 00000956
in.
o 000^4.4.
Bronze
O. OOOOOQ4.7
o. 000^4.1
Wrought Iron . . .
Cast Iron
Cast Steel
o. 00000611
o. 00000550
o 00000575
0. 000220
o. 000198
o 000° 07
Platinum
o. 00000476
o. 000171
It may here be seen that an iron standard yard alters its length
sensibly — that is to say, one ten-thousandth of an inch, with a variation
of temperature of half a degree Fahrenheit. At the same time, an
iron guage one inch in diameter will not alter the length of its diameter
to the extent of one ten-thousandth of an inch from dilatution with
less than an increase of 36° Fahr.
The conclusion to be drawn from a consideration of all these circum-
stances is, that whilst for practical uses, where mechanical accuracy is
required, end-standard measures may be satisfactorily used, line-
standards are preferable for primary standards where the highest
scientific accuracy is needed.
The CHAIRMAN : I am afraid we cannot go into a full discussion of
this very important and intricate subject, or of the relative merits of
measurement a but, and measurement a trait. If the commissions
•which have been sitting in this country and in France upon this sub-
ject for months have not arrived at a definite solution, it is to be feared,
that we, pressed as we are for time, shall not be able to do so, although
Q
226 SECTION— MECHANICS.
\ve have had the advantage of hearing three gentlemen on this subject,
who rank first as authorities. I think M. Tresca puts it very fairly,
that both methods have their advantages. The measurement a but,
as we have seen it explained by Sir Joseph Whitworth, seems to me
most adapted to the determination of very slight differences of linear
measure, provided the piece of substance measured is short, as is the
case in measuring thickness, whereas for the measurement of long
articles, the other method seems to possess advantages of its own.
Sir Joseph Whitworth will say a few words in reply to what has been
advanced, and then I am afraid we shall have to close this discussion,
as we have a great deal of business on hand.
Sir JOSEPH WHITWORTH : I will just say that the line-measure
previous to 1851, had engaged the attention of a number of gentlemen —
the Reverend Mr. Sheepshanks being one — who were appointed the
Commission, and were engaged for several years upon it. They had
rooms in Somerset House, and were going to get an Act of Parliament
for these standards which they recommended. The original standard
as was observed by Mr. Chisholm had been destroyed when the Houses
of Parliament had been burned down. In the meantime I was making
my experiments on end-measure, and I exhibited at the Exhibition of
1851 a standard yard measure, and showed there, that the differences
in length by small increments of heat was very great. In the machine
that I exhibited, which was the standard yard, I showed repeatedly
that when the feeling-piece at the end was adjusted, you could not
touch the bar with your finggr_jiaij, without the feeling-piece
being suspended. You can make, of course, any number of
standards, and supposing we had a room at the temperature of the
human body, we could then handle these things ; but the commission
determined that the degree of heat should be 62° Fahrenheit, and of
course you cannot touch anything with your hands without making it
longer. The way in which I supported the standard yard was objected
to before this commission, and it was said, it was better to support it
on rollers, but I may say that the gentlemen who were engaged in
determining what the standard yard should be, though they were
scientific gentlemen of the greatest eminence, did not know how to use
their hands. They recommended that the standard inch, which I con-
sidered was very important, should be our end-measure, and also the
SOLID MEASUREMENTS. 227
standard foot. I agree with my friend Dr. Siemens, that if we could
only have one measure it would be a great thing for all countries, and I
would go into the matter at once if the standard yard and our standard
inch would only divide into the metre, but unfortunately it will not ;
and as all our screws and all our machinery are made to the standard
inch, of course those standards must be used until everything is worn
out. Perhaps it may be advisable in the end to adopt the metre, but it
is quite impossible in our time. I have shown you the importance here
of very small differences, but the most important of all, perhaps, is with
reference to screws. A perfect screw is one of the most important
things in mechanism, and it would be impossible to alter the distance
of the thread of our screws, otherwise I fully admit it would be a great
advantage to all countries if we could have only one measure, and I am
sure I would do anything I could to promote it.
The CHAIRMAN : I am sure you will all agree with me in passing a - A*JAA A.
vote of thanks to Sir Joseph Whitvvorth, for his interesting communi- |
cation.
The vote of thanks was passed unanimously.
The PRESIDENT : The next paper on our list is by Mr. Merrifield,
ON SOLID MEASUREMENTS.
Mr. C. W. MERRIFIELD, F.R.S. : I have been desired to give you an
account of solid measurement, and I must ask you to excuse any
shortcomings, by telling you that it was not until Monday that it was
proposed that I should undertake this task, and it was only yesterday
that I was aware I should have anything to say about fluid measure.
It has also been suggested to me that, besides solid measurement, I
should touch on a subject you have not yet had before you, which
would otherwise have been omitted from the programme, namely,
surface measurement. That necessarily precedes solid measurement,
because, unless a measure of solid contents be mere replacement or
displacement, we must first be able to measure the surfaces, and from
them only can we measure solids ; at least, that is the usual course
pursued by geometers, and the only course to which geometrical
measurement applies. I must first say a word or two with reference
to the accuracy of this measurement. The only tangible idea we
have of infinitesimals, and the only clear idea of a boundary is, to my
223 SECTION— MECHANICS.
mind, a solid boundary, and from that comes one of the great
material advantages which you have heard described by Sir Joseph
Whitworth in accurate end-measurement. The next to that in facility
of perception probably is the boundary of a plane by straight lines,
or of a line by cross lines, for there is no such thing observable by us
as any reasonable approach to a point. The accuracy of lines is not
so easily felt as a surface. A surface, if highly polished, probably
presents a greater approach to an accurate boundary than anything
we can have in the way of lines. On lines there are more or less,
roughly — especially in regard to material lines, of which I am now
speaking— two sides to the line. They are not generally well defined,
but we can average the line by finding its middle, and in that consists
the accuracy of line-measurement. When we come, however, to
lines carelessly drawn perhaps, or ill-defined, to which we cannot give
great precision, we find we are dealing with a very indefinite thing
indeed. For instance, if you take a hard pencil, and draw as fine a
line as you can with it on a piece of paper, and put it under a micro-
scope, you will find a series of dots scattered about an irregular
breadth, more or less as if you had been dropping seed out of a hopper
in going across a field. If you do the same with a mathematical pen
you will then find under the microscope that you have got something
equivalent to a cart track on a road, with a rut on each side. Still, if
it is done with great care and precision, you are able to get a veiy
definite middle to that line. Now, with surface measurement, as ordi-
narily presented, we have a very different thing. The surfaces we have
to measure, are generally defined in a very different way, either by an
edge, which we have not ourselves had the means of making accurate,
or by a line which has been drawn for us with more or less accuracy,
generally with very small accuracy, because there is no very good
means of drawing with any degree of accuracy any line but a straight
line or a circle. Therefore, in this measurement of areas we have not
as yet felt the necessity of any instruments at all approaching in pre-
cision either the solid measures used and so greatly perfected by the
Warden of the Standards, or the still more accurate linear-measures,
whether those of the French or English Commission of Standards, or
Sir Joseph Whitworth's end-measures.
To return to the subject of ordinary plane measurement. The first
SOLID MEASUREMENTS. 229
idea of measurement of plane surface is to reduce it to one or more
square units, that is, having obtained its linear dimensions, and
taken account of the irregularities of its area, to find out the number
of square units contained in it. That is generally done geometrically
by cutting it up into strips of some definite shape, either by parallel
lines, or else by lines radiating from a point, and then these strips are
each separately measured with great ease and with tolerable accuracy ;
and the characteristic of the measurement is such that the error on
each strip, although noticeable when altogether, is still very small and
diminishes very much more rapidly than the number of strips into
which the area is divided. Every person accustomed to the quadra-
ture of curves is well aware of that. That is to say, if you use any
tolerably accurate mode of measuring, and cut up an area, either
physically or mathematically, into ten strips, you have a certain definite
error of, say, perhaps one-tenth of a square inch. But if you cut it up
into 100 pieces, instead of reducing the error by ten, you generally,
if your arrangements are well made, reduce it by 100. Now
when we come to solid quantities, the ordinary method of dividing
them is to cut them up into slices. You add the slices together to
make the solid, in the same way as you add the solids together to
make the surface. But that is hardly the case in general application.
We do not cut these cylinders before us into strips, but we are obliged
to have resort to means of replacement, this means being, for various
reasons, far less accurate than any of the modes of linear-measure
we have just described. But yet in the hands of a gentleman like
Mr. Chisholm we can get a degree of accuracy which few persons
unaccustomed to consider the thing would dream pf — probably far more
accuracy than we ordinarily meet with in surface measurement.
Now, there are also certain other beautiful little instruments called
Planimeters, by which a task, which at first sight would hardly be
considered conceivable, has been successfully accomplished, namely —
that by simply running a pen point round any irregular closed curve,
of which we wish to measure the area, a little wheel records the area
that the pencil -goes round. That seems conceivable enough if we
had to deal either with a circle or an ellipse, but it seems almost
inconceivable when we have to deal with curves with any amount of
irregularity. The most useful of these, as at present arranged, is
230 SECTION— MECHANICS.
probably Amsler's Planimeter. The principle of this, although really
very beautiful, is a little intricate, and has not always been well under-
stood. It depends upon this principle — that if you take a bar of definite
length, and give it a small motion, then you may measure the surface
swept over by that bar by simply multiplying the length of the bar
into the travel of the middle point resolved at right angles to the bar.
I can explain this perhaps more clearly by the aid of a diagram. The
way that principle is made use of in Amsler's planimeter is this. He
puts a §mall roller jon tjhe bar in the direction of its own length, and
|^VU Vfcu U***- •t vCf lJL+\ [V
if the bar moves me wheel simply slides, but if transversely it rolls. If
the bar moves in any intermediate direction it both rolls and slides, but
the wheel records only that component of the motion which is at right
angles to the bar. That of course only applies to small motions of the
bar, but as it applies to every small motion it must be true for the sum
of them as well as for every part. Supposing you have an irregular
curve to measure, you make one end of the bar follow the curve and
let the other end reciprocate along a certain curve. Its longitudinal
motion will have no record taken of it, but the motion at right angles
to the bar will be accurately counted by the little wheel. As it moves
in one direction, the wheel will run one way, and as it goes round the
other, it will go the other way ; and the difference of those two will be
recorded when the bar gets into its original position: and that, read to
a proper scale, and multiplied into the length of the bar, will give the
difference between the line swept out and the true area all round ;
consequently the difference between the readings of the wheel in its
first position and when it gets back to its first position will give the
area. It is quite immaterial what this curve may be so long as one
end of the bar moves backwards and forwards along the same curve,
no matter what ; the reading will be exactly the same. Those who
have used it will be aware that the wheel is not put at its middle point
as I have put it, but it may be proved geometrically that so long as you
measure a closed curve with a bar, one end of which is always outside
the curve, it is immaterial upon what part of the bar you put the little
wheel. It is, of course, material, if you are only going to measure a
part of the curve, but not when you measure the whole curve. That,
then, contains the whole principle of Amsler's Planimeter, that the
surface swept out by the bar is measured by the travel of the middle
SOLID MEASUREMENTS. 231
point, resolved at every instant at right angles to the bar, and the suc-
cess of the instrument depends on the little wheel recording that
transverse component only. The other points are mere details of
mechanism. One form of the instrument is shown here. Practically,
these are not generally made of a size to be used for any other
than small diagrams, but they really measure with great accuracy. In
fact,' when I was in the School of Naval Architecture we used to try it
upon squares, and we invariably found that it measured a square with
at least as great accuracy as we were able to draw it, and I need hardly .
tell you that in surface measurements it is not necessary to obtain an
accuracy that goes beyond the drawing.
There is another kind of Planimeter founded on a principle that is
well known to mechanicians in the form of a continuous indicator.
Suppose there is a disc turning on its centre and we have another little
disc at some point of it in rolling contact with it, the travel of this disc
will depend not only on the rapidity with which the primary disc
moves, but also largely on its distance from the centre, and, moreover,
supposing that the travel of the primary disc is uniform, the travel
of the follower will be exactly proportionate to its distance from
the centre. That circumstance is taken advantage of in a little
machine I have here. The disc you see the edge of is the following
disc, and the one which is horizontal when the instrument is in its
proper position is the driving disc. The bar that you see with a little
wire upon it is always kept parallel to a base line, and a tracing point
follows exactly the curve. Now, when this following disc is on the
line of centres it records nothing, but as it moves away from the line
of centres there is a specific ordinate to which the travel of the following
wheel is proportional, consequently the operation of the instrument is
to add this exactly as we do in ordinary algebraic integration. In that
way we get the surface recorded with as great accuracy as the drawings
are framed. In point of fact, I have very little doubt its performance is
quite equal to that of any drawings that can be submitted to it. A
modification of that is to be found in Professor James Thomson's
instrument down stairs. I do not propose to describe that, because it
it really very much more than an instrument for measuring an area,
and mav be applied to a great many things, but in its simplest form
it is a case of measurement of area, on exactly the same principle as
232 SECTION— MECHANICS.
this, with the exception that the sliding motion is entirely got rid of,,
being replaced by the motion of a sphere which rolls both on a sphere
and on a cylinder. The motion that it records depends upon the dis-
tance of the point of contact with the sphere from the centre of the
disc on which it rolls. In principle it is exactly the same as this, and
the principle of both is the same as in ordinary integration, namely,
the ordinary rule that the area equals the integral of y d x.
With regard to the measurement of solids, the general principle
of solid measurement in ordinary use is simply that of displacement
or replacement, namely, that a standard measure is made, and all other
measures are compared with that by actually pouring some kind of
material, either corn, or some dry material of that kind, or water, from
one to the other. The most obvious measurement of solids by displace-
ment, is by filling a vessel up to a certain edge with a liquid, and dipping
the solid into it either entirely, or up to some measured point, and
ascertaining the quantity that overflows. We have, I am afraid, no
exemplification of either of those modes of displacement here in their
simplest form. With regard to some instruments I have seen, I may
mention that it is necessary to observe great caution in the form of the
lip by which the overflow takes place if you wish to secure any accurate
measurement, for a difference in the form will make it measure differ-
ently, and there is also great difference in the viscosity or molecular
character of different liquids, and scarcely any two liquids measure
alike. It would not be fair, however, to say that is the only mode of
measuring solids. Of course, practically, the first thing you have to do
in order to compare solid-measure with linear, is to construct very
carefully a solid, either hollow or not, upon geometrical principles, so
as to connect it with linear-measure, and the most [ordinary mode of
doing that is by making cylinders of which you can measure the height
with very great accuracy, and in which you can secure a very con-
siderable degree of accuracy in form, and also are able with accuracy
to measure the diameter. Taking the three things together, I do not
think it can be said, that these measures at all approach in accuracy
the linear-measures. There are various reasons why they should not.
In the first place, they depend not only on three different sets of linear-
measure, each one of which requires to be got with accuracy, but also-
depend on accuracy of form, and upon the possibility of measuring
SOLID MEASUREMENTS. 233
round forms, which is scarcely so great as with the linear-measure.
They also depend on having square ends — that is, on the bottom or
top being set perfectly square to the edges. Still a very considerable
degree of accuracy is to be obtained by these methods.
With the purely geometrical modes of measurement by means of orcli-
nates I need not detain you, but I should be neglecting a very large part
of the subject, if I were to fail to call your attention to some very
important economical measures, namely, timber measuring and cask
gauging. In timber measuring, practically, one's first idea of measuring
a spar is to consider it as a cylinder. Of course any spar, as the tree
grows, is considerably thinner at one end than at the other, but the
correction for that is not very difficult to apply, and is ordinarily
applied by geometry, with which I need not trouble you here, parti-
cularly as we have before us no instruments for doing it. Sliding rules
are used for the purpose, but they are rather calculating than measuring
instruments. With regard to cask gauging, however, it may be done
with as much accuracy as the subject admits of. It has been made
the subject of very elaborate calculation by Hutton and others, and
great perfection has been obtained in the instruments with which the
measurements are taken, considering the mode of applying them.
The instruments I am now showing are those manufactured by Messrs.
Bring & Fage for the use of the English Customs and Excise officers.
This is the calliper with which the length of the cask is measured. Of
course the staves generally stick out an inch or two beyond the head
of the cask, and consequently the length is measured by two rules
sliding one upon another, which fit over the head of the cask, and enable
you to get a fairly accurate measurement of the length. The calliper for
obtaining the diameter of the cask is also here. It is constructed on
the same principle as the first. In getting the diameter of the cask
we have first to get the bung diameter, the diameter at the widest point,
and also at the head, and these are quite different. I only mention
for the sake of those who are not acquainted with round measure,
that it is necessary that the callipers should be applied in several
places : you have either to turn the cask or turn the calliper round the
cask, because you very seldom find that the cask is a perfect circle,
and for the measurement you have to take the average. Then when
you have got the diameter of the cask at the bung and at the head,
234 SECTION— MECHANICS.
for the internal diameter you have to allow for the thickness of the
planks and the curve of the cask. Supposing that you know the
shape of the cask, you would then have the elements for a tolerably
accurate measure of it. But, in the first place, casks are not always
in the same shape ; and no person has yet been able, so far as I can
discover, to make up his mind as to what the proper shape for a cask
ought to be. Those difficulties, however, are very small, and are not
very important. For fiscal purposes it has been found quite sufficient
to take the head diameter and the bung diameter. Where much more
accuracy is required — that is to say, where any large casks have to
be specially measured, it is necessary to take a diameter intermediate
between the bung and the head ; the actual measurement is then done
on paper and also by the slide rule. Here is one of the slide rules
ordinarily used. It is a good long one, and that is an advantage,
because it is read much more easily. The scales laid down upon it
are the ordinary ABC and D scales of a slide rule. These serve
generally for ordinary calculation, which merely requires the scale to
a half radius on one side of the rule and a whole radius on the other.
Besides this there is another method for measuring casks in a rough
way, and that is the diagonal measure. Here is a diagonal staff. It is
simply thrust through the bung, and put to the edge of cask, and then,
on the supposition that all casks are of the same size ; the volume of the
cask, of course, varies with the cube of the diagonal. There is also a
scale on the slide rule for that purpose. The ullage of a cask is also
of some importance. It means the measuring a cask which is partially
full. At the same time, as the measurement is chiefly done for fiscal
purposes, it is not a matter of much consequence, in measuring a cask
perhaps one-third full, whether there is a pint this way or the other.
Therefore the measurement is very rude. What is really done is to
dip a stick into it, and to see how much of it is wetted, and then by
comparing that with the known measurements of a standard cask you
find the quantity in the cask. There is no attempt at an accurate
geometrical measurement of ullage.
What remains for me to say is on the measurement of gases and
liquids, and on that I shall be very short. I shall first speak of gas
meters ; for although the engineers present are pretty certainly aware
of the construction both of dry and wet gas meters, some of my hearers
SOLID MEASUREMENTS. 235
would perhaps like to have them described in a general way. The
ordinary wet gas meter is a mere cylindrical box about half full of
water, in which there are four vanes fastened to a horizontal spindle.
The gas flows in at the bottom, and as it flows in it turns the vanes
round, then delivers the gas into the upper part, from whence it goes
into the house through the supply pipe. Therefore, for each quarter
revolution a definite measure of gas passes in, and consequently
passes out. There is a counter fixed on the spindle which counts
the number of revolutions, and as that is done to a scale, it is read
off in cubic feet or hundreds of cubic feet. I have not gone into
any details, and I dare say the rough sketch I have made does not
represent it with anything like accuracy, but that is the principle. It is
not very satisfactory for many reasons. It regulates with tolerable
truth, supposing the meter is perfectly and honestly arranged ; but it
has the disadvantage of wetting the gas, which makes it burn badly
for one thing, and it also tends to deposit water in the joints of the
pipes and to give trouble in that way. The dry meter is very much
like the cylinder of a steam engine, only differently arranged. If you
can imagine a steam engine with the piston fixed and the cylinder
moveable, it would be very like it, only instead of being made of rigid
materials there is a bag on each side of a fixed diaphragm. The gas
first comes into the bag on one side, and when it is full up to a cer-
tain point it presses the end of it against a stop which shuts it oft,
and at the same time opens an out-flow cock into the house. But at
the same time that it shuts off the one bag it opens an inflow cock into
the other bag so that the other side begins to fill. Thus at every
half stroke one bag gets filled, and the other emptied, and at the
opposite stroke the first gets emptied and the second filled. Each
stroke is recorded on a counter which thus registers the quantity of
gas passing through the meter. This is in several respects a much
better arrangement than the wet meter. I think it is a little more
expensive to make, and gas companies generally prefer wet meters.
There is a practical reason generally attributed to them for that,
although perhaps unfairly. That I cannot speak about with certainty,
but it is generally supposed that if anything goes wrong with the meters
the dry meter makes an error in favour of the consumer, while the
wet meter makes an error in favour of the gas company, and con-
236 SECTION— MECHANICS.
sequently the gas companys go in for wet meters, and will not let you
have dry meters if they can help it ; but if you take my advice, go in
for dry meters whenever it is possible.
Now, with respect to water meters. There are various kinds of
water meters. First, there is an absolute water meter, in which the
water is received into a receptacle, much in the same way as in the
dry gas meter, and delivered in the same way, a reciprocating motion,
and an arrangement giving the means of measuring it ; just as if you
passed water instead of steam through a steam-engine, the number of
strokes of the steam-engine would give the quantity of steam passed
into the engine, and out again. If you want absolute measurement,
that is doubtless the best you could arrange for, but it gives you an
intermittent current, and destroys the head of water ; consequently,
in all modern water meters the arrangement depends on either the
turbine or the screw. To put it in the simplest form, if you had a
screw, like a screw propeller, fixed in the middle of a pipe, and re-
volving, the number of revolutions of the screw would depend on the
velocity of the water going past it, and that would give you a rough
measure of the amount, but only a very rough measure, for there is a
certain amount of friction caused by turning the screw, and besides that
a part of the water escapes through the interstices of the screw without
acting upon it, and in that way the screw does not record the quantity
of water with any great degree of accuracy. Not only that, but it does
not record it with the same degree of accuracy at different speeds, and
therefore you are not able to apply an easy or certain correction for it.
An improvement of that has been introduced by a more complicated
form of screw called the turbine or Barker's Mill, where the water is
got under more complete control by directing it against vanes properly
arranged and proportioned, and in that way a very accurate water meter
can be obtained for all ordinary speeds. There is no doubt that if you
were to pass the same stream of water through at the rate of half-a-
mile an hour, and then, at some other time, at the rate at which water
is driven through the hose of a fire-engine, there would be considerable
errors, but with Dr. Siemens' turbine arrangement, under ordinary
circumstances, with considerable variation of velocity, there arc
practically very small limits of error. It really is a turbine or Barker's
Mill arrangement, with proper directive vanes to give compensation
SOLID MEASUREMENT. 237
All water meters more or less destroy the head of water; that is, make
a considerable difference between the velocities at which the water
enters the pipe and leaves it, and, consequently, where the stream is
used to develope power, any water meter is a very serious drawback,
but where no power is wanted from it, that is immaterial.
This machine before us, which is called Siemens' alcoholimeter, is
one used to determine both the quantity of liquid that passes out of a
still, and also the quantity of alcohol that it contains, and it is used
largely in Russia. There are two distinct parts, first, a water meter of
tolerably simple construction, not unlike what I said before about gas
and water meters ; a copper disc revolves in a box upon a horizontal
shaft, with three vanes at equal angles, and the water comes in at the
centre, and drives always in one direction, delivering at the circum-
ference like a water wheel or vertical turbine. So far, it merely mea-
sures the quantity of liquid that passes, and the lower scale upon the
instrument measures the volume of liquid that flows out of the still.
That may be, of course, either wholly alcohol, or wholly water, or any
mixture of the two. To indicate the quantity of alcohol there is another
counter, and the way it is set to work is this: — There is a weight at the
end of a lever, calculated either to represent a certain weight of pure
alcohol, or of proof spirit, in such a manner, that if there were no spirit
at all a second counter would always stand at zero; while if it were
entirely pure spirit, it would count the same as the lower one, which
shows the quantity of liquid passing. The spirit which passes is
generally considerably below proof. When pure water passes, this
upper counter is not affected, but when, on the contrary, pure alcohol
is passing, a bob comes down and pushes a second lever, with a
curved edge over, and this second lever regulates the difference
between the two counters. You may say that its edge ought to be a
straight line, and so it could be, but for the fact that one pint of water
and one pint of alcohol do not make a quart, but rather less, and
consequently there is a slight curvature in it. What happens in
the two receptacles is this. The liquid is weighed in one and
measured in another. One scale represents the measure, and the other
represents the joint effect of the weight and the measure; conse-
quently, one scale records the total quantity of liquid that passes, and
the other represents either the absolute quantity of pure alcohol
238 SECTION— MECHANICS.
passing through it, or of proof spirit, according to the way in which the
instrument is contrived and set. I am assured it works with great
accuracy, and being put under a glass case and locked up, the Russian
excisemen have not half the trouble with the distillery that our ex-
cisemen have. The distiller cannot tamper with it in any way without
being found out. The pipes coming from the still are completely in
sight ; he cannot tap them without the hole being discovered, and he
cannot tamper with this machine without showing signs of it. I think
I have now said all I need say with regard to these measurements, and
I hope I have made myself clear to you.
The PRESIDENT: I have only now to call upon you to pass a vote
of thanks to Mr. Merrifield for his very able and lucid explanation of
the different modes of measuring solids. He undertook this task only
upon two days' notice, and is therefore entitled to our special thanks.
The vote of thanks having been passed unanimously,
The PRESIDENT: I will now call on Sir Wm. Thomson to give us
some explanation upon that most difficult and important subject of
electrical measurements. I am afraid Sir William will not be able to
go as fully into the subject as it deserves to be gone into, inasmuch as
our time is exceedingly limited, but I am sure that whatever falls
from Sir Wm. Thomson will convey information to all, and that we
shall profit by it.
Professor Sir W. THOMSON, L.L.D., F.R.S. : The beginning of elec-
trical measurements, are, I believe, the measurements of Robinson in
Edinburgh, and of Coulomb in Paris of electrostatic forces. The great
results which followed from those measurements illustrated how
important is accurate measurement in promoting thorough scientific
knowledge in any branch of physical science. The earlier electricians
merely describe phenomena attractions and repulsions and flashes
and sparks, and the nearest approach to measurement which they
gave us, was the length of the spark under certain circumstances,
the other circumstances on which the length of the spark might
depend being left unmeasured. By Robinson's and Coulomb's
experiments was established the law of electrostatic force, according
to which two small bodies, each electrified with a constant quantity
of electricity, exercise a mutual force of attraction or repulsion, accord-
ing as the electricity is similar or dissimilar, and which varies
ELECTRICAL MEASUREMENT. 239
inversely as the square of the distance, when the distance between
two bodies is varied.
In physical science generally, measurement involves one or other of
two methods, a method of adjustment to a zero, or a what is called
a mill method, and again, a method of measuring some continuously
varying quantity. This second branch of measurement was illustrated
in Coulomb and Robinson's experiments, where the law according to
which the electric force varies, where the distance between the mutually
influencing bodies varies continuously, was determined. The other
mode of experimenting in connection with measurement, is illustrated
by another exceedingly important subject, bearing upon electrical
theory, and that is the evanescence of electrical force in the interior of
a conductor. Both kinds of measurements were practiced by Cavendish
in a very remarkable manner, and I look forward with great expecta-
tion to the results we are soon to have of Cavendish's work. One
most interesting result which will follow from the Cavendish labo-
ratory in Cambridge, from its director Professor Clerk-Maxwell, and
from the relationship thus established between the physical laboratory
of the University of Cambridge, and its director on the one hand, and
the munificent founder of the institution, the Duke of Devonshire, on
the other hand. The Cavendish manuscripts still remain in that
family, and are, I believe, at present in the possession of the Duke of
Devonshire, and have been by him put into the hands of Professor
Clerk-Maxwell for the purpose of having either the whole, or extracts
from, published, which may be found to be of scientific interest at the
present day. The whole of them, no doubt, had great scientific
interest at one time. A large part of these manuscripts, I believe, will
be found to be excessively interesting even now, and from something I
heard a few days ago from Professor Maxwell, when he was here on
the opening day of this exhibition, I learnt that much more than was
even imagined is to be found in these manuscripts, and particularly the
whole branch of electrical measurements worked out, from the mea-
surement of electrostatic capacity. The very idea of measuring electro-
static capacity in a definite scientific way is, as it now turns out, due to
Cavendish. A great many years ago, in 1846 or 1847, when the
Cavendish manuscripts were in the hands of Sir Wm. Snow Harris,
at Plymouth, I myself found one paper, out of a box full of unsorted
240 SECTION—MECHANICS.
manuscripts which startled me exceedingly. It contains the descrip-
tion of an experiment and its result, measuring the electrostatic
capacity of an insulated circular disc. That is one of the cases in
which the theory founded by Cavendish and Coulomb as developed
in the hands of the mathematicians who followed, allowed the result
to be calculated a priori, and I found the result agreed within, if I
remember rightly, one-half per cent, of Cavendish's measurements.
When I mention these cases of the measurement of electrical force
by Coulomb and Robinson, which has led to the true law of force and of
the measurement of electrostatic capacity, a subject which is the least
known generally, and held to be the most difficult, I have said enough
to show that we must not in this century claim all the credit of being
the founders of electrical measurement.
The other main method of experimenting in connection with mea-
surement to which I have referred is illustrated also by Cavendish's
writings, that is the seeking for a zero. It is very curious, that while
Coulomb and Robinson by direct measurement of a continuously
varying quantity discovered the law of the inverse square of the dis-
tance, Cavendish, quite independently, pointed out by very subtle
mathematical reasoning that the law must either be the inverse square
of the distance, or must vary in a determinate manner from the law
of the inverse square of the distance if in a certain case, which he
defined, either a perfect zero of electric force is observed, or if instead
of a perfect zero any particular amount of electric force is observed.
It is quite clear from Cavendish's writings that he believed that perfect
zero would be found when the experiment should be made, but with a
caution characteristic of the man and also proper to his position as
an accurate philosopher and mathematician he never would state the
law absolutely. He had that scrupulous conscientiousness which pre-
vented him from guessing at the conclusion which no doubt he arrived
at. His mind was probably a great deal quicker than are many other
minds in which the conclusion is jumped at and given as if it were
proved, but he conscientiously avoided stating it as a conclusion, and
held it over until exact measurement should prove whether or not it
was to be concluded.
The subject of measurement in this case of a null method pointed
out by Cavendish was this. If in the interior of a hollow electrified
ELECTRICAL MEASUREMENT. 241
conductor the electric static force upon a small insulated and
electrified body is exactly zero, then the law of variation of the electric
force must be according to the inverse square of the distance. On the
other hand, if a certain attraction of a small positively electrified body
towards the sides of the supposed hollow electrified conductor is
observed, then the force varies according to a law of greater variation
of the distance than the inverse square of the distance ; and vice versa
if a small body electrified in the opposite way to the electrification of
the conductor seems to be repelled from the sides, then the law of
diminution of force with the distance will be something less than would
be calculated according to the inverse square of the distance. The
case supposed is an insulated electrified body — an infinitely small
body — charged with electricity opposite to that of the electrified body.
If this small body, then, put into the interior as a test, exhibits attraction
towards the sides, the law of variation of the force will shew a greater
diminution according to the distance than according to the inverse
square of the distance, and vice versa. It was left for Faraday to make
with accuracy the concluding experiment which crowned Cavendish's
theory. Faraday found by the most thoroughly searching investiga-
tion that the electrical force in the circumstances supposed was zero,
and supplied the minor proposition of Cavendish's syllogism. There-
fore the taw of force varies with the inverse square of the distance.
This result was obtained with far less searching accuracy by Coulomb
and Robinson, because their method did not admit of the same search-
ing accuracy. On this law is founded the whole system of electrostatic
measurement in absolute measure. Mathematical theory lays down
the proper static unit — that quantity, which if a quantity equal to it is
possessed by two bodies, those two bodies react upon one another with
unit force at unit distance. On this is founded the system of absolute
measurement in electrostatics.
Cavendish's other experiments, and series of experiments — because
I believe Professor Clerk-Maxwell is to edit a whole series of experi-
ments measuring electrostatic quantities — led to the general system
of electrostatic measurement in absolute measure.
But now there is another great branch of electrical measurement,
and that is the measurement of electro-magnetic phenomena. Our
elementary knowledge of electrostatics was complete, with the
R
242 SECTION— MECHANICS.
exception of this minor proposition of Cavendish's syllogism, and the
great physical discovery of Faraday of the peculiar inductive quality
known as the electrostatic inductive capacity of dielectrics. With these
two exceptions the whole theory of electrostatics was completed in
the last century. It was left for us to work out the mathematical
conclusions from the theory of Cavendish, Coloumb, and Robinson ;
and it was not until after the end of the last century that the existence
of electro-magnetic force became known. Orsted made the great dis-
covery in 1820 of the mutual connection between a magnet and a
wire in which an electrical current is flowing, and the remarkable
developments which were very speedily given to that discovery by
Ampere, led to the foundation of the other great branch of electrical
science, and pointed to the subject of electro-magnetic measurement,
upon which I must say a word or two now.
I think the principles of the mathematical theory of the inter-
action of wires containing currents mutually between one another,
and again their mutual action upon magnets, was fully laid down by
Ampere in consequence of Orsted's discovery. The working out of
the accurate measurement of currents, and generally of the system of
measurement founded on these principles, was founded altogether in
Germany. The great work of Gauss and Weber on terrestrial mag-
netism belongs strictly to this subject. I believe Gauss first laid
down the system of absolute measurement for magnetic force. The
definitions and mathematical theory, of Poisson and Coulomb as to
magnetic polarity, and the magnetic force founded on it, was worked
out practically by Gauss, and made the foundation of the whole system
of magnetic measurement followed in our magnetic observatories.
This was an immense step in science, and one of great importance,
giving, not merely definite measurement, but measurement on a certain
absolute scale, which, even if all the instruments by which the mea-
surements were made were destroyed, would still give us a perfectly
definite result. It was, for the first time in physical science, worked
out in consequence of Gauss' foundation of the system for terrestrial
magnetism. That, then, is really the beginning of absolute measurement
in magnetic science, and for electro-magnetics and electrostatic science.
Gauss and Weber carried on the work for terrestrial magnetism
together, and Weber carried on by himself, I believe, during Gauss'
ELECTRICAL MEASUREMENT. 243
lifetime and also after his death — the system of absolute measurement
in electrostatics. One most interesting result, brought out by Weber,
is that the electric resistance of a wire, in respect of electro currents
forced to flow from it, is to be measured in terms of certain absolute
units, which lead us to a statement of velocity in units of length per
unit of time, as the proper statement for the electro-magnetic measure
of the resistance of a wire. It would take too long to occupy your
attention on matters of detail if I were to explain minutely how it is
that resistance is to be measured by velocity. It seems curious, but
you will form a very general idea of it in this way. Suppose you have
two vertical copper bars and a little transverse horizontal bar, placed
so as to press upon those two bars. Let the plane of those two bars
be perpendicular to the magnetic meridian ; place then a little trans-
verse bar, like one step of a ladder, across the two vertical bars. Let
this bar be moved rapidly upwards ; being moved across the line of
the horizontal component of the earth's magnetic force, it will, accord-
ing to one of Faraday's discoveries, experience an inductive effect,
according to which one end of it will become positively electrified, and
the other negatively. Now, let the two bars upon which this presses
be connected together : then the tendency I have spoken of will give
rise to a current. That current may be made, as in Orsted's discovery,
to cause the deflection of a galvanometer needle. Now, you will see
how resistance may be measured by velocity. Let the velocity of the
motion of this little bar, moved upwards in the manner I have
described, be such as to produce in the galvanometer a deflection of
exactly 45°. Then the velocity, which gives that deflection, measures
the resistance in the circuit, provided always the galvanometer be
arranged to fulfil a certain definite condition as to dimensions. The
essential point of this statement is that the result is independent of the
magnitude of the horizontal force of the earth's magnetism. The
galvanometer needle is attracted by the horizontal magnetic force of
the earth. Let us suppose that to be doubled ; the attracting force in
the needle is doubled, but the inductive effect is doubled also, and,
therefore, the same velocity which causes the needle of the galvano-
meter to be deflected 45° with one amount of magnetic force of the
earth, will cause the needle to be deflected by the same number of
degrees, with a different amount of magnetic force of the earth. Thus,
244 -££C 'TION— MECHANICS.
independently of any absolute measurement of the terrestrial magnetic
force, we get a certain velocity which gives a certain result. Thus,
it is that velocity is the proper measure of the resistance of a
metallic circuit to the flow of a current through it. Going
now to electrostatics, — the resistance of an insulator to the
transmission of electricity along it, may be measured in a curious
manner in connection with the velocity. It may be measured by the
reciprocal of a velocity, or in other words, the conducting power
of a wire may be measured, with reference to the electrostatic
phenomena, by a velocity. Thus, imagine a globe in the centre of
this room, at a great distance from the walls. Imagine that globe to be
two metres in diameter and one metre in radius ; let it be electrified^
and hung on a fine silk thread, perfectly dry, so as to insulate perfectly.
There we have a perfectly insulated globe in the middle of this room.
Now if you apply an excessively fine wire, say a wire one ten-
thousandth of an inch in diameter, to the globe, and bring that to a
plate of metal connected with the walls of the room, or you may
suppose the walls of the room to be metallic, so that we may have no
confusion owing to the imperfect conductors. When you apply this
very fine wire connecting the insulated globe with the walls of the
room, the globe instantly loses its electricity. By instantly, I mean in
so short a time as would be impossible to measure by any method we
could apply — I mean a time as small as one-millionth of a second —
the globe would lose its electricity, if we had connected to it ten or
twenty yards of the finest wire we could imagine. But suppose the
wire a million times finer (if we can suppose that) than we can apply,
the same thing would happen. Or take a cotton thread, and get such
a globe as I have been imagining, surrounded with metallic walls, that
moist cotton thread will gradually diselectrify it ; in a quarter of a
minute the globe will have lost perhaps half its electricity, in another
quarter half of the remainder, and so on. If the resistance of the
conductor I have supposed is constant, the loss will follow the com-
pound interest law — so much per cent, per second of the charge will be
lost. Now imagine a conductor of perfectly constant resistance to be
put between the ideal globe and the walls of the room, and imagine the
globe to be connected with one of these electrometers — of which I
shall say a word in conclusion— by an excessively fine wire going into
ELECTRICAL MEASUREMENT. 245
the instrument, and suppose the electrometer to indicate a certain
degree — a potential, as we now call it — that subject of electric measure-
ment really discovered by Cavendish in his measurement of electric
capacity. Now suppose, then, we are measuring the electric value — the
potential of the charge in the globe by an electrometer, then we shall see
the electrometer indications decreasing and the potential gradually going
down according to the logarithmic, or compound interest law, in the
circumstances I have supposed. But instead of this being carried out,
let us suppose the following conditions, which we can imagine, although
it would be impossible for any mechanician to execute it. Let the
globe by some imaginary means be gradually diminished in its
diameter. Suppose, in the first place, the insulation to be exceedingly
perfect, and suppose the resistance of the conducting wire to be enor-
mously great, so that in the course of a minute or two there is but
little loss of potential. Now let this globe, which is supposed to be
shrinkable or extendable at pleasure, be shrunk from the metre radius
to 90 centimetres radius, what will the effect be ? The effect will be
that the potential will increase in the ratio of 90 to 100. Shrink the
globe to half its dimensions the potential will be double, and so on.
That follows from the result of the mathematical theory that the
electrostatic capacity of a globe is numerically equal to its radius.
Now, while the globe is charged let its radius be diminished. Let the
globe shrink at such a speed that the potential shall remain constant.
There, then, you can imagine a globe losing a constant quantity of
electricity per unit of time, because it is kept now at a constant poten-
tial. A globe kept by this wonderful shrinking mechanism at a
constant potential will lose a constant quantity of electricity per unit
of time, losing in equal times equal quantities ; and the globe going
on shrinking and shrinking so as to keep a constant potential, the
velocity with which the surface approaches the centre measures the
conducting power of the wire in absolute electrostatic measurement.
So, then, we have the very curious result that according to the electro-
static law of the phenomena we can measure in terms of electrostatic
principles the conducting power of a wire by the velocity. Although
I have put an altogether ideal case to you, it would be very wrong for
me to allow you to suppose that this is an ideal kind of measurement ;
in point of fact, we measure regularly in electrostatic measurement
246 SECTION— MECHANICS.
the capacity of the Leyden jars in that way, and in future when anyone
goes to buy a Leyden jar of an optician, let him tell you to give him
one of one or two metres or whatever it may be, and require him to
find out how to produce it. I give that as a hint to anyone interested
in electrostatic apparatus, or in the furnishing of laboratories. There
is no likelihood that he will understand what you mean, but perhaps if
you teach him a little he will soon come to understand it, and I hope in ten
years hence, in every optician's shop where Leyden jars are sold, there
will be a label put on each jar saying the capacity is so many centi-
metres. It could be done to-morrow. We have all the means of
doing it, only we have not the knowledge.
The relation between electrostatic measurement and electro-magnetic
measurement is very interesting, and here from the supposed unin-
teresting realms of minute and accurate measurement we are led to the
depths of science, and to look at the great things of Nature. Thrse
old measurements of Weber led to an approximate determination of
the particular velocity at which the electro -magnetic resistance is
numerically equal to the electrostatic conducting power of a wire. The
particular degree of resistance of a wire which shall be such that the
velocity which measures the resistance in electro-magnetic measure
shall be the same as the velocity which measures the conducting power
in electrostatic measure, was worked out by Weber, and he found that
velocity to be just about 300 kilometres per second. I unhappily have
British statute miles in my mind, through the misfortune of being born
thirty years too soon, and I remember the velocity of light in British
statute miles. That used to be considered about 192,000 miles per
second, but more recent observations have brought it down to about
187,000. Now I think the equivalent of that in metres is about 300
kilometres per second, and that was the number found by Weber.
Professor Maxwell gave a theory leading towards a dynamical theory
of magnetism, part of which suggested to him that the velocity for
which the one measure is equal to the other in the manner I have
explained should be the velocity of light. This brilliant suggestion has
attracted great attention, and has rendered it an object of intense
interest, not merely for the sake of accurate electro-magnetic and
electrostatic measuring, the measuring with great accuracy the relation
between electrostatic and electro-magnetic units, but also in connection
ELECTRICAL MEASUREMENT. 247
with physical theory. It seems that the more accurate an experiment
up to the present time, the more nearly does the result approach to
being equal to the velocity of light, but still we must hold opinion
in reserve before we can say that. The result has to be much closer
than it is shown by the experiments already made. But you can all
see by the mere mention of such a subject how intensely interesting
the pursuing of these investigations further must be. I believe
Maxwell at present is making a measurement of this kind on a
different plan from any that have been yet made. I have now spoken
too long, or I should have described something of the methods already
followed in this department, but they are already fully published, and
can easily be referred to.
Now with respect to accurate measurement — theory was left far be-
hind by practice, and I need not to be reminded by the presence of our
President how very much more accurate were the measurements of
resistance in the practical telegraphy of Dr. Werner Siemens and his
brother, our President, than in any laboratory of theoretical science.
When in the laboratory of theoretical science it had not been discovered
that the conductivity of different specimens of copper differed at all, in
practical telegraphy workshops they were found to differ by from thirty to
forty per cent. When differences amounting to so much were overlooked
— when their very existence was not known to scientific electricians, the
great founders of accurate measurement in telegraphy were establishing
the standards of resistance accurate to one-tenth per cent. Dr. Werner
Siemens and our President were among the first to give accurate
standards of resistance, and the very first to give an accurate system of
units founded upon those standards. This Siemens unit is still well
known, and many of the most important measurements in connection
with submarine cables are stated in terms of that unit. By a coinci-
dence, which in one respect is a happy one, although there is something
to be said on the other side, the unit adopted by Messrs. Siemens
founded on the measurement of a certain column of mercury produces
and reproduces in the accurate resistance coils — the Siemens unit ap-
proaches somewhat nearly to the unit which in Weber's system
would be io10 or a thousand million centimetres per second. This is so
far convenient that measurements in Siemens units are very easily
reduced to the absolute measure. The committee of the British
248 SECTION— MECHANICS,
Association, of which our President was one, and I also had the honor
to be a member, proposed a method of measurement which was carried
out chiefly by Professors Clerk-Maxwell, Balfour Stewart and Jenkins,
who laid down what is called the British Association unit to which the
name, according to the advice of Mr. Latimer Clark, of " Ohm," was
given in commemoration of one of the great founders of electro-magnetic
science, Ohm being the man who gave us the first law of currents in
connection with electro-motive force, it was considered appropriate that
his name should be given to the electric unit, but I may mention as a
matter of great importance and interest in physical science, a revision
of the measurement of the British Association unit is being undertaken.
There is now an endeavour to measure with the greatest possible
accuracy what is the value of the "Ohm" in terms of the absolute scale of
centimetres per second. It will certainly come within a small percent-
age of being exactly a thousand metres per second. One per cent,
away from that amount, it may, Iput that it is two or three per cent, or
four per cent, or one-third per cent, is of course possible as anyone may
judge by looking at the difficulties that will have to be met with in
making the experiments. I will just say in connection with the electro
measurement that it touches on another point of measurement, that of
heat. Joule in a quite independent set of experiments which I can only
name, showed another way of arriving at similar results, and Joule's
electro-magnetic experiments taken in connection with other experi-
ments of his on the dynamical equivalent of heat, show some dis-
agreement from the British Association measurement of their unit of
resistance. There is something to be reconciled here. Joule on the
one side holds that the British Association unit, the Ohm, is a little too
much or rather too little, I forget which, but on the other side, in
Germany, Kohlrausch holds the Ohm to be a little on the other side
of the exact thousand million centimetres per second. I believe if you
eliminate doubt by the method of averages, Kohlrausch and Joule's
experiments would show the British Association to be very nearly
right, but I do not approve of that method of removing doubts, and we
shall not be satisfied until both Joule and Kohlrausch are satisfied.
I will now mention a number of experiments with electrometers
which, I am afraid, are of little interest to anyone in the world, but
myself. Here is the first attempt at a quadrant electrometer, but it is
ELECTRICAL MEASUREMENT. 249
exhibited below. It is well known now to many electricians, and a
descriptive pamphlet also accompanies it. I really do not know, con-
sidering that the British Association report on electrometers has been
republished in connection with the whole series of their reports, that I need
go into detail with respect to any of these instruments. This is the
very first portable electrometer, and I will tell you how it came into
existence. I had one that I was very proud of, I am ashamed to say in
these days. I was proud of its smallness, and how easily it could be
carried up to the top of Goatfell and back ; and there was one before
then, the highest character of which was, that it was heavier than a rifle;
but, that was in the days of what Lord Palmerston called the "rifle fever,"
and I was touched a little with that at the time, being a rifle volunteer ;
and I found that my electrometer weighed a pound less than my weapon.
It only weighed thirteen Ibs., and the rifle weighed fourteen Ibs.
I had that at Aberdeen, but it is not now to be found, although it has
been searched for, or it would have been exhibited. Part of it, the
stand that was on the top of it, is below. The next that followed, was
this one. I got down the weight to about one-half, and I was perfectly
satisfied then, and this one has gone up the Goatfell a great many times ;
but it is fully described in my book, and in the paper I have referred
to. I was showing it with great pride on one occasion to Professor
Tait, and I said to him : " You should get one like that." He said,
" I will wait until you can get one that you can put into your pocket.
Get one the size of an orange, and the'n I will have it." That literally
was the origin of this electrometer. I felt rather challenged by what
he said, and in the course of my next run up to Glasgow, Mr. White,
who is so indefatigable in making new things, and who has so admirable
an inventive capacity, helped me in my endeavour, and we had some-
thing like this one. In the course of a month, this very electrometer
was got into action. This is the first attracted disc electrometer. It
differs from the portable electrometers now known merely in some
minor details ; the moveable disc turns round with a micrometer screw
instead of moving up and down in a slide. In all other respects, it is
the same, except the awkward arrangement for placing the pumice,
which with my great care, did not lead to any accident, but with
almost any other person led to the instrument being destroyed
by the sulphuric acid placed on it getting shaken down into the
250 SECTION— MECHANICS.
instrument below. The more convenient arrangement of the pumice
is now made, but that is the only alteration. The mechanical arrange-
ment of the disc is only changed in the portable electrometer as it
now exists, and two specimens have been sent out to the Arctic
expedition. Just one word of practical advice, with respect to the
electrometers. I have been continually asked how to keep them in
order, and have frequently heard complaints that these will not hold ;
that they do not retain the charge. In each of these electrometers
there is a porous jar, the heterostatic system being adopted in each of
them. It is necessary the insulating should be perfect, and then it all
depends afterwards on the cleanness of the surface of the glass. If you
will allow me to use the phrase of Lord Palmerston, with regard to
water, when he said that, " Dirt is matter in its wrong place," and to
consider that water, or any moisture on the face of the glass— which
ought to be perfectly dry— is in its wrong place, and is, therefore, dirt,
you will understand what I mean. If there is no dirt on the glass it is
certain to insulate well. But then how to get the glass perfectly clean ?
In the first place, wash it well with soap and water. If you like you
may try nitric acid, and then pure water, or you may wash it with
alcohol, and then with pure water. I have gone through almost
incantations to get perfect cleanness of the surface of the glass, but I
doubt much whether I have got any result which I could not have got
with soap and water, and then running pure water over the surface of
the glass. After it is done, wash it well, somehow or other. You may
use acids, or alcohol, if you like ; but I think you will generally find
that soap and water, and enough clean water, to end with, will answer
as well as anything. Then shake it well, and get it well dry, but do
not use a duster, however clean, to dry it. Shake the moisture off, and
take a little piece of blotting paper, and suck up very carefully any
little portion of water which may remain by cohesion, but do not rub it
with anything that can leave shreds or fibres ; that is dirt. The
finest cambric will leave on the glass what will answer Lord
Palmerston's definition. When you have got the glass clean of every-
thing except water, then dry it, and you will sure to find it answer.
The way to dry it, and to keep it dry, is to have the sulphuric acid in
the proper receptacle. Each of these instruments has a receptacle for
sulphuric acid, which must be freed from volatile vapours by a proper
ELECTRICAL MEASUREMENT. 251
process; boiling with sulphate of ammonia suffices. The sulphuric
acid need not be chemically pure, but it must be purified from volatile
vapours, and it must be very strong. I believe, oftener than from any
other cause, these instruments fail to hold well because the sulphuric
acid is not strong enough, and frequently, when an electrometer has
failed, by putting in stronger acid, the defect has been perfectly
remedied.
The PRESIDENT, in rising to move a vote of thanks to Sir William
Thomson for his very profound observations on a subject which is, per-
haps, one of the most difficult in physical science, said : he would only
allow myself to make one criticism, namely, that Sir William Thomson
had dealt more with the labours of others than with his own. We all
know that he has worked more than any other living man to bring
theory and practice into one focus regarding this subject of applied
electricity. There are many apparatus with which his name is con-
nected, and will always be connected, such as electrometers for the
measurement of currents, and apparatus for working long submarine
lines. These he has not dwelt upon, except in a very cursory manner.
Regarding the electrometer, I heard Sir William Thomson give a
lecture at the Royal Institution, some years ago, when he brought some
Scottish electricity to London in this very instrument. These electro-
meters have had not only a theoretical importance, but are of practical
uses to the electrician, especially one variety of them, which is used
largely by those who apply electricity to practical work, Without
occupying your time longer, after listening to so lucid an explanation,
I beg to call upon you to pass a hearty vote of thanks to Sir William
Thomson.
The vote of thanks having been passed,
The PRESIDENT said : I will now call on M. Tresca to give us a
discourse upon his very remarkable experiments on the flow of solids.
This is a subject which is peculiarly the work of M. Tresca, of whom
we have all of us more or less heard, but we have not all of us had the
author himself to give us a lucid explanation of them, as I am sure he
will do now.
253 SECTION— MECHANICS.
ON THE FLUIDITY AND FLOW OF SOLID BODIES.
M. TRESCA : Gentlemen, when ten years ago, after many careful
experiments, I made use of, and commented on the scientific expression,
Flow of Solid Bodies, my first communications were not received
without some shadow of incredulity. I, therefore, feel it my duty to
mention with gratitude the names of Mr. Tyndall, Mr. Fairbairn, and
Mr. Scott Russell among the scientific men, who at the very outset,
interested themselves in this subject. I should wish to thank them
in your language, but I am afraid that I am not sufficiently familiar with
it, and I therefore rely on your indulgence for allowing me to address
you in French.
The question of the flow of solid bodies has been a great success ;
it is, thanks to it that I now hold a position to which I should never
have dared to aspire, and which allows me to represent French science
at this Exhibition. We have been most desirous, I can assure you, to
afford you heartily all the help that lay within our power.
The principal fact connected with the flow of solid bodies was very
simple. If a resisting mass, enclosed in a wrapper, be submitted to
an exteiior action of sufficient power, it will exert in every direction a
greater or less pressure, and if a hole be made in the wrapper, the
matter will escape through this aperture, forming a jet, which is
made up of different portions of the mass. When the latter is
homogeneous, and the shape of the mass is regular, and the hole is
in a certain symmetrical position with regard to it, the mode of final
distribution may be deduced from the mode of initial distribution, and
the first experiments made will determine the kinematical conditions of
such a flow.
Thus, in the formation of a cylindrical block by the superposition of
a certain number of slabs of lead, it was found that each one of the
slabs penetrated by turn into the jet, and formed there a concentric
tube when the aperture itself was concentric.
Why were we so astonished to find, on cutting, according to a
meridian plane the so formed jet, that it was composed of as many
continuous tubes as there were slabs, until the complete exhaustion of
the matter which supplied food for its formation ? Could, indeed,
ON THE FLOW OF SOLID BODIES. 253
the perfectly geometrical position of the natural phenomena be explained
in any other way ? It is always as you see, when the regularity could
not be more perfect, it appears to us like the most absolute evidence.
The indefinitely reducible molecular formation, could not, assuredly,
be better justified than by means of these parallel walls, which preserve
to a microscopic thickness natural tissues, and an equality of appear-
ance and movements which are very remarkable.
These experiments in concentric flow have, with regard to the
relative displacements, been submitted to calculations, and we are
now able, in such a deformation, to lay down the trajectory passage of
each one of the molecules of the mass, and establish with certainty the
final places which they will occupy, compared to those in which they
were at first ; and also, by the same means, the transformed of any
line or of any surface to their first position.
These experiments became far more convincing when the shape and
position of the apertures are varied ; tubes still replace the slabs, but
the relative thickness of these tubes, the juxtapositions and the con-
volutions which result are just as instructive with regard to the clearness
of their shapes and the distribution of the pressure in the whole extent
of the mass which is escaping. But this question will occupy our atten-
tion more especially in the study of "punching."
If a punch be driven into a plate of metal, it will propel before it the
material of which the plate is composed, which, at a given moment
begins to form a protuberance on the opposite site, and finally detaches
itself in the form of a cylinder of the same diameter as the punch, and
to which the very characteristic name of " debouchure " has been
given. Under certain thicknesses the "debouchure" preserves a
height equal to the thickness of the plate, but this is no longer the case
when the thickness of the plate is very high.
A "debouchure" one centimeter high has been made by a block
five centimeters thick. If the block be formed of several plates laid one
over the other, all these plates will be represented in the " debouchure."
The lower plates, pretty nearly, by their original thickness ; the superior
plates by a kind of convex lens, of which the curved side has for basis
the flat side which has remained in contact with the punch, and which
has kept, according to the common axis, almost the whole of its
original thickness ; the intermediate plates by a number of cups
254 SECTION— MECHANICS.
pressed one into another, which reach the same flat side, and the lower
parts of which have variable thicknesses, which become extremely
thin at a certain point of the axis of the " debouchure."
This point is the principal centre of the flow which has been pro-
duced from the axis to the circumference by the pressures caused and
transmitted by the punch to the very interior of the mass. When this
flow has been able to take place, the virtual resistance of the partition
to be punched through was necessarily greater than the latteral resis-
tance ; but these two resistances will, on the contrary, be of the same
force when the " debouchure " begins to detach itself, and the effort
necessary to continue the punching will go on, after this, quickly
decreasing to the end of the operation.
The mode of action of these resistances, which we can determine
from the facts themselves, has furnished us with the true knowledge of
the action of the transmitted pressures, and we have been able to
formulate the laws of the transmission of pressures in a solid mass in
course of deformation, in a zone more or less extended which we have
named the zone of activity. And, finally, by proving the force necessary
to be exerted at the moment when the " debouchure " separates itself,
we have been able to determine the true co-efficients of transversal
cuttings. They are as follows, for each square centimeter :
Kilog.
Lead 182
Tin 209
Alloy of Lead and Tin ... 230
Zinc 900
Copper 1893
Iron 3757
It is worthy of remark that these numbers come very near those of the
resistance to rupture by extension for each of the metals experimented on.
The results ot the calculations, with regard to the transmission of
mechanical work, from one layer to another next to it, allow us to
lay down the mathematical law for the distribution of pressures, not
only for punching, but also for the various methods of deformation
previously studied. The formula arrived at by this method have been
subsequently justified by M. de Saint Venant and by M. Levy ; quite
lately M. Boussinescq, of the Faculty of Lille, announced to us that he
ON THE FLOW OF SOLID BODIES. 255
has reached the same conclusions by purely mechanical theories, and
from this moment, therefore, they can be considered as belonging to
science in the most complete manner.
Another kind of research has occupied us for a long time ; it is that
connected with the planing of metals. The shaving which the tool
carries away, and which up to that time had not even attracted the
attention of practitioners, offers many remarkable peculiarities. Not
only does it often twist itself spirally, which is the result of the unequal
shortenings of the different files of molecules of which it is composed,
but speaking generally, it can be calculated by how much it will be
shortened in a given case. It is usually reduced about a fifth of its
original length under ordinary circumstances ; and we can also con-
sequently tell by how much its transversal dimension will increase
during the same time, its density not having varied to any sensible
extent. This shaving, which is the "transformed of the prism" carried
off by the graver, increases in thickness in an inverse ratio to the
variations of its length. With regard to those complex convolutions,
in which the definite forms no longer depend on those of the moulds, of
the drawing-frames, or of the punches of which we have spoken above,
but merely on the exterior and interior forces which are brought into
play, we have not yet been able to characterize them with certainty,
except in a small number of cases. Here, however, is a model, which
shows how matter, driven back by a tool of a peculiar and symmetrical
shape, passes from a square section to a triangular section of much
greater dimensions, under the influence of pressures transmitted in
passing through geometrical mediums, traced according to a theoreti-
cal diagram and belonging to analytically defined surfaces. Many a
discovery will be made in molecular mechanics by following up these
phenomena, which have been so entirely overlooked up to the present
time, and which are so closely allied to the properties of matter.
Smelting is also one of the means that can be employed in this
attractive study of molecular mechanic. A bar of iron is simply a
mass of agglutinated filaments placed in juxtaposition, which proceed
individually from a determined nucleus. In proportion as the number
of the filaments is increased, and the mass formed by their juxtaposition
is stretched out, they become more and more tenuous, and it is easy,
by special means of oxydation, to discover, in a manufactured piece of
256 SECTION— MECHANICS*
iron, all the accidents of the various processes which have been used
for its formation. You can, indeed, in smelting, make these filaments
expand or concentrate them ; you can unite or separate them ; but you
cannot make them disappear ; and we have here another mode of
investigation, which must be made use of for the study of the interior
convolutions which correspond to certain exterior changes of shape.
When once all the relative displacements, as well as the force
necessary to produce them are known, there will be no great difficulty
in determining the best way of carrying them out, and of calculating
the mechanical work which it will demand.
In one of our smelting experiments, made on a large scale upon
brightened platinum, an accessory phenomenon presented itself, which
attracted the whole of our attention, and which is so closely connected
with the deformation of solid bodies, that you will allow me, I am
sure, to say a few words about it, although the experiments which have
originated from it are not yet finished. It is, moreover, a great satis-
faction to me to be able to communicate to a gathering of English
scientific men the first results of these experiments, before any publi-
cation whatever of them has been made.
On the 8th of June, 1874, we only pointed out to the Academy of
Sciences "the principal fact : when the bar of platinum, at the moment
of smelting, had already cooled down to a temperature below that of
red heat, it has happened several times, that the blow of the stamp
hammer which occasioned, at the same moment, in this bar, both a
local depression and a lengthening, heated it anew along two inclined
lines, forming upon the sides of the piece the two diagonals of the
depressed portion, and this re-heating was so great, that the metal along
these two lines was brought back to the red hot temperature, plainly
enough for its form to be distinguished. These lines of greater heat
even remained luminous for several instants, and presented the
appearance of the two jambs of the letter X. In some cases we have
been able to count simultaneously as many as six of these X, produced
one after the other, as the bar under operation was being moved, in
order to draw it out by degrees to a certain part of its length.
The explanation of these luminous traces could not for an instant
be doubtful ; the lines of greater slipping were, at the same time, the
zones of greater developed heat, and we had before us a perfectly definte
ON THE FLOW OF SOLID BODIES. 257
thermo-dynamical fact. If this fact had never been observed before, it
was clearly owing to the circumstances necessary for its manifestation
never having been all united together in so favourable a manner.
Brightened platinum requires for its deformation a great amount of
work. Its surface is unalterable and almost translucent when the metal
is heated to a red hot temperature ; it is but a moderately good conduc-
tor of heat ; its calorific capability is somewhat feeble ; all conditions
rendering the phenomena visible in the smelting of platinum whilst it
has passed unnoticed in the case of all the other metals.
But, although anticipating this explanation, we, nevertheless, felt it
our duty to prove it by more direct experiments, of which I shall now
speak, and which constitute the chief novelty — may I say the chief
interest — of this communication.
Given a metallic bar at the ordinary temperature — if two of its
lateral surfaces be coated with wax or tallow, and is tnen subjected to
the action of a single stroke of a ram, the wax will melt opposite the
depression which is produced ; and it is proved that, in certain cases,
this melted wax takes the shape of the two arms of the letter X, which
we have noticed on the platinum ; in many cases, the jambs are curved,
having their convex sides in front. This happens when the heat has
spread to a greater extent, and the wax has melted in the whole
of the space between them.
The prism which has this line for its base, and the width of the bar
for its height, represents a certain bulk and a certain weight, and if it
be admitted that the whole of it has been raised to the temperature of
the melted wax, this rise in the temperature must represent a certain
quantity of heat, or. by its mechanical equivalent, a certain quantity of
interior work, which is directly proved by the experiment.
By comparing this converted work to the work furnished by the fall
of the ram, we find a co-efficient of mechanical return, which is not
less than 70 per cent. We do not consider this number definitive ;
it depends upon the conductibility of the metal, the solidity of the
apparatus used in carrying out the experiment, the cleanliness of the
surroundings of the melted surface. But what I wished to point out,
Gentlemen, is, that we have come back to M. Joule's first methods, and
that our labours on the flow of solid bodies are already bringing us
back to the verification of some thermo-dynamical statements.
s
,558 SECTION— MECHANICS.
We had, at the very beginning of these researches, expressed our
opinion, that the phenomena observed in glaciers are, in more than one
respect, due to the mechanical deformation of the ice which is subjected
to the action of the immense burdens which its plasticity allows it to
transmit in all directions.
Quite recently we were called in to help M. Daubree in his work on
the schistosity of rocks. The experiments made on this subject do
not let the slightest doubt remain as to the ease with which the very
least relative motion, caused in any mass whatever, were it even abso-
lutely homogeneous, would bring about perfectly manifest sliding ten-
dencies. The best way to make this most perfectly obvious is to
scatter in the mass little spangles of mica, which range themselves in
a line as exactly as may be observed in the micaschists following the
very plan of each one of the relative motions. In this specimen, for
example, which is the result of the flow of a piece of clay earth, through
the aperture of a rectangular drawing-frame, not a spangle can be seen
in the transversal fractures, whilst they all show themselves perfectly
ranged, one after another, on the clefts which are easily produced
longitudinally by taking advantage of the schistosity which earth pre-
serves as distinctly after its desiccation as in the schists of the different
formations.
On the other hand, the crushing of blocks of earth or of lead be-
tween compression moulds which allow the matter to escape in one
direction only, has given us strikingly true representations of the
straightening of certain strata, their convolutions with schistose
qualities that are distributed throughout the body, and finally real up-
heavings, of which the bends and the rents are equally satisfactory
imitations.
We are therefore quite authorised in saying that the study of the
flow of solid bodies, has already thrown some light upon geological
phenomena, or more generally, upon the phenomena of inorganic
nature. The question is, whether this will likewise be the case, in the
future, with regard to organic phenomena. The matter, however,
cannot yet be investigated scientifically : we only know that vegetable
growth is carried on by the formation of cells which always arrange
themselves in groups according to a tubular order, that certain animal
developments, such as the horny tissue?, assume, during their growth,
ON THE FLO IV OF SOLID BODIES. 259
forms which are invariably the same, and which seem to be derived
from their first disposition. Just as if, in either state, the final arrange-
ment were carried by means of the circulation of nutritive fluids into
casings formed by the tissues, and already completed and prepared to
receive them.
However distant this similarity maybe, which is, to a certain extent,
the predominant characteristic of all organic formations — I was going
to say, the mechanical characteristic of the phenomenon of the
development of all objects in the vegetable and animal kingdom — it is
nevertheless by no means unreasonable to suppose that the day will
come when these phenomena will be explained, at least in their
essentially mechanical characteristic, and independently of all other
purely physiological and the more frequently predominant actions, by
considerations similar to those which you have been kind enough to-
listen to to-day.
[// has been thought desirable that this important communication
should also be given in the original FrencJi\.
SUR LA FLUIDITE" ET L'E"COULEMENT DES CORPS SOLIDES.
Lorsqu'il y a dix ans, a la suite d'experiences soigneusement re'pe'te'es?
je pensai devoir associer, dans le langage de la science, ces deux mots :
e'coulement des corps solides (flow of solid bodies), mes premieres
communications ne furent pas accueillies sans quelque nuance d'incredu-
lite", et c'est pour moi un devoir de reconnaissance de citer ici M.
Tyndall, M. Fairbairn et M. Scott Russell parmi les savants qui les
ont tout d'abord conside're'es avec inteYet. Je voudrais les remercier
dans votre langue, mais elle ne m'est pas assez familiere et je compte
sur votre indulgence pour me permettre de vous entretenir en Francois.
Cependant,la question de 1'ecoulement des corps solides a fait fortune,
elle m'a valu des suffrages que je n'aurais pas ose ambitionner, et
qui me permettent aujourd'hui de saluer votre exposition au nom de la
science Frangaise, qui a tenu a vous preter a son sujet une large et
sympathique collaboration.
Le fait principal de 1'dcoulement des corps solides etait bien simple :
lorsqu'une masse rdsistante, enfermee dans une enveloppe, est soumise
25o SECTION— MECHANICS.
a une action extdrieure d'une intensite suffisante, elle transmet, dans
tous les sens, des pressions plus ou moins grandes, et si la paroi est
percde d'un orifice, la matiere s'echappera par cet orifice, en formant un
jet au c depens des differentes parties de la masse. Lorsque celle-ci
e. t h .mogene, lorsque la forme de la masse est re"guliere, lorsque 1'orifice
est place par rapport a elle dans certaines conditions de syme"trie,
le mode de repartition finale peut etre ddduit du mode de repartition
initiale, et les premieres experiences faites ddcident les conditions
cinematiques d'un tel e*coulement.
C'est ainsi qu'en constituant un bloc cylindrique par la superposition
d'un certain nombre de plaques de plomb, on a pu reconnaitre que
chacune de ces plaques venait a son tour p^ndtrer dans le jet et y
former un tube concentrique, lorsque 1'orifice est lui meme concentrique.
Pourquoi avons-nous dprouvd tant d'dtonnement lorsqu'en coupant,
suivant un plan mcridien,le jet ainsi forme", nous 1'avons trouvd compose
d'autant de tubes continus qu'il y avait de plaques, jusqu'a 1'dpuisement
complet de la matiere qui en avait alimentd la formation ? La precision
toute gdometrique des phenomenes naturels pouvait elle vraiment se
traduire d'une autre fagon ? Toujours est-il, comme vous le voyez, que
la rdgularite ne saurait etre plus complete, qu'elle nous apparait avec
le caractere de 1'dvidence la plus absolue. La constitution mole'culaire
indefiniment rdductible, ne saurait assurdment etre mieux justifide que
par ces parois paralleles, conservant jusqu'a 1'dpaisseur microscopique,
qui sont si souvent 1'apanage des tissus naturels, une dgalitd d'allure et
de direction bien remarquable.
Ces experiences d'e"coulement concentrique ont etd aussitot, au point
de vue des deplacements relatifs, soumises au calcul, et nous pouvons,
aujourd'hui, dans une telle deformation, assigner sa trajectoirede chacune
des molecules de la masse et fixer avec assurance sa position finale
par rapport a celle qu'elle occupait dans la masse primitive ; par les
memes moyens aussi, les transformees de toute ligne ou de toute surface
definie dans sa position premiere.
Ces experiences deviennent bien autrement probantes lorsqu'on varie
la forme et la position des orifices ; ce sont toujours des tubes qui
rcpondent aux plaques primitives, maisles dpaisseurs relatives des parois
de ces tubes, les juxtapositions et les contournements qui en resultent
sont aussi instructifs, au point de vue de la nettete de leurs formes et
ON THE FLOW OF SOLID BODIES. 261
de la repartition des pressions dans toute P&endue de la masse
qui s'ecoule. Cette question, d'ailleurs, va nous occuper d'une maniore
plus spetiale dans 1'etude du poingonnage.
Lorsqu'un poingon p^netre dans une plaque mdtallique, il chasse
devant lui la matiere de cette plaque, qui commence, a un moment
determine, par former une protuberance sur la face opposde, et qui
finit par s'en detacher, sous forme d'un cylindre de meme diametre
que le poingon, et que Ton ddsigne sous le nom bien caracte'ristique de
ddbouchure. Au dessous de certaines epaisseurs, la debouchure
conserve une hauteur egale a la dimension de la plaque en epaisseur,
mais il n'en est plus ainsi lorsque la plaque est beaucoup plus epaisse.
Une debouchure de i centimetre de hauteur a ete fournie par un bloc
d'une epaisseur de 5 centimetres. Si le bloc est forme de plaques
superposees, toutes les plaques sont cependant representees dans cette
debouchure : les plaques inferieures, a peu de chose pres, par leurs
epaisseurs primitives ; la plaque superieure par une sorte de lentille
plan-convexe, dont la face courbe a pour base la face plane, restee
en contact avec le poingon, et qui a conserve, suivant 1'axe commun,
la presquetotalite de son epaisseur primitive ; les plaques intermediates
par autant de gobelets emboutis les uns dans les autres, aboutissant a la
meme face plane, et dont les fonds ont des epaisseurs variables, d'une
minceur extreme sur un certain point de 1'axe de la debouchure.
Ce point est le centre principal de Fecoulement qui s'est produit
de 1'axe a la circonference, sous Tinfluence des pressions determinees et
transmises par le poingon a l'inte*rieur meme de la masse. Lorsque cet
ecoulement a pu se produire, la resistance verticale de la cloison a
poingonner etait necessairement plusgrande que la resistance laterale ;
les deux resistances seront, au contraire, du meme ordre lorsque la
debouchure commencera a se detacher, et 1'effort a faire pour continuer
le poingonnage ira ensuite en diminuant rapidement jusqu'a la fin
de 1'operation.
Cejeu des resistances, que nous pouvons conclure des faits eux-memes,
nous a donne la vraie connaissance du jeu des pressions transmises, et
nous avons pu formuler des lors les lois de la transmission des pressions
dans une masse solide en voie de deformation, dans toute une zone plus
ou moins etendue, que nous avons appeiee la zone d'activite. Enfin, en
constatant I'efTort a exercer au moment ou la debouchure se separe,
262 SECTION— MECHANICS.
nous avons pu determiner les veritables coefficients de cisaillement,
qui sont les suivants, par centimetre carrd :
Kilog.
Plomb 182
Etain 209
Alliage de plomb et d'e'tain 239
Zinc 900
Cuivre 1893
Fer ... 3757
II est a remarquer que ces chiffres se rapprochent beaucoup de ceux
de la resistance a la rupture par extension, pour chacun des metaux
experiment's.
Les re*sultats du calcul de la transmission du travail mecanique d'une
couche a la suivante ont permis d'etablir la loi mathematique de la
repartition des pressions, non-seulement pour le poingonnage, mais
encore pour les diffcrents modes de deformation pre'cedemment etuclies.
Les formules indiquees par cette methode ont ete justifiees ulteVieure-
ment par M. de Saint-Venant et par M. Levy. Tout recemment, M.
Boussinescq, de la Faculte de Lille, nous annongait qu'il les avait
retrouvdes par des considerations exclusivement mecaniques, et eiles
peuvent ces lors etre considerees coinme acquises ala science de la fagon
la plus complete.
Unautre genre de recherchesnous alongucmentoccupe ; ce sont celles
qui se rapportent au rabotage des me'taux. Le copeau que 1'outil enleve
et qui, jusqu'alors, n'avait pas meme attire 1'attention des praticiens.
offre des particularites bien remarquablcs. Non seulement ii se vrille
souvent en helice, ce qui est le rdsultat des raccourcissements inegaux
des differentes files de molecules qui le composent, mais, a un point de
vue plus general, on peut dire de combien il se raccourcira dans une
circonstance donnee, environ des quatre cinquiemes de la longueur
primitive dans le cas les plus ordinaires de la pratique, et de combien,
par consequent, sa dimension trans versale augmentera en meme temps,
sa densite n'ayant pas vane" sensiblement. Ce copeau, qui est la
transformee du prisme enleve par le burin, augmente en epaisseur
en raison inverse de sa variation en longueur. L'examen de ces
deformations complexes, dans lesquelles les formes de'finitives ne
dependent plus de celles des moules, des filieres ou des poingons
ON THE FLOW OF SOLID BODIES. 263
dont nous avons parld prc'cddemment, mais seulement des forces
extdrieures et intdrieures qui sont mises en jeu. Nous n'avons
pu encore les caractdriser surcment que dans un petit nombre de
circonstances ; mais voici cependant un modele qui montre comment
la matiere, refoulde par un outil d'une forme particuliere et symd-
trique, passe d'une section carrde a une section triangulaire tres
agrandie, sous 1'influence des pressions transmises, en passant par des
intermddiaires gdomdtriques trace's d'apres une dpure et appartenant k
des surfaces analytiquementdefinies. Plus d'une ddcouverte sera faite
en mdcanique moldculaire par la poursuite de ces phdnomenes,
absolument ndgligds jusqu'ici et qui touchent de si pres aux propridtes
memes de la matiere.
Le forgeage est aussi un des moyens qui peuvent etre employe's
dans cette dtude si attrayante de la mdcanique moldculaire. Une barre
de fer n'est rien autre chose qu'un paquet de filaments juxtaposds et
agglutines, provenant individuellement d'un noyau determind. A
mesure qu'on augmente le nombre des mises, et qu'on dtire davantage
la masse formde par leur juxtaposition, ces filaments deviennent plus
tdnus, et ilest facile, par des modes spdciaux d'oxydation, de reconnaitre
dans une piece fabriqude tous les accidents des diffdrents precedes qui
ont dte employds pour sa production. Vous pouvez bien, par le forge-
age, dpanouir ces filaments ou les concentrer, les rdunir ou les sdparer,
mais vous ne pouvez les faire disparaitre, et c'est encore Ik un des
moyens d'investigation qui doivent servir k 1'dtude des ddformations
interieures, correspondant a tel ou tel changement de forme extdrieure.
Une fois que chacun des ddplacements relatifs est connu, ainsi que
1'effort ndcessairepourleproduire,on est bien pres de pouvoir ddterminer
le mode d'exdcution le meilleur et d'dvaluer le travail mdcanique qu'il
exige.
Dans 1'une de nos expediences de forgeage, faite sur une grande
echelle et sur du platine iridid, il s'est prdsentd un phdnomen eaccessoire
qui a ndcessairement appeld toute notre attention et qui se rattache
si intimementa la deformation des corps solides, que vous me permettrez
d'en dire quelques mots, quoique les .experiences qui en ddrivent ne
soient pas encore termindes ; c'est pour moi, d'ailleurs, une grande
satisfaction d'en faire connaitre, avant toute publication, les premiers
rdsultats devant une assemblee de savants Anglais.
264 SECTION— MECHANICS.
Le 8 Juin, 1874, nous avons seulement indique a 1'Academie des
sciences le fait principal : lorsque la barre de platine, au moment du
forgeage, s'etait dejk refroidie jusqu'au-dessous de la temperature
rouge, il est arrive plusieurs fois que le coup de marteau pilon qui
determinait simultane'ment, dans cette barre, une depression locate et
un allongement, se r^jhauffait suivant deux lignes inclines formant
sur les cote's de la piece bs deux diagonales de la partie de'prime'e ; et ce
re'chauffemente'taittelquele metal etait, suivant cesdeux lignes, ramene'
assez franchement a la temperature rouge pour qu'on put en distinguer
tres-nettement la forme. Ces lignes de plus grande chaleur restaient
me'me lumineuses pendant quelques instants et prdsentaient Taspect de
deux jambages de la lettre X. Dans certaines circonstances, nous
avons pu compter simultan^ment jusqu'a six de ces X produits
successivement, les uns a la suite des autres, a mesure que 1'on
deplagait la piece en travail pour 1'etirer de proche en proche sur une
partie de sa longueur.
L'explication de ces traces lumineuses nepouvaient faire aucun doute :
les lignes des plus grand glissement etaient aussi les zones deplus
grande chaleurde'veloppe', et nous etions en presence d'un fait de themo-
dynamique parfaitement defini. Si ce fait n'avait pas etc* observe
encore, cela tenait eVidemment a ce que les circonstances ndcessaires
a sa manifestation ne s'etaient pas trouvdes, toutes ensemble, rdunies
d'une fac/m aus<i favorable. Le platine iridie exige pour sa defor-
mation une grande somme de travail ; sa surface est inalterable et
presque translucide lorsque le metal est porte a la temperature rouge ;
il est mediocrement conducteur de la chaleur ; sa capacite calorifique
est assez faible ; toutes conditions pour que le phenomene fut rendu
sensible dans le forgeage de ce metal, alors qu'il etait reste inapergu
avec tous les autres.
En anticipant cette explication, nous avions cependant pour devoir
de la justifier bientot par des experiences plus directes, dont nous avons
maintenant a vous entretenir, et qui constituent la principale nouveaute,
oserai-je dire le principal interet de cette communication.
Une barre metallique etant donnee, a la temperature ordinaire,
si apres 1'avoir enduite de cire ou de suif sur deux faces laterales, on la
soumet a 1'action d'un seul coup de mouton, la cire fond en regard de
la depression produite, et Ton constate que cette cire fondue affecte,
ON THE FLOW OF SOLID BODIES. 265
dans certains cas, la forme de deux branches de 1'X que nous avions
observees sur le platine ; dans d'autres cas, les jambages sont courbcs et
pre'sentent en regard leurs convexitds ; c'est qu'alors la chaleur s'est
disseminde davantage et que la cire s'est fondue clans tout 1'intervalle
qui les separe.
Le prisme qui a ce trace* pour base et pour hauteur la largeur meme
de la piece represente uncertain volume et uncertain poids, et si 1'on
admet qu'il a ete tout entier portd a la temperature de la cire fondue,
cette elevation de tempdrature reprdsente une certaine quantitd de
chaleur, ou, en raison de 1'dquivalent mdcanique, une certaine quantitd
de travail intdricur qui se trouve directement constatde par Fexpdrience.
En comparant ce travail transform^ au travail fourni par la chute du
mouton, on trouve un coefficient de rendement me'canique qui n'est
pas infdrieur a 70 pour 100. Nous ne considdrons pas ce chiffre pour
ddfinitif ; il ddpend de la conductibilitd du mdtal, de la stabilite de
l'installation,de la nettetd des contours de la surface fondue ; mais ceque
je voulais vous dire, messieurs, c'est que nous voila revenu aux premieres
mdthodes de M. Joule, et que nos travaux sur Fecoulement des corps
solides nous ramenent ddjh, k quelques constatations theraio-
dynamiques.
Nous avions, des Forigine de ces recherches, exprimd la pensee que
les phdnomenes observes dans les glaciers sont, sur plus d'un point,
dus a des deformations mdcaniques de la glace soumise a Faction des
charges immenses que sa plasticitd lui permet de transmettre dans tous
les sens. II nous a ete donnd, tout dernierement, d'aider M. Daubrde
dans son recent travail, sur la schistosite des roches.
Les experiences faites a ce sujet ne laissent plus subsister le moindre
doute sur la facilite avec laquelle le plus petit mouvement relatif,
distribue dans une masse quelconque, fut-elle absolument homogene,
determine des sens de glissement tout a fait manifestes. Le meilleur
moyen de les mettre en plus parfaite evidence consiste a dissdminer
dans cette masse de petites paillettes de mica qui s'alignent, aussi
exactement qu'on Fobserve dans les micaschistes, suivant le plan meme
de chacun des mouvements relatifs. Dans cet dchantillon, par
exemple, qui resulte de Fecoulement d'un pain de terre argileuse par
Forifice d'une filiere rectangulaire, on n'apergoit aucune paillette dans
les cassures transversales, tandis qu'elles se montrent toutes, parfaite-
266 SECTION-MECHANICS.
ment rangees les unes a la suite des autres, sur Ics fentes quo 1'on
determine facilement dans le sens longitudinal, en profitant de la
schistosite que conserve la terre aprcs sa dessication, aussi nettement
que dans les schistes des diffdrentes formations.
A un autre point de vue, 1'dcrasement de blocs de terre ou de
plomb produifentre des plans de compression, en permettant a la
matiere de s'echapper dans un scul sens, nous a donne" des reprdsen-
tations, frappantes de vdritd, du redressement de certaines couches, de
leurs contournements avec des caracteres de schistosite, distribues
comme ils le sont dans la nature, et, enfin, de vcritables soulevements
dont les courbures et les dechirures sont d'une imitation tout aussi
satisfaisante.
Nous sommes ainsi tres-fonde a dire que 1'etude de 1'ecoulement des
corps solides a deja jete quelque jour sur les phenomenes geologiques
ou plus gdndralement sur les phenomenes de la nature inorganique.
En sera-t-il de meme dans 1'avenir en ce qui concerne les phenomenes
organiques ? C'est la une question qui ne saurait etre encore envisagee
dans le domaine scientifique : nous savons seulement que les vegetaux
croissent par Faccession des cellules, qui se groupent toujours suivant
une disposition tubulaire, que certaines excroissances animates, telles
que les tissus cornes, affectent aussi, pendant leur devcloppement, des
formes qui sont invariablement les memes, et qui semblent derivees de
leur premiere disposition, comme si, dans 1'une et dans 1'autre condi-
tion, la disposition finale se trouvait deduite, par voie de circulation
des fluides nourriciers, dans les enveloppes formees par les tissus deja
confectionnes et prepares pour les recevoir.
Quelque eloignce que soit cette similitude, qui est en quelque sorte
le caractere dominant de toutes les formations organiquesj'allais dire le
caractere mecanique du phenomene de developpement des vegetaux et
des animaux, il n'est pas irrationnel de supposer qu'un jour viendra ou
cesphcnomenes s'expliqueront,au moins dans leur partie essentiellement
mdcanique, et independamment de toutes les actions plus purement
physiologiques et le plus souvent dominantes, par des considerations
analogues a celles dont vous avez bien voulu nous permettre de vous
entretenir aujourd'hui.
The PRESIDENT : You have already by your acclamations expressed
your gratification at hearing the remarkable explanation given to us by
ON THE FLO IV OF SOLID CODIES. 267
M. Trcsca. He has worked out a subject which was very little known
~ hardly conceived of, in fact, in any form whatever — before, he took it
up, and commencing by giving us the results of his experiments, he has
drawn one deduction after another, and his subject has extended into
one which promises to be of very great importance indeed in mechanical
science. I cannot follow him into physiology, because I am not suffi-
cient physiologist to say whether our nails are forced out of us in the
manner M. Tresca has described ; but it is my want of apprehension,
no doubt, rather than his want of perfect conception which is at fault.
M. Tresca, by his investigation, throws down as it were the boundary
line between solids and liquids, a solid, according to his view, being
only a liquid with greater viscosity, and this is an enlargement of our
general conception of matter which cannot fail to be of practical im-
portance in mechanical science. With these few observations, I beg to
call upon you to pass a hearty vote of thanks to M. Tresca.
Mr. J. SCOTT-RUSSELL, F.R.S. : I beg to second the vote of thanks,
and, in saying so, allow me to say, from my own observation, that M.
Tresca has given to this meeting to-day, in comparatively few words,
the whole result of some nearly twenty years of continuous thought
and continuous experiment devoted to this subject, in the most admi-
rable and methodical way. I have watched his progress for that
number of years with the deepest interest, and I cannot tell you how-
profound a gratification it was to me to find that all this was to be
brought before you to-day. And allow me to say this : that in addition
to washing away the curious and narrow prejudice in which our minds
are bound as to the radical difference between a solid and a fluid, and
we must get rid of this prejudice in order to go further in the matter of
science — he has paved the way for enormous improvements in the
important arts of metallic manufactures. He has given us the key to
make out of every kind of metal, on the first occasion in which it is
lignified, every kind of body to which we may wish it afterwards to be
converted. Whereas we, in our clumsy way, up to the present time,
take a body of metal, melt it, and then cool it ; and then to make a
little change in it, heat it again, and cool it again ; and then to make
another little change in it, heat it again, and again cool it. But he
now tells us that you have only to communicate to a little bit of melted
metal, the first day it comes to the state of metal, what you want it to
i
268 SECTION— MECHANICS.
come to, and you can put it into that shape of all sorts of sizes, at
once, with one heating instead of several. I think the mere getting
this idea, founded as it is on careful investigation, may be of the
greatest value to us. I therefore wish to say how warmly we should
appreciate the benefit M . Tresca has conferred upon us to-day by his
very humorous, and I may say enthusiastic and inspiring lecture.
SECTION— MECHANICS (including Pure and Applied
Mathematics and Mechanical Drawing).
Monday, May 2.2nd, 1876.
Dr. SIEMENS, President, in the chair.
The PRESIDENT : Ladies and Gentlemen, we now re-open the
Conference on mechanical subjects, and the first paper on our list is
that by Professor Kennedy, on Reuleaux's Collection of Kinematic
Models. I may take this opportunity of stating that it is the intention of
the department to organise a system of explanations at stated intervals
of the exhibits in the building. A list will be published stating the
days in the weeks at which exhibitors or their representatives, or
gentlemen qualified to do so, will give full explanations of certain
exhibits, and by this means it will be possible to extend the knowledge
to be obtained from this collection to a fuller extent than could be
realised by discussing these questions at these Conferences only. We
are naturally limited here to time, and can only sketch out the general
outline of the very large and interesting collection with which we have
to deal. I will now call on Professor Kennedy.
Professor Alex. B. W. KENNEDY, of University College, London,
then delivered the following address
ON THE COLLECTION OF KINEMATIC MODELS,
By Professor Reuleaux, of Berlin :
Most of the models, of which a small number are upon the table
before you, are a portion of an educational collection designed by
Professor Reuleaux, the Director of the Royal Polytechnic Academy
in Berlin, for use in the classes of that Institution, the rest have been
sent to the Exhibition by Messrs. Hoff and Voigt of Berlin, and
Messrs. Bock and Handrick, of Dresden. They have been designed
chiefly to illustrate Reuleaux's Theory of Machines, a theory which
differs in some very important respects from any treatment of
270 SECTION— MECHANICS.
mechanisms hitherto adopted. Looking at the models by them-
selves, some of them seem extremely intelligible, and some very
much the reverse. I shall endeavour, in the very limited time
at my disposal, to point out the leading ideas which run through
the whole, and connect the very familiar mechanisms with those
more complex ones which, although differing only in degree from
the former, appear at first sight so entirely dissimilar.
In the old books upon machinery, such as that of Ramelli for
instance (1588). each machine was taken up by itself, and treated as a
whole from beginning to end. One kind of pump after another, for
example, may be described without any recognition of their essential
identity, or the use of any single word to express the concept pump.
Each machine is described' separately as an apparatus which raises water
from such a place, in such a way, and delivers it at such a place. The
complex idea which we cover by the word pump, had not yet found a
place in the writer's mind.
Presently it was found, of course, that machines were not all different
from beginning to end, but consisted of various combinations and
repetitions of similar elements ; these elements in time became more
distinctly recognised, and were called mechanisms. Each machine
accordingly was not now described as a whole, but was analysed into
the mechanisms of which it consisted, and these received separate
treatment. Very much valuable matter has been written upon
machinery from this point of view. In our own country, Professor
Willis especially gave most valuable contributions to the science of
machinery on this basis. Hitherto, however, we have stopped at this
point. We have obtained each mechanism " somehow," but have not
yet troubled ourselves as to how it was invented, or what the elements
were. We have, that is, analysed the machine into mechanisms, but we
have not yet analysed the mechanisms themselves. We are all familiar
with the interesting and valuable work which has been done in the way
of examining the motions of particular pieces or members of a mechanism
after it has been presented to us, but it cannot be denied that in all cases
the mechanism itself has been in the first place taken as a whole.
Professor Reuleaux has attempted to perform the final analysis
to which I have alluded, and to discover of what elements mechanisms
consist, and how these elements have been combined. He starts
KIN EM A TIC MODELS. 27 1
from what appears to be the fundamental principle of every machinal
combination or arrangement ; that each particular part of the combi-
nation must have at each instant only one definite motion relatively to
every other part. If, in any machine, there be a piece which at any
one instant can move in two directions, there is obviously some defect
in the machine. Engineers are familiar with the many devices that
have to be employed in connexion with certain mechanisms to carry
them across " dead-points," £c. This condition, that it shall be
impossible for any point in a machine to move at any instant in any
direction other than that intended, is a universal one. The way in
which it is satisfied is by giving to certain portions of those pieces
which form the machine suitable geometric forms. These forms are
arranged in pairs, in such a way as to be reciprocally envelopes one of
the other. The one piece, then, so envelopes the other, on account of
the forms given to both, that each can move only one way relatively to
the other at any instant. The motion of such pieces is called
constrained motion. Let me take a very simple case — a screw and
nut. These two pieces are formed in such a way that the nut can
move only in one way at any instant relatively to the screw, and the
screw in one way relatively to the 'nut. If the pitch of the screw be
made zero, we have simply a pair of solids of revolution, or "re volutes,"1
having such profiles at the end as to prevent any axial motion ; and
again we have a pair of mutually enveloping forms, whose relative
motion is absolutely constrained. If, on the other hand, the pitch be
made infinite, we have a pair of prisms, in which the only possible
relative motion is axial. In the first case, the constrained relative
motion is twisting ; in the second, it is turning (twisting without any
translation) ; and in the last case, where the pitch is infinite, it is
simply sliding (twisting without any turning). You recognise, in these
three pairs of bodies, the geometrical forms which are used in ninety-
nine cases out of a hundred to constrain the motions of machinery.
Such bodies as these Reuleaux calls pairs of kinematic elements, and
—when they have the peculiarity that one entirely encloses the other, —
lower pairs or closed pairs.
It is not essential, however, that one should enclose the other.
There are before you a number of examples of higher pairs, the bodies
of which mutually constrain each other without complete enclosure.
272
SECTION— MECHANICS.
I may briefly point out the nature of one of these (Fig i.) The one
element is an equilateral curve-triangle,
which possesses the property that any pair
of parallel tangents to it are at the same
distance apart. The second element is
a square, the side-length of which is equal
to this distance. The two elements al-
ways touch each other in four points, the
normals to these points intersect in one
point (as O ), and at any instant motion
can take place about this point only. The
C
K
Figure i.
two bodies form a pair of elements in exactly the same sense as before,
but with one important difference. In the lower pairs the paths of all
points in the moving element are similar. Every point in the moving
element of the twisting pair, for instance, moves in a helix of the same
pitch, all points in that of the turning pair in concentric circles, &c.
Here, however, the paths of all the points are different. Some of
Figure
KINEMATIC MODELS.
these paths are very beautiful curves, as you will see if you can follow
the motion of the pointer in the model (see Fig. 2). These paths are,
in this case, combinations of epi-and-hypotrochoidal arcs. I cannot
here go more fully into their nature, I merely show them to illustrate
the fact that enclosure is not an essential characteristic of pairs of
elements having constrained motion.
If two elements be joined together rigidly by a body of any form
whatever, we have what is called a kinematic link. If I take, for
instance, this nut, and fasten it to this open cylinder, I have such a
link. This solid cylinder, connected to the screw, gives another link,
and so on. By pairing together a number of links we get a combination
Figure 3.
which Reuleaux has called very happily a kinematic chain. In the
particular chain which I have here (Fig. 3) there are four links, each
being a bar rigidly connecting two elements, and these elements
belong in each case to a turning (closed) pair of elements. Before me
on the table are a number of other chains similarly constituted, and
containing both turning and sliding pairs of elements.
I must now direct your attention to a matter which is of the greatest
simplicity, but of equally great importance. If I take any pair of
elements in my hands, and move it, you see at once that although the
motions of each element, relatively to the other, are perfectly determi-
nate, the absolute motions are perfectly indeterminate. The elements
may move anywhere in space. In the kinematic chain there is just the
274 SECTION— MECHANICS.
same peculiarity. It is none the less important that it is almost
absurdly obvious. The motions of every link relatively to every
other, in other words the relative motions of the links, are absolutely
determined ; the absolute motion of the whole chain, or, what is the
same thing for our purpose, the motion of the links relatively to this
table, is left entirely indefinite.
The conversion of the relative motion into absolute motion (in the
restricted sense in which we have used this expression) is a very simple
matter. In the case of the pair of elements, all that is required is that
one element should bejfe;/, that is prevented from moving relatively
to any portion of space which is, for our purposes, stationary — it may
be to a room (as here), or to a railway carriage, or a ship, &c. The
same method applied to the kinematic chain enables us to convert the
relative motions of the links into absolute motions. We must, that is
to say, fix or make stationary one link of the chain.
A combination of kinematic links, therefore, whose absolute motions
are unconstrained, is a kinematic chain. The same combination,
when one of its links is fixed, forms what is universally known as
a mechanism. By fixing, for instance, the link a h (Fig. 3), we obtain
a mechanism similar to the beam and crank of an ordinary beam
engine, b c revolves, while/ £• swings to and fro. But the chain has
four links, and it is obvious that I may fix any one of them. The
combination, that is the kinematic chain, remains the same, but the
nature of the mechanism may be entirely altered. Suppose, for
instance, the link b c be fixed, we obtain a mechanism which you see
at once differs entirely from the last, and which you will recognise as
the common drag link coupling, a h and d e both revolving as cranks
about the fixed centres b and c.
A mechanism is, therefore, a kinematic chain of which one link is
fixed. Two links cannot be fixed simultaneously without making the
whole chain immovable. Any one link, however, can be fixed, and
thus from any chain we can obtain as many mechanisms as it has
links. I shall endeavour to show you, by a few illustrations, what a
ivonderful insight this gives us into the nature of some familiar
mechanisms. I will only mention in passing what may, perhaps, be
new to some, that this chain (Fig. 3), with which we are so very
familiar, is not moveable because the axes of all its pairs are parallel,
KINEMATIC MODELS. 2;5
but because they all intersect in one point. In this particular case
Figure 4.
that point is at an infinite distance, but the chain moves equally wel
if the point of intersection be at a finite distance, as is illustrated by
Fig. 4. Upon this mechanism many engines (disc engines, &c.), and
other machines have been based. Hooke's universal joint is a familiar
illustration of it. The complex constructive forms of these, however,
make the recognition of their real nature almost impossible without the
aid of some such system as Reuleaux's analysis.
In order to obtain the constrained motion of a closed pair, it is not
necessary that both elements should be constructed as fully as in the
cases we have hitherto looked at. Grooves might be cut down the
sides of a pin, for instance, without affecting its motion in an eye.
Professor Reuleaux has made some investigations, which I can only
mention here, on the extent .to which this process can be carried.
Without further proof, I have no doubt you will recognise at once that
276 SECTION— MECHANICS.
by the use of the slot and sector of Fig. 5 instead of the pin and eye
Figure 5.
g h (Fig 3), no change has been made in the chain. The complete
cylinder pair has been replaced by a sector and a slot concentric with
it, but of totally different diameter ; the motions remain absolutely
identical. We obtain thus a very convenient method of altering
the length of the links of the chain, for the link f g has now
taken the form of the sector c (Fig. 5). To make that link longer,
herefore, all we have to do is to give the sector a larger radius. If we
make the link infinitely long, the sector becomes a prism, working in a
straight slot of which the axis passes through the centre of the pin i
(Fig 5), and we obtain this very familiar chain (Fig 6), the driving
Figure 6.
mechanism of the common steam engine. It is derived from the
KINEMATIC MODELS.
277
former merely by increasing the lengths of two of its links, making
them equal and infinitely long. I particularly wish to draw your attention
to this chain, both because it is very familiar, and because by its
inversion, that is by fixing one or another of its links, we get such very
notable results. I have already fixed one link (Fig. 6), and you have
seen the common steam engine driving train. If I fix another link, say
Figure 7.
the connecting rod, we have a mechanism which I think you will at once
recognise as the driving train of the common oscillating engine (Fig 7).
This appears even more distinctly if we reverse the sliding pair 4,
making the link d carry the full prism, and the link c the open prism
(Fig. 8). The link c becomes the steam cylinder, d (which was the
Figure 8.
frame in Fig. 6) the piston and rod, and b (the connecting rod in
Fig. 6), the framing of the engine.
278
SECTION— MECHANICS.
This intimate connexion between the driving mechanism of the
direct-acting and oscillating engines was never, I think, recognised
until Reuleaux pointed it out. They are the same chain., the only
kinematic difference between them being in the link which is fixed.
But we can go further ; we can fix, for instance, the crank- We ge'"
thus a mechanism doubtless familiar to most of my hearers (Fig. 9),
-r
Figure 9.
and which has often been described and applied. Sir Joseph Whit-
worth, for instance, has used it as a quick return motion. If the link b
KINEMATIC MODELS. 279
revolve with a uniform velocity, it gives to d the varying velocity
which has been so often utilised. The mechanism is obtained from
the same chain as before, simply by choice of a different link for the
stationary one* In general it is constructively disguised in such a way
as to be only recognisable with difficulty, but when put in this
schematic form it can easily be analysed into its kinematic elements.
From the same chain, we may obtain one more mechanism by
fixing the block (Fig. 10). This mechanism has been seldom used,
but it is occasionally employed. The motion of the link a is now
characteristic.
We must now proceed to look at a few other leading ideas illustrated
by these models. First, we may notice as long as the form of the
elements of the pairs remains unchanged, their relative size is a
matter of indifference. We have already seen this incidentally in
comparing Figs. 3 and 5. By utilising this principle we can obtain a
great number of very different-looking forms of one and the same
mechanism. Models of many of these are on the table before me :
some of them are constantly used by engineers, others have been
seldom or never applied. The ordinary eccentric is a familiar illus-
tration of this " expansion of elements." It differs from the train
shown in Fig. 6 only in the relative size of two of its elements. The
turning-pair at 2 (Fig. 6) is made so large as to extend beyond the
pair i ; all the motions in the train remain, however, as before.
i£o SEC TION— MECHANICS.
In order to illustrate the way in which the system of kinematic
analysis, which I have sketched to you, can be applied to actual
machines, Professor Reuleaux has examined analytically an immense
number of those unfortunate devices called rotary engines, on which
so much ingenuity and excellent brainwork has been wasted. In his
" Theoretische Kinematik," he gives illustrations of between sixty and
seventy of these machines, analysing every one of them into one or
other of the three chains which we have been examining (Figs. 3, 4,
and 6). The inventor has generally called his machine " rotary "
because of some notion that there were more rotating parts, or more
direct rotation, than in the ordinary engine. While there are a few
engines in which this is the case, in the vast majority it is entirely a
mistake. Here is one (see Fig. 1 1) which hasbeen invented over and over
again. I believe it was invented for the first time in 1805, by a Mr.
Trotter ; it was re-invented in 1831, 1843, 1863, 1866, 1870, 1872, 1873,
Figure n.
and possibly at many other times. One gentleman, whom I see here,
told me he had invented it himself twenty years ago ! After all, it is
KINEMA TIC MODELS. 28 1
absolutely identical with the chain of Fig. 6. The link fixed is the
crank, so that, as a mechanism, it is represented by Fig. 9. I am
sorry my time will not allow me to prove this, but by analysing the
pairs of elements which it contains it shows itself at once. Many
other rotary engines of which there are models on the table are of the
same kind. Here is one which was exhibited at the Exhibition of
1851, and which attracted a good deal of notice at the time— Simpson
and Shipton's machine. It is really nothing more than the mechanism
shown in Fig. 10, although its constructive form so disguises its real
character. I might go through a great many more in the same way,
but time compels me to leave this part of my subject.
In Reuleaux's work, to which I have alluded,. and of which I have just
completed the English translation, he uses a method which, while
it is by no means original with him, has never been formerly developed
to the same extent and in the same way. I must try in a few words to
indicate the general nature of this method. If we have any plane
figure moving in a plane, its motion, at any instant, may always be
considered as a motion about one particular point (it may be at a
finite or an infinite distance), and this point is called the instantaneous
centre, for the motion of the figure. The body may continue to move
about the same point, in which case the instantaneous centre becomes
a permanent centre ; but in general the motion of the body in
successive instants is about different points, each being for the time,
the instantaneous centre. The locus of the points which thus become
instantaneous centres for the motion of any figure is some curve, and
is called by Reuleaux Polbahn, for which I propose the use of the word
centroid. If we have any two figures A and B, having a definite relative
motion, and make the relative motion of B to A absolute by fixing A,
we can, by moving B, find as many points in the centroid as we wish, so
to construct the curve. This centroid remains, of course, stationary, like
the figure A, and is called the centroid of A. By fixing B and moving
A relatively to it, we can in the same way obtain the centroid of B.
We have then two curves, one connected with each figure, and these
possess certain properties which are of great value in the study of
mechanism. As the figures move these curves roll upon one another,
and their point of contact is always the instantaneous centre of motion
for the time being. It is, of course, impossible for me to prove these
SECTION— MECHANIC 9.
-i any other properties of these curves here ; many gentlemen here
must be quite familiar with the proofs. I must content myself with
simply showing you, by way of illustration, models of mechanisms in
which the centroids are constructed in such a way that their rolling can
be distinctly seen. By the aid of these centroids we can treat a great
number of kinematic and dynamic problems in an extremely simple
and beautiful manner, and can treat complicated and simple prob-
lems by one general method, instead of using different methods.
Centroids have not, so far as I know, been used in English text
books hitherto, but have not unfrequently found more or less
extended use in German and French works, principally in static
and kinematic problems. I have found them, however, even more
useful in Kinetics. Among the more recent books in which I have
noticed them, I may mention Dwelshauver's Dery's "Cine'matique,"
Schell's "TheoriederBewegungundder Krafte,"and Prdll's"Graphische
Dynamik."
Considering the constrained motion of bodies instead of plane figures
only, the instantaneous centre becomes an axis, and the centroidal
curve a ruled surface, the locus of all the axes. These surfaces are
called axoids. For bodies having complane motion, they are
cylinders ; for bodies having motion about a fixed point, cones ; and
for general motion in space, general ruled surfaces, in general non-
developable, of which successive generators twist upon each other.
Poinsot was, I believe, the first to mention these surfaces.^
I shall only mention one more point in connection with the subject
before us. Professor Reuleaux has devised, for the purpose of aiding
his kinematic work, a system of notation founded upon his analysis,
which can be used to represent these mechanisms in a perfectly simple
manner. Of course, to write down a description of them is a long
matter, but hitherto we have not known their real nature analytically,
and therefore could do nothing else. Now that we do know it, we
may treat them exactly as we do chemical compounds, where instead
of writing down the whole names of everything, we use short symbols
for known elements. This kinematic notation I can do no more than
mention. It seems to me very original, and I have myself found it
very useful in the analysis of really complicated machinery.
Mechanisms of great apparent complexity come out, often, in forms of
KINEMATIC MODELS. 283
really wonderful simplicity, and one's work is made at the same time
much more easy and much more satisfactory.
These models are very beautiful, but they are also necessarily some-
what expensive. I have here a couple of wooden ones, however, which
will serve to show that they can be constructed and used in schools
without any very extraordinary cost. These two models, and also the
stand for carrying them, have been made for me by M. Paul Nolet, of
University College.
I must now thank you for the kind attention with which you have
listened to my sketch of the nature of this beautiful collection of
models, and I should like also to take this opportunity of thanking
Herr Kirchner, of the Berlin Akademie, for the trouble he has taken
in preparing and arranging them for me.
The PRESIDENT : I am sure we have passed a very agreeable half
hour in listening to Professor Kennedy's explanations of these most
beautiful and instructive models. I think this new branch in
mechanism, kinematics, will be extremely useful in helping mechanical
engineers in devising improved means to an end, because by com-
bining motions into systems, we can resort to any combination that
seems likely to answer our purpose, without having to go to the
fountain head of our own brains to originate it. I regret that we have
so little time to go with Professor Kennedy into the details of the
various contrivances put before us, but I hope that Professor Kennedy
will give further explanations under the new arrangement which I have
had the pleasure of announcing. I will now call upon you to pass a
vote of thanks to Professor Kennedy for his interesting communication.
Dr. MANN : I wish to ask Professor Kennedy if the work he
referred to just now was a translation.
Professor KENNEDY : Yes.
The PRESIDENT : I will now call on Mr. Barnaby, the Chief Con-
structor of the Navy, to give us his communication on Naval Archi-
tecture. I will take this opportunity of announcing that we shall have
to make some little change in our programme. General Morin arrived
yesterday from France, and has to leave again in a couple of days.
As we should all like to hear him on the subject to which he has given
such very great attention, that of ventilation, it has been thought
desirable to take his paper at two o'clock to-day.
284 SECTION— MECHANICS.
ON NAVAL ARCHITECTURE,
In nominating for the distinguished position which I occupy this
morning in an International Assembly, the Director of Construction of
a War Navy, the Committee have exposed themselves to some possible
objections. I can find their defence not only in my own personal
fraternal and kindly feelings towards our guests, but also in the general
aspect of war machinery to the eyes of an Englishman. He would
show his newest ship of war or his newest gun to his foreign guest
with the same sort of feeling that he would exhibit the trappings and
weapons of the policeman or the special constable. They are the
means by which he hopes to make himself the terror of evil doers, and
he does not reckon his guest among them. Still the Admiralty has not
exhibited a single model of a ship of war, nor any warlike apparatus.
Every modern ship of war equipped for sea is in itself a series of
laboratories full of scientific instruments and apparatus, but they are
of such a character that they could not be well transferred bodily to
these galleries, and it is impossible to represent them by models or
drawings. But, thanks to the labours of the Committee, the Exhibition
in this department of Marine Architecture is not without interest.
Notwithstanding that ships and apparatus for modern naval warfare
are represented in such a very incomplete manner in this splendid
Exhibition, a state of things which, perhaps, no one much regrets,
I should not be justified in ignoring ships of war in an address on
Naval Architecture.
There is a model in the Exhibition of some of the floating batteries
originated by the late Emperor, Napoleon the Third, of France, built in
1854-56, by Messrs. Green, of Blackwall, and there is also a model of
the first English seagoing ironclad, the " Warrior," designed under the
superintendence of Mr. Isaac Watts.
The "Warrior" is a very remarkable ship, not because she is a
powerful fighting engine, for that she cannot be said to be, but because
in the material of construction and in the disposition of her armour,
she is precisely what experience has shown to be the best ; and our latest
designs, the " Ajax " and " Agamemnon " differing from her, as they do
widely, in proportions, in thickness of armour, in power of guns, in the
ON NA VAL ARCHITECTURE. 285
mode of propulsion, and in internal arrangements, are still like her in
that they are built of iron and use wood for only secondary purposes,
and are like her also in having no side armour at the bow or stern,
watertight decks under water, with cellular divisions over them, taking the
place of armour. This latter feature has been subsequently elaborated
at various times and with different degrees of completeness and success
by Mr. Reed; Mr. Michael Scott; by the present Minister of Italian
Marine, Signer Brin ; and by myself and colleagues. Our newest
design for seagoing battle-ships of 8,400 tons displacement, i. e., the
" Ajax " and " Agamemnon," differs broadly from this first ship in the
following respects : —
1. The length of the "Warrior" is six and a-half times her breadth,
and the " Ajax " and " Agamemnon " are only four and a half times.
2. She has four and a-half inches ,armour and 9-ton guns, while the
latter ships, although of less dimensions, are to have eighteen inches
of armour and 38-ton guns.
3. She obtained fourteen and a-third knots speed with engines indi-
cating o'6 of a horse-power per ton of displacement. In these new
designs we shall be content with a knot less speed, obtained by
means of a horse-powei per ton of displacement.
4. This speed is obtained in the " Warrior " with great draught of
water, a single screw, and fine lines ; it will be obtained in the "Ajax" and
" Agamemnon " with two screws, a light draught of water, and full lines.
5. In the " Warrior " there is only one means of propelling and one
means of steering, and the steering gear is exposed to shot. In these
latest ships there are two distinct isolated means of propelling, two
means of steering, and the steering gear is completely protected.
6. In the " Warrior " there is only a single bottom, except for a
small breadth of the ship ; in the latest ships, and in nearly all the
ironclads, there is a complete double bottom.
7. In the " Warrior " there is no fire from behind armour either
ahead or astern; in the latest designs the protected fire ahead and
astern is as powerful as that on the beam.
8. In the "Warrior" the consumption of fuel per norse-power
indicated is four and a-quarter pounds ; in our recent ships it is less
than three pounds.
The ships which I have thus compared with the " Warrior " are to
2C6 SECTION— MECHANICS.
be constructed on the same principle as the " Inflexible " but will have
a knot less speed than the " Inflexible," thinner armour (one and a-half
feet instead of two feet) and 38-ton guns.
These changes have been made in several steps extending over
several years. I do not know precisely to what extent Mr. Scott
Russell influenced the general conception of the design of the " War-
rior," but I believe he did so to a considerable extent. I know that
the influence he has exerted while the development of iron ship-
building has been going on in the Royal Navy has been far greater
than has ever been recorded or acknowledged.
It ought to be recorded by me here, I think, that the Exhibition
contains models of the three grandest ships of war in the navy of the
German Empire. The " Konig Wilhelm," and the " Kaiser " and
41 Deutschland," now forming part of the squadron commanded by
Admiral Batsch, were designed by an English architect, and built in
English dockyards, and I may also mention that China, which has now
an important naval establishment at Foochow, where ships of war and
marine engines are constructed under the superintendence of a French
officer, has recently had built for her in England two of the Rendel
gunboats, with 25-ton guns, the models of which are furnished by the
builders, Messrs. Laird. The Thames Company send a model of the
" Vasco da Gama," the first ironclad for the famous navy of Portugal.
I should like now in a few brief sentences to discuss and dismiss the
question of armour-plating, and pass on to matters of less national
moment, but of more general interest.
There are people who say that it would be a gain to the world, and
notably to England, if some one would find the way to get rid of
armour-plating. Their minds are distressed with a condition of things
of which they cannot pretend to foresee the probable end and issue, for
the contest between the armour and the gun is of this character.
I do not myself pretend to foretell at what point on the road we are
travelling we shall be obliged to turn off, but I do not doubt that
wherever it may be, and in whatever direction the new road may lie,
naval armaments will not become less costly or less subject to the
progress of mechanical invention. The introduction of artillery, of
steam, of armour-plating, and of torpedoes into naval warfare have all
tended to increase the power of civilisation, of wealth, and of
ON NA VAL ARCHITECTURE. 287
mechanical skill to assert themselves against the power of mere
numbers and of brute force, and the nations represented in this
assembly are the last in the world that should regret that naval battles
may be fought successfully by the few against the many, provided that
the few have on their side, in addition to the universal qualities of
animal courage and endurance, the rarer possessions of wealth, of
science, and of mechanical skill.
I would add that I do not advocate — indeed I have always opposed
— the protection of men in detail by armour. I would protect them in
the mass by protecting their ship, their signalling and steering instru-
ments, and their fighting power as a whole ; but I would not attempt
to protect each gun and each man. My own ideal of a fighting ship is
not the " Inflexible," the " Alexandra," the " Temeraire," or the
" Ajax," and " Agamemnon," although I am primarily responsible for
their designs, but it is the ships now building in Scotland, the
" Nelson" and " Northampton," which represent in my view the best
disposition of the offensive and defensive powers.
In these ships the central part is armoured up to a shot-proof deck
four feet out of water. The ends are without side-armour, but have an
under-water deck protecting everything that is vital. There is a high
battery with numerous heavy guns ; the battery is protected from end-on
fire, and the bow and stern guns, which fire in line with the keel,
and are the most powerful of any, are protected from broadside fire
also. The intermediate guns have in front of them a thin side incapable
of being splintered, and each gun's crew is cut off from the next by a
splinter-screen or traverse. This broadside of guns can be loaded and
laid in a close engagement under the shelter of the bow or stern
armour, and may be fired by electricity without exposing the crew.
The ships are propelled by two screws ; the propelling machinery is
divided into compartments separated from each other by water-tight
bulkheads, and there is for a time of peace good sail-power. In a time
of war only the lower masts would stand, and the ships could then
carry a very large supply of fuel. The cost of each of these ships for
hull and engines, exclusive of fittings and rigging, is about ^350,000.
To turn now to 'the Loan Collection more particularly I would
remark that in it there are examples of the beginnings of things which
have assumed gigantic proportions.
288 SECTION— MECHANICS.
There is a model and a drawing of the first steamboat in Europe
advertised for the conveyance of passengers and goods, and there is
also the original engine made and fitted on board that vessel.
That vessel was the " Comet," built in Scotland in 1811-12 for Mr.
Henry Bell, of Helensburgh, the boat being designed and built by Mr,
John Wood, at Port-Glasgow. The " Comet " was the first steam-
vessel built in Europe that plied with success in any river or open sea.
The little vessel was forty-two feet long and eleven feet wide. Her
engine was of about four horse-power, with a single vertical cylinder.
She made her first voyage in January, 1812, and plied regularly between
Glasgow and Greenock at about five miles an hour.
There had been an earlier commercial success than this with a
steam vessel in the United States of America, for a steamer called the
"Clermont" was built in 1807, and plied successfully on the Hudson
River. This boat, built for Fulton and Livingstone, was engined by
the English firm of Boulton and Watt.
The reason for this choice of engineers by Fulton appears to have
been that Fulton had seen a still earlier steamboat for towing in
canals, also built in Scotland, in 1801, for Lord Dundas, and having an
engine on Watt's double-acting principle, working by means of a con-
necting rod and crank, and single stern wheel.
This vessel, the " Charlotte Dundas," was successful so far as
propulsion was concerned, but was not regularly employed because of
the destructive effects of the propeller upon the banks of the canals.
This brings me to another interesting model. The engine of the canal
boat just spoken of was made by Mr. William Symington, and he had
previously made a marine engine for Mr. Patrick Miller, of Dalswinton,
Dumfriesshire. This last-named engine, made in Edinburgh in 1788,
marks, it is said, the first really satisfactory attempt at steam navigation
in the world, and the veritable engine is in this exhibition. It was
employed to drive two central paddle wheels in a twin pleasure-boat
(a sort of " Castalia") on Dalswinton Loch. The cylinders are only
four inches in diameter, but a speed of five miles an hour was attained
in a boat twenty-five feet long and seven feet broad. The models^
&c., which I have referred to, cover the period from 1788 to 1812.
There is also a model of the first steam vessel built in a royal dock-
yard. She too is called the " Comet." She appears to have been
ON NA VAL ARCHITECTURE. 289
built about the year 1819, and was engined by Boulton and Watt. This
ship had two engines of forty horse-power each, to be worked in pairs
on the plan understood to have been introduced by this firm in 1814.
In 1833-4 iron appears to have first come into use for the construc-
tion of steamships, and there are models of the "Rainbow," the
"Nemesis," and other vessels built soon after this date. In 1838 the
"Sirius" and "Great Western" commenced the regular Atlantic pas-
sage under steam. The latter vessel, proposed by the late I. K. Brunei,
and engined by Maudslay, Sons, and Field, made the passage at about
eight or nine knots per hour. There is an excellent model of the
engines of the " Great Western" in the collection. One year earlier,
i.e. in 1837, Captain Ericsson, a scientific veteran who is still among
us, towed the admiralty barge with their lordships on board from
Somerset House to Blackwall and back at the rate of ten miles an hour
in a small steam vessel, driven not by paddles, but by a screw. Messrs.
Laird supply a model of the " Robert L. Stockton," built by them in
1839, from Capt. Ericsson's designs. This vessel had the rudder be-
fore the screw, arranged as in the modern fast launches built by Mr.
Thorneycroft. This firm exhibits a model of a proposed screw ship-of-
war of a still earlier date, 1836. The screw did not come rapidly into
favour with the Admiralty, and it was not until 1842 that they first
became possessed of a screw vessel. This vessel, first called the
"Mermaid" and afterwards the "Dwarf," was designed and built by
the late Mr. Ditchburn, and engined by Messrs. Rennie. Her model
is in the exhibition.
In 1841-3 the "Rattler," the first ship-of-war propelled by a screw,
was built for and by the Admiralty under the general superintendence
of Mr. Brunei, who was also superintending at the same time the con-
struction of the "Great Britain," built of iron. The engines of the
"Rattler," of 200 nominal horse-power, were made by Messrs. Maudslay.
They were constructed, like the paddle-wheel engines of that day, with
vertical cylinders and overhead crank shaft, with wheel gearing to give
the required speed to the screw. The " Rattler," built of wood, does not
exist now, but the " Great Britain," built of iron is still at work.
The next screw engines made for the Royal Navy were those of the
"Amphion" 300 nominal horse-power, made in 1844 by Miller and
Ravenhill. In these the cylinders took the horizontal position, and they
u
290 SECTION— MECHANICS.
became the type of screw engines in general use. This ship had a
screw-well and hoisting gear for the screw.
In 1845 tne import nee of the screw propeller for ships of war became
fully recognised, and designs and tenders were invited from all the
principal marine engineers in the kingdom. The government of fhat
day then took the bold step of ordering at once nineteen sets of screw
engines of the following firms, viz., of Messrs. Maudslay, Sons, and Field,
four sets for the "Ajax," "Edinburgh," " Niger," and " Desperate ;" of
Messrs. Seaward and Capel four sets, for the "Blenheim," "Hoguc,"
"Conflict," and "Teimagant;" of Messrs. Jno. Penn and Sons two sets,
for the "Arrogant" and "Encounter;" of Messrs. Boulton and Watt
three sets, for the "Eurotas," "Horatia," and "Vulcan;" of Messrs.
Rennie two sets, for the "Forth" and the "Seahorse;" of Messrs.
Napier two sets, for the "Dauntless" and "Simoom;" of Messrs.
Fairbairn one set for the "Megcera ;" and of Messrs. Scott and Sinclair
one set for the "Greenock."
Of these, the four last-named vessels and the " Desperate "ami "Ter-
magant" had wheel gearing. In all the rest the engines were direct
acting. The steam pressure in the boilers was from five to ten pounds
only above the atmosphere, and if the engines indicated twice the
nominal power, it was considered to be a good performance.
The most successful engines were those of the "Arrogant" and
"Encounter" of Messrs. Penn. They had a higher speed of piston
than the others, and the air-pumps were worked direct from the
pistons, and had the same length of stroke. These engines developed
more power for a given amount of weight than other engines of their
day, and were the forerunners of the many excellent engines on the
double-trunk plan, made by this firm for the navy.
The engines with wheel-gearing for the screws were heavier, occu-
pied more space, and were not so successful as the others, and no
more of that description were ordered for the Royal Navy.
Up to 1860 neither surface-condensers nor super-heaters were used
in the Royal Navy. The consumption of fuel was about four and
a-half pounds per one horse-power per hour.
In 1860 a £ cp was taken in the Royal Navy which receives illus-
tration from a beautiful set of drawings contributed by the firm of
J. Elder & Co.
ON NAVAL ARCHITECTURE. 291
Three ships, the "Arcthusa," " Octavia," and "Constance," were
fitted respectively by Messrs. Pcnn, Messrs. Maudslay, and Messrs.
Elder, with engines of large cylinder capacity to admit of great
expansion, with surface-condensers and super-heaters to the boilers.
Those of the "Arcthusa" were djuble-trunk, with two cylinders; those
of the " Octavia " were three cylinder engines ; and those of the " Con-
stance," illustrated by the drawings referred to, were compound engines,
with six cylinders ; the two former were worked with steaiv. of twenty-
five pounds pressure per square inch, and the latter \vi:h steam of
thirty-two pounds pressure. All these engines gave good results as to
economy of fuel, but those of the " Constance," were the best, giving
one indicated horse-power wjth two and a-half pounds of fuel.
But the engines of the " Constance " were excessively complicated
and heavy. They weighed, including water in bjilers and fittings,
about five and a-half hundred weight per maximum indicated horse-
power, whereas ordinary engines varied between three and a-half and
four and three-quarter hundred weight.
For the next ten years engines with low pressure steam, surface-
condensers, and large cylinder capacity were employed almost exclu-
sively in the ships of the Royal Navy. A few compound engines, with
steam of thirty pounds pressure, were used in this period with good results
as to economy, but they gave trouble in some of the working parts.
Compound engines, with high pressure steam (fifty-five pounds), were
first used in the Royal Navy in 1867, on Messrs. Maudslay's plan, in
the " Sirius." These have been very successful. In the Royal Navy the
compound engine is now generally adopted. They are rather heavier
than the engines which immediately preceded them, but they are about
twenty-five per cent, more economical in fuel, and taking a. total
•weight of machinery and fuel together, there is from fifteen to twenty
per cent, gain in the distance run with a given weignt. We are now
introducing wrought iron largely in the framing in the place of cast ironr
and hollow propeller shafts made of Whitworth steel. By these means
the weight is being reduced, and it is to be hoped that a still further
reduction may yet be made by the use of high class materials in the
engines, and steel in the boilers. That there is room for improvement
is indicated by the marvellous results obtained by Mr.'Thorneycroft,
ol Chiswick, and others, by means of high piston speed, forced com
292 SECTION— MECHANICS.
bustion, and the judicious use of steel As much as 250 indicated
horse-power is obtained with a total weight of machinery of eleven tons,
including water in boilers and spare gear. The ordinary weight of a
sea-going marine engine of large size, with economical consumption of
fuel, would be four or five times as great.
Mr. Brotherhood, with his three-cylinder air-engine worked at high
speed, and with a pressure of forty atmospheres, indicates, as he
informs me, forty-three horse-power, with a weight of engine (not
including air or air reservoir) of only forty-three pounds. There is in
this Loan Collection an illustration of the three-cylinder plan, as
patented by Mr. Willans, in the shape of a complete launch engine.
I have dwelt longer upon steam machinery than I am probably
entitled to do, because Mr. Bramwell will go over the ground in his
address as prime mover. But I feel so strongly the great debt of
gratitude which naval architecture in England owes to her marine
engineers, that although I am not myself a marine engineer, I could
not help seeing that a discourse on English naval architecture without
the marine engine would be ridiculous.
There are three or four men of modern times who have done much
for naval architecture, as it concerns the hulls of ships, but England
owes at least as much, in my judgment, to Mr. John Penn, the late Mr.
Joshua Field, the late Mr. John Elder, and the late Mr. Thomas Lloyd,
for her position in the world as to steam navigation.
In the matter of the forms of ships I regret to say that opinions
differ outside the Admiralty as to whether ships intended for high speed
should be about as broad as they are long, or should have a length any
number of times, up to twelve times their breadth.
Mr. Scott Russell's experiments, made in 1832 and subsequently,
have long influenced, to a considerable extent and favourably, the forms
of steamships, but there does not appear to be any general agreement
among the designers of fast ocean-going ships, as to the best pro-
portions and form for securing the least resistance under the average
conditions of an ocean voyage. Splendid results are obtained in the
Atlantic service— ships averaging over fifteen knots an hour on the
whole passage.
For the Royal Navy all our proportions and forms are subjected to
the investigation which Mr. Froude is able to give by his beautiful
ON NA VAL ARCHITECTURE. 293
experimental apparatus at Torquay. We do not believe that the
resistances of the ships will accord exactly with those 3f their modeu,
but we are satisfied that the behaviour of the models as to resistance
approximates very closely to that of the ships in smooth water. But
even when we have obtained the best form for resistance in smooth
water, it is quite certain that that will not be the best form for service
among waves ; we are still open to the corrections of practice and
experience at sea.
The Admiralty are building fourteen-knot ironclad ships with only
four and a-quarter beams in the length ; and shallow draft, nine— knot
unarmoured vessels, with only three and a-quarter beams in the length.
The Admiralty experiments at Torquay are also directed towards the
discovery of the causes of the enormous loss of power in propelling
machinery indicated by the fact that only about thirty-seven to forty
per cent, of the maximum power of the steam delivered in the
engines is useful in propelling the ship. It is proposed to continue in
H.M.'s ships tried at the measured mile, the experiments commenced
by Mr. Denny, of Dumbarton, with this object.
The present condition of the case appears, according to Mr. Froude's
estimate, to be that, calling the effective horse-power (that is, the power
due to the net resistance) 100, then at the highest speeds the horse-
power required to overcome the induced negative pressure under the
stern consequent on the thrust of the screw is 40 more ; the friction of
the screw in the water is 10 more ; the friction in the machinery 67
more; and air-pump resistance perhaps 18 more; add to this 23 for
slip of screw, and we get that, in addition to the power required to
overcome the net resistance = 100, we need 40 + 10 4- 67 + 18 +
23, making in all 158, i.e.t at maximum speeds the indicated power of
the engines needs to be more than two and a-half times that which is
directly effective in propulsion.
I regret that the present practice of naval architecture has a side
about which I would rather say nothing, but which is yet, in my judg-
ment, so important that I do not feel justified in passing it by in silence.
That dark side is the tendency of keen competition among owners, and
consequent lowness of freights, to make them content with ships built
without that regard to their safety in the matter of division into com-
partments, which I hold to be in the highest degree desirable.
294 SECTION— MECHA NICS.
There can be no doubt that ships built of iron arc more liable to fatal
damage by collision or grounding than those built of wood, unless they
are properly divided into compartments. If so divided they are safer
than those built of wood. I regret to say that with few exceptions iron
passenger steamers are getting to be worse instead of better cared for
in this respect.
There is no law enforcing the existence of bulkheads, or regulating
the height to which they should be carried, or what doors there should
be in them, either in the regulations of the Board of Trade or in those
of the Surveyors to Lloyds, excepting that there must be one bulkhead
at each end of the ship in a steamship and at one end in a sailing ship.
A ship may be 500 feet long, and there may be over 400 feet of the
central ship practically in one compartment.
In some ships the bulkheads are sufficiently numerous, but they do
not extend above the deck which is nearly level with the water when
the ship is laden, so that if one compartment fills, the ship sinks far
enough to bring the tops of all the bulkheads under the water, and then
the bulkheads are of no more value in keeping the ship afloat than if
they did not exist.
In others the bulkheads are neither sufficiently numerous nor suf-
ficiently high out of water.
In others, even where there are good bulkheads, there are doorways
cut in them which destroy their integrity and there are no water-tight
doors to close them.
It may be supposed that the power of the pumps is so great, that
with even a large leak the water would not be allowed to rise up to the
top of a bulkhead dividing the compartments. But pump-power is a poor
resource. It is very difficult to provide, and very rare to find, pump-
power in even the finest ships sufficient to cope with a hole one square foot
(I might almost say half a square foot) in area ten feet under water.
It is quite true that by great care in management such ships can be
worked for yeai" without losses of life, but the loss of a single large
ship with hundreds cf women and children on board is such a terrible
event, that the security afforded by compartments sufficient in number
and in height to provide against immediate sinking, if any one is filled,
ought to be sought for. That this arrangement is consistent with
commercial success is proved by the practice of some of the best
ON NA VAL ARCHITECTURE. 295
English owners. I know too well how dependent the ship is, even
then, upon her water-tight doors ; but such cr.re bestowed upon them,
as is given by some owners and builders, would get over that difficulty.
I have been supplied at my request with sketches of some admirable
arrangements designed by Messrs. Hariand and Wolff, of Belfast, and
fitted in some ships recently built by them.
Description of Watertight Doors, frc., as fitted in the s.s. "Britannic"
and " Germanic?
No. i.— This floating door works on pivots and is placed at the
entrance of the screw shaft tunnel on the after side of the bulkhead,
and in case of the water rising in the tunnel, closes itself by the
buoyancy of the air-chamber attached to it. Chains are also fixed on
the foreside and extending to the engine-room platform on the middle
deck for closing by hand if any obstruction occurs.
No. 2. — Any irruption of water into the after boiler and engine space
would float and close the lower door of this pair, and at the same time
lower the upper one ; these two also have chains led to the middle
deck grating in the stokehold for closing by hand.
No. 3. — This floating door is fixed on the same bulkhead at No. 2,
but on the opposite side, and closes in case of water getting into the
forward boiler space, by a similar self-acting arrangement to No. r.
No. 4. — This door is opened by a rack and worm from the middle
deck, and can also be closed instantaneously from the stokehold by
means of the handle A, which works on an eccentric, throws the worm
out of gear with the rack, and lets the door drop, any shock being
prevented by the pistons above cushioning en the air in the cylinders,
which does not commence until the two hangers T T come in contact
with ends of piston rods S S.
I bring also an Admiralty contribution towards this good object, in
the shape of a model of a door which cannot be left open because it
never is open, but it nevertheless serves for passage. We are pro
posing to fit it in fore and aft bulkheads where ventilation is not
necessary, but where the integrity of the division is of the utmost
importance.
I do not wish it to be supposed that I complain of the action
of the Lloyd's surveyors in this matter. They can only enforce
296 SECTION— MECHANICS.
what the general sense of owners accepts as necessary. The excellent
and careful details of construction exhibited by the London surveyors
is an illustration of their skill and faithfulness, but they are powerless
here. So also is the Board of Trade so long as foreign ships
are in the same condition, and owners and builders are satisfied with
the existing state of things. I should not be faithful to the profession
which I represent if I did not ask owners and builders whether it is
not high time that there was an alteration.
In the matter of the material employed in shipbuilding I believe that
the iron in ordinary commercial use is better than is commonly sup-
posed. Still it is not sufficiently good or uniform in quality to come up
to the Admiralty tests, and tested iron is a special manufacture costing
from £4 to £& a ton more than that known as ship plates.
The fact that even this excess in cost is sometimes exceeded for
bottom plates in ships of war brings up the cost of first-class boiler plate
iron to near that at which excellent steel can be produced.
Steel is now being made suitable for shipbuilding and boiler making
at a reasonable cost by both the Siemens' and the Bessemer processes.
There are two ships of war now building for the Admiralty at Pem-
broke, of Siemens' steel in all parts of the hull and in the boilers, and
nearly all the other ships building have certain portions made of a similar
material produced by the Bolton Steel Company by the Bessemer pro-
cess. The Admiralty is also using a more costly material produced
by Sir Joseph Whitworth for cylinder liners and for propeller shafts,
and the bodies of the Whitehead torpedoes are made of the same
material, viz., fluid compressed steel, having about fifty tons per square
inch of tensile strength and twenty per cent, of ductility, whereas the
steel preferred for ships and boilers has only twenty-eight or twenty-
nine tons of tensile strength, and from twenty per cent, to twenty-five
per cent, ductility. This latter material corresponds in quality with
that produced by the works of Messrs. Schneider and used by the
French Government.
Ic is perhaps right that I should record that all vessels now building in
the Royal Navy have iron or steel frames. Wood is employed for that
purpose no longer. Timber is still largely used in some other national
navies, but I think unwisely. We have vessels as much as 220 feet
long, and with thirteen knots speed, having wood planking in two
ON NA VAL ARCHITECTURE. 297
thicknesses on such iron frames, but with no iron skin. The inner
thickness of wood is secured to the frames by Muntz metal screw bolts,
and the outer thickness to the inner by copper bolts, and the whole is
then sheathed with copper. There is an internal keel, stern, and stern
post of iron and also external ones of wood. This system of construc-
tion is but little used in merchant ships.
Some of the ships having iron skins are simply protected by a paint
composition. That of Dr. Sim, among others, gives excellent results
as to preservation of the iron, and very good results as to cleanliness.
In order to preserve a clean skin and maintain speed longer that can be
expected with paint upon the iron, it is the practice in some cases to
sheathe the outside either with copper or zinc. If copper is used, two
thicknesses of wood sheathing are wanted between the iron and the copper,
the outer one fastened with brass, and the stem and stern-post need to be
also of brass. There is still some risk, without careful workmanship,
of injury to the iron by galvanic action. To avoid this, and to simplify
and cheapen the work, zinc has been employed with only one thickness
of wood between, and iron fastening. It appears, so far as experiments
have gone, to preserve the iron perfectly, to keep as free from weed and
shell-fish as copper ; to be as readily cleansed or washed down as
copper, but to oxidate with a somewhat rougher surface and therefore
with more friction.
I would call attention to the life-saving apparatus exhibited, especially
to that of the National Life Boat Institution, and Mr. White's boat
bridge, as fitted in the troopship " Orontes."
In conclusion, I would refer to what is being done in training naval
architects and marine engineers in England.
In 1 864 the Education Department, at the instance of the Institution
of Naval Architects, established the Royal School of Naval Architects
at South Kensington. This school existed nearly nine years and
entered 119 naval architects and marine engineers, of whom thirty-
eight were private and eighty-one Admiralty students. In 1873 it
transferred twenty-four of its students to the Royal Naval College at
Greenwich, and ceased itself to exist. The entries at the Royal Naval
College between October, 1873, and the present date have been,
including those transferred from South Kensington, twenty-four naval
architects and 113 marine engineers.
298 SECTION— MECHANICS.
I regret to have to say that of these there is not a single English
private student in naval architecture, all have been sent by the
Admiralty, and there is but one private student in marine engineering. Of
foreign students there are at present ten at the College, viz. : three
Russians, two Italians, two Danes, one Spaniard, one Norwegian, and
one Brazilian. The total number of all classes trained between 1864
and 1876 has been 232, of which twenty-four have been foreign. These
foreign students have the full advantages of the Royal Naval College
in every particular.
The PRESIDENT : In rising to propose a vote of thanks to Mr.
Barnaby for his most important and valuable communication on Naval
Architecture, I wish only to point out that it is perhaps the most
important branch of engineering. If you take it in a national point
of view, it may be said that the safety of the island depends upon it ;
in a commercial point of view it carries the treasures of the world to
and from these shores ; and in a humanitarian point of view it
involves the safety of thousands of men who work hard for the interests
of the country. It is encouraging to find that in naval architecture
perhaps the most rapid progress has been made that could well be
imagined, in fact a progress which leaves us every year ir.ore in
advance of what we understood was the newest and the best the year
previously. I am sure you will all agree with me that our best thanks
are due to Mr. Barnaby, the Chief Director of Naval Construction,
who by his earnestness, his impartiality, and devotion, has himself
done so much to advance that branch of engineering.
I will now call on Mr. Froucle, who it is well known has worked
hand to hand wkh the authorities of the Admiralty in determining the
exact form of ships which gives the least resistance, and the greatest
form of safety and convenience. Mr. Froude's name has already
been mentioned by Mr. Barnaby very prominently, and his work is so
well known that I need make no furl her introduction, but will call
upon him to give us his communication.
Mr. FROUDE, M.A., F.R.S. : Mr. Barnaby's allusicn to the experi-
ments which I am conducting for the Admiralty on this subject h.is
made this an appropriate occasion for my telling you something of the
nature of the work. I regret that I have not had time to put on
paper in a carefully prepared and more intelligible form that which
ON NA VA L A RCIII TEC TURE. 299
I have to say, but I will endeavour to inalic it as clear as I can, and I
will only ask you to bear in mind that the attempt to be brief generally
leads to some obscurity.
I \vill divide what I have to Gay into three portions. I will tell you, first,
what it is I am doing ; secondly, a3 well as I can 1 will explain what is the
justification of the mode of procedure in U3ing models to test the forms
of ships ; and, thirdly, I will give you some slight sketch of the result
that we have obtained and arc obtaining. The thing to be clone is, to
determine by measuring the resistances of a model at various speeds,
what will be the resistances of a ship similar to the model at various
speeds, and for convenience I will in the first instance give you a, term,
which is very serviceable in reference to this subject, the term,
namely, which expresses the form in which we embody the ascertained
merits of the model or ship as a body moving with greater or less
resistance. We reduce the results obtained from each form, to
what we call a "curve cf resistance." \Ve introduced that term be-
cause it is a short expression and means a good deal. On a straight
base line are set off a series of speeds beginning with zero, and going on
to one, two, three, &c., in units of speed, whatever they may be. For
every speed for which the resistance is ascertained, the resistance is set
off a to scale, and is plotted as an ordinate on the base line at the appro-
priate speed. Having thus obtained a series of ordinates representing
thj resistances, a curve drawn through their summits constitutes the
curve of resistance. That curve expresses the resistance which the
model or ship will experience at any intermediate speed. In speaking
of the resistance of a mode!, I shall generally speak of its curve of
resistance as expressing this.
The object, then, is by the use of models to determine the curves of
resistance for ships, and in order to do that with effect, it is necessary to
be able to produce models, lapidiv, economically, and exactly. For
this purpose it was necessary to find some more suitable material than
wood. It is well known that to make a large exact model in wood,
occupies considerable time, requires skilled labour, and costs a great
deal ; but happily a rather new material in organic chemistry, paraffin,
— so called because it has little affinity for anything else — opportunely
presented itself, and by the use ^f this material we are able if we please
to complete a model sixteen feet long, cf the general dimensions of
300 SECTION— MECHANICS.
which this specimen is a. frustum, in twenty-four hours. We can pro-
duce that model, nd in eight hours more we can test all its properties of
resistance. That is a rate of operation which would soon outrun our
powers of rationalised analysis, but we can attain it whenever an
occasion requires it. Without describing in detail the modus operandi
by which the model is produced, I may say that this material lends
itself very easily to all the usual foundry processes. We cast the
models in a mould made of clay, shaped approximately to the figure
required, by means of cross sections planted in due order in the clay,
so that we need rot produce a pattern model in the first instance.
The interior of the casting is kept hollow by a core, just as in the
common foundry process, but the core is made of a light frame
work, built in cross sections, covered with lath, and with a skin of
calico, which is covered with a thin coating of clay and plaister of Paris,
and thus rendered impermeable to the melted paraffin. The core,
slightly loaded with ballast, is placed in the mould, and rests in it
like a ship in a dock, leaving an intermediate space for the paraffin
between the core and the mould, and the paraffin is run into this
space. As the space is filled, water is poured into the interior of the
core, and thus prevents its floating up, and, at the same time, assists to
cool the paraffin ; and by the next morning the cold model may be
taken out, washed, and placed on the shaping machine.
I will not describe that machine in full detail. It is simply a machine
in which the model travelling on a bed, like that of a planing machine,
between a pair of horizontal, highly speeded revolving-cutters which
possess a horizontal travel, transverse to that of the model, is operated
on by them at successive levels, their position being so governed that
they cut on the two sides of the model, a succession of true water
lines in pairs copied from the drawings of the model by an apparatus
under the control of an operator. Originally to guide the apparatus,
we used, instead of the water lines on the drawing, a succession of tem-
plates of the kind I have here, a very nice form, in which by the help
of adjustible steel ordinates, spring-steel ribbons are arranged in curves
to correspond with the waterlines in the drawing ; thus the series
of templates when fastened together in due superposition, would
constitute a skeleton model to the scale of the drawing ; but we have
lately found that, working with a magnifying glass, the operator can as
ON NA VAL ARCHITECTURE. 301
correctly follow the line on the drawing as it passes under the indicating
point : thus the cutters cut a pair of water lines, simultaneously on the
two sides of the model. The model is then change.1 in level and the
successive water lines are cut ; you see them here in a form analogous
to that which the ship builder adopts when he sets about making a
model. He gets his form by cutting out a series of pieces of board to
form the several water lines, the thickness of the boards representing
the interval between the lines, builds them together, and shapes off the
intermediate matter.
Our particular material, paraffin, is most delightful to operate upon.
It is quite strong enough for all the purposes of the model, but it is
very easily cut with a knife, and may be operated upon with ordinary
carpenter's tools, with the advantage that from being without grain it
does not misguide the cutting edge. It has the pleasant property that
it does not tend to choke the tools, there being no stickiness about
it, in fact, with a smoothing plane a shaving of about one thousandth
part of an inch in thickness can be taken off quite cleanly. The
model, after bdng cut to the water lines, is shaped by suitable tools
to the finished form. That form is represented by the bottoms of
these cuts ; but, as the bottom of a cut when once it is reached no
longer exists as a guiding line, the operator when he had reached it
would be " out of soundings," and would not know whether he had
gone too deep or not ; to get over that difficulty, as soon as the water
lines are cut, a spur with short points, the alternate points being very
short, is run along each line, leaving a series of corresponding punctures,
and a little black powder is run into these punctures, so that when the
work is finished it can easily be seen whether the operator has gone
deep enough and not too deep. We have another test of the model's
correctness. Its displacement is carefully calculated beforehand, and
when it is finished its weight is taken. It is then loaded with enough
ballast to give it exactly the displacement that it ought to have. It is
placed in the water, and, by very accurate means for testing the immer-
sion, we see whether it comes to its proper plane of flotation. With a
model weighing 400 or 500 Ibs. we generally get the displacement right
within about two pounds, and if we were three or four pounds out we
should think there was some error, and should probably cut the model
afresh, or go over the calculations to see if there were any mistake.
302 SECTION— MECHANICS.
Having told yon how I make the models, I must next tell you how
I test them. That is as important a part of the business as making
them. I will ask you for the present to take for granted, what I will
endeavour to explain presently in detail, that there is ?„ true scale of
comparison between the curve of resistance for a model, and that
for a ship similar to the model. Meantime, I wi'.l describe how we
ascertain the curve of resistance for the model. Our models vary
from six to sixteen feet in length, from eighteen inches to t\vo feet six
inches in breadth, and weigh from 200 pounds up to 600 pounds, 700
pounds, and 800 pounds. They are not puny little models. 1 believe
even much smaller models, if correctly interpreted would give valuable
results, but these are irreproachably large models. The apparatus for
testing consists of the place in which the testing is done, and the
testing apparatus itself. The place in which it is done consists of a
tank or water space, 280 feet in length, ten feet deep, and thirty-six
feet wide, roofed over throughout. Compared with the length of the
models we use, the run we are able to give them in testing, is
nearly equivalent to the measured mile for the largest ships in the
navy, and the depth of the water is about equivalent to the depth
of the British Channel, so that we proceed on a large scale of
operations, and one by which we have no fear of encountering an
adventitious resistance due to the formation of shallow-water waves.
The apparatus is arranged as follows :
Just above the surface of the water, throughout the length of the
water space, is laid a railway, perfectly level and firmly suspended
from theM'oof of the building without the interposition of any inter-
vening columns near the track of the model, so that there is nothing
to obstruct the motion of the water ; and a dynamometrical carriage
runs on th's railway. In the dynamometric carriage there is a
form of apparatus, well understood by many of you, a revolving
cylinder, the circumferential motion of which represents, to scale,
the progressive motion of the railway carriage. The scale is exactly
one-fifth of an inch to a foot, so that every foot the railway carriage
moves, is represented by one-fifth of an inch of circumferential
motion of the cylinder. There is under the railway carriage, a spring
balance, and to that the model is hooked or harnessed. The only
force which is applied to the model is through this spring balance,
ON NA VAL ARCHITECTURE. 303
•which serves as a tow rope, and the extension of the spring balance
will, in such a case, correctly represent the resistance experienced by
the model at whatever speed it may be moving for the moment, which
must be exactly equalled by the whole towing force which is being
administered to the model. The extension of the spring is recorded,
on an enlarged scale, on the revolving sheet of paper, that is to say,
an arm connected with and representing on a large scale the extensions
of the spring, makes a trace on the paper as it revolves, and, at the same
time, a piece of clockwork connected with an electric circuit makes
a contact, which inscribes a mark on the cylinder at each consecutive
half second, and by the intervals between these marks, measured by
the distance scale, we see how much distance is moved in each half
second, that is to cay, the speed at which the operation is conducted j
we thus obtain a graphic record of the exact resistance experienced by
the model and of the speed at which she is moving. I should mention
that it is necessary, besides pulling the model by this spring balance,
to guide her very inexorably, so that she may not swerve from her
course. Because it is a curious circumstance connected with" the
theory of the motion of cuch a body through the water, that if you start
a perfectly symmetrical model or ship freely on a rectilinear course,
though it will perhaps run straight for a little distance, it most likely will
suddenly begin to swerve, and will then very quickly turn broadside
on. It is not sufficient to lead the head end inexorably in a straight line.
If you tow a sixteen foot model by her nose inexorably in a straight line,
you would, probably, expect that the stern would follow in the straight
line, as a flag will follow the mast. But instead of that being the case,
after the model has gone a little distance you will see its stern swerve to
one side or the other indifferently, and there remain at an angle of
5Q, 6°, or even 10° out of the straight line, acccording to the form,
with a curious set of eddies on the two sides of it. To resist this
tendency, the only constraint to which the model is subject, is applied
at each end by a delicate knee-jointed nicely counterbalanced frame,
which allows its head and stern to rise or fall and move backwards or
forwards with perfect freedom, so that it does not experience the
slightest pressure, except that which restrains its desire to swerve
from its course, and this force being transverse and not in the line of
motion does not affect the model's resistance.
304 SECTION— MECHANICS.
The diagram we obtain then is an exact record of the resistance of
the model experimented on, when moving at the recorded speed.
The dynamometrical carriage is drawn by a wire rope, moved by a
steam engine, fitted with a delicate adjustible governor, which enables
us to administer such speed as is required. We can send the truck at
any required speed from 50 to 400 feet per minute, nay, even to 1200
were we to desire it. But besides that, we have the definite record of
the speed, and any small inexactness in the speed supplied by the
governor, is corrected by the record which I have described. When
we have thus got an exact transcript of the resistance of the model at
each speed, the analysed results constitute that curve of resistance
which I have described to you.
I should have mentioned that there is another phenomenon which we
also record in connection with the motion of every model, namely, its
rise or fall, that is to say the change of level it exhibits at either end.
It is a new fact, which, I believe, we were the first to show, that every
form moving along the surface of the water like a ship at reasonable
speed, subsides in the water ; some forms subside more at the head, some
more at the stern, but there is always a bodily subsidence produced
at the ordinary speeds of propulson. To record this, a little apparatus
connected with the ends of the model makes a second diagram on a
revolving piece of paper, one line for each end, showing any change
of level exhibited by the model in the course of the run. The model
immediately settles into condition, and the condition is maintained
throughout, and we have a diagram of it.
I have now described the manufacture of the models, the method
of testing them, and the result, viz., that for each model we obtain a
curve of resistance such as I have sketched. I will next endeavour to
explain the comparison between the curve of resistance of a ship and
that of her model, and in order to do that, I must travel a little into
theoretical view of the matter. The old notion of a ship's resistance
was, that you began with a midship-section, and that as you gave the
ship finer and finer ends you reduced the resistance to some fractional
multiple of tr^e resistance which would be experienced on moving the
midship-section itself through the water, as a plane moving at right
angles to itself; and various formula?, mathematical or emperical, were
supposed to define the appropiate multiplier. Now, mathematicians
ON NA VAL ARCHITECTURE. 305
were not unaware of the defects of that mode of viewing the question,
although in text books on mathematics and hydraulics, it was always
entered as a provisional way of looking at things ; but in recent years
the higher mathematicians have worked out, in a very correct and
conclusive form, what is called the theory of stream lines, a theory
which represents correctly all the motions that the particles of the
water would undergo in encountering any body which is passing
through them, and the force which they would exert on each other and
in the body if water were a frictionless fluid ; and in order to explain
that theory tolerably clearly I must first ask you to go with me
beneath the water. We will consider first what happens to a fish.
The theory of stream lines tells us that were water a frictionless fluid,
the fish would swim absolutely without resistance when once put in
motion. The proposition sounds extremely paradoxical, but I do not
mind stating it in the most paradoxical form. The theory of stream
lines has demonstrated most conclusively that if water were a perfectly
frictionless fluid, even a plane moving at right angles to itself would
not experience any resistance when once put in motion. It would
experience resistance while being put in motion, because of the dyna-
mical conditions of the surrounding fluid ; all the particles around it
must have some motion duly related to the motion of the plane or
other body, and that companion motion has to be established at
starting, and the force experienced by the plane or other body while
the motion is being established will be felt initially as a resistance ;
but when once the motion had become steady, no farther resistance
would be experienced. The converging stream lines behind the plane
or body would exercise just as great pressure on its back surface, as
would be experienced by its front surface, while forcing the particles
from their natural position into the divergent stream lines in front.
This seems paradoxical, but we can arrive at the conclusion by rational
steps by changing our mode of approaching the question.
If we imagine that the fish is a fixed body, and the ocean is moving
past it, we shall get a conception which will render it more easy to
follow the law that I am endeavouring to explain. If we imagine
the body, say this egg-shaped body, moving straight through the fluid,
in one direction, it is obviously the same thing to imagine the body at
rest and the water moving in straight lines past it. Let us trace out
3o6 SECTION— MECHANICS.
this supposition. If the body were out of the way, v/e could imagine
the whole ocean to be cut up into filaments or minute streams of fluid,
each following a straight course ad infiniium. Cut when the fixed
body intervenes those streams must behave differently in two separa'.e
respects. Each stream as it approaches the body, in the first place,
is deflected from its course in order to get past the body, and back
into its former course ; again when it has passed the body in the next
place it has to undergo changes of velocity, chiefly a temporary increase
of speed in passing the local con'.raction of the waterway, which the
presence of the body has created, so that the same ocean of water
may pass the body as would have passed through the whole of the
unoccupied space. These streams as they pass the body have an,
increased velocity and pass on and lose their increased velocity.
Now what the theory of stream lines shows indisputably is, in the
first place, that the dafiection of a stream from its course if it returns
to its former course, causes no total force in the line of motion. That
is easy enough to see if you imagine a pipe of parallel diameter all
throng'.}, bent into an easy curve, like the watcrline of a ship, and
terminating in the same direction which it had at its entrance. The
stream while being first deflected no doubt exercises centrifugal force
which tends to push the pipe forward, but when the deflection is
reversed the centrifugal force tends to push the pipe in the opposite
direction. If that operation is traced through exactly, it is easy to see
that the total result is that there is no aggregate pressure in the line of
motion. It is the ordinary problem of a marble running round a friction-
less curve ; the marble loses no total velocity, the curve it passes round
does not obstruct its run, nor does it push the curve in the aggregate in.
any direction, if it leaves the curve in the same direction, and with the
same velocity it had on entering the curve. By the time it has
traversed the whole curve it has pushed it just as much backward
as forward. The next proposition is, that a stream flowing through
a pipe of which one portion is contracted or enlarged, behaves
in a very different manner from what one would expect. If we
imagine a level parallel pipe of any length, and a stream of water
flowing through it with a steady speed, if the flow be frictionless the
pressure will be uniform throughout the length of the pipe. Now let
a portion of the pipe be tapered to a smaller diameter, and again
ON NA VAL ARCHITECTURE. 307
enlarged to its original diameter, the water must flow through the
narrow portion with increased velocity — that is a mere arithmetical
consequence. Prima facie, it seems certain that the water must be
very much squeezed in going through the narrow part, and must there
tend to push that part of the pipe forwards ; but on the contrary, the
moment you look into it, you will see that instead of the water being
more pressed at this point than anywhere else, is a great deal less
pressed, there is much less pressure there than anywhere else, and if
you have a series of vertical pipes connected with the interior of this
pipe and the water is allowed to rise in them until it stands at a height
representing the pressure, you will see that at the -part before the
contraction has been created, the water will rise its natural level, but
in the contracted part it will have been greatly lowered, and indeed
if the contraction is sufficient there may be produced a partial
vacuum. There is a little instrument which Lord Rayleigh showed me
the other day, in which by connecting a pipe of that sort with a' vessel of
mercury, and blowing through the pipe with the mouth, you are enabled
to raise eight, nine, or ten inches of mercury by the partial vacuum
that forms itself in the contracted portion. The rationale is clear. The
particles of water at the commencement of the contraction are going
at a certain speed, and in the narrow part the same particles are
inevitably going with a greater speed. How can particles have possibly
acquired increased speed in that direction except by the circumstance
that the pressure in front of them is less than the pressure behind them?
The very fact of this acceleration is a proof, in terms, that there is
less pressure in front than behind, and for that reason this contraction
is a region of small pressure, and the original pipe a region of com-
paratively large pressure. Vice versa, it you take a pipe and put an
enlargement into it, we find the opposite thing happens. There, the
particles which were going with a certain speed at the commencement,
when they arrive at the enlarged portion are going with a proportionately
reduced speed, and that can only have happened by there being more
pressure on each particle in front than behind it. Each particle as it
enters this region is being pushed backwards. As the pipe gradually
resumes its natural diameter after passing either a contraction or an
enlargement, the original pressure is also gradually resumed, and
regarded as endways forces, the alternations of pressure exactly balance
308 SECTION— MECHANICS.
each other, and the pipe experiences, on the whole, no endway push.
The exact modus operandi by which the particles adjust themselves
mutually to the change of speed is somewhat complicated, but that
the fact must be as described is I think obvious, and the fact is that
every contracted stream in the flow of an infinite ocean of fluid is a
region of increased speed and decreased pressure, and every enlarged
current is a region of decreased speed and increased pressure, and these
changes of pressure, if the fluid be frictionless, can produce, on the
whole, no endways push on the body whose presence causes the
changes of speed and pressure.
Now I think I may proceed to treat of the case of a fish moving
under water, or, rather, of the streams, so to speak, in the infinite
ocean flowing past a stationary fish, and show how the alterations
of speed and pressure which they experience would, but for friction,
result in an equilibrium of endways force on the fish. At the nose of
the fish, when the streams are being deflected outwards to get past
him, forming lines convex towards his nose, their aggregate centrifugal
force piles up an excess of pressure, constituting what I have called a
region of increased pressure, which must also be a region of diminished
speed and of enlargement of sectional area in the streams contiguous
to the nose, and there is thus established an increase of sternward pres-
sure on the nose, which however we shall presently see is counteracted
by an equivalent increased pressure on the tail. Along the fish's middle
body, where the streams, which have been put into outward motion by
the nose, are losing that motion, and by a reversal of curvature are being
deflected inwards into convergence, the modification of pressure just
described is reversed, establishing in the contiguous streams a region of
diminished sectional area, of increased speed, and of diminished pres-
sure, which acting partly on the widening forward half of the middle body,
partly on its narrowing after end, results in an equilibrium of endways
force : while at the tail where the converging streams are again being
deflected into purely parallel sternward lines, an excess of pressure,
depending on the same conditions as that experienced by the nose, and
exactly equivalent to it, becomes established. Thus, in the frictionless
fluid, equilibrium of endway pressure on the fish would on the whole
subsist, and when once put in motion with a steady speed the fish
would experience no resistance.
ON NA VAL ARCHITECTURE. 309
But water is not a frictionless but a frictional fluid. The conse-
quence of that circumstance is that the streams as they flow along the
side, do experience a great frictional drag, and pull the fish backwards
by dragging along its skin. It may seem absurd to say that so smooth
a surface as that of a fish can experience such a frictional drag, but it
is the fact ; indeed experiment shows that a slippery surface like that of
a fish, experiences more, not less, frictional resistance than a hard
smooth one ; and I may tell you that this friction on the surface not
only pulls the fish back, but like the friction of any other body also
disturbs that beautiful arrangement which constitutes the system of
stream line motions and forces. The mutual drag of the surface and
the water, extinguishes in frictional eddies some of the energy of the
contiguous streams, and prevents them from re-instating the pressure
at the stern of the fish. In the flow of water through pipes a great
amount of energy is lost in friction. Even in a straight pipe, as in a
contracted pipe or^ an enlarged pipe, there is a. loss of work by friction,
and that is exactly what happens in the case of a submerged fish.
The fish would experience no resistance in frictionless water, but it
does experience resistance from friction in actual water.
Now to go to the case of a ship moving on the surface. First I will
suppose the ship to be cut off at the level of the water, and I will sup-
pose the surface of the water to be held down by a sheet of rigid
frictionless ice which the ship will touch, but with no pressure ; that
ice-sheet, offering a reaction to the surface of the water equivalent to
that of an infinitely extended ocean, would enable the streams I have
just described in the ocean of a frictionless fluid, to flow past the ship
just as they would past a fish in a frictionless ocean at a great depth
beneath, that is to say, without tending to push her stern-ways.
The ice surface would in effect constitute the remainder of the
ocean ; but there would be impressed upon the ice considerable force
by the differentiated pressures induced in the stream lines as they flow
past. At the head end of the ship, where there is an excess of pres-
sure from the streams being retarded, the ice would be ptfshed upwards ;
along the sides, where the water is accelerated and there is a diminu-
tion of pressure, the ice would be pulled downwards, and at the stern
again the ice would be pushed upwards ; there would be a stress
put upon it. Now, if we were to remove the ice, the water which ha
3 ip SEC TIO N— M EC IT A NICS.
been held by it would arrange itself into hills and hollows. These hills
and hollows represent, not precisely the stream line pressures, but the
effect of those pressures. The pressures are in fact modified by the
deformations of surface, and those hills and hollows, when once formed,
assume the form of and behave as, waves, and become ihus to a cenain
extent independent of the parent that created them. Thus, they travel
off into the surrounding ocean, taking with them more or less, indeed
at high speed very much, of the energy which was put into them in their
creation, and this is one great cause of resistance to a ship moving at
high speed at the surface. Thus when the ship is moving only at
moderate speed — so moderate that the waves cannot raise themselves
but immediately subside in their track, they do not travel away into
the surrounding v/atcr, and then the ship's resistance consists, I may
say solely, of surface friction. There is indeed, besides, a small amount
of head resistance, due to the distortion of the stream lines, which results
from the frictio i of the streams against each ether, in addition to that
due to their friction against the sides of the ship, and'to the slight loss of
absolute pressure which thus ensues ; but if the ship, has rinp lines this
is inconsiderable, and at moderate speed the ship's resistance is, prac-
tically, simply that of surface friction. With our models, for instance,
whenever we go at very low speed — say fifty feet per minute, wi.h a
model ten or twelve feet long — we find by actual experiment the resis-
tance is just exactly that due to surface friction. I state that as a
fact, but I must tell you that in order to be able to state it with
certainty, it was necessary to ascertain the measures of the surface
frictional forces, and we instituted a very expensive scries of experi-
ments to determine that. We tried plane surfaces nineteen inches
wide across the line of motion, varying in length in the line of motion,
from three and four inches up to fifty feet, and scarcely more than
one-eighth of an inch in thickness, and by a dynamometer we ascer-
tained exactly the resistance at all speeds of all portions of these
planes. Several curious facts are connected with the law of such
resistance. One is this. The resistance is more ardent, if I may
use the expression, at the anterior end of the plane than at the
posterior. When one begins to think of the surrounding conditions,
it seems wonderful that the difference is not greater than it actually is.
Inch by inch along the length of the plane there must be growing into
O.\7 frAVAL ARCHITECTURE. 311
existence, in virtue of the frictionai force exerted on the contiguous
particles by the friction cf the plane, a pair of forward streams, along-
side, and if the plane is fifty feet long, they are seen to have, at the
tail end of the plane, a breadth of, say, seven or eight inches on each of
its sides, and to have a mean velocity, something like half that of the
plane itself. It is extraordinary how it happens that particles posscs^fi
of such large concurrent speed as those which form these streams, can
still exert a not very greatly diminished backward drag on the plane ;
it is true that the front edge of the plane the intensity is greatly
increased, and is quite incommensurable with what it is at the after
end. If the anterior edge is of polished metal quite keen, and a
very thin coating of tallow is put on it, the friction will strip this back,
and arrange it in a pair of thread-like ridges immediately behind the
edge ; but after this very narrow strip of mixinuni intensity is past
there is for the nVst few feet a rmderat^ly graduated d'.minution of
intensity ; and after ten feet cf length the diminuti< n of intensity is
relatively insensible. However, without affecting to have solved the
question theoretically, we have gone through it practically v/ith sufficient
completeness to know what mean resistance per square foot is exerted
by any given lengths of the different qualities of surface, and we know
that surface friction is a very sensitive fi. nation, and that until we learn
the exact quality of the surface of the ship or body, it is impossible
to predicate what its resistance will be. I may tell you that a plane,
coated with tin foil six or eight inches long, makes only half the
resistance of a plane coated with clean paint or varnish, but when you
get to fifty feet long the tin foil makes almost exactly the same resis-
tance as the clean paint ; and again a slimy surface, like that of a fish,
makes more resistance than a perfectly hard smooth surface. By the
help of these experiments I am able to say approximately what the
sv.rface friction of a ship of given quality of surface should be, and in
virtue of that determination I am able to tell you that with a model
of say twelve feet in length, at a speed of fifty or sixty feet, per minute,
which is a moderate speed for the model, and is equivalent to a speed
of six knots for a ship 300 feet long similar to the model, the resistance
is nothing more than that due to surface friction : we find, in fact, by the
dynamometer that there is not any more than1 that. I have, therefore,
ro hesitation in saying that the fundamental proposition I have
asserted is borne out by facts.
312 SECTION— MECHANICS.
But when we come to higher speeds we immediately see that the
other principal cause of resistance begins to operate ; the waves begin
to form themselves. The whole theory of an investigation of merit
in form is complicated by that condition, and you have to arrange your
form so as to produce the smallest amount of wave motion. I ought to
say that the problem to be solved in finding the best form for a ship
is one rather difficult even to state satisfactorily. When we say we
want to make a ship of a given length, breadth, and depth, which shall
go with the least resistance, or a ship of a given displacement, there
are, besides, a multitude of collateral conditions to be taken account of,
such as comparative first cost, comparative liabiliiy to wear and tear,
£c. ; but these considerations can perhaps be more properly introduced
as make-weights when an approximate solution has been supplied on
broader grounds. Viewing the matter thus broadly, the clearest state-
ment of the proposition I can frame to myself is, that we wish to carry an
amount of useful displacement at a given speed with the least expendi-
ture of power. By useful displacement, I mean displacement available
for the purposes for which the ship is primarily intented, ^.,the carriage
whether of goods or passengers, and exclusive of that devoted to weight
of hull, of engines, coals, rigging, crew, and stores ; not that these things
are, as a matter of fact otherwise than useful, and indeed necessary, but
that any reduction in their amount, compatible with the primary
purpose of the ship, is a gain, not a loss. Now as any variation in the
ship's form must affect the outcome of each of these conditions
separately, it is plain that the solution is a very complex one, and in
point of fact we cannot arrive at anything like a general determination
of what is the best form for a ship. Another circumstance that makes
that difficult, is that the relative merits of different forms will vary
with the speeds at which they are compared. The form which is best
for a ship to go seven, eight, or nine knots, if it is a long ship, would
be very sensibly different from what it would be if she is to go sixteen
or eighteen knots, again you should adopt a much shorter ship for
moderate speeds, because at such speeds the surface friction is the
greatest element of resistance, and is relatively greater in the longer ship.
What I have now to explain to you is how to frame the comparison
between a ship and her model. When we have got the curve of
resistance for the model, we draw on it a second curve, the ordinates of
ON NAVAL ARCHITECTURE. 313
which are lines representing the surface friction of the model. The
differences between the ordinates of the two curves are the forces
solely due to the formation of the models waves. Now it is a property
of waves that similar waves move with speeds proportionate to the
square roots of their dimensions, and from that, if it is fairly looked
into, it follows that comparing a ship and a model of given lengths,
the waves made by the ship, and the waves made by the model will
be exactly similar if the speeds at which the ship and the model
respectively move, are proportional to the square roots of their
respective dimensions. Bear in mind that the resistance consists in
effect of two elements, one surface friction and eddy-making, the other
wave-making ; I deal now with the latter in its comparative effect with
ship and model : If the ship of which we make the model is sixteen
times as long as the model, the waves that the ship makes at a speed
of ten knots, will be similar to those which the model makes at
two and-a-half knots, since four is the square root of sixteen, and
two and-a-half is a quarter of ten ; and on that basis we calculate
the resistance that the ship will experience in wave-making, compared
with that which the model experiences in wave-making. It comes out
that if the speeds are what I call the "corresponding speeds," that is are
proportionate to the square roots of the dimensions, at such speeds
the resistances due to wave-making are proportioned to the cubes of the
dimensions, that is to say, in the instance just given, the ship going
ten knots will have a wave-making resistance 4096 times that which
the model has at two and a-half knots, 4096 being the cube of sixteen,
and, as before, two and a-half being ten divided by the square root of
sixteen. In that way we can calculate the ship's resistance due to
wave-making from the model's resistance due to the same cause.
Then again in calculating the ship's surface friction, knowing her
surface, and the speed at which she is moving, and the quality of the
surface, we can calculate what will be the resistance due to it at each
speed, and by adding this to the resistance due to wave-making we
can construct a complete curve of resistance for the ship from the
resistance of a model similar to the ship. If the resistance due to
surface friction were simply as the area, and as the square of the speed,
irrespective of the question whether the given area were a long one or a
short one, it would follow that in comparing ship and model the
3 14 SECTION-MECHANICS.
relation between their entire resistances would follow the law just
•enunciated as governing the relation between their wave-making
resistances; but as has been explained the mean resistance'pcr square
foot of a long area is less than that of a short area, and thus the ship's
surface friction is relatively a little less than the models, and her sur-
face friction must be calculated separately ; but when similar ships are
compared the differences in length cf area will be unimportant, and the
law may be treated as exactly true, name!y, that the entire resistances of
similar ships at corresponding speeds are as the cubes of their respective
dimensions. The principles on which this law depends render it equally
true, however abnormally the wave-making resistance may grow, in
terms of the speed.
I aoi afraid it would take me too long if I were to attempt to tell
you in detail all the results ot this investigation, but speaking
generally, we must for high speeds have long ships, because short ships
at high speeds make very big waves ; but at moderate speeds short ones
do best, because there is less surface friction, and at such speed, that is
the chief element of resistance. Practically, what is meant by moderate
speed is a speed which, in knots, is quite short of the square root of
the ship's length in feet. If you make a well-shaped ship loofeet long
to go at a speed of ten knots she will begin to make a rapidly growing
resistance, and at such a speed with a ship of ordinary proportions
the total resistance will be about one two-hundredth part of the ship's
entire weight. At a speed in knots about 1*35 times the square root
of the length in feet, she would be making a very large resistance
indeed, probably there increasing nearly as the sixth power of the speed.
When that is the case, then a ship of larger dimensions and with the
same lines would make absolutely less resistance at that speed. I may
say the " Shah " in her recent measured mile trial, going at seventeen
knots wns propelled bya nett force which was equal to one two-hundrcth
part of her whole weight, while Mr. Thorneycroft's swift launch on the
contrary, which goes at such an extraordinary speed, requires, at a
speed of a little over eighteen knots, a propulsive force of one-fifteenth
part of her weight. So that you see at what an enormous rate the
resistance grows even with the finest forms when driven at extravagant
speeds. I think, therefore, the speed at which yen may rationally
aim is in knots about equal to the square root of the ship's length
ON LIGHT HO USE APPARA TUS. 315
in feet. At that speed with the best form the resistance is about, as I
said, one two-hundredth part of the ship's weight.
The PRKSIDENT: Ladies and gentlemen — Every one who has
listened to Mr. Fronde's lucid explanation must have been struck by
the important bearing which his experiments must exercise upon naval
architecture. Not long ago it was supposed by every naval architect
that the chief element of the resistance of a ship going through the
water was its mid-ships section, and that if only the mid-ships section
could be cut down the total resistance of the chip would be reduced
and its speed increased.
Hence the tendency to add to the length of the ship, by which we
reach the proportion of one in ten. Mr. Froude's experiments prove the
fallacy of that train of reasoning, and show that the midships section has
really nothing to do with the resistance of the water. That resistance
is made up by the skin resistance and by the waves engendered by the
rapid motion of the ship through the water. Hence this new principle
will give rise to new results, and the ship of the future will no doubt
differ very materially from the ship of the past. I wish now to propose
a vo*e of thanks to Mr. Froude for his very interesting communication.
The Conference then adjourned for luncheon.
On re assembling the President called upon Mr. Thomas Stevenson
to read his communication
ON LIGHTHOUSE APPARATUS.
Mr. THOMAS STEVENSON then made the following extemporaneous
statement : Perhaps I ought in the first instance to explain that the
object of my being asked here is not to give an address upon the subject
of light-houses generally, but merely to describe certain of the more
important irfiprovett'iCfitfi which originated in Scotland, and which have
been illustrated by models in the museum, some of which are now on the
table.
There arc many interesting subjects connected with lighthouses, to
which, therefore, I shall not refer ; for example, I shall not need to
refer to the electric light which emanated from the researches of our
illustrious countryman Faraday, and which in the hands of Professor
Hoimes and the Trinity House of London, has been cairied out so
successfully. Nor shall 1 need to refer to the very interesting experiments
3i6 SECTION— MECHANICS.
on sound now being carried on by Professor Tyndall, also under the
auspices of the Trinity House. All that I intend to do is to describe
some of the improvements whichhave originated in Scotland since 1822.
Perhaps I shall consult your comfort as well as my own convenience
best by adopting a somewhat historical form. Prior to the year 1822,
the best form of lighthouse apparatus consisted of a silver plated
parabola. The optical principle of the parabola is perfectly well
known. It is simply this: that all rays emanating from the focus and
incident on its surface are rendered parallel to each other, and also
parallel to the axis of the apparatus. Of course, if the radiant were
a mathematical point, the rays which emanated from the reflector
would be strictly parallel, but, inasmuch as instead of employing a
mathematical point, a bulky flame is used, the rays which proceed
exfocally have a certain amount of divergence, and without that, the
instrument would be practically useless for lighthouse illumination.
Owing to this divergence you are enabled to place reflectors round
about a frame, so as practically to light up the whole 360 degrees of the
horizon. In like manner, if you had three or four parabolas, each having
a flame in its focus, placed with their axes parallel upon a frame which
was made to rotate, then whenever the common axis of the parabolas was
pointed to a distant observer, that distant observer would receive a power-
ful flash of light, and as the frame moved round, and the axis was turned
away from his eye, it would gradually die out and produce darkness.
In the year 1822 — a year which will ever be memorable in the his-
tory of lighthouse optics, the distinguished philosopher Augustin
Fresnel introduced the dioptric system of lighchouses. For this pur-
pose he used a piano convex lens of the same form as had been pro-
posed, but for burning purposes only, by Buffon in 1748, and in an im-
proved form by Condorcet in 1788. A specimen, the finest I ever
saw, is in the museum from the workshop of Messrs. Barbier & Fenestre,
of Paris. The principle of the lens was simply this, that instead of
having a continuously spherical surface, Buffon proposed to cut out the
lens at the back so ab to reduce the thickness of the glass, and to save
the light lost by absorption in passing through the glass. Condorcet
not only did this, but assuming different radii for curvatures of the
different faces, was enabled to correct to a large extent the spherical
aberration, and not only so, but to make the lenses in separate pieces.
ON LIGHTHOUSE APPARATUS.
317
Fresnel further improved the lens by grinding the rings to different
centres, and so practically got rid of spherical aberration altogether.
Then, Fresnel, instead of using a number of lenses, and with separate
flames, used one central flame and surrounded it by a number of those
thin annular lenses, so that whenever the axis of one of those large
lenses is pointed to a distant observer he gets a flash of light, and
when it passes away he loses that light. But in order to save the light
which passes over the top of this apparatus, Fresnel had recourse to
two agents, namely, smaller lenses inclined to the horizon, and plane
silvered reflectors also inclined. By this compound arrangement the
light was thrown out above the main lenses in horizontal beams paral-
lel to those coming from the large lenses below. Such was Fresnel's
revolving light, figs, i & 2, but he did not stop there. He introduced
< .
Figure I and 2.
L principal lenses, / inclined lenses, M plane mirrors.
3 13 SECTION-MECHANICS.
very important improvements on the fixed light where he employed t\vo
totally new instruments. One cf these was called a cylindric refractor.
This consisted of the solid, which is generated by the revolution round
a vertical axis of the middle section of the great annular lens.
This cylindric refractor formed a hoop encircling the light, having
lenticular action only in the vertical plane. These refractors, when
of a large size, were made in the form of polygons, but in 1836, Mr.
Alan Stevenson, Who was the first to introduce the dioptric system
into this country, made the central belt of the first order lights truly
cylindrical, and adopted inclined instead of vertical joints for the
glass sectors by which an obscuration of the light by the brass set-
tings at any part of the horizon was rendered impossible." He after-
wards applied the same princip'e to the astragals of the outer
lanterns of the largest class of lights. The refractor does not in
the least degree interfere with the spread of the light by natural
divergence all round the horizon, but it parallelizes all the light that
falls upon it in a vertical plane. In order to utilize the light, which
passed over the cylindric refractor, Fresncl afterwards introduced a
totally new instrument, and not only so, but for the first time intro-
duced the principle of total reflection into lighthouse illumination.
The way in which he did this was by means of a scries of prisms
of a triangular section. The rays striking on the first face of the
prism were somewhat refracted, then on the second face they were
reflected, and passing to the last surface, emerged, after another
refraction, parallel to the light coming from the cylindric refractor.
Those rings are arranged horizontally round the vertical axis, and,
in connection with the refracting hoop, enclose the flame in a complete
cage.
I have now come to the year 1849, when certain improvements were
made in Scotland. It is quite obvious even to a superficial observer
that the parabolic reflector is a very imperfect instrument, inasmuch as
only a portion of the rays are incident on its surface. What
becomes of the rays which escape past that surface ? A large cone
of rays does escape past the lips of the reflector, and all of that cone
is utterly lost. In order to save this light, what is required is to place
a lens inside of the reflector (shown in fig. 3) and at such a distance in
front of the focus as to give parallel rays, and not only so, but this
ON LIGHTHOUSE APPARATUS.
319
Figure 3. •
a paraboloid, L lens, b spherical mirror.
lens must subtend the same angle at the flame as the cone of rays which
escapes past the lips of the reflector. If this lens be put in the position
I have spoken of, it is quite obvious that all the rays are rendered
parallel, and there is no loss of light. But I have only spoken of one
half of the light, namely, the front half, I have said nothing about the
back half. Now the rays falling on the back portion of a parabolic
reflector are parallelized by it. The object of the lens is also to
parallelize the rays, and therefore, if the rays being already parallelized
by the reflector were to fall on the lens they would be caused to con-
verge, and afterwards to diverge, and thus be lost as before. In order
therefore to utilise the light from behind, it is necessary to cut off the
back of the parabolic reflector, and to beat it into a spherical form, so
that the rays falling normally on this surface will be returned back
again through the flame, and proceeding in a diverging direction will
be intercepted either by the paraboloid or by the lens in front. In
this way, the whole of the light will be utilised, and this therefore ought
to be the light of maximum intensity. So far, it is an obvious im-
provement upon what Fresnel uszd for utilising the light which passed
above the lens, for you observe he used two agents in his revolving light,
whereas, if his plane mirrors had been made portions of parabolas,
he could have dispensed with the inclined lenses which are inside the
apparatus, and one agent would have done instead of two. But after
all, although optically considered, this form cf holophote is geo-
320
SECTION-MECHANICS.
metrically quite perfect, it is really not so perfect an instrument as might
at first sight be considered, owing to the inevitable loss of light from
the metal reflector by which a large portion of the rays is absorbed,
and annihilated. What was wanted was to substitute for metallic
reflection the principle of total reflection, which Fresnel had already
successfully employed in the fixed light. In order to do that it was
necessary to surround the lenses by prisms, having the same profile
as those of the fixed prisms of Fresnel ; but instead of being generated
round a vertical axis, they are generated round a horizontal axis, so
as to parallelize the rays not only in one plane as in the fixed light, but
in every plane. (Shown in fig. 4). On the table is an example of this
Figure 4.
g holophotal prisms, a, B, b prisms of dioptric spherical mirror.
light. But the apparatus described deals only with one half of the
diverging rays. The other half falls upon the dioptric mirror which
is composed of prisms which have their inner faces ground spherically
to the flame as a centre. Entering those surfaces, normally, the rays
suffer no refraction, and pass onwards to the reflecting surfaces of the
prisms wherebeing twice totally reflected, they return back again through
their first surfaces to the flame. In order to do this it is quite obvious
that thetwo backfaces of the prism must beportions of parabolas, having
ON LIGHTHOUSE APPARATUS. 321
their foci in the common focus of the apparatus, and their axes of
generation coincident with the horizontal axis. This is represented in
•the model on the table. (Shown in fig. 5). It is quite plain that if this
Figure 5.
Section of one of the prisms of dioptric spherical m't/or showing path of ray of light.
Instrument be properly constructed — and for this purpose I may men-
tion that I was indebted to Professor Swan, of St. Andrews, for the
formula — a person standing behind the apparatus will see no light,
although there is nothing between his eye and the intense flame which
is burning in the focus but a screen of transparent glass. You will
observe that in the focus of the apparatus on the table there is placed a
large red ball which you can see through the front half, but when I turn
the back of the apparatus to you, you will not be able to see it. You
•will cee part of the stick that supports the ball because a large portion of
it is exfocal, but the focus, and whatever is near the focus, will be
totally reflected by this screen of transparent glass, and therefore you
are not able to see it at the back of the apparatus.
I have to explain that since I designed this apparatus, which was
in 1850, my friend, Mr. James Chance, of Birmingham, suggested some
valuable improvements both as to the way of setting, and the mode
of generating the prisms. These totally reflecting spherical mirrors
Are now very generally used in lighthouses, and there is an example
of it down stairs to which I shall refer again presently.
I have now described the means of producing the most intense single
beam of light from a single flame, but for the purpose of producing the
revolving light it is better to adopt the plan which Fresnel employed of
having one large flame surrounded by a framework containing large lenses.
This is the holophotal revolving light (fig. 6) with the great annular lens
of Fresnel, and holophotal prisms above and below, which intercept
the light in the way I have spoken of. There is a beautiful example of
this apparatus made by Messrs. Chance, exhibited by the Trinity House
in the yard outside. The frame revolves round about the light, and when-
x
322 SECTION— MECHANICS.
ever the lenses and the holophotal reflecting prisms come opposite the
eye, you get a powerful flash which dies out as the axis is turned away.
You will observe the distinction between this apparatus and the one I
formerly described as constructed by Fresnel. He required two agents
for the purpose of parallelizing the light, whereas it is done here by a
single agent which produces a great saving of light. (Fresnel's revol-
ving light is shown in fig. i & 2, and the holophotal in fig. 6).
Figure 6.
L lenses,/ the holophotal prisms.
Hitherto I have restricted myself rigidly to matters which were
published, but I must now refer to an apparatus which I saw for the
first time last Saturday in the museum down stairs. It is a small
apparatus which is represented to have been made in 1825 by M.
Tabouret for Augustin Fresnel, and it contains prisms which though
not arranged for a revolving but for a fixed light, are of the same
forms as those I have described, which were first published in
1 849. I know nothing of the history of that apparatus, but I can state
positively that no description of it was ever published until 1852, and
that holophotal prisms were not introduced into lighthouses until 1850
when I introduced them, and not only so, but the fact is that during
no less than a quarter of a century after 1825, apparatus of even the
smallest size, where no difficulty of construction could possibly arise,
ON LIGHTHOUSE APPARATUS.
323
continued to be made at Paris and elsewhere in which two agents were
employed. Nor did Mr. A. Stevenson, who spent about a month
at the Lighthouse Works in Paris, in 1834, see or hear anything of
those prisms. Again, in Leonor Fresnel's description of apparatus
which he published in 1844, he represents some improvements made
in his brother's light, but he still employs two agents. I may also
state that in 1850 I went over to Paris with my late brother, Mr.
Alan Stevenson, in order to explain by means of a drawing and
model this, among other inventions, but at that time M. Fresnel
did not say anything about this old model; and still more striking
is the fact that M. Degrand, who succeeded Fresnel as. one of the
engineers of the Lighthouse Board in Paris, claimed these prisms as
an invention of his own in 1851. And equally inexplicable is the fact
that M. Tabouret, who is said to have made the model of 1825,
exhibited a new revolving light at the Great Exhibition of 1851, in
which no such prisms were used. The only apparatus at the Exhibi-
tion in which they were, was sent by the Scotch Board. Lastly, so late
as 1851 a first order revolving light was constructed for Cape L'Ailly
in France. It was originally ordered on the yth of May, 1851, by the
French Administration of the old construction in which there were no
prisms of the kind to which I have referred, but subsequently that order
was recalled and the light was made holophotal, after the French
engineers* had seen the holophotal apparatus which was then being
made for the Scotch Lighthouse Board, by M. Letourneau.
I shall now pass on to the azimuthal condensing principle for
lighthouses. There are many peculiar situations which the lighthouse
Figure 7.
324
SECTION-MECHANICS.
Figure 8.
engineer has to meet in a particular way. One of these is the case of a
narrow sound. Suppose, for instance, it were required, as in the case of
a place in Scotland, to light up a narrow sound. (Shown in figs. 7 & 8.)
It is quite obvious that if you make the light sufficiently powerful
to show across the sound, which is perhaps two or three miles
wide, it would be very insufficient for showing up the sound, where the
mariner had to see it at seven miles, and still more insufficient for
showing down the sound where the light is required to be seen for
fifteen miles. What is required, then, is a system by which the whole
light from the lamp is spread horizontally with strict equality over any
given arc in azimuth. Or in a light of equal range, where it must be seen
at different distances in different azimuths, the light must be allocated
to each of such arcs in the compound ratio of the number of degrees.
and the distance from which it is required to be seen. I might
describe this by a very simple case, but I prefer to allude to the
case of Buddon Ness condensing light, the apparatus of which may
ON LIGHTHOUSE APPARATUS.
be seen down stairs. (Shown in fig. 9 in section, and in fig. 10 in
plan). The object there, was to condense the whole of the light
Vertical Section. Horizontal Section.
Figs. 9 and 10.
a, b, c Fresnel's fixed light, p straight condensing prisms, i. h suspended portion of holophote,
£, /conoidal prisms.
coming from the flame into an arc of forty-five degrees in azimuth.
The first thing to be done was to intercept the front half of the light
by 108°. of Fresnel's fixed light apparatus. But all that is in this case
required to be illuminated is forty-five degrees. Fresnel's apparatus
answers the purpose perfectly for the forty-five degrees, but what be-
comes of the light which comes from the other part of his fixed
apparatus ? In order to condense that light into the required directions
there are straight prisms which were first used at Isle Oronsay in
1857, which straight prisms stand in front of the apparatus, as will be
seen down stairs, and all the light (less forty-five degrees) which
passes out of Fresnel's fixed light is received upon those straight
condensing prisms, and they spread the light over the forty-five
degrees, so that the whole of 0113 half of the light is condensed into
an arc of forty-five degrees ; that is to say, the light which passes
through the sides is so bent by refraction and total reflection as to
reinforce that which comes from the lorty-five degrees in front.
Of course those straight prisms do not reflect the light in the
vertical plane, but only in the horizontal. With regard to the back
325
SECTION— M EC II A NICS.
part of the light, we can at once avail ourselves of the spherical mirror ;
but the light that is passing above that would still be lost. In order
to intercept that, there is suspended above the flame a half holophote,
which has the property of combining the rays which fall upon it in a
parallel beam. Then, above this vertical beam of parallel rays there are
prisms which were first used at Buddon Ness — right angled conoidal
prisms, which also have the property of spreading the light which falls
upon them over forty-five degrees. In this way, by the union of the
following instruments, the whole light coming from the flame is com-
pressed into the arc of forty-five degress, viz., Fresnel's lens, Fresnel's
fixed light prisms, the azimuthal condensing prisms, the cylindric re-
fractor, the dioptric spherical mirror prisms, the holophote, and the
conoidal prisms above.
The next thing I shall allude to is a simple apparatus for illuminating
sunken rocks at sea. At Stornoway, in the Island of Lewis, in 1851,
it was proposed to place a lighthouse upon a sunken reef, which
would have been a very serious matter. Instead of that, a main
light was placed upon shore, and in order to point out the position of
the reef at night, the following plan was adopted. A perch or
beacon, which is comparatively an inexpensive structure, was erected
upon this sunken rock and on the top of the perch there was a lantern
containing certain optical prisms. Exactly on a level with that lantern
there was a window cut in the tower of the lighthouse, and in
r igure II.
ON LIGHTHOUSE APPARATUS.
327
that a holophote was placed, and a powerful beam of parallel rays
was projected upon the lantern in the perch. The optical prisms
redistributed the rays which fell upon them, and to a seaman
coming into the harbour the light appears to come from the
perch, whereas in reality it comes from the shore about 530 feet
distant. This kind of light is used in several other places. (Shown
in fig. 11). The only other matter which I think it is necessary
to mention is some new forms of prisms which have been recently
introduced at Islay. (Shown in fig. 12). They have the remark-
Figure 12.
a, b, c, lens and hoiophote ; a, g, c, h, new back prisms ; i, j, k, dioptric spherical
able property, of parallelizing rays, for an incidence as low as
about 1 80 degrees. I think it right to state that these prisms
were invented independently by Mr. Brebner and myself, and by
my friend Professor Swan of St. Andrews, who gave the formula
for constructing them. Another new form of prism, (fig. 13), which
was described in Nature some months ago, is called a twin prism.
This prism has its apex cut out, the object being not only to
carry out an ingenious suggestion of Professor Swan of passing the
light from a set of prisms through the chinks in another set placed
before them, but to reduce the thickness of the glass through which
the light has to pass. In this way you save much light, which
would otherwise be lost by absorption. The first example of this
kind of apparatus is now being made by Barbier and Fonestre of
Paris, for the Scotch Lighthouse Board.
328
SECTION— MECHANICS.
//'' '''/''' :!; :--''' !j >*'''' $ •-;'-'/'' x'x' ~--"'''*::
Figure 13.
B, Fresnel's fixed light: i, 2, 3, 10, 11, 12, 13, 14, straight condensing prisms ;
4> 5> 6, 7, 8, 9, new straight twin prisms.
I have nothing more to add, except with regard to the characteristics
of different lights, which I may mention in two words. Formerly there
used to be the fixed light and the revolving and coloured lights. But we
have now two other characteristics, namely, the flashing light, which is a
light producing extremely quick flashes, very distinctive from the revolv-
ing light, and the intermittent light which consists of occultations pro-
duced by frames coming down in front of the apparatus, and so cutting
off the light suddenly, as opposed to the gradual waxing and waning
which you have with a revolving light. These lights were introduced
by the late Mr. R. Stevenson in 1827 and 1830. In 1871, Mr. R. L.
Stevenson proposed an optically perfect intermittent light in which
the periods could be made of unequal duration by means of eclipsing
mirrors moving horizontally within the glasswork of a fixed light
apparatus.
The PRESIDENT : I will now call upon you to pass a vote of thanks
to Mr. Stevenson for his very interesting communication. I have
ON WARMING AND VENTILA TION. 329
little or nothing to add except to say that the art of projecting light
by mechanical means seems to have attained a wonderful perfection.
There are two branches of this subject which Mr. Stevenson might
have mentioned, which he has not done, for want of time. There is
the generation of light, either by the combustion of oils, or by electricity,
all of which form part of the general subject. There is also the con-
struction of lighthouses themselves, but we must be content with what
we can practically attain to in collecting information on the exhibits
which are here.
I must therefore ask you to pass a vote of thanks to Mr. Stevenson
for his paper.
The vote of thanks having been carried,
The PRESIDENT: I will now call on General Morin for his com-
munication on ventilation, a subject which no one has investigated
more deeply than he has.
NOTES ON WARMING AND VENTILATION.
ON VENTILATION.
GENERAL MORIN, Director of the Conservatoire des Arts et Me'tie'rs
at Paris : The subject which I am about to bring before you, cannot be
compared — with regard to scientific interest — to those questions which
have already been discussed ; but it affects so closely the well-being
of humanity, that it has, for a long time past, attracted public attention.
Indeed the principles and the results of which I intend to-day
giving you some examples, are by no means new. I will do no more
than briefly call your attention to them.
In a work entitled Illustrations of the Theory and Practice of
Ventilation, by Dr. Reid, of Edinburgh, and which was published in
1844, the principle is already expressed that the introduction of fresh
air must take place from the ceiling, and its escape from the floor.
The author had applied this system to the Club Room of the Royal
Society of Edinburgh. Mr. Goldworthy Gurney, a skilful engineer,
had also expressed this principle in these words : " It is desirable
„
330 SECTION— MECHANICS.
that fresh air should enter from above, and escape from below. (Com-
mittee of Enquiry of the House of Lords, page 41.)
The advice of these gentlemen was disregarded, and about the year
1845 there was st^ to De seen *n ^e subterranean galleries of the
Houses of Parliament two ventilators, 6 feet in diameter. They have
since been removed.
I will but say a few words upon heating apparatus. Ordinary
chimneys have the advantage of allowing an agreeable and whole-
some view of the fire, whilst at the same time they cause the renewal
of the air in the room ; but they are inconvenient inasmuch as they
occasion draughts through the doors and windows. Only from o.io
to o.i 2 of the heat given forth by the fuel is made use of.
The ventilating chimneys proposed long ago by Mr. Belmas, colonel
in the French Engineers, in the eleventh number of the " Memorial
de 1'officier du gdnie," and for the establishment of which Captain
Douglas Galton has made excellent suggestions, have the advantage
of bringing into the room as much air at a moderate temperature as
they carry out through the smoke-pipe, and of making use of from
0.30 to 0.33 of the heat furnished by the fuel.
Hot air stoves, made of cast iron, have the serious defects of altering
the air ; those made of hollow bricks are to be preferred to them.
Both kinds must have the necessary means at hand for the intro-
duction of fresh air.
The warming apparatus by means of the circulation of hot water,
have the advantage of carrying heat to almost any distance. At the
Sydenham Palace twenty-five boilers supply water to pipes, the united
length of which is nearly equal to the distance from London to Dover.
VENTILATION.
1. The object of ventilation is to get rid of tainted air, and to
replace it by fresh air.
2. The escape must take place near the deteriorating cause and far
from persons.
3. Experience shows the superiority of the " Systeme d'appel " over
the " Systeme d'insurflation."
4. The fresh air can be taken by " appel " at any height. Guy's
Hospital in London, and 1'hospital de Lariboisiere in Paris are
examples of this.
ON WARMING AND VENTILATION. 331
5. The means of causing the draughts is perfectly simple, it is merely
necessary to have a grate at the bottom of the chimney for the
escape of the air.
The volume of air to be renewed in places requiring to be purified
may be fixed as follows : —
HOSPITALS :—
Per hour and per individual.
M.C.
Ordinary cases 60 to 70
Wounded persons 100
Women lying-in 100
At times of epidemics ,. 150
PRISONS 50
WORKSHOPS, ordinary 60
„ unhealthy 100
BARRACKS, by day 30
„ by night 40 to 50
THEATRES, MUSIC-HALLS, &c 40
LONG GATHERINGS, MEETINGS 60
SHORT „ „ 30
INFANT SCHOOLS 12 to 15
ADULT „ -. 25 to 30
STABLES, &c. 180 to 200
These figures agree with those of English, American, and German
hygienists.
With regard to temperature, the necessary results to be obtained by
warming apparatus are the following : —
TEMPERATURE.
DAY-NURSERIES, for babies I5°c
ASYLUMS, SCHOOLS 15°
HOSPITALS, ordinary 16° to i8o°c
„ for the wounded ... ... ... ... 12°
WORKSHOPS, BARRACKS 15*
PRISONS 15°
THEATRES, MUSIC-HALLS, £c 19° to 20"
GATHERINGS, MEETINGS, &c 19° to 20°
•
332 SECTION— MECHA NICS.
NECESSARY CUBIC SPACE AND QUANTITY OF AIR.
Important studies were made in 1842 by M. Leblanc, a French
physician, under the title of Investigations upon the composition of air
in enclosed places j the conclusion to which he came may be expressed
as follows : —
The proportion of carbonic acid increases according to the degree of
unhealthiness (of the locality) and may be taken, so to speak, as its
gauge.
In a note entitled: On the Citbic Space and volume of air, necessary
to insure the healthiness of inhabited places, Dr. Chaumont, an
English army doctor, has given a Table of comparisons between the
proportions of carbonic acid and the impressions on the sense of smell.
He has proved that a bad smell, indicating unhealthiness, manifests
itself, as soon as the proportion of carbonic acid in the air is greater
than 0*0006.
I found it easy to deduce from it the volume of air which ought to be
renewed according to the cubic capacity of the inhabited places. Here
are the results :
Cubic space for each person :
M.C. I M.C. I M.C. I M.C. I M.C. I M.C. I M.C. I M.C.
10 I 12 I l6 I 20 30 I 40 50 60
Volume of air to be introduced per hour and for each person :
M.C. I M.C. I M.C. I M.C. I M.C. I M.C. I M.C. M.C
90 I 88 I 84 | 80 I 70 I 60 I 50 40
These figures agree with the practical rules adopted by French and
English engineers.
INFLUENCE OF THE EXTERNAL TEMPERATURE.
The fundamental condition of the uniformity of the "appel" is that
the temperature in the escape-chimney should always be equally greatei
than that of the external air. A difference of 2o°c is generally sufficient
Natural ventilation has the inconvenience of being subject to acciden-
tal distubances in its motions and consequently is inadequate to ensure
healthiness.
The application of the preceding principles has given the results
summed up below.
Creche de St. Ambroise a Paris. (Day nursery for babies). This
ON WARMING AND VENTILATION.
333
building was intended for fifty children, and the volume of air to be
drawn out had been fixed at 1800 M.C. per hour. It was equal to 1800
M.c. The consumption of coal for this purpose was 1^40 per hour.
Primary Schools, Rue des Petits-hotels, Paris.
Volume of air required. Quantity obtained.
First Floor
Second Floor
4000 M. in an hour.
2000 M.
those
4030 M.
1989 M.
And this in spite of serious defects in carrying out the process.
Barracks. — The arrangements for barracks are similar to
noticed above.
Ships. — Dr. Reid has, in his work, pointed out very sensible arange-
ments. M. Bertin, an engineer in the French navy, has, on a ship
adapted for the transport of 308 horses, made use of the heat escaping
from the steam boilers and cooking-fires. The quantity of air to be
got rid of, for each horse had been established at 150 M.c. per hour.
Total, 33,900 M. in one hour. The result of experiments made in calm
weather, with the auxiliary fires alone, gave 143 M.C. per horse, in all
31,934 M.c. per hour.
Hospitals. — At the hospital Ste. Eugdnie, Lille, the volume of air,
to be renewed per bed and per hour had been fixed at 45 M.C. — too
low a figure — corresponding, in a room with twenty-two beds, to a
total of 45 x 22 = 990 M.c. It was much exceeded, as may be seen
by the following results :
22 beds
on each
floor.
Ground floor
First do.
Second do.
Total per Room.
Per Bed.
3.906 M.C. per hr.
3,440 „ „
4,823 „ „
i;8 M.C.
157 „
217 „
Total: 12.169
Average: 184 „
RESULTS.
During the war, the number of sick-beds was augmented from twenty-
two to sixty, and for the wounded to fifty. But the ventilation rose to
5060 for sixty beds, or 84 M.c. per bed. Thanks to this thorough ven-
tilation, no case of hospital gangrene broke out.
With regard to Field Ambulances, the American system might be
adopted.
334 SECTION— MECHANICS.
The Lying-in Hospital at St. Petirsburg. Here M. le Baron de
Derschau, a skilful Russian engineer, has carried out the following
arrangements :
Single bedded rooms, for private patients 8
Four-bedded rooms for married women 16
Four-bedded rooms for unmarried women 28
The results obtained were : Volume of air got rid of per bed and
per hour= on average, 127 M.c.
Volume of air introduced by special apertures = 92 M.c.
Guy's Hospital in London, built by Mr. Rhode Hawkins. The
space per bed alloted is but from 45 to 48 M. The volume of air got
rid of has been found to be equal to 109 M.c. per hour and per bed.
Fresh air is taken in by two towers, 20 or 25 M. in height. It descends
into subterranean vaults, where it is heated by means of circulating
hot-water apparatus.
Its escape takes place by means of a central tower 60 M. high.
Corps Legislatif, Paris. The volumes of air got rid of per hour
have been :
Salle and Tribunes 28,639 M-C.
Lobbies, etc. 12,744 M.C.
Total 41,417 M.C.
Plus passages 2,500 M.C.
The proposed quantity was but of 30,000 M.c.
The places to be ventilated were as follows :
Halls, galleries, passages, staircases ... 11,354 M.C.
Eight saloons 8,988 M.c.
Total 20,342 M.C.
There is a renewal of air once and a half every hour.
Theatres. — The introduction can take place by interjoists at the
boxes, by the cupola, and by the tympans ; and the escape at the
bottom of the boxes, in the passages, stair-cases, and from under the
orchestra seats. Use ought to be made of the lights, for the exhaus-
tion.
At the " Theatre Lyrique," the quantity to be got rid of had been
fixed at 51.000 M.C. ; the result reached from 55,000 to 60,000 M.c.
ON WARMING AND VENTILATION. 335
Railway stations ought to be ventilated by means of lanterns
placed up high.
With regard to workshops and laboratories, it is merely necessary
to apply the general rules mentioned above.
Glass roofs and ceilings are inconvenient inasmuch as they allow
the interior air to become much heated in summer, and very cool in-
winter. They ought to be double. In the winter season it is necessary
to heat a room with a glass roof from 300 to 400.
In kitchens the heat which is wasted by the stoves may be employed
to warm baths.
Water-closets can easily be ventilated by means of gas burners.
The lecture-rooms of the " Conservatoire des Arts et Metiers" have
for eight years been warmed and ventilated according to the principles
of the above-named system. Air is introduced by the ceiling at the
rate of about o M. 50 in i" ami at a temperature of from 18° to 20°.
In the interior, the temperature is kept between 18° and 22° at the
most. The volume of air got rid of is 25 M.c. per hour and per indi-
vidual, when the amphitheatre is perfectly full.
In summer the renewal of the air keeps the temperature 2® or 3^
below that of the external air.
As an example of the advantages to be derived from good ventila-
tion, Dr. Reid, quotes, in his work, the agreeable effect produced in
the Banquetting Hall of the Royal Society of Edinburgh, by the system
which he had introduced.
At one of the entertainments, at which fifty guests were present, the
comfort produced by the renewal of air had the effect of keeping up
the flow of spirits and the appetite of the assembly, to such an extent
that the consumption of liquids was greatly increased and the number
of carriages required to carry the members home was doubled. But
the good doctor adds that these gentle excesses did harm to no one.
General Morin winds up by invoking the assistance of the ladies —
who are as much interested in the matter, as any one — in order to
carry out all necessary measures for ensuring the healthiness of all
inhabited places.
Drawing-rooms and ball-rooms, magnificently lit up, decorated with
flowers and filled with noble youths and lovely maidens, are no less
dangerous for the health of the body, than for the peace of the soul.
336 SECTION— MECHANICS.
The air is tainted with a thousand different effluvia, and however little
agreeable it may be to hear it spoken, this ill, which all the human
race is heir to, cannot be avoided. We may say of it, as the poet says
of death :—
" Le pauvre en sa cabane, ou le chaume le couvre
Est sujet a ses lois
Et la garde qui veille aux barrieres du Louvre
N'en defend pas les rois."
Let us therefore unite our efforts to ward off these evils, and to
establish healthy dwellings for the poor as well as for the rich, in order
that all alike may enjoy these two great blessings : —
" Mens sana in sano corpore."
The PRESIDENT : I am sure we have all enjoyed the discourse
which General Morin has given us upon this very important subject of
ventilation. The time has now come when we have all experienced
the great advantage of ventilation, and have all come to the conclusion
that it is very desirable. But opinions differ very widely on the best
modes of carrying into effect under different circumstances. It is a
very difficult subject, which General Morin has followed up with great
care and perseverance and the results which he has brought before us,
are, I think, such as will commend themselves to our most earnest
attention. I beg now to pass a most hearty vote of thanks to him for
his communication.
The vote of thanks having been passed,
The PRESIDENT : I will now call on Messrs. E. Dent & Co. to give
us their communication
ON TIME MEASURERS.
Messrs. E. DENT £ Co. : A clock consists of two distinct parts — a
pendulum oscillating in a certain small interval of time — and a
mechanism whose duty it is to register the number of these oscillations
and to maintain them by giving to the pendulum periodically a little
push or impulse — for without this it would soon come to rest.
In order that a clock may perform accurately it will be at once seen
that the time occupied by each oscillation of the pendulum must be a
constant quantity.
For this it is ncccssr.ry thnt its theoretical l^n^ili should be invariable;
ON TIME MEASURERS. 337
that its arc of oscillation should be invariable ; and finally that it be
unaffected by changes in the density of the atmosphere.
These conditions may at first sight appear very simple, but cannot
be so readily fulfilled as might be imagined.
In the first place, of whatever material the pendulum may be com-
posed, some small alteration in its length (which we have mostly to
consider) will occur at every change of temperature ; and as we cannot
ensure a perfectly uniform temperature, a correction or compensation
must be applied to counteract the effects of a variable one.
The arc of oscillation must not vary because the pendulum in its
swing does not describe a cycloidal curve, as it should do in order
that the long and short oscillations might be performed in the
same space of time ; but almost a segment of a circle which diverges
rapidly from the cycloid, consequently a change in the arc described
altering the amount of divergence from the true theoretical path, alters
the time of oscillation. This variation is known as the circular error,
and cannot be corrected. All we can do is to endeavour to make the
error a constant quantity by maintaining a constant arc of oscillation.
The variations in the density of the atmosphere affect the duration
of the oscillation of the pendulum although to a much less .extent than
a change of temperature or a change of arc. Still the variation is
sufficiently large to make a correction desirable. It amounts to about
03 sec. in 24 hours for a change of pressure indicated by one inch fall
or rise of the mercury in the barometric tube.
As we propose to invite your attention more particularly to the com-
pensation of the pendulum for changes of temperature, and to Sir Geo.
Airy's correction for changes of barometric pressure (as exemplified
in the clock downstairs which is almost a counterpart of the
Greenwich Sidereal Stand one), we will dismiss the problem of the main-
tenance of a constant arc of oscillation after stating that for its accom-
plishment we use an escapement and train of wheels actuated by a
weight, the whole being so constructed as to impart to the pendulum
at every oscillation or alternate oscillation a certain push or impulse
which shall be of uniform force, and just equal to the resistance
encountered by the pendulum in its swing from side to side. We will
not stop to describe the forms of escapement best fulfilling this condi-
tion but will simply mention that the three varieties most in favour are
y
333 SECTION—MECHANICS.
the dead-beat of Graham, invented early last century ; the detached
escapement invented by Sir Geo. Airy some thirty or forty years ago,
and the more modern gravity escapements.
The compensation of the pendulum for changes of temperature is
effected -in various ways, but the principle is the same in all. Two
metals, one expanding more freely than the other, are used, and so
applied that the expansion of the one counteracts and nullifies the ex-
pansion of the other, so that the centre of oscillation of the pendulum
is maintained at the same point.
Originally, brass and steel were the metals employed, but mercury
and steel or iron, or zinc and steel or iron are now generally used — so we
will at once pass to them.
A mercurial pendulum consists of a steel rod at the lower end of
which hangs a jar or vessel of glass or iron containing the mercury.
Now the jar of mercury forms the bob of the pendulum, and is at the
same time the compensating element. The action in changes of
temperature is as follows. In heat, the steel rod lengthens and the jar
descends, but the same cause which produces this, makes the mercury
expand and rise in the jar, so that one expansion compensates for the
other. In cold, the metals contract similarly, and the same effect is
produced by the contrary action.
In a zinc and steel compensation, as now made, the construction is
somewhat more complicated, but still is easily explained. The bob or
principal mass of the pendulum is of lead, and does not form part of the
compensation. It is supported by a steel tube, to the lower end of
which it is fastened at its centre. The upper end of this tube is fitted
with a collar which rests on the top of a zinc tube, this in its turn is
supported by a nut on the lower end of the central steel rod. In heat,
the steel tube and rod expand and would allow the bob to descend,
but the zinc expanding raises it up an equal amount, so that the same
theoretical length is preserved : the length of the zinc tube being such,
that its longiditudinal expansion in any given temperature exactly
equals the expansion of the steel rod and tube together. A drawing
of a zinc and steel compensation pendulum is here.
Now, for astronomical clocks in which the greatest accuracy is re-
quired, the mercurial pendulum so long stood unrivalled that it may
fairly be asked how it is that it now seems likely to be superseded by
ON TIME MEASURERS. 339
the zinc and steel compensation. The reason is this. The mercury
in the jar may be considered as a solid mass presenting but a com-
paratively small surface to the action of the atmosphere by which
changes of temperature are communicated to it, whilst the steel rod
and suspension spring present a much larger surface in proportion to
their bulk, and are acted on much more quickly, so that in .a variable
temperature you have one part of the pendulum expanding or con-
tracting, as the case may be, before the other, and an unsteady rate is
the result. It is obvious that the greater the diameter of the jar the
more sluggish will be the compensation, and it has been proposed to
put the mercury into several small jars, but there are inconveniences
to this.
Now, in a zinc and steel pendulum, those parts on which we depend
for the compensation are much more nearly of the same bulk, and
present nearly the same surface to the action of the atmosphere, so
that it is fair to infer they act simultaneously, or almost simultaneously.
In these pendulums you will observe that the bob is supported at its
centre, so that its expansion or contraction, let it occur when it may,
does not alter the theoretical length or affect the time of oscillation.
Some persons overlook or ignore the importance of suspending the
pendulum bob at its centre, and so nullifying the effect of changes of
temperature upon it ; but we cannot but think that a little careful con-
sideration on their part will lead them to allow that it is not without
advantage.
We have been favoured by the Astronomer Royal with a copy of
the rate of one of our clocks having a zinc and steel compensation.
This clock was going for several months in one of the small observa-
tories used in the Transit of Venus Expedition. It has been printed
for the purpose of showing the behaviour of a zinc and steel pendulum
under as trying circumstances as can well be conceived, the daily
variations of temperature being frequently fifty degrees.
We will now pass on to the barometric connection. The extreme
steadiness of rate of the Greenwich Standard Clock at equal pressures,
led Sir Geo. Airy to attempt the corrrection by means of the
magnetic apparatus you may have seen below, a drawing of which we
have here. Two bar magnets, having their poles reversed, are fastened
vertically one in front and the other at the back of the pendulum bob, and
340 SECTION— MECHANICS.
beneath them is a horse-shoe magnet carried by one arm of a lever,
the other end of which is in connection with a float icjting on the
lower limb of a bent barometric tube. Between the poles of the
horse-shoe magnet and those on the pendulum there is constant attrac-
tion, so that you have a force acting in the same direction as the force
of gravity, but variable with the density of the atmosphere.
It is found that the clock loses as the pressure increases, so with a
high barometer the horse-shoe magnet is raised, the attractive force
increased, and the clock made to gain a corresponding amount.
We have printed a copy of an instructive diagram prapared at the
Royal Observatory under the direction of the Astronomer Royal,
which shows in a very marked way the effect of changes of pressure
on the rate of the Greenwich standard clock before the magnetic
apparatus was applied. The red line shows the calculated rate, allow-
ing for the pressure, and the black line shows the actual observed rate
of the clock. It will be seen how nearly the one coincides with the other,
the greatest difference between them being less than one-tenth of a
second in twenty-four hours. The correction is now effected automa-
tically by the apparatus we have just described, and we have authority for
stating that it completely answers the purpose for which it was designed.
The time measuring power of a chronometer is dependent upon its
balance spring, which consists generally of a slight ribbon of hardened
and tempered steel, coiled round and round with an upward twist
somewhat in the form of a cylinder.
The elasticity of this little spring performs just the same duty for
the balance which gravity does for the pendulum — it keeps it swinging
backwards and forwards — with a degree of uniformity which is truly
surprising.
But as a controlling power the elasticity of this little spring labours
under one serious disadvantage as compared with gravity : it varies
rapidly with any increase or decrease of temperature.
It varies more or less according to the material of which the spring
is composed ; thus a gold spring suffers a greater change than a steel
spring, a steel spring than a palladium spring, and a palladium spring
than a glass spring.
It may surprise you to hear us speak of a glass spring, but the thing
has been done, and is here.
ON TIME MEASURERS. 341
This glass spring is the invention and handiwork of the late
Frederick Dent, and the chronometer before us represents the only
perfect specimen now in existence.
The elasticity and strength of this spring are so extraordinary that
until you had examined it you could scarcely credit its being glass, but
as seeing is believing, and we shall be happy to exhibit a portion of
another one to any person who may be interested in it after the
demonstrations.
But meanwhile, 'for illustration, we will tell you two experiments, the
second one being quite unintentional. In the first a chronometer was
taken having an ordinary steel spring, the balance of which was oscil-
lating 1 80° from rest — a glass spring was substituted, everything else
remaining exactly the same, the oscillation of the balance rose to 200°.
The unintentional experiment was that the chronometer was
knocked off a table, and though both points of the staff were broken
"Tn^^balance'spring sustained no injury.
With regard to the specimen before us you will see that with the
exception of having rather more coils, it is shaped like a steel spring.
The oscillation of the balance is 180° from rest. The glass spring was
under trial at the Royal Observatory for a period of nearly three years,
and the following results were attained. The figures are the average
daily rates calculated from periods of a month, the mean temperature
being given opposite each. There is one peculiarity about this per-
formance to which we must briefly call attention.
This rate shows that the chronometer had always a tendency to
accelerate or to advance upon its rate, and with regard to this it may
be interesting here to state that steel springs exhibit the same tendency
just in proportion to their hardness. And that a soft steel or gold
spring "accelerates" in the reverse direction, i.e., loses upon its rate.
Now let us return and inquire what is the behaviour of balance
springs of different materials under a given change of temperature.
Suppose that we take four chronometers, the first with a balance
spring of gold, the second with a balance spring of steel, the third with
a balance spring of palladium, and the fourth with a balance spring of
glass ; and in place of the ordinary balance we substitute upon each a
balance composed of a glass disc, so as practically to eliminate any
error due to the expansion of the balance. Then, if we regulate each
342 SECTION— MECHANICS.
chronometer to go right at the temperature of freezing, thirty-two
degrees fahr., we shall find that when we raise the temperature to-
100 degrees the chronometer with a gold spring will lose eight min.
four sec. a day, the chronometer with a steel spring six min. twenty-
five sec., the chronometer with a palladium spring two min. thirty-
one sec., and the chronometer with a glass spring forty seconds ouly.
It is with the compensation for these errors that we have practically
to deal in chronometers, the loss of time due to the expansion of the
balance being slight in comparison.
In the case of the glass spring chronometer, the smallness of this
error made it necessary to apply a very different to the usual form of
compensation balance : compound lamince formed of silver melted
upon platinum weighing about two grains, each are mounted upright
upon a disc of glass, and with any increase of temperature the tending
of these towards the axis of motion affords a sufficient compensation.
Unfortunately the amount of compensation required for a steel
spring is so great that in correcting it we introduce a secondary error,
the nature of which I will try to explain to you.
The loss of time due to the loss of elasticity of the spring varies
nearly in the same proportion as the temperature, and an ordinary
compensation balance advances or withdraws its weights to or from
the axis of motion practically in the same proportion.
But the time in which the balance swings, varies not as the distance
of its weights from the axis of motion, but as the square of their
distance, and thus it requires a greater motion of the weights inwards,.
to produce the same amount of effect as a lesser motion outwards.
Thus, in an ordinary compensation balance, if the weights were
adjusted to advance a sufficient distance to compensate the chrono-
meter for a rise in temperature of thirty degrees, a fall of the same
amount would make them retire so much too far as to make the
chronometer lose four seconds a day. And the best that could be done
under the circumstances would be to so adjust the chronometer as to
divide the error, and make it lose two seconds a day in the heat, and
two seconds a day in the cold.
Many methods have been introduced for correcting this secondary
error ; some are based upon the principle of increasing the motion
of the weights when they move inward, and reducing it when they
ON TIME MEASURERS. 343
move outward ; others are arranged to move an auxiliary weight
towards the axis of motion, both for an increase and decrease of
temperature ; others check the motion of the main weight away from
the axis of motion ; and others assist it only when it is going towards
it. Illustrations of all these different forms are here exhibited, but
not to occupy your time we propose only to describe one of them.
Here is a bar formed of brass, melted upon steel, the brass being
underneath. Do not consider the staples at present, but imagine for
the present that the weights by which they are crowned are mounted
upon little pillars straight from the main bar.
Now let us see what happens with any increase of temperature : the
brass expands, so does the steel, but the brass expands most, and the
only method by which the two can accomodate matters, is that the bar
shall form a curve, the brass being outside. In other words the bar
bends upwards and tilts the compensation weights in towards the axis
of motion. The reverse action takes place in the cold.
Now see, the weights move inwards and outwards equally for equal
rises and falls of the temperature. Now let us consider the action of
our staples. They themselves are compound pieces, and when the
weights are pointed towards the axis of motion in the heat, they open
and advance their progress a little ; and in the cold, when the weights
are pointed away from the axis of motion, they close and retard it,
producing in this way the necessary correction for the secondary error.
But although balance springs as compared with gravity are at this
very great disadvantage with regard to changes of temperature, they
have one exceedingly important peculiarity which their rival has not :
that is to say, that with a spring of suitable form and strength, by
slightly altering the length, or for very small amounts by arching it,
you are able almost completely to isochronise the long and short arcs
of oscillation of the balance. You can make the chronometer keep
the same rate when its balance is swinging 1 8oS from rest as when it
is swinging 22 59. The direction you alter the spring in is this :— if
the chronometer gains during the short arcs you shorten the spring,
and if during the long you lengthen it.
The property of the spring is exceedingly convenient, because by
leaving the spring rather fast in the short vibrations you can correct
the chronometer for any occasional irregularity owing to an increase
344 SECTION— MECHANICS.
of friction. For friction meaning retardation, in other words a check-
ing of the action of the balance. The oscillation falling off at the
same time, and the balance moving rather faster in consequence the
tendency to lose is corrected.
It would appear that this plan of leaving the chronometer fast in
the short vibrations also answers as a barometric compensation. For
instance, we took a chronometer which was going exactly right at the
normal atmospheric pressure and placing it under the receiver of an
air pump reduced the pressure to about 1 5 in. Before the pressure
was reduced the balance was swinging about 214° from rest, but in the
thinner atmosphere it rose to 270", and yet the time of the chrono-
meter did not vary more than three-tenths of a second a day — the
tendency to gain by the removal of the friction due to the denser
atmosphere being corrected by the tendency to lose during the longer
oscillations.
The advantage due to the power of isochronising the long and short
arcs of oscillation, and the mechanical superiority of its escapement
over any clock escapement ever yet invented, almost place the chrono-
meter alongside of the best astronomical clocks.
In conclusion, allow us to remind you that there is a fundamental
distinction between a clock and chronometer — the time-measuring
power of the one depending upon gravity, the time-measuring power
of the other depending upon the elasticity of its balance spring — •
that is to say, upon a property of matter. The chronometer is there-
fore much more absolute in its measurement of time than the clock,
and if for no other reason every effort should be made towards bring-
ing it to that perfection which would render it available for the highest
astronomical purpose.
The PRESIDENT : Mr. Glasgow, the representative of the British
Horological Institute, wishes to add to the information given to us
just now, and although the time for adjournment has arrived I am sure
you will be glad to hear him.
Mr. GLASGOW : I must apologise for coming before you at so late
an hour when I had no previous idea of saying anything, but I thought
it would be well as there is such an opportunity, and as the subject is
of such general interest to the public, that I should carry the matter a
little further than Messrs. Dent have done. The rather restricted
ON TIME MEASURERS. 345
paper which they have read on the compensation of pendulums I
will not deal with. A few years ago it would have been vastly
more interesting to scientific men than it is now, inasmuch as elec-
tricity is now the means of taking the exact time to all the large
cities, and electric clocks have to a great extent taken the place of
the accurate pendulum which we used to have so many experiments
upon. The very ingenious contrivance of the Astronomer Royal,
shown on the clock of the Messrs. Dent, and referred to in the paper
just read, for correcting the influence of the atmospheric pressure on
the pendulum, known as the barometric error, is. in the opinion of so
high an authority as Sir Edmund Beckett, unnecessary. He tells us
that when testing the Westminster clock for the barometric error, he
found it had none ; which he attributed to the rather unusual length
of the arc, or swing of the pendulum, and after careful experiments, he
found that this error of the pendulum could always be corrected by
regulating the length of arc. But as chronometers and pocket watches
have become vastly more important to the general public than they used
to be, I will say a few words upon chronometer balances, and those of
pocket watches. There are a variety of balances which may be seen
down stairs lent by the Horological Institute, and I am sorry they are
not properly displayed or catalogued. There are amongst these balances
specimens of various inventions, from the first made by Arnold and
Earnshaw to the latest sent for trial to Greenwich, and it is curious to
note how very little difference there is between the earliest and latest
examples, and not encouraging to see how little improvement has been
made during the seventy years that have elapsed since the invention
of Earnshaw : although there are in this collection alone some forty
differently constructed balances, all being the results of attempts to
improve upon it.
There is also a collection of balances shown by Messrs. Dent, most
of them being a modification of the form, known in the trade as " Dent's
Balances," and others exhibited of very complicated construction, but
after much time and trouble spent on these ingenious contrivances, it
has been found that simplicity of form is indispensable to a reliable
timekeeper, and the balance of Earnshaw without modification is what
is all but universally used for ship's chronometers at the present time.
So also is it with the pocket watch, although the manipulative skill oC
346 SECTION— MECHANICS.
the workman has greatly advanced, science has not kept pace with it,
and pocket chronometers are fast giving place to the best form of lever
escapement — that invented by Mudge and strangely enough abandoned
by Mudge himself in favour of a much inferior escapement.
The model of the balance shown by Mr. Dent differs in form from
that in general use, the ordinary form being that of a ring or rim com-
posed of a lamina of brass and steel melted together and so propor-
tioned to each other that when cut open the rim contracts in heat,
thereby decreasing its diameter and expands in cold, which increases
its diameter, and thus compensating for the error which is principally
in the balance spring, caused by its elongation and loss of elastic force
in heat, and its greater resistance when cold ; and it may be of impor-
tance to those who wear watches without compensation balance to
know on the authority of the Astronomer Royal, that for every difference
of ten degrees in temperature there is a difference in twenty-four hours
of one minute in the time of these watches.
Unfortunately for the scientific progress of watchmaking the trade
spirit so predominates that scientific men have not of late years
devoted themselves to its study as might have been expected from the
nature of the great interest attached to it, otherwise we might have
been further advanced than we are at present.
But what I want to say is this, and I am glad of the opportunity of
saying it here, the mode of testing and purchasing chronometers for
the navy is not satisfactory, and is not calculated to encourage the men
by whose efforts alone we can hope for a higher standard of excellence.
In the first place the prices paid by the Government are too small to
tempt such men from their ordinary pursuits to make the long and
careful experiments necessary for perfecting any new form of balance
or even improving upon old forms, and secondly, chronometers are sent
to Greenwich by scores from all the little towns in the kingdom, bear-
ing names of men who perhaps have never seen the instruments to
which they are affixed, but if purchased they are " chronometer makers
to the Admiralty," the chronometers being made in London.
I think this should not be, and that some means should be adopted
to insure that "chronometer maker to the Admiralty" be a distinction
worth coveting and competing for, and not merely to be used as a
trade "puff" by men who know nothing of chronometers.
ON TIME MEASURERS. 347
The PRESIDENT : It only remains for me to move a vote of thanks
to Messrs. Dent for their communication, which is very interesting
as coming from gentlemen whose names have been connected with
true chronometry for so many years.
The conference then adjourned.
SECTION— MECHANICS (including Pure and Applied
Mathematics and Mechanical Drawing).
Thursday, May 2$t/i, 1876.
Dr. SIEMENS, President, in the Chair.
F. J. BRAMWELL, M. Inst. C.E., F.R.S. : The subject on which I
have now the honour to address you, the subject which is to occupy our
attention to-day, is that of " Prime- Movers," that is to say, we are about
to consider that class of machines which, to use the words of Trc dgold,
41 enable the engineer to direct the great sources of power in Nature for
the use and convenience of man."
Although machines of this kind are in truth mere converters or
adapters of extraneous forces into useful and manageable forms, and
have not any source of life, power, or motion in themselves, never-
theless they impress us with the notion of vitality ; and it is difficult
to regard the revolving shaft of a water-wheel or turbine set in motion
"by some hidden stream, or to gaze upon the steam-engine actuated by
an unseen vapour, without, as I have said, the idea being raised in
our minds that the machines on which we are looking are really en-
dowed with some kind of life; and thereupon not inaptly, although
not quite accurately we speak of them as Prime-Movers.
The invention of Prime-Movers marks a very great step in the pro-
gress of mechanical science in the world, as it commences an era dis-
tinct from that in which mere machines, to be acted on by human or
animal muscular force, were alone in existence. Machines such as
these, highly useful as they may be, are, after all, only tools or imple-
ments more or less ingenious, and more or less complex.
Mankind could not have been very long upon the earth before they
must have found the need and must have discovered the utility of some
PRIME-MO VERS. 349
kind of tool or implement ; they must soon have found that the direct
action of the power of the arm, which was not enough by itself to break
up some obstacle, became sufficient if that action were applied by
the wielding of a heavy club, or by the putting into motion of a
large stone ; and thus the hammer, or its equivalent, must have been
among the earliest of inventions. Such an implement would soon
teach its users that muscular force when exercised through a con-
siderable space, could be scored up> and could be delivered in a
concentrated form by a blow.
Similarly it could not have been long before it must have been found
that to raise water in the hollow of the hand in small quantities and
by repeated efforts was not so convenient a mode as to raise at one
operation all that was required, and to do so by the aid of a bent leaf or
by the use of a shell, and in this way another implement would speedily
be invented. We might pursue this line of speculation, and doing so
we should readily arrive at the conclusion that (without attributing
to the early inhabitants of the earth any profound acquaintance
with mechanics) the hammer, the lever, the wedge, water vessels,
and other simple tools and utensils must soon have come into ex-
istence ; and we should also be led to believe that when even with
the aid of tools such as these a man singly could not accomplish any
desired object, the expedient of combining the power of more than
one man to attain an end would soon be thought of ; and that the
requisite appliances, such as large beams, for levers, numerous ropes
(which must very early in the history of the world have been twisted
from filaments) and matters of that kind would come into use. In
corroboration of this view, if a corroboration were wanted, the fact may
be cited that on the discovery of any isolated savage community, it
is, I think I may say invariably, found to have advanced thus far in
mechanical art.
But passing from such machines as these, which are rather of the
character of mere tools and implements than of that of machines, as
\ve now popularly use the word, one knows that even complicated
mechanism for the purpose of enabling muscular force to be more
readily applied, is of very ancient date. On this point I will quote
from only one Book, that is the Bible, and from that I will cite but a
few instances. At the tenth and eleventh verses of the eleventh
350 SECTION— MECHANICS.
chapter of Deuteronomy, a statement is made clearly indicating that
in Egypt irrigation was carried on by some kind of machine worked
by the foot, whether the tread-wheel, with water buckets round about
it, mentioned so many centuries later by Vitruvius, or whether the
plank-lever, with a bucket suspended at one end and raised by the
labourer running along the top of the lever to the other end (an
apparatus even now used in India), we do not know ; but that it was
some machine worked by the foot is clear, the statement being that
when the Israelites had reached the promised land they would find
it was one abounding in streams, so as to be naturally watered, and
that it would not require to be watered by the foot as in Egypt.
Again in Chronicles it is related that King Uzziah loved husbandry,
and that he made many engines, unhappily not in connexion with
agriculture, but for warlike purposes, "to shoot arrows and great
stones withal." Further, in the seventh chapter of the Book of Job,
we have the comparison of the life of man passing away swifter
than a weaver's shuttle, this points unmistakably to the fact that
there must in those days have been in existence a loom capable of
weaving fabrics of such widths that the shuttle required to be impelled
with a speed equal to a flight from one side of the fabric to the other ;
and no doubt such a fabric must have been made in a machine com-
petent at least to raise and depress alternately the halves of the warp
threads. The potter's wheel also is frequently mentioned in the
Bible.
Such instances as these are sufficient to show that considerable
progress must have been made in the very earliest days of history in
the construction of machines whereby muscular force was conveniently
applied to an end; but if we leave out of account, as we fairly
may, the action of the wind in propelling a boat by sails and the action
•of the wind in winnowing grain, I think we shall be right in consider-
ing that in the times of which I have been speaking there did not exist
any machine in the nature of a power giver or Prime-Mover.
Doubtless the want of a greater force than could be obtained from
the muscles of one human being must have soon made itself felt ; and
intelligent men, conscious of their own ability and of their mental
power of directing a large amount of work, must have been grieved
when they found the use of that power circumscribed by the limited
PRIME-MO VERS. 35 1
force of their own bodies ; and therefore, early in the world's history,
there must have been the attempt by the offer of some consideration
or reward to induce the robust in body but not in mind, to work
under the directions of these men of superior intelligence. But when
such aid as this became insufficient, the way in which, in all proba-
bility, the people of those days endeavoured to satisfy the further
demand would be to make captives of their enemies, and to reduce
them to a state of bondage — to grind at the mill, to raise water, or,
yoked by innumerable cords and beams, to draw along the huge
blocks required in the foundations of a temple, or for the building of a
pyramid, or to act in concert on the many oars of a galley — although
by what means this last-named operation was performed is not very
clear. And doubtless, coupled with this condition of bondage, there
must have been an amount of human suffering which is too frightful
to be contemplated.
Such machines as those to which I have called attention could not
have been invented and brought into use without the exercise of much
mechanical skill ; but considerable as this skill must have been, it had
never originated a Prime-Mover, it had given no source of power to the
world, but had left it dependent on the muscular exertions of human
beings and of animals.
Great then was the step, and a most distinct era was it in mechani-
cal science, when for the first time a Prime-Mover was invented and a
machine was brought into existence which, utilizing some hitherto
disregarded natural force, converted it into a convenient form of power
by which as great results could be obtained as were obtainable by
the aggregation of a large number of human beings, and could be
obtained without bondage and without affliction.
There are probably few sights more pleasing to one who has been
brought up in factories than to watch a skilful workman engaged in
executing a piece of work which requires absolute mastery over the
tools that he uses, and demands that they should "have the constant
guiding of his intelligent mind. Handicraft work of such a kind
borders upon the occupation of the artist ; and to see such work in the
course of execution is, as I have said, a source of pleasure. But when,
descending from this, the work becomes more and more of the charac-
ter of mere repetition, and when it is accomplished by the aid of im-
352 SECTION— MECHANICS.
plements which from their very perfection, require but little mind to
direct them, and demand only the use of muscle — then, although
the labour when honestly pursued is still honourable, and therefore to
be admired, there comes over one a feeling of fear and of regret that
the man is verging towards a mere implement. But when one sees,
as I have seen in my time, in England, and as I have seen very
recently on the Continent, men earning their living by treading within
a cage, to cause it to revolve and thereby to raise weights — an occupa-
tion demanding no greater exercise of intelligence than that which is
sufficient to start, to stop, and to reverse the wheel at the word of
command — one does indeed regret to find human beings employed in
so low an occupation ; an occupation that places them on the level with
the turnspit, and one which is most properly meted out in our prisons
as a punishment for crime ; accompanied, however, in the instance of
the prison, with the degradation that the force exerted shall be entirely
wasted in idly turning a fan in the free air ; and thus the prisoner,
in addition to the fatigue of his body, undergoes the humiliation of.
as he expresses it, " grinding the wind."
If they played no other part than that of relieving humanity from
such tasks as these, Prime-Movers would be machines to be hailed.
True it is that 'the labourers who were thus relieved would not than!,:
their benefactors ; and indeed, so far as the individuals subjected to
the change were concerned, they would have cause not to thank them,
because those individuals having been taught no other mode of earning
a livelihood, and finding the mode they knew set on one side by the
employment of a prime-mover, would be at their wits' end for a means
of subsistence ; and would be experiencing those miseries which arc
caused by a state of transition. But in some way the men of the tran-
sition state must be relieved ; and, in the next generation, it no longer
being possible to subsist by such wholly unintelligent labour, the
energies of their descendants would be devoted to gaining a livelihood
by some occupation more worthy of the mind of man.
Early Prime-Movers, from their comparatively small size, probably
did little more than thus relieve humanity, but when we come to con-
sider the prime-movers of the present day, by which we are enabled to
contain within a single vessel, and to apply to its propulsion 8000
ndicated horse-power, or an equivalent of the labour of nearly 50,000
PRIME-MOVERS. 353
men working at one time, we find that the prime-mover has another and
most important claim upon our interest, namely, that it enables us to
attain results it would be absolutely impossible to attain by any
aggregation of human or other muscular effort, however brutally indif-
ferent we might be to the misery of those who were engaged in that
effort.
Excluding from our consideration light and even electricity as
not being up to the present sources of power on which we rely in
practice, there remain three principal groups into which our Prime-
Movers may be arranged : — viz., those which work by the agency of
the wind, those which work by the agency of water, and those which
work by the agency of heat.
Of these three great groups two, heat and water, are capable of
division, and indeed demand division into various branches.
A water Prime-Mover may be actuated by the impact of water, as
in some kinds of water-wheels, turbines, and hydraulic rams, or by
water acting as a weight or pressure, as in other kinds of water-
\vheels, and in water pressure engines, or by streams of water in-
ducing currents, as in the case of the jet pump and of the " trombe
d'eau," or by its undulating movements, as in ocean waves. The
ability of water to give out motive power may arise from falls, from
the currents of rivers, from the tides, or, as has been said, from the
oscillation of the waves.
Prime-movers which utilize the force of the wind, are few in number,
and in all cases act by impact.
As regards those prime-movers which work by the aid of heat. We
may have that heat developed by the combustion of fuel, and being
so developed, applied to heating water, raising steam, and working
some of the numerous forms of steam-engines, or, as in the case of
the Giffard injector, performing work by currents induced by the
flow of steam ; or we may have the heat of fuel applied to vary
the density of the air, and thus to obtain motion as by the smoke-jack ;
or the fuel may be employed to augment the bulk and the pressure of
gases, as in the numerous caloric engines ; or we may have heat and
power developed in the combustion of gases, as in the forms of gas
engines, or in the combustion of explosives, as in gunpowder, dynamite,
and other like materials, used not only for the purposes of artillery and
z
354 SECTION—MECHANICS.
of blasting, but for actuating prime-movers in the ordinary sense of the
word.
Again, we may have the heat of the sun applied through the agency
of the expansion of gases to the production of power as in the sun
pumps of Salomon de Cans, and of Belidor, to the production of
power through the generation of steam as in the sun engine of
Ericsson ; or, finally, we may have it applied direct, as in the radio-
meter of Mr. Crooks.
A consideration of the foregoing heads under which prime-movers
range themselves, will speedily bring us to the conclusion that the
main source of all mechanical force on this earth is the sun. If the
prime-movers be urged by water, that water has attained the elevation
from which it falls, and thus has been made competent to give out
power, by reason of its having been evaporated and raised by the
heat of the sun. If the power of the water be derived from the tidal
influence, that influence is due to the joint action of the sun and its
assistant the moon. If the prime-mover depend upon the wind
for its force, either directly, as in windmills, or indirectly, as in
machines worked by the waves, then that wind is caused to
blow by variations of temperature due to the action of the sun.
If the prime-mover depend upon light or upon solar heat, as in the
case of the radiometer and of the Sun engine, then the connexion
is obvious ; and if the heat be due to combustion, then the fuel
which supports that combustion is, after all, but the sun's rays
stored up. If the fuel be, as is now sometimes the case, straw
or cotton stalks, we feel that there we have the growth of the
one season's effect of the sun's rays ; if the fuel be wood, it is equally
true that the wood is the growth of a few seasons' exercise of the
sun's rays ; but if it be the more potent and more general fuel —
coal — then, although the fact is not an obvious one, we know that coal
also is merely the stored-up result of many years of the exercise of the
sun's rays.
And even in the case of electrical prime-movers these depend on the
slow oxidation — that is, burning of metal which has been brought into
the metallic or unburnt state from the burnt condition (or that of ore)
by the aid of heat generated by the combustion of fuel.
The interesting lecture-room experiment with glass tubes charged
PRIME-MOVERS. 355
with sulphide of calcium, or other analogous sulphides, makes visible
to us the fact that the sun's rays may be stored up as light ; but that
they are as truly stored-up (although not in the form of light) in the
herb, the tree, and the coal, we also now know, and we appreciate the
far-seeing mind of George Stephenson, who astonished his friend by
announcing that a passing train was being driven by the sun : and we
know that the engineer was right and that the satirical author was
wrong, when he instanced as a type of folly the people of Laputa en-
gaged in extracting sunbeams from cucumbers. The sunbeams were
as surely in the cucumbers as they are in the sulphide of calcium
tubes, but in the latter case they can be seen by the bodily eye, while
in the former they demand the mind's eye of a Stephenson.
Although the sailing of ships and the winnowing of grain must from
very early times have made it clear that the wind was capable of
exercising a substantial power, nevertheless being an invisible agent,
it is not one likely to strike the mind as being fit to give effect to a
prime-mover, and therefore it is not to be wondered at that prime-
movers actuated by water are those of which we first have any record ;
unless indeed the toy steam-engine of Hiero may be looked upon as a
prime-mover, anterior to those urged by water. It would appear that
in the reign of Augustus water-wheels were well known, for Vitruvius,
writing at that time, speaks of them as common implements ; not so
common, however, as to have replaced the human turnspit, as we
gather from his writings that the employment of men within a tread-
wheel was still the more ordinary mode of obtaining a rotary force.
It would seem, however, that water-wheels driven by the impact of the
stream upon pallet boards were employed in the time^ of Augustus not
merely to raise water by buckets placed about the circumference of the
wheels, but also to drive millstones for grinding wheat. Strabo states
that a mill of this kind was in use at the palace of the King of Pontus.
Having thus mentioned the earliest record of hydraulic (or indeed
of any) prime-movers, I will not endeavour to trace their history down
to modern times, as it would be impossible to do so usefully within
the limits of an address. I will therefore, without further reference to
the historical part of the subject, ask you to join me in considering
\vhat are the conditions which govern the application of water to
hydraulic prime-movers.
356 SECTION— MECHANICS.
After all, water must be looked upon as a convenient form of descend-
ing weight. When the fall is not great it is always practicable by
means of water-wheels having buckets which retain the water to
employ, as I have said, its mere gravity as a motor, and probably it
is by this mode that the highest result is procured from any given
quantity of water falling through a given height. By the use of a back-
shot wheel as much as seventy-five per cent, of the total power is
rendered available. The twenty-five per cent, of loss arises from the
friction of the axle of the wheel and of the gearing transmitting the
force to the machine which is to utilize it ; from some of the water
being discharged out of the buckets before the bottom of the fall is
reached ; from the necessary clearance between the wheel and the
tail-water ; from the eddies produced in the water as it enters the
buckets ; and (to a small extent) from the resistance of the air.
When the difference of level between the source of water and its
delivery exceeds, however, forty or fifty feet, the water-wheel becomes
very unwieldy and expensive and revolves so slowly that it ceases to be
a desirable prime-mover. Then recourse can be had to water-pressure
engines, engines wherein pistons move in cylinders, and, being pressed
alternately in opposite directions by the head of water, set up rotary
motion in the machine, in the same way as if the pistons were acted
upon by steam. In the construction of such water-engines great care
must be taken to have ample inlets and outlets, in order that the loss
incurred either by the power requisite to drive the water through
restricted orifices, or by surface resistance caused by a too speedy flow
along the various passages, may be a minimum. Care has to be taken
also in the arrangements of the valves that the engines, when employed
for rotary movement, may be able to turn their centres without pro-
ducing an injurious pressure upon the water within the cylinders.
Water engines employed for pumping, but without rotary movement,
are mentioned by Belidor, in his " Architecture Hydraulique," pub-
lished in 1739, Article 1156. In England Sir William Armstrong has
brought these machines to great perfection. The first of his make,
erected many years ago, is still working most successfully at the Allan
Head Lead Mines. This machine is driven by a natural head of water
and not from an accumulator, and is employed in the mine as a
winding engine.
PRIME-MOVERS. 357
An extremely useful feature in engines of this kind, is their adapta-
bility to be driven by the pressure of water derived from an ordinary
water works, and in this manner small manufacturers carrying on
business in their own houses are enabled to obtain a prime-mover
with great ease and all things considered at small cost ; and not only
is advantage taken of such machines for the purpose of driving manu-
factories, but water cylinders are now largely used for working the
bellows of church organs, for which purpose, however, an overshot
water-wheel is shown as being employed as far back as Salomon de
Caus's book, date 1615.
Large water-wheels or even water-engines are comparatively costly
machines, and as large water-wheels make but few revolutions per
minute they require expensive and heavy gearing to get up speed, and
thus it is that it frequently becomes a desirable thing to dispense with
such machines and to resort to other modes of making available high
falls of water. In former times this was done by suffering the im-
petuous stream of water to beat upon the pallets of water-wheels, but
from such machines only a poor effect could be obtained, as a large
portion of the energy in the water was devoted to the formation of
eddies and the generation of heat and to the production of lateral
currents, leaving but a small percentage available as motive power.
Much of the evil effect, however, attendant upon using the impact of
water as a means of driving water-wheels is obviated by the con-
struction invented by the distinguished French engineer Poncelet.
For high falls, however, the implement now generally employed is
the turbine, of which the well-known Barker's Mill may be looked
upon as the germ.
I have got before me No. 1983, a model of Fourneyron's turbine.
This is not an apt model for my present purposes, inasmuch as it
represents a turbine to be employed with a comparatively low fall of
water; but even in such instances the turbine gives most excellent
results, and it has the advantage over the water-wheel of being capable
of working with great efficiency, although there may be a considerable
rise in the "tail-water," a rise which would materially check the
action of an ordinary water-wheel. In this turbine every care has
been bestowed to give a proper form to the pallets on which the
water acts, so as to take up step by step, as it were, the whole of the
358 SECTION— MECHANICS.
energy residing in the stream ; in order that the water may pass away
from the turbine in an inert condition, and that in acting upon the
vanes of the turbine eddies may not be formed, and that thus energy
may not be wasted.
There are probably few sights more surprising to the old-fashioned
millwright who has been used to see water-wheels of fifty or even seventy
feet diameter, employed for the utilization of a high fall, than that of
a turbine occupying only a few cubic feet of space, but running at such a
velocity as to consume the whole of the water of a considerable stream,
and so to consume it as to deliver nearly as large a percentage of
useful effect as would the cumbrous water-wheel itself.
If a fall of water be employed with the mere object of raising water,
this end can be attained without the employment of either water-
wheel or turbine by the aid of the Montgolfier ram, a very useful
machine for those cases wherein but a small percentage of the whole
fall is required to be raised, but is required to be raised to a consider-
able height. No. 1996, which I have before me, is a glass model of
such a ram, but I fear it is too small to be visible, except to those who
are very near to the table. You are, however, all aware that the prin-
ciple of action consists in the sudden arrestation of a column of water
flowing with a velocity due to the head. When the water is arrested,
a small portion of it raises an outlet valve, and thereby passes
into an air vessel against a pressure competent to drive the water
up to the desired height, while the main body recoils along the
supply pipe ; then an escape valve having fallen open the water
that has recoiled returns, a large portion passes out by this valve, and
then the velocity being once more fully established, the escape valve
shuts and causes another arrcsiation and a repetition of the working.
This is an implement by which a large volume of water, and having
but a low fall, can be made to raise a portion of itself to a great
height ; but there is a converse use of water, wherein the employment
of a small stream moving rapidly owing to its having descended iron)
a considerable height, is caused to induce a current in other water,
and to draw it along with itself with a diminished velocity, but with
a velocity still competent to raise the united stream to the insignificant
height which suffices for delivering the water from swamps and marshy
land.
PRIME-MOVERS. 359
This employment of the induced current as a prime-mover is
described by Venturi in the record of his experiments made at the
latter end of the eighteenth century, and within the last few years
Professor James Thomson has applied the same principle with great
success in his jet pump.
The next mode I shall notice of obtaining motive power from water,
is also one where it operates by an induced current — this is, the
trombe d'eau, an apparatus wherein water, falling down a vertical
pipe, induces a current of air to descend with it, and the lower end
of the vertical pipe being connected with the top of an inverted
vessel, the bottom of the sides of which vessel is sealed by a water
joint, the water dashing upon a block placed below, the mouth of
the pipe, is separated from the air, so that while the water descends
and escapes from under the sides of the vessel the air rises and is
accumulated in the upper part, and can be led away to blow a forge
fire. These machines are described in Belidor's work.
The utilization of the rise and fall of the tide is also fully described
by Belidor, who gives drawings of channels so arranged that during
both the rise and fall of the tide the water-wheel, notwithstanding the
reversal of the current, revolves in one and the same direction. The
tide is a source of power which it is highly desirable should be
utilized to a greater extent than it is ; if we consider the enormous
energy daily ebbing and flowing round our shores, it does seem to
be a matter of great regret that this energy should be wasted and that
coal should be burnt as a substitute.
The last mode in which power may be obtained from water, to which
I have to allude, is that of the employment of the waves.
Earl Dundonald, better known as Lord Cochrane, proposed by his
patent of 1 833, to utilize this power for propelling a vessel. This he hoped
to accomplish by means of cylinders containing mercury, the oscilla-
tions of which were to cause a vacuous condition in the cylinders, and
thereby give motion to an air-pressure engine ; and lately we have had
produced before the Institution of Naval Architects, and also before
the British Association at Bristol, the apparatus of Mr. Tower, by which
the motion of the waves is to be utilized. A model constructed on this
principle has driven, it is said, a boat against the wind at some two or
three miles an hour.
36o SECTION— MECHANICS.
The next kind of prime-movers in order of date to be considered are
those that are driven by the wind.
Although, undoubtedly, the propelling of a ship by sails, and even
the winnowing of grain, must have long preceded the invention of a
prime-mover driven by water, yet the employment of the wind as a
source of motive power for driving machinery appears to be but of
comparatively recent date. It is said that the knowledge of this kind
of prime-mover was communicated to Europe by the Crusaders on their
return from the East, but it is difficult to see what foundation there is
for this statement. It appears to be certain, however, that wind motors
were commonly employed in France, Germany, and Holland in the
thirteenth century.
We can easily understand that in countries where waterfalls and
rapid streams are abundant, the windmill would not (owing to its un-
certainty) be resorted to ; on the other hand, in arid countries, or even
in countries like Holland, where the streams are sluggish and where
there is a large amount of land to be drained, the wind, although
still uncertain, would nevertheless be a valuable power, and therefore
would be utilized.
Prime-movers to be worked by the wind appear to have been made
practically in only two forms — viz., the common one wherein a nearly
horizontal axle carries four or more twisted radial sails, and that one
wherein the axle is vertical and the arms project from it laterally,
either as radial fixed arms, as curved fixed arms, or as arms having a
feathering motion similar to that of paddle wheels. Where the arms
are straight and fixed, some contrivance must be resorted to, to obtain
a greater pressure of wind on one side than on the other.
Bessoni in his work, " The Theatre of Instruments and Machines,"
published at Lyons in 1582, describes a windmill with vertical spindle
and curved horizontal arms placed in a tower with a wind-guard, and
by the drawing shows it working a chain pump. Belidor also says, in
article 852, that windmills with vertical axles were well known in
Portugal and in Poland, and he describes how " that they work within
a tower," the upper part of which was fitted with a moveable portion to
act as a screen to one side of the mill.
I will not detain you by an allusion to the ancient sailing chariot
mentioned by Uncle Toby in "Tristram Shandy/' nor will I pause
PRIME-MO VERS. 361
to describe one of which, about thirty years since, was employed upon
Herne Bay Pier ; in fact, this exhibition in the midst of which we are
assembled, gives but little encouragement to pursue the subject of
prime-movers worked by wind, as I have not as yet come across in
the catalogue a reference to any apparatus illustrative of this branch
of mechanics.
It is to be regretted that the use of this kind of prime-mover, the
Windmill, is on the decline. It is a power that costs nothing ; the
machinery can be erected in almost any situation, and although such
power cannot be depended on, being of necessity as uncertain as the
wind, it nevertheless might be commonly employed as an auxiliary to
steam, diminishing the load upon the engine in exact proportion as the
windmill was urged by any wind which might happen to blow.
I may say to the credit of our American brethren that they
employ on their sailing ships a windmill, known by seamen as " The
Sailors' Friend," to pump, to work windlasses, and to do all those
matters which in a steamship fall to the lot of the donkey-engine and
steam winch, unless, as in a recent voyage in which all Englishmen
have been so much interested, these duties are imposed upon a baby
elephant.
There is one motor which may be put either into this class or into
the next where we consider the application of heat. I allude to the
smoke-jack ; but beyond recognising its existence as a prime-mover,
and a very early one indeed (it is to be found in Zonca's work pub-
lished in 1621), attention need not be bestowed upon it.
We now come to consider those prime-movers which are worked by
heat, and wre will commence with those which are worked by its
immediate and not by its secondary action.
The direct rays of the sun have for a very long time past been
suggested as a means of obtaining motive power. Salomon de Caus,
in his work published in 1615, describes a fountain which is caused
to operate by the heat of the sun's rays expanding the air in a box and
expelling thereby through a delivery valve the water from the lower
part of the box. When the sun's rays ceased to impinge upon the box
the air cooling, contracted a suction valve opened and admitted more
water into the box, to be again displaced on the following day. De
Caus also gives a drawing of an apparatus where the effect of the
362 SECTION— MECHANICS.
sun's rays is to be intensified by a number of lenses in a frame. He
proposes these apparatus as mere toys to work ornamental fountains,
but Belidor, by article 827, describes and shows a sun pump consisting
of a large metallic sphere fitted with a suction pipe and valve and a
delivery pipe and valve and occupied partly by water and partly by
air, the suggestion being, as in the case of Salomon de Caus, that the
heat of the sun in the day time expanding the air should drive up
the water into a reservoir, while the contraction of the air in the night
time should elevate the water by the suction pipe and thus re-charge the
sphere for the next day's work. In modern times, as we know, some
attempts to obtain practical motive power from the direct action of
the sun have been made, and notably by Mr. Ericsson.*
The temptation to endeavour to bring into ordinary and commercial
use a machine of this character is very great. We were told by our
President in a lecture delivered by him to the British Association at
Bradford, that the solar heat if fully exercised all over the globe, and
supposing that globe to be entirely covered with water, would be
sufficient to evaporate per annum a layer fourteen feet deep. Now
assuming ten pounds of water evaporated from the temperature of
the air into steam by the combustion of one pound of coal (a much
larger result than unhappily we get in regular work), this would
represent an effect obtained from the sun's rays on each acre of water
equal to the combustion of 1680 tons of coals per annum, or about ninety-
two hundredweight of coal per acre per twenty-four hours, that is to
say, enough to maintain an engine of two hundred gross indicated
horse-power day and night all the year round. When, however, we
consider the effect of the sun, not upon the surface of water but upon
the earth, and deal with its power of producing heat-giving material,
that power compares very unfavourably with the results above stated,
and this no doubt arises, first, from the fact that the sun is
* In the number of the " Revue Industrielle," of the 24th November last, page 455, are an
engraving and a description of the solar boiler of M. Mouchot, Professor at Tours. The
apparatus employed by M. Mouchot consisted of a framework shaped like the frustrum of a
cone, and mounted so that the axis could always be moved to point to the sun. The interior
of the framework was lined with mirrors, the diameter of the large mouth of 'the cone was
2 '6 metres, and of the base i metre, giving an effective area of sun's rays intercepted of
45 feet. The mirrors were placed at an angle of 45°, and reflected the rays of the sun upon a
blackened copper boiler, placed within a glass envelope in the axis of the cone. It is stated
that on a very hot day as much as n Ibs. of water were evaporated per hour by this apparatus.
PRIME-MOVERS. 363
frequently obscured, and secondly, from the fact that a large portion
of the energy of the sun is spent in evaporating moisture from the
ground and not in the direct production of combustible material. I
have found it extremely difficult to obtain any trustworthy data as to
the weight of fuel grown per acre per annum. If we take the sugar
cane we find that in extremely favourable cases as much megass and
sugar are produced per acre as together would equal in calorific effect
about five tons of good Welsh coal. Coming to our own country and
dealing with a field of wheat, the wheat and straw together may be
taken as being equal probably to about two tons of coal as a
maximum. The statements made to me with regard to the production
of timber per acre per annum, when grown for the purpose of burning,
are very various, but the best average I can make from them is that in
this country there is produced as much wood as is equal in calorific
effect to about one and a half tons of good coal per acre. Com-
paring these productions of heat-giving material with the energy of the
sun, as shown in the evaporation of water, one sees how tempting a
field is that of the direct employment of the solar rays as a source
of power, more especially when it is remembered that those rays are
obtained from week to week and year to year without having to wait
the tardy growth of the fuel-destined tree.
I will now ask you to consider with me the prime-movers that owe
their energy to the heat developed by the combustion of some ordinary
kind of fuel, coal or wood. Passing by as a mere toy and as being
not an actual prime-mover, the reactionary steam sphere, the seolipile
of Hiero, I will come at once to those simple forms of heat engine,
intended, whether worked by steam or by the expansion of air, for the
raising of water. Salomon de Caus, in his work of 1615, already
mentioned, says that if a globe be filled with water and have in its
upper part a pipe dipping nearly to the bottom, and if the globe be
put upon the fire the heat will cause the expansion of the contents,
and the water will be delivered in a jet out of the tube.
The Marquis of Worcester in his " Century of Inventions," pub-
lished in 1659, makes, as is well known, a similar proposition, but it
does not appear that these machines were seriously contemplated for
practical use. Papin (I take Belidor's article, No. 1276, as my
authority), in 1698 (as appears in his pamphlet of 1707), experimented
364 SECTION— MECHANICS.
by order of Charles the Landgrave, of Hesse-Cassel, with the view o
ascertaining how to raise water by the aid of fire. But his experi-
ments were interrupted, and he did not resume them until Leibnitz,
by a letter of 6th January, 1705, called his attention to what Savery
was doing in England, sending him a copy of a London print of a
description of Savery's engine. This engine, which of course is well
known to you, is illustrated by a model in this collection and now on
the table before me. Savery employed a boiler, the steam from which
was admitted into a vessel furnished like the sun pump of Belidor
with a suction pipe and clack, and a delivery pipe and clack. The
steam being shut off, cold water was suffered to flow over the vessel, a
partial vacuum was made, water was driven up into the vessel, and
was expelled through the delivery pipe upon the next admission of
steam, the cocks being worked by hand. This machine came into
very considerable use, and was undoubtedly the first practical working
steam-engine. It had, however, the defect of consuming a large
quantity of steam, as the steam not only came into contact with the
cold vessel, but also with the surface of the water in that vessel.
Papin, as we know, obviated a portion of this loss by the employment
of a floating piston placed so as to keep the steam from actual contact
with the surface of the water. I have put a rough diagram of Papin's
water raiser on the wall.
We have in the collection, No. 2007, a cylinder from Hesse-Cassel,
said to be of the date of 1699, and to have been intended for employ-
ment in Papin's machine ; but it is difficult to say for what part of the
apparatus it could have been designed, inasmuch as the cylinder is
provided with a flange at one end only, and no means, so far as I can
ascertain, exist for closing the other end. You will see from the diagram
(as no doubt is already well known to you), that Papin did not pro-
pose to condense the steam and by its condensation to " draw up"
the water (to use a familiar expression), but intended that the vessel
should be charged by a supply from above, and that the steam should
be employed only to press on the floating piston and to drive the
water out. Papin, however, hoped to use his engine not merely as a
water raiser, but as a source of rotary power by allowing the water to
issue under pressure from the air vessel, and so as to impinge upon
the pallets of a water-wheel and thus produce the required revolution.
eii
Made
Original model of Newcomen's Steam Engine.
about 1705. Now in the bins cum of King's College, London.
366 SECTION— MECHANICS.
We now come to Newcomen, who, I think, may fairly be looked upon
as the father of the steam-engine in its present form. No. 1942 is a
model of his engine, which is further illustrated by a rare engraving of
1712, the property of Mr. Bennet Woodcroft.
Here we have the steam boiler, the cylinder, the piston and rod, the
beam working the pumps in the pit, the injection into the cylinder, and
the self-acting gear making altogether a powerful and an automatic
prime-mover.
That conscientious writer, Belidor, to whom I have already frequently
referred, says that he hears of one of these machines having been set
up in the water-works on the banks of the Thames at York Buildings.
(I may say to those who are not aware of it, that those works
were situated where the Charing Cross Station now stands). He is
much interested in the accounts he receives, and on a Newcomen
engine being erected in France at a colliery at Fresnes near
Conde, Belidor paid several visits to it in order that he might under-
stand its construction thoroughly and be thereby enabled to explain
it to his readers. He has done so with a minuteness and faithfulness
of detail in description and in drawings that would enable any mechanic
to reproduce the very machine. This engine had a thirty-inch cylinder
with a six-foot stroke of the piston and of the pumps ; the boiler was nine
feet in diameter and three and a half feet deep in the body ; it had a
dome which was covered with masonry two feet six inches thick to
hold it down against the pressure of the steam. It had a safety valve
(the Papin valve) which Belidor calls a "ventouse," and says that its
object was to give air to the boiler when the vapour was too strong.
It had double vertical gauge cocks, the function of which Belidor
explains ; it made fifteen strokes in a minute, and he says that, being
once started, it required no attention beyond keeping up the fire, and
that it worked continuously for forty-eight hours, and in the forty-eight
hours unwatered the mine for the week ; whereas, previous to the
erection of the engine, the mine was drained by a horse-power
machine working day and night throughout the whole week, and
demanding the labour of fifty horses and the attendance of twenty men.
I should have said that the pumps worked by the steam-engine were
seven inches bore, and were placed twenty-four feet apart vertically in
363 SECTION— MECHANICS.
the pit, which was 276 feet deep, and that each pump delivered into a
leaden cistern from which the pump above it drew.
After having given a most accurate description of the engine,
Belidor breaks out into a rhapsody and says (I will give you a free
translation) : " It must be acknowledged that here we have the most
marvellous of all machines, and that there is none other of which the
mechanism has so close a relation to that of animals. Heat is the
principle of its movements ; in its various tubes a circulation like that
of the blood in the veins is set up ; there are valves which open and
shut ; it feeds itself and it performs all other functions which are neces-
sary to enable it to exist."
Smeaton employed himself in perfecting and in properly proportioning
the Newcomen engine, but it was not until James Watt that the next
great step was made. That step was, as we all know, the doing away
with condensation in the cylinder, the effecting it in a separate vessel,
and the exclusion of the atmosphere from the cylinder. These altera-
tions made a most important improvement in the efficiency of the
engine in relation to the fuel consumed ; but they were so simple that
I doubt not if examiners into the merits of patents had existed in those
days, Mr. Watt would have had his application rejected as being
" frivolous." We have here from case No. 1928, a model made by
Watt, which appears to be that of the separate condenser and air
pump. We have also 8£, which is a wooden model made by Watt ot
a single acting inverted engine having the top side of the cylinder
always open to the condenser, and a pair of valves by which the
bottom side of the piston can be put into alternate connexion with the
boiler and with the condenser, the contents of which are withdrawn
by the air pump, 3/5. From the same case is a model of a direct acting
inverted pumping engine made in accordance with the diagram ; 8£,
ib, is a model of Watt's single acting beam pumping engine, while ib
is a model of Watt's double acting beam rotary engine. lob, from the
same case, is Watt's model of a surface condenser. To Watt we owe
condensation in a separate vessel, exclusion of the air from the
cylinder, making the engine double acting, employment of the steam
jacket, employment of the steam expansively; the parallel motion,
the governor, and, in fact, all which made Newcomen's single acting
reciprocating pumping engine into that machine of universal utility that
& •£
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370 SECTION— MECHANICS.
the steam-engine now is, and not only so, but Watt invented the steam-
engine indicator, which enables us to ascertain that which is taking
place within the cylinder, and to detect whether or not the steam is being
economically employed. I have on the table before me a very excel-
lent model illustrating an inverted direct acting pumping engine in its
complete form, and I have also a model, of French manufacture, the
cylinder and other working parts of which are in glass, which shows a
form of beam condensing engine at one time common. I do not say,
however, that Watt was the first to make the suggestion of attaining
rotary motion from the power of steam. Leaving out of consideration
Hiero's toy, Papin, as I have remarked, hoped to get rotary movement
second hand by working a water-wheel with the water that had been
raised by his steam engine ; moreover, as early as 1737, Jonathan
Hulls proposed to obtain rotary motion from a Newcomen engine,
and to employ that motion in turning a paddle wheel to propel a tug
boat which should tow ships out of harbour, in a calm, or even against
an adverse wind. I have here one of the prints of his pamphlet, and
in order that you may better appreciate Hull's invention I have put
an enlarged diagram upon the wall, and I think I may take this as the
starting point for saying a few words about the steam-engine as a
prime-mover in steam vessels.
We have in the collection, No. 2150, Symington's engine tried
upon the lake at Dalswinton in 1788. Here a pair of single
acting vertical cylinders give by the up and down motion of their
pistons reciprocating movement to an overhead wheel ; this wheel
gives similar motion to an endless chain, which chain is led away
so as to pass round two pairs of ratchet wheels loose upon two
paddle shafts. By the use of a pair of ratchets the reciprocations
of the chain are converted into rotary motion in one direction only,
and that the driving direction, of the two paddle-wheels, placed one
behind the other. Symington's arrangement for obtaining the rotary
motion .always in one direction of his two paddle-wheels is very-
similar to that proposed by Jonathan Hulls for his single stern-wheel.
Want of time forbids me to do more than to just allude to the names
of Hornblower and Wolff in connexion with double cylinder engines —
engines wherein the expansion of steam is commenced in one cylinder
and continued in another and a larger one.
PRIME-MOVERS. 371
I wish to say a few words which will bring before you the changes
that have been made within a very few years in the construction of
steam-engines : when I was an apprentice the ordinary working
pressure of steam, except in the double cylinder engine, was only 3 Ibs.
above atmosphere, and in those days there was in a marine boiler
more pressure on its bottom when the steam was down due to the
mere head of water in the boiler than there was pressure on the
top when the steam was up due to the force of the steam, whereas
now condensing marine engines work commonly at 70 Ibs. ; and there
is a boat under trial where the steam is, I believe, as high as 400 Ibs.
To those who are curious on the subject I would recommend a
perusal of two Blue Books, one being the evidence taken before a
Parliamentary Commission in 1817, and the other before a Parlia-
mentary Committee in 1839, they will find there the weight of
evidence to be that the only use of high pressure steam is to dis-
pense with condensing water, and that as a steamboat must always
have plenty of condensing water in its neighbourhood, no engineer,
knowing his business, would suggest high pressure for a marine engine.
I have before me a model of a pair of engines which, although
they weie made not so very long ago (for I saw them put into
the ship), have nevertheless an historical interest. This model shows
Maudslay's engines of the Great Western, the first steamer built
for the purpose of crossing the Atlantic ; I think I am right in
saying that 7 Ibs. steam was the pressure employed in that vessel, and
that, in order to extract the brine from the boiler, it was necessary to
use pumps, as the pressure of the steam was not sufficient to expel
the brine and to deliver it against the pressure of the sea.
Time does not permit of nry touching upon the various improve-
ments in boilers, condensers, expansive arrangements, and other
matters which have gradually been introduced into our best engines
for land and for ocean purposes. I have hung upon the wall a
rough diagram, showing a pair of oscillating engines as applied to
driving a paddle steamer, and another showing a pair of inverted
compound cylinder engines to drive a screw propeller, a model of
such a pair of engines, with surface condensers and all modern
appliances, (being Messrs. Rennie's engines of the P. and O. Com-
372 SECTION— MECHANICS.
pany's S.S. Pera, by which I have had the pleasure of travelling), is
now before me.
I will conclude this part of the subject by saying, that to the com-
bination of science and sound practice is due the fact of the con-
sumption of coal having within the last ten years been reduced in the
marine engine from 5 Ibs. per gross indicated horse-power per hour
to an average of 2% Ibs., and in exceptional instances to as small a
quantity as i^lbs. per horse per hour.
Let us now devote a little of the time that is left to the considera-
tion of the locomotive on the common road as well as on the railway.
I have before me, No. 2145, a model of the actual Cugnot engine in
the Conservatoire des Arts et Metiers, which, in 1769, journeyed,
slowly it is true, but did journey, and did carry passengers along the
roads in Paris.
It is a most ingenious machine ; it has three wheels, and the motive
power is applied to the front — the castor or steering wheel — so that
engine and boiler turn with the wheel, precisely as within the last few
years Mr. Perkins has caused the engine and boiler to turn with the
steering wheel of his three-wheeled common road locomotive. The
steam makes the pistons in a pair of inverted single acting cylinders to
reciprocate, and their rods, by means of ratchet wheels, give rotary
motion to the castor wheel, and thus propel the carriage. I think
there is no doubt but what we must look upon this engine of Cugnot
as the father of steam locomotion in the same way as we must regard
Symington's engine as the parent of marine propulsion. I have before
me, No. 1926, Trevethick's engine of 1802. I have also before me a
Blenkinsop rail, one that has been in actual use for many years,
provided, as you will see, with teeth, into which a cogged flange
on the side of the driving wheel, geared, to insure that adequate
traction should be obtained. This plan has been revived within the
last few years, to enable the steam locomotive to climb the Righi. A
sketch of the Righi engine and rail is on the wall. It will be seen
that in the Righi instance the teeth, instead of projecting, as in the
Blenkinsop plan from the side of the rail, are ranged between two-
parallel bars, like the rungs of a ladder.
On the ground floor of the Exhibition we have the veritable
374 SEC2 ION— MECHANICS.
" Puffing Billy," an engine which began work in 1813, and got along
without the aid of cogs by mere adhesion upon plain rails ; it is a
rude-looking machine, but it laboured up till the date of the last Exhi-
bition (1862), doing its work for forty-nine years on the railway belonging
to the Wylams Colliery, and as tradition says, interesting George
Stephenson, who as a boy saw it in daily operation.
On the ground floor also we have, 1954, the " Rocket," with which
seventeen years after the starting of" Puffing Billy," George Stephenson
carried off the prize in the Manchester and Liverpool Railway compe-
tition. The leading particulars of this engine are as follows : A pair
of 7^ inch cylinders, i' 5" stroke, placed at an inclination, driving
4' 6" wheels, the boiler multi-tubular, having twenty-four three and a
half inch tubes, while the fire is urged by the waste blast. Before
alluding to this I ought to have mentioned that in one of the Blue Books
to which I have called your attention, that which gives the evidence
before the Commission in the year 1817, there is a statement by a witness
that in "those parts there are machines called locomotives," £c. &c.
Once more I am compelled to say that time will not admit of my
entering into any detail in respect of the modern locomotive, except to
remark that by the aid of excellent boilers, of high pressure (steam
140 Ibs. to the inch), of considerable, although rather imperfect ex-
pansion, effected by the link motion, there is provided for the use of
our railways a machine which in the " Passenger" form is competent to
travel with ease and safety sixty miles an hour ; and in the " Goods" form
is competent to draw a load of 800 to 1000 tons, and to attain these
results with a very commendable economy in fuel. I have put on the
wall two diagrams of Locomotives of the convenient form for local
traffic that we call Tank engines ; and I have before me No. 1957^, a
most beautifully made sectional working model of a Russian six-wheeled
" Goods" engine.
Within the last twenty years another description of steam-engine
has acquired a prominent and important place among our Prime-
movers ; I allude to the Portable engine, or to the Portable engine in
its more complete form of a self-propelling or Traction engine. The
general construction of these machines borders closely upon that of
the locomotive. Very great attention has been paid to all their details,
and the Royal Agricultural Society of England, by their excellent
The Locomotive Engine " Rocket."
Constructed by Messrs. Stephenson & Co. in 1829.
Now in the Patent Office Museum.
3/6 SECTION— MECHANICS.
arrangements for periodical trials, have stimulated engineers to devote
their best energies to the subject. No. 1942 is a model of one of
Aveling and Porter's common road traction engines, capable also of
acting as a source of power for driving farmyard machinery, or for
effecting steam ploughing. Upon the wall I have placed rough dia-
grams of another kind of traction engine — a kind wherein india-
rubber tires are used. This is manufactured by Messrs. Ransome,
Sims, and Head ; and I have also placed diagrams of the ordinary
Portable engine and of another most useful kind of Portable engine —
the Steam Fire engine. I have there likewise a sketch of Hancock's
common road steam coach, which some thirty years ago regularly plied
for hire from the Bank to Paddington in opposition to the ordinary
horse omnibus. Hancock's carriage was a vehicle which in my
judgment has never since been surpassed, and I ajn sorry to say
never to my knowledge equalled, as regards the various points which
should be attended to in making a steam carriage to circulate safely
among horse traffic.
There is another way in which steam may be employed as a
prime-mover. We saw that water in the form of the trombe-d'eau
could induce a current in air, and thereby blow a forge fire, and that
a rapid stream could be caused to induce a current in other water,
and thus drain marshy lands. Similarly steam can be caused to
induce a current in water, and thereby impel the water so as to raise it
to a height, or to force it as feed water into a boiler against a heavy
pressure. When used for a mere pumping apparatus such a mode of em-
ploying steam is very wasteful, because the steam is condensed in large
quantities by the water, and the water is needlessly heated at the
expense of the steam ; but when used in feeding a boiler the whole of
the heat is taken into that boiler, and thus this objection does not
apply. By means of that most elegant and scientific apparatus, the
Giffard injector, it is possible by a jet of steam to induce a current in
surrounding water powerful enough to take the water and the con-
densed steam into the boiler from which the steam had previously
issued. No. 1976, which I have before me, is a sectional model of a
Giffard injector.
I believe it was I who first gave a popular explanation of the
principle of action of the Giffard injector; and although a Scien-
PRIME-MO VERS. 377
tific Congress is probably not the place for a popular explanation, I
will venture to repeat it. The principle may be summed up in one
word, " concentration." The steam that issues from an orifice of an
area of I, when condensed, has a sectional area (according to the ori-
ginal pressure of the steam) of only ^th, or ^oth> or K^Q^) as the
case may be. Thus the velocity remaining the same, and the weight
the same, the energy of the steam issuing from an area of I is concen-
trated 200, 400, or 800 times upon the area, due to the smaller trans-
verse section of the liquid stream.
This concentration of energy is far more than sufficient to enable
the fluid stream to re-enter the boiler from which the vaporous stream
started ; and so much more than sufficient, that it may be diluted by
taking with it a certain quantity of water which was employed in the
condensation of the steam, and is required for the feeding of the
boiler.
With a view to obtaining economy in fuel many attempts have been
made to employ some other agent than steam as the means of de-
veloping the power latent in fuel, but it is imperative that I should
dismiss these with a mere enumeration. A very interesting engine of
this kind (because, excluding Hiero's toy and smoke jacks, it is, so
far as I know, the first proposition for obtaining rotary motion by
the aid of heat), was the fire wheel of M. Amonton, of which an
account is to be found in the first volume of the French Academy of
Sciences, date 1699. On referring to that volume I do not see
it is stated in terms the machine was ever put to work, although
it is said that M. Amonton made many experiments to convince
the Academy of the practicability of his invention. M. Amonton
proposed to have a metallic wheel revolving on a horizontal axis ;
the outer rim of the wheel was to be divided into a number of
separate air cells, each of which had a channel so as to communi-
cate with other cells, arranged round the wheel nearer to the centre
than the air cells ; the air cells as they passed over a fire were to be
heated, and the air was to drive the water up to one side of the wheel,
so as to keep that side always loaded, and thus give the wheel a ten-
dency to revolve. The cells, after leaving the neighbourhood of the
fire, were to be cooled by passing through water, to re-contract the air
ready for the next operation.
378 SECTION—MECHANICS.
No. 1940, which is before me, is a model of Stirling's hot-air engine,
but time does not remain to describe it.
Besides hot-air engines, we have had engines working by the explo-
sion of gunpowder, and others working by the explosion of gases. No.
1945 is Langen and Crossley's gas engine, from which, I believe, ex-
tremely excellent results have been obtained.
I will now ask you to look at a tabular statement which shows the con-
sumption of fuel in agricultural engines when under trial, expressed in
pounds per horse-power per hour, and also in millions of pounds raised
one foot high by the consumption of one hundredweight of coal. I told
you how excellent were the results at which our agricultural engineers
had arrived. You will see that one of those machines working with 80 Ibs.
steam, and of course without condensation, has developed not a gross
indicated horse-power, but an actual dynamometrical horse-power for
279 Ibs. of coal per horse per hour, giving a duty of as much as
seventy-nine millions. This high result was obtained by the excellence
of the boiler and of the combustion, as well as by that of the engine.
If you look at the column of evaporation you will find that as much
as 1 1 '83 Ibs. of water were converted from the temperature of the
boiling-point into steam by the combustion of I Ib. of coal. This was
due not to the excellence of the boiler alone, but to the extraordinary
ability of the stoker, and to the care and labour bestowed — a care and
labour far too expensive to be employed in practice. But should not
we engineers endeavour to ascertain whether we cannot by mechanical
means practically, with certainty and cheapness, procure an accuracy
of combustion as great or even greater than that which can be got by
the almost superhuman attention of a highly-trained man, who at the
end of four hours of such work is utterly exhausted ? Many forms of
fire-feeders have been attempted and used with more or less success ;
but I cannot help thinking that in order to obtain the accurate pro-
portioning of air and fuel by which alone can we get efficient and
economical combustion, we shall have to turn our attention in the
direction of dealing with the fuel in a comminuted state, either by
converting it into gas, as is done by our President, Dr. Siemens, by
availing ourselves of liquid fuel, or by employing the process of Mr.
Crampton, the making of the fuel into an impalpable powder, which
can be driven into the furnace by the air which is to consume it there.
PRIME-MO VERS. 379
By these and by other means \ve may hope to improve combustion ;
by strict attention to the proportioning of the parts of the boiler we
may hope to make the best use of this improved combustion; by
higher initial pressure, by greater expansion, and by the general
employment of condensation wherever practicable (and by the use of
the evaporative condenser there are very few cases in which it is
not practicable), we may trust that the steam-engine, even on its
present principle, may be rendered more economical than it has ever
yet been ; and may give us more than that one-eighth or one-ninth of
the total energy residing in the fuel which now alone we get under the
very best and most exceptional conditions. A large loss, however,
must with steam-engines as we now know them always be incurred.
We cannot hope to deal with initial pressures and temperatures corre-
sponding with steam of a density equal to that of water ; nor to carry
expansion down to the point where ice would be formed in the con-
denser. But wonderful as the steam-engine is, worthy as it was and
is of Belidor's eulogium (which I read to you), we know it is not the
only heat motor ; and we are aware that there are other f6rms of such
motors which theoretically at all events promise higher results.
By improvements in the existing steam-engine, by the invention
and development of other heat motors, by the employment of the
power of water and of wind, either as principal motors or as auxilia-
ries, we may hope for further progress in the machines the subject of
my address, " Prime-Movers."
I have brought before you, of necessity hastily, and therefore (and
also on account of my own incapacity for the task) imperfectly, the
leading improvements which have been made in Prime-Movers, from
the date of the water-wheels of Vitruvius to the best devised steam-
engines of our own day. These improvements have been effected by
men like Papin, Savery, Newcomen, Watt, Symington, Fulton,
Stephenson, and others, who were not mere makers of engines, but
were men full of an ardent love of their noble profession, who followed
it because of the irresistible attraction it had for them ; followed it
from their boyhood to their grave, and in that very following found
their great reward.
These men undoubtedly possessed that combination of science and
practice, which combination Dr. Tyndall has told us is necessary if
38o SECTION— MECHANICS.
cither science or practice is to continue to live, for to use his expres-
sive language, without this combination both die of atrophy — the
one becomes a ghost, the other a corpse.
We have every reason to believe that this combination will
become more intimate, not only in the engineers of the present day,
but in those of the next and of succeeding generations ; and to men
thus endowed with science and practice we may trustfully leave the
continued improvement of Prime-Movers, and may rest assured that
as a more general application of these machines must of necessity
follow such improvements, the day will soon dawn when in no civilized
country will there continue to be, from the hope of gain, the tempta-
tion to employ intelligent humanity in the brutal labour of the turnspit
or of the criminal on the treadwheel.
The PRESIDENT : Ladies and Gentlemen, — In coming here on this
wet morning to listen to Mr. B ram well on Prime-Movers we all expected
to hear something worth listening to, but I think our expectations have
been surpassed by the discourse to which we have actually listened.
Mr. Bramwell, after dealing with the theoretical principles upon which
prime motion must depend, has brought before us in review all those
early attempts by which the labour of man has been gradually sup-
planted by machine labour, and he has been aided in a way he could
not have been aided in any other place by the models which he has
had at his disposal. These models show us not only the principles
upon which those early pioneers acted, but they bring home to our
minds the difficulties — the mechanical difficulties — with which theymust
have had to contend. Altogether I look upon the communication to
which we have listened as a standard treatise on this subject : and I
hope that the department will do it ample justice in publishing it in the
Proceedings with such illustrations as will make it valuable. I call
upon you to accord your thanks to Mr. Bramwell for his com-
munication.
Mr. BRAMWELL : Ladies and Gentlemen, — I have to thank you most
sincerely for having responded in the way that you have to the kind
expressions of our President, Dr. Siemens. I regret the great length
to which my Address has extended, but I could not deal with it more
concisely ; in fact, I had not time to write a short one.
The PRESIDENT : The time is rather short before we adjourn, and
ON FURNACES. 381
I propose that Mr. Hackney should deliver his discourse on furnaces,
as far as he can before we adjourn, and that we should after the
adjournment view those models which there is not time at present to
display.
ON FURNACES.
Mr. HACKNEY : Furnaces, as used in the arts, may be defined as
the arrangements under which fuel is burned to produce heat, for the
purpose either of inducing permanent changes in the substances
heated, or of preparing them, by softening or fusion, for subsequent
treatment.
This excludes two of the applications of fuel which together take up
the larger proportion of that consumed. The domestic use — namely,
for cooking, and for warming, lighting, and ventilating inhabited
places ; and that for the generation of motive power.
Even thus limited, the amount of fuel burned in furnaces is very
great, and the possibility of effecting further economies in its use
is a problem of vast importance. The quantity of coal burned, in this
kingdom alone, for smelting ores and for refining and manufacturing
metals, was, according to the statistics published by the Mining
Record Office, 35,802,000 tons in 1873, and 34,400,000 tons in 1874.
Of these amounts the manufacture and working of iron, in its different
forms, took nearly the whole : — 35,039,000 tons in 1873, and 33,562,000
tons in 1874 ; or more than 100,000 tons on every working day.*
The subject of the construction and mode of working of the several
forms of furnaces in use is one of great extent, and can only be dealt
with briefly in such a paper as the present. They may be divided into
those in which solid fuel is intermixed with or directly surrounds the
matters to be heated, and those in which the heating is done, in one
way or another, by flame, without direct contact between the solid fuel
and the work.
The characters of the fuel best fitted for these two kinds of furnace
are essentially different. Where the matters to be acted on, or the
vessels that contain them, are in direct contact with the fuel, as in a
* Mineral Statistics, 1874, p. xiv.
332 SECTION— MECHANICS.
smithy fire, a cupola, or an ordinary coke furnace for melting- steel
or brass in crucibles, an intense local heat is required in the mass of
the fuel itself, and any heat developed above its surface is useless.
In flame furnaces, on the other hand, such as those for glass melting,
or for puddling or heating iron, in which the materials to be heated
are not embedded in the fuel, but placed in a chamber above or at
the side of it, the heat made use of is that of the flame ; the heat
that is carried into the working chamber by the current of gases
rising from the fire, together with that due to the further combustion
of these gases, on admixture with an additional amount of air.
Thus, for furnaces of the first class, the most suitable fuel is one,
such as charcoal, coke, or anthracite, consisting of nearly pure carbon,
free from volatile matter, as this is useless in them as a source of
heat, and the driving of it off renders latent a certain amount of that
generated by the combustion of the carbon, and so lowers the tem-
perature £>f the fire.
In flame furnaces, a lowering of the temperature at the fire-
grate, where the air and the solid fuel meet, is immaterial, or may
be even advantageous, as tending to diminish loss by radiation and to
preserve the furnace from injury by excessive heat. The only use of
the heat at the grate is to generate a full supply of combustible or
partly burned gases, at a high temperature, which in completing their
combustion, as they pass over the working bed, shall heat as strongly
as possible the matters placed there. The fuel preferred for use in such
furnaces, is thus either a combustible gas, or a solid fuel containing
hydrogen as well as carbon, such as coal or dried wood, that will pro-
duce on burning a long and powerful flame. A flame, it is true, may
also be obtained from fuels that contain little else than carbon and
mineral matter, by burning them in a thick bed, so that the greater
part or nearly the whole of the CO2 formed in the first instance by
the combustion of the carbon, is transformed into CO as it passes up
through the mass ; and by introducing with the air as large a pro-
portion of steam as can be used without lowering too much the tem-
perature of the fire. The steam is decomposed by the hot carbon,
producing, according to the temperature and thickness of the fire, a
mixture of either H and CO2 or H and CO. The gases thus gene-
ON FUR A7 ACES. 383
rated, together with the mixture of CO and N, produced by the passage
of the air itself through the mass of fuel, flow forward into the
working chamber, and there burn, on mixing with a further supply of
air, introduced above the fire.
Examples of the simplest form of the class of furnace in which solid
fuel is mixed directly with the matters to be heated are the heaps in
which brick clay is buined to make ballast, and in which iron and
other ores are often calcined. In these, the ore or dried clay, in pieces
of convenient size, is thrown into a heap, together with a little coal ;
and the mass, being lighted at one end, burns through to the other.
In calcining in such heaps, there is a considerable waste of heat, as
a great proportion of the burned gases from the fire pass off at a high
temperature ; and when the calcination is completed, all the heat that
the red-hot mass contains is lost.
In an ordinary limekiln, and in kilns for calcining iron ore, such as
are used in Wales and Cleveland, a much larger proportion of the
heat produced by the combustion of the fuel is utilized, and the amount
of this required is proportionately reduced. The process in such a kiln
is carried on continuously ; the coal and raw stone being filled in,
together, at the top, and the calcined material drawn at intervals
from the bottom. By this mode of working, the air that maintains
the combustion of the fuel is drawn up through the material already
burned; cooling this down from a red heat to a temperature not
much above that of the atmosphere, and being itself considerably
heated : while the burned gases and excess of air, passing
away, rise through the mass of cold freshly charged material, and
leave in it the greater part of their available heat, escaping nearly
cool.
In such a kiln, according to Gjers, calcining 800 tons of Cleveland
iron ore per week, the consumption of small coal is about one ton to
twenty-four or twenty-five tons of ore.* In kilns of somewhat smaller
size, both in Wales and in Cleveland, in which the regenerative action
is less complete, and in which the loss of heat also, by radiation and
conduction, is greater, the consumption is stated by Phillips to be one
* Journal of the Iron and Steel Institute, i8ji, p. 213.
384 SECTION— MECHANICS.
ton of small coal to twenty tons of ore ; and in calcining in open heaps,
in South Wales and Staffordshire, it is given as one ton of small coal,
and five hundredweight of large, to ten tons of ore.*
A similar economy in fuel to that which characterizes such continu-
ous kilns is attained, even more perfectly, in calcining limestone
or other materials, and more especially in burning bricks, by the system
of annular kilns patented some years ago by F. Hoffmann of Berlin,
and now very generally used. In this form of kiln, which is continuous
in its working, the air to supply the fire is drawn through the bricks
already burned, cooling them down to the temperature of the air, and
carrying forward their heat to the part where it is required ; and the
burned gases, mixed with excess of air, pass, on their way to the
chimney, through the stacks of damp air-dried bricks, that have not
yet been fired ; and escape, finally, at a comparatively low temperature,
and saturated with moisture.
The kiln is built in the form of an arched passage, eight or nine feet
high, and of the same width. This tunnel or passage is bent on itself,
in the form of a ring of any convenient diameter, and provided with
twelve equidistant doorways for putting in and removing the bricks,
and twelve corresponding flues, leading to a central chimney, and each
provided with a damper. The entire kiln thus consists of twelve
or more chambers or compartments, arranged in a circle and com-
municating freely with each other; each compartment having an
independent entrance door and chimney flue.
The successive compartments being numbered one to twelve, the
working of the kiln is as follows : — Supposing No. 2 to be the com-
partment from which the burned bricks are being removed, and No. i
to be the adjoining compartment, last emptied, and now being filled
with new unburned bricks ; then No. 12, on the other side of No. I,
will be the compartment last filled with new bricks, which are now
being dried preparatory to burning. When the work is in this posi-
tion, the damper in the flue leading from compartment No. 12 to the
chimney, and tha entrance doorways of Nos. I and 2 are open, all the
other chimney flues and the other door openings being closed ; and
* Metallurgy, J. A. Phillips, pp. 181, 189.
ON FURNACES. 385
a large damper or partition is fixed between the compartments No. I
and No. 12. Thus the air entering through the open doorways of
No. i and No. 2 has to make the entire circuit of the kiln, before it
escapes, through the flue leading from No. 12, to the common chimney.
In the course of this circuit, it passes first among bricks almost cold,
and takes up their heat, and then goes forward to warmer bricks, and
then to hotter and hotter, carrying the heat of the cooling bricks for-
ward with it, until it reaches the part of the ring diametrically opposite
to the two open and cold compartments. At this place it gets a final
accession of heat, from the burning of a small quantity of coal dust,
which is dropped in among the bricks, from time to time, through
numerous small openings furnished with air-tight moveable lids.
Thus, at this part of the kiln, there is generated the full intensity of
heat which is required for burning the bricks. The products of com-
bustion then pass forward to the bricks not yet burned, which are thus
heated by their continuous current, and so from the hottest bricks to
those that are less and less hot, heating them as they go, and thence
to those that are still damp, drying them as they go ; and thence they
pass finally to the chimney, in a state almost cold, and loaded with
moisture from the damp bricks.
On the following day, the partition is removed from between the
compartments Nos. 12 and i, and placed between Nos. I and 2; the
compartment No. i having been by this time filled with fresh damp
bricks, and its doorway built up. The damper in the flue leading from
No. 1 2 compartment to the chimneyis shut, and that from No. i is opened.
No. 2 compartment being now empty is refilled with unburned bricks ;
and the removal of cold burned bricks from No. 3 is commenced.
The place where the small coal for fuel is thrown in is also advanced
round the circle by one compartment ; and the products of combustion,
at the end of their circuit in the annular chamber, and just before their
escape to the chimney, now pass among the fresh bricks that were
built in on the day before ; and so the process goes on, just as on
the previous day ; and the fire makes a complete circuit of the kiln
in twelve working days.
The saving in fuel effected by thus utilizing the heat of the burned
gases, and of the red-hot bricks, as well as the greater part of that
B B
386 SECTION— MECHANICS.
taken up by the walls of the kiln, is very great : amounting to from
two-thirds to three-fourths, in quantity, and frequently to much more
in value, as cheap dust coal does the work for which in the older
kilns a better coal is required.
The large amount of water to be evaporated from the unburned
bricks can only be carried off, without risk of condensing a portion on
the cold bricks next to the chimney, and so wetting and softening them
instead of drying them, by drawing through the kiln a very large
excess of air, even more than the rude mode of firing adopted renders
inevitable ; and as this makes it difficult to maintain a temperature so
high as is required for burning fire-bricks, particularly for Welsh
Dinas bricks, Mr. Ensor, a fire-brick maker near Burton, adds a by-
pass flue to kilns for work of this kind, by which part of the warm air,
from the bricks already burned, is led round to the unburned bricks
that are being dried, without passing through those compartments in
which the highest heat is required ; no more being passed through
these than is needed for the combustion of the fuel. In a Hoffmann
kiln, thus modified, sufficient heat may be maintained to burn Dinas
bricks very satisfactorily.
Since the continuous Hoffmann kiln has been in use, several forms
of what may be termed semi-continuous kilns have been brought
forward, in which, as in it, the heat of the burned gases, and of the hot
burned bricks, is more or less perfectly utilized. Tunnel-kilns have
also been put up, with the same object : in these the position of the fire
is fixed, and the bricks or other articles to be burned are drawn past
it, stacked on suitable trucks or waggons.
The small furnaces, fired with coke, that are commonly used for
melting steel or brass in crucibles, require no detailed notice. In
these, the crucible is imbedded in the fuel, and a rapid combustion
and high temperature are maintained round it, by closing the upper
part of the furnace and connecting it to a high chimney.
Where, as in the case of a smithy fire, the top of the furnace cannot
be conveniently closed in, or where a keener combustion is required
than can be obtained by chimney draught, the plan is adopted of
forcing air into the fire by mechanical means.
Blast furnaces and cupolas, so arranged, are used largely in smelting
ON FURNA CES. 387
the ores of iron, lead, and copper, and in fusing cast iron and other
substances. In all these, the fuel and the materials to be melted or
otherwise acted on are charged, together, into the upper end of a
vertical shaft ; and the combustion is maintained by air forced in
through one or more openings or tuyeres near the bottom. Of such
furnaces, those employed for the manufacture of cast iron are by far
the largest and most important, and may be taken as the type of the
class.
The blast furnace for iron making has attained to its present con-
struction, and to its colossal size, by what may be described as a
process of natural selection ; a gradual advance and improvement,
and the survival of the fittest. Representatives of its earliest stages
are to be found in the small and simple furnaces that are described
as still in use, for the direct production of malleable iron, in the more
remote parts of Africa, India, and Borneo. Some of these are little
shafts of clay, hardly larger than a chimney-pot, and charged with a
mixture of rich iron ore and charcoal. A draught, to maintain the
combustion, is obtained either by placing the furnaces so that they are
exposed freely to the prevailing winds, or by forcing air in at the
bottom of the shaft by some simple form of hand-bellows. The
Osmund furnace of Sweden, with a shaft six feet high, and making
one and a half to two tons of malleable iron per week, and the
Stuckofen, ten to sixteen feet high, and yielding blooms of iron
weighing four to six hundredweight, were merely enlargements of
these primitive furnaces, and like them produced, not cast iron,
but malleable masses resembling puddled balls. The blast furnace,
yielding liquid cast iron, grew however directly from the Stuckofen ;
as, in a furnace of this height, cast iron was obtained at will, by
increasing the proportion of fuel and keeping the metal in the hearth
covered with slag ; and when the height was still further increased,
nothing but liquid metal was produced.* The possibility of obtaining
iron from the ore in a liquid form, that could be tapped out, greatly
cheapened its production, and permitted the use of still larger furnaces
and the smelting of poorer ores ; and it was found that the cheaper
* Metallurgy, Iron and S J. Percy, 1864, pp. 325 et seqq. Ibid., J. A. Phillips, p. 170
383 SECTION— MECHANICS.
way to make malleable iron, with the appliances then available, was
not, except in rare cases, to produce it directly from the ore, but to re-
duce the metal first to the state of cast iron, and to make malleable
metal from that by a second process.
Among the further steps that have led up to the modern form of
blast furnace are the very general substitution of coke or coal for
charcoal as fuel, the use of hot blast, a very great increase in the size
of the furnaces, and the collection and use of the waste gases.
The most recently erected furnaces in the Cleveland district are
eighty to ninety feet high, and from 26,000 to 30,000 cubic feet in
capacity.* The blast supplied to them is at a temperature of 500° C.
to 750° C., and the waste gases are collected, and so efficiently em-
ployed, to heat the blast and to raise steam for working the blowing
engines, that in many works no fuel, except the coke charged into the
furnaces, is used.
The economies effected by the late increases in the height of blast
furnaces and in the temperature of the blast have been very great.
Thus, with blast at a temperature in each case of about 540° C., and
with other conditions the same, the consumption of coke which in
furnaces forty-eight feet high and of 6000 cubic feet capacity, built at
the Clarence Works in 1853, was twenty-nine hundredweight per ton of
iron made, is reduced, in more recently erected furnaces, by increasing
the height to eighty feet and the capacity to 12,000 cubic feet or more,
to twenty-two and a half hundredweight.f
Again, in furnaces of the same size, each increase in the temperature
of the blast has been attended with a marked economy ; the extent of
which, however, diminishes, for equal increments of temperature, the
higher this is raised. When blast, for instance, heated from the tem-
perature of the air, which may be taken at 10° C., to 150° C., was first
introduced by Nielson, at the Clyde ironworks in 1830, the saving in
fuel effected by raising the temperature by 140° C. was equal to about
two tons of coke per ton of pig iron made, or thirty-six per cent, of the
whole consumption ;$ whereas, in modern practice, the further economy
* J. Gjers, On Cleveland Blast Furnaces, Journal of the Iron and Steel Institute, 1871,
p. 202.
t Isaac Lowthian Bell, Blast Furnace Phenomena. Ibid., Proceedings of the Institution
of Mechanical Engineers, 1875, p. 364.
t J . Percy, op. cit, p. 391.
ON FURNA CES. 389
obtained by an equal rise in temperature, from 620° C. to 760° C, is
not more, even according to the strongest advocates of highly-heated
blast, than two hundredweight per ton, or nine per cent. ; a reduction,
that is, in the amount of coke used to smelt ordinary Cleveland ores,
and in furnaces eighty feet high, from rather less than twenty-two
hundredweight per ton to twenty hundredweight.*
Mr. Bell's investigationst show that the remarkable saving in fuel,
obtained by the use of highly heated blast, is due to the lower tem-
perature at which the gases escape from the furnace top, and the
smaller proportion of CO that they contain ; the ratio of the amount
of CO2 to that of CO, in the gases, being the index of the more or less
advantageous manner in which the fuel is burned ; and he has pointed
out that the economy of large and high furnaces over smaller furnaces
is to be traced to the same causes ; — the gases from a high furnace
carry off less sensible heat ; and up to a certain limit, which he
fixes, for the materials in use in the Cleveland district, at a height of
eighty or ninety feet, they are poorer in CO than those from lower
furnaces.
Thus height of furnace and temperature of blast appear to be
capable in a great measure of replacing each other 'in their effect on
economy of working ; and the benefit to be derived from working
with very hot blast is likely to be greater in the case of furnaces
which, from the characters of the fuel and ore used, cannot be
made very high, than it is in the high furnaces in use in Cleveland.
As an instance of the similar effect, on the consumption of fuel, of the
use of hot blast and of an increase in height, Mr. Bell quotes the
working of the furnaces at Lillieshall. There, in furnaces fifty-three
feet high, the consumption of coke, with cold blast, was forty hundred-
weight per ton of iron made ; and this consumption was equally
reduced, to twenty-eight hundredweight per ton, in the case of one
furnace, by increasing the height to seventy-one feet ; and in another,
with the old height of fifty-three feet, by heating the blast.
In the Glasgow district, the fuel generally used in the blast furnaces
is uncoked free burning coal ; and with this comparatively soft fuel it
* C. Corhrane, Proceedings of the Institution of Mechanical Engineers, 1869, p. 21, and
1870, p. 62.
1 Blast Furnace Phenomena.
390 SECTION— MECHANICS.
is not found practicable to work furnaces, of the ordinary form, much
exceeding fifty-two feet in height. In the self-coking furnace, how-
ever, as it is termed, of Mr. Ferric, the barrier thus imposed to
increased economy appears to be got over successfully, and in a
somewhat remarkable way. Mr. Feme's furnace is eighty-three feet
high, with a closed top, the charging being effected by a bell and
cone ; and for a height of thirty feet, near the top, the shaft is divided
by cross walls into four sections. These cross walls and the cor-
responding portions of the side walls are built hollow, with flues in
their thickness, in which a portion of the gas is burned, so as to assist
the ascending current, in the furnace, in coking the coal and heating
up the charge. The amount of raw coal that this furnace burns is
thirty-four hundredweight per ton of iron made, against nearly
fifty-three hundredweight in ordinary furnaces, fifty-two feet high,
and working under the same conditions : a difference of about
nineteen hundredweight. Mr. Bell, who has studied the working of
the Ferrie furnace, attributes this saving, half to its increased height,
which is rendered practicable by the additional support given to the
charge by its friction against the cross walls, and half to the effect of
the heat communicated, through the walls, by the burning of a part of
the gases in their flues.*
The older, and still the more common, method of heating the air for
blast furnaces is by passing it through a series of cast iron pipes,
heated to redness, by the waste furnace gases or otherwise, in suitable
hot blast stoves. The greatest temperature of blast that can be
maintained, in this way, without causing the rapid destruction of the
pipes, hardly exceeds, however, 550° C. to 600° C. ; and where higher
heats are desired, recourse must be had to the system of regenerative
fire-brick stoves, first introduced by Dr. Siemens and Mr. Cowper.t
A model of one of Mr. Cowper's stoves is on the table. In principle it
s very simple. Each stove consists of a large cylinder of boiler plate,
lined with fire-brick work, and filled with loose fire bricks, stacked
together so as to form a series of vertical slightly zigzagged flues, and
to expose the greatest possible extent of surface. To heat the stove,
* Journal of the Iron and Steel Institute, March soth, and August 29th, 1871.
t E. A. Cowper, Proceedings of the Institution of Civil Engineers, vol. xxx. p. 309.
C. Cochrane, Proceedings of the Institution of Mechanical Engineers, 1870, p. 62.
ON FURNA CES. 391
gas from the furnace is burned, with a suitable admixture of air, in a
brick shaft in its interior ; and the products of combustion are drawn
down, throu0h the mass of bricks, by the draught of a high chimney.
When this operation has been continued for three or four hours, the
greater part of the mass of brickwork, filling the body of the stove, is
at a uniform red heat ; and the heat decreases, thence, towards the
bottom, so that the gases passing off to the chimney are at a tempera-
ture not exceeding 150° C. ; no more than is sufficient to maintain a
draught. When the stove has thus been heated, the air, gas, and
chimney valves are closed ; and by opening the cold and hot blast
valves, blast is sent through it, in the reverse direction, passing first
among the nearly cool bricks in the lower part, next to the chimney,
and then over hotter and hotter surfaces, until before it reaches the
top of the stove, it has attained nearly to the temperature of the bricks
themselves. The hot blast thence rises through the remainder of the
column of chequer work, and passes down the brick shaft or combus-
tion chamber, and through the hot blast valve, to the furnace. By the
time that the current of blast, flowing through the stove, has begun to
cool down, sensibly, the uppermost courses of chequer work and the
walls of the combustion chamber, a second stove, which has meantime
been heating up, is put " on blast," and the first stove is heated again
in turn. By working a set of either two or three stoves, in this way, a
constant supply of hot blast is maintained ; the temperature of the
blast, between the beginning and the end of a shift, not varying more
than 50° or 100° C. When three stoves are worked together, two are
generally kept at a time "on gas," or heating up, and one "on
blast."
The difficulty that was experienced in keeping the earlier forms of
the Cowper stove free from deposited dust, carried over from the fur-
nace, led to the introduction of a modification of it, by Mr. Whitwell,
that has also been extensively adopted. In this, the brickwork pro-
vided to take up the heat of the burning gas, and give it out again
to the blast, is arranged in the form of a series of parallel vertical
walls. These present less heating surface than bricks arranged on
the plan adopted in the Cowper stove ; and the stoves, being of less
height, take up also more floor space. The advantage claimed
them is that they are more easily cleaned.
392 SECTION— MECHANICS.
In cupolas, for the simple melting of cast iron, less alteration has
been made, during recent years, than in blast furnaces.
Considerable savings in fuel have, however, been effected, by melting
more rapidly, so as to diminish the loss of heat by radiation from the
outer surface, and by making the cupola considerably smaller in area
at the tuyeres than in the rest of the shaft, in order to obtain a more
concentrated heat at the point of fusion. Larger cupolas have also
been employed, as, for instance, to melt the metal for the Bessemer
process, than were generally in use before ; and the plan has become
common of providing these and other large cupolas with fore hearths,
or receptacles for the melted metal, of a capacity of five or ten tons,
which are kept warm by allowing a part of the flame to escape
through them, and into which the metal flows at once, as it melts,
instead of accumulating in the bottom of the cupola in contact with
the coke.
An arrangement that presents some points of interest is the " flame-
less" cupola of M. Voisin. The principle of this is to admit a second
and carefully moderated supply of air to the upper part of the shaft,
sufficient to burn the carbonic oxide contained in the escaping gases,
without wasting any sensible quantity of coke, or producing suffi-
cient heat to transform the CO2, that has been produced by the
burning of the gas, again at the expense of the coke to CO.
It is claimed that in this way the CO in the gases may be burned,
without wasting coke, and that the top of the cupola is thus maintained
cool and flameless ; while as the metal and fuel are heated to redness,
by the combustion of the, waste gas, a smaller proportion of coke
is required. Thus, in foundry cupolas, to which the plan has been
chiefly applied, a saving is effected by it, according to some state-
ments, equal to 40 Ibs. of coke per ton of metal melted ; the con-
sumption per ton having been reduced from 200 to 160 Ibs. ; and in
other cases the coke consumption of foundry cupolas on Voisin's
plan, exclusive of the first charge, is stated at as little as 140 or even
134 Ibs. per ton.
That when the coke used in a cupola is fairly hard, the materials
of the charge may be thus raised to a red heat, by the combustion of
the gases, with little or no loss of coke, is shown by one of the experi-
ments made by Mr. Bell, in the course of his investigations of the
ON FURNACES. 393
working of the Cleveland blast furnace. Mr. Bell found that on passing
a slow current of CO2 over ordinary Durham blast furnace coke, con-
tained in a glass tube, no CO was formed when the heat of the coke
did not exceed 550° to 650° C, and only traces even when the tem-
perature was raised to such a point that the combustion tube, of hard
German glass, began to soften.*
In blast furnaces, no such saving as that above quoted is to be looked
for, by burning the gases in the upper part of the shaft ; as in these the
proportion that the fuel bears to the other materials of the charge is so
much greater than in a cupola, that the sensible heat, alone, of the gases
is more than sufficient to heat up the whole charge to their own tem-
perature ; and in addition to this there is, as Mr. Bell has shown, an
actual evolution of heat, in the upper part of the furnace, due to the
dissociation of a portion of the CO. In the case of the furnace, for
instance, eighty feet high, erected at the Clarence Works in 1866, the
total capacity for heat of the ore, coke, and limestone charged, is less
than half that of the gases ; so that, neglecting the absorption of
heat by chemical action, and its evolution by dissociation, the sensible
heat alone of these would be sufficient to heat up twice as much solid
material as is charged.
The furnaces of the second group, or flame furnaces, are veiy varied
in form and character. In these, the useful effect is obtained by bring-
ing a flame, or current of highly heated and burning gas, into contact
with the matters to be acted on, instead of imbedding these in or
mixing them with the solid fuel.
The ordinary reverberatory or flame furnace, with a fire grate, a
flame chamber or working chamber, and beyond that again a flue
leading to the chimney, is well known, and there is no need to go over
in detail the variations from the general type by which it is adapted to
different uses.
The most important recent modification of this form of furnace is
the regenerative gas furnace of Messrs. Siemens, of which models and
a diagram are in the room. In this, which dates in its present form
from 1 86 1, the fuel is transformed, in a separate gas producer, into a
* Proceedinss of the Institution of Mechanical Engineers, 1869, p. $$.
B C 2
394 SECTION— MECHANICS.
combustible gas, consisting chiefly of carbonic oxide and nitrogen,
mixed with hydrogen and hydrocarbon gases and vapours, distilled
from the fuel, some vapour of water, and more or less carbonic acid.
The gas is led, through flues or pipes, to the furnace, which may be
at any distance from the gas producers, and is there burned. Gas,
capable of producing, in such furnaces, the highest temperatures
ordinarily used in the arts, may be made from any description of
carbonaceous fuel, from anything in fact that will burn, however
much mineral matter it may contain, and whether it is wet or dry.
In Sweden, for instance, damp sawdust is used as the fuel to furnish
gas for welding and other high heat furnaces ; the large amount of
water that the gas from such a material contains being first removed
by cooling it, either by sprays of water or by passing it through a sur-
face condenser.
The furnace consists essentially of a heating chamber, of any con-
venient shape, below which are placed four regenerator chambers, for
taking up the waste heat from the flame, on its way to the chimney,
and giving it out again to the entering air and gas. These chambers
are filled with loosely stacked fire bricks, and each of them is precisely
analogous in its action to a Cowper hot blast stove on a smaller scale.
The air and gas, entering the furnace, pass up through two of the
chambers, and are thus highly heated, before they are brought together,
and burn, at the entrance to the working chamber, or furnace proper,
in which the matters to be heated are placed ; and the spent flame,
from this, is at the same time drawn down to the chimney through the
other two chambers ; and, leaving the greater part of its available heat
in the brickwork filling these, escapes to the chimney nearly cool. At
intervals of half an hour to an hour the direction of the draught is re-
versed ; the air and gas being introduced, in the opposite direction,
through the two chambers that have been heated by the waste flame,
and the current passing to the chimney being turned through the first
pair of chambers, to reheat them in turn.
As the heated gases are made to pass downwards, through the
regenerators, and the cool currents of air and combustible gas ascend,
the heating and cooling of the masses of brickwork take place very
uniformly ; the hot current descending always most freely through the
coolest channels, and the ascending current rising chiefly through the
ON FURNACES. 395
hottest. The position of the regenerators, below the level of the work-
ing chamber, gives also the advantage of an absence of indraughts of
cold air into this ; as owing to the ascending draught of the hot pas-
sages, through which the gas and air are introduced, a balance of
pressure, or even an outward pressure, may be maintained in it, while
the furnace is in full work.
The saving of fuel in the regenerative gas furnace amounts in
average practice, when the furnaces are well managed, to fully fifty
per cent, on the quantity used in an ordinary furnace doing the same
work. The saving is greater, the higher the heat that is required in
the working chamber ; and where the most intense heats are needed,
as in making or melting mild steel on the open hearth of a rever-
beratory furnace, no other than a regenerative furnace can be used ;
in no other is a sufficiently steady and intense heat maintained,
without cutting draughts.
Other advantages of the system are the freedom of the flame from
dust ; its diminished oxidizing or cutting action, (the waste on iron
piles, heated in a well-designed and well-managed gas furnace, being
only one-half or one-third as great as in an ordinary coal furnace) ;
and thirdly, the facility with which, whatever fuel is used, a uniform,
living flame, of any required length, may be obtained, by making the
mixture of the gas and air more or less rapid and intimate ; from two
or three feet only, as in the furnaces for melting steel in crucibles, to
thirty or forty feet, in large plate-glass furnaces ; the hottest part of
the flanie, in the latter case, being not where the gas and air meet,
but some five-and-twenty feet away, where they begin to be thoroughly
mixed.
Since the Siemens furnace has been in use, several other gas fur-
naces, with continuous tube regenerators, have been brought forward.
Furnaces, that is, in which the air, and in some also the gas, are
heated, not by being introduced through masses of brickwork, pre-
viously raised to a high temperature, but by being passed, in con-
tinuous currents, without reversing, through fireclay tubes or hollow
bricks, round which the burned gases are drawn away to the chimney.
The Ponsard furnace, which has been recently brought into use, to
some extent, in France and Belgium, appears to be the best designed
of these modifications ; and the quoted results of its working, when in
396 SECTION— MECHANICS.
good order, are very satisfactory. In this arrangement, the air only is
heated by the regenerator ; the gas producer being placed close to
the furnace, and the gas from it taken directly, without further
heating, to the point where it is burned. In the case of such a
furnace, there are several advantages in thus heating the air, only, by
the waste heat ; the tubes of the regenerator are not choked up by
deposits from the hot gas, nor is there the risk of loss of gas by
teakage ; and as the volume of burned gases is sufficient to heat
nearly twice as much air as is required for combustion in the furnace, a
moderate leakage of air, in the regenerator, into the current passing
to the chimney, does no harm ; since, if the regenerator exposes
sufficient surface, as much air, heated to nearly the full temperature of
the waste gases, may still be drawn into the working chamber as is
required there. The ordinary Siemens furnace, however, though
apparently more complicated, is probably a stronger and more
durable arrangement than any furnace working with continuous
tube regenerators can be made, and is better fitted to bear the
rough treatment that is generally the fate of such appliances in actual
work.
A proposed modification of the Ponsard system of furnace, that
presents considerable theoretical advantages, is to supply the gas pro-
ducer, as well as the working chamber of the furnace, with highly
heated air from the regenerator ; the hot gas being taken, as in the
ordinary Ponsard furnace, direct, without further heating, from the gas
producer to the working chamber in which it is burned. The carrying
out of such an arrangement, in the case either of the Siemens furnace, or
of a furnace with tube regenerators, appears likely to present great prac-
tical difficulty, but if it can be successfully worked out, the increased
economy will be great ; as, in such a furnace, the whole of the heat
evolved from the fuel, except that still inevitably lost by external
cooling, and that carried off by the gases passing to the chimney, at
a temperature that need not exceed 100° or 150° C. would be avail-
able, in the working chamber, as heat of high temperature.
In the Siemens furnace, in which the gas producer is supplied with cold
air, the sensible heat of the gases, as they leave the producer, does
not affect the temperature of the flame in the furnace ; for the amount
of heat contained in the products of combustion is sufficient to heat
ON FURNA CES. 397
up the entering gas and air, from the temperature of the atmosphere,
to a temperature nearly equal to that at which the spent flame leaves
the working chamber ; and the effect of sending in hot gas instead of
cold gas, is not that the gas is much hotter when it reaches the top of
the regenerator, but simply that the bottom of the regenerator, where
the gas enters, is less cooled down ; and, on reversing, the burned
gases, after traversing it, escape at a higher temperature to the chim-
ney. In practice, the heat of the gas, as it leaves the producer, is in
most cases purposely thrown away, by leading it through overhead
sheet iron " cooling tubes," in order to obtain a better pressure, at the
furnace, from the syphon action between the ascending hot column
and the descending heavier cool column, and to remove the greater
part of the vapour of water that it generally contains.
Again, in the Ponsard furnace, as has been pointed out, when only
the air, to burn the gas in the working chamber, is heated by the
waste flame, the quantity of heat carried into the regenerator is about
twice as great as is required to heat this amount of air ; and however
perfect the action of the regenerator may be, however great may be
its extent of surface, the burned gases necessarily escape to the
chimney at a high temperature.
If, on the contrary, the air to supply the gas producer, as well as
that to burn the gas, were heated by the waste heat ; and the hot gas
from the producer were led direct, without passing through a regene-
rator, to the working chamber, and burned there ; the volume of air to
be heated would be sufficient to take up all the available heat of the
waste flame, and the heat that is otherwise inevitably lost, either by
the chimney in the one case, or from the cooling tube in the other,
would be rendered available.
The system of burning powdered fuel, that has been worked out by
Mr. Crampton, is another remarkable deviation from the ordinary form
of flame furnace.
A model of such a furnace, arranged for mechanical puddling, is on the
table. The coal, burned, is first ground between ordinary millstones to
such fineness that it will pass through a sieve with thirty holes to the
linear inch (which Mr. Crampton estimates may be done, on the large
scale, at a total cost of less than a shilling a ton) ; and the powdered coal
is supplied, at any required rate, by a mechanical feeding arrangement
398 SECTION— MECHANICS.
connected with each furnace, and is led into a jet of air, from a fan, at a
pressure equal to three or four inches of water column, by which it is
carried forward into the furnace. In this, the jet of mixed coal dust and air
takes fire, and burns like a jet of combustible gas, except that the flame
is solid, not hollow like a gas flame burning in air. The revolving
puddling furnace is in form a short cylinder, closed at one end and
slightly narrowed at the other, and consists of a double casing, of thin
boiler plate, kept cool by a current of water flowing through it, and
lined with a " fettling," of oxide of iron, five or six inches thick. The
air and coal dust are blown in through the line-piece, that fits against
the open end of the revolving puddling chamber, and the waste flame
escapes to the chimney by the same opening, round the entering jet.
The combustion of the fuel is thus effected in the working chamber,
itself, and as the coal and air are mixed intimately throughout the
flame, it is very complete. The consumption of coal, in puddling ten-
hundredweight charges of pig iron, run liquid into the furnace, is stated
to be nine hundredweight per ton of puddled bar produced.
This system of furnace, though in most respects remarkably perfect,
and giving every promise of success as applied to revolving puddling
furnaces, is not found to be suited for use in those more ordinary ar-
rangements, in which the working chamber is built of brickwork or other
siliceous material, as the fluxing action of the ash of the coal destroys,
very rapidly, any such work that is in contact with the flame and ex-
posed to its full heat.
Among the directions in which improvements have been effected in
flame furnaces of the ordinary type, are the use of the waste heat to
raise steam, a system now carried out, to a greater or less extent, in all
iron works where such furnaces are used ; the employment of a blast
or forced draught under the fire-grate, (the air forced in being frequently
more or less heated,) in order to allow of burning cheaper small coal,
and to give a command, such as that possessed by the regenerative
gas furnace, over the pressure in the working chamber ; and, lastly,
arrangements for preventing the cooling down of the fire, each time
that fresh fuel is put on, and the rush of cold air into the furnace,
through the opened fire-door, when a pressure is not maintained in it
by blast.
ON FURNA CES. 399
The Newport furnace of Mr. Jeremiah Head* may be taken as an
example of those furnaces in which blast, heated by the waste flame,
is introduced under the fire-grate. In this, the blast pressure is obtained
by a steam jet, and the resulting damp air is heated to about 290° C.
by passing it through a cast iron heating stove, round which the waste
flame is led on its way to the chimney. The hot blast is conducted
partly under the fire-grate, and partly to a row of holes in the furnace
roof, immediately over the fire, through which a supply of air is thus
introduced, sufficient to complete the combustion of the gases rising
from the fire. Mr. Head states that in a hand puddling furnace of this
construction, working four-hundredweight charges, the temperature
at which the burned gases finally pass to the chimney is reduced
from 1112° C. (the average temperature found in the chimney of a
similar furnace, in which the air was not heated) to 860° C. ; the heat at
the same time at the fire bridge being estimated at 1370° C. The
consumption of coal is reduced from twenty-four and a half hundred-
weight, per ton of puddled bar produced, to sixteen and a half hundred-
weight, and the yield is stated to be also from one to three per cent,
greater than in the ordinary furnace.
In Price's retort furnace the fire is supplied with air forced in by a
fan, and heated by the waste heat to between 200° and 260° C., and
the coal used is also heated, before it is pushed forward on to the grate,.
by charging it through a high vertical retort, round which the spent
flame passes to the chimney. The saving in fuel effected, in fur-
naces for puddling and heating iron, by thus making use of the waste
heat, is stated to amount to between thirty and forty-five per cent.
An American arrangement, known as Frisbie's feeder, that has been
recently introduced into this country, avoids in a different way the
cooling of the surface of the fire each time that fresh coal is put on ;
and the burst of smoke, after firing, from the evolution for a short
time, from the suddenly heated fuel, of hydrocarbon gases and vapours
that pass away only partly burned ; as well as the necessity for fre-
quently opening the fire door. In this mode of firing, each charge of
coal is filled into a moveable charging box, and pushed up, from below,
* Journal of the Iron and Steel Institute, 1872, pp. 220 et seq.
400 SECTION— MECHANICS.
into the middle of the fire-grate, so that the surface of the fire remains
always hot, and as the distillation of the gases from the raw coal goes
on continuously, the fire remains uniform in character and maybe readily
kept smokeless. The arrangement has been applied, in this country,
to boilers, flint glass furnaces, and puddling furnaces, and is said to
effect a decided economy in fuel and give altogether satisfactory results.
The use of hydrogen and hydrocarbon gases, as furnace fuel, is
chiefly limited to the heating of small laboratory furnaces, or to work
on a scale but little greater ; as the cost of such gases, when artificially
produced, is too great to admit of their competing on a larger scale
with coal. In the comparatively few localities, however, in which
such gases have been found to flow naturally from bore holes, pene-
trating to beds of coal or shale, they form a valuable fuel, that is made
use of to a considerable extent. In some parts of Pennsylvania,
from bore holes put down for petroleum, a supply of gas, consisting
chiefly of marsh gas (CH4), mixed with other hydrocarbons and with
hydrogen, has been found to rush steadily, for years, at a pressure
estimated at nearly one hundred pounds per square inch ;* and in the
case of at least one such "gas well," that at Leechburg, the gas has
been very effectively turned to account. There, according to a recent
number of the Enginnering and Mining Journal*; the gas is conveyed
from the well, through a distance of between one hundred and two hun-
dred yards, to adjoining sheet iron works, where it heats five puddling
furnaces, six heating furnaces, two annealing furnaces, and so on, and
furnishes in fact all the fuel required for turning out nearly thirteen
tons of sheet iron a day. Before the gas was brought to the works, the
daily consumption of coal had been seventy-five tons, and the make
per day of sheet iron did not then exceed ten tons ; so that the gas does
now as much work as would have required, on the former plan, ninety-
seven and a half tons of coal per day.
Petroleum and other liquid fuels have also been used for heating
furnaces, both in England and in America, but on a scale only experi-
mental rather than really industrial. The results obtained are, how-
* Engineering and Mining Journal (New York), March i8th, 1876, p. 269.
t Engineering and Mining Journal (New York), May 22nd, 1875, p. 367; and June 26th,
1875, p. 476.
ON FURNACES. 401
ever, very remarkable. In 1869 an extended trial was made, at Chat-
ham Dockyard, of the system of Messrs. Dorsett and Blyth, for heating
with creosote or other heavy oils. The furnaces to which the plan
was applied were those used for heating ship plates and armour plates
for bending. The oil was vaporized in a small boiler or generator,
and supplied to the furnaces through jets one-eighth of an inch in
diameter, at a pressure of thirty pounds per square inch ; and the
air, not previously heated, was simply drawn in by the chimney
draught. The heating, both of the armour plates and of thin ship
plates, was done in one-third the time taken in heating in the
ordinary way, with coal ; and the weight of oil burned, per ton of plates
heated, was between one-sixth and one-eighth of the former con-
sumption of coal. More recently, in the course of last year, a report
by Professor H. Wurtz has been published,* of the working, in America,
of Eames's system of firing furnaces with petroleum, which quite
corresponds with the results obtained at Chatham. On Eames's plan,
the crude petroleum used is evaporated and carried into the furnace
by a current of highly superheated steam, at a pressure of ten pounds
per square inch. The furnace to which it was applied was one for
heating scrap iron piles, for rolling into plates ; and the air supply, as
at Chatham, was cold. The furnace was heated up, ready for charging,
in forty-five minutes, and with a consumption of only twenty-two and
a half gallons of oil. The output, per shift of ten hours, was eight tons
of rolled plates, with a consumption of 300 gallons=2ooo pounds of oil :
the same furnace, when fired with coal, having heated the piles for only
six tons of plates per shift, and burned five and a half tons of coal.
The effective heating value of equal weights of oil and coal was thus
in the proportion of eight to one.
The much less weight of mineral oil than of coal that is required, ac-
cording to these two statements, to do an equal amount of work, is pro-
bably due in part to the combustion of the oil-vapour being effected with
the admission of a smaller excess of air than is found in the products of
combustion from a furnace fired with coal ; to the combustion taking
place wholly in or at the entrance to the working chamber ; and to the
work being done in less time, so that there is less loss of heat by outside
* Engineering and Mining Journal (New York), Aug. Jth, 1875, p. 122.
cc
402 SECTION— MECHANICS.
cooling ; but it is chiefly to be attributed to the greater heating power
of the hydrogen, of which such oils largely consist, than that of carbon.
As Dr. Percy has pointed out, though the great weight, and the high
specific heat, of the gases resulting from the combustion of hydrogen
in air, lower the theoretical maximum temperature produced to a little
under that due to the combustion of carbon, yet if the products of
combustion pass off at any ordinary furnace temperature, considerably
below the theoretical maximum, the number of available units of heat
produced by the combustion of hydrogen is much greater than that
obtained from an equal weight of carbon. Thus, if the burned gases
pass off at 1500° C., the available heating effect of hydrogen is nearly
four times as great as that of carbon.
It does not appear that any trials have been made of working re-
generative furnaces either with mineral oil or with natural gas ; nor,
indeed, even of burning these fuels with air moderately heated, such
as is used in Head's or Price's furnace ; though the advantage of thus
making use of the waste heat, to increase still further the temperature
of the flame, would evidently be great. It is not too much to say. that
a regenerative furnace, with regenerators, of course, only for heating
the air, and fired either with hydrocarbon gas, or with liquid fuel, on
such a plan as either of those above referred to, would far surpass any
furnace now in use, (except those, such as Deville's, in which the fuel
is burned by a current of oxygen,) in the weight of material that it
would heat with a given consumption of fuel.
In nearly all furnaces, the amount of heat that is utilized is an ex-
tremely small proportion of the total heat due to the combustion of
the fuel ; the greater part being carried off by the burned gases, or lost
by conduction and radiation. M. Gruner calculates, in a recent paper
published in the "Annales des Mines," on the proportion of heat that
is utilized in furnaces of different kinds, that in the fusion of steel, in
crucibles, in ordinary coke furnaces, the heat utilized does not exceed
1 7 per cent, of the total amount that the fuel would be capable of
giving out, if perfectly burned ; and that even on the extreme suppo-
sition that half of the fuel is burned only to CO, the heat utilized
amounts to only 2'6 per cent, of that evolved. In flame furnaces, the
proportion of heat utilized is higher ; reaching, as a maximum, fifteen to
twenty per cent, of the total heat due to the amount of coal burned, in
ON FURNA CES. 403
well-arranged regeneiative gas furnaces for reheating iron. In those
arrangements in which there is little heat lost by external cooling, and
in which the heat of the products of combustion is most fully utilized,
the useful effect is much higher : thus, in large blast furnaces,
M. Gruner estimates that it is as much as seventy to eighty per cent,
of the heat actually developed in the furnace and introduced into it
by the blast, or between forty and fifty per cent, of the total heat that
the fuel could evolve if completely burned ; and in the annular
Hoffmann brick kiln, it is estimated to amount also to between
seventy and eighty per cent, of that given out by the fuel.
A greater proportion of the heat evolved is lost, in the burned gases,
the less the difference is between the temperature of the flame and that
required to be maintained in the working chamber ; for as soon as any
portion of the flame is cooled down to the temperature of the matters
lo be heated, however high this may be, it can impart no more heat to
them, and must be drawn away and replaced by hotter flame from the
fire. Hence, a small increase in the initial temperature of the flame,
such as that obtained by effecting the combustion of the fuel by means
of moderately heated blast, or a small diminution in the proportion of
heat lost from the working chamber by external cooling, effects a great
saving in the consumption of fuel that is required to do a given
amount of work.
The effect of a high flame temperature, on the proportion of heat
utilized, is strikingly shown by the very economical working of fur-
naces on Deville's system, that of burning coal gas with oxygen, instead
of with air. The theoretical temperature of such a flame, if not limited
by dissociation, would probably amount to 7000° or 8000° C, and it is
in any case far above the fusing point of platinum, which is estimated
at about 1900° C. In an example, of which M. Gruner gives particulars,
in the paper above referred to, of the fusion of a charge of 250 kilo-
grammes of platinum by this method, the cold furnace was heated up,
and the metal melted in it, in one and a quarter hours, and with a
consumption of only twenty-four cubic metres (848 cubic feet) of gas ;
the proportion of heat actually utilized, in the fusion of the metal,
being fourteen per cent, of that due to the combustion of the gas.
Thus, on account of the intense heat of the oxyhydrogen flame, as
good an economical result was obtained, in this little furnace, as in the
re 2
404 SECTION— MECHANICS.
best of the flame furnaces used in ordinary metallurgical work ; though
the proportionate loss of heat from the surface cooling of so small a
furnace, (a little trough not more than thirty inches long,) must have
been enormous, the products of combustion cannot have escaped at a
lower temperature than 2000° C., and neither the coal gas nor the
oxygen was heated. »
The system of working furnaces under high pressure, on which some
experiments were made a few years ago by Mr. Bessemer, offers a
possible method of increasing, considerably, the temperature of com-
bustion of ordinary fuels, and with it the proportion of available heat ;
but since the first experiments were made, of which an account was
published in the technical journals in 1869, nothing further has been
done to test the practical value of the scheme.
The diminished proportion of heat that is lost by suiface cooling, in
the case of large furnaces, and the consequent higher temperature of
their flame, render them in all cases much more economical in fuel than
furnaces of smaller size. In the case of ordinary puddling furnaces, for
instance, when the coal consumption in those working five-hundred-
weight charges is about twenty-three and a half hundredweight per ton
of bar produced, the consumption is reduced to eighteen hundred-
weight per ton in working ten-hundredweight charges, and to fifteen
hundredweight per ton in still larger furnaces working charges of
fifteen hundredweight ; and in the welding furnaces, in use at Wool-
wich Arsenal, the larger the furnace is, the higher by actual experiment
is the temperature of the flame as it passes over the bridge, and the
smaller is the amount of coal required per ton of metal heated. A
furnace of ordinary size, heating six tons at a charge, consumes about
eight hundredweight of coal per ton ; a larger furnace, heating a charge
of thirteen tons, does the workr with only seven hundredweight per
ton ; and the largest of all, capable of heating at once a mass of iron
weighing sixty-five tons, gets this up to a full welding heat with a coal
consumption of only five and a half hundredweight per ton. In copper
smelting, in glass making, and in other work, large furnaces are
similarly found to use less fuel, in proportion to the work done ia
them, than furnaces of smaller size.
The Conference then adjourned,
ON FURNACES. 405
The PRESIDENT : As Mr. Hackney was rather limited in time
before luncheon, I will now call upon him to add anything he
may desire, or to explain any of the models which were not up here
before.
Air. HACKNEY : I have nothing to add formally to the paper which
was read before the adjournment, but I will say a word or two on some
of the models which have been brought up since. There is, for instance,
a model somewhat old-fashioned of a blast furnace, showing the hearth
and the form of the stack. Here, also, is an interesting diagram, showing
the increase in the size of blast furnaces. The first one is about fifty
feet high, and had a capacity of 5076 cubic feet, and in it about twenty-
nine-hundredweight of coke was consumed per ton of iron produced.
By increasing the size to a height of eighty feet, and the capacity to
from 12,000 to 30,000 cubic feet, the consumption of coke has been marvel-
lously reduced — viz., from twenty-nine or thirty-hundredweight to about
twenty-two-hundredweight per ton, the other conditions remaining the
same. There is a model and also a large diagram of the Regenerator gas
furnace, which was mentioned in the paper. In the diagram the arrange-
ments are shown all on one plan, in order to make the action clear. Then
there is another model of Mr. Head's furnace, an ordinary furnace, work-
ing with coal, in which the air is supplied by a steam jet. The whole
of the arrangements are of cast-iron. In this model a regenerating
gas furnace is shown as the work is actually arranged in practice ; the
regenerators being under the furnace; and the reversing valves and
flues, which are shown on the diagram below the furnace, are placed
at the back. It is really on the principle as the hot-blast stove,
which was first introduced, and the application of it to blast furnaces
came afterwards. In fact, there are four hot-blast stoves on a small
scale under each furnace. Here again is a model of the coal-dust
furnace of Mr. Crampton, as applied to puddling. In this furnace
there is a chamber lined with oxide of iron, open at one end and
enclosed at the other ; it has a removable flue piece, by means of
which the charge is introduced and withdrawn. In actual work, as I
explained before, the jet of coal-dust and air is blown in at the centre
of the flue piece, and the flame passing to the chimney escapes round
the jet, and so goes to the chimney.
4o6 SECTION-MECHANICS.
The PRESIDENT : I rise now to propose a vote of thanks to Mr.
Hackney for his interesting communication, which I am sure you will
accord.
I will now call on Mr. Preece for his address on Electric Telegraphs
— a subject of vast interest and great detail. I fear Mr. Preece will
not have as much time as we should like to give to it, but I have na
doubt he will make it interesting.
ELECTRIC TELEGRAPHS.
Mr. PREECE : Mr. President, ladies, and gentlemen, telegraphy is
the art of conveying the first .elements of written language to distances
beyond the reach of the ear and the eye. When electricity is used to
effect this operation we have the electric telegraph, and inasmuch as
there are many fundamental phenomena of electricity which are used
as the bases of these telegraphs, so we have these telegraphs divided
into different systems. I propose to show you how these systems of
telegraphy have grown by a principle of evolution from the first in-
cipient idea to the present almost complete form of perfection by
stages of growth which will be represented by instruments displayed
in this noble collection. The invention of the telegraph cannot be
claimed by any one, for the simple reason that the very first idea con-
veyed by the notion of electricity and its action at a distance must
have given the first idea of conveying information to a distance.
Electricity, or that form of electricity which is used — namely, voltaic
electricity — dates from the commencement of this century. In the year
1800 Volta developed that instrument that is called the voltaic pile, and
which has been the parent of all our batteries. In the same year, 1800,
Nicholson and Carlyle discovered the decomposition of water by the
aid of a current, and in, less than nine years the combined notion of a
current of electricity and the decomposition of water led to the first
electric telegraph.
Professor Sommering of Gottingen — by means of this little
apparatus here, — which is the original and identical apparatus made
and constructed under his own eyes — by means of thirty-five wires
connected between two places, by means of a series of little points
ELECTRIC TELEGRAPHS. 407
each of which represented either a letter of the alphabet or a numeral^
and by means of this voltaic pile — the identical original instrument —
was able by attaching the ends of two wires to these little brass
spots to cause gases — to be evolved from these two points — hydrogen
from one, oxygen from the other, hydrogen being evolved in greater
quantity ; hydrogen always indicated the first letter sent. Supposing
he wanted to send the word " now :" by putting the hydrogen point to
" n" and the oxygen to " o," he made a quantity of gas appear from the
" n" point and a smaller quantity from the " o" point. And in order
to attract attention he devised the first electric alarum — a little bell
which you see here, which by the evolution of gas caused a ball to
drop and started the mechanism ringing as you see there. Here is
also some of the identical wire used on that occasion. This was in
the year 1809. Very few years afterwards the attention of the Russian
Baron Schilling was attracted to this instrument of Sommering's, and
he developed a form of instrument based, not upon the decomposition
of water, but upon the deflection of the magnetic needle in face of the
current. This is one of the forms of Schilling's telegraph. It was
used in the year 1830; and passing from that we come to the year
1833, when the two great German philosophers, Gauss and Weber, at
Gottingen established between the cabinet of the university and the
observatory, about a mile and a quarter distant, a telegraph, a copy of
which is to be seen in the room downstairs. It is too bulky to bring
up here, but it is well worth a visit as being one of the most valuable
historical instruments downstairs. From these two instruments, about
the year 1836, Mr. William Fothergill Cooke, who was studying at
Heidelberg, heard a lecture delivered on the art of telegraphy. He at
once grasped the idea. He came to England and associated himself
with Sir Charles Wheatstone, and the two together brought out the
first needle instrument used in England. This is the identical instru-
ment brought out on that occasion, and here you will see that there
are five needles suspended in a line. Each of these needles has two
movements — the one to the left, the other to the right ; and when two
of these are deflected their line of convergence always points to a
letter. When, for instance, this last needle is diverging in this direc-
tion and this one in the other, they point to the letter " a," when the
first and the fourth are deflected they point to the letter " b," the first
4o3 SECTION— MECHANICS.
and the third to the letter " e," and so on ; by that means any letter of
the alphabet is instantly indicated to the observer. Now you will ob-
serve that this instrument has five needles and requires five wires, but
very short practice, very small experience, soon showed that the re-
quired letters of the alphabet could be formed by means of four needles
instead of five ; so that we come now to the four-needle telegraph,
which was practically used for the conveyance of messages in this
country up to the year 1844. Here is also an actual original piece of
the wires that were used on that occasion. This was dug up on the
incline between Euston and Camden, and you will see if you examine
it that it contains five copper wires covered with hemp, tarred and
let into wood. This was buried below the ground, and used in con-
nexion with this instrument. That instrument was employed on the
Blackwall Railway, and it happened that two operators at two distant
stations on the Blackwall Railway — brothers — found that by making
certain preconcerted signals on this instrument, instead of using, as
was previously done, one motion to the left and one to the right — by
taking two needles and using two and three motions to the right or
left, they were able to converse between these intermediate stations.
This at once showed to Mr. Cooke that it was possible to reduce the
four wires to two. Accordingly, immediately afterwards this instru-
ment was introduced, which is the original double-needle instrument.
This identical instrument was used at the Slough station on the Great
Western Railway ; and there are many interesting records of the mes-
sages— strange in those days — which were carried by this wire. In
fact this identical instrument has engraved upon its foot-plate a mes-
sage which was sent in the year 1845 tnat l£d to the capture of a cele-
brated murderer, the Quaker Tawell. One curious point connected
with that is this, that neither of these instruments form the letter Q,
so that when the word " Quaker" had to be sent there was a great dif-
ficulty in supplying it, and it was sent " Kwaker." The clerk at the
distant station — Paddington — could not at first conceive what
" Kwaker" meant ; but after a short time the truth occurred to him,
the message was delivered, and the man was captured. Now this, as
you see, is a heavy and cumbrous instrument, which only transmitted
its message at the rate of about five or six messages an hour, a rate of
speed which would at the present day cause all our wires to become
ELECTRIC TELEGRAPHS. 409
congested. Accordingly, the cumbrous form of the double needle was
converted into the lighter and more rapid instrument that we have
here.
This is the last and latest form of the double-needle instruments
used in England. It is still very largely employed on the railways,
but it is rapidly making its disappearance. It was very evident at
once that if it were possible to form the letters of the alphabet by the
combinations of the motions of the needle to the right or left, that it
was quite possible to form such an alphabet by means of one needle —
in fact, there is no doubt that the very first needle telegraph ever in-
vented, that of Schilling, was based upon a combination of the move-
ments of the needle to the right and the left. Here we have the first
form of needle instrument so introduced. We have a single needle
which by its deflections to the right or left would form an alphabet :
one motion to the left, one to the right, the letter " a ;" one to the
right and three to the left, the letter " b," and so on ; by the combina-
tion in that way the letters of the alphabet are formed.
This is a second form of a needle instrument of the same kind, and
this is the form that is used in the present day. These instruments
are very largely employed at some of our smaller post-offices ; and
they have one great merit about them — extreme simplicity and the
avoidance of the necessity of employing skilled clerks. Very little
instruction, very small pay, induce clerks speedily to acquire a know-
ledge of the single needle.
Now, as we progress in telegraphy, speed has become an essential
quality. The first instruments, the four-wire and the double-needle
seen here, were made of galvanometer coils of great depth and magnets
of great length, their form necessarily became sluggish and cumbrous.
The first to make any alteration in that direction was Mr. Holmes,
who succeeded in reducing the six-inch needle to this little diamond-
shaped form, and by the simple reduction of the size the speed of the
instrument was at once increased nearly fourfold. We have by various
alterations and suggestions and additions, arrived now at the form of
needle which I hold in my hand, and with this needle the motions can
be made so rapidly that the eye can scarcely follow them. Now, as
you have perceived, these instruments are simply transitory in their
signals.
4io SECTION— MECHANICS.
Very early in the history of telegraphy, in the year 1837, a year that
was prolific of telegraphic invention, Morse, in America, conceived the
idea of recording the signals sent by the current. His first notion
was to have a style which would make a mark as the paper passed the
needle, and his first signals were of this character, representing the
numerals. He formed a telegraphic dictionary, and by simply accord-
ing to each word a certain number, messages were sent by sending a
series of numbers. The first message ever sent was " 215," " success-
ful ;" "36," "experiment ;" "2," uwith ;" "58," "telegraph ;" and the
first instrument employed registered its signals by a lead pencil.
Then, finding that the lead rapidly wore out, he passed to a common
pen, which he found great difficulty in keeping supplied with ink.
From that he proceeded to the common carbonic paper, and lastly he
arrived at a common Morse embosser, where the marks are recorded
by the indentation of dots and dashes upon paper. We have here a
form of the Morse embosser that was used generally in England up
to the year 1853, and you will find that upon this piece of paper are
recorded in raised characters the dots and dashes that form the
alphabet. Now, in the first place, the pressure on the paper, and the
form of these characters upon the paper, means a certain amount of
work done by the current. It required pressure ; it required force to
make these impressions ; and, more than that, the constant reading of
a white strip of paper, whether merely by a shade or ridge, or by the
marks made, became very tedious to the eye, and it was at once
apparent that any means which would overcome this difficulty would
be a great improvement. Accordingly, an Austrian of the name of
John, in the year 1854, produced this instrument that we see here,
recording the marks by permanent lines of ink. This very speedily —
as soon, in fact, as it reached the prolific house of Siemens — received
that finishing touch which genius and skill always impart to works of
this class, and we soon had produced the instrument you see here,
known all over the world as Siemen's Direct Writing Morse Inker.
Here you will find the words recorded in permanent ink upon a strip
of paper.
Another Recorder is also on the table — Bains's Chemical Recorder.
It differs from the others in recording its signals by the same power
which electricity exented in Sommering's— that is, by the decomposi-
ELECTRIC TELEGRAPHS. 411
tion of chemical materials, and so by decomposing the chemical material
in which the paper is steeped, it recorded in a bright colour marks upon
the paper. It has a special merit of its own, which in some respects
renders it superior to any other form of instrument, and that is, that it
is quite independent of magnetism or electro-magnetism. An electro-
magnet always means certain force expended, certain time consumed —
what we call magnetic inertia ; and we find where speed is essential a
considerable advantage is to be found by the use of Bains's Chemical
Recorder, and so an instrument which had a fitful existence between
1853, '54 and '56, is now coming again into use, and probably, in
England at least, will receive very general acceptance.
Now in all these instruments you will see we require skilled labour.
A clerk who has to send the Morse alphabet of dots and dashes has to
spend many months in acquiring the art of sending by his hand those
intervals of time which require to be recorded. But it very early
appeared that advantage would accrue if we could produce an instru-
ment which would indicate directly before the eye of the receiver the
simple letters of the alphabet, and in the year 1816 Francis Ronalds
designed an instrument which was never tried except in his own
house. That was an A B C instrument. In 1841, when telegraphs
had become a matter of fact, Cooke and Wheatstone directed their
thoughts to the production of an A B C instrument. We have here
the original instruments made at that period. Here is one of the first
dial instruments. It contains a dial upon which the letters of the
alphabet were once depicted. Age has gradually removed them, so
that even an opera-glass can scarcely read them. Now here you have
this dial with the letters of the alphabet, and here you have an indi-
cator that rotates and stops or hesitates at every letter that it wants
to indicate. Here we have the apparatus that was used to send these
letters. This instrument itself is not quite complete ; the outer case
has disappeared, but there was at the top an index or fiducial spot
which always brought the hand up as it were, so that when you
wanted to send the letter '• K," for instance, " K" would be brought
there, and so with any other letter. We have here two dials of the
same character, but in one we have a little opening through which
the letters appear ; the brass window, as it were, has disappeared
from it, but the letter to be indicated was simply shown in front of
412 SECTION— MECHANICS.
this window. The other is merely an index as in the first instance.
This ABC instrument was also very largely used ; it was the first
form of instrument that was used by Messrs. Siemens in Prussia
in the year 1846. Here is one of the identical instruments that were
very largely employed in that country, and they were only after
great difficulty and opposition replaced by the Morse apparatus ;
but these two forms, in England under the hands of Sir Charles
Wheatstone and in Prussia under the hands of Mr. Siemens, have
been so changed and altered and improved and shaped that probably
a more exquisite instrument can scarcely be conceived than the simple
ABC apparatus of the present day. This is the simplest form of
Wheatstone's ABC. It is so accurate in its working and so simple,
that I have known a case at a post-office where an old lady over
seventy acquired the art of working this instrument with an hour's
practice, and the very next day the office was open to the public, the
messages were sent — that is now six years ago — and from that day to
this I have not heard a complaint from that office. Children work it,
private people work it, and it has really become one of the most
valuable instruments for telegraphic purposes. It is rather slow in
its operation, so that for the ordinary commercial requirements of the
country it is not adapted. The idea of an A B C instrument which
indicates the letters of the alphabet to the eye very speedily led to the
conception of an instrument which should permanently record the
letters of the alphabet upon paper — in fact, that it should print from
ordinary type the messages that were sent. The first recorded form
of type instrument was made by Mr. Vail in America ; and it is a
matter of great regret, as far as this collection is concerned, that the
Exhibition at Philadelphia should occur at this particular time, for
there is no doubt that in America they have many exceedingly inte_
resting historical apparatuses that would have added considerably to
the interest of this Exhibition. Amongst the rest, this original type
printer, which did not take root in England until the year 1841, when
Sir Charles Wheatstone produced this type printing instrument that
you see there. It was not successful. It is very pretty as a philo-
sophical toy, but as a practical instrument it never acted, and after
having passed through the mill in every electrician's studio in England,
on the continent of Europe, and in America, the instrument which has
ELECTRIC TELEGRAPHS. 413
really at last proved itself to be the survival of the fittest, is the type-
printing instrument we have here, viz., that of Hughes. There is also
an exceedingly beautiful type-printing instrument by Mr. Siemens
which is to be seen at work downstairs. This is a type-printing
instrument which has been sent over by a French house, and has
evidently been sent in such a form as to prevent the possibility of
any foreign fingers interfering with it. We have tried to get it in
order for this meeting, but unfortunately have failed. However, you
will find on examining it, we have a type-wheel on which the letters
of the alphabet are raised, and we find as these keys are depressed
the letters are printed in bold, unmistakable Roman type on strips of
paper.
Now the next system to which I shall call your attention is one de-
pendent upon quite a different organ of the body, and that is the
acoustic system of telegraphy ; it appeals to the understanding, not
through the eye, but through the ear. Now an alphabet of the Morse
type is based, as I told you, on dots and dashes. We can make sounds
to represent these dots and dashes. We can have a short sound or a
long sound. I am not quite sure that I can make it heard through the
whole room, but we will try and make short sounds or long sounds. The
letter " e," which is that most frequently used in the English language,
can be represented b'y a short sound. The letter " t," which is also
very frequently used, by a long sound. The letter " b" can be pro-
duced by one long and three short dots, and so on throughout the whole
alphabet. Well, those dots and dashes can also be indicated by bells.
For instance, we have here two bells which give out strokes, of different
tones, and based upon that was constructed one of the earlier telegraphs
suggested by Steinheil. These two little bells that are used are really
made to represent Steinheil's Bell Telegraph, and here is one of his
coils. The deflexion of the needle simply caused a little hammer to
fly out and strike the bell, but in this instrument which we have here
this system has been carried to a more practical issue by Sir Charles
Bright and his brother, Mr. Edward Bright. This is called the Bell
Telegraph. It was exclusively used in England by the Magnetic
Telegraph Company, and is now very largely employed in different
parts of England by the Post Office. It is an instrument exceedingly
rapid in its action, and enables clerks to read with great freedom
4i4 SECTION— MECHANICS.
because their whole attention is devoted to their paper and nothing
•else. The defect of that instrument is probably its complication, and
it requires skilled clerks to work it.
The form of Sounder that has been introduced in America is this
little instrument, which we call the " Pony Sounder." This is sim-
plicity itself. It simply consists of a coil, through which the currents
flow and an armature which is attracted. There is nothing here to
get out of order, and the rate of rapidity with which the instrument
is read is something wonderful at times. The rate at which these
instruments are worked depends upon the skill of the clerk in
manipulating his key. Here is the key that is commonly used. The
clerk simply depresses that key, and the rate at which he depresses
that key is practically the rate at which the instrument records and
the rate at which the clerk receives. But human nature will tire. A
clerk who commences to send in the morning at the rate of forty words
a minute, in an hour or two descends to thirty-five words a minute,
and then gets to thirty words a minute, and in the course of the day
his rate is still further lowered. It therefore speedily struck our
electricians that an advantage would be obtained if we could replace
the skilled labour of the clerk by some automatic apparatus which
would send his currents for him — indeed, the very earliest form of
telegraphy suggested by Morse in America was an automatic sender.
His letters, his numbers, were formed by pieces of type, and these
were simply placed in a stick and passed through a machine which
sent the currents which made the record at the distant stations.
In the year 1846, Bains conceived the idea of punching these
dots and dashes in broad paper, and by passing this strip underneath a
spring he thought that he could send to the distant station the signals
and have them properly recorded — in fact, the experiment was perfectly
successful, and the speed with which messages were sent was some-
thing astonishing. In an office of short circuit we were able to attain
a speed of about 400 words a minute, and when I mention that the
fastest speed previously attained was from thirty to forty words a
minute, you will easily understand that the advantage was very con-
siderable. But the conditions of our lines in those days, the character
of the instruments themselves was such, that while we were able to get
this high speed on short circuits in our own rooms, the instrument
ELECTRIC TELEGRAPHS. 415
totally failed to obtain the same results on our open lines. The result
was that punching, as it was called, or automatic sending fell into
disuse really because it was not wanted. The instruments we then
used were able to transmit messages as fast as the public favoured us
with them. The result was that the same desire for fast telegraphy
did not exist in the years 1846 and 1848 as it does in the present day.
In the present day telegrams have flown in so fast and so thick that
the ingenuity of every telegraph engineer is devoted to increasing the
capacity of his wires to transmit messages. Forty words a minute,
fifty words a minute, sixty words a minute, is not enough. We have
to go up to 100, 150, and even to 200 words a minute, and yet the cry
is still for more. At the present time the instruments we have prac-
tically in use dc> not exceed 130 words a minute. We have now in
work Wheatstone's automatic apparatus, where the messages are
punched by means of a little apparatus that is on the table. Clerks are
able to punch messages at such a rate that the ear can hardly distin-
guish differences in the sound, and by such operations these papers
are stripped. These punched strips are placed in an instrument, and
record the letters of the alphabet upon these strips.
Now there are other forms of automatic senders, one of which I
should have liked very much to have shown you. It is in operation
downstairs, and it is also the production of Mr. Siemens. There are
a series of keys like the keys of an accordion, and the clerk, by
moving these keys, is able to raise a species of type which sends the
currents in their proper order. The rate at which this instrument
works is not so rapid, but for many purposes — accurate sending,
duplex working, and so on — it is one which is very likely to receive
considerable attention.
There is another form of instrument to which I must allude, but
which I am unable to exhibit to you, and that is an instrument called
Thomson's Recorder, which is used in connexion with submarine
cables. In working a submarine cable we incur difficulties that are
not met with on open lines — the currents flow more slowly, more
sluggishly, and we are also obliged to use currents of considerably
less intensity, less strength, than upon land lines. Consequently the
desire of the telegraph engineer is to form an instrument which shall
move with the slightest possible current and with the greatest possible
416 SECTION— MECHANICS.
velocity. Now, Sir William Thomson has devised two or three forms
of instruments, one of which is simply a needle instrument ; but,
instead of having the needle a mass of matter which moves, the needle
is a mere spot of light, or rather the indicator is a spot of light, the
needle proper being an excessively minute piece of steel so light that,
if I remember rightly, it only weighs about a quarter of a grain.
From this mirror instrument he has proceeded to what he calls his
Recorder, and there he records upon a strip of paper a thin line
of ink, not made by the depression of a wheel or a pen, or any
apparatus upon the paper, but simply by a small thin film of ink that
is spurted upon it by electrical repulsion. There is no instrument
more beautiful in construction than this of Sir William Thomson's,
and I am very sorry it is not here for you to see. Probably in a week
or two one will be fitted up in the collection, and it will be well worth
your inspection.
Now I have rapidly glanced through the different systems of
apparatus in use in England and generally throughout the world. In
England we really have at the present moment five systems in use,
each of which may be called, as I said at first, an example of the
survival of the fittest. We have the ABC, which is used at all small
post-offices where skilled labour, from its expense, cannot be employed
— that is, where messages are few and far between ; sometimes where
they only reach one a week, others one a day, and so on, where busi-
ness is slack. It is also used very largely between the merchant and
his office, between the hall and the stable, between the counting-house
and the drawing-room, and for various purposes of that kind. As
business increases and the offices become more important, so we in-
troduce the single-needle instrument, which has this especial merit
that it does not require skilled labour. It also has the advantage that
a number of instruments can be connected together on the same wire.
Sometimes on railways from twelve to fifteen instruments are formed
on one circuit. On post-office circuits eight and sometimes ten have
been so applied. As the business of the station increases, some
proceed from the single-needle to the Morse system, and in the Morse
system I include the Sounder. The Morse system is really and truly
a relic of the past. Its doom has been sealed so far as England is
concerned, and we are replacing the Morse instrument by the more
ELECTRIC TELEGRAPHS. 417
rapid little Pony Sounder. It is rather a remarkable fact that in this
instrument, which contains no record whatever of the message which
has been sent, we have an instrument which is the most accurate that
has ever been produced. The reason for that is simply this :
The sending of the clerk i^ guided by his ear. If his ear has been
trained to read the dots and dashes properly upon this instrument,
his hand, which follows his ear, must record the messages he is
receiving accurately, and experience proves that to be perfectly true.
A short time ago I was visiting a station where some eighteen months
since the Morse apparatus had been replaced by the Sounder, and the
postmaster told me that although that instrument had been at work
eighteen months, not one single case of error had been brought to his
notice, whereas, previous to that, scarcely a week elapsed without some
mistake having been made in a message. Another great advantage of
it is the rapidity, for a clerk having his own attention confined to
reading, is in just the same position as you are to me at the present
moment. I might be for instance in Southampton, and you here,
and yet this little instrument, if your ears were skilled, would have
conveyed to you almost as fast as I speak the words I am uttering.
Now as business increases, as circuits become crowded, as messages
increase, so the necessity far rapidity arises, and then we fly to
Wheatstone's automatic apparatus, which records messages in many
instances as fast as they come in ; but even then between very busy
places — between London and Glasgow, for instance — that apparatus is
not sufficient, and we are now, by means of Bains's Chemical Recorder,
still further increasing the rapidity with which the work is done ; so
that we hope to be able to keep ahead of the work by improving the
rate at which the instruments record.
Now the question naturally arises when considering these various
forms of instruments, to whom are we to ascribe the chief merit of a
successful and practical invention ? Is it to the philosopher who sug-
gests in a misty future some -visionary project? Is it to the engineer
who renders the abstract concrete — the dream a reality ? Is it to the
financier or the commercial man who risks his fortune on his foresight,
and on his estimate of the value of the philosophical idea and of the
engineer's skill and practice ? In all these applications of science to
practice these three characters are involved. Take, for instance, tele-
DD
4i8 SECTION— MECHANICS.
graphy. We have here the dream of Sommering, of Schilling ; we
have the genius of Wheatstone and of Steinheil. On the other hand,
Ave have the practical enterprise of Cooke, of Morse, and of Siemens.
We have again the financial foresight of men who are little known —
Ricardo, Bidder, Weber, of the great railway companies of this
country, of the Government, and of the Governments of Europe — all
of whom have lent their assistance in establishing telegraphy on its
present great basis. Take again one of the greatest branches of tele-
graphy— submarine telegraphy. See how our coasts are joined to the
Continent, how our country is joined to all parts of the world, enabling
us to waft a sigh from Indus to the Pole, or put a girdle round the
earth in far less time than forty minutes ! Here we have a specimen
of the submarine cable which connected our shores with France and
Holland. The great genius Wheatstone, as early as the year 1839, I
think, formed the idea of a cable connecting England with France.
The genius of Faraday and the skill of Siemens succeeded in making
submarine cables practicable ; but it was the foresight of Crampton,
of Carmichael, and others who succeeded in rendering this project
successful ; so that we see in all branches of telegraphy the philo-
sopher, the engineer, and the commercial man must take their fair
share of credit.
Time will not allow me to pursue this matter further. There
are many points I have omitted. I have been unable to say
anything to you of relays and translators which enable us to
speak to distant places ; for instance, every day we hold incessant
communication with India by means of translators. We have that
beautiful system of time apparatus downstairs which transmits time
to all parts of the United Kingdom at one o'clock every day,
and we have various forms of apparatus used for signalling upon
our railways ; and before I conclude, I will simply ask this question,
which probably has suggested itself to many minds :— If the past
shows so much indication of progress, is that progress still in force ?
Has perfection been reached ? I am quite sure it has not. We are
still in the infancy of telegraphy. Scarcely a day passes by without
some improvement. Some defect shows itself requiring a remedy.
Some improvement is suggested increasing speed, and the condition of
our lines, the condition of our apparatus, and the various processes by
ELECTRIC TELEGRAPHY. 419
which messages are sent and messages are prepared are daily receiving
improvement and accession ; and you may depend upon it that if the
direction of our telegraphists is maintained as it is at the present
moment, if it is succoured by such exhibitions as this, we may expect
in a very short time not only to produce greater speed in telegraphy,
but what the public want a great deal more — we shall be able to
introduce cheaper telegraphy.
The PRESIDENT : Ladies and gentlemen — In rising to propose a
vote of thanks to Mr. Preece for his very lucid and satisfactory ex-
planation of the progress of telegraphy, I can but bear testimony to
the great difficulty with which the subject is surrounded. We have
seen that telegraphy dates from a comparatively short time ago, but
that its progress has been very rapid, involving researches in science
as well as the practical work of the engineer to an extent which is
perhaps unrivalled by the development of any other invention. The
Note as to the origin of Submarine Telegraphy.
Submarine telegraphy in 1851 was deemed by most engineers and the public to be
visionary, if not impracticable.
Its extension over the whole world since its first practical introduction in 1851 has been
immense, and the advantages to the world at large incalculable. It was established in the
following manner : —
Various propositions were from time to time put forth to effect the object, but few people
were prepared to take the risk until a Company was formed having most influential men on
the direction, who advertised in the usual manner for subscriptions. Such, however, was the
want of confidence felt in the scheme, that only about two per cent, of the necessary capital
•was subscribed, and this money was consequently returned to the applicants. Notwith-
standing this apathy of the public, some of the directors and their friends did not cease to
entertain a full conviction of its possibility ; and they subsequently consulted Mr. T. R.
Crampton, C.E., on the subject, and offered to assist towards providing the funds if he felt
sufficiently confident of ultimate success. Mr. Crampton undertook the entire charge and
responsibility of the form, construction, and laying of the cable ; also took upon himself
rather more than one-half the pecuniary risk, the other half of the money being found by
Lord de Mauley, Sir James Carmichael, Bart., Messrs. Davies, Son, and Campbell (the
Solicitors of the Company), t'ie Hon. Frederick W. Cadogan, and Mr. Haddow. The
calle.was in the same year (1851) successfully laid by Mr. Crampton between Dover and
Calais.
The great risk the parties ran can be appreciated from the fact that three successive
attempts to establish submarine cables between England and Ireland by other paities
occurred soon afterwards, and all failed,
The above-named gentlemen were also instrumental in laying the next successful cable
between Dover and Ostend, which was constructed in a similar manner to the original one.
No great improvement has yet been effected in the form and mode of construction of heavy
cables, thus proving satisfactorily that the first type of submarine cable laid upwards of
twenty- five years ago is practically right in principle.
420 SECTION— MECHANICS.
subjects here touched upon are very various, and it would be im-
possible to do full justice to all their branches. For instance, sub-
marine telegraphy has been perhaps rather slightly touched upon by
Mr. Preece, though it is in itself a very large and important branch of
the whole. I am quite sure you will join me in a vote of thanks to
Mr. Preece for his very able paper.
The next paper on our list, Mr. Henrici's, will not be brought
forward to-day, and therefore there is a short time for discussion if
any one wishes to continue the subject.
If not, I have, in closing the meeting, to close this section of the
Conference. We have had before us important communications on all
the leading branches of applied science, and I think that we may con-
gratulate ourselves upon the manner in which these subjects have been
brought before us, and have been illustrated by the models from the
collection downstairs, a collection which is unrivalled of its kind. The
Conferences will be followed by a series of lectures or explanations of the
exhibits themselves, because it was impossible at these general meetings
to enter into the merits of the particular exhibits, and time not being
sufficient for the purpose. It may be objected that we have not done
justice to many of the most interesting machines which may be found
downstairs, but if we had attempted to discuss the merits of particular
exhibits, we should certainly have failed to give a bird's-eye view, so
to speak, of the riches contained in this exhibition, and by having
obtained this bird's-eye view, we shall be better able to turn our
attention to particular exhibits, and range them amongst the whole.
I myself would have liked to have given an explanation of one or two
apparatus in which I feel particular interest, but for the same reason
I have abstained from doing so. I hope we shall all separate with the
conviction that these discussions have not been without profit.
END OF VOL. L
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