Full text of "The boy's playbook of science : including the various manipulations and arrangements of chemical and philosophical apparatus required for the successful performance of scientific experiments : in illustration of the elementary branches of chemistry and natural philosophy"

No.

Division ...

Received ...187^.

Wheatstone's telephonic concert at the Polytechnic, in which the sounds and vibra-
tions pass inaudible through an intermediate hall, and are reproduced in the lecture-
room unchanged in their qualities and intensities. Frontitpiece.

THE

BOY'S PLAYBOOK OF SCIENCE:

THE

anfo ^rrattgemen; i$

INCLUDING THE

CHEMICAL AND PHILOSOPHICAL APPARATUS REQUIRED

FOR THE SUCCESSFUL PERFORMANCE OF

SCIENTIFIC EXPERIMENTS.

IN ILLUSTRATION OF THE ELEMENTARY BRANCHES OF
CHEMISTRY AND NATURAL PHILOSOPHY.

JOHN HENRY PEPPER,

P.C.S., A. INST. C.E.; LATE PROFESSOR OF CHEMISTRY AT THE ROYAL POLYTECHNIC,

ETC. ETC.
AUTHOR OF "THE PLAYBOOK OF METALS."

NEW EDITION.

. Illustrated foitjj 47

CHIEFLY EXECUTED FROM THE AUTHOR'S SKETCHE S,
BY H. G. HIKE.

LONDON :
GEORGE EOUTLEDGE AND SONS,

THE BROADWAY, LUDGATE.
NEW YOEK: 416, BROOME STREET.

1869.

Z.OND01T.

BDWARDS AND CO., PRINTERS, CSABDOS 8TRBET.
COYBlfT GAEDES.

PROFESSOR LYON PLAYFAIR, C.B., F.R.S,

PROFESSOR OF CHEMISTRY IN THE UNIVERSITY OF
EDINBURGH,

DEAE SIR,

I DEDICATE these pages to your Children, whom I
often had the pleasure of seeing at the Polytechnic during
my direction of that Institution. I do so as a mark of
respect and appreciation of your talent and zeal, and of
your public-spirited advocacy of the Claims of Science in
this great and commercial country.

Without making you responsible in any way for the
shortcomings of this humble work on Elementary Science,,
allow me to subscribe myself,

Dear Sir,

Yours most respectfully,

JOHN HENRY PEPPER.

CONTENTS.

PAGB

INTRODUCTION 1

CHAPTER I.

THE PROPERTIES OF MATTER IMPENETRABILITY 3

CHAPTER II.

CENTRIFUGAL FORCE 17

CHAPTER III.

THE SCIENCE OF ASTRONOMY 19

CHAPTER IV.

CENTRE OF GRAVITY 32

CHAPTER V.

SPECIFIC GRAVITY 48

CHAPTER VI.

ATTRACTION OF COHESION , 59

CHAPTER VII.

ADHESIVE ATTRACTION 67

CHAPTER VIII.

CAPILLARY ATTRACTION , 69

V 1 CONTEXTS.

CHAPTER IX.

PAGB
CRYSTALLIZATION 73

CHAPTER X.

CHEMISTRY 81

CHAPTER XL

CHLORINE, IODINE, BROMINE, .FLUORINE 129

CHAPTER XII.

CARBON, BORON, SILICON, SELENIUM, SULPHUR, PHOSPHORUS . .151

CHAPTER XIII.

FRICTIONAL ELECTRICITY 173

CHAPTER XIV.

VOLTAIC ELECTRICITY 193

CHAPTER XV.

MAGNETISM AND ELECTRO-MAGNETISM 206

CHAPTER XVI.

ELECTRO-MAGNETIC MACHINES 211

CHAPTER XVII.

THE ELECTRIC TELEGRAPH 21S

CHAPTER XVIII.

RUHMKORFF'S, HEARDER'S, AND BENTLEY'S COIL APPARATUS . .230

CHAPTER XIX.

MAGNETO-ELECTRICITY 241

CHAPTER XX.

DIA-MAGNETISM , .247

CONTENTS. <VU

CHAPTER XXI.

PAGB
LIGHT, OPTICS, AND OPTICAL INSTRUMENTS . . 255

CHAPTER XXII.

THE REFRACTION OF LIGHT 298

CHAPTER XXIII.

REFRACTING OPTICAL INSTRUMENTS 303

CHAPTER XXIV.

THE ABSORPTION OF LIGHT 327

CHAPTER XXV.

THE INFLECTION OR DIFFRACTION OF LIGHT 328

CHAPTER XXVI.

THE POLARIZATION OF LIGHT 335

CHAPTER XXVII.

HEAT 352

CHAPTER XXVIII.

THE STEAM-ENGINE 406

CHAPTER XXIX.

THE STEAM-ENGINE continued . 4J

INTRODUCTION.

ALTHOUGH "The South Kensington Museum" now takes the lead, and
surpasses all former scientific institutions by its vastly superior collec-
tion of models and works of art, there will be doubtless many thousand
young people who may remember (it is hoped) with some pleasure the
numerous popular lectures, illustrated with an abundance of interesting
and brilliant experiments, which have been delivered within the walls of
the Royal Polytechnic Institution during the last twenty years.

On many occasions the author has received from his young friends
letters, containing all sorts of inquiries respecting the mode of performing
experiments, and it has frequently occurred that even some years
after a lecture had been discontinued, the youth, now become the young
man, and anxious to impart knowledge to some "home circle" or
country scientific institution, would write a special letter referring to a
particular experiment, and wish to know how it was performed.

The following illustrated pages must be regarded as a series of philo-
sophical experiments detailed in such a manner that any young person
may perform them with the greatest facility. The author has endea-
voured to arrange the manipulations in a methodical, simple, and popular
form, and will indeed be rewarded if these experiments should arouse
dormant talent in any of the rising generation, and lead them on
gradually from the easy reading of the present "Boy's Book," to the
study of the complete and perfect philosophical works of Leopold
Gmelin, Faraday, Brande, Graham, Turner, and Pownes.

Every boy should ride " a hobby-horse" of some kind ; and whilst
play, and plenty of it, must be his daily right in holiday time, he ought
not to forget that the cultivation of some branch of the useful Arts and
Sciences will afford him a delightful and profitable recreation when

2 IXTKODUCTION.

satiated with mere play, or imprisoned by bad weather, or gloomy with
the unamused tediousness of a long winter's evening.

The author recollects with pleasure the half-holidays he used to devote
to Chemistry, with some other King's College lads, and in spite of
terrible pecuniary losses in retorts, bottles, and jars, the most delightful
amusement was enjoyed by all who attended and assisted at these
juvenile philosophical meetings.

It has been well remarked by a clever author, that bees are geome-
tricians. The cells are so constructed as, with the least quantity of
material, to have the largest sized spaces and the least possible interstices.
The mole is a meteorologist. The bird called the nine-killer is an arith-
metician, also the crow, the wild turkey, and some other birds. The
torpedo, the ray, and the electric eel are electricians. The nautilus is
a navigator. Ea raises and lowers his sails, casts and weighs anchor,
and performs nautical feats. Whole tribes of birds are musicians. The
beaver is an architect, builder, and wood-cutter. He cuts down trees
and erects houses and dams. The marmot is a civil engineer. He does
not only build houses, but constructs aqueducts, and drains to keep
them dry. The ant maintains a regular standing army. Wasps are
paper manufacturers. Caterpillars are silk-spinners. The squirrel is a
ferryman. With a chip or a piece of bark for a boat, and his tail for a
sail, he crosses a stream. Dogs, wolves, jackals, and many others, are
hunters. The black bear and heron are fishermen. The ants are day-
labourers. The monkey is & rope dancer. Shall it, then, be said that any
boy possessing the Godlike attributes of Mind and Thought with Free-
will can only eat, drink, sleep, and play, and is therefore lower in the
scale of usefulness than these poor birds, beasts, fishes, and insects ?
No ! no ! Let " Young England" enjoy his manly sports and pastimes,
but let him not forget the mental race he has to run with the educated
of his own and of other nations ; let him nourish the desire for the
acquisition of " scientific knowledge," not as a mere school lesson, but
as a treasure, a useful ally which may some day help him in a greater or
lesser degree to fight " The Battle of Life."

THE

BOY'S PLAYBOOK OF SCIENCE.

CHAPTER I.

THE PROPERTIES OP MATTER IMPENETRABILITY.

IN the present state of our knowledge it seems to be universally agreed,
that we cannot properly commence even popular discussions on astro-
nomy, mechanics, and chemistry, or on the imponderables, heat, light,
electricity, and magnetism, without a definition of the general term
" matter ;" which is an expression applied by philosophers to every
species of substance capable of occupying space, and, therefore, to
everything which can be seen and felt.

The sun, the moon, the earth, and other planets, rocks, earths, metals,
glass, wool, oils, water, alcohol, air, steam, and hosts of things, both
great and small, all solids, liquids and gases, are included under the
comprehensive term matter. Such a numerous and varied collection of
bodies must necessarily have certain qualities, peculiarities, or properties;
and hence we come in the first place to consider " The general powers
or properties of matter." Thus, if we place a block of wood or stone in
any position, we cannot take another substance and put it in the space
filled by the wood or stone, until the latter be removed. Now this is
one of the first and most simple of the properties of matter, and is called
impenetrability, being the property possessed by all solid, liquid, and
gaseous bodies, of filling a space to the exclusion of others until they be
removed, and it admits of many amusing illustrations, both as regards
the proof and modification of the property.

Thus, a block of wood fills a certain space: how is it (if impenetrable)
that we can drive a nail into it ? A few experiments will enable us to
answer this question.

Into a glass (as depicted at fig. 1) filled with spirits of wine, a quantity
of cotton wool many times the bulk of the alcohol may (if the experiment
is carefully performed) be pushed without causing a drop to overflow
the sides of the vessel.

Here we seem to have a direct contradiction of the simple and indis-

BOY'S PLAYBOOK OF SCIENCE.

Fig. 1.

putable truth, that " two things cannot occupy the same space at once."
But let us proceed with our experiments :

We have now a flask full of water,
and taking some very finely-powdered
sugar, it is easy to introduce a not-
able quantity of that substance with-
out increasing the bulk of the water ;
the only precaution necessary, is not
to allow the sugar to fall into the
flask in a mass, but to drop it in
grain by grain, and very slowly, al-
lowing time for the air-bubbles (which
will cling to the particles of sugar)
to pass off, and for the sugar to dis-
solve. Matter, in the experiments
adduced, appears to be penetrable,
and the property of impenetrability
seems only to be a creation of fancy :
reason, however, enables us to say
that the latter is not the case.
A nail may certainly be hammered into wood, but the particles are
thrust aside to allow it to enter. Cotton wool may be placed m spirits
of wine because it is simply greatly extended and bulky matter, which
if compressed, might only occupy the space of the kernel of a nut, and

Fig. 2.

THE PROPERTIES OP MATTER IMPENETRABILITY. 5

if this were dropped into a half-pint measure full of alcohol, the increase
of bulk would not cause the spirit to overflow. The cotton-wool expe-
riment is therefore no contradiction of impenetrability. The experi
ment with the sugar is the most troublesome opponent to our term, and
obliges us to amend and qualify the original definition, and say, that the
ultimate or smallest particles or atoms of bodies only are impenetrable ;
and we may believe they are not in close contact with each other, because
certain bulks of sugar and water occupy more space separately than
when mixed.

If we compare the flask of water to a flask full of marbles, and the
sugar to some rape-seed, it will be evident that we may almost pour
another flask full of the latter amongst the marbles, because they are not
in close contact with each other, but have spaces between them ; and
after pouring in the rape-seed, we might still find room for some fine
sand.

The particles of one body may thus enter into the spaces left between
those of another without? increasing its volume ; and hence, as has been
before stated, " The atoms only of bodies are truly impenetrable."

This spreading, as it were, of matter through matter assumes a very
important function when we come to examine the constitution of the
air we breathe, which is chiefly a mechanical mixture of gases : seventy-
nine parts by volume or measure f of nitrogen gas, twenty-one parts of
oxygen gas, and four parts of carbonic acid vapour in every ten thousand
parts of air having the following relations as to weight :

Specific gravity.

Nitrogen 972

Oxygen 1105

Carbonic acid 1524

It might be expected that these gases would arrange themselves in
our atmosphere in the above order, and if that were the case, we should
have the carbonic-acid gas (a most poisonous one) at the bottom, and
touching the earth, then the oxygen, and, last of all, the nitrogen ; a

BOY S PLAYBOOK OF SCIENCE.

state of things in which oraanizedMfe could not exist. The gases do not,
however, separate : indeed, they seem to act as it were like vacuums to

one another, and " the diffusion of gases" has become a

recognised fact, governed by fixed laws. This fact is

curiously illustrated, as shown in our cut, by filling a

bottle with carbonic acid, and another with hydrogen ;

and having previously fitted corks to the bottles, perfo-

rated so as to admit a tube, place the bottle containing

the carbonic acid on the table, then take the other full

of hydrogen, keeping the mouth downwards, and fit in

the cork and tube : place this finally into the cork of

the carbonic-acid bottle, which may be a little larger than

the other, in order to make the arrangement stand firmer ;

and after leaving them for an hour or so, the carbonic

acid, which is twenty-two times heavier than the hydro-

gen, will ascend to the latter, whilst the hydrogen will

descend to the carbonic acid. The presence of the car-

bonic acid in the hydrogen

bottle is easily proved by

pouring in a wineglassful

of clear lime-water, which

speedily becomes milky,

owing to the production of

carbonate of lime; whilst

the proof of the hydrogen

being present in the car-

bonic acid is established

by absorbing the latter

with a little cream of lime

i.e., slacked lime mixed

to the consistence of cream

with some water and set-

ting fire to the hydrogen

that remains, which burns

quietly with a yellowish

flame if unmixed with air ;

but if air be admitted to

the bottle, the mixture of

air and hydrogen inflames

rapidly, and with some

noise. One of the most

elegant modes of showing
the diffusion of gases is by taking a large
round dry porous cell, such as would be
employe/ in a voltaic battery, and having

Cemented a brass cap With a glass tube di

attached to its open extremity, it may then

be supported by a small tnpod of iron porous ceU and tube in tumbler.

{Carbonic:

Fig. 4.

Fig. 5.
The porous cell.

B. The jar

ips into the tumbler containing

THE PROPEKTIES OF MATTER IMPENETRABILITY. 7

wire, and the end of the glass tube placed in a tumbler containing a
small quantity of water coloured blue with sulphate of indigo, if a
tolerably large jar containing hydrogen is now placed over the porous
cell, bubbles ot gas make their escape at the end of the tube, because
the hydrogen diffuses itself more rapidly into the porous cell than the
air which it already contains passes out. When the jar is removed, the
reverse occurs, hydrogen diffuses out of the porous cell, and the blue
liquid rises in the tube.

This diffusive force prevents the accumulation of the various noxious
gases on the earth, and spreads them rapidly through the great bulk of
the atmosphere surrounding the globe.

Although air and other gases are invisible, they possess the property
of impenetrability, as may be easily proved by various experiments.
Having opened a pair of common bellows, stop up the nozzle securely,
and it is then impossible to shut them ; or, fill a bladder with air by
blowing into it, and tie a string fast round the neck ; you then find that
you cannot, without breaking the bladder, press the sides together.

It is customary to say that a vessel is empty when we have poured out
the water which it contained. Having provided two glass vessels full
of water, place each of them in an empty white pan, to receive the over-

Fig. 6 represents the water overflow-
ing, as the glass, with the orifice closed, Fig. 7. The orange has entered the
is pressed down, proving the impene- glass vessel, and the air having passed
trability of air. from the orifice, no water overflows.

flow, then lay an orange upon the surface of the water of one of them,
and being provided with a cylindrical glass, open at one end, with a
hole in the centre of the closed end, place your finger firmly over the
orifice, and endeavour, by inverting the glass over the orange, and
pressing upon the surface of the water, to make it enter the interior
of the glass cylinder ; the resistance of the air will now cause the water
to overflow into the white pan, whilst the orange will not enter. The

BOY'S PLAYBOOK OF SCIENCE.

orange may now be transferred to the other vessel of wa-ter, and on
removing the finger from the orifice of the cylindrical glass, and in-
verting it as before over the orange, the air will rush out and the orange
and water will enter, whilst there will be no overflow as in the preceding
experiment. The comparison of the two is very striking, and at once
teaches the fact desired.

Whilst the vessels of water are still in use, another pretty experiment
may be made with the metal potassium. First throw a small piece of
the metal on the surface of the water, to show that it takes fire on con-
tact with that fluid; then, having provided a gas-jar, fitted with a cap

Fig. 8. Gas-jar with stop-stock closed,
and potassium in ladle ; air prevents the
entrance of the water.

Fig. 9. Gas-jar; stop-cock open ;
the air passes, the water enters, and
the potassium is inflamed.

and stop-cock, and a little spoon screwed into the bottom of the stop-
cock inside the gas-jar, place another piece of potassium in the little
spoon, and, after closing the stop-cock, push the jar into one of the
vessels of water : as before, the impenetrability of the air prevents the
water flowing up to the potassium ; but, on opening the stop-cock, the
air escapes, the water rushes up, and directly it touches the potassium,
combustion ensues.

^ Having sufficiently indicated the nature and meaning of impenetra-
bility, we may proceed to discuss experimentally three other marked
and special qualities of matter viz., inertia, gravity, and weight.

INERTIA, OR PASSIVENESS.

Inertia is a rjower which (according to Sir Isaac Newton) is implanted
in all matter ot resisting any change from a state of rest. It is sometimes
called vis inertia, and is that property possessed by all matter, of re-
maining at rest till set in motion, and vice versa; and it expresses, in
brief terms, resistance to motion or rest.

A pendulum clock wound up and ready to go, does not commence its
movements, until the inertia of the pendulum is overcome, and motion
imparted to it. On the other hand, when seated in a carriage, should
any obstruction cause the horse to stop suddenly, it is only perhaps by
a violent effort, if at all, that we can resist the onward movement of our

Fig. 10. Tin tray, with glass bottom, full of water; candle placed underneath.

bodies. To illustrate inertia, construct a metal tray, about three feet
long, two feet wide, and two inches deep, with a glass bottom, and
arrange it on a framework supported by legs, like a table, and having
filled it with water, let the room be darkened, and then place under the
tank a lighted candle, at a sufficient distance from the glass to prevent
the heat cracking it. If a piece of calico or paper, stretched on a frame-
work, be now held over the water at an angle of about thirty degrees,
all that occurs on the surface of the water will be rendered visible on
such screen. Attention may now be directed to the quiescence, or the
inertia of the water, while the opposite condition of movement and
formation of the waves may be beautifully shown by touching the sur-
face of the water with the finger ; the miniature waves being depicted
on the screen, and continuing their motion till set at rest by striking
against the sides of the tin tray.

BOYS PLAYBOOK OF SCIENCE.

Fig. 11.

Same tray, with calico screen ; showing the waves as they are produced by
touching the surface of the water with the finger.

Should the above experiment be thought too troublesome or expen-
sive to prepare, inertia may be demonstrated by filling a tea-cup or other
convenient vessel with water, and after moving rapidly with it in any
direction, if we stop suddenly, the rigidity of all parts of the cup we
hold brings them simultaneously to a state of rest ; but the mobility of
the liquid particles allows of their continuing in motion in their original
direction, and the liquid is spilled. Thus, carelessness in handing and
spilling a cup of tea (though not to be recommended) serves to illustrate
an important principle. The inertia of bodies in motion is further and
lamentably illustrated by the accidents caused from the sudden stoppage
of a railway train whilst in rapid motion, when heads and knees come in
contact with frightful results. It is more especially demonstrated by
the earth, the moon, and the other planets continuing their motion for
ever in the absence of any friction or resistance to oppose their onward
progress. It is the friction arising from the roughness of the ground,
the resistance of the air, and the force of the earth's attraction, which
puts a stop to bodies set in motion about the surface of the earth.

GRAVITATION.

Inertia represents a passive force, gravitation, an active condition of
matter ; and this latter may truly be termed a force of attraction, because
it acts between masses at sensible or insensible distances : it is illus-
trated by a stone, unsupported, falling to the ground ; by the stone
pressing with force on the earth, and requiring power to raise it from the
ground : indeed, it is commonly reported that it was by an accident
" an apple falling from a tree" that the great Newton was led to reflect
on the universal law of gravitation, and to pronounce upon it in the
following memorable words :

" Every particle of matter in the universe attracts every other particle
of matter with a force or power directly proportional to the quantity oj
matter in each, and decreasing as the squares of the distances which sepa-
rate the particles increase"

These words may appear very obscure to our juvenile readers ; but
when dissected and examined properly, they clearly define the property
of gravitation. For instance, " every particle attracts every other with
a force proportional to the quantity of matter in
each." This statement was verified some years
back by Maskelyne, who, having sought out and
discovered a steep, precipitous rock in the
Schichallion mountains, in Scotland, suspended
from it a metal weight by a cord, and going to
a convenient distance with a telescope, and ob-
serving the weight, he found that it did not
hang perpendicularly, like an ordinary plumb-
line, but was attracted, or impelled, to the sides
of the rock by some kind of attraction, which, of
course, could be no other than that indicated
by Newton as the attraction of gravitation.

This truly wonderful power of attraction per-
vades all masses; and being, as before stated,
proportional to the quantity of matter, if a man
could be transported to the surface of the sun,
he would become about thirty times heavier : he
would be attracted, or impelled, to the sun with
thirty times more gravitating force than on the
surface of the earth, and would weigh about two
tons. Of course, nursing a baby on the sun's
surface would be a very serious affair with our
ordinary strength ; whilst on some of the smaller

planets, such as Ceres and Pallas, we should pro- line, whilst the line "of the
bably gravitate with a force of a few pounds eight ?..

i i j i 1 1 i coursG, witn some t?xn.c >fT e-

only, and with the same muscular power now ration) the attractive power
possessed, we should quite emulate the exploits f t] ? e mass of "
of those domestic little creatures sometimes d ns " tfromt

Pig. 12. The Schichallion
Bocks. The dotted line and

rock

BOY'S PLAYBOOK OP SCIENCE.

called " the industrious fleas," and our jumping would be something
marvellous.

There is no very good lecture-table experiment that will illustrate
gravitation, although attention may be directed to the fact of a piece of
potassium thrown on the surface of water in a plate generally rushing
to the sides, and, as if attracted, attaching itself with great force to the
substance of the pottery or porcelain ; or, if a model ship, or lump of
wood, be allowed to float at rest in a large tank of water, and a number
of light chips of wood or bits of straw be thrown in, they generally col-
lect and remain around the larger floating mass.

A very good idea, however, may be afforded of the universal action of
gravity maintaining all things in their natural position on the earth by

Fig. is.

A. The centre ball, representing the earth's centre of gravity.

w w w w. Four wires fixed into centre ball, and passing through and secured ir. the
hoop, projecting about one foot from the circumference.

B B B B. Two balls a model ship and toy working on the wires like beads, with vul-
canized India-rubber straps attached to them and the circumference of the hoop.

GRAVITATION.

taking a hoop and arranging in and upon it balls, or a model ship, or
other toy, and wires, as depicted in our diagram.

With this simple apparatus we may illustrate the upward, downward,
and sideway movement of bodies from the earth, and the counteraction
by the force of gravitation of any tendency of matter to fall away from
the globe, which is represented in the model by the india-rubber springs
pulling the balls and toys back again to the circumference of the hoop.

The attraction of gravitation decreases (quoting the remainder of
Newton's definition) as the squares of the distances which separate
the particles increase i.e., it obeys the principle called "inverse pro-
portion" viz., the greater the distance, the less gravitating power ; the
less the distance, the greater the power of gravitation. Gravitation is
like the distribution of light and other radiant forces, and may be thus
illustrated.

Fig. 14. Place a lighted candle, marked A, at a certain distance from No. 1, a board one
foot square ; at double the distance the latter will shadow another board, No. 2, four feet
square ; at three times, No. 3, nine feet square ; at four, No. 4, sixteen feet ; and so on.

To make the comparison between the propagation of light and the
attraction of gravitation, we have only to imagine the candle, a, to
represent the point where the force of gravity exists in the highest
degree of intensity ; suppose it to be the sun the great centre of this
power in pur planetary system. A body, as at No. 1, at any given
distance will be attracted (like iron-filings to a magnet) wiih a certain
force ; at twice the distance, the square of two being four, and by in-
verse proportion, the attraction will be four times ( less; at thrice
the distance, nine times less ; at the fourth distance, sixteen times less ;
and so on. "With the assistance of this law, we may calculate,
roughly, the depth of a well, or a precipice, or a column, by ascer-
taining the time occupied in the fall of a stone or other heavy sub-
stance. A falling body descends about 16 feet in one second, 64 feet
in two seconds, 144 feet in three seconds, 256 feet in four seconds,
400 feet in five seconds, 576 feet in six seconds ; the spaces passed over
being as the squares of the times.

Suppose a stone takes three seconds in falling to the surface of the
_water in a well, then 3 X 3 = 9 x 16 = 144 feet would be a rough
estimate of the depth. The calculation will exceed the truth ia con-
sequence of the stone being retarded in its passage by the resistance of
the air.

BOY'S PLAYBOOK OF SCIENCE.

All bodies gravitate equally to the earth : for instance, if an open box,
sav one foot m length, two inches broad, and two inches deep, be pro-
vided with a nicely-fitted bottom, attached by a hinge, a number of
substances, such as wood, cork, marble, iron, lead, copper, may be
arr:;n^cd in a row ; and directly the hand is withdrawn, tne moveable
flap flies open, and if the manipulation with the disengagement of the
trap-door is good, the whole of the substances are seen to proceed to the
earth in a straight line, as shown in our drawing.

Fig. 15.

Fig. 16.

If a heavy substance, like gold, be greatly extended by hammering
and beating into thin leaves, and then dropped from the hand, the re-
sistance of the air becomes very apparent ; and a gold coin and a piece
of gold-leaf would not reach the earth at the same time if allowed to
fall from any given height. This fact is easily displayed by the assis-
tance of a long glass cylindrical vessel placed on the air-pump, with suit-
able apparatus arranged with little stages to carry the different sub-
stances ; upon two of them may be placed a feather and a gold coin, and
on the third, another gold coin and a piece of gold-leaf.

In arranging the experiment, great care ought to be taken that the
little stages are all nicely cleaned, and free from any oil, grease, or other
matter which might cause the feathers or the cold-leaf to cling to the
stages when they are disengaged, by moving the brass stop round that
works in the cottar of leathers. Sometimes these leathers are oiled, and

GRAVITATION.

in that case, when the vacuum is made, the oil, by the pressure, is

squeezed out, and, passing down, may reach the stages and spoil the

experiment, by causing the feathers and gold-
leal to stick to the brass, producing great dis-
appointment, as the illustration, usually called

the "guinea and feather glass experiment"

takes some time to prepare. The air-pump

being in good order, the long glass is first

greased on the lower welt or edge, and then

placed firmly on the air-pump plate. The top

edge, or welt, may now be greased, and the

gold coins, feathers, and gold-leaf arranged in

the drop-apparatus ; this is carefully placed on

the top of the glass, and firmly squeezed down.

The author has always found a tallow candle,

rolled in a sheet of paper (so as to leave about

half the candle exposed), the best grease to

smear the glass
with for air-
pump experi-
ments; if the

weather is cold, Fig. 17.

the caudle may

be placed for a few minutes before an
ordinary fire to soften the tallow. Po-
matum answers perfectly well when the
surfaces of glass and brass are all nicely
ground; but as air-pumps and glasses
by use get scratched and rubbed, the
tallow seems to fill up better all ordi-
nary channels by which air may enter
to spoil a vacuum.

The apparatus being now arranged,
the air is pumped out ; and here, again,
care must be taken not to shake the
gold off the stages. When a proper
vacuum has been obtained, which will
be shown by the pump-gauge, the stop
is withdrawn from one of the stages,
and the gold and feather are seen to
fall simultaneously to the air-pump

Elate. Another stage, with the gold-
;af and coin, may now be detached;
both showing distinctly, that when the
resistance of the air is withdrawn, all
bodies, whether called light or heavy,
gravitate equally to the earth. Then,
Fig. is. the screw at the bottom of the pump-

16 BOY'S PLAYBOOK OF SCIENCE.

barrels being opened, attention may be directed to the whizzing noise
the air makes on entering the vacuum, and when the air is once more
restored to the long glass vessel, the last stage may be allowed to fall ;
and now, the gold coin reaches the pump-plate first, and the feather,
lingering behind, loses (as it were) the race, and touches the plate after
the gold coin ; thus demonstrating clearly the resistance of the air to
falling bodies.

Another, and perhaps less troublesome, mode of showing the same fact,
is to use a long glass tube closed at each end with brass caps cemented
on. One cap should have the largest possible aperture closed by a
brass screw, and the other may fit a small hand-pump.

If a piece of gold and a small feather are placed in the tube, it may
be shown that the former reaches the bottom of the tube first, whilst it
is full of air, and when the air is withdrawn by means of the pump, and
the tube again inverted, both the gold and the feather fall in the same
time.

Fig. 19. A B. Glass tube containing a piece of gold and a feather, which are placed in at
the large aperture A. c. Small hand-pump.

For this reason, all attempts to measure heights or depths by observing
the time occupied by a falling body in reaching the earth must be in-
correct, and can only be rough approximations. An experiment tried at
St. Paul's Cathedral, with a stone, which was allowed to fall from the
cupola, indicated the time occupied in the descent to be four and a half
seconds : now, if we square this time, and multiply by 16, a height of
324 feet is denoted ; whereas the actual height is only 272 feet, and the
difference of 52 fee.t shows how the stone was retarded in its passage
through the air; for, had there been no obstacle, it would have reached
the ground in 4^ths seconds.

The force of gravitation is further demonstrated by the action of the
sun and moon raising the waters of the ocean, and producing the tides ;
and also by the earth and moon, and other planets and satellites, being
prevented from flying from their natural paths or orbits around the sun.
It is also very clearly proved that there must be some kind of attractive
force resident in the earth, or else all moveable things, the water, the
air, the living and dead matters, would fly away from
the surface of the earth in obedience to what is called
" centrifugal force." Our earth is twenty-four hours
in performing one rotation on its axis, which is an ima-
ginary line drawn from pole to pole, and represented
by the wire round which we cause a sphere to rotate.
All objects, therefore, on the earth are moving with
the planet at an enormous velocity ; and this movement
Fig. 20. is called the earth's diurnal, or daily rotation. Now,

CENTEIFUGAL FORCE.

it will be remembered, that mud or other fluid matter flies off, and is
not retained by the circumference of a wheel in motion : when a mop is
trundled, or a dog or sheep, after exposure to rain, shake themselves,
the water is thrown off by what is called centrifugal force (centrum, a
centre, fogio, to fly from).

CHAPTER II.

CENTRIFUGAL FORCE.

THAT power which drives a revolving body from a centre, and it
may be illustrated by turning a closed parasol, or umbrella, rapidly-
round on its centre, the stick being the axis the ribs fly out, and if
there is much friction in the parts, the illustration is more certain by
attaching a bullet to the end of each rib, as shown in our drawing.

Fig. 23.

Fig. 21.

The same fact may be illustrated by a square mahogany rod, say one
inch square and three feet long, with two flaps eighteen inches in length,
hanging bv hinges, and parallel to the sides of the centre rod, which
immediately fly out on the rotation of the long centre piece.

The toy called the centrifugal railway is also a very pretty illustration
of the same fact. A glass of water, or a coin, may be placed in the
little carriage, and although it must be twice hanging perpendicular in a
line with tne earth, the carriage does not tumble away from its ap-
pointed track, and the centrifugal force binds it firmly to tne interior of
the circle round which it revolves.

BOY'S PLAYBOOK OF SCIENCE.

Fig. 23.

Another striking and very simple illustration is to suspend a hemi-
spherical cup by three cords, and having twisted them, by turning round
the cup, it may be filled with water, and directly the hand is withdrawn,
the torsion of the cord causes the cup to rotate, and the water describes
a circle on the floor, flying off at a tangent from the cup, as may be
noticed in the accompanying cut.

Fig. 24

A hoop when trundled would tumble on its side if the force ot gravi-
tation was not overcome by the centrifugal force which imparts to it a
motion in the direction of a tangent (tango, to touch) to a circle. The
same principle applies to the spinning-top^ this toy cannot be made to
stand upon its point until set in rapid motion.

Returning again to the subject of gravitation, we may now consider
it in relation to other and more magnificent examples which we dis-
cover by studying the science of astronomy.

19
CHAPTER III.

THE SCIENCE OF ASTKONOMY.

IN a work of this kind, professedly devoted to a very brief and popular
view of the different scientific subjects, much cannot be said on any
special branch of science ; it will be better, therefore, to take up one
subject in astronomy, and by discussing it in a simple manner, our young
friends may be stimulated to learn more of those glorious truths which
are to be found in the published works of many eminent astronomers,
and especially in that of Mr. Hind, called "The Illustrated London
Astronomy." One of the most interesting subjects is the phenomenon
of the eclipse of the sun; and as 1858 is likely to be long remembered
for its " annular eclipse," we shall devote some pages and illustrations
to this subject.

Eclipses of the sun are of three kinds partial, annular, and total.
Many persons have probably seen large partial eclipses of the sun, and
may possibly suppose that a total eclipse is merely an intensified form of
a partial one ; but astronomers assert that no degree of partial eclipse,
even when the very smallest portion of the sun remains visible, gives
the slightest idea of a total one, either in the solemnity and overpower-
ing influence of the spectacle, or the curious appearances which accom-
pany it.

The late Mr. Baily said of an eclipse (usually called that of Thales),
which caused the suspension of a battle between the Lydians and Medes,
that only a total eclipse could have produced the effect ascribed to it.
Even educated astronomers, when viewing with the naked eye the sun
nearly obscured by the moon in an annular eclipse, could not tell that
any part of the sun was hidden, and this was remarkably verified in the
annular eclipse of the 15th March of this year.

During the continuance of a total eclipse of the sun, we are permitted
a hasty glance at some of those secrets of Nature which are not revealed
at any other time glories that hold in tremulous amazement even
veteran explorers of the heavens and its starry worlds.

The general meaning of an eclipse may be shown very nicely by light-
ing a common oil, or oxy-hydrogen lantern in a darkened room, and
throwing the rays which proceed from it on a three-feet globe. The
lantern may be called the sun, and, of course, it is understood that cor-
rect comparative sizes are not attempted in this arrangement ; if it were
so, the globe representing the earth would have to be a mere speck, for
if we make the model of the sun in proportion to a three-feet globe, no
ordinary lecture hall would contain it. This being premised, attention
is directed to the lantern, which, like the sun, is self-luminous, and is
giving out its own rays ; these fall upon the globe we have designated
the earth, and illuminate one -half, whilst the other is shrouded in dark-
ness, reminding us of the opacity of the earth, and teaching, in a familiar

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^.-"-"A ? .". "-.-:. 1 - ^.^-l..":" ? ' 5 --' ' r "

T-:

-J?-.l*

to he

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BOY'S PLAYBOOK OF SCIENCE.

With respect to' an annular eclipse, it must be remembered, that the
'paths of all bodies revolving round others are elliptical ; i.e., they take
place in the form of an ellipse, which is a figure easily demonstrated ;
and is, in fact, one of the conic sections.

If a slice be taken off a cone, parallel with the base, we have a circle
thus

Fig. 29.

If it be cut obliquely, or slanting, we see at once the figure spoken of,
and have the ellipse as shown in this picture.

Fig. 30.

Now, the ellipse has two points within it, called " the foci," and these
are easily indicated by drawing an ellipse on a diagram-board, in which
two nails have been placedina straight line, and about twelve inches apart.
Having tied a string so as to make a loop, or endless cord, a circle
may first be drawn by putting the cord round one of the nails, and
holding a piece of chalk in the loop of the string, it may be extended
to its full distance, and a circle described ; here a figure is produced
round one point, and to show the difference between a circle and an
ellipse, the endless cord is now placed on the two nails, and the chalk
being carried round inside the string, no longer produces the circle, but
that familiar form called the oval. As a gardener would say, an oval
has been struck ; and the two points round which it has been described,

THE SCIENCE OP ASTRONOMY.

Fig. 31.

are called fheftci. This explanation enables us to understand the next
diagram, showing the motion of the earth round the sun ; the latter
being placed in one of the foci of a very moderate ellipse, and the
various points of the earth's orbit designated by the little round globes
marked A, B, c, D, where it is evident that the earth is nearer to the sun
at B than at D. In this diagram the ellipse is exaggerated, as it ought,
in fact, to be very nearly a circle.

Bf)l-

Fig. 32.

We are about three millions of miles nearer to the sun in the winter
than we are in the summer ; but from the more oblique or slanting
direction of the rays of the sun during the winter season, we do not
derive any increased heat from the greater proximity. The sun, there-
fore, apparently varies in size ; but this seeming difference is so trifling
that it is of no importance in the discussion : and here we may ask, why

BOY'S PLAYBOOK OF SCIENCE.

does the earth move round the sun ? Because it is impelled by two
forces, one of which has already been fully explained, and is called the
centrifugal power, and the other, although termed the centripetal force,
is only another name for the " attraction of gravitation."

cr"

Fig. 33.

To show their mutual relations, let us suppose that, at the creation of
the universe, the earth, marked A, was hurled from the hand of its
Maker ; according to the law of inertia, it would continue in a straight
line, A c, for ever through space, provided it met with no resistance or
obstruction. Let us now suppose the earth to have arrived at the
point B, and to come within the sphere of the attraction of the sun s ;

Fig. 34.

THE SCIENCE OF ASTRONOMY.

here we have at once contending forces acting at right angles to eact
other ; either the earth must continue in its original direction, A c, or
fall gradually to the sun. But, mark the beauty and harmony of the
arrangement : like a billiard-ball, struck with equal force at two points
at right angles to each other, it takes the mean between the two, or
what is termed the diagonal of the parallelogram (as shown in our
drawing of a billiard-table), and passes in the direction of the curved
line, B D ; having reached D, it is again ready to fly off at a tangent ;
the centrifugal force would carry it to
E, but again the gravitating force con-
trols the centripetal, and the earth
pursues its elliptical path, or orbit, till
the Almighty Author who bade it move
shall please to reverse the command.

The mutual relations of the centri-
petal and centrifugal forces may be
illustrated by suspending a tin cylin-
drical vessel by two strings, and
having filled it with water, the vessel
may be swung round without spilling
a single drop ; of course, the movement
must be commenced carefully, by mak-
ing it oscillate like a pendulum.

The cord which binds it to the finger
may be compared to the centripetal
force, whilst the centrifugal power is
illustrated by the water pressing against the sides and remaining in the
vessel. Upon the like principles the moon revolves about the earth,

but her orbit is more ellip-
tical than that of the earth
around the sun ; and it is
evident from our diagram
that the moon is much fur-
ther from the earth at A
than at B. As a natural
consequence, the moon ap-
pears sometimes a little
larger and sometimes
smaller than the sun ; the
apparent mean diameter of
the latter being thirty-two
minutes, whilst the moon's

Fig. 36. apparent diameter varies

from twenty-nine and a

half to thirty-three and a half minutes. Now, if the moon passes exactly
between us and the sun when she is apparently largest, then a total eclipse
takes place ; whereas, if she glides between the sun and ourselves when
smallest i.e., when furthest off from the earth then she is not suffi-

Fig. 35.

26 BOY'S PLAYBOOK OF SCIENCE.

ciently large to cover the sun entirely, but a ring of sunlight remains
visible around her, and what is called an annular eclipse of the sun
occurs. This fact may be shown in an effective manner by placing the
oxy-hydrogen lantern before a sheet, or other white surface, and throw-

Fig. 37.

ing a bright circle of light upon it, which may be called the sun ; then,
if a round disc of wood be passed between the lantern and the sheet, at
a certain distance from the nozzle of the lantern, all the light is cut off,
the circle of light is no longer apparent, and we have a resemblance to
a total eclipse.

By taking the round disc of wood further from the lantern, and re-
peating the experiment, it will be found that the whole circle of light
is not obscured, but a ring of light appears around the dark centre, cor-
responding with the phenomenon called the annular (ring-shaped)
eclipse.

If a bullet be placed very near to one eye whilst the other remains
closed, a large target may be wholly shut out from vision; but if the
bullet be adjusted at a greater distance from the eve, then the centre
only will be obscured, and the outer edge or ring of the target remains
visible.

When the advancing edge, or first limb, as it is termed, of the moon
approaches very near to the second limb of the sun, the two are joined
together for a time by alternations of black and white points, called
Bailv's beads.

This phenomenon is supposed to be caused partly by the uneven and
mountainous edge of the moon, and partly by that inevitable fault of
telescopes, and of the nervous system of the eye, which tends to enlarge
the images of luminous objects, producing what is called irradiation. It
is exceedingly interesting to know that, although the clouds obscured
the annular eclipse of 1858, in many parts of England, we are yet

THE SCIENCE OF ASTRONOMY.

Fig. 38.

left the recorded observations of one fortunate astronomer, Mr. John
Yeats, who states that

" All the phenomena of an annular eclipse were clearly and beautifully
visible on the Fotheringay- Castle-mound, which is a locality easily iden-
tified. Baily's beads were perfectly plain on the completion of the
annulm, which occurrence took place, according to my observation, at
about seventy seconds after 1 o'clock ; it lasted about eighty seconds.
The 'beads/ like drops of water, appeared on the upper and under sides
of the moon, occupying fully three-fourths of her circumference.

" Prior to this, the upper edge of the moon seemed dark and rough,
and there were no other changes of colour. At 12'4<3, the cusps, for a
few moments, bore a very black aspect.

" There was nothing like intense darkness during the eclipse, and less
gloom than during a thunderstorm. Bystanders prognosticated rain;
but it was the shadow of a rapidly-declimn; day. At 12 o'clock, a lady
living on the farm suddenly exclaimed, 'The cows are coming home
to be milked!' and they came, all but one; that followed, however,
within the hour. Cocks crowed, birds flew low or fluttered about
uneasily, but every object far and near was well defined to the eye.

".A singular broadway of light stretched north and south for upwards
of a quarter of an hour ; from about 12'54 to I'lO P.M.

If the annular eclipse of the sun be a matter for wonderment, the total
eclipse of the same is much more surprising ; no other expression than
that of awfully grand, can give an idea of the effects of totality, and of
the suddenness with which it obscures the light of heaven. The dark-
ness, it is said, comes dropping down like a mantle, and as the moment
of full obscuration approaches, people's countenances become livid, the
horizon is indistinct and sometimes invisible, and there is a general
appearance of horror on all sides. These are not simply the inventions

28 BOY'S PLAYBOOK OF SCIENCE.

of active human imaginations, for they produce equal, if not greater
effects, upon the brute creation. M. Arago quotes an instance of a half-
starved dx)g, who was voraciously devouring some food, but dropped it
the instant the darkness came on. A swarm of ants, busily engaged,
stopped when the darkness commenced, and remained motionless till
the fight reappeared. A herd of oxen collected themselves into a circle
and stood still, with their horns outward, as if to resist a common
enemy ; certain plants, such as the convolvulus and silk-tree acacia,
closed their leaves. The latter statement was corroborated during the
annular eclipse of the 15th of March, 1858, by Mr. E. S. Lane, who
states, that crocuses at the Observatory, Beeston, had their blossoms
expanded before the eclipse ; they commenced closing, and were quite
shut at about one minute previous to the greatest darkness ; and the
flowers opened partially about twenty minutes afterwards. A " total
eclipse" of the sun has always impressed the human mind with terror
and wonder in every age : it was always supposed to be the forerunner
of evil ; and not only is the mind powerfully impressed, as darkness
gradually shuts out the face of the sun, but at the moment of totality,
a magnificent corona, or glory of light, is visible, and prominences, or
flames, as they are often termed, make their appearance at different-
points round the circle of the dark mass. This glory does not flash
suddenly on the eye; but commencing at the first limb of the sun,
passes quickly from one limb to the' other. Our illustration shows

Fig. 39.

"the corona" and the "rose-coloured prominences," whose nature we
shall next endeavour to explain. Professor Airy describes the change
from the last narrow crescent of light to the entire dark moon, sur-
rounded by a ring of faint light, as most curious, striking, and magical
in effect. The progress of the formation of the corona was seen dis-

THE SCIENCE OF ASTKONOMY. 29

tinctly. It commenced on the side of the moon opposite to that at
which the sun disappeared, and in the general decay and disease which
seemed to oppress all nature, the moon and the corona appeared almost
like a local sore in that part of the sky, and in some places were seen
double. Its texture appeared as if fibrous, or composed of entangled
threads ; in other places brushes, or feathers of light proceeded from
it, and one estimate calculated the light at about one-seventh part of a
full moon light. The question, whether the corona is concentric with
the sun and moon, was specially mooted by M. Arago, and Professor
Baden Powell has produced such excellent imitations of the " corona"
by making opaque bodies occult, or conceal, very bright points, that it
cannot be considered as material or real, although it ought to be re-
membered that the best theory of the zodiacal light represents it to be
a nebulous mass, increasing in density towards the sun, and yet no
portion of this nebulous mass was seen during the totality. But by far
the most remarkable of all the appearances connected with a " total
eclipse" are the rose-coloured prominences, mountains, or flames, pro-
jecting from the circumference of the moon to the inner ring of the
corona; and, although they had been observed by Vaserius (a Swedish
astronomer) in 1733, they took the modern astronomers entirely by
surprise in 1842, and they were not prepared with instruments to ascer-
tain the nature of these strange and almost portentous forms. In 1851,
however, great preparations were made to throw further light on the
subject. Professor Airy went to make his observations, and he says,
"That the suddenness of the darkness in 1851 appeared much more
striking than in 1842, and the forms of the rose-coloured mountains were
most curious. One reminded him of a boomerang (that curious weapon
thrown so skilfully by the aborigines of Australia) ; this same figure has
been spoken of by others as resembling a Turkish scimitar, strongly
coloured with rose-red at the borders, but paler in the centre. Another
form was a pale-white semicircle based on the moon's limbs ; a third
figure was a red detached cloud, or balloon, of nearly circular form,
separated from the moon by nearly its own breadth ; a fourth appeared
like a small triangle, or conical red mountain, perhaps a little white in
the interior ;" and the Professor proceeds to say, " I employed myself
in an attempt to draw roughly the figures, and it was impossible, after
witnessing the increase in height of some, and the disappearance of
another, and the arrival of new forms, not to feel convinced that the
phenomena belonged to the sun, and not to the moon."

Still the question remains unanswered, what are these "rose-
coloured prominences ?" If they belong to the sun, and are moun-
tains in that luminary, they must be some thirty or forty thousand miles
in height.

M. Faye has formally propounded the theory, that they are caused by
refraction, or a kind of mirage, or the distortion of objects caused by
heated air. This phenomenon is not peculiar to any country, though
most frequently observed near the margin of lakes and rivers, and on
hot sandy plains. M. Monge, who accompanied Buonaparte in his

30 BOY'S PLAYBOOK OF SCIENCE.

expedition to Egypt, witnessed a remarkable example between Alex-
andria and Cairo, where, in all directions, green islands appeared sur-
rounded by extensive lakes of pure, transparent water. M. Monge
states that " Nothing could be conceived more lovely or picturesque
than the landscape. In the tranquil surface of the lake, the trees and
houses with which the islands are covered were strongly reflected with
vivid and varied hues, and the party hastened forward to enjoy the
refreshment apparently proffered them ; but when they arrived, the lake,
on whose bosom the images had floated the trees, amongst whose
foliage they arose, and the people who stood on the shore, as if in-
viting their approach, had all vanished, and nothing remained but the
uniform and irksome desert of sand and sky, with a few naked and
ragged Arabs."

If M. Monge and his party had not been undeceived, by actually
going to the spot, they would, one and all, have been firmly convinced
that these visionary trees, lakes, and buildings had a real existence.
This kind of mirage is known in Persia and Arabia by the name of
" serab" or miraculous water, and in the western districts of India by
that of " scheram." This illusion is the effect of unusual refraction, and
M. Faye attempts to account for the rose-coloured mountains by some-
thing of a similar nature.

It is right, however, to mention, that learned astronomers do not con-
sider this theory of any value.

Lieutenant Patterson, one of the observers of the eclipse of 1851,
says, that " It is very remarkable that the flames or prominences cor-
respond exactly (at least as far as he could judge) with the spots on the
sun's surface." Taking this statement with that of M. Faye, it may
be assumed, as a new idea, and nothing more, that these prominences
are, after all, mere aerial pictures of these openings in the sun's atmo-
sphere, or what are called " sun spots." In the " Edinburgh Philoso-
phical Journal," it is said, that although it has lately been shown in the
Edinburgh Observatory that it is possible to produce, by certain optical
experiments, red flames on the sun's limb of precisely the rose-coloured
tint described, yet, on weighing the whole of the evidence, there does
seem a great preponderance in favour of the eclipse flames being real
appendages of the sun, and in that case they must be masses of such
vast size as to play no unimportant part in the economy of that stupen-
dous orb.

During the last eclipse great disappointment was felt that the dark-
ness was so insignificant, although, when we consider the enormous
light-giving power of the sun, and know that it was not wholly
obscured, we could hardly have expected any other result. There can
be no doubt that a decided change in the amount of light is only to
be observed during a total eclipse of the sun, one of wnich occurred
on the 7th of September, 1858 ; but, unfortunately, it was only visible
in South America ; we must therefore content ourselves with the de-
scriptions of those astronomers who can be fully relied on. From
the graphic account given by Professor Piazzi Smyth, the astronomer-

THE SCIENCE OP ASTRONOMY. 31

royal for Scotland, of a total eclipse as seen by him on the western
coast of Norway, we may form some notion of the imposing appearance
of the surrounding country wlien obscured during the occurrence of this
rare astronomical phenomenon.

The Professor remarks, " To understand the scene more fully, the
reader must fancy himself on a small, rocky island on a mountainous
coast, the weather calm, and the sky at the beginning of the eclipse
seven-tenths covered with thin and bright cirro-strati clouds. As the
eclipse approaches, the clouds gradually darken, the rays of the sun are
no longer able to penetrate them through and through, and drench
them with living light as before, but they become darker than the sky
against which they are seen. The air becomes sensibly colder, the clouds
still darker, and the whole atmosphere murkier.

" From moment to moment as the totality approaches, the cold and
darkness advance apace ; and there is something peculiarly and terribly
convincing in the two different senses, so entirely coinciding in their
indications of an unprecedented fact being in course of accomplishment.
Suddenly, and apparently without any warning (so immensely greater
were its effects tnan those of anything else which had occurred), the
totality supervenes, and darkness comes down. Then came into view
lurid lights and forms, as on the extinction of candles. This was the
most striking point of the whole phenomenon, and made the Norse
peasants about us flee with precipitation, and hide themselves for their
lives.

" Darkness reigned everywhere in heaven and earth, except where,
along the north-eastern horizon, a narrow strip of unclouded sky pre-
sented a low burning tone of colour, and where some distant snow-
covered mountains, beyond the range of the moon's shadow, reflected
the faint mono-chromatic light of the partially eclipsed sun, and exhi-
bited all the detail of their structure, all the light, and shade, and
markings of their precipitous sides with an apparently supernatural
distinctness. After a little time, the eyes seemed to get accustomed to
the darkness, and the looming forms of objects close by could be dis-
cerned, all of them exhibiting a dull-green hue ; seeming to have exhaled
their natural colour, and to have taken this particular one, merely by
force of the red colour in the north.

"Life and animation seemed, indeed, to have now departed from
everything around, and we could hardly but fear, against our reason,
that if such a state of things was to last much longer, some dreadful
calamity must happen to us all ; while the lurid horizon, northward,
appeared so like the gleams of departing light in some of the grandest
paintings by Danby and Martin, tnat we could not but believe, in spite
of the alleged extravagances of these artists, that Nature had opened
up to the constant contemplation of their mind's -eye some of those
magnificent revelations of power and glory which others can only get a
glimpse of on occasions such as these."

It can be easily imagined, that under such peculiar and awful circum-
stances, the careful observation of these effects must be somewhat dif-

32 BOY'S PLAYBOOK OP SCIENCE.

ficult, and the only wonder is that the astronomical observations are
conducted with any certainty at all.

In the eclipse of 1842, it was not only the vivacious Frenchman who
was carried away in the impulse of the moment, and had afterwards to
plead that " he was no more than a man" as an excuse for his unfulfilled
part in the observations, but the same was the case with the grave
Englishman and the more stolid German. In 1851, much the same
failure in the observations occurred ; and on some person asking a worthy
American, who had come with his instruments from the other side of
the world expressly to observe the eclipse, what he had succeeded in
doing ? he merely answered, with much quiet impressiveness, " That if
it was to be observed over again, he hoped he would be able to do some-
thing ', but that^ as it was, he had done nothing : it had been too much
for him" This is not quite so bad as the fashionable lady who
Jbad been invited to look at an eclipse of the sun through a grand
telescope, but arriving too late, inquired whether " it could not be shown
over again"

With this brief glance at the science of astronomy, we once more
return to the term "gravity," which will introduce to us some new
and interesting facts, under the head of what is called " centre of
gravity."

CHAPTER IV.

CENTRE OP GRAVITY.

That point about which all the parts of a body do, in any situation,
exactly balance each other.

THE discovery of this fact is due to Archimedes, and it is a point in
every solid body (whatever the form may be) in which the forces of
gravity may be considered as united. In our globe, which is a sphere,
or rather an oblate spheroid, the centre of gravity will be the centre.
Thus, if a plummet be suspended on the surface of the earth, it points
directly to the centre of gravity, and, consequently, two plummet-lines
suspended side by side cannot, strictly speaking, be parallel to each
other.

If it were possible to bore or dig a gallery through the whole substance
of the earth from pole to pole, and then to allow a stone or the fabled
Mahomet's coffin to fall through it, the momentum i.e., the force of the
moving body, would carry it beyond the centre of gravity. This force, how-
ever, being exhausted, there would be a retrograde movement, and after
many oscillations it would gradually come to rest, and then, unsupported
by anything material, it would be suspended by the force of gravitation, and
now enter into and take part in the general attracting force; and being
equally attracted on every side, the stone or coffin must be totally without
weight. Momentum is prettily illustrated by a series of inclined planes

THE CENTRE OF GRAVITY.

Fig. 40. p. The centre. ABODE. Plummet-lines, all pointing to the centre, and
therefore diverging from each other.

cut in mahogany, with a grooved channel at the top, in imitation of the
famous Russian ice mountains : and if a marble is allowed to run down

Fig. 41. P r P. Inclined planes, gradually decreasing in height, cut out of inch mahogany,
with a groove at the top to carry an ordinary marble. BBS. Different positions of the
marble, which starts from B A.

BOY'S PLAYBOOK OF SCIENCE.

the first incline, the momentum will carry it up the second, from whicn
it will again descend and pass up and down the third and last miniature
mountain.

In a sphere of uniform density, the centre of gravity is easily dis-
covered, but not so in an irregular mass ; and here, perhaps, an explana-
tion of terms may not be altogether unacceptable.

Mass, is a term applied to solids, such as a mass of lead or stone.
Bulk, to liquids, such as a bulk of water or oil.
Volume, to gases, such as a volume of air or oxygen.
To find the centre of gravity of any mass, as, for example, an ordinary
school-slate, we must first of all suspend it from any part of the frame ;
then allow a plumb-line to drop from the point of suspension, and mark

its direction on the slate. Again,
suspend the slate at various other
points, always marking the line of
direction of the plummet, and at
the point where the lines intersect
each other, there will be the centre
of gravity.

If the slate be now placed (as
shown in Fig. 43) on a blunt

Fig. 42. A B D. The three points of sus-
pension, c, The point of intersection, and,
therefore, the centre of gravity, p, The line
of plummet.

Fig. 43.,

wooden point at the spot where the
lines cross each other, it will be
found to balance exactly, and this
place is called the centre of gravity >
oeinff the point with which all other
particles of the body would move with parallel and equable motion during
its fall. The equilibrium of bodies is therefore much affected by the
position of the centre of gravity. Thus, if we cut out an elliptical figure
from a board one inch in thickness, and rest it on a flat surface by one
of its edges (as at No. 1, fig. 44), this point of contact is called the point
of support, and the centre of gravity is immediately above it.

In this case, the body is in a state of secure equilibrium, for any
motion on either side will cause the centre of gravity to ascend in these
directions, and an oscillation will ensue. But if we place it upon the
smaller end, as shown at No. 2 (fig. 44), the position will be one of

THE CENTRE OF GRAVITY.

equilibrium, but not stable or secure; although the centre of gravity
is directly above the point of support, the slightest touch will displace

N92

Fig. 44. The point of support, o, The centre of gravity.

the oval and cause its overthrow. The famous story of Columbus and
the egg suggests a capital illustration of this fact ; and there are two
modes in which the egg may be poised on either of the ends.

The one usually attributed to the great discoverer, is that of scraping
or slightly breaking away a little of the shell, so as to flatten one of the
ends, thus

Fig. 45. A. Represents the egg in its natural state, and, therefore, in unstable equilibrium ;
B, another egg, with the surface, s, flattened, by which the centre of gravity is lowered, and
if not disturbed beyond the extent of the point of support the equilibrium is stable.

The most philosophical mode of making the egg stand on its end and
without disturbing the exterior shell is to alter the position of the yolk,
which has a greater density than the white, and is situated about the
centre. If the egg is now shaken so as to break the membrane enclosing
the yolk, and thus allow it to sink to the bottom of the smaller end, the
centre of gravity is lowered; there is a greater proportion of weight.

BOY'S PLAYBOOK OF SCIENCE.

IM-2

concentrated in the small end, and the egg stands erect, as depicted at

fig. 46.

It is this variable position of the centre of gravity in ivory balls (one

part of which may be more
dense than another) that so
frequently annoys even the
best billiard-players ; and on
this account a ball will de-
viate from the line in which
it is impelled, not from any
fault of the player, but in
consequence of the ivory
ball being of unequal den-
sity, and, therefore, not hav-
ing the centre correspond-
ing with the centre of gra-
vity. A go o d billiard-player
should, therefore, always try

i I

No.2c. anto* of gravity, much lowered. *. The the ball before he engages
yolk at the bottom of the egg. to play for any large sum.

The toy called the " tombola" reminds us of the egg-experiment, as
there is usually a lump of lead inserted in the lower part of the hemi-

N'-l

Fig. 47 No. 1. c. Centre of gravity in the lowest ]

No. 2. c. Centre of gravity raised as the figure is inclined on either side, but falling
again into the lowest place as the figure gradually conies to rest.

sphere, and when the toy is pushed down it rapidly assumes the upright
position because the centre of gravity is not in the lowest place to which
it can descend ; the latter position being only attained when the figure
is upright.

There is a popular paradox in mechanics viz., "a body haying a
tendency to fall by its own weight, may be prevented from falling by
adding to it a weight on the same side on which it tends to fall," and
the paradox is demonstrated by another well-known child's toy as de-
picted in the next cut.

THE CENTRE OF GRAVITY.

Fig. 48. The line of direction falling beyond the base; the bent wire and lead weight
throwing the centre of gravity under the table and near the leaden weight ; the hind legs
become the point of support, and the toy is perfectly balanced.

After what has been explained regarding the improvement of the
stability of the egg by lowering the situation of the centre of gravity, it
may at first appear singular that a stick loaded with a weight at its
upper extremity can be oalanced perpendicularly with greater ease and
precision than when the weight is lower down and nearer the hand ;
and that a sword can be balanced best when the hilt is uppermost ;

N'-l

N'-2

Fig. 49. No. 1. Sword balanced on handle : the arc from c to D is very small, and if the

centre, c, falls out of the line of direction it is not easily restored to the upright position.

No 2. Sword balanced on the point : the arc from c to D much larger, and therefore the

sword is more easily balanced.

BOYS PLAYBOOK OF SCIENCE.

but this is easily explained when it is understood that with the
handle downwards a much smaller arc is described as it falls than when
reversed, so that in the former case the balancer has not time to re-
adjust the centre, whilst in the latter position the arc described is so
large that before the sword falls the centre of gravity may be restored
within the line of direction of the base.

Por the same reason, a cliild tripping against a stone will fall
quickly; whereas, a man can recover himself; this fact can be very
nicely shown by fixing two square pieces if mahogany of different

Fig. 50. No. 1. The two pieces of mahogany, carved to represent a man and a boy. one
being 10 and the other 5 inches long, attached to board by hinges at H H.

N?2

IfJlW '' '

Fig. 51. No. 2. The board pushed forward, striking against a nail, when the
short piece falls first, and the long one second.

lengths, by hinges on a flat base or board, then if the board be pushed
rapidly forward and struck against a lead weight or a nail put in the

THE CENTRE OP GRAVITY.

table, tlie short piece is seen to fall first and the long one afterwards ;
the difference of time occupied in the fall of each piece of wood (which
may be carved to represent the human figure) being clearly denoted by
the sounds produced as they strike the board.

Boat-accidents frequently arise in consequence of ignorance on the
subject of the centre of gravity, and when persons are alarmed whilst
sitting in la boat, they generally rise suddenly, raise the centre of gravity,
which falling, by the oscillation of the frail bark, outside the line of direc-
tion of the base, cannot be restored, and the boat is upset ; if the boat were
fixed by the keel, raising the centre of gravity would be of little con-
sequence, but as the boat is perfectly free to move and roll to one side
or the other, the elevation of the centre of gravity is fatal, and it
operates just as the removal of the lead would do, if changed from the
base to the head of the " tombola" toj.

A very striking experiment, exhibiting the danger of rising in a boat,
maybe shown by the following model, as depicted at Nos. 1 and 2, figs.
52 and 53.

Fig. 52. No. 1. Sections of a toy-boat floating in water. B B B. Three brass wires placed
at regular distances and screwed into the bottom of the boat, with cuts or slits at the top
so that when the leaden bullets, ILL, which are perforated and slide upon them like
beads, are raised to the top, they are retained by the brass cuts springing out ; when the

bullets are at the bottom of the lines they represent persons sitting in a boat, as shown
in the lower cuts, and the centre of gravity will be wit" "

be within the vessel.

We thus perceive that the stability of a body placed on a base depends
upon the position of the line of direction and tne height of the centre
of gravity.

Security results when the line of direction falls within the base. In-
stability when just at the edge. Incapability of standing when falling
without the base.

BOY'S PLAYBOOK OF SCIENCE.
N2Z

Pig. 53. No. 2. The leaden bullets raised to the top now show the result of persons sud-
denly rising, when the boat immediately turns over, and either sinks or floats on the
surface with the keel upwards.

The leaning-tower of Pisa is one hundred and eighty-two feet in
height, and is swayed thirteen and a half feet from the perpendicular,

Pig. 54. P. Board cut and painted to represent the leaning-tower of Pisa. o. The centre
of gravity and plummet-line suspended from it. H. The hinge which attaches it to the
base board, i. The string, sufficiently long to unwind and allow the plummet to hang out-
side the base, so that, when cut, the model falls in the direction of the arrow.

but jet remains perfectly firm and secure, as the line of direction falls
considerably within the base. If it was of a greater altitude it could
no longer stand, because the centre of gravity would be so elevated
that the line of direction would fall outside the base. This fact may
be illustrated by taking a board several feet in length, and having cut

THE CENTRE OF GRAVITY.

it out to represent the architecture of the leaning-tower of Pisa, it may
then be painted in distemper, and fixed at the right angle with a hinge
to another board representing the ground, whilst a plumb-line may be
dropped from the centre of gravity ; and it may be shown that as long
as the plummet falls within the base, the tower is safe ; but directly the
model tower is brought a little further forward by a wedge so that the
plummet hangs outside, then, on removing the support, which may be a
piece of string to be cut at the right moment, the model falls, and the
fact is at once comprehended.

The leaning-towers of Bologna are likewise celebrated for their great
inclination ; so also (in England) is the hanging-tower, or, more cor-
rectly, the massive wall which has formed part of a tower at Bridge-
north, Salop ; it deviates from the perpendicular, but the centre of
gravity and the line of direction fall within the base, and it remains
secure ; indeed, so little fears are entertained of its tumbling down, that
a stable has been erected beneath it.

One of the most curious paradoxes is displayed in the ascent of a
billiard-ball from the thin to the thick ends of two billiard-cues placed

is a---0

Fig. 55. No. 1. Two billiard-cues arranged for the experiment and fixed to a board : the
ball is rolling up.

No. 2. Sections showing that the centre of gravity, c, is higher at A than at B, which
represents the thick end of the cues; it therefore, in effect, rolls down hill.

at an angle, as in our drawing above ; here the centre of gravity is
raised at starting, and the ball moves in consequence of its actually
falling from the high to the low level.

Much of the stability of a body depends on the height through which
the centre of gravity must be elevated before the body can De over-
thrown. The greater this height, the greater will be the immovability
of the mass. One of the grandest examples of this fact is shown in
the ancient Pyramids ; and whilst gigantic palaces, with vast columns,

BOY S PLAYBOOK OF SCIENCE.

and aU 4 the solid grandeur belonging to Egyptian architecture, have
succumbed to time and lie more or less prostrate upon the earth, the

Fig. 56. c. Centre of gravity, which must be raised to D before it can be overthrown.

Pyramids, in their simple form and solidity, remain almost as they were
built, and it mil be noticed, in the accompanying sketch, how difficult,
if not impossible, it would be to attempt to overthrow bodily one of these
great monuments of ancient times.

The principles already explained are directly applicable to the con-
struction or secure loading of vehicles ; and in proportion as the centre
of gravity is elevated above the point of support (that is, the wheels),
so is the insecurity of the carriage increased, and the contrary takes
place if the centre of gravity is lowered. Again, if a waggon be loaded

No.l.

No. 2.

Fig. 57. No. 1. The centre of gravity is near the ground, and falls within the wheels.
No. 2. The centre of gravity is much elevated, and the line of direction is outside the wh0els

THE CENTRE OP GKAVITY. 43

with a very heavy substance which does not occupy much space, such
as iron, lead, or copper, or bricks, it will be in much less danger of an
overthrow than if it carries an equal weight of a lighter body, such as
pockets of horjs, or bags of wool or bales of rags.

In the one instance, the centre of gravity is near the ground, and falls
well within the base, as at No. 1, fig. 57. In the other, the centre of gravity
is considerably elevated above the ground, and having met with an ob-
struction which has raised one side higher than the other, the line
of direction has fallen outside the wheels, and the waggon is over-
turning as at No. 2.

The various postures of the human body may be regarded as so many
experiments upon the position of the centre of gravity which we are
every moment unconsciously performing.

To maintain an erect position, a man must so place his body as to
cause the line of direction of his weight to fall within the base formed
by his feet.

The more the toes are turned outwards, the more contracted will be
the base, and the body will be more liable to fall backwards or forwards ;
and the closer the feet are drawn together, the more likely is the body
to fall on either side. The acrobats, and so-called "India-Rubber

Fig. 58.

Brothers," dancing dogs, &c., unconsciously acquire the habit of accu-
rately balancing themselves in all kinds of strange positions ; but as
these accomplishments are not to be recommended to young people,
some other marvels (such as balancing a pail of water on a stick laid
upon a table) may be adduced, as illustrated in fig. 59.

Let A B represent an ordinary table, upon which place a broomstick,
c D, so that one-half shall lay upon the table and the other extend from

BOYS PLAYBOOK OP SCIENCE.

it ; f lace over the stick the handle of an empty pail (which may possibly
require to be elongated for the experiment) so that the handle touches
or falls into a notch at H ; and in order to bring the pail well under the

Fig. 59.

table, another stick is placed in the notch E, and is arranged in the
line G P E, one end resting at G and the other at E. Having made these
preparations, the pail may now be filled with water ; and although it
appears to be a most marvellous result, to see the pail apparently
balanced on the end of a stick which may easily tilt up, the principles
already explained will enable the observer to understand that the centre
of gravity of the pail falls within the line of direction shown by the
dotted line ; and it amounts in effect to nothing more than carrying a pail
on the centre of a stick, one end of which is supported at E, and the
other^ through the medium of the table, AB.

This illustration may be modified by using a heavy weight, rope, and
stick, as shown in our sketch below.

Fig. 60.

Before we dismiss this subject it is advisable to explain a term re-
ferring to a very useful truth, called the centre of percussion ; a know-
ledge of which, gained instinctively or otherwise, enables the workman
to wield his tools with increased power, and gives greater force to the
cut of the swordsman, so that, with some physical strength, he may
perform the feat of cutting a sheep in half, cleaving a bar of lead, or

THE CENTRE OF GRAVITY.

neatljr dividing, a la Saladin, in ancient Saracen fashion, a silk hand-
kerchief floating in the air. There is a feat, however, which does not
require any very great strength, but is sufficiently startling to excite
much surprise and some inquiry viz., the one of cutting in half a broom-
stick supported at the ends on tumblers of water without spilling the
water or cracking or otherwise damaging the glass supports.

Fig. 61.

These and other feats are partly explained by reference to time : the
force is so quickly applied and expended on the centre of the stick that
it is not communicated to the supports ; just as a bullet from a pistol
may be sent through a pane of glass without shattering the whole square,
but making a clean hole through it, or a candle may be sent through a
plank, or a cannon-ball pass through a half opened door without causing
it to move on its hinges. But the success of the several feats depends
in a great measure on the attention that is paid to the delivery of the
blows at the centre of percussion of the weapon; this is a point in a
moving body where the percussion is the greatest, and about which the
impetus or force of all parts is balanced on every side. It may be better
understood by reference to our drawing below. Applying this principle
to a model sword made of wood, cut in half in the centre of the blade,
and then united with an elbow -joint, the handle being fixed to a board
by a wire passed through it and the two upright pieces of wood, the
fact is at once apparent, and is well shown in JNOS. 1, 2, 3, fig. 62.

BOY'S PLAYBOOK OF SCIENCE.

AB IMM

\ \ AB

N23

Fig. 62. No. 1, is the wooden sword, with an elbow-joint at c. No. 2. Sword attached to
board at x, and being allowed to fall from any angle shown by dotted-line, it strikes
the block, w, outside the centre of percussion, p, and as there is unequal motion in the
parts of the sword it bends down (or, as it were, breaks) at the elbow-joint, c.

No. 3 displays the same model ; but here the blow has fallen on the block, w, precisely
at the centre of percussion of the sword, p, and the elbow-joint remains perfectly firm.

When a blow is not delivered with a stick or sword at the centre of
percussion, a peculiar jar, or what is familiarly spoken of as a stinging
sensation, is apparent in the hand ; and the cause of this disagreeable
result is further elucidated by fig. 63, in which the post, A, corresponds
with the handle of the sword.

THE CENTRE OF GRAVITY.

Pig. 63. A. The post to which a rope is attached. B and c are two horses running round
in a circle, and it is plain that B will not move so quick as c, and that the latter will have
the greatest moving force ; consequently, if the rope was suddenly checked by striking
against an object at the centre of gravity, the horse c would proceed faster than B, and
would impart to B a backward motion, and thus make a great strain on the rope at A. But
if the obstacle were placed so as to be struck at a certain point nearer c, viz., at or about
the little star, the tendency of each horse to move on would balance and neutralize the other,
so that there would be no strain at A. The little star indicates the centre of percussion.

All military men, and especially those young gentlemen who are
intended for the army, should bear in mind this important truth during
their sword-practice and with one of Mr. Wilkinson's swords, made
only of the very best steel, they may conquer in a chance combat which
might otherwise have proved fatal to them. To Mr. Wilkinson, of Pall
Mall, the eminent sword-cutler, is due the great merit of improving the
quality of the steel employed in the manufacture of officers' swords ;
and with one of his weapons, the author has repeatedly thrust through
an iron plate about one-eighth of an inch in thickness without injuring
the point, and has also bent one nearly double without fracturing it, the
perfect elasticity of the steel bringing the sword straight again. These,
and other severe tests applied to Wilkinson's swords, show that there is
no reason why an officer should not possess a weapon that will bear
comparison with, nay, surpass, the far-famed Toledo weapon, instead of
submitting to mere army-tailor swords, which are often little better than
hoops of beer barrels ; and, in dire combat with Hindoo or Mussulman
fanatics' Tulwah, may show too late the folly of the owner.

Fijr. 64

BOYS PLAYBOOK OF SCIENCE.

CHAPTER V.

SPECIFIC GRAVITY.

IT is recorded of the great Dr. Wollaston, that when Sir Humphry
Davy placed in his hand, what was then considered to be the scientific
wonder of the day viz., a small bit of the metal potassium, he ex-
claimed at once, " How heavy it is," and was greatly surprised, when
Sir Humphry threw the metal on water, to see it not only take fire,
but actually float upon the surface ; here, then, was a philosopher
possessing the deepest learning, unable, by the sense of touch and by
ordinary handling, to state correctly whether the new substance (and
that a metal), was heavy or light ; hence it is apparent that the pro-
perty of specific gravity is one of importance, and being derived from
the Latin, means species, a particular sort or kind ; and gravis, heavy
or weight i.e., the particular weight of every substance compared with
a fixed standard of water.

We are so constantly in the habit of referring to a standard of perfec-
tion in music and the arts of painting and sculpture, that the youngest
will comprehend the office of water when told tnat it is the philosopher's
unit or starting-point for the estimation of the relative weights of solids
and liquids. A good idea of the scope and meaning of the term specific
gravity, is acquired by a few simple experiments, thus : if a cylindrical

Fig. 65. A. A large cylindrical vessel containing water, in which the egg sinks till it
reaches the bottom of the glass. B. A similar glass vessel containing half brine and half
water, in which the egg floats in the centre viz., just at the point where the brine and
water touch.

SPECIFIC GRAVITY.

glass, say eighteen inches long, and two and a half wide, is filled with
water, and another of the same size is also filled, one half with water
and the other half with a saturated solution of common salt, or what is
commonly termed brine, a most amusing comparison of the relative
weights of equal bulks of water and brine, can be made with the help
of two eggs ; when one of the eggs is placed in the glass containing
water, it immediately sinks to the bottom, showing that it has a greater
specific gravity than water ; but when the other egg is placed in the
second glass containing the brine, it sinks through the water till it
reaches the strong solution of salt, where it is suspended, and presents
a most curious and pretty appearance ; seeming to float like a balloon in
air, and apparently suspended upon nothing, it provokes the inquiry,
" whether magnetism has anything to do with it ?" The answer, of
course, is in the negative, it merely
floats in the centre, in obedience to
the common principle, that all bodies
float in others which are heavier than
themselves ; the brine has, therefore,
a greater weight than an equal bulk
of water, and is also heavier than the
egg. A pleasing sequel to this expe-
riment may be shown by demonstrat-
ing how the brine is placed in the
vessel without mixing with the water
above it ; this is done by using a glass
tube and funnel, and after pouring
away half the water contained in the
vessel (Fig. 65), the egg can be floated
from the bottom to the centre of the
glass, by pouring the brine down the
funnel and tube. The saturated solu-
tion of salt remains in the lower part
of the vessel and displaces the water,
which floats upon its surface like oil
on water, carrying the egg with it.

The water of the Dead Sea is said
to contain about twenty-six per cent,
of saline matter, which chiefly con-
sists of common salt. It is perfectly
clear and bright, and in consequence
of the great density, a person may
easily float on its surface, like the egg'graduallynses?
egg on the brine, so that if a ship
could be heavily laden whilst floating on the water of the Dead Sea,
it would most likely sink if transported to the Thames. This illus-
tration of specific gravity is also shown by a model ship, which being
first floated on the brine, will afterwards sink if conveyed to another
vessel containing water. One -of the tin model ships sold as a magnetic

BOYS PLAYBOOK OF SCIENCE.

toy answers nicely for this experiment, but it must be weighted or
adjusted so that it just floats in the brine, A ; then it will sink, when
placed, in another vessel containing only water.

Fig. 67. A. Vessel containing brine, upon which the little model floats.
B. Vessel containing water, in which the ship sinks.

Another amusing illustration of the same kind is displayed with gold
fish, which swim easily in water, floating on brine, but cannot dive to
the bottom of the vessel, owing to the density of the saturated solution
of salt. If the fish are taken out immediately after the experiment, and
placed in fresh water, they will not be hurt by contact with the strong
salt water.

These examples of the relative weights of equal bulks, enable the
youthful mind to grasp the more difficult problem of ascertaining the
specific gravity of anv solid or liquid substance; and here the strict
meaning of terms should not be passed by. Specific weight must not be
confounded with Absolute weight ; the latter means the entire amount
of ponderable matter in any body : thus, twenty-four cubic feet of sand
weigh about one ton, whilst specific weight means the relation that sub-
sists between the absolute weight and the volume or space which that
weight occupies. Thus a cubic foot of water weighs sixty-two and a half
pounds, or 1000 ounces avoirdupois, but changed to gold, the cubic
foot weighs more than half a ton, and would be equal to about 19,300
ounces 4ience the relation between the cubic foot of water and that of

SPECIFIC GRAVITY. 51

gold is nearly as 1 to 19' 3 ; the latter is therefore called the specific
gravity of gold.

Such a mode of taking the specific gravity of different substances
viz., by the weight of equal bulks, whether cubic feet or inches, could not
be employed in consequence of the difficulty of procuring exact cubic
inches or feet of the various substances which by their peculiar proper-
ties of brittleness or hardness would present insuperable obstacles to any
attempt to fashion or shape them into exact volumes. It is therefore
necessary to adopt the method first devised by Archimedes, 600 B.C.,
when he discovered the admixture of another metal with the gold of
King Hiero' s crown.

This amusing story, ending in the discovery of a philosophical truth,
may be thus described : King Hiero gave out from the royal treasury a
certain quantity of gold, which he required to be fashioned into a crown ;
when, however, the emblem of power was produced by the goldsmith,
it was not found deficient in weight, but had that appearance which
indicated to the monarch that a surreptitious addition of some other
metal must have been made.

It may be assumed that King Hiero consulted his friend and philoso-
pher Archimedes, and he might have said, " Tell me, Archimedes, without
pulling my crown to pieces, if it has been adulterated with anv other
metal ?" The philosopher asked time to solve the problem, and going
to take his accustomed bath, discovered then specially what he had never
particularly remarked before that, as he entered the vessel of water,
the liquid rose on each side of him that he, in fact, displaced a certain
quantity of liquid. Thus, supposing the bath to have been full of water,
directly Archimedes stepped in, it would overflow. Let it be assumed
that the water displaced was collected, and weighed 90 pounds, whilst
the philosopher had weighed, say 200 pounds. Now, the train of
reasoning in his mind might be of this kind : " My body displaces 90
pounds of water ; if I had an exact cast of it in lead, the same bulk and
weight of liquid would overflow ; but the weight of my body was, say
200 pounds, the cast in lead 1000 pounds ; these two sums divided by
90 would give very different results, and they would be the specific
gravities, because the rule is thus stated : ' Divide the gross weight by
the loss of weight in water, the water displaced, and the quotient gives
the specific gravity.' " The rule is soon tested with the help of an
ordinary pair of scales, and the experiment made more interesting by
taking a model crown of some metal, which may be nicely gilt and
burnished by Messrs. Elkington, the celebrated electro-platers of Bir-
mingham. For convenience, the pan of one scale is suspended by
shorter chains than the other, and should have a hook inserted in the
middle ; upon this is placed the crown, supported by very thin copper
wire. For the sake of argument, let it be supposed that the crown weighs
Yl\ ounces avoirdupois, which are duly placed in the other scale-pan,
and without touching these weights, the crown is now placed in a
vessel of water. It might be supposed that directly the crown enters
the water, it would gain weight, in consequence of being wetted,

E 2

BOY'S PLAYBOOK OF SCIENCE.

but the contrary is the case, and by thrusting the crown into the water,
it may be seen to rise with great buoyancy so long as the 17 ounces are
retained in the other scale-pan ; and it will be found necessary to place
at least two ounces in the scale-pan to which the crown is attached
before the latter sinks in the water ; and thus it is distinctly shown that
the crown weighs only about 15 ounces in the water, and has therefore
lost instead of gaining weight whilst immersed in the liquid. The rule
may now be worked out :

Ounces.

Weight of crown in air 17^

Ditto in water ] 5 J

Less in water . , . . . . 2

The quotient 8| demonstrates that the crown is manufactured of
copper, because it would have been about 19 if made of pure gold.

Fi?. 88. A. Ordinary pair of scales. B. Scale-pan, containing 17 ounces, being the
weisrht of the crown in air. c. Pan, with hook and crown attached, which is sunk in the
water contained in the vessel D ; this pan contains the two ounces, which must be placed
there to make the crown sink and exactly balance B.

SPECIFIC GRAVITY. 53

Table of the Specific Gravities of the Metals in common use.

Platinum 20 '98

Gold 19-26 to 19-3 and 19-64

Mercury 13'57

Lead 11-35

Silver 10'47 to 1O5

Bismuth 9'82

Copper 8-89

Iron 7-79

Tin 7-29

Zinc 6-5 to 7"'i .

The simple rule already explained may be applied to all metals of any
size or weight, and when the mass is of an irregular shape, having
various cavities on the surface, there may be some difficulty in taking
the specific gravity, in consequence of the adhesion of air-bubbles ; but
this may be obviated either by brushing them away with a feather, or,
what is frequently much better, by dipping the metal or mineral first
into alcohol, and then into water, before placing it in the vessel of
water, by which the actual specific gravity is to be taken.

The mode of taking the specific gravity of liquids is very simple, and
is usually performed in the laboratory by means of a thin globular bottle
which holds exactly 1000 grains of pure distilled water at 60 Fahrenheit.
A little counterpoise of lead is made of the exact weight of the dry
globular bottle, and the liquid under examination is poured into the
bottle and up to the graduated mark in the neck ; the bottle is then
placed in one scale-pan, the counterpoise and the 1000-grain weight in
the other ; if the liquid (such as oil of vitriol) is heavier than water,
then more weight will be required viz., 845 grains and these figures
added to the 1000 would indicate at once that the specific gravity of oil
of vitriol was 1*845 as compared with water, which is I'OOO. When the
liquid, such as alcohol, is lighter than water, the 1000-grain weight will
be found too much, and grain weights must be added to the same scale-
pan in which the bottle is standing, until the two are exactly balanced.
If ordinary alcohol is being examined, it will be found necessary to place
180 grains with the bottle, and these figures deducted from the 1000
grains in the other scale-pan, leave 820, which, marked with a dot before
the first figure (sic '820), indicates the specific gravity of alcohol to be
less than that of water.

The difference in the gravities of various liquids is displayed in a
very pleasing manner by an experiment devised by Professor Griffiths,
to whom chemical lecturers are especially indebted for some of the most
ingenious and beautiful illustrations which have ever been devised.
The experiment consists in the arrangement of five distinct liquids of
various densities and colours, the one resting on the other, and dis-
tinguished not only by the optical line of demarcation, but by little balls
of wax, which are adjusted by leaden shot inside, so as to sink through

BOY'S PLATBOOK OF SCIENCE.

the upper strata of liquids, and rest only upon the one that it is in-
tended to indicate.

The manipulation for this experiment is somewhat troublesome, and
is commenced by procuring some pure bright quicksilver, upon which an
iron bullet (black-leaded, or painted of any colour) is placed, or one of
those pretty glass balls which are sold in such quantities at the Crystal
Palace.

Secondly. Put as much white vitriol (sulphate of zinc) into a half
pint of boiling water as it will dissolve, and, when cold, pour off the
clear liquid, make up a ball of coloured wax (say red), and adjust it by
placing little shot inside, until it sinks in a solution of sulphate of
copper and floats on that of the white vitriol.

Thirdly. Make a solution of sulphate of copper in precisely the same
manner, and adjust another wax ball to sink in water, and float on this
solution.

Fourthly. Some clear distilled water must be provided.
Fifthly. A little cochineal is to be dissolved in some common spirits
of wine (alcohol), and a ball of cork painted white provided.

Finally. A long cylindrical glass, at least eighteen inches high, and
two and a half or three inches diameter, must be made to receive these

five liquids, which are ar-
ranged in their proper order
of specific gravity by means
of a long tube and funnel.
The four balls viz., the
iron, the two wax, and the
cork balls, are allowed to
slide down the long glass,
which is inclined at an angle;
and then, by means of the
tube and funnel, pour in the
Solution of white vitriol, tincture of cochineal, and
all the balls will remain at
the bottom of the glass.
The water is poured down
next, and now the cork ball
floats up on the water, and
marks the boundary line of
the alcohol and water. Then
Fig. 69. Long cylindrical glass, 18 x 3 inches, con- the solution of blue vitriol,
taining the five liquids. when a wax ball floats upon

it. Thirdly, the solution of

white vitriol, upon which the second wax ball takes its place ; and lastly,
the quicksilver is poured down the tube, and upon this heavy metallic
fluid the iron or glass ball floats like a cork on water.

The tube may now be carefully removed, pausing at each liquid, so
that no mixture take place between them ; and the result is the arrange-
ment of five liquids, giving the appearance of a cylindrical glass painted

Alcohol.

Water.

Solution of blue vitriol.

Quicksilver.

SPECIFIC GRAVITY. 55

with bands of crimson, blue, and silver ; and the liquids will not mingle
with each other for many days.

A more permanent arrangement can be devised by using liquids which
have no affinity, or will not mix with each other such as mercury,
water, and turpentine.

The specific weight or weights of an equal measure of air and other
gases is determined on the same principle as liquids, although a diffe-
rent apparatus is required. A light capped glass globe, with stop-cock,
from 50 to 100 cubic inches capacity, is weighed full of air, then
exhausted by an air-pump, and weighed empty, the loss being taken as
the weight of its volume of air ; these figures are carefully noted,
because air instead of water is the standard of comparison for all gases.
When the specific gravity of any other gas is to be taken, the glass
globe is again exhausted, and screwed on to a gas jar provided with a
proper stop-cock, in which the gas is contained; and when perfect
accuracy is required, the gas must be dried by passing it over some
asbestos moistened with oil of vitriol, and contained in a glass tube, and
the gas jar should stand in a mercurial trough. (Fig. 70.) The stop-

Fig. 70. A. Glass globe to contain the gas. B. Gas jar standing in the mercurial
trough, D. c. Tube containing asbestos moistened with oil of vitriol.

cocks are gradually turned, and the gas admitted to the exhausted globe
from the gas jar ; when full, the cocks are turned off, the globe unscrewed,
and again weighed, and by the common rule of proportion, as the weight
of the air first found is to the weight of the gas, so is unity (1*000, the
density of air) to a number which expresses the density of the gas
required. If oxygen had been the gas tried, the number would be I'lll,
being the specific gravity of that gaseous element. If chlorine, 2'470.
Carbonic acid, 1*5 00. Hydrogen being much less than air, the number
would only be 69, or decimally 0'069.

A very good approximation to the correct specific gravity (particularly
where a number of trials have to be made with the same gas, such as

BOY'S PLAYBOOK OF SCIENCE.

ordinary coal gas) is obtained by suspending a light paper box, with holes
at one end, on one arm of a balance, and a counterpoise on the other.
The box can be made carefully, and should have a capacity equal to a

FIgf. 71. A* The balance. B. The paper box, of a known capacity, c. Gas-pipe blowing
in coal-gas, the arrows showing entrance of gas and exit of the air.

half or quarter cubic foot ; it is suspended with the holes downward, and is
filled by blowing in the coal gas until it issues from the apertures, and can
be recognised by the smell. The rule in this case would be equally simple :
as the known weight of the half or quarter cubic foot of common air is
to the weight of the coal gas, so is I'OOO to the number required.

(Kg- 71.)

As an illustration of the different specific weights of the gases, a
small balloon, containing a mixture of hydrogen and air, may be so
adjusted that it will just sink in a tall glass shade inverted and sup-
ported on a pad made of a piece of oilcloth shaped round and bound
with list. On passing in quickly a large quantity of carbonic acid, the
little balloon will float on its surface ; and if another balloon, containing
only hydrogen, is held in the top part of the open shade, and a sheet of
glass carefully slid over the open end, the density of the gases (although
they are perfectly invisible) is perfectly indicated ; and, as a climax to
the experiment, a third balloon can be filled with laughing gas, and
>nay be placed in the glass shade, taking care that the one full of pure
hydrogen does not escape ; the last balloon will sink to the bottom of the

SPECIFIC GRAVITY.

3 5

jar, because laughing gas is
almost as heavy as carbonic
acid, and the weight of the
balloon will determine its
descent. (Sis. 72.)

A soap-bubble will rest
most perfectly on a surface
of carbonic acidgas,and the
aerial and elastic cushion
supports the bubble till it
bursts. The experiment is
best performed by taking a
class shade twelve inches
broad and deep in propor-
tion, and resting it on a
pad; half a pound of ses-
quicarbonate of soda is
then placed in the vessel,
and upon this is poured a mixture of half a pint of oil of vitriol and half
a pint of water, the latter being previously mixed and allowed to cool
before use. An enormous quantity of carbonic acid gas is suddenly gene-
rated, and rising to the edge, overflows at the top of the glass shade. A
well-formed soap-bubble, detached neatly from the end of a glass-tube,
oscillates gently on the surface of the heavy gas, and presents a most
curious and pleasing appearance. The soapy water is prepared by
cutting a few pieces of yellow soap, and placing them in a two-ounce

Balloon.
Pure hydrogen.

(Air.)

Balloon.
Hydrogen & air.

(Carbonic acid.)

Balloon.

Laughing gas.

Fig. 72. Inverted large glass shade, containing half
carbonic acid and half common air.

Fig. 73. A. Inverted glass shade, containing the material, B, for generating carbonic acid
gas. c. The soap-bubble. D D. The glass tube for blowing the bubbles. E. Small lantern, to
throw a bright beam of light from the oxy-hydrogen jet upon the thin soap-bubble, which
then displays the most beautiful iridescent colours.

bottle containing distilled water. (Fig. 73.) The specific gravity of the
gases, may therefore be either greater, or less than atmospheric air,

VQ BOYS PLAYBOOK OP SCIENCE.

which has been already mentioned as the standard of comparison, and
examined by this test the vapours of some of the compounds of carbon
and hydrogen are found to possess a remarkably high gravity ; in
proof of which, the vapour of ether may be adduced as an example,
although it does not consist only of the two elements mentioned, but
contains a certain quantity of oxygen. In a cylindrical tin vessel, two
feet high and one foot in diameter, place an ordinary hot-water plate,
of course full of boiling water ; upon this warm surface pour about half
an ounce of the best ether ; and, after waiting a few minutes until the
whole is converted into vapour, take a syphon made of half-inch pewter
tube, and warm it by pouring through it a little hot water, taking care
to allow the water to drain away from it before use. After placing the
syphon in the tin vessel, a light may be applied to the extremity of the
long leg outside the tin vessel, to show that no ether is passing over
-until the air is sucked out as with the water-syphon; and after this has
been done, several warm glass vessels may be filled with this heavy
vapour of ether, which burns on the application of flame. Finally, the
remainder of the vapour may be burnt at the end of the syphon tube,
demonstrating in the most satisfactory manner that the vapour is
flowing through the syphon just as spirit is removed by the distillers
from the casks into cellars of the public-houses. (Fig. 74.)

Fl. 74. A. Tin vessel containing the hot-water plate, B, upon which the ether is
poured, c. The syphon. D. Glass to receive the vaoour. z. Combustion of the ether
vapour in another vessel.

SPECIFIC GRAVITY. 59

Before dismissing the important subject of specific gravity (or, as it
is termed by the French savants, " density"), it may be as well to state
that astronomers have been enabled, by taking the density of the earth
and by astronomical observations, to calculate the gravity of the planets
belonging to our solar system ; and it is interesting to observe that the
density of the planet Venus is the only one approaching the gravity of
the earth :

The Earth TOOO

The Sun -254)

The Moon '742

Mercury 2*583

Venus 1-037

Mars -650

Jupiter -258

Saturn -104

Herschel '220

CHAPTER VI.

ATTRACTION OF COHESION.

IN previous chapters one kind of attraction viz., that of gravita-
tion, has been discussed and illustrated in a popular manner, and
pursuing the examination of the invisible, active, and real forces of
nature, the attraction of cohesion will next engage our attention.
There is a peculiar satisfaction in pursuing such investigations, because
every step is attended bv a reasonable proof; there is no ghostly
mystery in philosophic studies ; the mind is not suddenly startled at one
moment with that which seems more than natural ; it is not carried away
in an ecstasy of wonder and awe, as in the so-called spirit-rapping ex-
periments, to be again rudely brought back to the material by the disclo-
sure of trickeries of the most ludicrous kind, such as those lately ex-
posed by M. Jobert de Lamballe, at the Academy of Sciences at Paris.
This gentleman has unmasked the effrontery of the spirit-rappers by
merely stripping the stocking from the heel of a young girl of fourteen.
M. Velpeau declares that the rapping is produced by the muscles of the
heel and knee acting in concert, and quotes the case of a lady once
celebrated as a medium, who has the power of producing the most
curious and interesting music with the tendons of the thigh. This
music is said to be loud enough to be heard from one end of a long
room to the other, and has often played a conspicuous part in the reve-
lations made by the medium. M. Jules Clocquet also explained the
method by which the famous girl pendulum had so long abused the cre-
dulity of the Paris public. This girl, whose self-styled faculty is that
of striking the hour at any time of the day or night, was attended at
the Hospital St. Louis by M. Clocquet, who states that the vibrations in

BOY S PLAYBOOK OF SCIENCE.

this case were produced by a rotatory motion in tlie lumbar regions of
the vertebral column. The sound of these (a la rattlesnake) was so
powerful, that they might be distinctly heard at a distance of twenty-
five feet.

In studying the powers of nature, which the most sceptical mind
allows must exist, there is an abundant field for experiment without
attempting the exploits of Macbeth's witches, or the fanciful powers of
Manfred ; and, returning to the theme of our present chapter, it may be
asked, how is cohesion defined? and the answer may be given, by
directing attention to the three physical conditions of water, which
assumes the form of ice, water, or steam.

In the Polar regions, and also in the Alpine and other mountains
where glaciers exist, there the traveller speaks of ice twenty, thirty, forty,
nay, three hundred feet in thickness. Here the withdrawal of a certain
quantity of heat from the water evidently allows a new force to come
into full play. We may call it what we like ; but cohesion, from the Latin
cum, together, and hareo, I stick or cleave, appears to be the best and
most rational term for this power which tends to make the atoms or
particles of the same kind of matter move towards each other, and to
prevent them being separated or moved asunder. That it is not merely
hypothetical is shown by the following experiments.

If two pieces of lead are cast, and the ends nicely scraped, taking
care not to touch the surfaces with the fingers, they may by simple
pressure be made to cohere, and in that state of attraction may be lifted

from the table by the ring which is
usually inserted for convenience in
the upper piece of lead ; they may be
hung for some time from a proper
support, and the lower bit of lead
will not break away from the upper
one ; they may even be suspended, as
demonstrated by Morveau, in the va-
cuum of an air-pump, to show that the
cohesion is not mistaken for the pres-
sure of the atmosphere, and no se-
paration occurs. And when the union
is broken by physical force, it is sur-
prising to notice the limited number
of points, like pin points, where the
cohesion has occurred; whilst the
weight of the lump of lead upheld
against the force of gravitation re-
minds one forcibly of the attraction
of a mass of soft iron bv a powerful
magnet, and leads the philosophic in-

Fig. 75. A A. Two pieces of lead, scraped quirer to speculate on the principle
c. stand, sup- of co h es ion being only some masked
form of magnetic or electrical attrac-
tion. (Fig. 75.)

clean at the surfaces B B

porting the two pieces of lead attached

to each other by cohesion.

ATTRACTION OF COHESION.

A fine example of the same force is shown in the use of a pair of flat
iron surfaces, planed by the celebrated Whitworth, of Manchester.

Fig. 76. A. Whitworth'i planes, with film of air between them.
B. Film of air excluded when cohesion occurs.

These surfaces are so true, that when placed upon each other, the upper
one will freely rotate when pushed round, in consequence of the thin
film of air remaining between the surfaces, which acts like a cushion,
and prevents the metallic cohesion. When, however, the upper plate is
slid over the lower one gradually, so as to exclude the air, then the two
may be lifted together, because cohesion has taken place. (Fig. 76.)

A glass vessel is a good example of cohesion. The materials of which
it is composed have been soft and liquid when melted in the fire, and on
the removal of the excess of heat it has become hard and solid, in
consequence of the attractive force of cohesion binding the particles
together ; in the absence of such a power, of course, the material would
fall into the condition of dust, and a mere shapeless heap of silicates of
potash and lead would indicate the place where the moulded and co-
herent glass would otherwise stand.

A lump of lead, six inches long by four broad, and half an inch
thick, may be supported by dexterously taking off a thick shaving
with a proper plane, and after pressing an inch or more of the strip on
the planed surface of the large lump of lead, the cohesion is so powerful
that the latter may be lifted from the table by the strip of metal.

The bullets projected from Perkins' steam- gun, at the rate of three
hundred per minute, are thrown with such violence, that, when received
on a thick plate of lead backed up with sheet iron, a cold welding takes
place between the two surfaces of metal in the most perfect manner,
just as two soft pieces of the metal potassium may be squeezed and
welded together. The surfaces of an apple torn asunder will not readily
cohere, but if cut with a sharp knife, cohesion easily occurs ; so with a
wound produced by a jagged surface, it is difficult to make the parts

BOY'S PLAYBOOK OF SCIENCE.

heal, whereas some of the most desperate sabre-cuts have been healed,
the cohesion of the surfaces of cut flesh being very rapid ; hence, if the
top of a finger is cut off, it may be replaced, and will grow, in conse-
quence of the natural cohesion of the parts.

The art of plating copper with silver, which is afterwards gilt, and
then drawn out into flattened wire for the manufacture of gold lace and
epaulets, usually termed bullion, is another example of the wonderful
cohesion of the particles of gold, of which a single grain may be ex-
tended over the finest plate wire measuring 345 feet in length.

The process of making wax candles is a good illustration of the
attraction of cohesion ; they are not generally cast in moulds, as most
persons suppose, but are made by the successive applications of melted
wax around the central plaited wick. Other examples of cohesion are
shown by icicles, and also stalagmites ; which latter are produced by the
gradual dropping of water containing chalk (carbonate of lime) held in
solution by the excess of carbonic acid gas ; the solvent gradually
evaporates, and leaves a series of calcareous films, and these cohere in
succession, producing the most fantastic forms, as shown in various
remarkable caverns, and especially in the cave of Arta, in the island of
Majorca.

In metallic substances the cohesion of the particles assumes an im-
portant bearing in the question of relative toughness and power of
resisting a strain ; hence the term cohesion is modified into that of the
property of "tenacity."

The tenacity of the different metals is determined by ascertaining the
weight Tequired to break wires of the same length and guage. Iron

Fig. 77. B. Paa supported by leaden wire broken by a weight which the iron
wire at A easily supports.

appears to possess the property of tenacity in the greatest, and lead in
the least degree. (Eig. 77.)

ATTRACTION OP COHESION.

The tenacity of iron is taken advantage of in the most scientific
manner by the great engineers who have constructed the Britannia Tube,
and that eighth wonder of the world, the Leviathan, or Great Eastern,
steam-ship. In both of these sublime embodiments of the genius and
industrial skill of Great Britain the advantage of the cellular principle
is fully recognised. The magnitude of this colossal ship is better
realized when it is remembered that the Great Eastern is six times the
size of the Duke of Wellington line-of-battle ship, that her length is more
than three times that of the height of the Monument, while in breadth
it is equal to the width of Pall Mall, and that a promenade round the
deck will afford a walk of more than a quarter of a mile. Up to the
water-mark the hull is constructed with an inner and outer shell, two
feet ten inches apart, each of three-quarter-inch plate ; and between
them, at intervals of six feet, run horizontal webs of iron plates, which
convert the whole into a series of continuous cells or iron boxes. (Fig. 78.)

Fig. 78. Transverse section of Great 'Eastern, showing the cellular construction
from keel to water-line, A A.

This double ship is useful in various ways ; in the first place, the
ganger arising from collision is diminished, as it is supposed that the
jvuter web only would be broken through or damaged ; so that the water
ivould not then rush into the steam-ship, but merely fill the space
Between the shells. In the second place, if there should be any difficulty
in procuring ballast, the space can be filled with 2500 tons of water, or
again pumped out, according to the requirements of the vessel. The
strength of a continued cellular construction can be easily imagined, and
may be well illustrated by a thin sheet of common tin plate. If the ends
be rested on blocks of wood, so as to lap over the wood about one inch,
they are easily displaced, and the mimic bridge broken down from its

BOY S PLAYBOOK OF SCIENCE.

supports by the addition to the centre of a few ounce weights ; whilst
the same tin plate rolled up in the figure of a tube, and again rested on the
same blocks, will now support many pounds weight without bending or
breaking down. (Fig. 79.)

Fig. 79. A. Flat tin plate, breaking down with a few ounce weights.
u. Same tin plate rolled up supports a very heavy weight.

The deck of the ship is double or cellular, after the plan of Stephenson
in the Britannia Tubular Bridge, and is 692 feet in length. The ton-
nage register is 18,200 tons, and 22,500 tons builder's measure;
the hull of the Great Eastern is considered to be of such enormous
tenacity, that, if it were supported by massive blocks of stone six feet
square, placed at each end, at stem and stern, it would not deflect, curve,
or bend down in the middle more than six inches even with all her
machinery, coals, cargo, and living freight.

In adducing remarkable instances of the adhesive power and tenacity of
inorganic matter, it may not be altogether out of place to allude to the
strength and force of living matter, or muscular power. It is stated that
Dr. George B. Winship, of Roxbury in America, a young physician, twenty-
five years old, and weighing 143 pounds, is the strongest man alive ; m
fact, quite the Samson of the nineteenth century. He can raise a barrel of
flour from the floor to his shoulders ; can raise himself with either little
finger till his chin is half a foot above it ; can raise 200 pounds with
either little finger ; can put up a church bell of 141 pounds ; can lift with
his hands 926 pounds dead weight without the aid of straps or belts of
any kind. As compared with Topham, the Cornish strong man, who
could raise 800 pounds, or the Belgic one, his power is greater; and
as the use of straps and belts increases the power of lifting by about
four times, it is stated that Winship could lift at least 2500 pounds
weight.

With these illustrations of cohesion we may return again to the ab-
stract consideration of this power with reference to water, in which we
have noticed that the antagonist to this kind of attraction is the force or
power termed caloric or heat. The latter influence removes the frozen
bands of winter and converts the ice to the next condition, water. In
this state cohesion is almost concealed, although there is just a slight

ATTRACTION OF COHESION.

excess to hold even the particles of water in a state of unity, and

this fact is beautifully illustrated by the formation of the brilliant dia-

mond drops of dew on the surfaces of various leaves, as also in the force

and power exercised by great volumes of water, which exert their mighty

strength in the shape of breaker-waves, dashing against rocks and

lighthouses, and making them tremble to their very base by the violence

of the shock ; here there must be some unity of particles, or the col-

lective strength could not be exerted, it would be like throwing a hand-

ful of sand against a window a certain amount of noise is produced, but

the glass is not fractured ; whilst the same sand united by any glutinous

material, would break its way through, and soon fracture the brittle

glass. It is so usual to see the particles of water easily separated, that it

becomes difficult to recognise the presence of cohesion ; but this bond of

union is well illustrated in the experiment of the water hammer. The

little instrument is generally made of a glass tube with a bulb at one

end ; in this bulb the water which it contains is boiled, and as the steam

issues from the other extremity, drawn out to a capillary tube, the open-

ing is closed by fusion with the heat of a blowpipe flame. As the

water cools the steam condenses, and a

vacuum, so far as air is concerned, is

produced; if now the tube is suddenly

inverted, the whole of the water falls en

masse, collectively, and striking against

the bottom of the tube, produces a me-

tallic ring, just as if a piece of wood or

metal were contained within the tube.

If the end to which the water falls is

not well cushioned by the palm of the

hand, the water hammers itself through

and breaks away that part of the glass

tube. Hence it is better to construct the

water hammer of copper tube, about

three-quarters of an inch in diameter and

three feet long ; at one end a female screw-

piece is inserted, into which a stop-cock

is fitted ; when the tube is filled to the

height of about six inches with water, and

shaken, the air divides the descending

volume of water, and the ordinary splash-

ing sound is heard ; there is no unity or

cohesion of the parts ; if, however, the

end of the copper tube is thrust into

a fire and the water boiled so that steam

issues from the cock, which is then closed,

and the tube removed and cooled, a smart

blow is given, and distinctly heard when

the copper tube is rapidly inverted or

shaken so as to cause the water to rise the end to be placed in the fire at a

Pig 80> A ordinary glass water
hammer. B. Copper tube ditto,

and fall. The experiment may be rendered still more instructive by
turning the cock and admitting the air, which rushes in with a whizzing
sound, and on shaking the tube the metallic ring is no longer heard,
but it may be again restored by attaching a small air syringe or hand
pump, ancl removing the air by exhaustion. (Fig. 80.)

In the fluid condition water still possesses a surplus of cohesion over
the antagonistic force of heat ; when, however, the latter is applied in
excess, then the quasi-struggle terminates; the heat overpowers the
cohesive attraction, and converts the water into the most willing slave
which has ever lent itself to the caprices of man viz., into steam-
glorious, useful steam : and now the other end of the chain is reached,
where heat triumphs ; whilst in solids, such as ice, cohesion is the con-
queror, and the intermediate link is displayed in the fluid state of water.
If any fact could give an idea of the gigantic size of the Great Eastern,
it is the force of the steam which will be employed to move it at the
rate of about eighteen miles perhourwith a power estimated at the nominal
rate of 2600 horses, but absolutely of at least 12,000 horses. This
steam power, coupled with the fact that she has been enormously
strengthened in her sharp, powerful bows, by laying down three complete
iron decks forward, extending from the bows backward for 120 feet, will
demonstrate that in case of war the Great Eastern may prove to be a
powerful auxiliary to the Government. These decks will be occupied
by the crew of 300 or 400 men, and with this large increase of strength
forward, the Great Eastern, steaming full power, could overtake and cut
in two the largest wooden line-of-battle ship that ever floated. Should
war unhappily spread to peaceful England, and the enormous power of
this vessel be realized, her name would not inappropriately be changed
from the Great Eastern to the Great Terror of the ocean. The Times
very properly inquires, " What fleet could stand in the way of such a
mass, weighing some 30,000 tons, and driven through the water by
12,000 horse-power, at the rate of twenty-two or twenty-three miles per
hour. To produce the steam, 250 tons of coal per diem will be re-
quired, and great will be the honourable pride of the projectors when they
see her fairly afloat, and gliding through the ocean to the Far West."

A good and striking experiment, displaying the change from the
liquid to the vapour state, is shown by tying a piece of sheet caoutchouc
over a tin vessel containing an ounce or two of water. When this boils,
the india-rubber is distended, and breaks with a loud noise; or in
another illustration, by pouring some ether through a funnel carefully
into a flask placed in a ring stand. If flame is applied to the orifice,
no vapour issues that will ignite, provided the neck of the flask has not
been wetted with the ether. When, however, the heat of a spirit-lamp
is applied, the ether soon boils, and now on the application of a lighted
taper, a flame some feet in length is produced, which is regulated by the
spirit-lamp below, and when this is removed, the length of the flame
diminishes immediately, and is totally extinguished if the bottom of the
flask is plunged into cold water ; the withdrawal of the heat restores the
power of cohesion. Another illustration of the vast power of steam

ADHESIVE ATTRACTION. 67

will be shortly displayed in the Steam Ram ; and, " Supposing," says the
Times, "the new steam ram to prove a successful design, the finest
specimens of modern men-of-war will be reduced by comparison to the
helplessness of cock boats. Conceive a monstrous fabric floating in
mid-channel, fire proof and ball proof, capable of hurling broadsides of
100 shot to a distance of six miles ; or of clapping on steam at pleasure
and running down everything on the surface of the sea with a momentum
utterly irresistible.

" This terrible engine of destruction is expected to be itself indestruc*
tible. We are told that she may be riddled with shot (supposing any
shot could pierce her sides), that she may have her stem and her stern
cut to pieces, and be reduced apparently to a shapeless wreck, without
losing her buoyancy or power. Supposing that she relies upon the
shock of her impact instead of fighting her guns, it is calculated that
she would sink a line-of-battle ship in three minutes, so that a squadron
as large as our whole fleet now in commission would be destroyed in about
one hour and a quarter."

CHAPTER YH.

ADHESIVE ATTRACTION.

THE term cohesion must not be confounded with that of adhesion, which
refers to the clinging to or attraction of bodies of a dissimilar kind. The
late Professor Daniell defines cohesion to be an attraction of homogeneous
(6fjLos, like, and yevos, kind) or similar particles ; adhesion to be an at-
traction subsisting between particles of a heterogeneous, erepos, different,
and ycvos, kind.

There are numerous illustrations of adhesion, such as mending china,
and the use of glue, or paste, in uniting different surfaces, or mortar, in
building with bricks ; it is also well shown at the lecture table by means
of a pair of scales, one scale-pan of which being well cleaned with alkali at
the bottom, may then be rested on the surface of water contained in a
plate ; the adhesion between the water and the metal is so perfect, that
many grain weights may be placed in the other pan before the adhesion
is broken ; and after breakage, if the pan be again placed on the water,
and a few grains removed from the other, so as to adjust the two pans,
and make them nearly equal, a drop of oil of turpentine being added, in-
stantly spreads itself over the water, and breaking the adhesion between
the latter and the metal, the scale-pan is immediately and again broken
away, as the adhesion between the turpentine and the metal is not so great
as that of water and metal. The adhesion of air and water is well dis-
played in an apparatus recommended for ventilating mines, in which a
constant descending stream of water carries with it a quantity of air,
which being disengaged, is then forced out of a proper orifice. The same
kind of adliesion between air and water is displayed in the ancient

* 2

BOY'S PLAYBOOK OF SCIENCE.

Spanish Catalan forge, where the blast
is supplied to the iron furnace on a simi-
lar principle, only, a natural cascade is
taken advantage of instead of an artificial
fall of water through a pipe.

The adhesion of air and water be-
comes of some value when a river
flows through a large and crowded city,
because the water in its passage to and
fro, must necessarily drag with it, a
continuous column of air, and assist
in maintaining that constant agitation of
the air which is desirable as a preventive
to any accumulation of noxious air
charged with foetid odours, arising from
mud banks or from other causes. The
fact of adhesion, existing between water
and air, is readily shown, by resting one
end of a long glass tube, of at least one
inch diameter, on a block of wood one
foot high. If water is allowed to flow
down the tube, so as to leave a sufficient
space of air above it, the adhesion be-
tween the two ancient elements becomes
apparent, directly a little smoke is pro-
duced, near the top end of the glass tube
resting on the block of wood. The
smoke, which has a greater tendency to
rise than to fall, is dragged down the
glass tube, and accompanies the water

Fig. 81. Model of the apparatus f s it flows from the higher to the lower
r drawing down air. A, cistern of level. 1 he same truth is aJ so illustrated
in horizontal troughs or tubes through
wnich water IS Caused to HOW.

The adhesion between air and glass is
<> great, that it is absolutely necessary
There is another ball- to boil the mercury m the tubes of the
SKA^S best barometers; and if this is not
level; the end of the pipe always dips carefully attended to, the adhering ail-
some inches into this water, whilst between the glass and mercurv gra-
the air escapes from the jet,!,. ^^ ^^ ^ ^ d estrO/S/ the

Torricellian vacuum at the top of the barometer tube. Even after
the mercury is boiled, the air will creep up in course of years ; and
in order to prevent its passage between the glass and quicksilver, it
has been recommended, that a platinum ring should be welded on to the
end of the glass tube, because mercury has the power of wetting or en-
filming the metal platinum, and the two being in close contact, would, as it
were, shut the only door by which the air could enter the barometer tube.

for

runs down the sides of the tube, and
draws down the air in the centre, B

tube, T.

09
CHAPTER VIII.

CAPILLARY ATTRACTION.

THIS kind of attraction is termed capillary, in consequence of tubes, of
a calibre, or bore, as fine as hair, attracting and retaining fluids.

If water is poured into a glass, the surface is not level, but cupped
at the edges, where the solid glass exerts its adhesive attraction for the
liquid, and draws it from the level. If the glass be reduced to a very
narrow tube, having a hair-like bore, the attraction is so great that the
water is retained in the tube, contrary to the force of gravitation.
Two pieces of flat glass placed close together, and then opened like a
book, draw up water between them, on the same principle. A mass of
salt put on a plate containing a little water coloured with indigo displays
this kind of attraction most perfectly, and the water is quickly drawn up,
as shown by the blue colour on the salt. A little solution of the ammonio-
sulphate of copper imparts a finer and more distinct blue colour to the
salt. A piece of dry Honduras mahogany one inch square, placed in a
saucer containing a little turpentine, is soon found to be wet with the
oil at the top, which may then be set on fire.

Almost every kind of wood possesses capillary tubes, and will float, on
account of these minute vessels being filled with air ; if, however, the air is
withdrawn, then the wood sinks, and by boiling a ball made of beech wood
in water, and then placing it under the vacuum of an air pump in
other cold water, it becomes so saturated with water that it will no
longer float. A remarkable instance of the same kind is mentioned by
Scoresby, in which a boat was pulled down by a whale to a great depth
in the ocean, and after coming to the surface it was found that the wood
would neither swim nor burn, the capillary pores being entirely filled
with salt water.

A piece of ebony sinks in water on account of its density, closeness,
and freedom from air. A gauge made of a piece of oak, with a hole
bored in it of one inch diameter, accurately receives a dry plug of willow
wood which will not enter the orifice after it is wetted. Millstones are
split by inserting wedges of dry hard wood, which are afterwards wetted
and swelled, and burst the stone asunder. One of the most curious
instances of capillary attraction is shown in the currying of leather, a
process which is intended to impart a softness and suppleness to the
skin, in order that it may be rendered fit for the manufacture of boots,
harness, machine bands, &c. The object of the currier is to fill the
pores of the leather with oil, and as this cannot be done by merely
smearing the surface, he prepares the way for the oil by wetting the
leather thoroughly with water, and whilst the skin is damp, oil is
rubbed on, and it is then exposed to the air ; the water evaporates
at ordinary temperatures, but oil does not ; the consequence is that the

BOY'S PLAYBOOK OF SCIENCE.

pores of the leather give up the water, which disappears in evaporation,
and the oil bv capillary attraction is then drawn into the body of the
leather, the oil in fact takes the place vacated by the water, and renders
the material very supple, and to a considerable extent waterproof. In
paper making, the pores of this material, unless filled up or sized, cause
the ink to blot or spread by capillary attraction. The porosity of soils is
one of the great desideratums of the skilful agriculturist, and drainage
is intended to remove the excess of water which would fill the pores of
the earth, to the exclusion of the more valuable dews and' rains con-
veying nutritious matter derived from manures and the atmosphere.

A cane is an assemblage of small tubes, and if a piece of about six
inches in length (cut off, of course, from the joints) be placed in a bottle
of turpentine, the oil is drawn up and may be burnt at the top ; it is on
this principle that indestructible wicks of asbestos, and wire gauze
rolled round a centre core, are used in spirit lamps. Oil, wax, and
tallow, all rise by capillary attraction in the wicks to the flame, where
they are boiled, converted into gas, and burnt.

The capillary attraction of skeins of cotton for water was known
and appreciated by the old alchemists; and Geber, one of the most
ancient of these pioneers of science, and who lived about the seventh
century, describes a filter by which the liquid is separated from the
solid. This experiment is well displayed by putting a solution of
acetate of lead into a glass, which is placed on the highest block of a
series of three, arranged as steps. Into this glass is placed the short end

Fig. 82. Gcber's filter. A. The solu-
tion of acetate of lead. B. The dilute
sulphuric acid. c. The clear liquid, sepa-
rated from the sulphate oflead in B.

Fig. 83. Prawn syphon.

CAPILLAEY ATTRACTION. 71

of a skein of lamp cotton, previously wetted with distilled water ; the lon
.end dips into another glass below, containing dilute sulphuric acid, and
as the solution of lead passes into it, a solid white precipitate of sulphate
of lead is formed; then another skein of wetted cotton is placed in
this glass, the long end of which passes into the last glass, so that the
clear liquid is separated and the solid left behind. (Kg. 82.)

In this filter the lamp cotton acts as a syphon through the capillary
pores which it forms. On the same principle, a prawn may be washed
in the most elegant manner (as first shown by the late Duke of Sussex),
by placing the tail, after pulling off the fan part, in a tumbler of water,
and allowing the head to hang over, when the water is drawn up by
capillary attraction, and continues to run through the head. (Fig. 83.)
The threads of which linen, cotton, and woollen cloths are made are small
cords, and the shrinkage of such textile fabrics, is well known and
usually inquired about, when a purchase is made ; here again capillary
attraction is exerted, and the fabric contracts in the two directions _ of
the warp and woof threads ; thus, twenty-seven yards of common Irish
linen will permanently shrink to about twenty-six yards in cold water.
In these cases the water is attracted into the fibres of the textile
material, and causing them to swell, must necessarily shorten their
length, just as a dry rope strained between two walls for the purpose of
supporting clothes, has been known to draw the hooks after being sud-
denly wetted and shortened by a shower of rain.

In order to tighten a bandage, it is only necessary to wind the dry
linen round the limbs as close as possible, and then wet it with water,
when the necessary shrinkage takes place.

If a piece of dry cotton cloth is tied over one end of a lamp glass, the
other may be thrust into, or removed from the basin of water very easily,
but when the cotton is wetted, the fibres contract and prevent air from
entering, so that the glass retains water just as if it were an ordinary
gas jar closed with a glass stopper.

A Spanish proverb, expressing contempt, says, "go to the well ^ with
a sieve," but even this seeming impossibility is surmounted by using a
cylinder of wire gauze, which may be filled with water, and by means of
the capillary attraction
between the meshes of
the copper-wire gauze
and the water, the whole
is retained, and may be
carefully lifted from a
basin of water ; the ex-
periment only succeeds
when the air is com-
pletely driven out of the
interstices of the gauze,
and the little cylinder A . Basin of water. B. Cylinder of wire gauze

completely filled with do JJ at both ends ^ ih gauze- when fuU of water it may
water ; this may be done be lifted from the basin by the handle, c.

72 BOY'S PLAYBOOK OP SCIENCE.

by repeatedly sinking and drawing out the cylinder, or still more
effectually, by first wetting it with alcohol and then dipping the cy Under p
in water.

A balloon, made of cotton cloth, cannot be inflated by means of a pair
of bellows, but if the balloon is wetted with water, then it may be swelled
out with air just as if it had been made of some air-tight material ;
hence the principle of varnishing silk or filling the pores with boiled oil,
when it is required in the manufacture of balloons.

Biscuit ware, porous tubes for voltaic batteries, alcarrazas, or water
coolers, are all examples of the same principle.

Whilst speaking most favourably of the benevolent labours of many
gentlemen (beginning with Mr. Gurney) who have erected " Drinking
Fountains" in London's dusty atmosphere and crowded streets, it must
not be forgotten that pious Mohammedans have, in bygone times, already
set us the example in this respect ; and in the palmy days of many of
the Moorish cities, the thirsty citizen could always be refreshed by a
draught of cool water from the porous bottles provided and endowed bv
charitable Mussulmans, and placed in the pubUc streets.

Fig 85. Moorish niche and porous earthenware
bottle, containing water.

CHAPTER IX.

CRYSTALLIZATION.

Library

IT has been already stated that the force of cohesion binds the similar
particles of substances together, whether they be amorphous or shape-
less, crystalline or of a regular symmetrical and mathematical figure.

Fig. 86. Crystals of snow.

The term crystal was originally applied by the ancients to silica in the
form of what is usually termed rock crystal, or Brazilian pebble ; and
they supposed it to be water which had been solidified by a remarkable
intensity of cold, and could not be thawed by any ordinary or summer
heat. Indeed, this idea of the ancients has been embodied (to a certain
extent) in the shape of artificial ice made by crystallizing large quan-
tities of sulphate of soda, which was made as flat as possible, and upon

74 BOY'S PLAYBOOK OF SCIENCE.

which skaters were invited to describe the figure of eight, at the usual
admittance fee, representing twelve pence. A crystal is now defined to-
be an inorganic body, which, by the operation of affinity, has assumed
the form of a regular solid terminated by a certain number of planes or
smooth surfaces.

Thousands of minerals are discovered in the crystallized state such as
cubes of iron pyrites (sulphuret of iron) and of fluor spar (fluoride of
calcium), whilst numerous saline bodies called salts are sold only in the
form of crystals. Of these salts we have excellent examples in Epsom
salts (sulphate of magnesia), nitre (nitrate of potash), alum (sulphate of
alumina), and potash ; the term salt being applied specially to all sub-
stances composed of an acid and a base, as also to other combinations
of elements which may or may not take .a crystalline form. Thus, nitre
is composed of nitric acid and potash; the first, even when much
diluted, rapidly changes paper, dipped in tincture of litmus and stained
blue, to a red colour, whilst potash shows its alkaline nature, by changing
paper, stained yellow with tincture of turmeric, to a reddish-brown. The
latter paper is restored to its original yellow by dipping it into the
dilute nitric acid, whilst the litmus paper regains its delicate blue colour
by being passed into the alkaline solution. An acid and an alkali com-
bine and form a neutral salt, such as nitre, which has no action whatever
on litmus or turmeric; whilst the element iodine, which is not an acid,
unites with the metallic element potassium, and therefore not an
alkali, and forms a salt that crystallizes in cubes called iodide of
potassium. Again, cane sugar, which is composed of charcoal, oxygen,
and hydrogen, crystallizes in hard transparent four-sided and irregular
six-sided prisms, but is not called a salt. Silica or sand is found crystal-
lized most perfectly in nature in six-sided pyramids, but is not a salt ;
it is an acid termed silicic-acid. Sand has no acid taste, because it is
insoluble in water, but when melted in a crucible with an alkali, such as
potash, it forms a salt called silicate of potash. Magnesia, from being
insoluble, or nearly so, in water, is all but tasteless, and has barely any
alkaline reaction, yet it is a very strong alkaline base ; 20'7 parts of it
neutralize as much sulphuric acid as 47 of potash. A salt is not always a
crystallizable substance, and vice versa. The progress of our chemical
knowledge has therefore demanded a wider extension and application of
the term salt, and it is not now confined merely to a combination of an
acid and an alkali, but is conferred even on compounds consisting only
of sulphur and a metal, which are termed sulphur salts.

So also in combinations of chlorine, iodine, bromine, and fluorine,
with metallic bodies, neither of which are acid or alkaline, the term
haloid salts has been applied by Berzelius, from the Greek (a\s, sea salt,
and fl8os form), because they are analogous in constitution to sea salt ;
and the mention of sea salt again reminds us of the wide signification of
the term salt, originally confined to this substance, but now extended
into four great orders, as defined by Turner :

ORDER I. The oxy-mlts. This order includes no salt the acid or
base of wliich is not an oxidised body (ex., nitrate of potash).

CRYSTALLIZATION. 75

ORDER II. The hydro-salts. This order includes no salt the acid or
base of which does not contain hydrogen (ex., chloride of ammonium).

ORDER III. The sulphur salts. This order includes no salt the
electro-positive or negative ingredient of which is not a sulphuret (ex.,
hydrosulphuret of potassium).

ORDER IV. The haloid salts. This order includes no salt the electr^-
positive or negative ingredient of which is not haloidal (Exs., iodide of
potassium and sea salt). To fix the idea of salt still better in the youthful
mind, it should be remembered that alabaster, of which works of art are
constructed, or marble, or lime-stone, or chalk, are all salts, because they
consist of an acid and a base.

In order to cause a substance to crystallize it is first necessary to
endow the particles with freedom of motion. There are many methods
of doing this chemically or by the application of heat, but we cannot by
any mechanical process of concentration, compression, or division, per-
suade a substance to crystallize, unless perhaps we except that remark-
able change in wrought or fibrous iron into crystalline or brittle iron,
by constant vibration, as in the axles of a carriage, or by attaching a
piece of fibrous iron to a tilt hammer.

If we powder some alum crystals they will not again assume their
crystalline form ; if brought in contact there is no freedom of motion. It
is like placing some globules of mercury on a plate. They have no
power to create motion ; their inertia keeps them separated by certain
distances, and they do not coalesce ; but incline the plate, give them
motion, and bring them in contact, they soon unite and form one
globule. The particles of alum are not in close contact, and they have
no freedom of motion unless they are dissolved in water, when they
become invisible; the water by its chemical power destroys the
mechanical aggregation of the solid alum far beyond any operation of
levigation. The solid alum has become liquid, like water ; the particles
are now free to move without let or hindrance from friction. A solution,
(from the Latin solvo, to loosen) is obtained. The alum must indeed be
reduced to minute particles, as they are alike invisible to the eye
whether assisted by the microscope or not. No repose will cause the
alum to separate ; the solvent power of the water opposes gravitation ;
every part of the solution is equally impregnated with alum, and the
particles are diffused at equal distances through the water ; the heavy
alum is actually drawn up against gravity by the water.

How, then, is the alum to be brought back again to the solid state ?
The answer is simple enough. By evaporating away the excess of
water, either by the application of heat or by long exposure to the
atmosphere in a very shallow vessel, the minute atoms of the alum are
brought closer together, and crystallization takes place. The assumption
of the solid state is indicated by the formation of a thin film (called a
pellicle) of crystals, and is further and still more satisfactorily proved by
taking out a drop of the solution and placing it on a bit of glass, which
rapidly becomes filled with crystals if the evaporation has been carried
sufficiently far (Fig. 87).

BOYS PLAYBOOK OF SCIENCE.

After evaporating away sufficient water, the dish is placed on one
bide and allowed to cool, when crystals of the utmost regularity of form

fig. 87. E E. Ring-stand, s s. Spirit-lamps. Fij. 88.

A. FJask containing boiling solution of alum.
Solution. B. Funnel, with a bit of lamp-cotton
stuffed in the bottom. Filtration, c. Evapo-
rating dish. Evaporation. D. Drop on glass.
Crystallization.

are produced, and, denoted by a geometrical term, are called octphedral
or eight-sided crystals, when in the utmost state of perfection (Fig. 88).

The science of crystallography is too elaborate to be discussed at
length in a work of this kind ; the various terms connected with crystals
will therefore only be explained, and experiments given in illustration of
the formation of various crystals.

When the apices i.e., the tips or points of crystals are cut off, they
are said to be truncated ; and the same change occurs on the edges of
numerous crystals.

If some of the salt called chloride of calcium in the dry and amor-
phous state is exposed to the air, it soon absorbs water, or what is termed
deliquesces: the same thing occurs with the crystals of carbonate
of potash, and if four ounces are weighed out in an evaporating dish,
and then exposed for about half an hour to the air, a very perceptible
increase in weight is observed by the assistance of the scales and grain
weights. Deliquescence is a term from the Latin deliyueo, to melt, and
is in fact a gradual melting, caused by the absorption of water from
the atmosphere. The reverse of this is illustrated with various crystals,
such as Glauber's salt (sulphate of soda), or common washing soda
(carbonate of soda) ; if a fine clear crystal is taken out of the solution,
called the mother liquor, in which it has been crystallized, wiped dry,
and placed under a glass shade, this salt may remain for a long period

CRYSTALLIZATION. 7 <

without change, but if it receive one scratch from a pin, the door is
opened apparently for the escape of the water which it contains, chemi-
cally united with the salt, and called water of crystallization; the
white crystal gradually swells out, the little quasi sore from the pin-
scratch spreads over the whole, which becomes opaque, and crumbling
down falls into a shapeless mass of white dust ; this change is called
efflorescence, from effloresce, to blow as a flower caused by the
abstraction from them of chemically-combined water by the atmosphere.
With reference to the preservation of crystals, Professor Griffiths re-
commends them to be oiled and wiped, and placed under a glass shade,
if of a deliquescent nature ; or if efflorescent, they are perfectly pre-
served by placing them under a glass shade with a little water in a cup
to keep the air charged with moisture and prevent any drying up of the
crystal.

Deliquescent crystals may be preserved by placing them, when dry,
in naphtha, or any liquor in which they are perfectly insoluble. Some
salts, like Glauber's salts, contain so much water of crystallization that
when subjected to heat they melt and dissolve in it, and this liquefac-
tion of the solid crystal is called " watery fusion." Other salts, such as
bay salt, chlorate of potash, &c., when heated, fly to pieces, with a
sharp crackling noise, which is due sometimes, to the unequal expansion
of the crystalline surface, or the sudden conversion of the water (retained
in the crystal by capillary attraction) into steam ; thus nitre behaves in
this manner, and frequently retains water in capillary fissures, although
it is an anhydrous salt, or salt perfectly free from combined water. The
crackling sound is called decrepitation, and is well illustrated by
throwing a handful of bay salt on a clear fire ; but this property is
destroyed by powdering the crystals.

Many substances when melted and slowly cooled concrete into the most
perfect crystals ; in these cases heat alone, the antagonist to cohesion,
is the solvent power. Thus, if bismuth be melted in a crucible, and
when cooling, and just as the pellicle (frompellis, a skin or crust) is
forming on the surface, if two small holes are instantly made by a
rod of iron and the liquid metal poured out from the inside (one of the
holes being the entrance for the air, the other the exit for the metal) ; on
carefully breaking the crucible, the bismuth is found to be crystallized
in the most lovely cubes. Sulphur, again, may be crystallized in pris-
matic crystals by pursuing a similar plan; and the great blocks of
spermaceti exhibited by wax chandlers in their windows, are crys-
tallized in the interior and prepared on the same principle.

There are other modes of conferring the crystalline state upon sub-
stances viz., by elevating them into a state of vapour by the process
called sublimation (from sublimis, high or exalted), the lifting up and
condensation of the vapour in the upper part of a vessel ; a process
perfectly distinct from that of distillation, which means to separate
drop by drop. Both of these processes are very ancient, and were in-
vented by the Arabian alchemists long antecedent to the seventh century.
Examples of sublimation are shown by heating iodine, and especially

BOY'S PLAYEOOK OP SCIENCE.

benzoic acid ; with the latter, a very elegant imitation of snow is pro-
duced, by receiving the vapour, on some sprigs of holly or other ever-

green, or imitation paper snow-
drops and crocuses, placed in a
tasteful manner under a glass
vessel. The benzoic acid should
first be sublimed over the sprigs
or artificial flowers in a gas jar,
which may be removed when the
whole is cold, and a clear glass
shade substituted for it. (Fig. 89.)
All electro deposits on metals
are more or less crystalline ; and
copper or silver may be deposited
in a crystalline form by placing
a scraped stick of phosphorus in
a solution of sulphate of copper
or of nitrate of silver. The phos-

Ehorus takes away the oxygen
:om the metal, or deoxidizes the
solution, and the copper or silver
reappears in the metallic form.
The surface of the phosphorus
must not be scraped in the air,
but under water, when the opera-

tion is perfectly safe

A Singular and almost mstan-
taneous crystallization can be
Prdaced * saturating boiling
water With Glaubers salt, of

which one ounce and a half of
water will usually dissolve about two ounces ; having done this, pour
the solution, whilst boiling hot, into clean oil flasks, or vials of any
kind, previously warmed in the oven, and immediately cork them, or tie
strips of wetted bladder, over the orifices of the flasks or vials, or pour
into the neck a small quantity of olive oil, or close the neck with a
cork through which a thermometer tube has been passed. When cold,
no crystallization occurs until atmospheric air is admitted ; and it was
formerly believed that the pressure of the air effected this object, until
some one thought of the oil, and now the theory is modified, and crystal-
lization is supposed to occur in consequence of the water dissolving
some air which causes the deposit of a minute crystal, and this being
the turning point, the whole oecomes solid. However the fact may be
explained, it is certain that when the liquid refuses to crystallize on the
admission of air, the solidification occurs directly a minute crystal of
sulphate of soda, or Glauber's salt, is dropped into the vessel.

"When the crystallization is accomplished, the whole mass is usually
so completely solidified, that on inverting the vessel, not a drop of liquid
falls out.

Fig. 89. A. Gas-jarwith stopper open at

first, to be shut when the lamp is withdrawn.

Wooden stand, with hole to carry the cup c,

M.
ranged on pieces of rock or mineral.

CRYSTALLIZATION.

It may be observed that the same mass of salt will answer any
number of times the same purpose. All that is necessary to be done, is
to place the vial or flask, in a saucepan of warm water, and gradually
raise it to the boiling point till the salt is completely liquefied, when the
vessel must be corked and secured from the air as before. When the
solidification is produced much heat is generated, which is rendered
apparent by means of a thermometer, or by the insertion of a copper
wire into the pasty mass of crystal in the flask, and then touching an
extremely thin shaving or cutting of phosphorus, dried and placed on
cotton wool. Solidification in all cases produces heat. Liquefaction
produces cold.

In Masters's freezing apparatus certain measured quantities of crystal-
lized sal-ammoniac, nitre, and nitrate of ammonia, are placed in a
metallic cylinder, sur-
rounded with a small
quantity of spring water
contained in an outer
vessel. Directly the
crystals are liquefied by
the addition of water, in-
tense cold is produced,
which freezes the water
and forms an exact cast
of the inner cylinder in
ice, and this may after-
wards be removed, by

nring away the lique-
salts, and filling the
inner cylinder, with water
of the same temperature
as the air, which rapidly

Fi - 90 - A - The inner cylinder which contains the

freezing mixtur e. B B. The outer one containing spring
ice, and allows it to slip water, oc. The ice slipping away from the inner cylinder.
off into any convenient
vessel ready to receive it. (Pig. 90.) ^

For an ingenious method of obtaining large and perfect crystals of
almost any size, experimentalists are indebted to Le Blanc. His method
consists in first procuring small and perfect crystals say, octohedra of
alum and then placing them in a broad flat-bottomed pan, he pours
over the crystals a quantity of saturated solution of alum, obtained
by evaporating a solution of alum until a drop taken out crystallizes on
cooling. The positions of the crystals are altered at least once a day
with a glass rod, so that all the faces may be alternately exposed to the
action of the solution, for the side on which the crystal rests, or is in
contact with the vessel, never receives any increment. The crystals
will thus gradually grow or increase in size, and when they have done so
for some time, the best and most symmetrical, may be removed and
placed separately, in vessels containing some of the same saturated

BOYS PLAYBOOK OF SCIENCE.

solution of alum, and being constantly turned they may be obtained of
almost any size desired.

Unless the crystals are removed to fresh solutions, a reaction takes
place, in consequence of the exhaustion of the alum from the water, and
the crystal is attacked and dissolved. This action is first perceptible on
the edges and angles of the crystal ; they become blunted and gradually
/ose their shape altogether. By this method crystals may be made to
grow in length or breadth the former when they are placed upon their
sides, the latter if they be made to stand upon their bases.

On Le Blanc's principle, beautiful crystal baskets are made with alum,
sulphate of copper, and bichromate of potash. The baskets are usually
.made of covered copper wire, and when the salts crystallize on them as a
nucleus or centre, they are constantly removed to fresh solutions, so
that the whole is completely covered, and red, white, and blue sparkling
crystal baskets formed. They will retain their brilliancy for any time,
by placing them under a glass shade, with a cup containing a little
water.

The sketch below affords an excellent illustration of some of Nature's
remarkable concretions in the peculiar columnar structure of basalt.

Fig. 91. The Giant's Causeway,

Fig. 92. Alchemists at work.

CHAPTER X.

CHEMISTKY.

THERE is hardly any kind of knowledge which has been so slowly
acquired as that of chemistry, and perhaps no other science has offered
snch fascinating rewards to the labour of its votaries as the philosopher's
stone, which was to produce an unfailing supply of gold ; or the elixir
of life, that was to give the discoverer of the gold-making art the time,
the prolonged life, in which he might spend and enjoy it.

Hundreds of years ago Egypt was the great depository of all learning,
art, and science, and it was to this ancient country that the most cele-
brated sages of antiquity travelled.

Hermes, or Mercurius Trismegistus, the favourite minister of the
Egyptian king Osiris, has been celebrated as the inventor of the art of
alchemy, and the first treatise upon it has been attributed to Zosymus,
of Chemnis or Panopolis. The Moors who conquered Spain were re-

82 BOY'S PLAYBOOK OF SCIENCE.

markable for their learning, and the taste and elegance with which they
designed and carried out a new style of architecture, with its love
Arabesque ornamentation. They were likewise great followers of the
art of alchemy, when they ceased to be conquerors, and became more
reconciled to the arts of peace. Strange that such a people, thirsting
as they did in after years for all kinds of knowledge, should have
destroyed, in the persons of their ancestors, the most numerous collection
of books that the world had ever seen : the magnificent library of
Alexandria, collected by the Ptolemies with great diligence and at an
enormous expense, was burned by the orders of Caliph Omar ; whilst it
is stated that the alchemical works had been previously destroyed by
Diocletian in the fourth century, lest the Egyptians should acquire by
such means sufficient wealth to withstand the Roman power, for gold
was then, as it is now, " the sinews of war."

Eastern historians relate the trouble and expense incurred by the suc-
ceeding Caliphs, who, resigning the Saracenic barbarism of their an-
cestors, were glad to collect from all parts the books which were to
furnish forth a princely library at Bagdad. How the learned scholar
sighs when he reads of seven hundred thousand books being consigned
to the ignominious office of heating forty thousand baths in the capital
of Egypt, and of the magnificent Alexandrian Library, a mental fuel for
the lamp of learning in all ages, consumed in bath furnaces, and affording
six months' fuel for that purpose. The Arabians, however, made amends
for these barbarous deeds in succeeding centuries, and when all Europe
was laid waste under the iron rule of the Goths, they became the pro-
tectors of philosophy and the promoters of its pursuits ; and thus we
come to the seventh century, in which Geber, an Arabian prince lived, and
is stated to be the earliest of the true alchemists whose name has reached
posterity.

Without attempting to fill up the alchemical history of the intervening
centuries, we leap forward six hundred years, and now find ourselves in
imagination in England, with the learned friar, Roger Bacon, a native of
Somersetshire, who lived about the middle of the thirteenth century : and
although the continual study of alchemy had not yet produced the
" stone," it bore fruit in other discoveries, and Roger Bacon is said,
with great appearance of truth, to have discovered gunpowder, for he
says in one of his works : " From saltpetre and other ingredients we
are able to form a fire which will burn to any distance ;" and again
alluding to its effects, " a small portion of matter, about the size of the
thumb, properly disposed, will make a tremendous sound and corusca-
tion, by which cities and armies might be destroyed." The exaggerated
style seems to have been a favourite one with all philosophers, from the
time of Roger Bacon to that of Muschenbroek of the University of Ley den,
who accidentally discovered the Leyden jar in the year 1746, and re-
ceiving the first shock, from a vial containing a little water, into which
a cork and nail had been fitted, states that " he felt himself struck in
his arms, shoulders, and breast, so that he lost his breath, and was
two days before he recovered from the effects of the blow and the

CHEMISTHY. 83

terror ;" adding, that " he would not take a second shock for the kingdom
of France." Disregarding the numerous alchemical events occurring
from the time of Roger Bacon, we again advance four hundred years
viz., to the year 1662, when, on the 15th of July, King Charles II.
granted a royal charter to the Philosophical Society of Oxford, who
had removed to London, under the name of the Royal Society of London
for Promoting Natural Knowledge, and in the year 1665 was published
the first number of the Philosophical Transactions ; this work contains
the successive discoveries of Mayow, Hales, Black, Leslie, Cavendish,
Lavoisier, Priestley, Davy, Faraday; and since the year 1762 lias been
regularly published at the rate of one volume per annum. With this
preface proceed we now to discuss some of the varied phenomena of
chemical attraction, or what is more correctly termed

CHEMICAL AFFINITY.

The above title refers to an endless series of changes brought about
by chemical combinations, all of which can be reduced to certain fixed
laws, and admit of a simple classification and arrangement. A me-
chanical aggregation, however well arranged, can be always distinguished
from a chemical one. Thus, a grain of gunpowder consists of nitre,
which can be washed away with boiling water, of sulphur, which can be
sublimed and made to pass away as vapour, of charcoal, which remains
behind after the previous processes are complete; this mixture has
been perfected by a careful proportion of the respective ingredients, it
has been wetted, and ground, and pressed, granulated, and finally
dried; all these mechanical processes have been so well carried out
that each grain, if analysed, would be similar to the other ; and yet it
is, after all, only a mechanical aggregation, because the sulphur, the
charcoal, and the nitre are unchanged. _ A grain of gunpowder mois-
tened, crushed, and examined by a high microscopic power, would
indicate the yellow particles of sulphur, the black parts of charcoal,
whilst the water filtered from the grain of powder and dried, would
show the nitre by the form of the crvstal. On the other hand,
if some nitre is fused at a dull red heat in a little crucible, and two
or three grains of sulphur are added, they are rapidly oxidized, and
combine with the potash, forming sulphate of potash ; and after this
change a few grains of charcoal may be added in a similar manner, when
they burn brightly, and are oxidized and converted into carbonic acid,
which also unites in like manner with the potash, forming carbonate of
potash ; so that when the fused nitre is cooled and a few particles
examined by the microscope, the charcoal and sulphur are no longer
distinguishable, they have undergone a chemical combination with
portions of the nitre, and have produced two new salts, perfectly dif-
ferent in taste, gravity, and appearance from the original substances
employed to produce them. Hence chemical combination is defined
to be "*that property which is possessed by one or more substances,
of uniting together and producing a third or other body perfectly dif-

a 9

84 BOY'S PLAYBOOK OF SCIENCE.

ferent in its nature from either of the two or more generating the new
compound"

To return to our first experiment with the gunpowder : take sulphur,
place some in an iron ladle, heat it over a gas flame till it catches fire, then
ascend a ladder, and pour it gently, from the greatest height you can
reach, into a pail of warm water : if this experiment is performed in a
darkened room a magnificent and continuous stream of fire is obtained,
of a blue colour, without a single break in its whole length, provided
the ladle is gradually inclined and emptied. The substance that drops
into the warm water is no longer yellow and hard, but is red, soft, and
plastic ; it is still sulphur, though it has taken a new form, because that
element is dimorphous (fiig twice, and \iop$T] a form), and, Proteus-like,
can assume two forms. Take another ladle, and melt some nitre in it at
a dull red heat, then add a small quantity of sulphur, which will burn as
before ; and now, after waiting a few minutes, repeat the same experiment
by pouring the liquid from the steps through the air into water ; observe
it no longer flames, and the substance received into the water is not
red and soft and plastic, but is white, or nearly so, and rapidly dis-
solves away in the water. The sulphur has united with the oxygen of
the nitre and formed sulphuric acid, which combines with the potash
and forms sulphate of potash ; here, then, oxygen, sulphur, and potas-
sium, have united and formed a salt in which the separate properties
of the three bodies have completely disappeared ; to prove this, it is
only necessary to dissolve the sulphate of potash in water, and after
filtering the solution, or allowing it to settle, till it becomes quite clear
and bright, some solution of baryta may now be added, when a white
precipitate is thrown down, consisting of sulphate of baryta, which is in-
soluble in nitric or other strong acids. The behaviour of a solution of
sulphate of potash with a nitrate of baryta may now be contrasted with
that of the elements it contains ; oh the addition of sulphur to a solu-
tion of nitrate of baryta no change whatever takes place, because the
sulphur is perfectly insoluble. If a stream of oxygen gas is passed from
a bladder and jet through the same test, no effect is produced ; the nitrate
of baryta has already acquired its full proportion of oxygen, and no
further addition has any power to change its nature ; finally, if a bit of
the metal potassium is placed in the solution of nitrate of baryta it does
not sink, being lighter than water, and it takes fire ; but this is not in
any way connected with the presence of the test, as the same thing will
happen if another bit of the metal is placed in water it is the oxygen
of the latter which unites rapidly with the potassium, and causes it to
become so hot that the hydrogen, escaping around the little red-hot
globules, takes fire ; moreover, the fact of the combustion of the potas-
sium under such circumstances is another striking proof of the opposite
qualities of the three elements sulphur, oxygen, and potassium as
compared with the three chemically combined and forming sulphate of
potash. The same kind of experiment may be repeated with charcoal ;
if some powdered charcoal is made red-hot, and then puffed into the air
with a blowing machine, numbers of sparks are produced, and the char

CHEMISTRY. 85

coal burns away and forms carbonic acid gas, a little ash being left
behind; but if some more nitre be heated in a ladle, and charcoal
added, a brilliant deflagration (deflayro, to burn) occurs, and the charcoal,
instead of passing away in the air as carbonic acid, is now retained in
the same shape, but firmly and chemically united with the potash of the
nitre, forming carbonate of potash, or pearl-ash, which is not black and
insoluble in water and acids like charcoal, but is white, and not only
soluble in water, but is most rapidly attacked by acids with effer-
vescence, and the carbon escapes in the form of carbonic acid gas. Thus
we have traced out the distinction between mechanical aggregation and
chemical affinity, taking for an example the difference between gun-
powder as a whole (in which the ingredients are so nicely balanced that
it is almost a chemical combination), and its constituents, sulphur,
charcoal, and nitre, when they are chemically combined ; or, in briefer
language, we have noticed the difference between the mechanical mix-
ture, and some of the chemical combinations, of three important elements.
Our very slight and partial examination of three simple bodies does not,
however, afford us any deep insight into the principles of chemistry ; we
have, as it were, only mastered the signification of a few words in a lan-
guage ; we might know that chien was the French for dog, or cheval
horse, or homme man ; but that knowledge would not be the acquisition of
the French language, because we must first know the alphabet, and
then the combination of these letters into words ; we must also acquire
a knowledge of the proper arrangement of these words into sentences,
or grammar, both syntax and prosody, before we can claim to be a
French scholar : so it is with chemistry any number of isolated experi-
ments with various chemical substances would be comparatively useless,
and therefore the " alphabet of chemistry," or " table of simple ele-
ments/' must first be acquired. These bodies are understood to be
solids, fluids, and gases, which have hitherto defied the most elaborate
means employed to reduce them into more than one kind of matter.
Even pure light is separable into seven parts viz., red, orange,
yellow, green, blue, inaigo, and violet ; but the elements we shall
now enumerate are not of a compound, but, so far as we know, of an
absolutely simple or single nature ; they represent the boundaries, not
the finality, of the knowledge that may be acquired respecting them.

The elements are sixty-four in number, of which about forty are
tolerably plentiful, and therefore common; whilst the remainder, twenty-
four, are rare, and for that reason of a lesser utility : whenever
Nature employs an element on a grand scale it may certainly be called
common, but it generally works for the common good of all, and fulfils
the most important offices.

BOY'S PLAYBOOK OF SCIENCE.

CLASSIFICATION OF THE ALPHABET OF CHEMISTRY.

13 Non-Metallic Bodies.

Combining

Coi

nbining

Name.

ymbol

pro

portion
nt.nmift

Name. i

3ymbo

prc

' nr

(portion,
fitnmio.

weight.

Oxygen . .

Carbon . .

Hydrogen

Boron . . .

10-9

Nitrogen . .

10.

Sulphur . .

;

Chlorine . .

35-5

11.

Phosphorus .

Iodine . . .

127-1

12.

Silicon . .

21-3

Bromine . .

80-

13.

Selenium . .

39-5

Fluorine . .

18-9

51 Metals.

Aluminum .

13-7

27.

Nickel. . .

29-6

Antimony

129

28.

Norium . .

Arsenic . .

29.

Niobium . .

Barium . .

68-5

30.

Osmium . .

99-6

Bismuth . .

213

31.

Platinum . .

987

Cadmium . .

32.

Potassium .

39-2

Calcium . .

33.

Palladium

53-3

Cerium . .

34.

Pelopium . .

Chromium

B-

26-7

35.

Rhodium . .

52-2

10.

Cobalt. . .

29-5

36.

Rhuthenium .

52-2

11.
12.

Copper . .
Donarium . .

"~~

31-7

37.

38.

Silver . . .
Sodium . .

108-1
23

13.

Didymium. .

39.

Strontium

43-8

14.

Erbium . .

40.

Tin. . . .

15,

Gold . . .

197

41.

Tantalum . .

184

16.

Glucinum . .

42.

Tellurium . .

64-2

17.

Iron . . .

43.

Terbium . .

18.

Ilmenium . .

44.

Thorium . .

59-6

19.

Iridium .

45.

Titanium . .

20.

Lead . . .

103-7

46.

Tungsten . .

21.

Lanthanium .

47.

Uranium . .

22.

Lithium . .

6-5

48.

Vanadium

68-6

23.

Magnesium .

12-2

49.

Yttrium . .

24.

Manganese .

27-6

50.

Zinc- . . .

32-6

25.

Mercury . .

100

51.

Zirconium

22-4

26.

Molybdenum .

(N.B. The elements printed in italics are at present unimportant.

A few words will suffice to explain the meaning of the terms which
head the names, letters, and numbers of the Table of Elements. The

* From the mineral Wolfran, and now exceedingly valuable, as when alloyed with iron
it is harder than, and will bore through steel.

CHEMISTEY. 87

names of the elements have very interesting derivations, which it is not
the object of this work to go into; the symbols are abbreviations,
ciphers of the simplest kind, to save time and trouble in the frequent re-
petition of long words, just as the signs -|- plus, and minus, are used
in algebraic formulae. For instance the constant recurrence of water
in chemical combinations must be named, and would involve the most
tedious repetition; water consists of oxygen and hydrogen, and by taking
the first letter of each word we have an instructive symbol, which not
only gives us an abbreviated term for water, but also imparts at once a
knowledge of its composition by the use of the letters, HO.

Again, to take a more complex example, such as would occur in the
study of organic chemistry a sentence such as the hydrated oxide of
acetule,^ is written at once by C 4 H 4 2 , the figures referring to the number
of equivalents of each element viz., 4 equivalents of C, the symbol for
carbon, 4 of H (hydrogen), and 2 of (oxygen).

The long word paranaphthaline, a substance contained in coal tar, is
disposed of at once with the symbols and figures C 30 H 12 .

The figures in the third column are, however, the most interesting
to the precise and mathematically exact chemist. They represent the
united labours of the most painstaking and learned chemists, and are
the exact quantities in which the various elements unite. To quote one
example : if 8 parts by weight of oxygen viz., the combining propor-
tions of that element are united with 1 part by weight of hydrogen, also
its combining number, the result will be 9 parts by weight of water ;
but if 8 parts of oxvgen and 2 parts of hydrogen were used, one only of
the latter could unite with the former, and the result would be the
formation again of 9 parts of water, with an overplus of 1 equivalent of
hydrogen.

It is useless to multiply examples, and it is sufiicient to know that
with this table of numbers the figures of analysis are obtained. Sup-
posing a substance contained 27 parts of water, and the oxygen in
this had to be determined, the rule of proportion would give it at once,
9 : 27 : : 8 : 24. 9 parts of water are to 27 parts as 8 of oxygen (the
quantity contained in 9 parts of water) are to the answer required
viz., 24 of oxygen. The names, symbols, and combining proportions
being understood, we may now proceed with the performance of many
interesting

CHEMICAL EXPERIMENTS.

As the permanent gases head the list, they will first engage our
attention, beginning with the element oxvgen Symbol 0, combining
proportion 8. There is nothing can give a better idea of the enormous
quantity of oxygen present in the animal, vegetable, and mineral king-
doms, than the statement that it represents one-third of the weight of
the whole crust of the globe. Silica, or flint, contains about half its
weight of oxygen ; lime contains forty per cent. ; alumina about thirty-
three per cent. In these substances the element oxygen remains inactive
and powerless, chained by the strong fetters of chemical affinity to the

BOY'S PLAYB00K OF SCIENCE.

silicium of the flint, the calcium of the lime, and the aluminum of the
alumina. If these substances are heated by themselves they will not
yield up the large quantity of oxygen they contain.

Nature, however, is prodigal in her creation, and hence we have but
to pursue our search diligently to find a substance or mineral containing
an abundance of oxygen, and part of which it will relinquish by what
used to be called by the " old alchemists" the torture of heat. Such a
mineral is the black oxide of manganese, or more correctly the binoxide
of njjhganese, which consists of one combining proportion of the metal
manganese viz., 27'6, and two of oxygen viz., 8 X 2 = 16. If three
proportions of the binoxide of manganese are heated to redness in an
iron retort, they yield one proportion (equal to 8) of oxygen, and all
that has just been explained by so many words is comprehended in the
symbols and figures below :

3 Mn0 2 = Mn 3 O 4 + 0.

Thus the 3 Mn0 2 represent the three proportions of the binoxide of
manganese before heat is applied, whilst the sign =, the sign of equation
(equal to), is intended to show that the elements or compounds placed
before it produce those which follow it ; hence the sequel Mn 3 4 -f(?
shows that another compound of the metal and oxygen is produced,
whilst the + indicates the liberated oxygen gas. The iron retort
employed to hold the mineral should be made of cast iron in preference
to wrought iron, as the latter is very soon worn out by contact with
oxygen at a red heat. A gun-barrel will answer the purpose for an
experiment on the small scale, to which must be adapted a cock and
piece of pewter tubing. Such a make-shift arrangement may do very
well when nothing better offers ; but as a question of expense, it is
probably cheaper in the end to order of Messrs. Simpson and Maule, or
of Messrs. Griffin, or of Messrs. Bolton, a cast-iron bottle, or cast-iron
retort, as it is termed, of a size sufficient to prepare two gallons of

Pig. 93. A. The iron bottle, containing the black oxide of manganese, with pipe passing to
the pneumatic trough, B B, in which is fixed a shelf, c, perforated with a hole, under which
the end of the pipe is adjusted, and the gas passes into the gas-jar, D.

oxygen from the binoxide of manganese, which, with four feet of iron
conducting-pipe, and connected to the bottle with a screw, does not

PREPARATION OF OXYGEN GAS.

cost more than six shillings an enormous dip, perhaps, in the juvenile
pocket, and therefore we shall indicate presently a still cheaper appa-
ratus for the same purpose. (Eig. 93.)

The oxygen is conveyed to a square tin box provided with a shelf at
one end, perforated with several holes at least one inch in diameter,
called the pneumatic trough ; any wooden trough, butter or wash-tub,
foot-pan or bath, provided with a shelf, may be raised by the same
title to the dignity of a piece of chemical apparatus. The gas jar rn^t
be filled with water by withdrawing the stopper and pressing it down
into the trough, and when the neck is below the level of the water, the
stopper is again inserted, and the jar with the water therein contained

A D

Fig. 94. A A. Pneumatic trough, with gas jar raised to shelf; bubbles of air are rushing
in at B, as the level of the water is below the shelf viz., at c c. D D. Same trough and
gas jar with water kept over the shelf by the introduction of the stone pitchers, full of
water.

lifted steadily on to the shelf, the entry of atmospheric air being prevented
by keeping the lower part of the gas jar, called the welt, under the water.
Sometimes the pneumatic trough contains so small a quantity of water
that on raising the gas jar to the shelf the liquid does not coyer the bottom,
and the air rushes up in large bubbles. Under these circumstances it
is better to provide a galWstone jug full of water, so that when the
jar is being raised to the shelf it may be thrust into the trough (on the
same principle as the crow and the pitcher in the fable), and thus by its
bulk (as the stones in the pitcher) raise the water to the proper level.
When the gas jar is about half filled with gas the jug may be withdrawn.
This arrangement saves the trouble of constantly adding and baling out
water from the pneumatic trough. (Fig. 94.)

There are other solid oxygenized bodies in which the affinities are less
powerful, and hence a lower degree of heat suffices to liberate the
oxygen gas, and one of the most useful in this respect is the salt termed
chlorate of potash. If the substance is heated by itself, the temperature
required to expel the oxygen is almost as high as that demanded for
the black oxide of manganese ; but, strange to say, if the two substances
are reduced to powder, and mixed in equal quantities by weight, then a
very moderate increase of heat is sufficient to cause the chlorate of

BOY'S PLAYBOOK OF SCIENCE.

potash to give up its oxygen, whilst the oxide of manganese undergoes
no change whatever. It seems to fulfil only a mechanical office possibly
that of separating each particle of chlorate of potash from the other, so

Fig. 95. Preparation of oxygen from

KO.C10 5 ={ a

that the heat attacks the substance in detail, just as a solid square of
infantry might repel almost any attack, whilst the same body dispersed
over a large space might be of little use ; so with the chlorate of potash,
which undergoes rapid decomposition when mixed with and divided
amongst the particles of the oxide of manganese ; less so with the red
oxide of iron, and still less with sand or brick-dust. (Fig. 95.)

This curious fact is explained usually by reference to what is called
catalytic action, or decomposition by contact (Kara, downwards, and \va>, I
unloosen), being a power possessed by a body of resolving another into a new
compound without undergoing any change itself. To make this term still
clearer, we may notice another example in linen rags, which may be
exposed for any length of time to the action of water without fear of
conversion into sugar ; if, however, oil of vitriol is first added to the
linen rags, and they are subsequently digested at a proper temperature
with water, then the rags are converted into sugar (the author has seen
a specimen made of an " old shirt") ; but, curious to relate, the oil of
vitriol is unchanged in the process, and if the process be commenced with a
pound of acid, the same quantity is discoverable at the end of the chemical
decomposition of the linen rags, and their conversion into sugar.

If a mixture of equal parts of oxide of manganese and chlorate of
potash is placed in a clean Florence flask, with a cork, and pewter, or
glass tube attached, great quantities of oxygen are quickly liberated, on
the application of the heat of a spirit lamp. Such a retort would cost
about fourpence, and if the flask is broken in the operation it can be
easily replaced by another, value one penny, as the same cork and tube
will generally suit a number of these cheap glass vessels. Corks may

PREPARATION OP OXYGEN GAS.

always be softened by using either a proper cork squeezer, or by placing
them under a piece of board or a flat surface, and rolling and pressing
the cork till cpite elastic.

Whilst fitting the latter into the neck of a flask, it is perhaps safer
to hold the thin and fragile vessel in a cloth, so that if the flask breaks
the chemical experiment may not be arrested for many days by the
severe cutting and wounding of the fingers. After the cork is fitted, it
is to be removed from the flask and bored wifti a cork borer. This
useful tool is sold in complete sets to suit all sizes of glass tubes, and
the pewter or glass being inserted, the flask and tube will be ready for
use, provided the tube is bent to the proper curve. This is easy enough
to perform with the pewter, but not quite so easy with the glass tube,
which must be held over the flame of a spirit lamp till soft, and then

Fig. -96. A. The cork squeezer. B. The cork borers, c. The operation of bending the
glass tube over the flame of the spirit-lamp. D. The neck of the flask, with cork and tube
bent and fitted complete for use.

bent very gradually to the proper curve. If a short length of the glass
tube is heated, it bends too sharply, and the convexity of the glass is
flattened, whilst the internal diameter of the tube is lessened, so that at
least three inches in length should be warmed, and the heat must not
be continued in one place only, but should be maintained in the direc-
tion of the bend, the whole manipulation being conducted without any
hurry. (Fig. 96.)

Having filled a gas jar with oxygen, it may be removed from the
pneumatic trough by sliding it into a plate under the surface of the
water, and to prevent the stopper being thrust out accidentally from the
jar by the upward pressure of the gas, whilst a little compressed, during
the act of passing it into the plate, it is advisable to hold the stopper
of the jar firmly but gently, so that it cannot slip out of its place. A
number of jars of oxygen may be prepared and arranged in plates, all of
which of course must contain a little water, and enough to cover the
welt of the jar.

BOY'S PLAYBOOK OF SCIENCE.

EXPERIMENTS WITH OXYGEN GAS.

This gas was originally discovered by Priestley, in August, 1 774, and
was first obtained by heating red precipitate i.e., the red oxide ot
mercury.

HgO=Hg + 0.

We leave these symbols and figures to be deciphered by the youthful
philosopher with the aid of the table of elements, &c., and return to the
experiments.

There are certain thin wax tapers like waxed cord, called bougies,
which can be bent to any shape, and are very convenient for experiments
with the gases. If one of these tapers is bent as
in Tig. 97, then lighted and allowed to burn for
some minutes, a long snuff is gradually formed,
which remains in a state of ignition when the flame
of the taper is blown out. On plunging this into
a jar of oxygen, it instantly re-lights with a sort
of report, and burns with greatly-increased bril-
liancy, as described by Dr. Priestley in his first
experiment with this gas, and so elegantly repeated
by Professor Brande in his refined dissertation on
the progress of chemical science.

"The 1st of August, 1774, is a red-letter day in
the annals of chemical philosophy, for it was then
that Dr. Priestley discovered dephlogisticated air.
Some, sporting in the sunshine of rhetoric, have
called this the birthday of pneumatic chemistry ;
but it was even a more marked and memorable
period ; it was then (to pursue the metaphor) that
this branch of science, having eked out a sickly and infirm infancy in
the ill-managed nursery of the early chemists, began to display symp-
toms of an improving constitution, and to exhibit the most hopeful
and unexpected marks of future importance. The first experiment,
which led to a very satisfactory result, was concluded as follows:
A glass jar was filled with quicksilver, and inserted in a basin of the
same; some red precipitate of quicksilver was then introduced, and
floated upon the quicksilver in the jar; heat was applied to it in this
situation with a burning-lens, and to use Priestley's own words, I pre-
sently found that air teas expelled from it very readily. Having got
about three or four times as much as the bulk of my materials, 1 ad-
mitted wetter into it, and found that it was not imbibed by it. But
what surprised me more than I can well express was, that a candle
burned in this air with a remarkably vigorous flame, very much like that
enlarged flame with which a candle burns in nitrous air exposed to iron
or lime of sulphur (i.e., laughing gas) ; but as I had got nothing like
this remarkable appearance from any kind of air besides this peculiar

Fig. 97.

EXPERIMENTS WITH OXYGEtf GAS.

Fig. 98. A. Glass vessel full of mercury, con-
taining the red precipitate at the top, and stand-

modification of nitrous air, and
I kneio no nitrous acid was used
in the preparation of mercurius
calcinatus, I was utterly at a loss
how to account for it" (Fig. 98.)

Second Experiment.

The term oxygen is derived
from the Greek \ofrar, acid, and
yevvao), I give rise to), and was
originally given to this element
by Lavoisier, who also claimed
its discovery ; and if this honour
is denied him, surely he has de-
served equal scientific glory inhis

masterly experiments, through ing in the dish B^lso'containing mercury, c. The
if ,J j ',, , ,? burning-glass concentrating the sun's rays on the

Which he discovered that the re d precipitate, being Priestley's original experi-
mixture of forty-two parts by ment.

measure of azote, with eight parts by measure of oxygen, produced a
compound precisely resembling our atmosphere. The name given to
oxygen was founded on a series of experiments, one of which will now
be mentioned.

Place some sulphur in a little copper ladle
attached to a wire, and called a deflagrating
spoon, passed through a round piece of zinc
or brass plate and cork, so that the latter
acts as an adjusting arrangement to fix the
wire at any point required. The combus-
tion of the" sulphur, previously feeble, now
assumes a remarkable intensity, and a pecu-
liar coloured light is generated, whilst the
sulphur unites with the oxygen, and forms
sulphurous acid gas. It produces, in fact,
the same gas which is formed by burning an
ordinary sulphur match. This compound is
valuable as a disinfectant, and is a very im-
portant bleaching agent, being most exten-
sively employed in the whitening of straw
employed in the manufacture of straw bon-
nets. It is an acid gas, as Lavoisier found,
and this property may be detected by pour-
ing a little tincture of litmus into the bot-
tom of the plate in which the gas jar stands. The'gasjarT
The blue colour of the litmus is rapidly
changed to red, and it might be thought that no further argument
could possibly be required to prove that oxygen was the acidifying
agent, themore particularly as the result is thesameinthe next illustration.

Fig. 99. A. The deflagrating

9i BOY'S PLAYBOOK OF SCIENCE.

Third Experiment.

Cut a small piece from an ordinary stick of phosphorus under
water, take care to dry it properly with a cloth, and after placing it
in a deflagrating spoon, remove the stopper from the gas-jar, as there
is no fear of the oxygen rushing away, because it is somewhat heavier
than atmospheric air ; and then, after placing the spoon with the phos-
phorus in the neck of the jar, apply a heated wire and pass the spoon
at once into the middle of the oxygen; in a few seconds a most
brilliant light is obtained, and the jar is filled with a white smoke ;
as this subsides, being phosphoric acid, and perfectly soluble in water,
the same litmus test may be applied, when it is in like manner
changed to red. The acid obtained is one of the most important con-
stituents of bone.

Fourth Experiment.

A. bit of bark-charcoal bound round with wire is set on fire either
by holding it in the flame of a spirit-lamp, or by attaching a small piece
of waxed cotton to the lower part, and igniting this ; the charcoal may then
be inserted into a bottle of oxygen, when the most brilliant scintilla-
tions occur. After the combustion has ceased and the whole is cool,
a little tincture of litmus may also be poured in and shaken about,
when it likewise turns red, proving for the third time the generation
of an acid body, called carbonic acid an acid, like the others already
mentioned, of great value, and one which Nature employs on a stu-
pendous scale as a means of providing plants, &c., with solid char-
coal. Carbonic acid, a virulent poison to animal life, is, when properly
diluted, and as contained in atmospheric air, one of the chief alimen-
tary bodies required by growing and healthy plants.

In three experiments acid bodies have been obtained ; can we specu-
late on the result of the next ?

Fifth Experiment.

Into a deflagrating spoon place a bit of potassium, set this on fire
by holding it in the spoon in the flame of a spirit-lamp, and then rapidly
plunge the burning metal into a bottle of oxygen. A brilliant ignition
occurs in the deflagrating spoon for a few seconds, and there is little or no
smoke in the jar. The product this time is a solid, called potash,
and if this be dissolved in water and -filtered, it is found to be clear
and bright, and now on the addition of a little tincture of litmus to
one half of the solution, it is wholly unaffected, and remains blue ;
but if with the other half a small quantity of tincture of turmeric is
mixed, it immediately changes from a bright yellow solution to a
reddish-brown, because turmeric is one of the tests for an alkali ; and
thus is ascertained by the help of this and other tests that the result
of the combustion is not an acid, but an alkali. The experiment
is made still more satisfactory by burning another bit of potassium
in oxygen and dissolving the product in water, and if any portion of

EXPEIUMENTS WITH OXYGEN GAS. 05

the reddened liquid derived from the sulphurous, phosphoric, and car-
bonic acids taken from the previous experiments, be added to separate
portions of the alkaline solution, they are all restored to their original blue
colour, because an acid is neutralized by an alkali ; and the experiment is
made quite conclusive by the restoration of the reddened turmeric to a
bright yellow on the addition of a solution of either of the three acids
already named. Moreover, an acid need not contain a fraction of
oxygen, as there is a numerous class of %dracids, in which the acidi-
fying principle is hydrogen instead of oxygen, such as the hydrochloric,
hydriodic, hydro-bromic, and hydrofluoric acids.

Sixth Experiment.

A. piece of watch-spring is softened at one end, by holding it in the
flame of a spirit-lamp, and allowing it to cool. A bit of waxed cotton,
is then bound round the softened end, and after being set on fire, is
plunged into a gas jar containing oxygen ; the cotton first burns away,
and then the heat communicates to the steel, which gradually takes fire,
and being once well ignited, continues toburn with amazing rapidity, form-
ing drops of liquid dross, which fall to the bottom of the plate and also
a reddish smoke, which condenses on the sides of the jar ; neither the
dross which has dropped into the plate, nor the reddish matter condensed
on the jar, will affect either tincture of litmus or turmeric; they are
neither acid nor alkaline, but neutral compounds of iron, called the
sesquioxide of iron (Ee^), and the magnetic oxide (Fe 3 4 =EeO.

Some oxygen gas contained in a bladder provided with a proper
jet may be squeezed out, and upon, some liquid phosphorus con-

Fig. 100. A. Bladder containing- oxygen, provided with a stop-cock and jet leading to,
B, B. Finger glass containing boiling water, c. The cup of melted phosphorus under the
water. The gas escapes from the bladder when pressed.

tained in a cup at the bottom of a finger glass full of boiling water,
when a most brilliant combustion occurs, proving that so long as the
principle is complied with viz., that of furnishing oxygen to a com-
bustible substance it will burn under water, provided it is insoluble,
and possesses the remarkable affinity for oxygen which belongs to
phosphorus. The experiment should be performed with boiling water,
to keep the phosphorus in the liquid state j and it is quite as well to hold

BOY'S PLAYBOOK OF SCIENCE.

a square foot of wire gauze over the finger glass whilst the experiment
is being performed. (Eig. 100.)

Eighth Experiment.

Oxygen is available from many substances when they are mixed with
combustible substances, and hence the brilliant effects produced by
burning a mixture of nitre, meal powder, sulphur, and iron or steel
filings ; the metal burns with great brilliancy, and is projected from the
case in most beautiful sparks, which are long and needle-shaped with
steel, and in the form of miniature rosettes with iron filings ; it is the
oxygen from the nitre that causes the combustion of the metal, the
other ingredients only accelerate the heat and rate of ignition of the
brilliant iron, which is usually termed a gerb.

Ninth Experiment.

A mixture of nitrate of potash, powdered
charcoal, sulphur, and nitrate of strontium,
driven into a strong paper case about two
inches long, and well closed at the end with
varnish, being quite waterproof, may be set on
fire, and will continue to burn under water
until the whole is consumed ; the only precau-
tion necessary being to burn the composition
from the case with the mouth downward, and
if the experiment is tried in a deep glass jar it
has a very pleasing effect. (Fig. 101.)

The red-fire composition is made by mixing
nitrate of strontia 40 parts by weight, flowers
of sulphur 13 parts, chlorate of potash 5 parts,
sulphuret of antimony 4 parts. These ingre-
dients must first be well powdered separately,
and then mixed carefully on a sheet of paper
with a paper-knife. They are liable to explode
if rubbed together in a mortar, on account of
^he presence of sulphur and chlorate of potash,
and the composition, if kept for any time, is
liable to take fire spontaneously.

Fig.'ioi. A. Case of red fire
downwards, and at-

?f* s?nk a

U. c c. Jar containing water.

Tenth Experiment.

Some zinc is melted in an iron ladle, and made quite red hot ; if a
kittle dry nitre is thrown upon the surface, and gently stirred into the
metal, it takes fire with the production of an intense white light, whilst
large quantities of white flakes ascend, and again descend when cold,
being the oxide of zinc, and called by the alchemists the " Philosopher's
Wool" (ZnO). In this experiment the oxygen from the nitre effects
the oxidation of the metal zinc.

THE BUDE LIGHT.

Eleventh Experiment.

A mixture of four pounds of nitre with two of sulphur and one and
a half of lamp black produces a most beautiful and curious fire, con-
tinually projected into the air as sparks having the shape of the rowel
of a spur, and one that may be burnt with perfect safety in a room, as
the sparks consume away so rapidly, in consequence of the finely divided
condition of the charcoal, that they may be received on a handkerchief
or the hand without burning them. The difficulty consists in effecting the
complete mixture of the charcoal. The other two ingredients must
first be thoroughly powdered separately, and again triturated when
mixed, and finally the charcoal must be rubbed in carefully, till the
whole is of a uniform tint of grey and very nearly black, and as the
mixture proceeds portions must be rammed into a paper case, and set
on fire ; if the stars or pinks come out in clusters, and spread well
without other and duller sparks, it is a sign that the whole is well
mixed; but if the sparks are accompanied with dross, and are pro-
jected out sluggishly, and take some time to burn, the mixture and
rubbing in the mortar must be continued ; and even that must not be
carried too far, or the sparks will be too small. N.B. If the lamp-black
was heated red hot in a close vessel, it would probably answer better
when cold and powdered.

Twelfth Experiment.

Into a tall gas jar with a wide neck project some red-hot lamp-black
through a tin funnel, when a most brilliant flame-like fire is obtained,
showing that finely divided charcoal with pure oxygen would be suf-
ficient to afford light; but as the atmosphere consists of oxygen
diluted with nitrogen, compounds of charcoal with hydrogen, are the
proper bodies to burn, to produce artificial light.

Thirteenth Experiment. The Bude
Light.

This pretty light is obtained by pass -
ing a steady current of oxygen gas (es-
caping at a very low pressure) through
and up the centre pipe of an argand oil
lamp, which must be supplied with a
highly carbonized oil and a very thick
wick, as the oxygen has a tendency to
burn away the cotton unless the oil is
well supplied, and allowed to overflow
the wick, as it does in the lamps of the
lighthouses. The best whale oil is
usually employed, though it would be
worth while to test the value of Price's
"Belmontine Oil" for the same pur-
pose. (Fig. 102.) fl F !f- 10 . 2 - A - Reservoir of oil. B. The
v flexible pipe conveying oxygen to centre

of the argand lamp.

BOY S PLAYBOOK OP SCIENCE.

Fourteenth Experiment. A Red Light.

Clear out the oil thoroughly from the Bude light apparatus ; or, what
is better, have two lamps, one for oil, and the other for spirit ; fill the
apparatus with a solution of nitrate of strontia and chloride of calcium
in spirits of wine, and let it burn from the cotton in the same way as
the oil, and supply it with oxygen gas.

Fifteenth Experiment. A Green Light.

Dissolve boracic acid and nitrate of baryta in spirits of wine, and
supply the Bude lamp with this solution.

Sixteenth Experiment. A Yellow Light.

Dissolve common salt in spirits of wine, and burn it as already de-
scribed in the Bude light apparatus.

Seventeenth Experiment. The Oxy -calcium Light.

This very convenient light is obtained in a simple manner, either by
using a jet of oxygen as a blowpipe to project the flame of a spirit
lamp on to a ball of lime ; or common coal-gas is employed instead of the

No.l.

No. 2.

Pig. 103. No. 1. A. Oxygen jet. B. The ball of lime, suspended by a wire. c. Spirit
lamp.

No. 2. i>. Oxygen jet. E. Gas (jet connected with the gas-pipe in the rear by flexible
pipe) projected on to ball of lime, r.

spirit lamp, being likewise urged against a ball of lime. By this plan
one bag containing oxygen suffices lor the production of a brilliant light,
not equal, however, to the oxy-hydrogen light, which will be explained in
the article on hydrogen. (Fig. 103.)

Eighteenth Experiment.

To show the weight of oxygen gas, and that it is heavier than air,
the stoppers from two bottles containing it may be removed, one bottle
may be left open for some time and then tested by a lighted taper, when

EXPERIMENTS WITH OXYGEN GAS. 99

it will still indicate the presence of the gas, whilst the other may be
suddenly inverted over a little cup in whicli some ether, mixed with a
few drops of turpentine, may be burning the flame burns with much
greater brilliancy at the moment when, the oxygen comes in contact
with it.

The theory of the effect of oxygen upon the system when inhaled
would be an increase in the work of the respiratory organs ; and it is
stated that after inhaling a gallon or so of this gas, the pulse is raised
forty or fifty beats per second : the gas is easily inhaled from a large
indiarubber bag through an amber mouthpiece ; it must of course be
quite pure, and if made from the mixture of chlorate of potash and
oxide of manganese, should be purified by being passed through lime
and water, or cream of lime.

There are certain colouring matters that are weakened or destroyed
by the action of light and other causes, which deprive them of oxygen
gas or deoxidize them. A weak tincture of litmus, if long kept, often
becomes colourless, but if this colourless fluid is shaken in a bottle
with oxygen gas it is gradually restored ; and if either litmus, turmeric,
indigo, orchil, or madder, paper, or certain ribbons dyed with the same
colouring matters, have become faded, they may be partially restored by
damping and placing them in a bottle of oxygen gas. The effect of the
oxygen is to reverse the deoxidizing process, and to impart oxygen to
the colouring matters. By a peculiar process indigo may be obtained
quite white, and again restored to its usual blue colour, either by ex-
posure to the air or by passing a stream of oxygen through it.

Twenty-first Experiment.

Messrs. Matheson, of Torrington- street, Russell-square, prepare
in the form of wire some of the rarest metals, such as magnesium,
lithium, &c. A wire of the metal magnesium burns magnificently in
oxygen gas, and forms the alkaline earth magnesia. The metal lithium,
to which such a very low combining proportion belongs viz., 6'5, can
also be procured in the state of wire, and burns in oxygen gas with an
intense white light into the alkaline lithia, which dissolved in alcohol
with a little acetic acid, and burnt, affords a red flame, making a curious
contrast between the effects of colour produced by the metallic and oxi-
dized state of lithium.

THE ALLOTROPIC CONDITION OF OXYGEN GAS.

The term allotropy (from aXXorpoTro?, of a different nature) was
first used by the renowned chemist Berzelius. Dimorphism, or diver-
sity in crystalline form, is therefore a special case of allotropy,
and is most amusingly illustrated with the iodide of mercury (Hgt),
which is made either by rubbing together equal combining proper-

IT I

100 BOYS PLAYBOOK OF SCIENCE.

tions of mercury and iodine (both of which are to be found in the
Table of Elements, page 86), or by carefully precipitating a solution of
corrosive sublimate (chloride of mercury (HgCl) ) with one of iodide of
potassium, just enough and no more of the latter being added to pre-
cipitate the metal, or else the iodide of mercury is redissolved by the
excess of the precipitant. It is first of a dirty yellow, and then gradually
changes when stirred to a scarlet ; if this be collected on a filter, and
washed and drained, it is a beautiful scarlet, and when some of this
substance is rubbed across a sheet of paper, a bright scarlet is apparent,
which may be rapidly changed to a lemon-yellow by heating the paper
over the flame of a spirit lamp ; and the iodide of mercury is again brought
back to a scarlet colour by rubbing down the yellow crystals with the
fingers. This experiment may be repeated over and over again with
the like results. If some of the scarlet iodide of mercury is sublimed from
one bit of glass to another, it forms crystals, derived from the right
rhombic prism ; when these are scratched with a pin they change again to
the scarlet state, the latter when crystallized being in the form of the
square-based octohedron.

Other cases of dimorphism may be mentioned viz., with sulphur,
carbonate of lime, and lead, and many others, whilst allotropy is
curiously illustrated in the various conditions of charcoal, which, in
the more numerous examples, is black and opaque, and in another instance
transparent like water. Lamp-black is soft, but the diamond is the
hardest natural substance. The allotropic state of sulphur has been
already alluded to ; phosphorus, again, exists in three modifications : 1st,
Common phosphorus, which shines in the dark and emits a white smoke.
2nd, White pnosphorus. 3rd, Red or amorphous phosphorus, which
does not shine or emit white smoke when exposed to the air, and is so
altered in its properties that it may be safely carried in the pocket.

Enough evidence has therefore been offered to show that the allo-
tropic property is not confined to one element or compound, but is dis-
coverable in many bodies, and in no one more so than in the allotropic
state of the element oxygen called

OZONE.

The Greek language has again been selected by the discoverer, Schon-
bein, of Basle, for the title or name of this curious modification of
oxygen, and it is so termed from ogeiv, to smell. The name at once
suggests a ^narked difference between ozone and oxygen, because the
latter is pe/fectly free from odour, whilst the former has that peculiar
smell which is called electric, and is distinguishable whenever an
electrical machine is at work, or if a Ley den jar is charged by the

Sowerful Rhumkoff, or Hearder coil; it is also apparent when water is
ecomposed by a current of electricity and resolved into its elements,
oxygen and hydrogen. When highly concentrated it smells like chlorine ;
and the author recollects seeing the first experiments by Schonbein, in
England, at Mr. Cooper's laboratory in the Blackfriars-road. Ozone
is prepared by taking a clean empty bottle, and pouring therein a very

EXPERIMENTS WITH OZONE.

101

little distilled water, into
which a piece of clean
scraped phosphorus is
introduced, so as to ex-
pose about one-half of
its diameter to the air in
the bottle, whilst the
other is in contact with
the water. (Fig. 104.)

Tor the sake of pre-
caution, the bottle may
stand in a basin or soup
plate, so that if the
phosphorus should take
fire, it may be instantly
extinguished by pour-
ing cold water into the
bottle, and should this

crack and break, the

phosphorus is received

into the plate. D D . A soup-plate.

When the ozone is
formed the phospho i s can be withdrawn, and the phosphorous-acid
smoke washed out by shaking the bottle ; it is distinguishable by its
smell, and also by its action on test paper, prepared by painting with
starch containing iodide of potassium on some .Bath post paper ; when
this is placed in the bottle containing ozone, it changes the test blue,
or rather a purplish blue.

Ozone is a most energetic body, and a powerful bleaching agent ; if
a point is attached to the prime conductor of an electrical machine,
and the electrified air is received into a bottle, it will be found to smell,
and has the power of bleaching a very dilute solution of indigo. Ozone

quart bottle, with the stopper loosely

Fig. 105. v. A small voltaic battery standing on the stool with glass legs, a s, and
capable of heating a thin length of platinum wire about two inches long, and bent to form
a point between the conducting wires, ww. N.B. The voltaic current can be cut off at
pleasure, so as to cool the wire when necessary. A is the prime conductor of an ordinary
cylinder electrical machine. B is the wire conveying the frictional electricity to the
conducting wires of the voltaic battery, where the point P being the sharpest point in the
sirrangement, delivers the electrified and ozonized air.

102 BOY'S PLAYBOOK OP SCIENCE.

is not a mere creation of fancy, as it can not only be produced by certain
methods, but may be destroyed by a red heat. If a point is prepared
with a loop of platinum wire, and this latter, after being connected with
a voltaic cattery, made red hot, and the whole placed on an insulating
stool, and connected with the prime conductor of an electrical machine,
it is found that the electrified air no longer smells, the ozone is destroyed;
on the other hand, if the voltaic battery is disconnected, and the electri-
fied air again allowed to pass from the cold platinum wire, the smell is again
apparent, the air will bleach, and if caused to impinge at once upon
the iodide of starch test, changes it in the manner already described.
(Eig. 105.)

Ozone is insoluble in water, and oxidizes silver and lead leaf, finely
powdered arsenic and antimony ; it is a poison when inhaled in a con-
centrated state, whilst diluted, and generated by natural processes, it is a
beneficent and beautiful provision against those numerous smells originat-
ing from the decay of animal and vegetable matter, which might produce
disease or death : ozone is therefore a powerful disinfectant. The test for
ozone is made by boiling together ten parts by weight of starch, one of iodide
of potassium, and two hundred of water ; it may either be painted on
Bath post paper, and used at once, or blotting paper may be saturated
with the test and dried, and when required lor use it must be damped,
either before or after testing for ozone, as it remains colourless when
dry, but becomes blue after being moistened with water.

Paper prepared with sulphate of manganese is an excellent test for
ozone, and changes brown rapidly by the oxidation of the proto-salt of
manganese, and its conversion into the binoxide of the metal.

Ozone is also prepared by pouring a little sulphuric ether into a
quart bottle, and then, after heating a glass rod in the flame of the spirit
lamp, it may be plunged into the bottle, and after remaining there a few
minutes ozone may be detected by the ordinary tests.

NITROGEN, OB AZOTE.

Nirpov, nitre ; ye vvam, I form ; a, privative ; far), life. Symbol, N >
combining proportion, 14. Also termed by Priestley, phlogisticated air.

In the year 1772, Dr. Rutherford, Professor of Botany in the Uni-
versity of Edinburgh, published a thesis in Latin on fixed air, in which
he says : " By the respiration of animals healthy air is not merely
rendered mephitic (i.e., charged with carbonic acid gas), but also suffers
another change. For after the mephitic portion is absorbed by a caustic
alkaline lixivium, the remaining portion is not rendered salubrious ; and
although it occasions no precipitate in lime-water, it nevertheless extin-
guishes flame and destroys life'' Such is the doctor's account of the
discovery of nitrogen, which may be separated from the oxygen in the
air in a very simple manner. The atmosphere is the great storehouse
of nitrogen, and four-fifths of its prodigious volume consist of this
element

PREPARATION OF NITROGEN GAS.

103

Oxygen .
Nitrogen

Composition of Atmospheric Air.

Bulk. Weight.

20 22-3

80 777

100 100-

The usual mode of procuring nitrogen gas is to abstract or remove
the oxygen from a given portion of atmospheric air, "and the only point
to be attended to, is to select some substance which will continue to
burn as long as there is any oxygen left. Thus, if a lighted taper is
placed in a bottle of air, it will only burn for a certain period, and is
gradually and at last extinguished ; not that the whole of the oxygen is
removed or changed, because after the taper has gone out, some burning
sulphur may be placed in the vessel, and will continue to burn for a
limited period ; and even after these two combustibles have, as it were,
taken their fill of the oxygen, there is yet a little left, which is snapped
up by burning phosphorus, whose voracious appetite for oxygen is only
appeased by taking the whole. It is for this reason that phosphorus is
employed for the purpose of removing the oxygen, and also because the
product (phosphoric acid) is perfectly soluble in water, and thus the
oxygen is first combined, and then washed out of a given volume of air,
leaving the nitrogen behind.

First Experiment.

To prepare nitrogen gas, it is only
necessary to place a little dry phos-
phorus in a Berlin porcelain cup on a
wine glass, and to stand them in a
soup plate containing water. The
phosphorus is set on fire with a hot
wire, and a gas jar or cylindrical jar
is then carefully placed over it, so that
the welt of the jar stands in the water
in the soup plate. At first, expansion
takes ])lace in consequence of the heat,
but this effect is soon reversed, as the
oxygen is converted into a solid by
union with the phosphorus, forming a
white smoke, which gradually disap-
pears. (Fig. 106.)

Supposing two grains of phospho-
rus had been placed in a platinum
tube, and just enough atmospheric air
passed over it to convert the whole

into phosphoric acid, the weight Of glass, supporting c, the cup containing

the phosphorus would be increased to the burning phosphorus, and the whole
4* grains by the addition of 2| grains S ngm a soup - plate ' D D ' contaaiuns

104

BOY'S PLAYBOOK OF SCIENCE.

of oxygen ; now one cubic inch of oxygen weighs 0'3419, or about |rd
of a grain, hence 7 '3 cubic inches of oxygen disappear, which weigh
as nearly as possible 2?r grains, so that as 36 - 5 cubic inches of air con-
tain 7'3 cubic inches of oxygen, that quantity of air must have passed
over the 2 grains of phosphorus to convert it into 4 grains of phos-
phoric acid.

For very delicate purposes, nitrogen is best prepared by passing air
over finely-divided metallic copper heated to redness ; this metal absorbs
the whole of the oxygen and leaves the nitrogen. The finely-divided copper
is procured by passing hydrogen gas over pure black oxide of copper.

A very instructive experiment is performed by heating a good mass of
tartrate of lead in a glass tube which is herme cally sealed, and being

placed on an iron sup-
port, is then covered
by a capped air jar
with a sliding rod and
stamper, the whole
being arranged in
a plate containing
water. When the
stamper is pushed
down upon the glass
the latter is broken
(Fig. 107), and the air
gradually penetrates
to the finely divided
lead, when ignition oc-
curs, and the oxygen
is absorbed, as demon-
strated by the rise
of the water in the
jar. On the same
principle, if a bottle
is filled about one-
third full with a liquid
amalgam of lead and
mercury, and then
stopped and shaken
for two hours or
more, the finely di-
vided lead absorbs
the oxygen and

Fig. 107. A. Glass jar, with collar of leather, through which
the stamper, c, works. B B. The tube containing the finely-
divided lead, part of which falls out, and is ignited, and
retained by the little tray just below, being part of the iron
stand, D D, with crutches supporting the ends of the glass
tube, and the whole stands in the dish of water, B E.

leaves pure nitrogen. Or if a mixture of equal weights of sulphur
and iron filings, is made into a paste with water in a thin iron cup,
and then warmed and placed under a gas jar full of air standing on the

EXPERIMENTS WITH NITROGEN GAS. 105

shelf of the pneumatic trough, or in a dish full of water, the water
gradually rises in the jar in about forty-eight hours, in consequence of
the absorption of the oxygen gas.

Third Experiment.

Nitrogen is devoid of colour, taste, smell, of alkaline or acid qualities ;
and, as we shall have occasion to notice presently, it forms an acid
when chemically united with oxygen, and an alkali in union with hydro-
gen. A lighted taper plunged into this gas is immediately extinguished,
while its specific gravity, which is lighter than that of oxygen or air,
is demonstrated by the rule of proportion.

Weight of 100 cubic
inches of air at 60
Fahr., bar. 29'92 in.

30-829

Unity.

Weight of 100 cubic
inches of nitrogen at
60 Fahr., bar. 29'92 in

: 29-952 :

Specific
gravity of
nitrogen.

971

And its levity may be shown very prettily by a
simple experiment. Select two gas jars of the
same size, and after filling one with oxygen gas
and the other with nitrogen gas, slide glass
plates over the bottoms of thej ars, and proceed
to invert the one containing oxygen, placing
the neck in a stand formed of al)ox open at
the top; then place the jar containing nitro-
gen over the mouth of the first, withdrawing
the glass plates carefully ; and if the table
is steady the top gas jar will stand nicely
on the lower one. Then (having previously
lighted a taper so as to have a long snuff)
remove the stopper from the nitrogen jar
and insert the lighted taper, which is im-
mediately extinguished, and as quickly re-
lighted by pushing it down to the lower
jar containing the oxygen. This experi-
ment may be repeated several times, and is
a good illustration of the relative specific
gravities of the two gases, and of the im-
portance of the law of universal diffusion
already explained at p. 6, by which these
gases mix, not combine together, and the
atmosphereremains in one uniform state of
composition in spite of the changes going
on at the surface of the earth. Omitting ^^ IL> ai
the aqueous vapour, or steam, ever present jar Ml of c
in variable quantities in the atmosphere, ten ghted X at n8 o
thousand volumes of dry air contain, ac- porting the jars,
cording to Graham :

The taper,
Stan? ^iT"

106

BOY S PLAYBOOK. OF SCIENCE.

Nitrogen 7912

Oxygen . t 2080

Carbonic acid 4

Carburetted hydrogen (CH 2 ) ... 4
Ammonia a trace

Fourth Experiment.

10,000

It was the elegant, the accomplished, but ill-fated Lavoisier who dis-
covered, by experimenting with quicksilver and air, the compound
nature of the atmosphere ; and it was the same chemist who gave the
name of azote to nitrogen ; it should, however, be borne in mind that it

does not necessarily
follow because a gas
extinguishes flame
that it is a poison.
Nitrogen extinguishes
flame, but we inhale
enormous quantities
of air without any ill
effects from the nitro-
gen or azote that it
contains ; on the other
hand, many gases that
extinguish flame are
specific poisons, such as
carbonic acid, carbonic
oxide, cyanogen, &c.

Lavoisier's experi-
ment may be repeated
by passing into a mea-
sured jar, graduated
into five equal vo-
lumes, four measures
Fig. 109. A. Gas jar divided into five equal parts. B B. of nitrogen and one
Section of pneumatic trough, to show the decantation of gas measure of OXVffen a
from one vessel to another. The gas is being passed from c , , , J f i ,J

to A, through the water. glass plate should then

be slid over the mouth

of the vessel, and it may be turned up and down gently for. some little
time to mix the two gases, and when the mixture is tested with a lighted
taper, it is found neither to increase nor diminish the illuminating power
and the taper burns as it would do in atmospheric air. (Fig. 109.1

PREPARATION OF HYDROGEN GAS.

107

HYDROGEN.

Hydrogen (vSoop, water; yewaa), I give rise to), so termed by Lavoisier
called by other chemists inflammable air, and phlogiston. Symbol, H ;
combining properties, 1. The lightest known form of matter.

Every 100 parts by weight of water contain 11 parts of hydrogen
gas ; and as the quantity of water on the surface of the earth represents
at least two-thirds of the whole area, the source of this gas, like that of
oxygen or nitrogen, is inexhaustible. Van Helmont, Mayow, and
Hales had shown that certain inflammable and peculiar gases could be
obtained, but it was reserved for the rigidly philosophic mind of Cavendish
to determine the nature of the elements contained in, and giving a spe-
ciality to, the inflammable gases of the older chemists. By acting with
dilute acids upon iron, zinc, and tin, Cavendish liberated an inflammable
elastic gas ; and he discovered nearly all the properties we shall notice
in the succeeding experiments, and especially demonstrated the compo-
sition of water in his paper read before the lloyal Society in the year
1784.

Hydrogen is prepared in a very simple manner, by placing some zinc
cuttings in a bottle, to which is attached a cork and pewter or bent
glass tube, and pouring upon the metal
some dilute sulphuric or hydrochloric
acid. Effervescence and ebullition take
place, and the gas escapes in large quanti-
ties, water being decomposed ; the oxygen
passes to the zinc, and forms oxide of
zinc, and this uniting with the sulphuric
acid forms sulphate of zinc, which may
be obtained after the escape of the hy-
drogen by evaporation and crystallization.
(Fig. 110.)

Zn + HO.S0 3 = ZnO.S0 3 + H;

or,
Zn + HC1 = ZnCl + H.

In nearly all the processes employed
for the generation of hydrogen gas, a
metal is usually employed, and this fact
has suggested the notion that hydrogen
may possibly be a metal, although it is
the lightest known form of matter ; and it
will be observed in all the succeeding expe-

rimeilts that a metallic substance Will be marked B, containing a funnel,

employed to take away the oxygen and ^ ae^nip^c add
displace the hydrogen. through the pipe c.

108

BOY'S PLAYBOOK OF SCIENCE.

Whenever hydrogen is prepared it should be allowed to escape from
the generating vessel for a few minutes before any flame is applied, in
order that the atmospheric air may be expelled. The most serious acci-
dents have occurred from carelessness in this respect, as a mixture of
hydrogen and air is explosive, and the more dangerous when it takes
fire in any close glass bottle.

Second Experiment.

If a piece of potassium is confined in a little coarse wire gauze cage,
attached to a rod, and thrust under a small jar full of water, placed
on the shelf of the pneumatic trough, hydrogen gas is produced with
great rapidity, and is received into the gas jar. The bit of potassium
being surrounded with water, is kept cool, whilst the hydrogen escaping
under the water is not of course burnt away, as it is whenever the metal
is thrown on the surface of water.

Third Experiment.

Across a small iron table-furnace is placed about eighteen inches of
1-inch gas-pipe containing iron borings, the whole being red-hot ; and
attached to one end is a pipe conveying steam from a boiler, or flask, or
retort, whilst another pipe is fitted to the opposite end, and passes to
the pneumatic trough. Directly the steam passes over the red hot iron
borings it is deprived of oxygen, which remains with the iron, forming
the rust or oxide of iron, whilst the hydrogen, called in this case water
gas, escapes with great rapidity. When steam is passed over red-hot
charcoal, hydrogen is also produced with carbonic oxide gas, and this in
fact is the ordinary process of making water gas, which being puri-
fied is afterwards saturated with some volatile hydrocarbon and burnt.
At first sight, such a mode of making gas would be thought extremely
profitable, and in spite of the numerous failures the discovery (so called)
of water gas is reproduced as a sort of chronic wonder; but experience
and practice have clearly demonstrated that water gas is a fallacy, and
as long at we can get coal it is not worth while going through the
round-about processes of first burning coal to produce steam ; secondly,

Fig. 111. A. Flask containing water, and producing steam, which passes to the iron
tube, B B, containing the iron borings heated red hot in the charcoal stove c. The
hydrogen passes to the jar D, standing on the shelf of the pneumatic trough.

EXPERIMENTS WITH HYDROGEN GAS.

109

of burning coal to heat charcoal, over which the steam is passed to be
converted into gas, which has then to be purified and saturated with a
cheap hydrocarbon obtained from coal or mineral naphtha ; whilst ordi-
nary coal gas is obtained at once by heating coal in iron retorts.
(Fig. 111.)

Thus, by the metals zinc, tin, potassium, red-hot iron (and we might
add several others), the oxygen of water is removed and hydrogen gas
liberated.

Fourth Experiment.

If bottles of hydrogen gas
are prepared by all the processes
described, they will present the
same properties when tested un-
der similar circumstances. A
lighted taper applied to the
mouths of the bottles of hydro-
gen, which should be inverted,
causes the gas to take fire with a
slight noise, in consequence of
the mixture of air and hydrogen
that invariably takes place when
the stopper is removed; on
thrusting the lighted taper into
the bulk of the gas it is extin-
guished, showing that hydrogen
possesses the opposite quality to
oxygen viz., tnat it takes fire,
but does not support combustion.
By keeping the bottles contain-
ing the hydrogen upright, when
the stopper is removed the gas
escapes with great rapidity, and
atmospheric air takes its place,
so much so that by the time a
lighted taper is applied, instead
of the gas burning quietly, it fre-
quently astonishes the operator
with a loud pop. This sudden
attack on the nerves may be pre-
vented by always experimenting
with inverted bottles. (Eig. 112.)

Fifth Experiment.

Hydrogen is 14'4 lighter than air, and for that reason may be passed
into bottles and jars without the assistance of the pneumatic trough.
One of the most amusing proofs of its levity is that of filling paper bags
or balloons with this gas ; and we read, in the accounts of the fetes at

110

BOY'S PLAYBOOK OF SCIENCE.

Paris, of the use of balloons ingeniously constructed to represent animals,
so that a regular aerial hunt was exhibited, with this drawback only,
that nearly all the animals preferred ascending with their legs upwards,
a circumstance which provoked intense mirth amongst the volatile
Frenchmen. The lightness of hydrogen may be shown in two ways
first, by filling a little goldbeater's-skin balloon with' pure hydrogen
(prepared by passing the gas made from zinc and dilute pure sulphuric
acid through a strong solution of potash, and afterwards through one
of nitrate of silver), and allowing the balloon to ascend; and then
afterwards, having of course secured the balloon by a thin twine or strong
thread, it may be pulled down and the gas inhaled, when a most curious
effect is produced on the voice, which is suddenly changed from a manly
bass to a ludicrous nasal squeaking sound. The only precaution's
necessary are to make the gas quite pure, and to avoid flarne whilst
inhaling the gas. It is related by Chaptal that the intrepid (quaere, foolish)
but unfortunate aeronaut, Mons. Pilate de Rosio, having on one occasion
inhaled hydrogen gas, was rash enough, to approach a lighted candle,
when an explosion took place in his mouth, which he says " was so
violent that he fancied all his teeth were driven out" Of course, if it
were possible to change by some extraordinary power the condition of
the atmosphere in a concert-room or theatre, all the bass voices would
become extremely nasal and highly comic,
whilst the sopranos would emulate railway
whistles and screech fearfully ; and supposing
the specific gravity of the air was continu-
ally and materially changing, our voices
would never be the same, but alter day by day,
according to the state of the air, so that the
" familiar voice" would be an impossibility.
A bell rung in a gas jar containing air
emits a very different sound from that which
is produced in one full of hydrogen a simple
experiment is easily performed by passing a jar
containing hydrogen over a self-acting bell,
such as is used for telegraphic purposes.
(Fig. 113.)

Sixth Experiment.

Some of the small pipes from an organ
may be made to emit the most curious sounds
by passing heavy and light gases through
them ; in these experiments bags containing
Fig. 113. A. stand and bell, the gases should be employed, which may

*^d^i^4a5 * t> f ygen ' carb?nic ac f idj or hyd r^ n '

depressed at pleasure, by lifting through the organ pipes at precisely tne

it with the knob at the top, same pressure,
when the curious changes in the
sound of the bell are audible.

BALLOONS AND AEROSTATION.

Ill

Seventh Experiment.

One of those toys called " The Squeak-
ing Toy" affords another and ridiculous
example of the effect of hydrogen on sound,
when it is used in a jar containing this
gas. (Eig. 114.)

Eighth Experiment.

An accordion played in a large receptacle
containing hydrogen gas demonstrates still
more clearly what would be the effect of
an orchestra shut up in a room containing
a mixture of a considerable portion of
hydrogen with air, as the former, like
nitrogen, is not a poison, and only kills in
the absence of oxygen gas.

Ninth Experiment.
Some very amusing experiments with .,,,,., , ^

in i i i 11 -\ir T\ i I iff. 114. The squeaking toy. used

balloons have been devised by Mr. Darby, in ajar of hydrogen.

the eminent firework manufacturer, oy

which they are made to carry signals of three kinds, and thus the
motive or ascending power may be utilized to a certain extent.

Mr. Darby's attention was first directed to the manufacture of a
good, serviceable, and cheap balloon, which he made of paper, cut with
mathematical precision; the gores or divisions being made equal,
and when pasted together, strengthened by the insertion of a string
at the juncture; so that the skeleton of the balloon was made of
string, the whole terminating in the neck, which was further stif-
fened with calico, and completed when required by a good coating
of boiled oil. These balloons are about nine feet high and five feet in
diameter in the widest part, exactly like a pear, and tapering to the
neck in the most graceful and elegant manner. They retain the hydrogen
gas remarkably well for many hours, and do not leak, in consequence of
the paper of which they are made being well selected and all holes
stopped, and also from the circumstance of the pressure being so well
distributed over the interior by the almost mathematical precision with
which they are cut, and the careful preparation of the paper with proper
varnish. One of their greatest recommendations is cheapness ; for
whilst a gold-beater's skin balloon of the same size would cost about 51.,
these can be furnished at 5s. each in large quantities.

A balloon required to carry one or more persons must be constructed
of the best materials, and cannot be too carefully made ; it is therefore
a somewhat costly affair, and as much as 200/., 500/., and even 1000/.
have been expended in the construction of these aerial chariots.

The chief points requiring attention are : first, the quality of the
silk ; secondly, the precision and scrupulous nicety required in cutting

112 BOY'S PLAYBOOK OF SCIENCE.

out and joining the gores ; thirdly, the application of a good varnish to
fill up the pores of the silk, which must be insoluble in water, and suf-
ficiently elastic not to crack.

The usual material is Indian silk (termed Corah silk), at from 2.?. to
2s. 6d. per yard.

The gores or parts with which the balloon is constructed require, as
before stated, great attention; it being a common saying amongst
aeronauts, "that a cobweb will hold the gas if properly shaped," the
object being to diffuse the pressure equally over the whole bag or
balloon.

The varnish with which the silk is rendered air-tight can be made
according to the private recipe of Mr. Graham, an aeronaut, who states
that he uses for this purpose two gallons of linseed oil (boiled), two
ditto (raw), and four ounces of beeswax ; the whole being simmered
together for one hour, answers remarkably well, and the varnish is
tough and not liable to crack.

For repairing holes in a balloon, Mr. Graham recommends a cement
composed of two pounds of black resin and one pound of tallow,
melted together, and applied on pieces of varnished silk to the apertures.
The actual cost of a balloon will be understood from information also
derived from Mr. Graham. His celebrated " Victoria Balloon," which
has passed through so many hairbreadth escapes, was sixty-five feet
hih, and thirtv-eight feet in diameter in the broadest part ; and the
following articles were used in its constructiou

s. d.
1400 yards of Corah silk, at 2*. bd. per yard . . 175

The netting weighed 70 Ibs 20

Extra ropes weighed 20 Ibs. at 2*. per Ib. ... 200

The car weighed 25 Ibs 700

Varnish, wages, &c 16

220

Thirty-eight thousand cubic feet of coal gas were required to fill this
balloon, charged by one company 20/., by others from 9/. to 10/. ; and
eight men were required to hold the inflated baggy monster.

Such a balloon as described above is a mere soap bubble when com-
pared with the " New Aerial Ship" now building in the vicinity of New
York ; the details are so practical and interesting, that we quote nearly
the whole account of this mammoth or Great Eastern amongst balloons,
as given in the New York Times.

" An experiment in scientific ballooning, greater than has yet been
undertaken, is about to be tried in this city. The project of crossing
the Atlantic Ocean with an air-ship, long talked of, but never accom-
plished, has taken a shape so definite that the apparatus is already pre-
pared and the aeronaut ready to undertake his task.

" The work has been conducted quietly, in the immediate vicinity of
New York, since the opening of spring. The new air-ship, which has

AEROSTATION. 113

been christened the City of New York, is so nearly completed, that but
few essentials of detail are wanting to enable the projectors to bring it
visibly before the public.

" The aeronaut in charge is Mr. T. S. C. Lowe, a New Hampshire
man, who has made thirty-six balloon ascensions.

" The dimensions of the City of New York so far exceed those of
any balloon previously constructed, that the bare fact of its existence is
notable. Briefly, for so large a subject, the following are the di-
mensions : Greatest diameter, 130 feet ; transverse diameter, 104 feet ;
height, from valve to boat, 350 feet ; weight, with outfit, 3 tons ;
lifting power (aggregate), 22^ tons ; capacity of gas envelope, 725,000
cubic feet.

" The City of New York, therefore, is nearly five times larger than
the largest balloon ever before built. Its form is that of the usual
perpendicular gas-receiver, with basket and lifeboat attached.

" Six thousand yards of twilled cloth have been used in the con-
struction of the envelope. Reduced to feet, the actual measurement of
this material is 54,000 feet or nearly 11 miles. Seventeen of Wheeler
and Wilson's sewing machines have been employed to connect the
pieces, and the u^per extremity of the envelope, intended to receive the
gas-valve, is of triple thickness, strengthened with heavy brown linen,
and sewed in triple seams. The pressure being greatest at this point,
extraordinary power of resistance is requisite. It is asserted that 100
women, sewing constantly for two years, could not have accomplished
this work, which measures by miles. The material is stout and the
stitching stouter.

" The varnish applied to this envelope is a composition the secret of
which rests with Mr. Lowe. Three or four coatings are applied, in
order to prevent leakage of the gas.

" The netting which surrounds the envelope is a stout cord, manu-
factured from flax expressly for the purpose. Its aggregate strength is
equal to a resistance of 160 tons, each cord being capable of sustaining
a weight of 400 Ibs. or 500 Ibs.

" The basket which is to be suspended immediately below the balloon
is made of rattan, is 20 feet in circumference and 4 feet deep. Its form
is circular, and it is surrounded by canvas. This car will carry the
aeronauts. It is warmed by a lime-stove, an invention of Mr. 0. A.
Gager, by whom it was presented to Mr. Lowe. A lime-stove is a new
feature in air voyages. It is claimed that it will furnish heat without
fire, and is intended for a warming apparatus only. The stove is 1| feet
high, and 2 feet square. Mr. Lowe states that he is so well convinced
of the utility of this contrivance, that he conceives it to be possible to
ascend to a region where water will freeze, and yet keep himself from
freezing. This is to be tested.

" Dropping below the basket is a metallic lifeboat, in which is placed
an Ericsson engine. Captain Ericsson's invention is therefore to be
tried in mid-air. Its particular purpose is the control of a propeller,
rigged upon the principle of the screw, by which it is proposed to obtain

114 BOY'S PLAYBOOK OF SCIENCE.

a regulating power. The application of the mechanical power is in-
geniously devised. The propeller is fixed in the bow of the lifeboat,
projecting at an angle of about forty-five degrees. From a wheel at
the extremity twenty fans radiate. Each of these fans is 5 feet in
length, widening gradually from the point of contact with the screw to
the extremity, where the width of each is 1^ feet. Mr. Lowe claims
that by the application of these mechanical contrivances his air-ship
can be readily raised or lowered, to seek different currents of air ; that
they will give him ample steerage way, and that they^ will prevent the
rotatory motion of the machine. In applying the principle of the fan, he
does not claim any new discovery, but simply a practical development
of the theory advanced by other aeronauts, and partially reduced to
practice by Charles Green, the celebrated English aeronaut.

"Mr. Lowe contends that the application of machinery to aerial
navigation has been long enough a mere theory. He proposes to
reduce the theory to practice, and see what will come of it. It is
estimated that the raising and lowering power of the machinery will be
<jqual to a weight of 300 Ibs., the fans being so adjusted as to admit of
very rapid motion upward or downward. As the loss of three or four
pounds only is sufficient to enable a balloon to rise rapidly, and as the
escape of a very small portion of the gas suffices to reduce its altitude,
Mr. Lowe regards this systematic regulator as quite sufficient to enable
him to control his movements and to keep at any altitude he desires.
It is his intention to ascend to a height of three or four miles at the
start, but this altitude will not be permanently sustained. He prefers,
he says, to keep within a respectable distance of mundane things, where
* he can see folks.' It is to be hoped his machinery will perform all
that he anticipates from it. It is a novel affair throughout, and a
variety of new applications remain to be tested. Mr. Lowe, expressing
the utmost confidence in all the appointments of his apparatus, assured
us that he would certainly go, and, as certainly, would go into the ocean,
or deliver a copy of Monday's Times in London on the following
Wednesday. He" proposes to effect a landing in England or France,
and will take a course north of east. A due easterly course would
land him in Spain, but to that course he objects. He hopes to make
the trip from this city to London in forty-eight hours, certainly in sixty-
four hours. He scouts the idea of danger, goes about his preparations
deliberately, and promises himself a good time. As the upper currents,
setting due east, will not permit his return by the same route, he pro-
poses to pack up the City of New York, and take the first steamer for
home.

" The air-ship will carry weight. Its cubical contents of 725,000
feet of gas suffice to lift a weight of 22| tons. "With outfit complete
its own weight will be Batons." With this weight 39 tons of lifting
power remain, and there is accordingly room for as many passengers as
will care to take the venture. We understand, however, that the
company is limited to eight or ten. Mr. Lowe provides sand for
ballast, regards his chances of salvation as exceedingly favourable,

AEROSTATION. 115

places implicit faith in the strength of his netting, the power of his
machinery, and the buoyancy of his lifeboat, and altogether considers
himself secure from the hazard of disaster. If he accomplish his voyage
in safety, he will have done more than any air navigator has yet ventured
to undertake. If he fail, the enterprise sinks the snug sum of 20,000
dollars. Wealthy men who are his backers, sharing his own enthusiasm,
declare failure impossible, and invite a patient public to wait and see."
A night ascent witnessed at any of the public gardens is certainly a
stirring scene, particularly if the wind is rather high. On approaching
the balloon, swayed to and fro by the breeze, it seems almost capable of
crushing the bold individual who would venture beneath it ; seen as a
large dark mass in the yet dimly-lighted square, it appears to be inca-
pable of control ; when the inflation is completed, the aeronaut, all im-
portance, seats himself in the car, and blue lights, with other fire-
works, display the victim who is to make a " last ascent," or perhaps
descent. Finally the word is given, the ropes are cast off, and the bulky
chariot rises majestically to the sound of the National Anthem. The
crowd see no more, but the next day's Times reports the end of the aerial
journey.

Balloons can never be of any permanent value as means of locomotion
until they can be steered ; and this is a problem, the solution of which is
something like perpetual motion. In the first place, a balloon of any size
exposes an enormous surface to the pressure and force of the winds ;
and when we consider that they move at the rate of from three to eighty
miles per hour, it will be understood that the fabric of the balloon itself
must give way in any attempt to tear, work, or pull it against such a
force. Secondly and lastly, the power has not yet been created which
will do all this without the inconvenience of being so heavy that the
steering engine fixes the balloon steadily to the earth by its obstinate
gravity. When engines of power are constructed without the aeronaut's
obstacle of weight when balloons are made of thin copper or sheet-iron,
then we may possibly hear of the voyage of the good ship Aerial, bound
for any place, and quite independent of dock, port, and the host of dues
(quere), which the sea-going ships have to disburse. It is, however, gratify-
ing to the zeal and perseverance of those who dream of aerial navigation, to
know that a balloon is not quite useless ; and here we may return to the
consideration of Mr. Darby's signals, which are of various kinds, and in-
tended to appeal to the senses by night as well as by day ; and first, by
audible sounds. Such means have long been recognised, from the ancient
float and bell of the " Inchcape Rock," to the painful minute-gun at sea, or
the shrill railway whistle and detonating signals employed to prevent the
horrors of a collision between two trains. The signal sounds are pro-
duced by the explosion of shells capable of yielding a report equal to
that of a six-pounder cannon, and they are constructed in a very simple
manner. A ball, composed of wood or copper, and made up by screwing
together the two hemispheres, is attached to a shaft or tail of cane or
lance-wood, properly feathered like an arrow ; at the side opposite to
that of the arrow viz., at its antipodes, is placed a slight protuberance

I 2

116

BOY'S PLAYBOOK OF SCIENCE.

containing a minute bulb of glass filled with oil of vitriol, and sur-
rounded with a mixture of chlorate of potash and sugar, the whole being
protected with gutta-percha, and communicating by a touch-hole with
the interior, which is of course filled with gunpowder. These shells are
attached to a circular framework by a strong whipcord, which passes
to a central fuse, and are detached one after the other as the slow fuse
(made hollow on the principle of the argand lamp) burns steadily away.
Directly a shell falls to the ground, the little bulb containing the oil of
vitriol breaks, and the acid coming in contact with the chlorate of
potash and sugar, causes the mixture to take fire, when the gunpowder
explodes. During the siege of Sebastopol many similar mines were
prepared by the Russians in the earth, so that when an unfortunate
soldier trod upon the spot, the concealed mine blew up and seriously
injured him ; such petty warfare is as bad as shooting sentries, and a
cruel application of science, that unnecessarily increases the miseries of
war without producing those grand results for which the truly great
captains, Wellington and Napoleon, only warred. (Fig. 115.)
The bill distributor consists of a long piece of wood, to which are

Fig. 115. A. King attached to balloon, ,.

carrying an hexagonal framework with six \^

shells. B. Hollow fuse, which burns slowly

up to the strings, and detaches each shell in Fig. 116. The bill distributor, consisting

succession, c. Section of shell. The shaded of three hollow fuses, with bills attached in

portion represents the gunpowder. packets.

BALLOON SIGNALS.

117

attached a number of hollow fuses, with packets of bills, protected from
being burned or singed by a thin tin plate; 10,000 or 20,000 bills can
thus be delivered, and the wind assists in scattering them, whilst the bal-
loon travels over a distance of many miles. It must be recollected that
in each case the shells and the bills are detached by the string burning
away as the fire creeps up from the fuse. (Fig. 116,)

Another most ingenious arrangement, also prepared by Mr. Darby,
is termed by the inventor, the " Land and Water Signal," and may be
thus described : A short hollow ball of gutta-percha, or other con-
venient material, five or six
inches in diameter, and filled
with printed bills, or the in-
formation, whatever it may
be, that is required to be
sent, is attached to a cap to
which a red flag, having the
words " Open the shell" and
four cross sticks, canes, or
whalebones with bits of cork
at equal distances, are fitted.
The whole is connected by
a string to the fuse as before
described. These signals
are adapted for land and
water : in either case they
fall upright, and in conse-
c[uence of the sticks pro-
jecting out they float well
in the water, and can be
seen by a telescope at a dis-
tance of three miles. (Fig.
117.) Many of these sig-
nals were sent away by Mr. w

Darby from Vauxhall; one

was nirlfprl nr> at Harwirh F *%' 117 ' The land and water signal, which re-

as picKea up at narwicn, mains upright on land> or floats On 8 the gurface of

another at Brighton, a third water. A. The water-tight gutta-percha shell, con-
at Crovdon : in the latter tuning th e message or information. B B B. Sticks

case it was found by a cot- tL^l^t^fg^^^ P siti n; at
tager, who, fearing gunpow-
der and combustibles, did not examine the shell, but having mentioned
the circumstance to a gentleman living near him, they agreed to cut it
open ; and intelligence of their arrival, in this and the other cases, was
politely forwarded to Mr. Darbv at Vauxhall Gardens.

Balloons, like a great many other clever inventions, have been despised
by military men as new-fangled expedients, toys, which may do very well
to please the gaping public, but are and must be useless in the field.
Over and over again it has been suggested that a balloon corps for
observation should be attached to the British army, but the scheme has

118 BOY'S PLAYBOOK OF SCIENCE.

been rejected, although the expense of a few yards of silk and the gene-
ration of hydrogen gas would be a mere bagatelle as compared with the
transport and use of a single 32-pounder cannon. The antiquated notions
of octogenarian generals have, however, received a great shock in the
fact that the Emperor Napoleon III. was enabled, by the assistance of
a captive balloon, to watch the movements and dispositions of the
Austrian troops ; and with the aid of the information so obtained, he
made his preparations, and was rewarded by the victory of Solferino ;
and as soon as the battle was over Napoleon III. occupied at Cavriana
the very room and ate the dinner prepared for his adversary, the Emperor
IVancis Joseph.

Over and over again the most excellent histories have been written of
aerostation, but they all tend to one truth, and that is, the great danger
and risk of such excursions ; and to enable our readers to form their
own judgment, a chronological list of some of the most celebrated
aeronauts, &c., is appended.

1675. Bernair attempted to fly killed.

1678. Besnier attempted to fly.

1772. I/ Abbe Desforges announced an aerial chariot.

1783. Montgolfier constructed the first air balloon.

Roberts freres, first gas balloon, destroyed by the peasantry of
Geneva, who imagined it to be an evil spirit or the moon.

1784. Madame Thible, the first lady who was ever up in the clouds ;

she ascended 13,500 feet.
Duke de Chartres, afterwards Egalite Orleans, travelled 135

miles in five hours in a balloon.
Testu de Brissy, equestrian ascent.

D'Achille, Desgranges, and Chalfour Montgolfier balloon.
Bacqueville attempted a flight with wings.
Lunardi gas balloon.

Rambaud Montgolfier balloon, which was burnt.
Andreani Montgolfier balloon.

1785. General Money gas balloon, fell into the water, and not rescued

for six. hours.

Thompson, in crossing the Irish Channel, was run into with the
bowsprit of a ship whilst going at the rate of twenty miles
per hour.
Brioschi gas balloon ascended too high and burst the balloon ;

the hurt he received ultimately caused his death.
A Venetian nobleman and his wife gas balloon killed.
Pilatre de Rozier and M. Romain gas balloon took fire botli

killed.
1806. Mosment gas balloon killed.

Olivari Montgolfier balloon killed.
1808. Degher attempted a flight with wings.
1812. Bittorf Montgolfier balloon killed.
1819. Blanchard, Madame gas balloon killed.

BALLOON ACCIDENTS.

119

1819. Gay Lussac gas balloon, ascended 23,040 feet above the level of

the sea. Barometer 12'95 inches ; thermometer 14*9 Eah.
Gay Lussac and Biot gas balloon for the benefit of science.

Both philosophers returned safely to the earth.
1824. Sadler gas balloon killed.
Sheldon gas balloon.
Harris gas balloon killed.
1836. Cocking parachute from gas balloon killed.
1847. Godard Montgolfier balloon fell into and extricated from the

Seine.

1850. Poitevin, a successful French aeronaut.
Gale, Lieut. gas balloon killed.
Bixio and Barral gas balloon.
Graham, Mr. and Mrs. gas balloon. Serious accident ascending

near the Great Exhibition in Hyde Park.
Green, the most successful living aeronaut of the present time.

Of the 41 persons enumerated, 14 were killed, and nearly all the
aeronauts met with accidents which might have proved fatal.

Fig. 118. Flying machine (theoretical).

120 BOY'S PLAYBOOK OF SCIENCE.

Tenth Experiment.

Soap bubbles blown with hydrogen gas ascend with great rapidity,
and break against the ceiling ; if interrupted in their course with a
lighted taper they burn with a slight yellow colour and dull report.

Eleventh Experiment.

By constructing a pewter mould in two halves, of the shape of a
tolerably large flask, a balloon of collodion may be made by pouring the
collodion inside the pewter vessel, and taking care that "every part is
properly covered ; the pewter mould may be warmed by the external
application of hot water, so as to drive off the ether of the collodion,
and when quite dry the mould is opened and the balloon taken out.
Such balloons may be made and inflated with hydrogen by attaching to
them a strip of paper, dipped in a solution of wax and phosphorus, and
sulphuret of carbon ; as the latter evaporates, the phosphorus takes fire
and spreads to the balloon ; which burns with a slight report. The pewter
moulo must be very perfectly made, and should be bright inside ; and if
the balloons are filled with oxygen and hydrogen, allowing a sufficient
excess of the latter to give an ascending power, they explode with a
loud noise directly the fire reaches the mixed gases.

Twelfth Experiment.

In a soup-plate place some strong soap and water ; then blow out
a number of bubbles with a mixture of oxygen and hydrogen ; a loud
report occurs on the application of flame, and if the room is small the
window should be placed open, as the concussion of the air is likely to
break the glass.

Thirteenth Experiment.

Any noise repeated at least thirty-two times in a second produces a
musical sound, and bv producing a number of small explosions of
hydrogen gas inside glass tubes of various sizes, the most peculiar
sounds are obtained. The hydrogen flame should be extremely small,
and the glass tubes held over it may be of all lengths and diameters ;
a trial only will determine whether they are fit for the purpose or not.

Fourteenth Experiment.

Flowers, figures, or other designs, may be drawn upon silk with a
solution of nitrate of silver, and the whole being moistened with water,
is exposed to the action of hydrogen gas, which removes the oxygen
from the silver, and reduces it to the metallic state.

In like manner designs drawn with a solution of chloride of gold are
produced in the metallic state by exposure to the action of hydrogen
gas. Chloride of tin, usually termed muriate of tin, may also be
reduced in a similar manne care being taken in these experiments that

EXPERIMENTS WITH HYDROGEN.

121

the fabric upoii which the letters, figures, or designs are painted with
the metallic solution be kept quite damp whilst exposed to the
hydrogen gas.

Fifteenth Experiment.

A mixture of two volumes of hydrogen with one volume of oxygen
explodes with great violence, and produces two volumes of steam, which
condense against the sides of the strong glass vessel, in which the
experiment may be made, in the form of water. As the apparatus
called the Cavendish bottle, by which this experiment only may be
safely performed, is somewhat expensive, and requires the use of an
air-pump, gas jars with stop-cocks, and an electrical machine and Leyden
jar, other and more simple means may be adopted to show the combi-
nation of oxygen and hydrogen, and formation of water.

If a little alcohol is placed in a cup and set on fire, whilst an empty
cold gas jar is held over the flame, an abundant deposition of moisture
takes place from the combustion of the hydrogen of the spirits of wine.
Alcohol contains six combining properties of hydrogen, with four of
charcoal and two of oxygen. If a lighted candle, or an oil, camphine,
Belmontine, or gas flame, is placed under a proper condenser, large
quantities of water are obtained by the combustion of these substances
(Fig. 119).

Fig. 119. A. A burning candle, or oil or gas lamp. Copper head and long pipe fitting
into B c, the receiver from which the condensed water drops into D. E E. Two corka
fitted, between which is folded some wet rag.

122 BOY'S PLAYBOOK OF SCIENCE.

Sixteenth Experiment.

During the combustion of a mixture of two volumes of hydrogen with
one of oxygen, an enormous amount of heat is produced, which is use-
fully applied in the arrangement of the oxy-hydrogen blowpipe. The
flame of the mixed gases produces little or no light, but when directed
on various metals contained in a small hole made in a fire brick, a most
intense light is obtained from the combustion of the metals, which is
variously coloured, according to the nature of the substances employed.
With cast-iron the most vivid scintillations are obtained, particularly if
after having fused and boiled the cast-iron with the jet of the two gases,
one of them, viz., the hydrogen, is turned off, and the oxygen only
directed upon the fused ball of iron, then the carbon of the iron burns
with great rapidity, the little globule is enveloped in a shower of sparks,
and the whole affords an excellent notion of the principle of Bessemer's
patent method of converting cast-iron at once into pure malleable iron,
or by stopping short of the full combustion of carbon, into cast-steel.

The apparatus for conducting these experiments is of various kinds,
and different jets have been from time to time recommended on account
of their alleged safety. It may be asserted that all arrangements pro-
posed for burning any quantity of the mixed gases are extremely aan-

gerous : if an explosion takes place
it is almost as destructive as gun-
powder, and should no particular
damage be done to the room, there
is stiff the risk of the sudden vibra-
tion of the air producing permanent
deafness. If it is desired to burn
the mixed gases, perhaps the safest
apparatus is that of Gurney ; in this
arrangement the mixed gases bubble
up through a little reservoir of water,

and thus the gasholder viz., a

Fig. 120. Gurney's jet. A. Pipe with bladder, is cut off from the jet when

stop-cock leading from the gas-holder, the Combustion takes place, (.rig.

"V?^ 6 *?** 16 . res f voir of , w K a * er thr 3 Q 120 ) This let is much recom-

which the mixed gases bubble, c. The ^ f/ ^ J -) j-f-rj ^ , ,, ,. ,,

jet where the gases burn. D. Cork, which mended by Mr. Woodward, thehighly
is blown out if the flame recedes in the respected President of the Islington
pipe ' c * Literary and Scientific Institution,

and may be fitted np to show the phenomena of polarized light, the
microscope, and other interesting optical phenomena.

Mr. Woodward states, that a series of experiments, continued during
many years, has proved, that while the bladder containing the mixed
gases is under pressure, the flame cannot be made to pass the safety
chambers, and consequently an explosion is impossible; and even if
through extreme carelessness or design, as by the removal of pressure or
the contact of a spark with the bladder, an explosion occurs, it can
produce no other than the momentary effect of the alarm occasioned by

THE OXY-HYDROGEN OR LIME LIGHT.

123

Pig. 121. A. The bladder of mixed gases, pressed by the board, B B, attached by wire
supports to another board, c c, which carries the weights, D D. BE. Pipe to which the
bladder, A, is screwed, and when A is emptied, it is re-filled from the other bladder, B.
p p p. Pipe conveying mixed gases to the lantern, G G, where they are burnt from a
Gurney's jet, H.

the report ; whereas, when the gases are used in separate bags under a
pressure of two or three half hundredweights, if the pressure on one of
the bags be accidentally removed or suspended, the gas from the other
will be forced into it, and if not discovered in time, will occasion an ex-
plosion of a very dangerous character ; or if through carelessness one
of the partially emp-
tied bags should be
filled up with the
wrong gas, effects of
an equally perilous
nature would ensue.

In the oxy-hydro-
gen blowpipe usually
employed, the gases
are kept quite sepa-
rate, either in gas-
ometers or gas bags,
and are conveyed oy

distinct pipes to a rig< 122 ^^ jet
jet of very simple
construction, devised
by the late Professor
Daniell, where they
mix in very small volumes, and are burnt at once at the mouth of the
jet. (Fig. 122.)

The gases are stored either in copper gasometers or in air-tight bags
of Macintosh cloth, capable of containing from four to six cubic feet of
gas, and provided with pressure boards. The boards are loaded with
two or three fifty-six pound weights to force out the gas with sufficient

Fig. 122. DanielTs jet. o o. The stop-cock and pipe con-
veying oxygen, and fitting inside the larger tube H H, to which
is attached a stop-cock, H, connected with the hydrogen re-
ceiver. A. The orifice near which the gases mix, and
they are burnt.

irhere

BOY'S PLAYBOOK OF SCIENCE.

pressure, and of course must be equally weighted ; if any change of
weight is made, the stop-cocks should be turned off and the light put out,
as the most disastrous results have occurred from carelessness in this
respect. (Fig. 123.)

Fig. 123. Gas bag and pressure boards.

The oxy-hydrogen jet is further varied in construction by receiving
the gases from separate reservoirs, and allowing them to mix in the
upper part of the jet, which is provided with a safety tube filled with

Fig. 124. A A. Board to which B B is fixed, o. Oxygen pipe. H. Hydrogen pipe.
c c. Space filled with wire gauze. D. Lime cylinder.

circular pieces of wire gauze. (Fig. 124.) With this arrangement a
most intense light is produced, called the Drummond or lime light, and
coal gas is now usually substituted for hydrogen.

ANALYSIS AND SYNTHESIS OF WATER. 125

There are many circumstances that will cause the union of oxygen and
hydrogen, which, if confined by themselves in a glass vessel, may be pre-
served for any length of time without change ; but if some powdered glass,
or any other finely-divided substance with sharp points, is introduced
into the mixed gases at a temperature not exceeding 660 Fahrenheit,
then the gases silently unite and form water.

This curious mode of effecting their combination is shown in a still
more interesting manner by perfectly clear platinum foil, which if intro-
duced into the mixed gases gradually begins to glow, and becoming red-
hot causes the gases to explode. Or still better, by the method first
devised by Dobereiner, in 1824, by which finely prepared spongy pla-
tinum i.e., platinum in a porous state, and exposing a large metallic
surface is almost instantaneously heated red-hot by contact with the
mixed gases. When this fact became known, it was further applied to
the construction of an instantaneous light, in which hydrogen was made
to play upon a little ball of spongy platinum, and immediately kindled.
These Dobereiner lamps were possessed by a few of the curious, and
would no doubt be extensively used if the discovery of phosphorus had
not supplied a cheaper and more convenient fire-giving agent. When
the spongy platinum is mixed with some fine pipeclay, and made into
little pills, they may (after being slightly warmed) be introduced into
a mixture of the two gases, and will silently effect their union. The
theory of the combination is somewhat obscure, and perhaps the simplest
one is that which supposes the platinum sponge to act as a conductor of
electric influences between the two sets of gaseous particles ; although,
again, it is difficult to reconcile this theory with the fact that powdered
glass at 660, a bad conductor of electricity, should effect the same
object. The result appears to be due to some effects of surface by
which the gases seem to be condensed and brought into a condition
that enables them to abandon their gaseous state and assume that of
water.

When Sir H. Davy invented the safety-lamp, he was aware that, in
certain explosive conditions of the air in coal mines, the flame of the
lamp was extinguished, and in order that the miner should not be left
in the dreary darkness and intricacies of the galleries without some
means of seeing the way out, he devised an ingenious arrangement with
thin platinum wire, which was coiled round the flame of the lamp, and
fixed properly, so that it could not be moved from its proper place by
any accidental shaking. When the flame of the safety -lamp, having the
platinum wire attached, was accidentally extinguished by the explosive
atmosphere in which it was burning, the platinum commenced glowing
with an intense heat, and continued to emit light as long as it remained
in the dangerous part of the mine. Sir H. Davy warned those
who might use the platinum to take care that no portion of the
thin wire passed outside the wire gauze, for the obvious reason
that, if ignited outside the wire gauze protector, it would inflame the
fire-damp.

126

BOYS PLAYBOOK OP SCIENCE.

Eighteenth Experiment.

Water is decomposed
by passing a current
of voltaic electricity
through it by means of
two platinum plates,
which may be connected
with a ten-cell Grove's
battery. The gases are
collected in separate
tubes, and the experi-
ment offers one of the
most instructive illus-
trations of the composi-
tion of water. (Fig. 125.)
There is a current of
electricity passing from
and between two plati-
num plates decomposing
water, offering the con-
verse of the Dobereiner
Fig. 125. p P. Two platinum plates connected with experiment, and highly
wires to the cups. The wires are passed through holes suffffestive of the proba-
in the finger-glass, B B, and are fixed perfectly steady by viV ~f -t-l, 1,
pouring in cement composed of resin and tallow to the blllt y ot tne theory al-
line i L. Two glass tubes filled with water acidulated with ready advanced in CX-
sulphuric acid, and placed over the platinum plates in nln-nnfinn r>f HIP cinmi
finger-glass, which ako contains dilute sulphuric acid to P lanatlon . ottne sm g u -
improve the conducting power of the water. The wires of lar combination or oxy-
the battery are placed in the cups, and the arrows show the ran and hvdrogen in the
direction of the current of electricity. ^^ $ ^ ^

num foil, and more especially when we consider the operation of Grove's
gas battery, in which a current of electricity is produced by pieces of
platinum foil covered with finely-divided platinum, called platinum black ;
each piece is contained in a separate glass tube filled alternately with
oxygen and hydrogen, and by connecting a great number of these tubes
a current of electricity is obtained, whilst the oxygen and hydrogen are
slowly absorbed and disappear, having combined and formed water,
although placed in separate glass tubes. (Fig. 126.)

The analysis of water is shown very perfectly on the screen by fitting
up some very small tubes and platinum wires in the same manner as
shown in fig. 125. The vessel in which the tubes and wires are con-
tained with the dilute sulphuric acid must be small, and arranged so as to
pass nicely into the space usually filled by the picture in an ordinary
magic lantern, or, still better, m one lighted by the oxy-hydrogen or
lime light. If the dilute acid is coloured with a little solution of indigo,
the gradual displacement of the fluid by the production of the two gases
is very perfectly developed on the screen when the small voltaic battery
is attached to the apparatus ; and of course a large number of persons
may watch the experiment at the same time.

With respect to the application of the light produced from a jet 01

THE SYNTHESIS OF OXYGEN AND HYDBOGSX.

12'

Fig. 126. Grove's gas battery consists of tubes containing oxygen and hydrogen alternately,
and haying a thin piece of platinum foil, f, inserted by the blowpipe in each glass tube.
The foil hangs down the full length of the interior of the glass. Each pair of tubes is
contained in a little glass tumbler containing some dilute sulphuric acid, and the
hydrogen tube, H, of one pair, is connected with the oxygen tube, Oj of the next, w w.
The terminal wires of the series.

the mixed gases thrown upon a ball of lime, it may be stated that for
many years the dissolving view lanterns and other optical effects have
been produced with the assistance of this light ; and more lately Major
Titzmaurice has condensed the mixed gases in the old-fashioned oil
gas receivers, and projected them on a ball of lime; and it was this
light thrown from many similar arrangements that illuminated the
British men-of-war when Napoleon III. left her Majesty's yacht at night
in the docks at Cherbourg.

Mr. Sykes Ward, of Leeds, has also proposed a most simple and excel-
lent application of the oxy-hydrogen light for illumination under the

Fig. 127. Cherbourg.

128

BOY S PLAYBOOK OF SCIENCE.

Fig. 128. A A. Tube re-
servoir to hold the mixed
gases. B. The jet and lime
ball. 3>. The first glass
shade, held down by a cap
and screw, c. The second
glass shade. E E. The
handle by which it is low-
ered into the water.

surface of water, and for the convenience of
divers, who are frequently obliged to cease their
operations in consequence of the want of light.
Mr. Ward's submarine lamp consists of a series
of very strong copper tubes, which are filled
with the mixed gases by means of a force-pump ;
and in order to prevent the lamp being extin-
guished, it burns under double glass shades,
which are desirable in order to prevent the glass
immediately next to the light cracking by con-
tact with the cold water.

The author tried this lamp at Hyde, and
although the coast-guards objected to the pro-
duction of a brilliant light at night, which they
stated might be mistaken for a signal and
would cause some confusion amongst the war
vessels in the immediate neighbourhood, enough
experiments were made, to show that the Ward
lamp would burn for a considerable time under
water, and could be kept charged with the gas
by means of a process that was easily work-
able in the boat. The gases were taken out
mixed in gas bags, and pumped into the reser-
voir when required. With a much larger reser-
voir greater results could be obtained; and if
nautilus diving bells are to be used in modern
warfare, they will require a powerful light to
show them their prey, so that they may attach
the explosives which are to blow great holes in
the men-of-war.

Fig. 129. Submarine lamp.

129

CHLORINE, IODINE, BROMINE, FLUORINE.

The four Halogens, or Producers of Substances like Sea Salt.

Chlorine (^Xwpos, green). Symbol, Cl. Combining proportion, 35 '5.
Specific 'gravity, 2'l4. Scheele termed it dephlogisticated muriatic
acid; Lavoisier, oxymuriatic acid; Davy, chlorine.

The consideration of the nature of this important element introduces
to our notice one of the most original chemists of the eighteenth
century viz., the illustrious Scheele, who was born at Stralsund, in 1742,
and in spite of every obstacle, fighting his " battle of life" with sickness
and sorrow, he succeeded in making some of the most valuable dis-
coveries in science, and amongst them that of chlorine gas. It was in
the examination of a mineral solid viz., of manganese that Scheele
made the acquaintance of a new gaseous element; and in a highly
original dissertation on manganese, m 1774, he describes the mode of
procuring what he termed dephlogisticated muriatic acid a name which
is certainly to be regretted, from its absurd length, but a title which

was strictly in accordance with the then established theory of phlogiston ;
and if the latter is considered synonymous with hydrogen, quite in
accordance with our present views of the nature of this element.

Scheele discovered the leading characteristics of chlorine, and especially
its power of bleaching, which is alone sufficient to place this gas in a
hign commercial position, when it is considered that all our linen used
formerly to be sent to Holland, where they had acquired great dexterity
in the ancient mode of bleaching viz., by exposure of the fabric to
atmospheric air or the action of the damps or dews, assisted greatly by
the agency of light. Some idea may be formed of the present value
of chlorine, when it is stated that the linen goods were retained by the
Dutch bleachers for nine months ; and if the spring and summer hap-
pened to be favourable, the operation was well conducted ; on the other
hand, if cold and wet, the goods might be more or less injured by con-
tinual exposure to unfavourable atmospheric changes. At the present
time, as much bleaching can be done in nine weeks as might formerly
have been conducted in the same number of months ; and the whole of
the process of chlorine bleaching is carried on independent of external
atmospheric caprices, whilst the money paid for the process no longer
passes to Holland, but remains in the hands of our own diligent
bleachers and manufacturers.

First Experiment.

As Scheele first indicated, chlorine is obtained by the action of the
black oxide of manganese, on "the Spirit of Salt," or hydrochloric
acid ; and the most elementary and instructive experiment snowing its
preparation can be made in the following manner :

130

BOY S PLAYBOOK OF SCIENCE.

Fig. 130.

Place in a clear Florence oil-flask, to which a cork and bent tube have
been first fitted, some strong fuming hydrochloric acid. Arrange the
flask on a ring-stand, and then pass the bent tube either to a Wolfe's
bottle containing some pumice stone moistened with oil of vitriol, or to

a glass tube containing
either pumice or as-
bestos wetted with the
same acid. , Another
glass tube, bent at
right angles, passes
away from the Wolfe's
bottle into a receiving
bottle. (Fig. 130). On
the application of heat,
the hydrochloric gas is
driven off from its so-
lution in water, and
any aqueous vapour
carried up is retained
by the asbestos or pu-
mice stone wetted

A. Flask containing the fuming hydrochloric .ui, ^i n t ^f^Cryl 4V,a
acid,"which is gently boiled by the heat of the spirit lamp. W11J A O 11 . 01 vlinoi , me
B. Tube passing to the Wolfe's bottle, containing pumice- application of the lat-
stone or asbestos moistened with sulphuric acid. c. f pr jc nallprl dniinn f}>/>
Second tube passing into a dry empty bottle, which receives lb .~^J ^F? 9

the hydrochloric acid gas. gas i.e., depriving it

of all moisture ; some-
times the salt called chloride of calcium is used for the same purpose, and
it must be understood by the juvenile chemist that gases are not dried
like towels, by exposure to heat, or by putting them in bladders before the
fire, as we once heard was actually recommended, but by causing the gas
charged with invisible steam to pass over some substance having a great
affinity for water. The dry hydrochloric gas falls into the bottle, and dis-
places the air, beinj* about one-fourth heavier than the latter, and gradu-
ally, overflowing from the mouth of the vessel, produces a white smoke,
which is found to be acid by litmus paper, but has no power to bleach,
and is not green ; it is, in fact, a combination of one combining pro-
portion of chlorine with one of hydrogen, and to detach the latter, and
set the chlorine free, it is necessary to convey the hydrochloric gas to
some body which has an affinity for hydrogen. Such a substance is
provided in the use of the black oxide of manganese, which is placed
either in a small flask or in a tube provided with two bulbs, and when
heated with the lamp it separates the hydrogen from the hydrochloric
gas, and forms water, which partly condenses in the second bulb. And
now the gas that escapes is no longer acid and fuming with a white
smoke on contact with the air; but is green, has a strong odour,
bleaches, and is so powerful in its action on all living tissues, that it
must be carefully avoided and not inhaled ; if a small quantity is acci-
dentally inhaled, it produces a violent fit of coughing, which lasts a

THE PREPARATION OF CHLORINE GAS.

131

-considerable time, and is only abated by inhaling the diluted vapour of
ammonia, or ether, or alcohol, and swallowing milk and other softening
drinks. (Kg. 131).

Fig. 131. A. The flask containing the fuming hydrochloric acid, heated by spirit lamp.
B. Tube passing to Wolfe's bottle, containing the pumice-stone or asbestos wetted with
oil of vitriol, c. Second tube, which passes into a wide-mouthed small flask containing
black oxide of manganese, partly in powder and partly in lump ; and the third tube
conveys the chlorine to any convenient vessel. The double bulb tube, E E, may be substi-
tuted for the flask, the oxide of manganese being contained hi the bulb M. N.B. Any tube
may be joined on to another by a bit of india-rubber tubing, which is tied by string.

C B

Tube A is joined to tube B by the caoutchouc pipe c, tied with packthread.

The mode of preparing chlorine, as already given, though very in-
structive, is troublesome to perform ; a more simple process may there-
fore be described :

Pour some strong hydrochloric acid upon powdered black oxide of
manganese contained in a Florence oil-flask, taking care that the whole
of the black powder is wetted with the acid so that none of it clings to the
bottom of the flask in the dry state to cause the glass to crack on the
application of heat. A cork and bent glass tube is now attached, and
conveyed to the pneumatic trough ; on the application of heat to the
mixture in the flask the chlorine is evolved, and may be collected in
stoppered bottles, the first portion that escapes, although it contains
atmospheric air, should be carefully collected in order to prevent any

132

BOY S PLAYBOOK OF SCIENCE.

accident from inhaling the gas, and it will do very well to illustrate the
bleaching power of the gas, and therefore need not be wasted. The
above process may be described in symbols, all of which are easily deci-
phered by reference to the table of elements, page 86.

Mn0 3 +2 HCl=MnCl+2 IIO+C1.

Third Experiment.

Another and still more expeditious mode of preparing a little chlorine,'
is by placing a small beaker glass, containing half an ounce of chlorinated

lime, usually termed chloride of
lime or bleaching powder, care-
fully at the bottom of a deep and
large beaker glass, and then, by
means of a tube and funnel, con-
veying to the chloride of lime
some dilute oil of vitriol, com-
posed of half acid and half
water ; effervescence immedi-
ately occurs from the escape of
chlorine gas, and as it is pro-
duced it falls over the sides of
the small beaker glass into the
large one, when it may be dis-
tinguished by its green colour.
If a little gas be dipped out with
a very small beaker glass ar-
ranged as a bucket, and poured
into a cylindrical glass contain-
ing some dilute solution of in-
digo, and shaken therewith, the
colour disappears almost instan-
taneously; and if a piece of
Dutch metal is thrown into the
beaker glass it will take fire if

Fig. 132. ^ The large beaker glass. B. enough chlorine has been gene-
The small one, containing the chloride of lime, rated, Or some very nnely-pow-
c. The tube and funnel down which the dilute d erec l antimony will demonstrate
sulphuric acid is poured. D D. Sheet of paper , ^, rpv.no f],

over top of large glass, with hole in centre to the same result. Ihus, With a
admit the tube. u. The little beaker used as a f ew beaker glasses, some chlo-
ride of lime, sulphuric acid, a

solution of indigo, and a little Dutch metal, the chief properties of
chlorine may be displayed. (Eig. 132.)

Fourth Experiment.

Into a little platinum spoon place a small pellet of the metal sodium
aud after heating it in the flame of a spirit lamp, introduce the metal

EXPERIMENTS WITH CHLORINE GAS. 133

into a bottle of chlorine, when a most intense and brilliant combustion
occurs, throwing out a vivid yellow light, and the heat is frequently so
great that the bottle is cracked. After the combustion, and when the
bottle is cool, it is usually lined with a white powder, which will be
found to taste exactly the same as salt, and, in fact, is that substance,
produced by the combination of chlorine, a virulent poison, with the
metal sodium, which takes fire on contact with a small quantity of
water ; and hence the use of salt for the preparation of chlorine gas
when it is required on the large scale.

Parts.

Common salt 4

Black oxide of manganese .... 1

Sulphuric acid 2

Water 2

'Fifth Experiment.

Some Dutch metal, or powdered antimony, or a bit of phosphorus,
immediately takes fire when introduced into a bottle containing chlorine

fas, forming a series of compounds termed chlorides, and demonstrating
y the evolution of heat and light, the energetic character of chlorine,
and that oxygen is not the only supporter of combustion ; chlorine
gas has even, in some cases, greater chemical power, because some
time elapses before phosphorus will ignite in oxygen gas, whilst it takes
fire directly when placed in a bottle of chlorine.

Sixth Experiment.

The weight and bleaching power of chlorine are well shown by placing
a solution of indigo in a tall cylindrical glass, leaving a space at the
top of about five inches in depth. By inverting a bottle of chlorine
over the mouth of the cylindrical glass, it pours out like water, being
about two and a half times heavier than atmospheric air, and then, after
placing a ground glass plate over the top of the glass, the chlorine
is recognised by its colour, whilst the bleaching power is demonstrated
immediately the gas is shaken with the indigo solution.

As a good contrast to the last experiment, another cylindrical jar of
the same size may be provided, containing a solution of iodide of potas-
sium with some starch, obtained by boiling a teaspoonful of arrowroot
with some water ; any chlorine left in the bottle (sixth experiment) may
be inverted into the top of this glass and shaken, when it turns a beautiful
purple blue in consequence of the liberation of iodine by the chlorine,
whose greater affinity for the base produces this result. The colour is
caused by the union of the iodine and the starch, which form together a
beautiful purple compound, and thus the apparent anomaly of destroying
and producing colour with the same agent is explained.

134

BOY S PLAYBOOK OF SCIENCE.

Eighth Experiment.

Dry chlorine does not bleach, and this fact is easily proved by taking
a perfectly dry bottle, and putting into it two or three ounces of fused

chloride of calcium broken
in small lumps, then if a
bottle full of chlorine is
inverted over the one con-
taining the chloride of cal-
cium, taking the precau-
tion to arrange a few
folds of blotting paper
with a hole in the centre
on the top of the latter to
catch any water that may
run out of the chlorine
bottle at the moment it is
inverted, the gas will be
dried by contact with the
chloride of calcium, and
if a piece of paper, with
the word chlorine written

Fig. 133. A A. Dry bottle, containing chloride of On $ th indi ?> \

calcium. B. Bottle of chlorine. The arrow indicates the previously made not and

gas. c c. The blotting-paper, to catch any water from dry, is placed in the chlo-

the bottle, B. . The bottle closed, and containing the ^ no change ^^

but directly the paper is

removed, dipped in water, and placed in a bottle of damp chlorine, the
colour immediately disappears. (Fig. 133.)

This experiment shows that chlorine is only the means to the end,
and that it decomposes water, setting free oxygen, which is supposed to
exert a high bleaching power it its nascent state, a condition which many
gases are imagined to assume just before they take the gaseous state, a
sort of intermediate link between the solid or fluid and the gaseous con-
dition of matter. The nascent state may possibly be that of ozone, to
which we have already alluded as a powerful bleaching agent.

Ninth Experiment.

A piece of paper dipped in oil of turpentine emits a dense black
smoke, and frequently a flash of fire is perceptible, 'directly it is plunged
into a bottle containing chlorine gas ; here the gas combines only with
the hydrogen of the turpentine, and the carbon is deposited as soot.

Tenth Experiment.

If a lighted taper is plunged into a bottle of chlorine it continues to
burn, emitting an enormous quantity of smoke, for the reason already
explained > and demonstrating the perfection of the atmosphere in which.

EXPEKIMENTS WITH CHLORINE GAS.

135

we live and breath, and showing that had oxygen gas possessed the
same properties as chlorine, the combustion of compounds of hydrogen
and carbon would have been impossible, in consequence of the enormous
quantity of soot which would have been produced, so that some other
element that would freely enter into combination with it must have
been provided to produce both artificial light and heat. Chlorine is a
gas which cannot be inhaled, and ozone presents the same features, as a
mouse confined for a short time with an excess of ozone soon died ; but
ozone is the extraordinary condition of
oxygen ; the element in the ordinary state
is harmless, and is the one which enters
so largely into the composition of the air
we breathe.

When one volume of olefiant gas (pre-
pared by boiling one measure of alcohol
and three of sulphuric acid) is mixed
with two volumes of chlorine, and the two
gases agitated together in a long glass ves-
sel for a few seconds, with a glass plate
over the top, which should have a welt
ground perfectly flat, they unite on the ap-
plication of flame, with the production of a
great cloud of black smoke, arising from
the deposited carbon, whilst a sort of
roaring noise is heard during the time
that the flame passes from the top to the
foot of the glass. (Fig. 134.)

Twelfth Experiment.

Formerly Bandannah handkerchiefs
were in the highest estimation, and no
gentleman's toilet was thought complete
without one. The pattern was of the
simplest kind, consisting only of white
spots on a red or other coloured ground.
These spots were produced in a very in-
genious manner by Messrs. Monteith, of
Glasgow, by pressing together many
layers of silk with leaden plates perforated
with holes ; a solution of chlorine was
then poured upon the upper plate and
pressure being applied it penetrated the O f chlorine,
whole mass in the direction of the holes,
bleaching out the colour in its passage. This important commercial
result may be imitated on the small scale by placing a piece of calico
dyed with Turkey red between two thick pieces of board, each of which

Fig. 134. Eemarkable deposition

136 BOY'S PLAYBOOK OF SCIENCE.

is perforated with a hole two inches in diameter, and corresponding
accurately when one is placed upon the other. The pieces of board
may be squeezed together in any convenient way, either by weights,
strong vulcanized india-rubber bands or screws, and when a strong

solution of chlorine
gas or of chloride of
lime is poured into
the hole and perco-
lates through the
cloth, the colour is
removed, and the
part is bleached al-
most instantaneously
by first wetting the
_ calico with a little
weak acid, and then
pouring on the solu-
Fig. 135. A. Circular hole in the upper piece of wood, a 4-; nn n f phlnrirlp nf
similar one being perforated in the lower one. B B. The strong P. 1013 le . Ot

india-rubber bands. The bleaching solution is poured into A. lime. Un removing

and washing the fol-
ded red calico it is found to be bleached in all the places exposed to the
solution, and is now covered with white spots. (Fig. 135.)

IODINE.

Iodine (la>8rjs, violet coloured). Symbol, I; combining proportion,
127'1 ; specific gravity, 4*948. Specific gravity of iodine vapour, 8716.

In the previous chapter, devoted to the element chlorine, little or
nothing has been said of that inexhaustible storehouse of chlorine,
iodine, and bromine viz., the boundless ocean. Some one has remarked
that, as it is possible the air may contain a little of everything capable
of assuming the gaseous form, so the ocean may hold in a state of solu-
tion a modicum of every soluble substance, in proof of which we have
lately read of some very important experiments resulting in the separa-
tion of the metal silver from sea water, not certainly in any profitable
quantity, but quite enough to prove its presence in the ocean.

No elaborate research is necessary to ascertain the presence of chlorine,
when it is remembered that Schafhautl has calculated, that all the oceans
on the globe contain three millions fifty-one thousand three hundred and
forty-two cubic geographical miles of salt, or about five times more than
the mass of the Alps.

Now, salt contains about 60 per cent, of chlorine gas, and therefore
the bleachers can never stand still for want of it ; but iodine is not so
plentiful, and was discovered by M. Courtois, of Paris, in kelp, a sub-
stance from which he prepared carbonate of soda, or washing soda ; but
as this is now more cheaply prepared from common salt, the kelp is at
present required only for the iodine salts it contains, as also for the
chloride of potassium. Kelp is obtained by burning dried sea-weeds in a

EXPERIMENTS WITH IODINE.

137

shallow pit ; the ashes accumulate and melt together, and this fused mass
broken into lumps forms kelp. The ocean bed no doubt has its fertile and
barren plains and mountains, and amongst the so-called "oceanic
meadows" are to be mentioned the two immense groups and bands of
sea-weed called the Sargasso Sea, which occupy altogether a space
exceeding six or seven times the area of Germany.

The iodine is contained in the largest proportion in the deep sea
plants, such as the long elastic stems of the fucus palmatus, &c. The
kelp is lixiviated with water, and after separating all the crystallizable
salts, there remains behind a dense oily -looking fluid, called "iodine
ley," to which sulphuric acid is added, and after standing a day or two
the acid "ley" is placed in a large leaden retort, and heated gently
with black oxide of manganese. The chlorine being produced very
slowly, liberates the iodine, as already de-
monstrated in experiment seven, p. 133,
and it is collected in glass receivers.

Iodine, when quite pure and well crys-
tallized, has a most beautiful metallic lustre,
and presents a bluish-black colour, afford-
ing an odour which reminds one at once
of the " sea smell."

First Experiment.

A few grains of iodine placed in a flask
may be sublimed at a very gentle heat, and
afford a magnificent violet vapour, which
can be poured out of the flask into a warm
bottle. If the bottle is cold the iodine
condenses in minute and brilliant crystals.
(Fig. 136.)

Second Experiment.

Upon a thin slice of phosphorus place a
few small particles of ioSine ; the heat pro-
duced by the combination or the two ele- Cold flask above to receive the
ments soon causes the phosphorus to take y a P r - op. Sheet of cardboard

to cut off the heat from the spirit
"*. lamp.

Third Experiment.

Heat a brick, and then throw upon it a few grains of iodine ; by
holding a. sheet of white paper behind, the spleadid violet colour of the
vapour is seen to great advantage. It was by the discovery of iodine in
the ashes of sponge which had long been used as a remedy for goitre, a
remarkable glandular swelling that this element began to be used for
medical purposes, and the important salt called iodide of potassium is
now used in large quantities, not only in medicine, bat likewise for that
most fascinating art, which has made its way steadily, and is now
practised so extensively, under the name of photography.

138 BOY'S PLAYBOOK OF SCIENCE.

THE ART 01 PHOTOGRAPHY.

It was the great George Stephenson who asked the late Dean Buckland
the posing question, " Can you tell me what is the power that is driving
that train ?" alluding to a train which happened to be passing at the
moment. The learned dean answered, "1 suppose it is one of your
big engines." "But what drives the engine?" "Oh, very likely a
canny Newcastle driver." " What do you say to the light of the sun ?"
"How can that be?" asked Buckland. "It is nothing else," said
Stephenson. " It is light bottled up in the earth for tens of thousands
of years ; light, absorbed by plants and vegetables, being necessary for
the condensation of carbon during the process of their growth, if "it be
not carbon in another form ; and now, after being buried in the earth
for long ages in fields of coal, that latent light is again brought forth
and liberated, made to work as in that locomotive for great human
purposes."

Such was the opinion of the most original and practical man that
ever reasoned on philosophy ; and could he have lived to realize the
thorough adaptation and business use of light in the art of photography,
he would have said, man is only imitating nature, and in producing
photographs he must employ the same agent which in ages past assisted
to produce the coal.

In another part of this elementary work we shall have to consider
the nature of light; here, however, the chemical part only of the
process of photography will be discussed.

Many years ago (in the year 1777) Jenny Lind's most learned
countryman, Scheele, discovered that a substance termed chloride of
silver, obtained by precipitating a solution of chloride of silver with
one of salt, blackened much sooner in the violet rays than in any other
part of the spectrum. He says, " Fix a glass prism at the window,
and let the refracted sunbeams fall on the floor ; in this coloured light
put a paper strewed with luna cornua (horn silver or chloride of silver),
and you will observe that this horn silver grows sooner black in the
violet ray than in any of the other rays."

In 1779, Priestley directed especial attention to the action of light on
plants ; and the famous Saussure, following up these and other experi-
ments, determined that the carbonic acid of plants was more generally
decomposed into carbon and oxygen in the blue rays of the spectrum ;
these facts probably suggested the bold theory of Stephenson already
alluded to. Passing by the intermediate steps of photography, we
come to the second year of the present century, and find in the Journal of
the Royal Institution a paper by Wedgwood, entitled " An Account of
a Method of Copying Paintings upon Glass, and of making Profiles, by
the Agency of Light upon Nitrate of Silver ; with observations, by
H. Davy." Such a paper would lead the reader to suppose that very
little remained to be effected, and that mere details would quickly
establish the art ; but in this case the experimentalists were doomed to

THE ART OP PHOTOGRAPHY. 130

disappointment, as, after producing their photographs, they could not
make them permanent ; they had not yet discovered the means of fixing
the pictures. Nearly fourteen years elapsed, when the subject was
again taken up by Niepce, of Chalons, with little success, so far as the
fixing was concerned ; and twenty-seven years had passed away since
the experiments of Wedgwood and Davy, when, in 1829, Niepce and
Daguerre executed a deed of co-partnership for mutually investigating
the matter. These names would suggest a rapid progress ; but, strange
to relate, ten years again rolled away, the father Niepce had in the
meantime died, and a new contract was made between the son and M.
Daguerre, when, in January, 1839, the famous discovery was made
known to the world, and in July of the same year the French Govern-
ment granted a pension for life of six thousand francs to Daguerre,
and four thousand to the son of Niepce, who had so worthily continued
the experiments commenced by his father. The triumph of the indus-
trious French experimentalists was not, however, to be unique ; across
the Channel another patient and laborious philosopher had completed on
paper precisely the same kind of results as those obtained by Daguerre
on silver plates. Mr. Fox Talbot, in England, had immortalized himself
by a discovery which was at once called the Talbotvpe, and for which a
patent was secured in 1841. Having thus hastily sketched a brief
history of the art, we may now proceed to the details of the process.

First Experiment.

A. photogenic drawing, so called, but now termed a positive copy, is
prepared by placing some carefully selected paper, which is free from
spots or inequalities (good paper is now made by several English manu-
facturers, although some kinds of French paper, such as Cansan's, are
in high repute), in a square white hard porcelain dish containing a
solution of common salt in distilled water, 109 grains of salt to the pint.
The paper is steeped in this solution for ten minutes, and then taken
out and pressed in a clean wooden press, or it should be dabbed dry on a
clean flat surface with a clean piece of white calico, which may be kept
specially for this duty and not used for anything else, and it is well that
all would-be photographers should understand that neatness and cleanli-
ness are perfectly indispensable in conducting these processes. If a
design were required for the armorial bearings of the art of photo-
graphy, it might certainly be most fanciful, but the motto must be
cleanliness and neatness, and in preparing paper it should not be unne-
cessarily handled, but lifted by the corners only. The object of dabbing
the paper is to prevent the salt accumulating in large quantities in one
part of the paper and the reverse in another, and to distribute the salt
equally through the whole. The paper being now dried, is called salted
paper, and is rendered sensitive when required by laying it down on a
solution of ammpnio-nitrate of silver, prepared by adding ammonia to a
solution containing sixty grains of nitrate of silver to the ounce of dis-
tilled water, until the whole of the oxide of silver is re-dissolved, except

140 BOY'S PLAYBOOK OF SCIENCE.

a very small portion. A few drops of nitric acid are also recom-
mended to be added, and after allowing the solution to stand, it may be
poured off quite clear, and is ready for use either in the bath, or if
economy must be rigidly adhered to, the salted paper may be laid flat
on a board, and held in its place with four pins at the corners, and then
just enough to wet the surface of the paper may be run along the side
of a glass spreader, and the liquid gently drawn over the surface of the

Fig. 137. A. The glass spreader with cork handle. B. The silver solution clinging to
rod and paper by capillary attraction, c c c c. Four pins holding down the paper on a
board. N.B. The spreader is made of glass rod three-eighths thick.

salted paper, which is allowed to dry on a flat surface for a few minutes,
and afterwards hung up by one corner to a piece of tape stretched
across the room, until quite dry, and then placed in a blotting-book
fitting into a case which completely excludes the light. Copying-paper
should be made at night, as the day is then free for all photographic
operations requiring an abundance of light. It will not keep long, and
should be used the next day.

A piece of lace, a skeleton leaf, a sharp engraving on thin paper, and
above all things, a negative photograph on glass or paper, is easily copied
by placing the prepared paper with the prepared side (carefully protected
from the light) upwards on any flat surface, such as plate glass; upon
this is arranged the bit of lace or the negative photograph with the face
or picture downwards, another bit of plate glass is then placed over it,
and weights arranged at the corners ; after exposure to the sun's rays for
thirty minutes, more or less (according to the dullness or bright aspect of
the day), the picture is brought into a dark room and examined oy the
light of a candle or by the light from a window covered with yellow
calico, and after placing a paper weight on one corner of the lace, or

PHOTOGRAPHIC MANIPULATIONS.

141

negative picture, or copying paper, it may be carefully lifted in one
part, and if the copy is sufficiently dark, is ready for fixing, but if it
is faint the lifted corner is carefully replaced, the upper glass is laid
on, and the picture again exposed to the light. Should the position of the
lace or negative be changed during the examination, re-exposure is use-
less, and would only produce a double and confused picture, as it would
be impossible to lay the lace or the negative exactly in the same place
again on the copying paper.

The manipulations just de-
scribed are much facilitated by
using a copying-frame or press,
which consists of a square
woodenframe with a thick plate-
glass window; upon this are
placed the negative picture and
the copying paper, and the two
are brought in close contact by-
means of a board at the back
Pressed by a hand-screw. (Fig.
38.) After the photogenic
drawing or positive copy is
taken, it is fixed by being placed

in a solution of hyposulphite

of soda consisting of one fluid

Ounce ot saturated solution to and is of course the part exposed to the light.

eight of water. The saturated

solution of hyposulphite of soda is conveniently kept in a large bottle

for use, and in order to improve the colour a very little chloride of

gold is added to the fixing solution, the picture must now be thoroughly

washed, dried, and pressed.

Another mode of preparing the copying paper, called albumen paper,
is to take the whites of four eggs, and four ounces of distilled water
containing one hundred and sixty grains of chloride of ammonium;
these are beaten up with a fork or a bundle of feathers, and as the froth
is produced it is skimmed off by a silver spoon into another basin,
or a beaker glass, and being allowed to settle for twelve hours it is
strained through fine muslin, and is ready for use. The best paper is
floated on the surface of this liquid for three minutes, taken out, and
dried at once on a hot plate.

In floating paper one corner is first laid down, and care taken not to
enclose any air bubbles, which would prevent the fluid wetting the
paper, whilst the remainder of the paper is slowly laid upon the surface
of the fluid.

The albumen paper is excited by laying it for five minutes on a
solution of nitrate of silver, seventy-two grains to the ounce of water,

142 BOY'S PLAYBOOK OF SCIENCE.

and when dry it will keep for three days. This copying paper is used
in the same manner as the last, and fresh eggs only must be used in
its preparation, because stale ones soon cause the copy to change and
blacken all over from the liberation of sulphur, which unites with the
silver. The colour of the copy is sometimes improved by a solution of
hot potash, and by dipping the well-washed picture, after the use of the
hyposulphite of soda, in a very dilute solution of hydrosulphuret of
ammonia.

Third Experiment.

In the Daguerreotype process, a silver plate, after being thoroughly
cleaned and polished, is exposed to the vapour of iodine, and is thus
rendered so sensitive that it may be at once exposed in the camera.
In the Talbotype process, the same principle is apparent, and paper is
prepared by first covering its surface with iodide of silver, which is
afterwards rendered sensitive to the action of light by means of au
excess of nitrate of silver, as follows :

One side of a sheet of selected Cansan's paper is first covered
(by means of a spreader) with a solution of nitrate of silver (thirty
grains to the ounce of water), hung up in a dark room and dried;
it is then immersed in a solution of iodide of potassium of five
hundred grains to a pint of distilled water, for five or ten minutes,
and immediately changes, to a yellow colour in consequence of the pre-
cipitation of the yellow iodide of silver ; it is then well washed with
plenty of water, and being dried, may be kept for any length of time,
and is called " iodized paper." Light has no action whatever upon it.
To render the paper sensitive, three solutions are prepared in separate
bottles, and marked 1, 2, 3.

No. 1, contains a solution of nitrate of silver, fifty grains to the ounce
of water.

No. 2, glacial acetic acid.

No. 3, a saturated solution of gallic acid.

With respect to No. 3, Mr. William Crookes has shown, that when
a saturated solution of gallic acid is required in large quantities, that
it is better to dissolve at once two ounces of gallic aciu in six ounces
of alcohol (60 over proof) ; to hasten solution, the flask may be con-
veniently heated by immersion in hot water ; when cold it should be
filtered, mixed with half a drachm of glacial acetic acid, and preserved
in a stoppered bottle for use ; so prepared it will keep unaltered for
a considerable length of time. The gallic acid is not precipitated from
this solution by the addition of water ; consequently, if in any case
desirable, the development of a picture may be effected with a much
stronger bath than the one usually employed. To obtain a solution
of about the same strength as a saturated aqueous solution, such as
No. 3, half a drachm of the alcoholic solution is mixed with two ounces
of water ; but for my particular purpose, says Mr. Crookes, referring
to the wax-paper process, " I prefer a weaker bath, which is prepared
by mixing half a drachm with ten ounces of water." In either case it

PHOTOGRAPHIC MANIPULATIONS. 143

will be found necessary to add solution of nitrate of silver in small
quantities, as the developing picture seems to require it.

Returning again to the solutions marked 1, 2, 3, the numbers will
assist the memory in mixing the proportions of each. If the paper
is required to be used at once, a drachm of each may be mixed to-
gether and spread over the iodized paper (of course, in a dark room),
which is then transferred to a clean blotting-book of white bibulous
paper, and being placed in the paper-holder may be taken to the camera
ami exposed at once. If the paper is not required to be used imme-
diately, the solutions are mixed in the proportions of the numbers viz.,
one of No. 1, two of No. 2, three of No. 3 ; and in making the mixture, it
is advisable to keep a measure specially for No. 3, the gallic acid, or
else the measure, if used for the three solutions, will have to be washed
out every time, which is very troublesome, particularly where water is
not plentiful.

If the excited paper is required to be kept some hours before use,
No. 3 must be added in still larger proportion, as much as ten or even
twenty measures of No. 3 to two of No. 2, and one of No. 1, being used,
and even this large dilution is frequently insufficient to prevent the
paper spoiling in hot weather; therefore if the temperature is high,
too much reliance must not be placed on this paper, as it is peculiarly
disappointing, after walking some miles to romantic and beautiful
scenery, to find, when developing the pictures in the evening, that the
paper used was all spoilt before exposure ; and it will be seen presently
that when the excited paper is to be carried about for use, it is better
to adopt the wax-paper process.

After the excited iodized paper is exposed in the camera and the
time of exposure cannot be taught, as that speciality is only acquired by
experience, and may vary from five to thirty minutes, or even more
the invisible picture is developed and rendered visible, not by exposure
to the vapour of mercury, as in Daguerre's process with silver plates,
but by a mixture of one of No. 1 with four of No. 3. The development
is carefully watched by looking through the negative placed before a
lighted candle, and the time of development may vary from ten to thirty
minutes, and all the time the picture must be kept wet with the
solution, so that it is better perhaps to make a bath of the solution
and lay the picture on its surface than to pour the liquid over the
picture. After the development is matured, the picture is now washed
in clean water, and fixed temporarily, if required, by immersion in a
bath containing 200 grains of bromide of potassium in one pint of water,
or permanently by the hyposulphite of soda, made by mixing one part
of a saturated solution with five or ten of water, or one ounce of the
salt to six or twelve of water ; but, as before mentioned, it is better to
keep a Winchester quart full of a saturated solution of hyposulphite
of soda, and then it is always ready for use instead of employing the
weights and scales, and continually weighing out portions of the salt.
The picture after fixing is thoroughly washed with water, and being

144 BOY'S PLAYBOOK OF SCIENCE.

dried is now placed between the folds of a wax book i.e., some leaves
of blotting-paper are kept saturated with white wax, and when a
picture is placed between them, and a hot iron passed over the outside
sheet, the wax enters the pores of the paper, and after removing any
excess of wax by passing the picture through a book of bibulous paper,
over which the hot flat iron is passed, the negative picture at last is
ready for use, and any number of positive copies may be taken from it,
as already described in the first experiment, page 139.

This mode of manipulation is called the Talbotype, and before
dismissing the subject another process of iodizing the paper may be
explained.

To a solution of nitrate of silver of twenty, thirty, or fifty grains
to the ounce of water, a sufficient number of the crystals of iodide of
potassium is added, first to produce the yellow iodide of silver, and
then to dissolve it, so that the yellow precipitate appears with a
small quantity, and disappears with an excess of the iodide. If this
solution is spread over sheets of paper, and these latter then placed
in a bath of water, the iodide of silver is precipitated on the surface,
and after plenty of washing to remove the excess of iodide of
potassium, the paper may be dried, and will keep for any length of time
without change. This paper may be excited, exposed, developed, fixed,
and waxed, as already explained.

Fourth Experiment. The Wax-paper Process.

This mode of taking negative photographs begins where the talbo-
type ends viz., by first waxing the paper perfectly and evenly, as
already explained, Cansan's negative paper being preferred. The wax
paper is now well soaked in a bath, made by dissolving one hundred
grains of iodide of potassium, six grains of cyanide of potassium,
four grains of fluoride of potassium, ten grains of bromide of potassium,
ten grains of chloride of sodium, in one pint of fresh whey, with the
addition of a little alcohol and a few grains of iodine. When soaked
in this solution for about one hour, the paper is taken out and hung up
to dry.

N.B. With respect to iodizing the wax paper, it is almost better to
obtain it ready prepared, and then every sheet may be relied on. Mr.
Melhuish, of Blackheath and Holborn, supplies it in any quantity, and
his paper never fails; the operator has then only to perform the sensi-
tizing and developing processes. To render the iodized paper sensitive it
is immersed for about six minutes in a bath containing a solution of
nitrate of silver (thirty-five grains to the ounce of water, with forty
drops of glacial acetic acid); the paper is now removed, and washed in
two trays of common clear rain-water or distilled water, and is then
dried off between folds of blotting-paper.

This process may be performed on the previous evening by the light
of a candle, or by day in a room lit by one window covered with four
thicknesses of yellow calico, and after the paper is dry it will keep for three

PHOTOGRAPHIC MANIPULATIONS.

145

weeks or a month, and may be exposed in a camera with a three-inch
lens of eighteen-inch focus, with the inch diaphragm, on a bright day
from five to fifteen minutes ; in bad weather the exposure must be longer.
The picture may be carried home and rendered visible or developed
by immersion in a bath containing a saturated solution of gallic acid,
and as the developing continues, a few drops of the sensitizing solution
of nitrate of silver and glacial acetic acid may be added. Finally, the

Eicture is fixed by immersion for a quarter of an hour in a solution of
yposulphite of soda (four ounces of the crystal to one pint of water, or
one part of the saturated solution to eight of water), and being well
washed, is then dried, hung before the fire to melt the wax, and is now
ready to print from.

Fifth Experiment. Albumen on Glass Process.

Albumen is the scientific name for the white of egg, of which four
ounces by measure are mixed with one ounce and a half of distilled
water, and after being whisked to a
froth, are removed by a spoon into
another basin or a beaker glass, and
allowed to stand for several hours
and then filtered. Mr. Crookes has
recommended a very ingenious, simple,
and useful ^ filter. (Fig. 139.) He
says : " This simple and inexpensive
piece of apparatus, which any instru-
ment maker or glass-blower can supply
at a few hours' notice, will be found in-
valuable in almost every photographic
process on glass. The sponge has this
great advantage over all other kinds of
filters, that thick gelatinous liquids
phoney, albumen,gelatme,meta-gela-

tine, or the various preservative syrups squeezed into the head of the tube,
flow through it with the utmost readi- ny liquid poured in at B will flow

i ., , & , ., ,. i , . through the sponge until it has at-

ness ; whilst at the same time dust, air tained the same level in A.
bubbles, or froth, and dried particles

floating iii the liquid, are effectually kept back, and if fitted with stop-
pers, collodion might be filtered in it ; or if the ends were fitted together
with a bit of flexible pipe, the stoppers might be dispensed with altogether.
Having poured the albumen on a perfectly clean glass plate, taking
care to have sufficient to run freely over the surface of the glass,
the excess is then gently drained off and the plate turned so as to
have the coated side downwards ; it is then fixed in a sline^ made by
taking a stout bit of string about three feet long, which is doubled
and knotted at the fold, leaving the two ends free ; two small triangles
or stirrups of silver wire looped at one corner are now tied on to the
ends of the string, and these form a support for the opposite edges of
the glass plate to rest on ; the two strings are knotted together at a

BOY'S PLAYBOOK OF SCIENCE.

Fig. 140. A. Loop for finger. B. The knot
which prevents the stirrups of silver wire, c c,
slipping off the corners of the glass plate.
D D. The opposite corners of the glass plate
on which the stirrups are placed.

Fig. 141. A A. Tin box, with partitions to
hold glass plates. B B. The outer jacket, be-
tween which and the boz, A, the lid or cover,
c, slides.

convenient distance from the
stirrups to prevent the glass slip-
ping out, and the plate is now
rotated rapidly over a heated me-
tallic surface, such as an iron
box containing some burning
charcoal or the warming pan,
care being taken to avoid dust as
much as possible, and to use only
the whites of new-laid eggs.
(Tig. 140.) The glass plate, co-
vered with dry albumen, is now
iodized to a straw colour by ex-
posure over a box containing
iodine, as in the Daguerreotype
process, and is sensitized by im-
mersion for three or four minutes
in a bath containing a solution
of nitrate of silver (twenty -five
grains to an ounce of water) ;
the plate is afterwards washed in
distilled water and left to dry
spontaneously, of course in a
darkened room. The plates may
then be placed ready for use in a
very ingenious tin box devised by
Mr. Crookes, which keeps them
perfectly light-tight even in the
sun, and at the same time is less
bulky than the ordinary wooden
ones. It is made of tin plate,
the cover sliding tight over the
top, and more than half way down
the sides; light is further ex-
cluded by means of an outer
jacket of tin, which is soldered
to the box a little below the
centre. The cover thus slides
between the case and the jacket,
and renders injury to the plates
by the entrance of light an im-
possibility. (Tig. 141.)

The sensitive albumenized
glass plate is exposed in the
camera from fifteen to thirty
minutes, and developed (much in
the same way as the paper pic-
tures) with one ounce oi a satu-

PHOTOGRAPHIC MANIPULATIONS. 14.7

rated solution of gallic acid containing ten or fifteen drops of the sen-
sitizing solntion. The plate is usually placed on a levelling stand, and
the solution poured on the glass plate ; the development is slow, and may
be quickened sometimes by the application of heat.

The picture is fixed by immersion for a short time in a bath con-
taining one part of a saturated solution of hyposulphite of soda in
eight of water. The pictures produced by this process are exquisitely
denned, provided always the camera is well focussed, and to assist .this
operation a magnifying glass may be employed. After removal from the
hyposulphite of soda the plate is well washed with water, and being
allowed to dry spontaneously, is now ready to print from.

Sixth Experiment. Tfie Collodion on Glass Process.

The glass plates for this, as well as the albumen on glass process,
should be cleaned by rubbing them over first with a mixture of Tripoli
powder and ammonia, which is washed off under a tap, and the glass
being drained is rubbed dry and polished with a clean calico duster kept
exclusively for this purpose.

The iodized collodion is now poured on, and the excess re-
turned to the bottle. Collodion can be made very easily, but if prepared
without due precautions, it cannot be used afterwards, and reminds one
of the old story of the enthusiastic son, who, when asking his father's
permission to espouse the beloved, enumerated amongst her other ac-
complishments, the fact that she could make a pudding, and was
answered by the bluff question, " But can you eat it afterwards ?"
So it is with collodion : a great deal of messing and loss of time
is saved by purchasing it of the various makers, amongst whom
may be specially noticed Mr. Richard Thomas, of 10, rail Mall,
who has devoted the whole of his attention to the preparation of this
important photographic chemical, and with a success which his numerous
patrons can well testify. The collodion is sold either mixed with the
iodizing solution, or the two can be obtained separately, with direc-
tions on the bottles as to the quantities to be mixed together.

The plate covered with the iodized collodion is quickly transferred to
a bath containing a solution prepared in the following manner :
Dissolve four ounces of nitrate of silver in eight ounces of water, and to
this add twenty grains of iodide of potassium in one ounce of water ;
shake them together, and then pour the whole into fifty-six ounces of
distilled water, and in half an hour add one ounce of alcohol and half an
ounce of ether ; agitate the whole and filter the next morning. The
collodion plate is kept in this solution for ?, certain period, only learnt
by experience, and should be occasionally lifted out to see if a uniform
transparency is obtained ; say that the immersion may be continued for
five minutes, it is now ready for the camera, and may be exposed from
about one to two minutes, or more if the light is deficient ; the time of
exposure is also a matter of practice, mere directions can be of no use
in this stage of the process.

The picture is developed on a levelled stand, with a solution of three

148

BOY'S PLAYBOOK OF SCIENCE.

Fig. 142. A. Glass or gutta-percha bath to
hold the sensitizing solution. B. Glass, with
piece cemented on the end to hold the prepared
glass plate, c, whilst dipped in the bath, A.
The plate c has a cross in one corner to show
prepared side.

grains of pyrogallic acid in three
ounces of water, to which sixty
drops of glacial acetic acid have
been added. When fully deve-
loped the plate is washed with
water and fixed with a solution
of hyposulphite of soda, consist-
ing of one part of the saturated
solution to eight of water, again
thoroughly but gently washed,
so as not to endanger the sepa-
ration of the film from the glass ;
it is allowed to dry spontaneously,
and being coated with amber var-
nish (a solution of amber in chlo-
roform) is now ready to print
from. (Fig. 123.) It is, perhaps,
hardly necessary to add, that the
sensitizing and developing pro-
ared cesses must be performed in a
dark room.

Fig. 143. First effect of peripatetic photography on the rural population.

CHEMISTRY. 149

BUOMINE.

Bromine Opoofio?, a bad odour). Symbol, Br. Combining propor-
tion, 80. Specific gravity, 2'966.

In a previous portion of this work, the connexion between chlorine,
iodine, and bromine has been pointed out ; and as we have to notice the
colour of the element bromine, the chromatic union of the triad may
be alluded to. These elements present very nearly all the colours of
the spectrum :

Bromine red to orange.

Chlorine yellow to green.

Iodine blue, indigo, violet.

These three elements also furnish examples of the three conditions of
matter; iodine being a solid, bromine a. fluid, chlorine a gas; the
relation of their combining proportions is also curious : as might be ex-
pected, the fluid bromine takes an intermediate position, and (according
to the axiom that half the sum of the extremes is equal to the mean)
by dividing the combining proportions of iodine and chlorine, and
adding them together, we nave, as nearly as possible, the combining
proportion of bromine :

Chlorine 35 ~ 2 = 17'75

Iodine 126 ~ 2 = 63

80-75

The combining proportion of bromine is 80, but 80'75 is so near,
that it may reasonably be conjectured future experiments will reduce the
number of the three elements, and may prove that they are only modifi-
cations of a single one. This is the only kind of alchemy which is
tolerated in the nineteenth century, and any philosopher who will reduce
the number of elements, and prove that some of them are only modi-
fications of others, will achieve a renown that must transcend the eclat
of all previous discoverers.

Bromine was discovered by Balard, in 1826, and, like chlorine and
iodine, is a constituent of sea water. The chief source of bromine is
a mineral spring at Kreutznach, in Germany. The process by which it
is obtained offers a good example of chemical affinity ; the water of the
mineral spring is evaporated, alt crvstallizable salts removed, and a current
of chlorine gas passed through the remaining solution, which changes
to a yellow colour, in consequence of the liberation of the bromine by
the combinations of chlorine with the bases previously united with the
former ; the liquid is then shaken with ether, which dissolves out the
bromine. In the next place, the etherial solution is agitated with
strong solution of potassa, and is thus obliged to part with the bromine^
which is converted into bromate of potassa ; this is ultimately changed
by fusion to bromide of potassium ; and by distillation with black oxide
of manganese and sulphuric acid, the bromine is finally obtained. Six

150 BOY'S PLAYBOOK OF SCIENCE.

processes are therefore necessary before the small quantity of bromine
contained in the mineral spring-water, is separated.

First Experiment.

Bromine is a very heavy fluid, which should be preserved by keeping
it in a bottle covered with water ; when required, a few drops may be
removed by means of a small tube, and dropped into a warm bottle,
which is quickly filled with the orange-red vapour. If some phosphorus
is placed in a deflagrating spoon, and exposed to the action of bromine
vapour, it takes fire spontaneously.

Second Experiment.

Powdered antimony sprinkled into the vapour of bromine immediately
takes fire.

Third Experiment.

A burning taper immersed in a bottle containing the vapour of bromine
is gradually extinguished.

Fourth Experiment.

Liquid bromine exposed to a freezing mixture of ice and salt, or
reduced to a temperature of about eight degrees below zero, solidifies
into a yellowish-brown, brittle, crystalline mass.

Fifth Experiment.

A solution of indigo shaken' with a small quantity of the vapour of
bromine is quicklv bleached. Many substances, when brought in contact
with liquid bromine, combine with explosive violence, and therefore
experiments with liquid bromine are not recommended, as all the most
instructive and conclusive results can be obtained by the use of the
vapour of bromine, which is easily procured by allowing a few drops to
fall' into a warm, dry bottle.

Bromine, as already mentioned, is used in the art of photography.

FLTJOEINE.

Symbol, F. Combining proportion, 19.

This singular element seems almost to embody the ancient idea of
the alchemists, being a sort of alkahest, or universal solvent ; or in
plainer language, its affinities for other bodies are so powerful, that it
attacks every substance (not even excepting gold), at the moment of
its liberation, and combines therewith, so that its isolation has not
yet been effected. Chemists who assert that they have been able to
obtain fluorine in the elementary condition, pronounce it to be a gas
which possesses the colour of chlorine ; but the experiments, as hitherto
conducted, render that statement extremely doubtful.

ETCHING ON GLASS. 151

The only interesting fact connected with fluorine, is the remarkable
property of attacking glass and other silicious bodies, belonging to its
combination with hydrogen gas, called hydrofluoric acid. This acid is
easily obtained and used by placing some powdered fluorspar in a leaden
tray six inches square and two inches deep. If sulphuric acid is now mixed
with the powdered spar, so as to form a thin paste, and heat applied,
the vapour of the hydrofluoric acid quickly rises, and can be employed
to etch a glass plate upon which a drawing may have been previously
traced by scratching away the wax, with which it is first coated. By
heating the glass plate before a fire, a sufficient quantity of wax is soon
melted on to it by merely rubbing the wax against the glass j>late ; any
excess should be avoided, if a well-executed drawing is required to be
etched on its surface. (Fig.' 144.)

Fig. 144. A A A. The glass plate, with the waxed side downwards, placed on the
leaden tray containing the fluorspar and sulphuric acid. u. Spirit lamp.

The wax plate must not remain too long over the leaden tray, as the
heat is apt to melt the wax, when the acid not only attacks those parts
from which the wax has been removed by the etching needle, but also
the surface of the glass generally, and thus the clearness of the design
is spoilt. After exposure and it is as well to prepare two or three
glass plates for the experiment the wax is quickly removed by rubbing
and washing with oil of turpentine, and the design (beautifully etched
into the glass) is then apparent.

CHAPTER XII.

CARBON, BORON, SILICON, SELENIUM, SULPHUR, PHOSPHORUS.

THIS group of non-metallic elements has been frequently styled
" Metalloids," meaning substances allied to, but not possessing, all the
properties belonging to a metallic substance; and therefore perhaps
the expression, non-metallic solids, is the best that can be adopted. They
may be subdivided into two classes of three each, which have properties
more or less allied to each other viz.,

Carbon, Boron, Silicon; and

Selenium, Sulphur, Phosphorus.

152 BOY'S PLAYBOOK OF SCIENCE.

CARBON.

Symbol, C ; Combining Proportion, 6.

This element has almost the property of ubiquity, and is to be found
not only in all animal and vegetable substances, in common air, sea, and
fresh water, but also in various stones and minerals, and especially in
chalk and limestone.

There is, perhaps, no element which oifers a greater variety of amusing
experiments and elementary facts than carbon, whether it be considered
either in its simple or combined state.

A piece of carbon, in the shape of the Koh-i-Noor, was one of the
chief attractions at the first Exhibition in Hyde Park. The diamond is
the hardest and most beautiful form of charcoal ; how it was made in
the great laboratory of nature, or how its particles came together, seems
to be a mystery which up to the present time has not yet been solved,
at all events no artificial process has yet produced the diamond.

Sir D. Brewster, speaking of the Koh-i-Noor, remarks that on placing
it under a microscope, he observed several minute cavities surrounded
with sectors of polarized light, which could only have been produced
by the expansive action of a compressed gas or fluid, that had existed in
the cavities when the diamond was in the soft state.

Now it is known that bamboo, which is of a highly silicious nature,
has the property of depositing in its joints a peculiar form of silica,
called tabasheer. Silicon is one of the triad with carbon i.e., it is allied
to carbon on account of certain analogies ; may it not then be supposed
that, in times gone by, ages past, when the atmosphere was known to
be highly charged with carbonic acid gas, there might possibly have
existed some peculiar tree which had not only the power of decomposing
carbonic acid (possessed by all plants at the present period), but was
enabled, like the bamboo, to deposit, not silica, which is the oxide of,
silicium, but carbon, the purest form of charcoal viz., the diamond ?
Speculation in these matters is ever more rife than stern proof, and it
may be stated, that all attempts to manufacture this precious gem
(like those of the alchemists with gold and silver) have most signally
failed.

First Experiment.

Box and various woods, dried bones, and different organic matters,
placed in a nearly close iron or other vessel, and heated red hot, so that all
volatile matter may escape, leave behind a solid black substance called
charcoal. If that kind obtained from bones, and termed bone black or
ivory black, is roughly powdered, and placed in a flask with some solu-
tion of indigo or some vinegar, or syrup obtained by dissolving common
moist sugar in water, and boiled for a short period, the colour is re-
moved, and on filtering the liquid it is found to be as clear and colour-
less as water, provided sufficient ivory black has been employed.

COMBUSTION OP THE DIAMOND.

153

Second Experiment.

Charcoal is a disinfectant, and is used for respirators ; it has even been
recommended medically, and charcoal lozenges can be bought at various
chemists' shops. If a few drops of a strong solution of hydrosulphuret
of ammonia (which has the agreeable odour belonging to putrid eggs)
is mixed with half a pint of water, it will of course smell strongly, and
likewise precipitate Goulard water, or a solution of acetate ol lead
black ; but on shaking the water with a few ounces of charcoal, it no
longer smells of sulphuretted hydrogen, and if filtered and poured into
a solution of lead does not turn it black. This chemical action of
charcoal, independent of its seeming mechanical attraction for colouriog
matter, would appear to show that the pores of charcoal contain oxygen,
which in that peculiar condensed state destroys colouring matter, and
oxidizes other bodies.

Third Experiment.

A very satisfactory experiment, proving that the diamond and plum-
bago or black lead are identical with charcoal, although differing in
outward form and purity, can be made at a little cost,
by purchasing a fragment of refuse diamond, called
"boart," of Mr. Tennant of the Strand. A small
piece costs about five shillings. The fragment should
be carefully supported by winding some thin platinum
wire round it, as, if the wire is too thick, it cools
down the heat of the bit of diamond and prevents it
kindling in the oxygen gas. A difficulty may arise in
preparing the fragment, in consequence of the wire
continually slipping off. The " boart" should there-
fore be grasped by the thumb and first finger, and the
wire wound round ; then it must be carefully turned
and again wound across with the platinum wire, as
in the sketch below. (Fig. 145.)

A piece of black lead (so called) may now be taken
from a lead pencil and also supported by platinum
wire ; likewise a bit of common bark charcoal or hard
coke. Three bottles of oxygen should now be pre-
pared from chlorate of potash and oxide of manga-
nese, an extra bottle being provided for the diamond or^B^amondT
in case there should be any failure in its ignition.
The bark charcoal can be first ignited by holding a corner in the spirit
lamp for a few seconds ; when plunged into oxygen it immediately
kindles and burns with rapidity, and if the cork is well fitted, the
product of combustion viz., carbonic acid gas is retained for future
examination. The small piece of black lead is next heated red hot in
the flame of the spirit lamp, and being attached by its platinum sup-
port to a stiff copper wire thrust through a cork, which fits the bottle
of oxygen, is placed whilst red hot in the gas, and continues to glow
until consumed. The fragment of diamond is by no means, however so

Pig. 146. i. The

154

BOY S PLAYBOOK OF SCIENCE.

easily ignited, the flame of the spirit lamp must be urged upon it with
the blowpipe ; when quite red hot, an assistant may remove the stopper
from the bottle of oxygen, and the person heating the diamond should
plunge it instantly into the gas ; if this is dexterously managed, the
fragment of boart glows like a little star, and the combustion frequently
continues till the piece diminishes so much that it falls out of its platinum
support.

Sometimes the diamond cools down without igniting, the same pro-
cess must therefore be repeated, and a few extra bottles of oxygen
will prevent disappointment, as every failure destroys the purity of the

'as by admixture with atmospheric air when the stopper is removed.

Fig. 146.)

Fig. 146.

Bottle containing bark charcoal. B. Ditto the plumbago or
black lead. c. Ditto the diamond.

The combustion having ceased in the three bottles, the corks are
removed, and the glass stoppers again fitted for the purpose of testing
the products, which offer no apparent indication of any change, as oxygen
and carbonic acid gas are both invisible. In each bottle a new com-
bination has been produced ; the charcoal, the black lead, the diamond
have united with the oxygen, in the proportion of six parts of carbon to
sixteen parts of oxygen, to form twenty-two parts of carbonic acid gas,
which may be easily detected by pouring into each bottle a small quan-
tity of a solution of slacked lime in water, called lime water. This
test is easily made by shaking up common slacked lime with rain or
distilled water for about an hour, and then passing it through a calico
or paper filter. The test, though perfectly clear when poured in, be-
comes immediately clouded with a white precipitate, usually termed a
milkiness, no doubt in allusion to the London milk, which is supposed to
contain a notable proportion of chalk and water, for in this case the
precipitate is chalk, the carbonic acid from the diamond and the charcoal
having united with the lime held in solution by the water and formed
carbonate of lime, or chalk, a substance similar in composition to
marble, limestone, Iceland or double refracting spar, these three being
la early similar in composition, and differing only, like carbon and the
diamond, in external appearance.

PREPARATION OF CARBONIC ACID GA.S. 155

The milkiness, however, must not be held as conclusive of the pre-
sence of carbonic acid gas until a little vinegar or other acid, such as
hydrochloric or nitric, has been finally added; if it now disappears
with effervescence (like the admixture of tartaric acid, water, and car-
bonate of soda), the little bubbles of carbonic acid gas again escaping
slowly upwards, leaving the liquid in the three bottles quite clear, then
the experimentalist may sum up his labours with these effects, which
prove in the most decisive manner that common charcoal, black lead,
and the diamond, are formed of one and the same element viz.,
carbon.

Fourth Experiment.

Having effected the synthesis (or combining together) of the diamond
and oxygen, it is no longer possible to recover it in its brilliant and
beautiful form. If the product of combustion is retained in a flask
made of thin, hard glass, and two or three pellets of the metal potassium
are placed in directly after the diamond has ceased to burn, and the
flame of a spirit lamp applied till the potassium ignites, then the metal,
by its great affinity for oxygen, takes away and separates it again from
that which was formerly the diamond ; but instead of the jewel being
deposited, there is nothing but black, shapeless, and minute particles of
carbon obtained, if the potash produced is dissolved in water, and the
charcoal separated by a filter.

Fifth Experiment.

Chalk is made by uniting carbonic acid gas with lime ; it may there-
fore be employed as a source of the gas, by placing a few lumps of
chalk, or marble, or limestone, in a bottle such as was used in the gene-
ration of hydrogen gas ; on the addition of some water and hydrochloric
acid, effervescence takes place from the escape of carbonic acid gas, and
the cork and pewter pipe being adapted, it may be conveyed by its own
gravity into glasses, jugs, or any other vessels, and a pneumatic trough
will not be required. Carbonic acid gas has a specific gravity of 1'529,
and is therefore rather more than half as heavy again as atmospheric air.

Sixth Experiment.

In order to satisfy the mind of the operator that the gas obtained
from chalk is similar to the product of combustion from the diamond, some
lime-water may be placed in a glass, and the gas from the bottle allowed
to bubble through it ; instantly the same milkiness is apparent, which
again vanishes on the addition of acid. And this experiment is rendered
still more striking if a lighted taper be placed in the glass just after the
addition of the acid, when it will be immediately extinguished.

Seventh Experiment.

If a lady's muff-box, supported by threads or chains, is hung on one end
of a scale-beam, and counterbalanced by a scale pan and a few shot, it is

156

BOY'S PLAYBOOK OF SCIENCE.

immediately depressed on pouring into the muff-box a quantity of car-
bonic acid gas, which may have been previously collected in a large tin
vessel. After showing the weight of the gas, the box is detached
from the scale-beam, and the contents poured upon a series of lighted
candles, which are all extinguished in succession. (Fig. 147.)

Fig. 147. A. Carbonic acid gas poured out of the tin box into B, the muff-box.
B B. Detached muff-box, and candles extinguished by the carbonic acid gas poured from it.

Eighth Experiment.

The property of carbonic acid gas of extinguishing flame, as com-
pared with the contrary property of oxygen, is nicely shown by first
passing into a large and tall gas jar one half of its volume of oxygen
gas; a large cork perforated with holes may be introduced, so as
to float upon the surface of the water in the gas jar, and is usefully
employed to break the violence with which the carbonic acid enters the
gas jar, as it is passed in to fill up the remaining half volume of the gas
lar, which now contains oxygen at the top, and carbonic acid gas at the
bottom. On testing the, contents of the jar with a lighted taper, it
burns fiercely in the oxygen, but is immediately extinguished in the

EXPERIMENTS WITH CAEBONIC ACID GAS. 157

carbonic acid gas, being alternately lighted and put out as it is raised or
depressed in the gas jar.

Ninth Experiment.

A little treacle, water, and a minute portion of size, may be placed
with some yea,st in a quart bottle, to which a cork and pewter or glass
pipe is attached; directly the fermentation begins, quantities of car-
oonic acid gas may be collected, and tested either with lime-water or the
lighted taper.

Tenth Experiment.

Some clear lime-water placed in a convenient glass is quickly rendered
milky on passing through it the air from the lungs by means of a glass
tube; thus proving that respiration and (as shown by the ninth ex-
periment) fermentation, as well as the combustion of charcoal, produce
carbonic acid gas.

Eleventh Experiment.

Qarbonic acid gas is not only generated by the above processes, but
is liberated naturally in enormous quantities from volcanoes, and from
certain soils : hence the peculiar nature of the air in the Grotto del
Cane. Dogs thrust into this cave drop down immediately, and are
immediately revived by the tender mercies of the guides, who throw
them into the adjoining lake. This natural phenomenon is well imitated
by taking a box, open at the top, and nailing on to it a frame of card-

Fig. 148. A A. The box model of the Grotto del Cane. B B. Cardboard fixed in front
of box, and painted to imitate rocks, c. Carbonic acid gas bottle, with bent tube passing
through hole in the side of the box. A taper introduced at D burns in the upper, and ia
extinguished in the lower, part of the model.

158 BOY'S PLAYBOOK OF SCIENCE.

board, which may be painted to represent rocks, taking care that a portion
(about three inches deep) at the lower part is well pasted to the box at
the edges, so that the gas may be retained ; a hole is perforated at the
top side to admit a lighted taper, and another at the side for the pipe
from the carbonic acid bottle ; when the bottom is filled with gas, a
taper is applied, which is found to burn in the upper part, but is imme-
diately extinguished when it reaches the lower division, where the three
inches of pasteboard prevent it falling out : thus showing in a simple
manner why a guide may enter the cave with impunity, whilst the dog-
is rendered insensible because immersed in the gas. (Fig. 148.)

Twelfth Experiment.

Many fatal accidents have occurred in consequence of the air in deep
pits, graves, &c., becoming unfit for respiration by the accumulation of
carbonic acid gas, which may arise either from cavities in the soil, where
animal matter has undergone decomposition, or it may happen from Jhe
depth and narrowness of the hole or well preventing a proper draught
or current of air, so that it becomes foul by the breathing of the man
who is digging the pit. Air which contains one or two per cent, of
carbonic acid will support the respiration of man, or maintain the flame
of a candle ; but it produces the most serious results if inhaled for
any length of time ; a lighted candle let down into a well (suspected
to contain foul air) before the descent of the person who is to work
in it, may burn, but does not indicate the presence of the small
percentage of the poison, carbonic acid. Frequently no trouble is taken
to test the air with a lighted candle ; a man is lowered by his com-
panions, who see him suddenly become insensible, another is then lowered
quickly to rescue him, and he shares the same fate ; and indeed cases
have occurred where even a third and a fourth have blindly and igno-
rantly rushed to their death in the humane attempt to rescue their fellow
creatures. What is to be done in these cases? Are the living to
remain idle whilst the unfortunate man is suffocating rapidly at the
bottom of the pit ? No ; provided they do not venture themselves into
the pit, they may try every known expedient to alter the condition of
the foul air, so as to enable them to descend to the rescue. One should
be despatched to any neighbouring house or cottage for a pan of burning
coals; if any slacked lime is to be had, it may be rapidlv mixed with
water, and poured down the side of the pit ; a bundle of shavings set
on fire and let down, keeping it to one side, so as to establish a current ;
or even the empty buckets constantly let down empty and pulled up full
of the noxious air, may appear a somewhat absurd step to take, but
under the circumstances any plan that will change the air sufficiently to
enable another person to descend must be adopted ; in proof of which
the following experiments may be adduced :

Fill a deep glass jar with carbonic acid, and ascertain its presence
with a lighted taper ; if a beaker glass to which a string is attached is
jet down into the vessel and drawn up, and then inverted over a lighted

EXPERIMENTS WITH CARBONIC ACID GAS.

taper, the utility of
this simple plan is at
once rendered appa-
rent ; the beaker glass
represents the empty
bucket, and can be let
down and pulled up
full of carbonic acid
until a sensible change
in the condition of the
atmosphere is pro-
duced. The best plan,
however, is to set the
air in motion by heat
obtained from burning
matter, or even a kettle
of boiling water, low-
ered by a cord, and
this fact is well shown
by putting a small flask
full of boiling water,
and corked, at the bot-
tom of the deep glass
iar containing the car

Fig. 149. A. Deep jar containing carbonic acid gas, which
is being removed by the little glass bucket. B. Jar con-
taining corked flask of boiling water on a pad; the heated
gas rises and the cold air descends to take its place.

bonic acid gas, which rises like other gases when sufficiently heated, and
passing away, mixes with the surrounding air. (Fig. 149.)

Thirteenth Experiment.

Carbonic acid gas dissolved in water under considerable pressure,,
forms that most agreeable drink called soda-water ; the gas is not only
useful in this respect, but has been applied most successfully by Mr.
Gurney to extinguish a fire on a gigantic scale, which had been burning
for years in the waste of a coal mine in Scotland. The same gas, gene-
rated suddenly by the combustion of a mixture of nitre, coke dust, and
clay, or plaster of Paris, in vessels of a peculiar construction, has
formed the subject of a patent by Phillips, since merged into the Fire
Annihilator Company. The instrument is peculiarly adapted for ship-
ping, and might, if properly used, be the means of saving many ships and
valuable lives. (Fig. 150.)

Its practical value is established by the test of actual use : in the
streets, by the Leeds Fire Brigade, and by firemen of the Fire Anni-
hilator Company, temporarily stationed at Liverpool and Manchester.

The Fire Anninilator has been formally recognised by the Government
Emigration Commissioners, who introduced into the Passengers' Act,
1852, in 24, the alternative, " Or other apparatus for extinguishing fire"
with distinct reference to this invention, and subsequently by formal
order authorized their officers to pass ships carrying Fire Annihilators.

160

BOY S PLAYBOOK OP SCIENCE.
A

Fig. 150. A. A carriage with six fire annihilators, No. 5 size, fitted with moveable pipes.
The body of the carriage forms a tank for forty gallons of water ; the tank is filled at a
bunghole in the platform ; a patent tap is fitted to the rear of the carriage; a spigot is
placed near the end upright of the rail ; a hand-pump is placed in the box at rear ol
carriage ; a leather bucket with foot-holds and three canvas buckets are hung on the
carriage ; a hammer for removing and driving on the cover of the fire annihilator, and a
nut wrench for the No. 10 truck, are placed in the box. B. A fire annihilator, No. 10 size,
with moveable pipe, on a spring truck, is attached to the carriage.

The battery is fitted with shafts for one horse. A pole is also provided to fix across the
shafts, so that the battery may be drawn by hand.

Monsieur Adolphe Girard has proposed that all houses should be
provided with an apparatus for the generation of carbonic acid gas,

Pig. 151. A. Tank containing acid, communicating by a pipe with B, half filled with
chalk and water, c c c c. Pipes conveying carbonic acid from the generator B, to the
ceiling, where it is discharged from numerous holes on the fire beneath.

CHEMISTRY. 161

placed outside the building, which is to be conveyed along the ceiling
by means of pipes perforated with numerous holes, and to be put in
operation directly a fire breaks out. This plan, however ingenious,
could hardly supply the carbonic acid gas with sufficient rapidity, and
it is to be feared would utterly fail in practice. (Fig. 151.)

BORON.
Symbol, B ; combining proportion, 10'9.

Discovered by Homberg, in 1702, in borax, which is a biborate of
soda (NaO,2B0 3 ), and is used very extensively in the manufacture of
glass ; also for glazing stoneware and soldering metals ; it is also a
valuable flux in various crucible operations, whilst in testing minerals
with the blowpipe it is invaluable. Borax is made either from tincal, a
substance that occurs naturally in some parts of India, China, and
Persia, or by the addition of carbonate of soda to boracic acid, a sub-
stance obtained from the volcanic districts of Tuscany, whence it is
imported to this country, and used in the manufacture of borax.

The element boron may be obtained by placing some pure boracic
acid and some small bits of potassium in a tube together, and applying
the flame of a spirit-lamp, a glow of heat takes place, and when the tube
is cold the potash may be washed away, and the boron remains as a
dark brownish powder somewhat resembling carbon. M. -St. Claire
Deville and Wohler have lately made some important discoveries with
respect to this element, and disproved the statement that it is uncrystal-
lizable. Their researches prove it to be producible under three forms
and of various colours, such as honey -yellow and garnet-red, the crystals
in some cases being like diamonds of the purest water /.<?., limpid
and transparent. A new combination of aluminium and boron is
stated to possess the most remarkable properties. It is harder than
the diamond, and in the state of powder will cut and drill rubies, and
even the diamond itself, with more facility than diamond powder.
Deville and Wohler incline to the belief that the diamond is dimorphous,
and capable (in conditions yet to be described) of assuming the same forms
as boron. At a high temperature, boron, like titanium, absorbs nitrogen
only from the atmosphere, and rejects the oxygen. (Query, may not
some of those remarkably hard black diamonds prove to be boron ?)

SILICON.
Symbol, Si ; combining proportion, 21' 3.

The great Berzelius was the first to obtain this element in 1823.
Silicon in the pure state is a dark brown powder ; if ignited at a very
high temperature it assumes a chocolate colour, which is supposed to
be the allotropic condition, because it no longer burns when heated
moderately in oxygen or air, and is not attacked by hydrofluoric acid.

162 BOY'S PLAYBOOK OF SCIEXCE.

The most interesting combination of silicon is the teroxide called
silicic acid, silica (SiO 3 ). Silicon is next to oxygen so far as regards
its plentifulness, and is found in the state of silica in nearly every
mineral, but especially in rock crystal, quartz, flint, sand, jasper, agate,
and tripoli. It is largely used in the manufacture of glass, and a most
useful " soluble glass" is obtained by melting together in a crucible
fifteen parts of sand, ten parts of carbonate of potash, and one part of
charcoal.

Cold water merely washes away the excess of alkali, and after this is
done the powdered soluble glass may be boiled with water in the pro-
portion of one of the former with five of the latter, when it gradually
dissolves ; the solution may be evaporated to a thick pasty fluid, which
looks like jelly when cool, and on exposure to the air in thin films
changes to a transparent, colourless, brittle, but not hard glass. Wood,
cotton, and linen fabrics are rendered less combustible when coated
with this glass, which excludes the oxygen of the air, and it has lately
been employed to fill up the porous and capillary openings in stone
exposed to the atmosphere, and is stated to be very efficacious as a
preservative of the stone in some cases.

SULPHUR.
Symbol, S ; combining proportion, 16.

Sulphur, like charcoal, is of common occurrence in nature, and is
chiefly supplied from the volcanic districts of Tuscany and Sicily : there
is an abundance of this element in the United Kingdom, but then it is
locked up in combination with iron, copper, and lead, under the name
of iron pyrites, copper pyrites, galena ; and whilst Sicily and Tuscany
supply thousands of tons weight in the uncombined state, it is not, of
course, worth while to go through expensive operations at home for the
separation of sulphur from the ores. During the dispute between Sicily
and England, several patents were secured for new and economical pro-
cesses by which sulphur was obtained from various minerals ; and had
this country been excluded from a supply of native sulphur, no doubt
some of these patents would now be in active operation.

It is almost possible to estimate the commercial prosperity of a country
by the sulphur it consumes, not, happily, by their warlike operations, but
in the manufacture of oil of vitriol or sulphuric acid, which is the starting
point of a great number of useful arts and manufactures.

First Experiment.

Some very curious results may be obtained by heating sulphur at cer-
tain temperatures ; in the ordinary state it is a pale yellow solid, and
when subjected to a temperature of 226 Fahr. it melts to a brownish-
yellow, transparent, thin fluid ; according to all preconceived notions of
the properties of substances which liquify by an increase of heat, it
might oe imagined that every additional degree of heat would onlv

EXPERIMENTS WITH SULPHUR. 163

render the melted sulphur still more liquid, but strange to say, when it
reaches a temperature of about 320 Fahr. it changes red, and thick
like treacle ; and as the heat rises it becomes so tenacious, that the ladle
in which it is contained may be inverted, and the sulphur will hardly
flow out : at about 482 Fahr. it again becomes liquid, but not so fluid
as at the lower temperature. If allowed to cool from 482 Fahr., the
above results are simply inverted; the sulphur becomes thick, again
liquid, and finally crystallizes in long, thin, rhombic prisms, which are
seen most perfectly by first allowing a crust of sulphur to form on the
liquid portion, and then having made two holes in this crust, the sulphur
is poured out, when the remainder is found in the interior of the crucible
crystallized in the form already mentioned. Sulphur takes fire in the
air when exposed to a heat of about 560 Fahr., and burns with a pale
blue flame ; and, as already stated, it may be poured from a considerable
height on a still dark night, and produces a continuous column of blue
fire, just like an unbroken current of electricity. If the melted and
burning sulphur is received into a vessel containing boiling water, it is
no longer yellow, but assumes a curious allotropic state, in which it is a
reddish-brown, transparent, shapeless mass, that may be easily kneaded
and used for the purpose of taking casts of seals, which become yellow
in a few days, and are found then to be hard and crystallized.

Second Experiment.

Sulphur vapour, in one sense, may be regarded as a supporter of com-
bustion : if a clean Florence oil-flask is filled with copper turnings, and a
little roughly-powdered sulphur sprinkled in, and heat applied, the copper
glows with an intense heat, and burning in the vapour of the sulphur, pro-
duces a sulphuret of copper ; from this compound the sulphur maybe again
obtained by boiling the powdered sulphuret with weak nitric acid, which
oxidizes and dissolves the copper, leaving the greater part of the sul-
phur behind, which may be collected, melted, and burnt, and will be
found to display all the properties belonging to that element. This
experiment is a very good example of simple analysis; and if the
copper is weighed and likewise the combined sulphur, a good notion may
be formed of the principles of combining proportions.

Third Experiment.

A little sulphur burnt under a gas jar, or in any convenient box (a
hat-box, for instance), produces sulphurous acid (S0 2 ), which will bleach
a wetted red rose or dahlia, and many other flowers. This gas is em-
ployed most extensively in bleaching straw, and sundry woollen goods,
such as blankets and flannel, and likewise silk, and is perhaps one of the
best disinfectants that can be employed ; when fever has been raging in
the dwellings of the poor, as in cottages, &c., all metaDic substances
should be removed, the doors and windows closed, the bedding, &c., well
exposed, and then a quantity of sulphur should be burnt in an old fry-

1 BOY'S PLAYBOOK OF SCIENCE.

ing-pan placed on a brick, taking care to avoid the chance of setting the
place on fire ; after a few hours the doors and windows may be opened, and
the disinfectant will be found to have done its work cheaply and surely.

Fourth Experiment.

The presence of sulphur in various organic substances, such as hair,
the white of egg, and fibrine, is easily detected by heating them in a
solution of potash, and adding acetate of lead as long as the precipi-
tate formed is redissolved ; finally the solution must be heated to the
boiling point, when it instantly becomes black by the separation of sul-
phuret of lead.

Fifth Experiment.

Sulphuric acid, HO,S0 3 , or oil of vitriol, is made in such enormous
quantities that it is never worth while to attempt its preparation on a small
scale. In consequence of its great affinity for water, many energetic
changes are produced by its action. Oil of vitriol poured on some loaf
sugar placed in a breakfast-cup with the addition of a dessert-spoonful of
boiling water, rapidly boils and deposits an enormous quantity of black
charcoal. If a word be "written on a piece of white calico with dilute
sulphuric acid, and then rapidly and thoroughly washed out, no visible
change occurs ; but if the calico is exposed to heat, so that the excess
of water is driven off, the remaining and now concentrated oil of vitriol
attacks the calico, and the word is indelibly printed in black by the
decomposition of the fabric of cotton. A very remarkable process has
lately been introduced by Mr. Warren de la Rue, by which paper is con-
verted into a sort of tough parchment-like material, called ametastine, by
the action of oil of vitriol and water of a certain fixed strength ; and any
departure from the exact proportions destroys the toughness of the paper.
After the paper has been acted upon by the acid, it oecomes extremely
tenacious, and will support a considerable weight without breaking. Mr.
Smee has used this ametastine in the construction of an hygrometer, and
states that it may save many a traveller from catching a severe rheu-
matism in a damp bed.

Sixth Experiment.

When the vapour of sulphur is passed over red-hot charcoal and the
product carefully condensed, a peculiar liquid is obtained, called bisul-
phide of carbon (CS 2 ), which possesses a peculiar odour, is extremely
transparent and brilliant-looking, and enjoys a high refractive power.
This liquid is used as a solvent for phosphorus and other substances, and
is extremely volatile and combustible, and burns silently with a pale
blue flame. The combustion of its vapour, mixed with certain gases,
offers a good example of the fact that slow burning may be a peaceful
experiment, whilst very rapid combustion often resolves itself into an
explosion. Thus, if a few drops of bisulphide of carbon are dropped into
a narrow-mouthed dry quart bottle containing common air, and flame
applied, the combustion takes place with rapidity, a rushing or

EXPERIMENTS WITH SULPHUR.

165

roaring sound being audible, in consequence of the diffused vapour being
supplied with more oxygen, and burning more rapidly than it would do
if simply consumed from a stick or glass rod wetted with the fluid. A
still greater rapidity of combustion is ensured by dropping some bisul-
phide of carbon into a long stout cylindrical jar, fifteen inches long
and three inches in diameter, containing nitric oxide gas (N0 2 ) ; when
flame is applied the mixture burns with a bright flash and some noise,
and if burnt in a narrow mouthed bottle would most likely blow it to
atoms.

The greatest rapidity of combustion, and of course the loudest noise,
is obtained by shaking some bisulphide of carbon in a similar stout and
strong cylindrical jar filled with oxygen gas, but in this case the jar
must DC protected with a double cylinder of stout wire gauze; it does
not always break, but if it is blown to fragments each particle becomes
a lancet-shaped piece of glass, which is capable of producing the most
dangerous wounds. (Fig. 152.)

Fig. 152. A. Air and bisulphide of carbon. B. Nitric oxide and ditto, c. Oxygen and
ditto. D D. Stout cylinder of double wire gauze, open top and bottom.

SELENIUM.

Selenium (o-eAqin/, the Moon*) ; symbol, Se ; combining
proportion, 39 '5.

This new metallic element is allied to sulphur, and is a species 01
chemical curiosity, being found in minute quantities in various minerals ;
it may be melted and cast into any form. Medallions of the discoverer
(Berzelius) of selenium, in little cases, are imported from Germany,
for the cabinets of the curious.

* Called selenium on account of its strong analogy to the metal tellurium (tellus, the

earth).

166 BOY'S PLAYBOOK OF SCIENCE.

PHOSPHORUS.

Phosphorus ((f)S)s, light ; typeiv, to bear ; symbol, P ; combining
proportion, 32.)

Monsieur Salverte, in his work on the Occult Sciences of the
Ancients, quotes a remarkable story respecting the probable discovery
of the nature of phosphorus in 1761 : " A Prince San Severe, at
Naples, cultivated chemistry with some success ; he had, for example,
the secret of penetrating marble with colour, so that each slab sawed
from the block presented a repetition of the figure imprinted on its
external surface. In 1761, he exposed some human skulls to the action
of different reagents, and then to the heat of a glass furnace, but paying
so little attention to his manner of proceeding, that he acknowledged
he did not expect to arrive a second time at the same result. From the
product he obtained a vapour, or rather a gas was evolved, which
kindling at the approach of a light, burned for several months
without the matter appearing to die or diminish in weight. San
Severo thought he had found the impossible secret of the inextin-
guishable lamp, but he would not divulge his process, for fear that
the vault in which were interred the princes of his family should
lose the unique privilege with which he expected to enrich it, of being
illuminated with a perpetual lamp" Had he acted like a philosopher of
the present day, San Severo would have attached his name to the im-
portant discovery of the existence of phosphorus in the dones, and made
public the process by which it might be obtained.

This element, formerly sold at four or five shillings the ounce, has now
fallen so much in price, from the greater demand and larger production,
that it may be bought for a few shillings the pound, and is imported in
tin cases in large quantities from Germany. It was discovered about
two hundred years ago by Brandt, a merchant of Hamburg, and may
be prepared on a small scale by distilling at a red heat phosphoric
acid previously fused with one-fourth, of its weight of powdered
charcoal.

First Experiment.

Phosphorus, when pure, is without taste or colour, but generally of a
very pale buff-colour, and semi-transparent ; it is extremely combus-
tible, and is usually preserved under the surface of water ; when per-
fectly dry, a thin slice will take fire at 60 Fah., and burns with
great brilliancy. Considering the heat produced during the com-
bustion of phosphorus, it might be thought that it would infallibly set
fire to any ordinary combustible, such as paper or wood, but this is not
the case when phosphorus is employed by itself, as may be proved by
the following experiment.

Cut five very small pieces of phosphorus, and place them like the
five of diamonds on a sneet of cartridge-paper laid upon the table, set
the bits of phosphorus on fire, when they will be rapidly burnt away

EXPERIMENTS WITH PHOSPHORUS. 167

leaving only five black spots, but not firing the paper, as would be the
case if some red-hot coals or charcoal were placed in the same position.
The cause is very simple. Phosphorus in burning produces phosphoric
acid, which is an anti-combustible, and coats the surface of the paper
round the spot where the combustion occurs, and acting as a kind of
glaze or glass, excludes the oxygen of the air, and prevents the fire
spreading.

If some powdered sulphur is sprinkled round the spot where the bit
of phosphorus is to be burnt, the case is very different ; the heat melts
and sets fire to the sulphur, which being uncoated with the phosphoric
acid, communicates to the paper ; and it is on this principle that lucifer-
matches can be used as instantaneous lights. The tip of the wood of
which they are composed is first dipped in sulphur, and then the phos-
phorus composition made of gum, chlorate of potash, vermilion, and
phosphorus, is placed over it ; and if the latter were used alone without
the sulphur, not one match in a hundred would take fire properly.

Common phosphorus is perfectly and rapidly dissolved by bisulphide
of carbon. The solution must be carefully preserved, as it is a liquid
combustible, which takes fire spontaneously after the bisulphide of
carbon evaporates ; so that wherever it is dropped, a flame, arising from
the spontaneous combustion of the finely-divided phosphorus, is sure to
be produced. This liquid was recommended many years ago to the
Government for the purpose of setting sails of ships or other combus-
tible matter on fire. The solution of phosphorus alone did not answer
the purpose, as already explained in the first experiment ; but when wax
was dissolved with the phosphorus, it then became a most dangerous
fluid, which it was recommended should be used in shells, and discharged
from a mortar or howitzer in the ordinary manner. Dr. Lypn Playfair
.was the first to make this proposed application of the solution, and it
has since, we believe, been recommended by Captain Norton in his liquid-
fire shells.

Third Experiment.

One of the most curious facts in connexion with phosphorus,
is its assumption of the allotropic state in what is termed amorphous
(shapeless) or red phosphorus. This substance, when handled for the
first time, might be mistaken for a lump of badly-made Venetian red.
There is no risk of its taking fire like the common phosphorus, and it
does not (according to Schrotter, of Berlin, who discovered this peculiar
condition) exhale those fumes which are so prejudicial to the lucifer-
match makers. When the vapour of common phosphorus is continually
inhaled, it is said to cause a peculiar and disgusting disease, which,
terminates in the destruction of the jaw-bone ; whilst the bones in other
parts of the body become brittle, and arm-bones thus affected are
fractured with the slightest blow.

The difference between common and red phosphorus is well shown

163 BOY'S PLAYBOOK OF SCIENCE.

first, by placing a few small pieces of both kinds in separate bottles or
vials containing bisulphide of carbon; the common phosphorus, as
already explained, quickly dissolves in the liquid, and if poured on a
sheet of paper, and hung up, is soon on fire ; whilst the red variety is
wholly unaffected, and if the bisulphide of carbon is poured off on to
paper, it merely evaporates, and no combustion occurs.

The similarity in composition, though not in outward form, is further
shown by filling two jars with oxygen gas. and having provided two
deflagrating spoons, some common phosphorus is placed in one, and red
phosphorus in the other; a wire, gently heated by dipping it into
some boiling water, is now applied to the former, which immediately
takes fire, and may be plunged into the jar of oxygen gas, when it burns
with the usual brilliancy. The red phosphorus, however, must be brought
to a much higher temperature (500 Fah.) before it will even shine in
the dark, and then with a still further increase of heat it takes fire, and on
being placed in the other jar of oxygen burns up much more slowly than
the yellow phosphorus, but at last exhibits that brilliant flash of light
which is so characteristic of the combustion of phosphorus in oxygen.

The amorphous or red phosphorus is employed in the manufacture of
safety chemical matches, and M. A. Meunons has secured a patent in
England for an improvement in lucifer matches, with a view to obviate
the risks of accidental ignition. To attain this end the matches are first
cut by a machine from cubes of wood, the cut being stopped at a
short distance from the end of each cube, so as to leave the lower ex-
tremities adherent. The upper or free extremity of each packet of
splints thus formed being coated with wax or sulphur, is dipped in one
of the following preparations : Chlorate of potash, two parts; pul-
verized charcoal, one part ; umber, one part ; or, chlorate of potash,
sulphur, and umber, in equal parts, thoroughly mixed with glue. The
opposite extremity or " cut" of each packet is then painted over with
amorphous phosphorus blended with size, so that on separating the
matches the phosphorus is only found en the top of each. The matches
thus prepared are ignited by breaking off a small piece of the phos-
phorised end and rubbing it on the opposite extremity covered with the
inflammable preparation.

Loud exploding and dangerous lucifers were formerly made by dipping
bundles of matches, previously coated with sulphur at the tips, into a
thick solution of gum, at a temperature of 104 Fahr., coloured with
smalt or red lead, in which was dissolved a certain proportion of chlorate
of potash, and also containing finely divided particles of phosphorus ob-
tained by the constant stirring and rubbing of the materials in a mortar.
When dry the matches exploded if rubbed against a gritty surface, and
there was always a risk of a fragment flying off and entering the eye.
To obviate this danger, silent or noiseless lucifer matches were invented,
and the composition used (according to Bottger) is as follows : Gum
arabic, 16 parts by weight ; phosphorus, 9 parts ; nitre, 14 parts ; pow-
dered black oxide of manganese, 16 parts. The above ingredients are
worked up in a mortar with water, at 104 Fahr., and the matches pre-
viously tipped with sulphur are dipped therein and afterwards dried.

EXPERIMENTS WITH PHOSPHORUS.

169

Fourth Experiment.

The combustion of
phosphorus under
water is easily de-
monstrated by plac-
ing some ordinary
stick phosphorus in
a metallic cup, and
then plunging it ra-
pidly under the sur-
face of boiling water.
If a jet of oxygen
gas is now directed
upon the liquid phos-
phorus, it burns
with great brilliancy.

Fig. 153. A A. Fin
a metallic cup with.

gas. D D. Sheet of wire gauze.

lass of boiling water containing
phosphorus, c. J et of oxygen

When the oxygen escapes too rapidly from the jet, it causes some small
particles to be thrown out of the water, so that it is advisable to defend
the face with a sheet of wire gauze held a few inches above the glass
whilst the experiment is being conducted. (Eig. 153.)

Fifth Experiment.

Phosphorus burns and emits beautiful
flashes of light in the presence of the
gas called peroxide of chlorine (C10 4 ),
which must be very carefully generated
under the surface of water by first placing
some cut phosphorus and chlorate of pot-
ash at the bottom of a long and stout
cylindrical glass nearly full of water ;
sulphuric acid is then conveyed to the
chlorate, of potash by means of a syphon,
the end of which must be drawn out to a
small opening, or else the oil of vitriol
will descend too rapidly, and the glass
will be cracked by the heat. Immediately
the peroxide of chlorine comes in contact
with the phosphorus it explodes, and
passes again to its original elements,
oxygen and chlorine. These bubbles en-
velope minute particles of phosphorus,
which rapidly ascend, like water-spiders,
to the surface, and burn as they pass up-
wards, producing a continual series of
sparks of fire, which have an extremely
pretty effect. (Fig. 154.) The syphon is of
course first filled with water, and as that is
displaced, the oil of vitriol takes its place.

Fig. 154. A A. Tall glass nearly
full of water ; at the bottom are the
chlorate of potash and phosphorus.
B. Wolfe's bottle and syphon, con-
veying the oil of vitriol to bottom
of A A.

170

BOY'S PLAYBOOK OF SCIENCE.

Sixth Experiment.

If a little phosphorus is placed in a small copper boiler, and tho
steam allowed to escape from a jet, it is observed to be luminous, in
consequence of a minute portion of phosphorus being carried up mecha-
nically with the steam. The same fact is shown very prettily by boiling
water in a flask containing some phosphorus.

Seventh Experiment.

Phosphorus explodes violently when
rubbed with a little chlorate of potash,
and in order to perform this experi-
ment safely, it should be made in a
strong iron mortar, the pestle of which
must oe surrounded with a large circle
of cardboard and wire gauze ; so that
when it is brought down upon the
phosphorus and chlorate of potash,
any particles that may fly out are de-
tained by the shield. "Without this
precaution the experiment is one of
the most dangerous that can be made.
155.)

Eighth Experiment.

Phosphuretted hy-
drogen owes its pro-
perty of spontaneous
combustion to the
presence of the va-
pour of a liquid,
phosphide of hydro-
gen (PH 2 ), which
may be prepared by
placing some phos-
phide of calcium into
a flask with water
heated to a tempera-
ture of 140 JFah.,
and conveying the

tube surrounded with
a mixture of ice and
salt. The liquid obtained is colourless, and must be preserved from
contact with air, as it takes fire spontaneously directly it is exposed
to the atmosphere. (Fig- 156.)

Fig. 155. A. The iron mortar con-
taining the phosphorusav.il chlorate of
potash. B. The pestle, with the shield,
c c, composed of a circle of wire gauze,
covered with one of cardboard.

rig. 156. A. The flask containing the phosphide of calcium
and water, and placed in a water-bath heated to 140 Fan.
B. Bent tube conveying the gas to c c, the U-shaped tube,
to which it is attached by india-rubber tubing, c c. The U-
shaped tube, surrounded with a freezing mixture. D D. Bent
tube, passing into a cup of water to prevent contact with air.

EXPERIMENTS WITH PHOSPHORUS. 171

Ninth Experiment.

Phosphide of calcium is quickly prepared by placing some small
pieces of lime in a crucible and making them red-hot ; if lumps of dry
phosphorus are thrown into the crucible, and the cover placed on
quickly, and immediately after the phosphorus, the latter unites with
the calcium, and forms a brown substance which produces gaseous
phosphide of hydrogen (PH 3 ) when placed in water, and the gas takes
fire spontaneously when it comes in contact with the air.

Tenth Experiment.

Phosphorus placed in a retort with a tolerably strong solution of
potash, and a small quantity of ether, affords a large quantity of phos-
phide of hydrogen (commonly called phosphuretted hydrogen) when
boiled. The neck of the retort must dip into a basin of water, and the
object of the ether is to prevent the combustion of the first bubbles of
gas inside the retort, which by their explosion would probably break the
glass. If the neck of the retort is kept under water in which potash is
dissolved, the gas may be generated for many days at pleasure, although
it is not a desirable experiment to renew too often, on account of the
disagreeable odour produced. (Eig. 157.)

Fig. 157. A retort containing the phosphorus, water, potash, and ether, u. Neck dipping
into a basin of water, c. The gas burning, and producing beautiful rings of smoke.

Eleventh Experiment.

When ajar of oxygen is held over the neck of the retort generating the
phosphuretted hydrogen, a bright flash of light and explosion are ob-
served ; and if the experiment is performed in a darkened room, it is just
like a sudden flash of lightning. A bottle of chlorine held over the neck

172 BOY'S PLAYBOOK OF SCIENCE.

of the retort, and dipping of course in the water of the basin, produces
a green flame every time the bubble of gas passes into it. That curious
appearance of light, sometimes seen in marshy districts, called will-o'-the-
wisp, is supposed to be due to the escape, from decomposing matter, of
bubbles of hydrogen, nitrogen, &c., through which the spontaneously
inflammable phosphide of hydrogen is diffused.

At a place called Dead Man's Island, near Sheerness, magnificent
effects of this kind are sometimes apparent when the rnud banks are
accidentally stirred at night by a boat-hook. A credible observer says,
he once saw there a flash of yellowish-green light, accompanied with
noise, about thirty feet in height. The apparent height might be due to
the duration of the impression of the flash on the eye, as the light from
the burning phosphuretted hydrogen ascended rapidly upwards. The
source of this gas appears to be due to the fact, that during the time some
Russian ships were watched by the Brest fleet, a number of the sailors
died of cholera, and were buried in the banks ; the decomposition of the
bone containing phosphorus would account for the appearance of light
already described.

With the discussion of some of the most interesting properties of the
thirteen non-metallic elements we take leave of the subject of chemistry,
reserving the consideration of the metals for another popular juvenile
work, of which they will form the subject.

In answer to the oft-repeated question, " Where can I get the things
for the experiments P" it may be stated that every kind of glass vessel
and the chemicals mentioned in this chapter, can be procured either of
Messrs. Simpson, Maule, and Co., Kennington, or of Griffin and Co.,
Bunhill-row, or Bolton and Co., High Holborn.

Fig. 153. Will-o'-the-wisp.

173

Fig. 159. Franklin and his kite.

CHAPTER XIII.

PBICTIONAL ELECTRICITY.

OP all the agents with which man is acquainted, not one can afford a
greater source of wonderment to the ignorant, of meditation to the
learned, than the effects of that marvellous force pervading all matter
called electricity. We look at matter endowed with life, and matter
wanting this divine gift, with some degree of interest, depending on our
various tastes and occupations ; we know at a glance a bird, a beast, or
a fish ; we observe with pleasure and admiration the wonderful changes
of nature, and know that a few seeds thrown into the broken clods and
well-tilled earth may become either the waving, golden corn-field or in
time may grow from the tender little shrub . to the stately forest-tree ;
we know all these things because they belong to the visible world, and
are continually passing before our eyes : but in looking at the visible,
we must not forget and ignore the invisible. It may with truth be

BOYS PLAYBOOK OP SCIENCE.

stated that the greatest powers of nature are all concealed, and if any
truth would leacl us from Nature to Nature's God, it is the fact that
no visible, solid, tangible agent can work with so much force and
power as invisible electricity. Many centuries passed away since the
commencement of the Christian era, before the human mind was pre-
pared to appreciate this great power of nature ; other forces had claimed
attention, and the difference in the presence or absence of two of the
imponderable agents, heat and light, as derived from the sun, in the
effects of the change of the seasons, and other common facts, had led
philosophers to speculate early upon their nature ; but electricity, from
its peculiar properties, long escaped observation, and it was not until
the beginning of the eighteenth century (about 1730) that any material
facts had been discovered in this science, when Mr. Stephen Grey, a
pensioner of the Charterhouse, discovered what he termed electrics
and non-electrics, and also the use of insulating materials, such as silk,
resin, glass, hair, &c. ; and it is obvious that, until the latter fact was
discovered, the science would remain in abeyance, because there would
be no mode of preserving the electrical excitement in the absence of
non-conductors of this force.

The year 1750 was remarkable for Volta's discoveries and Dr. Frank-
lin's identification of the electricity of the machine with the stupendous
effects of the thunderstorm. Sir Humphry Davy, in 1800, with his
commanding genius, threw fresh light upon the already numerous
electrical effects discovered. In 1821, Faraday commenced his studies
in this branch of philosophy ; which he has since so diligently followed
up, that he has been for some years, and is still the first electrician of
the age. From the commencement of the present century, discoveries
have succeeded each other in regular order and with the most amazing
results ; and now electricity is regularly employed as a money-getting
agent in the process of the electrotype and electro-silvering and gilding ;
also in the electric telegraph ; and in a few years we may possibly see
it commonly employed as a source of artificial light.

The nature of electricity, says Turner, like that of heat, is at present
involved in obscurity. Both these principles, if really material, are so
light, subtle, and diffuse, that it lias hitherto been found impossible to
recognise in them the ordinary characteristics of matter ; and therefore
electric phenomena may be referred, not to the agency of a specific sub-
stance, but to some property or state of common matter, just as sound
and light are produced by a vibrating medium. But the effects of
electricity are so similar to those of a mechanical agent, it appears so
distinctly to emanate from substances which contain it in excess, and
rends asunder all obstacles in its course so exactly like a body in rapid
motion, that the impression of its existence as a distinct material sub-
stance sui generis forces itself irresistibly on the mind. All nations,
accordingly, have spontaneously concurred in regarding electricity as a
material principle ; and scientific men give a preference to the same
view, because it offers an easy explanation of phenomena, and suggests
a natural language intelligible to all.

SOURCES OF ELECTRICITY.

175

There are five well-ascertained sources of electricity, and three which
are considered to be uncertain. The five sources are friction, chemical
action, heat, magnetism, peculiar animal organisms. The three uncertain
sources are contact, evaporation, and the solar rays.

First Experiment.

A stick of sealing-wax or a bit of glass tube, perfectly dry, rubbed
against a warm piece of flannel, has
elicited upon its surface a new power,
which will attract bits of paper, straw, or
other light materials; and after these sub-
stances are endowed with the same force,
a repellent action takes place, and they
fly off. One of the most convenient ar-
rangements for making experiments with
the attractive and repellent powers of
electricity is to fix with shell-lac varnish
round discs of gilt paper, of the size of
a half-crown, at each end of a long straw
that is supported about the centre with
a silk thread, which may hang from the
ceiling or any other convenient support.
(Kg. 160.)

The varnish is easily prepared by
placing four or eight ounces of shell-
lac in a bottle, and pouring enough
pyroxylic spirit (commonly termed wood
naphtha) upon the lac to cover it. After
a short time, and by agitation, solu-
tion takes place. In a variety of ways
friction is proved to be a source of jjj&- 16 2; A * T v lass iP iUa ? SU ,P*
electricity, and forms a distinct branch ^thread? ' ^ *

of the science, under the name of /fic-
tional electricity.

The nature of chemical action has been already explained, and is
alluded to here as a source of electricity of which the proof is very
simple. Apiece of copper and a similar-sized plate of zinc have attached
to them copper wires ; these plates are placed opposite to, but do not
touch each other, in a vessel containing water acidulated with a small
quantity of sulphuric acid. When the wires are brought in contact, a
current of electricity circulates through the arrangement, but has no
power to attract bits of paper, straw, &c. In order to ascertain whether
the current of electricity passes or not, a piece of covered copper wire
is bent several times round a magnetic needle, so that it has freedom of
motion inside the core or hollow formed by twisting the copper wire.
This arrangement, properly constructed, is called the galvanometer

176

BOY S PLAYBOOK OF SCIENCE.

needle, and is invaluable as a means of ascertaining the passage of
electricity derived from chemical action. (Fig. 161.)

Fig. 161. A. The galvanometer needle, u. Vessel containing weak acid and the zinc and
copper plates. The arrows show the path of the electric current.

When the wires leading from the metal plates are connected with the
extremities of the coil in the galvanometer, the needle is deflected or
pushed aside to the right hand or to the left, according to the direction
of the current.

Third Experiment.

The third source of electricity is heat, and the effect of this agent is
well shown by twisting together a piece of platinum and silver wire, so
as to form one length. If the silver end is attached to any screw of the
galvanometer, and the platinum end to the second screw, no movement
of the magnetic needle takes place until the heat of a spirit-lamp is
applied for a moment to the point of juncture between the silver and
platinum wires, when the magnetic needle is immediately deflected.

Fig. 162. A. The galvanometer needle, with wires attached, s, s. Silver wire joined
to P, P, the platinum wire. The heat of the spirit-lamp is applied at the point of
juncture, +.

Fourth Experiment.

The fourth source of electricity viz., magnetism requires a some-
what more complicated arrangement ; and a most delicate galvanometer
needle must be provided, to which is attached the extremities of a long
spiral coil of copper wire covered with cotton or silk. Every time a
bar magnet is introduced inside the coil, so that the conducting wire cuts
the magnetic curves, a deflection of the galvanometer needle takes place,

SOURCES OF ELECTRICITY. 177

and the same effect is produced on the withdrawal of the magnet, the
needle being deflected in the opposite direction.

The magnetic spark can be obtained by employing a magnet of suffi-
cient power ; and the arrangement for this purpose is very simple. A
cylinder of soft iron is provided, and round its centre are wound a few
feet of covered thin copper wire, one end of which is terminated with a
copper disc well amalgamated, and the other end, after being properly
cleaned and coated with mercury, is brought into contact with the disc.
Directly this cylinder is laid across the poles of the magnet, and as
quickly removed, the point and disc, from the elasticity of the former,
separate for the moment, the contact is broken between the point and
disc, and a brilliant but tiny spark is apparent.

Pig. 163. A B. Horse-shoe magnet, c. Cylinder of soft iron. D. Coil of copper
wire and contact breaker.

Fifth Experiment.

The fifth mode of procuring electricity would require the assistance
of an electrical eel, a fine specimen of which (forty inches in length) was
exhibited at the Adelaide Gallery some years ago. Various experiments
were made with this animal, and the author had the pleasure of wit-
nessing all the ordinary phenomena of frictional electricity, illustrated
by Dr. Faraday, with the assistance of the animal electricity derived
from this curious creature. Recent experiments have, however, proved
that the electric current is induced through the agency of the nervous

178 BOY'S PLAYBOOK OF SCIENCE.

system. This important fact has been communicated by M. Dubois-
llaymond, whose experiment is thus recorded: A cylinder of wood is
firinly fixed against the edge of a table ; two vessels filled with salt and
water are placed on the table, in sucli a position that a person grasping
the cylinder may, at the same time, insert the fore-finger of each hand
in the water. Each vessel contains a metallic plate, and communicates,
by two wires, with an extremely sensitive galvanometer. In the instru-
ment employed by M. Dubois-Raymond, the wire is about 3|- miles in
length. The apparatus being thus arranged, the experimenter grasps
the cylinder of wood firmly with both hands, at the same time dipping
the fore-finger of each hand in the saline water. The needle of the
galvanometer remains undisturbed ; the electric currents passing by the
nerves of each arm, and being of the same force, neutralize eacn other.
Now, if the experimenter grasp with energy the cylinder of wood with
the right hand, the left hand remaining relaxed and free, immediately the
needle will move from west to south, and describe an angle of 30, 40,
and even 50; on relaxing the grasp, the needle will return to its original
position. The experiment may be reversed by employing the left arm,
and leaving the right arm free : the needle will, in this case, be deflected
from west to north. The reversing of the action of the needle proves the
influence of the nervous force. The conditions, it may be added,
essential to the success of the experiment are : 1st, Great muscular and
nervous energy ; 2nd, The contraction of only one arm at a time ; 3rd,
Dryness and cleanliness of skin ; and 4th, Freedom from any kind of
wound on the immersed part.

Sixth Experiment.

In making electrical experiments of the simplest kind, it soon becomes
apparent that certain substances, such as glass, sealing-wax, &c., retain
the condition of electrical excitement ; whilst other bodies, and especially
the metals, seem wholly incapable of electrical excitation : hence the
classification of bodies into conductors and non-conductors of electricity.
This arrangement is not strictly correct, because no substance can be
regarded as absolutely a conductor, or vice versa. It is better to con-
sider these terms as meaning the two extremes of a long chain of inter-
mediate links, which pass by insensible gradations the one into the other.
In the manufacture of electrical apparatus, glass is of course largely
employed, and this substance, with brass and wood, constitute the usual
materials. One of the most instructive pieces of apparatus is the elec-
troscope, which can be made with a gas jar, a cork, a piece of glass
tube, brass wire and ball, or a flat disc of brass, with some Dutch metal,
or still better, gold leaf. The latter is first cut into strips by retaining
the leaf between a sheet of well-glazed paper and cutting through the
paper and the copper or gold leaf, otherwise it would be impossible to
cut the metal, on account of its excessive thinness, except with a guder's
knife and cushion. The cork is next fitted to the gas jar, and perforated
with a hole to admit the glass tube, which must be thoroughly dry, and

THE ELECTROSCOPE.

179

is best coated both inside and out with the shell-lac varnish described
at page 175. Some dry silk is wound round the
brass wire, so that it remains fixed and upright in
the glass tube, the end outside the jar having a
ball, or still better, a flat disc of brass attached,
and the other extremity being split so as to act
like a pair of forceps, to retain a piece of card to
which the gold leaves are attached. By removing
the cork, tube, and brass wire bodily from the neck
of the gas jar, and then in a perfectly still atmo-
sphere carefully bringing the card, slightly wetted
with gum. at the extremity, on two of the cut
gold leaves, they may be stuck on, and the whole
is again arranged inside the dry gas jar, and forms
the important instrument called the electroscope.
(Fig. 164.) With the help of this arrangement,
a number of highly instructive experiments are
performed.

First, the difference between conductors and
non-conductors is admirably shown by rubbing a
bit of sealing-wax against a piece of woollen cloth Fig. 164. A. The brass
or flannel : on bringing the wax to the brass disc of wire, with flat disc out-
the electroscope the gold leaves no longer hang ^d'TeafTSd^thf
quietly side by side, but stand out and repel each jar. c c. The glass
other, in obedience to the law " that bodies simi- tube -
larly electrified repel each other." If the brass cap is touched whilst the
leaves are in this electrical state, they fall again to their original posi-
tion, showing that sealing-wax, after being excited, retains its electrical
condition, as also the gold leaves, because they are supported on glass,
or what is termed insulated i.e., cut off from conducting communica-
tion with surrounding objects. When, however, the sealing-wax is
passed through a damp hand, or the brass disc of the electroscope
touched, the electricity is conveyed away to the earth, because the human
body is a conductor of electricity.

Eighth Experiment.

When a brass wire is rubbed and brought to the electroscope, the
leaves do not move, in consequence of the electricity passing away to the
earth through the body as fast as it is generated : it is just like pouring
water into a leaky cistern ; but if the brass wire is tied to a long stick
of sealing-wax, and this latter held in the hand whilst the wire is rubbed
with a bit of flannel, then the gold leaves of the electroscope are affected,
on account of the insulation of the metal, as everj substance which can
be rubbed (even fluids, as water) produces electricity.

180

BOY'S PLAYBOOK OF SCIENCE.

Ninth Experiment.

An insulating stool is merely a piece of strong square board, supported
on glass legs, which should be well varnished. If the assistant stands
on this stool and touches the disc of the electroscope, no movement of
the leaves takes place until his coat is briskly struck with a piece of dry
silk or skin, when the usual repulsion occurs.

Fig. 165. Assistant standing on the insulating stool and touching the disc of the
electroscope whilst being struck with a dry handkerchief.

Tenth Experiment.

If a little powdered chalk is placed inside a pair of bellows, and then
forcibly ejected on to the disc of the electroscope, the friction of the
particles of chalk against the inside of the nozzle of the bellows and
against the disc of the instrument soon liberates sufficient electricity to
cause the gold leaves to stand out and repel each other.

Eleventh Experiment.

Whilst the leaves of the electroscope aie repelled from each other by
the application of a bit of rubbed sealing-wax, they may be again caused
to approach each other on bringing a dry glass tube previously rubbed
with a silk-handkerchief ; because the electricity obtained from sealing-
wax is different from that procured from glass : the former is called
resinous or negative electricity, the latter positive or vitreous electricity.
Either, separately, is repulsive of its own particles, but attractive of the

ELECTKICAL EXPERIMENTS. 181

other. No electrical excitation can occur without the separation of
these two curious states of electricity, and electrical quiescence takes
place when the two electricities are brought together ; hence the fall of
the gold leaves repelled by rubbed wax when the excited glass is brought
towards the disc of the electroscope. This experiment may be reversed
by repelling the leaves first with the excited glass, and then bringing the
rubbed wax, when the same effect takes place.

Twelfth Experiment.

To show the important elementary truth, that in all cases of electrical
excitation the two kinds of electricity are generated, take a dry roll of
flannel, and holding it as lightly as possible, rub it against a bit of wax.
If the flannel is brought to the electroscope, the leaves repel each other,
and they immediately fall when the wax is now approached, because the
flannel is in the positive or vitreous state of electricity, whilst the
sealing-wax is in the negative or resinous condition.

Thirteenth Experiment.

Any kind of friction generates electricity. A little roll brimstone
placed in a dry mortar and powdered, and then thrown on to the electro-
scope, quickly causes the repulsion of the leaves.

Fourteenth Experiment.

A sheet of dry brown paper laid on a flat surface, and vigorously
rubbed with a piece of india-rubber, produces so much electricity
that sparks and flashes of light are apparent in a dark room when it
is lifted from the table ; and it affects the leaves of the electroscope
very powerfully, so much so that care must be taken to apply it very
carefully to the disc, or the violence of the repulsion may cause the
fracture of the gold leaves, and then a great deal of time is wasted
before they can be put on again.

A dry wig or bunch of horse- hair when combed becomes electrical,
and likewise affects the leaves of the electroscope.

Sixteenth Experiment.

Two dry silk ribbons, the one white and the other black, passed
rapidly together through the fingers, exhibit sparks and flashes of
light when drawn asunder, and also cause the gold leaves to repel each
other.

Seventeenth Experiment.

Much instructive amusement is afforded by testing the gold leaves
when separated from each other during either of the former experiments.

183 BOY'S PLAYBOOK OF SCIENCE.

with an excited piece of sealing-wax. If the electricity produced is
negative, they repel each other further when the excited wax is ap-
proached ; if positive, they fall when the excited wax is brought near
them.

'Eighteenth Experiment.

When fresh, dry, ground coffee is received on to the disc of the elec-
troscope, as it falls from the mill, powerful electrical excitation is
displayed, and this is sometimes so apparent, that the particles cling
around the lower part of the mill or to the sides of the cup or basin
held to catch it.

Nineteenth Experiment.

After playing a tune on a violin, hold the bow (well rosined) to the
electroscope, when the usual divergence of the leaves will be apparent.

Twentieth Experiment.

Cut some chips from a piece of wood with a knife attached to a glass
handle, and as they fall on to the electroscope the leaves are repelled.

Twenty-first Experiment.

Warm a piece of bombazine by the fire and then draw out some of the
threads (which are of two kinds viz., silk and wool), and place them
on the electroscope, when divergence of the leaves immediately takes
place.

Twenty-second Experiment.

Put upon the same leg a worsted stocking and over that a silk one,
if the latter is now quickly rubbed all over with a dry hand and near
the fire, and then suddenly slipped off, the sides repel each other, and
the silk stocking retains very much the same shape as if the leg still
remained in it, and of course collapses as the electricity passes away.

Twenty-third Experiment.

Electrical machines consist only in the better arrangement of larger
pieces of glass and a more convenient mechanical contrivance for rubbing
them, and are of two kinds viz., the cylinder and plate machines ; it is
usual to give directions for the manufacture of an electrical machine
from a common bottle, and doubtless such rude instruments have been
made, but as Messrs. Elliott Brothers, of 30, Strand, now supply excel-
lent small machines at a very low cost, it is hardly worth while to incur
even a small expense for an instrument that must at the best be a very
imperfect one and frequently out of order. (Fig. 166.)

ELECTRICAL MACHINES.

Fig. 166. A cylinder electrical machine.

Plate machines are somewhat more expensive than cylinder ones, but
at the same time are more quickly prepared for experiments, and Mr.
Hearder, of Plymouth, states, that the secret in obtaining the greatest
amount of electricity from a cylinder machine, is to keep the inside of
the glass absolutely clean, dry, and free from dust. Sometimes the
glass of which electrical machines are made is wholly unfit for elec-

Fig. 167. The ordinary plate electrical machine.

184

BOY'S PLAYBOOK OF SCIENCE.

trical purposes, in consequence of the decomposition of the surface
from imperfect manufacture and the liberation of the alkali. (Figs.
167, 168.)

Fig. 168. Woodward's double plate electrical machine, giving a much la "src
quantity of electricity than Fig. 167.

Cylinder and plate machines are furnished with proper rubbers, and
before using the instrument it is usual to remove them, and after care-
fully cleaning the glass with a dry silk handkerchief before a fire,
the rubbers are scraped with a paper-knife to remove the old amalgam,
and fresh applied by first melting the end of a tallow candle slightly,
and after passing this over the rubber, the finely powdered amalgam is
now dusted on to it. Electrical amalgam is prepared by fusing one part
of zinc with one of tin, and then agitating the liquid mass with two
parts of hot mercury placed in a wooden box; when cold it should
be carefully powdered and kept in a well-stoppered bottle for use.
When the amalgam has been applied, the rubbers are again screwed
in their places, and the machine when turned (if the atmosphere is
tolerably dry) will emit an abundance of bright sparks.

Twenty-fifth Experiment.

Attraction and repulsion are shown on a larger scale, with the as-
sistance of electrical machines, by placing a fishing rod (the last joint of

ATTRACTION AND REPULSION.

185

which is made of glass) in an erect position, and attaching to the ex-
tremity a long tassel of paper from
which a thhrwire passes to me prime
conductor of the electrical machine ;
on turning the instrument, the
strips of paper all stand out and
repel each other. (Fig. 169.)

Twenty -sixth Experiment.
Suspend from the prime conductor
by a chain a circular brass plats

Fig. 170. A. Prime conductor.
B. Upper brass-plate. c. Lower
ditto. The figures are seen between
B and c.

Fig. 169. A A. The glass joint of the
fishing-rod, from which the last joint,
carrying the paper tassel, B, projects, c.
The electrical machine.

and under this place another supported by a brass adjusting stand.
If pith figures of men and women are placed on the lower plate, they rise
directly the machine is turned, although sometimes, in consequence of
irregularity in the adjustment of the centre of gravity, they perversely
dance on their heads instead of the usual position ; out of half a dozen
figures, one only perhaps will be found to dance well, by alternately
jumping to the upper plate and falling to the lower one to discharge the
excess ^of electricity ; and indeed the experiment will be found to
succeed better with one or two only on the plate instead of a number,
as they cling together and impede each other's movements. (Fig. 170.)

186

BOY S PLAYBOOK OF SCIENCE.

Twenty-seventh Experiment.

An assistant provided with a wig of well-combed hair presents a
most ridiculous appearance when standing on the insulating stool and
connected by a wire with the prime conductor of the electrical
machine, every hair, when not matted together, standing out in the most
absurd manner, when the machine is put in motion.

Twenty-eighth Experiment.

Whilst standing on the stool, sparks may be obtained from his body,
and if some tow is tied over a brass ball, and moistened with a little
ether, and presented to the tip of his finger, a spark flies off which
quickly sets fire to the inflammable liquid.

Twenty-ninth Experiment.

If small discs of tinfoil, cut out with a proper stamp, are pasted in
continuous lines over plate glass, or spirally round glass tubes, a very

171 A A A. A ring: of brass wire supported on a glass pillar inside which the spiral
tube"B, revolves, and produces beautiful and ever-changing circles of light, when connected
'

ueB, revov,
with' the conductor, c, of the electrical machine.

EFFECTS OF INDUCTION.

187

pretty effect is produced when they receive the sparks from the electrical
machine, and the passage of the electricity from one disc to the other
produces a vivid spiral or other line of light. When the tube is
mounted in a proper apparatus, so as to revolve whilst the sparks pass
down the spiral tube, the effect of the continuous electric sparks is much
heightened. (Fig. 171.)

Thirtieth Experiment.

A great variety of experiments, depending on the proper arrangement
of discs of tinfoil on various tubes of coloured glass are manufactured,
and some in the form of windmills, the sails being made luminous by the
passage of the electricity. The names of illustrious electricians, beautiful
crescents, stars, and even profile portraits, have been produced in con-
tinuous streams of electric sparks.

Thirty-first Experiment.

When an electrified body is brought towards another which is not
electrical, the latter is thrown into the opposite state of electricity as
long as the excited body remains in its neighbourhood ; and this con-
dition of electrical disturbance, set up without any contact or supply of
electricity, is called induction, and involves a vast number of interesting
facts, which are thoroughly discussed in Dr. Noad's excellent work on
electricity, but can only be briefly alluded to here.

If a number of lengths of brass wire, supplied with balls at the ex-
tremities, are supported on glass legs and arranged in a line, with a
little pith ball attached to a thread hanging from each end of the length
of brass wire, the effect of induction is shown very nicely ; and when an
excited glass rod is brought towards one end of the series, the rising of
the pith balls to each other betrays the change which has occurred in

Fig. 172. The lengths of brass wire supported on glass rod pillars indented by blowpipe,
so as to retain the brass wires with the pith balls hanging from each series, the letters
p and N mean Positive and Negative, and the signs for these terms are placed above.
The letters p and N are painted on the blocks which support the glass rods.

the electrical state of the brass wires by the mere neighbourhood of the
excited glass tube. The glass tube is electrified positively, and attracts
the negative electricity from the brass wire towards the end nearest to

188 BOl'S PLAYBOOK OF SCIENCE.

it ; the other extremity of the brass wire is found to be in the positive
state, and this re-acting on the next, and so on throughout the lengths,
completes the electrical disturbance in the whole series. (Pig. 172.)

Tli irty -second Experiment.

If an insulated brass rod (such as has been described in the last
experiment) is touched by the finger whilst under induction, it remains
permanently electrified on the removal of the disturbing electrified body ;
and it is on this principle that the useful electrical machine called the
Electrophorus is constructed. This constant electrical machine for it
will remain in action during weeks and months if kept sufficiently dry
was invented by Volta in the year 1774, and has been brought to great
perfection by Mr. Lewis M. Stuart, of the City of London School ; so that
with a little additional apparatus the whole of the fundamental prin-
ciples of electricity can be demonstrated. It consists of a flat brass or
tin circular dish about two feet in diameter and half an inch deep, which
is filled with a composition of equal parts of black rosin, shell-lac, and
Venice turpentine ; the rosin and the Venice turpentine being first
melted together, and the shell-lac added afterwards, care of course being
taken that the materials do not boil over and catch fire, in which case
the pot must be removed from the heat, and a piece of wet baize or other
woollen material thrown over it. Another tin or brass circular plate of
twelve inches diameter, and supported in the centre with a varnished
glass handle nine inches long, is also provided, and the resinous plate
being first excited by several smart blows with a warm roll of flannel,
the plate held by the glass handle is now laid upon the centre of the
resinous one, and if removed directly afterwards, does not afford the
electric spark ; but if, whilst standing upon the excited resinous plate,
it is touched, and then removed by the glass handle, a powerful electric
spark is obtained ; and this may be repeated over and over again with
the like results, provided the plate with the glass handle is touched with
the finger just before lifting it from the resinous plate. (Fig. 173.)

Fig. 173. A A. Large circular tin or brass disc with turned-up edge half an inch deep,
and containing the resinous mixture B, which is rubbed with the warm flannel, c c. The
upper plate supported by the glass handle D, a pith ball attached to a wire shows the
electrical excitation, and the spark is supposed to be passing to the hand B.

THE ELECTROPHORUS. 189

The electricity excited on the resinous plate is not lost, and by induc-
tion sets up the opposite condition in the plate with the glass handle.
The resinous plate, being excited with negative electricity, disturbs the
electrical quiescence of the upper plate, and positive electricity is found
on the surface touching the resinous plate, and negative electricity on
the upper one, so that when it is removed without being touched, the
two electricities come togeth&r again, and no spark is obtained ; but if,
as already described, the upper plate is touched whilst under induction,
then positive electricity appears to pass from the finger to the negative
electricity on the upper side of the plate, when the two temporarily
neutralize each other, and then, when the plate is removed, the excess
of electricity derived from the earth through the finger becomes appa-
rent. Induction requires no sensible thickness in the conductors, and
can be just as well produced on a leaf of gold as on the thickest plate of
metal ; and it should be remembered that non-conductors do not retain
their state of electrical excitation when the disturbing cause is removed,
whereas conductors possess this power, and this fact brings us to the
consideration of the Ley den jar.

Thirty-third Experiment.

If one side of a dry glass plate is held before and touches a brass ball
proceeding from the prime conductor of an electrical machine whilst in
action, the other side is soon found to be electrical ; this does not arise
from the conduction of the electricity through the particles of the glass,
but is produced by induction, the side nearest the ball being in the
positive state, and the other side negative : as glass is a non-conductor
of electricity, the effect is much increased by coating each side with tin-
foil, leaving a margin of about two inches of uncovered glass round the
covered portion, then, if one side of such a plate is held to the prime
conductor of the electrical machine, and the other connected with the
ground, a powerful charge is accumulated ; and if the opposite sides
are brought in contact with a bent brass wire, a loud snapping noise is
heard, and the two electricities resident on either side of the glass come
together with the production of a brilliant spark, or if the hands are
substituted for the bent brass wire, that most disagreeable result is
obtained viz., an electric shock ; hence these glass plates are some-
times fitted up as pictures, and when charged and handed to the
unsuspecting recipient, he or she receives the electric discharge to the
great discomfort of their nervous system.

Mica is sometimes substituted for glass, and the late Mr. Crosse, the
celebrated electrician, constructed a powerful combination of coated
plates of this mineral. It consisted ot seventeen plates of thin mica,
each five inches by four, coated on both sides with tinfoil within half
an inch of the edge. They were arranged in a box with a glass plate
between each mica plate, all the upper sides were connected by strips
of tinfoil to one side of the box, and all the under surfaces in the same
manner with the opposite extremity of the box. They were charged like
an ordinary Leyden battery.

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BOYS PLAYBOOK OF SCIENCE.

Fig. 174. A A. Glass plate or stand coated
with tinfoil on each side, B. c. Wire
with pith balls oscillating during the
discharge of the glass plate.

Thirty-fourth Experiment.

If the glass plate coated with tin-
foil is charged, and then placed up-
right on a stand, it may be slowly dis-
charged by placing a bent wire on the
edge with the extremities covered with
pith balls. The wire balances itself,
and continues to oscillate \dth noise
until the electricities of the two sur-
faces neutralize each other. (Fig. 174.)

Thirty-fifth Experiment.

It is easy to imagine the glass
plate of the last experiment rolled up
into the more convenient form of the
Leyden jar, which consists of a glass
vessel lined both inside and out with tinfoil, leaving some two or three
inches of the glass round the mouth uncovered and varnished with

shell-lac ; a piece of dry wood is fitted
into the mouth of the jar, through
which a brass wire and chain are
passed, and the end outside is fitted
with a ball. The Leyden jar is
charged by holding the ball to the
prime conductor of the electrical
machine until a sort of whizzing
noise is heard, caused by the excess
of electricity passing round the un-
covered part of the jar and not
through it, as the smallest crack in
the glass of the Leyden jar would
render it useless. Electricity is
sometimes called a fluid, and the fact
of collecting it like water in a jar,
helps us to understand this analogy.
The noise, the bright spark, or the
shock are obtained by grasping the outside with one hand and touching
the ball with a brass wire held in the other. (Fig. 175.)

Fig. 175. The Leyden jar and brass
wire discharger.

Thirty -sixth Experiment.

The jar is silently discharged if the balls are removed from the dis-
charger and points used instead ; so, also, the whole of the electricity
produced by an electrical machine in full action may be readily drawn
off by a pointed conductor, such as a needle, placed at the end of a brass
wire. Electricity passes much more rapidly through points than rounded
surfaces, hence the reason why all parts of electrical apparatus are free
from sharp points and rough asperities.

THE LEYDEN BATTERY.

191

Thirty -seventh Experiment.

Extremely thin wires may be burnt by passing the charge of a large
Leyden jar through them. The show jars, called specie jars, usually
decorated and placed in the windows of chemists' shops, make excel-
lent Leyden jars, when not too thick; and with two of the largest, all

Fig. 176. A. Mahogany board with a sheet of white paper and three pairs of brass wire*
and balls fixed in the wire, three on each side. The thin wires are stretched between the
balls, and the lower one is in course of deflagration. B u. Charged large Leyden battery
of two jars; the arrows indicate the path of the electricity.

the interesting effects produced by accumulated electricity may be dis-
played. To pass the discharge through wires, nothing more is required
than to strain them across a dry mahogany board, between two brass
wires and balls, and if a sheet of white paper is placed under them, most
curious markings are produced by the fine particles of the deflagrated
metal blown into the surface of the paper. An arrangement of two or
more Leyden jars is usually called a Leyden Battery, just as a single
cannon is spoken of as a gun, whilst two or more constitute a battery.
(Kg. 176.)

Thirty -eighth ^Experiment .

Little models of houses, masts of ships, trees, and towers are sold by
the instrument makers, and by placing a long balanced wire on the top
of the pointed wire of a large Leyden jar, having one end furnished
with wool to represent a cloud, a most excellent imitation of the eifects
of a charged thunder-cloud is produced. The mechanical effect of a
flash of lightning has been analysed, and it has been stated, in one
instance, that the power developed through fifty feet was equal to a
12,220 horse-power engine, or about the power of^c-' engines of the
Great "Eastern, and that the explosive power was <<5qufll' 'to a pressure of -^
three hundred millions of tons. (Fig. 177.) //'<& -- '^. -*V

Oftltforni*v

192

BOY'S PLAYBOOK OF SCIENCE.

r. 177. A. Charged Leyden jar with balanced wire and wool at B, representing a thunder-
cloud, c. The obelisk overturned with the discharge. . Another model of the gable
end of a house ; the square pieces of wood fly out when the continuity of the conductor is
broken.

It was the learned but humble minded Dr. Franklin who established
the identity between the mimic effects of the electrical machines (such
as have been described), and the awe-inspiring thunder and lightning of
nature. A copper rod, half an inch thick, pointed and gilt at the ex-
tremity, and carried to the highest point of a building, will protect a
circle with a radius of twice its length. The bottom of the rod must be
passed into the earth till it touches a damp stratum.

Fig. 178. A storm.

193
CHAPTER XIV.

VOLTAIC ELECTRICITY.

IN describing the various means by which electricity may be obtained,
it was stated that " Chemical Action" was a most important source of
this remarkable agent ; at the same time it must be understood that it
is not every kind of chemical action which is adapted for the purpose ;
there are certain principles to be rigidly adhered to first, in the
generation of the force ; and secondly, in carrying it by wires so as to
be applicable either for telegraphic purposes, or for the highly valuable
processes of electrotyping and electro-silvering, plating, and gilding.

A lighted candle, or an intense combustion of coal, coke, or charcoal,
no doubt involves the production of electricity, but there are no means at
present known by which it may be collected and conducted ; when that
problem is solved, the cheapest voltaic battery will have been constructed,
m which the element decomposed is charcoal, and not a metal, such as iron
or zinc. The first and most simple experiment that can be adduced in
proof of electrical excitation by chemical means, is to take a bit of clean
zinc and a clean half-crown, and placing one on the tongue and the other
below it, as long as they remain separate no effect is observed, but
directly they are made to touch each other, whilst in that position, a
peculiar thrill is rendered evident by the nerves of the tongue, which in
this case answers the same purpose as the electroscope already de-
scribed, and in a short time a peculiar metallic taste is perceptible.

It has been stated over and over again that it was to a somewhat
similar circumstance we owe the discovery of voltaic electricity, and
the story of the skinned frogs agitated and convulsed by an accfdental
communication with two different metals, or, as some say, with the
electricity from an ordinary machine, has been repeated in nearly every
work on the science. Professor Silliman, however, asserts that the gal-
vanic story is doubtful, and is a fabrication of Alibert, an Italian writer
of no repute, and that greater merit is due to Galvani than that of being
merely the accidental discoverer of tliis kind of electricity, because he had
been engaged for eleven years in electro-physiological experiments, using
frogs' legs as electroscopes. It was whilst experimenting on animal
irritability, Galvani noticed the important fact that when the nerve of a
dead frog, recently killed, was touched with a steel needle, and the muscle
with a silver one, no convulsions of the limb were produced until the two
different metals were brought in contact, and he explained the cause of
these singular after-death contortions by supposing that the nerves and
muscles of all animals were in opposite states of electricity, and that
these nervous contractions were caused by the annihilation, for the time,
of this condition, by the interposition of a good conductor between them.

This theory of Galvani had several opponents, one of whom, the cele-

194

BOY S PLAYBOOK OF SCIENCE.

brated Volta, succeeded in pointing out its fallacy ; lie maintained that
the electrical excitement was due entirely to the metals, and that the
muscular contractions were caused by the electricity thus developed
passing along the nerves and muscles of the dead animal.

To Volta we are indebted for the first voltaic battery, and the distin-
guished philosopher may truly be said to have laid the foundation of this
now commercially valuable branch of science.

First Experiment. ,

If a plate of clean bright zinc is placed in a vessel containing some
dilute sulphuric acid, energetic action occurs from the oxidation of the
metal, and its union as an oxide with the acid, and the escape of a mul-
titude of bubbles of hydrogen gas. After the action has proceeded some
time, the zinc may be removed, and if a little quicksilver is now rubbed
over the surface with a woollen rag tied on the end of a stick, it unites

with the metal, and the sur-
face of the zinc assumes a
brilliant silvery appearance,
and is said to be amalga-
mated. In that condition it
is no longer acted upon by
dilute sulpnuric acid, and for
the sake of economy this is
the only form in which zinc
should be employed in the
construction of voltaic batte-
ries or single circles. If a
clean plate of copper, with a
^ wire attached, is now placed

in the dilute acid opposite to

Fig. 179. A single voltaic circle, consisting of a and not touching the amal-

^&F^^&$FF& gamated zinc plate, which may
current. also be furnished with a con-

ducting wire, no bubbles of

hydrogen escape until the wires from the two metals are brought in
contact, and then, singular to relate, the hydrogen escapes from the
copper plate, whilst the oxygen is rapidly absorbed by the zinc, and a
current of electricity will now be found to pass from the zinc through
the fluid to the copper, and back again through the wire to the starting-
point, and if the wires are disconnected, the chemical action ceases, and
no more electricity is produced. (Fig. 179.)

The passage of the current of electricity is not discoverable by the
electroscope, because it is adapted only to indicate electricity of high
tension or intensity, such as that produced from the electrical machine,
which will pass rapidly through a certain thickness of air, and cause
pith balls to stand out and repel each other ; such effects are not pro-
ducible by a single voltaic circle, or even an ordinary voltaic battery,
although one comprising some hundreds of alternations would produce

THE GALVANOMETER. 195

an effect on a delicate electrometer ; hence voltaic electricity is said to
be of low intensity, and this property makes it much more useful to
mankind, because it has no desire to leave a metallic path prepared for
it, and does not seize the first opportunity, like the electricity from the
electrical machine, to run away to the' earth through the best and
shortest conductor offered for it. If electricity had only been producible
by friction, we should never have heard of electrotyping, and the other
useful applications of electrical force of low intensity.

Second Experiment.

To ascertain the
passage of a current
of voltaic. electricity,
the instrument called
the galvanometer
needle IS provided, Fig m A ga i va nometer needle, consisting of a coil of
which consists OI a covered copper wire, the ends of which terminate at the
nnil nf pnrmpr wirp binding screws. The magnetic needle is suspended on a

)i copper wire, point in the centre) aQd the coil ia surrounded writh a gradu .
surrounding a mag- ated circle,
netic needle, so as to

leave the latter freedom of motion from right to left, or vice versa.
When this coil is made part of the voltaic circle it becomes magnetic,
and reacting on the magnetized needle, deflects it to one side or the
other, according to the direction of the current. (Fig. 180.)

Third Experiment.

If a number of simple voltaic circles, such as the one described in the
first experiment, are connected together, they form a voltaic battery,
in which of course the quantity of electricity is greatly increased.
Batteries of all kinds, from the original Volta's pile, consisting of round
zinc and copper plates soldered together with interposed cloth moistened
with dilute sulphuric acid, or his couronne des tosses, consisting of zinc
and silver wires soldered together in pairs, and placed in glass cups
containing dilute acid, to the improved batteries of Cruikshank, Wil-
kinson, Babington, Wollaston, and the still more perfect arrangements
of Daniell, Mullins, Shillibeer, and Grove, have been from time to time
recommended for their own peculiar features.

Amongst these several inventions, none will be found more useful
than the constant battery of Daniell for electrotyping, silvering, gilding,
and other purposes, and Grove's battery for all the more brilliant results,
such as the deflagration of the metals or the production of the electric
light. The construction of the Daniell and Grove batteries will there-
fore be described. The former consists of a cylindrical vessel made of
copper, in which is suspended or placed (as it is open at the top) a
membranous, brown-paper, canvas, or porous earthenware tube, con-
taining an amalgamated rod of zinc. To charge this arrangement, a
strong solution of sulphate of copper, with some sulphuric acid, is
poured into the copper vessel, which is provided usually with a sort of

106

BOYS PLAYBOOK OF SCIENCE.

colander at the top to hold crystals of sulphate of copper, and in the
porous tube containing the zinc rod is poured dilute sulphuric acid. A
number of these cylinders of copper, twenty inches high and three inches
and a half in diameter, arranged in wooden frames to the number of

Fig. 181. A A. Copper cylindrical vessel with colander to hold the crystals of sulphate
of copper. B. The amalgamated zinc rod inside the porous cell c c. D. A series of single
cells forming a DanielFs battery.

twenty, afford a quantity of electricity sufficient to demonstrate all the
usual phenomena. (Fig. 181.)

Protessor Grove's battery consists of a flat glazed earthenware vessel
containing a flat porous cell. An amalgamated zinc plate is placed
outside the porous cell, and a platinum plate inside the latter. The
arrangement is put in action by pouring dilute sulphuric acid round the
zinc and strong nitric acid inside the porous cell. A set of Grove's
nitric acid battery, as manufactured by Messrs. Elliott, Brothers, of
30, Strand, with fifty pairs of sheet platinum, five inches by two inches
and a quarter, and double amalgamated zinc plates, flat porous cells, and
separate earthenware troughs for each pair, and stout mahogany stand,
arranged '
one
sition

arranged as a single series of fifty pairs of plates. Even thirty pairs
exhibit the most splendid effects, whilst forty may be regarded as the
happy medium, giving all the results that can be desired. (-Fig. 182.)

The advantage of employing amalgamated zinc is very prominently
illustrated whilst using any powerful arrangements of either Daniell's or
Grove's batteries, as they will remain for hours quiescent, like a giant
asleep, until the terminal wires of the series are brought in contact

BATTERIES OF DANIELL AND GROVE.

197

C C A.

Fig. 182. A A. Amalgamated zinc plate in flat earthenware trough. Attached to a bind-
ing screw is the platinum plate in porous cell, c c. D. A series of single cells forming a
Grove's battery.

either through the intervention of some fluid under decomposition or by
means of charcoal points. The author had the pleasure of witnessing
at King's College some of the effects of an enormous battery, prepared
by the late Professor Daniell, and consisting of seventy of his cells.

A continuous arch of flame was produced between two charcoal points,
when distant from each other three quarters of an inch, and the light
and heat were so intense that the professor's face became scorched and
inflamed, as if it had been exposed to a summer heat. The rays col-
lected by a lens quickly fired paper held in the focus.*

Fourth Experiment.

It is bv " chemical action" the electricity is produced, and as action
and reaction are always equal, but contrary, we are not surprised to find
that the electricity from the voltaic battery will in its turn decompose
chemically many compound bodies, of which water is one of the most
interesting examples. It was in the year 1800, and immediately after
Volta's announcement -to Sir Joseph Banks of his discovery of the pile,
that Messrs. Nicholson and Carlisle constructed the first pile in England,
consisting of thirty-six half-crowns, with as many discs of zinc and paste-
board soaked in salt water. These gentlemen, whilst experimenting
with the pile, observed that bubbles of gas escaped from the platinum
wires immersed in water and connected with the extremities of the
Volta's pile, and covering the wires with a glass tube full of water, on
the 2nd of May, 1800, they completed the splendid discovery of the
fact that the Volta's current had the power to decompose water and
other chemical compounds.

* By the light from the same battery photogenic drawings were taken, and the heating
power was so great as to fuse with the utmost readiness a bar of platinum one-eighth of an
inch square ; and all the more infusible metals, such as rhodium, iridium, titanium, &c.,
were melted like wax when placed in small cavities in hard graphite and exposed to ths
current of electricity.

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BOYS PLAYBOOK OF SCIENCE.

Fig. 183. A A. A finger glass with two holes drilled
to pass the wires through, which are imbedded in
cement up to the platinum plates. B B. Glass tubes,
closed at one end and open at the other, which are
placed over the platinum plates to receive the liberated
oxygen and hydrogen. The scale at the side shows
the respective volumes of two of H to one of 0.

In 1801, Davy had sue-
ceeded to a vacant post in
the Royal Institution, and
on Oct. 6th, 1807, made
his transcendent discovery
of potassium with the aid
of the voltaic battery, and
from that and other expe-
riments inferred that the
whole crust of the globe
was composed of the oxides
of metals. To exhibit the
decomposition of water,
two platinum plates with
proper connecting wires,
passing to small metallic
cups full of mercury, are
cemented inside a glass
vessel, which is then filled
with dilute sulphuric acid.
Just above the platinum
plates and over them, stand
two glass tubes also con-
taining the same fluid in
contact with the battery.
Two measures of hydrogen
are found in one tube, and
one of oxygen in the other.
(Fig. 183.)

To measure the quan-
tity power of the voltaic
battery, an important in-
strument invented by Fa-
raday is used. It consists
of separate platinum plates
cemented in a wooden
stand, and over which a
capped air-jar with a bent
pipe is also cemented. Tin's
apparatus contains dilute
sulphuric acid of the same

Fig. 184. A. Gas jar with cap and bent tube passing , ' ,1 f i , ,

to the graduated tube c; the jar is cemented in the f?*^*" l j 1 T

same stand which carries the connecting cups, wires, the battery under exami-
and platinum plates, which are bent round each other Cation ancl bv takin " the
to improve the action of the voltameter. .. '-, '*.*. *J J.-L

time, tne quantity 01 tne

mixed oxygen and hydrogen gases producible by a battery per minute is
accurately determined, the gases of course being collected in a gra-
duated jar. (Fig. 184.)

ELECTRO-CHEMISTRY.

199

Fifth Experiment.

By grouping the simple circles forming a voltaic battery in various
numerical relations, the quantity and intensity effects are modified.

Thus, if a series of thirty pairs of Grove's battery are all connected
together in consecutive order, the smallest quantity and the largest
intensity effect is produced.

If changed to two groups of fifteen each, the quantity is doubled
that is to say, it will produce double the quantity of the mixed gases
from the voltameter with half the intensity.

If arranged in three groups of ten each, it is trebled with a propor-
tional loss of intensity, until the grouping reaches six series of five each,
when a maximum supply of the mixed gases is obtained from the
voltameter.

In arranging the groups, all the zinc ends of each series are con-
nected, and all the platinum ends are likewise joined by proper wires.

Sixth Experiment.

A plate-glass trough, con-
taining a few grains of iodide
of potassium dissolved in
water with some starch, is
quickly decomposed into its
elements by placing in two
platinum plates and connect-
ing them with the wires of
the voltaic battery. If the
glass trough is divided in the
centre with a bit of cardboard,
the purple colour of the iodine
and starch is shown very beau-
tifully on one side, but not on
the other, as iodine is libe-
rated at one pole and the al-
kali at the other. (Fig. 185.)

Seventh, Experiment.

Some solution of common salt coloured with sulphate of indigo and
placed in the trough is decomposed into chlorine, which bleaches one
side of the indigo solution, and the alkali liberated on the other does
not affect it.

Eighth Experiment.

Some nitrate of potash dissolved in water and coloured with litmus
placed in the glass trough, changes red on one side of the cardboard by
the liberation of acid, and is not affected on the other.

In these experiments the oxygen, iodine, chlorine, and nitric acid are
liberated at the electro-positive pole, and are hence termed electro-
negative bodies, whilst hydrogen and the alkalies are set free at the
electro-negative pole, and are therefore called electro-positive bodies.

Fig 1 . 185. A A. A glass trough containing the
salt dissolved in water, and divided temporarily
with a bit of cardboard, B. c c are the two platinum
plates connected with the battery, and the shaded
side is supposed to represent the liberation of the
iodine.

200

BOY'S PLAYBOOK OF SCIENCE.

Faraday has modified these terms, and calls the two classes "unions"
and " cathions" and the two poles "anodes" and "cathodes."

Anode, from az/a, up, and 686s, a way : the way which the sun rises.
Anions, from ai/a, up, ei/w, to go : that which goes up ; a substance
which passes to the anode during the passage of a current of elec-
tricity. Cathode, from /caret, down, and 6S6s, a way : the way which
the sun sets. Cathion, from Kara, down, and el/j.1, to go : that which
goes down ; a substance which passes to the cathode during the passage
of electricity from the anode to the cathode.

Ninth Experiment.

In the process of the electrotype is presented a valuable application
of the chemical power of the voltaic circle or battery, and it may be
conducted either as a single cell operation or by distinct batteries. In
the former case the most simple arrangement will suffice; the only
articles necessary are a large mug or tumbler ; some brown paper and
a ruler ; a bit of amalgamated zinc, four inches long and half an inch
wide ; a short length of copper wire ; some black lead, blue vitriol, and
oil of vitriol.

The mould from which the electrotype is to be taken can be made
of common sealing wax, plaster of Paris, white wax, gutta percha,
or fusible alloy. Supposing the first to be selected viz., a common

seal, it is first thoroughly black-leaded,*
then one end of the copper wire is bent
round the top of the amalgamated zinc,
and the other is gently warmed and
melted into the side of the seal, leaving
a small portion uncovered by the wax,
which is then well black-leaded. A few
ounces of blue vitriol are dissolved in
boiling water, and when cold the solu-
tion is poured into the tumbler, and the
porous cell to contain the mixture of
eight parts water to one of sulphuric
acid is made by rolling the brown paper
three or four times round the ruler and
closing the end, and fixing the side with
a little sealing wax. The porous cell of
brown paper is now filled with the di-
lute acid, and placed in the tumbler
containing the solution of blue vitriol,
the amalgamated zinc being arranged in
the paper cell, and the attached seal in
Fig. 186. A A The tumbler con- th solution; in about twelve

tamine the solution of sulphate ot . rr '

copper B B. The brown paper cell hours a good deposit of copper IS pro-
containing the dilute sulphuric acid, duced, and a perfect cast in metal of
inside which is the amalgamated zinc ,, , Ju*. _il /ENo- 1 QA "\

with wire attached to the seal D. the seal obtained. (* ig. 1 SO.)

* The application of plumbago, or black lead, for electrotype purposes, was first nude
by the late lamented Mr. Robert Murray.

THE ELECTROTYPE.

201

Messrs. Elliott provide every kind of convenient vessel for the pur-
pose, and in the picture below it will be noticed that the single cell appa-
ratus, though not so economical as the simple tumbler arrangement already
described, is perhaps more convenient for electrotyping. (Fig. 187.)

Fig. 187. A. Single cell apparatus with proper vessel, porous tube, and binding screws.
B. A large trough divided by a diaphragm of biscuit-ware or very thin porous wood.

Tenth Experiment.

A single cell apparatus is only adapted to produce small electrotypes,
but when larger ones are required, a separate battery of three or four

Fitr. 188. A. A single cell, Darnell's, attached to B, the trough containing the mould
and the plate of copper. Below is a Smee's battery ready to be attached to a larger trough
for the purpose of electrotyping a great number of moulds at the same time.

202

BOY S PLAYBOOK OF SCIENCE.

Dnuirll's or Smcc's cells is required; and it is usual to place the mould
to be copied in a separate wooden trough, ul.ladiing it to the cathode
wire, whilst a copper plate is connected with the anode, so that as the
solution of sulphate pi copper undergoes decomposition by the passage
of the electricity, it is kept almost in a normal state, in consequence of
the oxygen of the water and the acid passing to the copper plate, which
they attack and dissolve as fast as the oxide of copper and hydrogen
are liberated at the cathode, where the latter deoxidizes the oxide of
copper, and by a secondary action deposits metallic copper; the object
being to dissolve fresh metal as the copper is deposited on the mould.
(Fig? 188.)

Eleventh Experiment.

To silver electrotypes or other brass and copper articles, the first
attention must be paid to the cleanness of them ; and when an electrotype
is just removed from the copper solution, and washed in clean water,
it is at once ready to receive the coating of silver ; otherwise, if it has
been handled, or is slightly greasy, it should be first boiled in a solution
of common washing soda, and then the oxide removed by passing it
rapidly in and out of some "Dipping Acid," which is prepared by
mixing together equal parts of oil of vitriol and nitric acid; when
removed from the "Dipping Acid," it must be well washed in water,
and may remain under the surface of the water until the silvering
solution is ready. A silver solution may be prepared by dissolving a
sixpence in some nitric acid contained in a flask ; it is then poured into
a solution of common salt, which precipitates the chloride of silver, and
leaves the copper in solution the latter is poured off when the chloride
has subsided, and after being well washed in some boiling water, is
dissolved in a solution of cyanide of potassium. If a clean electrotype
is plunged into this solution, it is imme-
diately covered with a very thin coating of
silver, which of course would soon wear off,
and in order to increase the thickness of
the silver deposit, a single cell arrangement
may be constructed of a large gallipot con-
taining a wide porous cell and a circle of
amalgamated zinc around it; the arrange-
ment is set in action by pouring a solution
of salt (or, still better, sal ammoniac) into
and around the porous vessel, and the sil-
vering solution into the latter ; a connect-
ing wire passes from the zinc, and the ar-
ticlc being attached to it, is now plunged
into the porous cell, when a current of
electricity slowly passes and deposits the
screw to which tho medal is silver on the copper article, (l<ig.

attached, and contained in the
porous vessel holding the silvering
solution and mcdul.

Fig. 189. The gallipot con-
ining tho solution of sal ammo-

ELECTRO-SILVERING AND GILDING. 203

Twelfth Experiment.

Separate batteries and large troughs containing a solution of cyanide
of silver in cyanide of potassium are used on a grand scale in the electro-
plating establishment of Messrs. Elkin^ton ot Birmingham, where the
finest specimens of the art are to be obtained; a plate of silver being
attached to the anode to supply the loss of silver in these troughs.

Thirteenth Experiment.

The art of gildingr by the agency of electricity is quite as simple as
the processes already described, although greater care is necessary to
avoia any loss of the precious metal. A small bit of gold is dissolved
in a mixture of three parts muriatic acid and one of nitric acid, which
forms the chloride of gold. This is then digested with an excess of
calcined magnesia, and the gold is precipitated as an oxide of the metal;
the latter is collected and washed, and then boiled in strong nitric acid
to remove the magnesia clinging to it, and being again thoroughly washed
with water, is dissolved in a solution of cyanide of potassium, forming
a solution of cyanide of gold and potassium, which may be placed in
the* porous cell of the single cell arrangement already described in
the Eleventh Experiment.

Fourteenth Experiment.

The safest and surest mode of making a gilding solution is to dissolve
some cyanide of potassium in water in a gallipot, and having placed a
porous vessel therein containing the same solution, put a plate of copper
into the porous cell, and some thin foil of pure gold into the gallipot ;
connect the gold with the anode of a single cell of Daniell, and the
copper in the porous cell with the cathode, and in a few hours sufficient
gold will be dissolved for the purpose of gilding.

It is usually recommended to warm the gilding solution till it reaches
a temperature of about 150 Fahr., and a very moderate battery power
is employed in Electro Gilding. Indeed the same arrangement, shown
in the Eleventh Experiment, Eig. 189, will also answer tor the gilding
solution. After being gilt, the articles may be rubbed with a little
tripoli, or burnished (with taste) by the handle of a key.

Fifteenth Experiment.

Passing on to the more brilliant results obtainable from a powerful
voltaic battery (of at least thirty pairs of Grove), the beautiful incan-
descence of platinum wire may first be noticed. If a wire of this metal
is stretched oetweeii the brass standards of two ring stands, the length
must be proportioned to the power of the battery; the adjustment can
be made verv conveniently by twisting the platinum wire on one ring
stand, and tlien leaving the other end loose, the second ring stand may
be brought nearer and nearer to the first, until the desired intensity of

204

BOY S PLAYBOOK OF SCIEXCE.

light from the incandescent
wire is obtained. (Fig. 190.)
If the wire is contained in
a glass tube the cooling
effect of currents of air is
prevented, and a much
greater length of wire can
be made hot.

Sixteenth Experiment.

With the same arrange-
ment, a chain composed of
alternate links of silver and
platinum wire presents a
very pretty effect, every

. Two ring stands with the battery alternate link of platinum

being incandescent, whilst
the silver, from its excellent
conducting power, remains

comparatively cool.

Fig. 190,

wires B B (which should be a convenient length) at
tached. c. Platinum wire, fixed end. D. The other
end held in one hand and shortened as the stand is
moved by the other hand.

Fireworks or gunpowder, arranged
in proper cases, are fired at a great
distance from the voltaic battery by
heating a thin iron or platinum wire
contained within them by the pas-
sage of the electricity; and sub-
marine and other explosions of gun-
powder by the same agency have
become a common engineering ope-
ration. (Fig. 19].)

During the operation of blasting
the hard marl rocks in the River
Severn by Mr. Edwards, C.E., a
number of holes were made side by
side in the bed of the river, and
rSuncfthe cartridges formed of strong duck or

battery wires tied to the outside of the case. Canvas, tapered at the bottom,
c. A gut bladder containing the thin wire were fiU e( J w ith charges of powder
and powder for a miniature submarine f , f ,

explosion. f rom two to f ur pounds, accord-

ing to the depth of the marl;

thus, two pounds for four feet, three pounds for four feet six inches, and
four pounds for five feet. Into the bag were conveyed the wires of the
voltaic battery, or Bickford's fuse, and being then coated with pitch and
tallow, and finally greased all over and dusted with whitening, thev
rarely failed, and were all fired simultaneously under water. The pitcu
and tallow first, and afterwards the simple tallow, effectually excluded
the water from the gunpowder contained in the canvas bag.

THE ELECTRIC LIGHT.

205

Eighteenth Experiment.

The burning of various
metals by the battery is
displayed with great effect
by De la Rue's discharger,
as also the incandescence
of the charcoal points pro-
ducing the electric light.
The illuminating power
derived from a forty-cell
Grove's battery of the or-
dinary size is about equal
to the light of 500 candles.

Fizeau and Foucault
have made a careful com-
parison of the light ob-

Fig. 192. De la Rue discharger, containing a series
of six pairs of difl'crent substances, such as charcoal,
iron, lead, zinc, copper, antimony, in six pair of crayon
holders, and turning on a centre, so as to be charged at
pleasure.

tained from 92 carbon couples as arranged in a Bunsen's battery, and
of the oxy-hydrogen, or Drummond Light, as compared with that of
the sun, and they state that " On a clear August day, with the sun two
hours high, the electric light (assuming the sun as unity) bore to it the
ratio of one to two and a half i.e., the s-un was two and a half times
more powerful, while the Drummond Light was only T^th that of the
sun." Bunsen found the light from 48 carbons equal to 572 candles.
In Bunsen's battery carbon is substituted for the platinum in Grove's
arrangement; and simultaneously witli Bunsen, Cooper (in England)
had applied charcoal for the same purpose.

At night the giant ship (Polyphemus like) is to have an electric light
at the masthead whilst steaming across the Atlantic.

Fig. 193. Gnat: Lantern, with electric light.

206

BOY S PLAYBOOK OF SCIENCE.

CHAPTER XV.

MAGNETISM AND ELECTRO-MAGNETISM.

IF a small helix, or coil of covered wire, is arranged with an unmag-
netized steel needle within it, so that the discharge of a large Leyden

jar may take place
through the coil, the
needle will be found
strongly magnetic af-
ter the discharge of
the electricity. "(Fig.
194.) Many years
before this was
known, it had been
noticed that when a
ship was struck by
lightning, the com-
passes were generally
reversed; and in a
special case, where a
house was struck, the
electricity entered a

Fig. 194. A A. A plass tube supported on two uprights of h nx n f Vnivpq fnsi no-
wood, with coil of copper wire passing round it, terminating in D l Kmve . s > IU& i n g
the balls B B. c. Needle to place inside glass tube. some, tearing the

handles off others,

but leaving' them strongly magnetic. Electricians tried to repeat the
effect by sending the discharge of powerful Leyden batteries through
bars of steel without any important result; and it was not until
Oersted, in the year 1819, made his important discovery that the copper
lire conveying the electricity possessed peculiar magnetic power, that

the principle began
to be understood, and
then the electricians
succeeded in imitat-
ing the effects of
lightning on steel, as
already described in
the beginning of this
chapter. (Fig. 194.)
When the electri-
city has passed away
from the Leyden jar
Fig. 105. through the coil of

THE LOADSTONE. 207

copper wire, it no longer possesses any power to affect a piece of steel
or iron, but if the wires of the voltaic battery are now connected with
the coil of copper wire, which should be covered with cotton or silk,
and many yards in length, then a bar of steel or soft iron is not only
rendered magnetic, but remains permanently so, as long as the current
of electricity continues to pass along the coil of wire, so that if some
nails or iron filings are brought to the bar of iron, one end of which
projects from the coil, they cling to it with great force, and a great
number of nails may be hung on in this manner, but they imme-
diately fall off when the contact is broken with the battery. (Pig. 195.)

Electricity thus becomes a source of magnetism, and the discoverer,
Oersted, found that only needles or bars of steel or iron were thus
affected, and not those of brass, shell-lac, sulphur, and other substances ;
he termed the conducting wire " a conjunctive wire," and described the
effect of the electric current or " electric conflict" as he called it, as
resembling a Helix (from eXiVo-o), to turn round; a screw or spiral), and
that it is not confined to the conducting wire, but radiates an influence
at some distance. This latter statement is exactly in accordance with
our present notions, and hence the coil conveying the current is said to
induce magnetism in the iron or steel, just as the phenomena of induction
are produced with frictional electricity. The effect of Oersted's disco-
very-, says Silliman, was truly electric; the scientific world was ripe
for it, and the truth he thus struck out was instantly seized upon by
Arago, Ampere, Davy, Faraday, and a crowd of philosophers in all coun-
tries. The activity with which this new field of research has been cul-
tivated, has never relaxed even to this hour, while it has borne fruit in
a multitude of theoretical and practical truths, and above all, in the
electro-magnetic telegraph, truly called, and especially in connexion
with the Atlantic telegraph wire, " the great international nerve of
sensation"

Magnetism is not only the result of a current of electricity through
any good conductor, but there are certain
oxides of iron, called magnetic iron ores,
which have the property of attracting iron
filings, and are mostly found in primitive
rocks, being abundant at Roslagen, in
Sweden, and called the loadstone, from its
always pointing, when freely suspended, to
the Polar, North, or Load Star. If a tole-
rably large specimen of this mineral is exa-
mined, there will be found usually two points
where the iron filings are attracted in larger
quantities than in other parts of the same
specimen. These attractive points are called
poles, and the loadstone being properly F} 196 A
mounted with soft iron bars, termed cheeks, mounted in brass or sliver,
bound round it (in old-fashioned loadstones) with the iron cheeks B B at-
silver plate and dulv ornamented with ' S ft

208

BOY S PLAYBOOK OF SCIENCE.

engraving, has its magnetic power greatly increased, and is then said to
be endowed with magnetic polarity; and to prevent the loss of power, a
soft piece of iron, called the armature, is placed across and attracted
to the poles of the loadstone. (Fig. 196.)

Second Experiment.

If a needle of tempered steel (fitted with a little brass cup in the
centre to work upon a point) is rubbed with the loadstone iu one direc-
tion only, it is rendered permanently magnetic, and will now be found
to take a certain fixed position, pointing always in a direction due north
and south. The end which points towards the north is called the north
pole, and the other extremity the south pole, and it is usual to mark
the north pole with an indent or scratch to distinguish it at all times.

Third Experiment.

If another bar of steel is magnetized, and the north pole duly marked,
and then brought towards the same pole of the suspended magnet, in-
stant repulsion takes
place; the magnet, of
course, grasped in
the hand is not free
to move, but the
small magnet imme-
diately shows the
same fact noticed
with electricity, viz.,
Pig. 197. A magnetic needle, the north pole v being at- " th a similar maqne-
tracted to the south pole of the bar magnet s, and repelled from , . ; m__

the north end. tttmt repel. Iwo

n>i th poles repel each

other, but when the bar of steel is reversed, the opposite effect occurs,
and the suspended magnet is attracted, showing that dissimilar mag-
netisms attract, and a north will attract a south pole. (Fig. 197.)

Fourth Experiment.

By contact, the magnetic power is transferred from the magnet to a

piece of unmagnetized
steel, and it is stated
that the highest magnet-
izing effect is that pro-
duced by the simple me-
thod of Jacobi. A horse-
shoe magnet has its poles
brought in contact with
the intended poles of an-
tagnet, and another one other bar of steel, like-
snd; the one shaded and w i se bent in the torm

Fig. 198. The horse-shoe m
nnmagnetized, placed end to en

nnmagnetized, placed end to end; the one shaded and wlse bent in tne lorm
lettered K and s is the magnet. A A. The piece of soft f horseshoe, and by
iron moved in the direction of the arrow.

ELECTRO-MAGNETS.

209

drawing the feeder over the unmagnetized horse-shoe in the direction of
the arrow in the cut, and when it reaches the curve, bringing it back
again to the same place, say at least twelve times, and after turning
the whole over without separating the poles, and repeating the same
operati<~yn on the other side likewise twelve times, the steel is then
powerfully magnetized ; and it is said that a horse-shoe of one pound
weight may be thus charged so as to sustain twenty-six and a half
pounds, and that by the old method of magnetizing it would only have
sustained about twenty -two pounds. (Fig. 198.)

Fifth Experiment.

If the horse-shoe magnet is placed on a sheet of paper, and some iron
filings are dusted between the poles, a very beautiful series of curves are
formed, called the magnetic curves, which indicate the constant passage
of the magnetic power from pole to pole.

The magnetic force
exerted by a horse-
shoe-shaped piece of
soft iron, surrounded
with many strands of
covered copper wire
in short lengths, is
extremely powerful
(Fig. 199), and enor-
mous weights have
been supported by an
electro-magnet when
connected with a vol-
taic battery. Sup-
posing a man were
dressed in complete
armour, he might be
held by an electro-
magnet, without the

limself, thus realiz-
ing the fairy story of
the bold knight who
was caught by a rock
of loadstone, and,
in full armour, de-
tained by the un-
friendly magician.

Sixth Experiment.

Fig. 199. A. Powerful electro-magnet supporting a great
weight. B. The battery.

210

EOT S PLAYBOOK OF SCIENCE.

Seventh Experiment.

When a piece of soft iron is held sufficiently near one of the poles
of a powerful magnet, it becomes by induction endowed with magnetic
poles, and will support another bit of soft iron, such as a nail, brought,
in contact with it. When the magnet is removed, the inductive action
ceases, and the soft iron loses its magnetic power. Tliis experiment
aifords another example of the connexion between the phenomena of
electricity and magnetism. It is in consequence of the inductive action
of the magnetism of the earth that all masses of iron, especially
when they are perpendicular, are fcTind to be endowed with magnetic
polarity ; hence the reaction of the iron in ships upon the compasses,
which have to be corrected and adjusted before a voyage, or else serious
errors in steering the vessel would occur, and there is no doubt that many
shipwrecks are due to this cause. No other metals beside iron, steel,
nickel, cobalt, and possibly manganese, can receive or retain magnetism
after contact with a magnet.

The remarkable effect of magnetism upon all matter, so ably investi-
gated by Faraday and others, will be explained in another part of this
book viz., in the article on Dia-Magnetism.

I":;,'. 200. JIagiciaii and bis loadstone-rock. Vide Fairy Talt.

211

CHAPTER XVI.

ELECTRO-MAGNETIC MACHINES.

THE experiments already described in illustration of some of the phe-
nomena of electro-magnetism are of such a simple nature that they
may be comprehended without difficulty ; but it is not such an easy
task to appreciate the curious fact of an invisible power producing
motion. It has already been explained that a copper or other metallic
wire conveying a current of electricity becomes for the time endowed
with a magnetic power, and if held
above, or below, or close to, a sus-
pended magnetized steel needle,
affects it in a very marked degree,
causing it to move to the right or
left, according to the direction of
the electric current ; and in order
to form some notion of the con-
dition of a metallic wire whilst the
electricity is passing through it,

v * Fig. 201. Portion of a square copper con-

the annexed diagrams may DC re- ductor, in which A B represents the direction

of the electricity, and the small arrows, c c c c,
the magnetic current or whirl at right angles

ferred to. (Figs. 201, 202.)

Dr. Rpget says: "The magnetic to^h^eiectricai' current, and exercising a
force which emanates from the elec- tangential action,
trical conducting wire is entirely
different in its mode of operation
from all other forces in nature with
which we are acquainted. It does
not act in a direction parallel to
that of the current which is pass-
ing along .the wire ,nor many plane
passing through that direction. It f orce .
is evidently exerted in a plane per-
pendicular to the wire, but still it has no tendency to move the poles of
the magnet in a right or radial line, either directly towards, or directly
from, the wire, as in every other case of attractive or repulsive agency.
The peculiarity of its action is that it produces motion in a circular
direction all round the wire that is, in a direction at right angles to
the radius, or in the direction of the tangent to* a circle described round
the wire in a plane perpendicular to it ; hence the electro-magnetic force
exerts a tangential action, or that which Dr. Wollaston called a vertigi-
nous or whirling motion.

513

BOY'S PLAYBOOK OF SCIENCE.

Dr. Faraday concluded that there is no real attraction or repulsion
between the wire and either pole of a magnet, the action which imitates
these effects being of a compound nature ; and he also inferred that the
wire ought to revolve round a magnetic pole of a bar magnet, and a

magnetic pole round a wire,
if proper means could be de-
vised for giving effect to
these tendencies, and for
isolating the operations of a
single pole. For the first
idea of electro-magnetic ro-
tation the world is indebted to
Dr. Wollaston; but Dr. Fara-
day, with his usual ingenuity,
was the first who carried out
the theory practically. The
rotation of a wire (conveying
a current of voltaic electri-
city) round one of the poles
of a magnet is well displayed
with the simple contrivance
devised by him. (Fig. 203.)
By a careful observation of
the complex action of an
electrified wire upon a mag-
netic needle, Dr. Faraday was
enabled to analyse the phe-
nomena with his usual pene-
Fig. 203. IT. A small bar magnet cemented into , i i , n .K;i:*.

a wineglass, the north pole being at K. A is a tration and exhaustive ability,
moyeable wire looped over the hook, which is the and he found, as Daniell
positive (+) pole of the battery; the free extremity
rotates round the pole of the magnet when the cur-
rent of electricity passes. The dotted line repre- _,, , . ,, , , .,, ,
sents the level of the mercury which the glass con- * lf the electrified wire is
tains. The electricity passes in at A, and out at P laced * perpendicular position,
the wire B, as shown by the arrows, c is connected an ? mad to approach towards one
with the negative, and with the positive, pole of P ole . of the needle the pole wi 11 not
the batterv ' be simply attracted or repelled, but

will make an effort to pass off on
one side in a direction dependent

upon the attractive or repulsive power of the pole ; but if the wire be continually made to
approach the centre of motion by either the one or the other side of the needle, the ten-
dency to move in the former direction will first diminish, then become null, and ulti-
mately the motion will be reversed, and the needle will principally endeavour to pass in
the opposite direction. The opposite extremity of the needle will present similar phe-
nomena in the opposite direction ; hence Dr. Faraday drew the conclusion that the direc-
tion of the forces was tangential to the circumference of the wire, that the pole of the
needle is drawn by one force, not in the direction of a radius to its centre, but in that of
a line touching its circumference, and that it is repelled by the other force in the opposite
direction. In this manner the northern force acted all round the wire in one direction,
and the southern in the opposite one. Each pole of the needle, in short, appeared to have
a tendency to revolve round the wire in a direction opposite to the other, and, conse-
quently, the wire round the poles. Each pole has the power of acting upon the wire by
itself, and not as connected with the opposite pole, and the apparent attractions and
repulsions are merely exhibitions of the revolving motions in different parts of their
circles."

FARADAY S EXPERIMENTS.

213

The same fact il-
lustrated at Fig. 203,
is also demonstratedin
a still more striking
manner by means of
wire bent into a
rectangular form, and
so arranged that whilst
the current of electri-
city passes, it is free
to move in a circle ;
and when the poles of
a magnet are brought
towards the electrified
wire, it may be at-
tracted or repelled at
pleasure, and in fact

Fig. 204 A A A A. The rectangular wire covered with silk becomes a magnetic

and varnished, one end of which being pointed, rests on the indicator and places

little cup B, connected with a covered wire passing down the ,-f 00 if f\c nnva e^\^

centre of the brass support to the binding screw c let into ltse V (" Carelully SUS-

ivory. D. The other extremity of the rectangular wire; this peilded) at right angles

being covered and varnished, is not in metallic contact with '
the end B, but is likewise pointed, and dips into the mercury -, ,-. - Q

contained in the large cup E E. The upper and lower cups Qian. (1: Ig. 2
do not touch, and are separated by ivory, marked by the
shaded portion, and the cup E E is in metallic communication <?

with the brass pillar, and is connected with the negative pole menlS 01 a magnetized

of the battery at r, whilst c is connected with the positive needle, and rotations

pole of the battery, and the electricity circulates round the ^f T T 7 ; T .po onrl msn-ripfc

wire in the direction of the arrows. When a bar magnet, N, is ?* wir nd ueib,

brought towards the wire, the latter is immediately set in brought about by the

motion, and by alternately presenting the opposite poles of agency of ail active
the magnet, the rectangular wire rotates freely round the J , e i , ,

CU p B> current or electricity,

have induced Sir David

Brewster to advance his admirable theory, which supposes the affection
of the mariner's compass needle, and all other suspended pieces of
steel, to be due to the agency of electrical currents continually circu-
lating around the globe ; and Mr. Barlow contrived the following expe-
riment in illustration of Brewster's theory. A wooden globe, sixteen
inches in diameter, was made hollow, for the purpose of reducing its
weight, and while still in the lathe, grooves one-eighth of an inch deep
and broad were cut to represent an equator, and parallels of latitude
at every four and a half degrees each way from the equator to the poles.
A groove of double depth was also cut like a meridian from pole to pole,
but only half round. The grooves were cut to receive the copper wire
covered with silk, and the laying on was commenced by taking the
middle of a length of ninety feet of wire one-sixteenth of an inch in
diameter, which was applied to the equatorial groove so as to meet in the
transverse meridian ; it was then made to pass round this parallel, re-
turned again along the meridian to the next parallel, and then passedround
this again, and so on, till the wire was thus led in continuation from pole

These Curious mOVC-

BOY'S PLAYBOOK OF SCIENCE.

to pole. The length of wire still remaining at each pole was returned
from each pole along the meridian groove to the equator, and at this
point, each wire being fastened down with small staples, the wires from
the remaining five feet were bound together near their common ex-
tremity, when they opened to form separate connexions for the poles of
a voltaic battery. When the battery was connected, and magnetic
needles placed m different positions, they behaved precisely as they
would do on the surface of the earth, the induction set up by the elec
trified wire being a perfect imitation of that which exists on the globe.

The opposite effect to that
already described viz., the
rotation of one pole of a
magnet round the electri-
fied wire, was also arranged
by Faraday in the following
manner. (Fig. 205.)

In the examination of the
magnetic phenomena ob-
tained from wires trans-
mitting a current of elec-
tricity, it should be borne
in mind that any conducting
medium which forms part of
a closed circuit i.e., any
conductor, such as charcoal,
saline fluids, acidulated
water, which form a link
in the endless chain re-
quired for the path of the
electricity, will cause a
magnetic needle placed near
it to deviate from its natu-
ral position.

These positions of the
electrified wire and the
magnetic needle are of
course almost unlimited,
and in order to assist the
memory with respect to the
fixed laws that govern these

Fig. 205. IT s. A little magnet floating in mercury
contained in the glass A A; the north pole is allowed
to float above the surface of the quicksilver, and the
south pole is attached to the wire passing through
the bottom of the glass vessel. The electricity passes
in at B, and taking the course indicated by the arrows
travels through the glass of quicksilver to the other
pole of the battery at c. Directly contact is made
with the battery, the little magnet rotates round the
electrified wire, w. The dotted line shows the level of
the mercury in glass.

relative movements, Monsieur Ampere has suggested a most useful
mechanical aid, and he says : " Let the observer regard himself as the
conductor, and suppose a positive electric current to pass from his head
towards his feet, in a direction parallel to a magnet ; then its north
pole in front of him will move to his right side, and its south pole to
his left.

" The plane in which the magnet moves is always parallel to the plane
in which the observer supposes liimself to be placed. If the plane of his

ELECTRO-MAGNETIC ROTATION.

215

chest is horizontal, the plane of the magnet's motion will be horizontal,
but if he lie on either side of the horizontally-suspended magnet, his
face being towards it, the plane of his chest will be vertical, and the
magnet will tend to move in a vertical plane."

This very lucid comparison will be seen to apply perfectly to the
direction of the rotations in Tigs. 203 and 205.

The whole of this apparatus is
made in the most elegant and
finished manner by Messrs.Elliott,
of 30, Strand; and by a modi-
fication of the latter arrangement
(Fig. 206), the opposite rotations
of the opposite poles of the mag-
nets round the electrified wire, are
shown in the most instructive
manner. The apparatus (Fig.
206) was devised oy the late Mr.
Francis Watkins, and consists of
two flat bar magnets doubly bent
in the middle, and having agate
cups fixed at the under part of
the bend (by which they are sup-
ported) upon upright" pointed
wires, the latter being fixed
upright on the wooden base of
the apparatus, and the magnets
turn round them as upon an axis.

Two circular boxwood cisterns,
to contain quicksilver, are sup-
ported upon the stage or shelf
above the base. A bent_ pointed wire is directed into the cup of each
magnet, the ends of which dip into the mercury contained in the box-
wood circular troughs on the stage. By using a battery to each magnet,
and taking care that the currents of electricity flow precisely alike, they
will then rotate in opposite directions.

Directly after the ingenious experiments of Faraday became known, a
great number of electro- magnetic engine models were constructed, and
many thought that the time was fast approaching when steam would
be superseded by electricity; and really, to see the pretty electro-
magnetic models work with such amazing rapidity, it might be supposed
that if they were constructed on a larger scale, a great amount of hard work
could be obtained from them. This idea, however, has been proved to be a
fallacy, for reasons that will be presently explained. The figure on p. 216
displays two of these engines, one of which represents the rotation
of electro-magnets within fovrjixed steel magnets, and the other the
rotation of steel magnets by the fixed electro-magnets. The latter
(No. 2) moves with such o;reat velocity, that unless the strength of the
battery is carefully adjusted, the connexions are soon destroyed. (Fig. 207.)

Fig. 206. A. Wire conveying the current
of electricity. B B. The magnets balanced on
points rotating round the wires.

21G

OY'S PLAYBOOK OF SCIENCE.

Fig. 207. No. 1 consists of vertical permanent steel magnets and horizontal soft-iron
electro-magnets which rotate.

No. 2 consists of two fixed soft-iron electro-magnets, and four bent permanent steel
magnets, which rotate, in both cases of course, only when connected with the battery.

Considering the prodigious power or pull of a soft-iron electro-
magnet, and its capability of supporting considerable weight, the most
reasonable expectations of success might be entertained with machines
acting by the direct pull. It was, however, discovered that they soon
became inefficient, from the circumstance that the repeated blows re-
ceived by the iron so altered its character, that it eventually assumed
the quality of steel, and had a tendency to retain a certain amount of
permanent magnetism, and thus to interfere with the principle of making
and unmaking a magnet. It was this fact that induced Professor Jacobi,
of St. Petersburg, after a large expenditure of money, to abandon
arrangements of this kind, and to employ such as would at once produce
a rotatory motion. The engine thus arranged was tried upon a tolerably
large scale on the Neva, and by it a boat containing ten or twelve
people was propelled at the rate of three miles an hour.

Various engines have been constructed bv Watkins, Botta, Jacobi,
Armstrong, Page, Hjorth ; the engine made by the latter (Hjorth) ex-
cited much attention in 1851-52, and consisted of an electro-magnetic
piston drawn within or repelled from an electro-magnetic cylinder ; and
by this motion it was thought that a much greater length of stroke
could be secured than by the revolving wheels or discs, but the loss of
power (not only in this engine, but in others) through space is very
great, and the lifting power of any magnet is greatly reduced and

ELECTRO-MAGNETIC MACHINES. 217

altered at the smallest possible distance from its poles. This loss of
power is therefore a great obstacle in the way of the useful application
of electro-magnetic force, and can be appreciated even with the little
models, all of which may be stopped with the slightest friction, although
they may be moving at the time with great velocity.

In the second place, supposing the reduced force exerted by the two
magnets, a few lines apart, was considered available for driving
machinery, the moment the magnets begin to move in front of one
another there is again a great loss of power, and as the speed increases,
there is curiously a corresponding diminution of available mechanical
power, a falling-off in the duty of the engine as the rotations become
more rapid. In the third place, the cost of the voltaic battery, as com-
pared with the consumption of coal in the steam-engine, is very startling,
and extremely unfavourable to electro-magnetic engines.

Mr. J. P. Joule found that the economical duty of an electro-magnetic
engine at a given velocity and for a given resistance of the battery is
proportioned to the mean intensity of the several pairs of the battery.
With his apparatus, every pound of zinc consumed in a Grove's battery
produced a mechanical force (friction included) equal to raise a weight
of 331,400 pounds to the height of one foot, when the revolving magnets
were moving at the velocity of eight feet per second. Now, the duty of
the best Cornish steam-engine is about one million five hundred thousand
pounds raised to the height of one foot by the combustion of each pound
of coal, or nearly five times the extreme duty that could be obtained
from an electro-magnetic engine by the consumption of one pound of
zinc. This comparison is therefore so very unfavourable, that the idea
of a successful application of electricity as an economic source of power,
is almost, if not entirely abandoned.

By instituting a comparison between the different means of producing
power, it has been shown that for every shilling expended there might be
raised by

Pounds.

Manual power . . . 600,000 one foot high in a day.

Horse 3,600,000

Steam 56,000,000

Electro-magnetism . 900,000

A powerful magnet has been compared to a steam-engine with an
enormous piston but with an exceedingly short stroke. Although
motive power cannot be produced from electricity and applied success-
fully to commercial purposes, like the steam-engine, yet the achievements
of the electric telegraph as an application of a small motive power must
not be lost sight of, whilst the fall of the ball at Deal and other places,
by which the chronometers of the mercantile navy are regulated, as also
the means of regulating the time at the General Post Office and various
railway stations, are all useful applications of the power which fails to
compete in other ways with steam.

218

CHAPTER XVII.

THE ELECTRIC TELEGRAPH.

THE engineering and philosophical details of this important instrument
have grown to such formidable dimensions, that any attempt (short of
devoting the whole of these pages to the subject) to give a full account
of the history and application of the instrument, the failures and successes
of novel inventions, and the continued onward progress of this mode
of communication, must be regarded as simply impossible, and there-
fore a very brief account of the principle only will be attempted in these
pa^es.

For the complete history of the discovery and introduction of the
principle of the Electric Telegraph the reader is referred to the Society
of Arts Journal (Nos. 348-9, vol. viii.), where it is stated that it is half
a century, dating from August, 1859, since the first galvanic telegraph
was made. "It was the Russian Baron Schilling's electro-magnetic
telegraph which, without its being known to be his, was brought to
London, and caused the establishment of the first practically useful
telegraph lines, not only in Great Britain, but in the world." Dr.
Hamel says : " The small sprout nursed on the Neva, which had been
exhibited on the Rhine, and thence brought to the Thames, grew up
here to a mighty tree, the fruit-laden brandies of which, along with
those from trees grown up since, extend more and more over the lands
and seas of the Eastern hemisphere, whilst kindred trees planted in the
Western hemisphere have covered that part of the world with their
branches, some of which will, ere long, be interwoven with those in our
hemisphere."

The first telegraph line in England was constructed by Mr. Cooke
from Paddington along the Great Western Railroad to West Drayton
in 1S38-39 ; and it must be remembered that it was in February, 1837,
that Mr. Cooke first consulted Professor Charles Wheatstoue, having
previously visited Dr. Faraday and Dr. Roget, and on the 19th
November, 1837, a partnership contract was concluded between Messrs.
Cooke and Wheatstone.

To the distinguished philosopher, Professor Wlieatstone, the merit of
the ingenious construction of the vertical-needle telegraph is due;
whilst Mr. Cooke's name will always be associated with the practical
establishment of the first telegraph lines in England. The first line in
the United States, from Washington to Baltimore, was completed in
1844, being arranged and worked by Professor Morse.

In British India, in April and "May, 1839, the first long line of
telegraph, twenty-one miles in length, and embracing 7000 feet of
river surface, was constructed by Dr. (now Sir William) Q'Shaughnessy

THE ELECTRIC TELEGRAPH. 219

The construction of the electric telegraph may be considered under
three heads :

1st. The Battery, the motive power.
2nd. The Wires, the carriers of the force.
3rd. The Instruments to be worked the bell and the needle telegraph.

THE BATTERY.

The construction and rationale of the batteries generally in use have
been explained in another part of this work ; those used for telegraphic
purposes consist of one or more couples, of which zinc is one, the second
being copper, silver, platinum, or carbon. Each couple is termed an
element, and a series of such couples a battery.

The batteries employed chiefly on the English lines consist of a plate
of cast-zinc four inches square and T 3 6-ths of an inch thick, attached by a
copper strap one inch broad to a thin copper plate four inches square.
The zinc is well amalgamated with mercury. Twelve of these couples
are arranged in a trough of wood, porcelain, or gutta-percha, divided by
partitions into twelve water-tight cells, 1 men wide. The zinc and
copper preserve the same order and direction throughout, and when
arranged, the trough is filled with the finest white sand, and then
moistened with water previously mixed with five per cent, by measure of
pure sulphuric acid. This mode of applying the acid is the clever prac-
tical improvement of Mr. Cooke, and prevents any inconvenience from
the spilling of the acid, and at the same time renders the battery quite
portable. The voltaic arrangement thus prepared is found to remain
in action for several weeks, or even months, with the occasional addition
of small quantities of acid, and answers well for working needle tele-
graphs in fine and dry weather. In fogs and rains, at distances ex-
ceeding 200 miles at most, their action is not so perfect, and a vast
number of couples must be employed, 144 to 288 being frequently in
use. In Erance, Prussia, and America, sand batteries do not appear to
answer, and Daniell's arrangement is preferred. Sixty couples suffice in
France for some of the long lines viz., from Paris to Bordeaux, 284
miles ; Paris to Brussels, 231^ miles ; and in fact, the advantages of
the Daniell's battery have become so apparent, that they are now being
used on English lines. In Prussia, Bunsen's carbon battery is much
used ; in India, a modification of Grove's battery is preferred, the zinc
being acted upon by a solution of common salt in water. Two of these
elements were found sufficient to work a line of forty miles totally un-
insulated, and including the sub-aqueous crossing of the Hooghly River,
6200 feet wide.

The continual energy of the battery, whatever may be its construc-
tion, depends on the circulation of the electricity, the object being to
pass the force from the positive end of the series through the wires,
back again to the negative extremity of the voltaic series.

The wire (the carrier of the force) must be continuous throughout,
unless, of course, water or earth forms a part of the endless conducting
chain.

220

BOY'S PLAYBOOK OF SCIENCE.

THE CONDUCTING WIRES.

These roads for the electricity may be of any convenient metal, and
the one preferred and used is iron, which is well calculated from its
great tenacity (being the most tenacious metal known) and cheapness

to convey the electricity, al-
though it is not such a good
conductor as copper, and
offers about six times more
resistance to the flow of the
current than the latter metal.
The wire does not appear to
be made of iron, because
it is galvanized or passed
through melted zinc, which
coats the surface anddefends
it from destructive rust,
at the same time does not
destroy its valuable property
of tenacity or power of re-
sisting a strain. About one
ton of wire is required for
every five miles, and to sup-
port this weight, stout posts
of fir or larch are erected
about fifty yards apart, and
from ten to twenty-five feet
high . At e verv quarter
mile, on many lines, are
straining - posts with
ratchet wheel winders,
for tightening the
wires. On some of the
lines the wires are at-
tached to the posts by
side brackets carrying
the insulators invented
by Mr. C. V. Walker,
which are composed
of brown salt-glazed
stoneware of the hour-
glass shape, as shown
in the drawing. (Fig.
208.)

There are some ob-
jections to the hour-
glass .insulators, and
they have been modi-
Fig. 209. Clark's insulator. fied by Mr. Edwin

Fig. 208. Walker's insulator.

THE ELECTKIC TELEGKAPH.

221

Clark, who employs a very strong stone-ware hook open at the side,
so that the wire can be placed on the hook without threading, and the
hooks can be replaced in case of breaking, without cutting the tele-
graph wire, which is securely fastened to each insulator by turns of
thinner wire. An inverted cap of zinc is used to keep the insulator
dry. (Fig. 209.)

In India the conductor is rather a rod than a wire, and weighs about
half a ton per mile ; it is erected in the most substantial manner, and
many miles of the rod are supported on granite columns, other portions
on posts of the iron-wood of Arracan, or of teak.

The number of wires required by the electric telegraph often puzzles
the railway traveller, and people ask why so many wires are used on
some lines and so few on others ? The answer is very simple : they are
for convenience. Two wires only are required for the double needle
telegraph, and one for the single needle instrument. But as so many
instruments are required at the terminal stations, an increased number
of wires, like rails for locomotives, must be provided; thus, on the
Eastern Counties, seven wires are visible, and are thus employed. The
two upper wires pass direct from London to Norwich ; the next pair
connect London, Broxbourne, Cambridge, Brandon, Chesterfield, Ely;
the third pair all the small stations between London and Brandon ; and
the seventh wire is entirely devoted to the bell.

If the earth was not a conductor of electricity, and employed in the
telegraphic circuit, four wires would be required for the double needle
telegraph, and two for the single instrument. To understand this, let
us suppose a battery circuit extending from Paddington to the instru-
ment at Slough, and the wire returning from Slough to Paddington, it
is evident that one wire would take the electricity to Slough, and the
other return it to London, as in the diagram below. (Fig. 210.)

LONDON

SLOUGH

Fi#. 210. A. The battery. B. The instrument. The arrows show the passage of the
electricity to the single needle telegraph instrument by one wire, and the return current
fly the other.

If the whole of the return wire is cut away except a few feet at each
end, which are connected by plates of copper with the damp earth, the
current not only passes as before, but actually has increased m intensity,
and will cause a much more energetic movement of the needle in the
telegraph instrument. (Fig. 211.) These plates are called "Earth
Plates ;" and Steinheil, in 1837, was the first who proved that the earth
might perform the function of a wire.

222 BOY'S PLAYBOOK OF SCIENCE.

Fig. 211. A. The battery. B. The instrument, c. Earth plate at Slough. D. Earth
plate at London. The arrows show the direction of the electric current.

It must be obvious that a message may be received at any station
without a battery, but in order to be able to return an answer, every
station must have its own battery.

Ingeniously-constructed lightning-conductors are attached to the posts
which carrv the wires, so that in case of a storm, the natural electricity
is conveyed to the earth, whilst the voltaic electricity artificially pro-
duced pursues its own course without deviation. Protectors are also
required for the instruments at the stations, and the plan devised by
Mr. Highton is thus described by the inventor :

" A portion of the wire circuit say for six or eight inches is enve-
loped in blotting-paper or silk, and a mass of metallic filings, in con-
nexion with the earth, is made to surround it. This arrangement is
placed on each side of the telegraph instrument at a station. When a
flash of lightning happens to be intercepted by the wires of the tele-
graph, the myriads of infinitesimally fine points of metal in the filings
surrounding the wire at the station, on having connexion with the
earth, at once draw off nearly the whole charge of lightning, and carry
it safely to the earth."

THE INSTRUMENTS TO BE WORKED THE BELL AND THE TELEGRAPH.

The bell or alarum resembles in construction that of an ordinary
clock, and is in fact a piece of clockwork wound up and ready to ring
a bell, when the detent or preventive is removed. The detent is con-
nected with a piece of soft iron placed before an electro-magnet, and
directly the current passes, the electro-magnet attracts the soft piece of
iron attached to a perpendicular lever which the bell-crank lever rests
upon ; the detent is removed, and the bell rings, and again stops when
the current of elsctricity ceases to pass.

One of the most simple alarum clocks is a common American clock,
wound up daily. A small electro-magnet surrounded with thick wire
is placed below a moveable piece of tinned iron, so that when this is
attracted, the fly of the clock is released, and its bell tolls unceasingly

THE BELL OE ALARU:

223

the magnet is excited. This
arrangement is employed by Sir W.
O'Shaughnessy in the Indian tele-
graph system. (Fig. 212.)

It will readily be comprehended
from this description that the alarum
is sounded by ordinary mechanism,
and that the duty of the current of
the electricity is simply comprised in
the act of removing the lever and
liberating machinery, which may be
large or small; and if it were
thought necessary, the bells of the
great clock-tower of the Houses of
Parliament, which chime the quar-
ters, or even "Big Ben" himself
(when his constitution is restored),
could be rung by a person at York
or Edinburgh, supposing wires, bat-
teries, and a powerful electro-
magnet with a detent mechanism
for the bells, were properly arranged
and connected with the. clock-
work.

la certam cases, Mr. Charles V. *
vy alker states that a single and dis- liberates the detent,
tinct wire is used for the bell only,
with his special mechanism, called the ringing key. If the bell was al-
ways on the same wire as the needle-coil, the bell would not only call the
attention of, but seriously annoy the clerk (unless, of course, he hap-
pened to be a very deaf person) by its ringing whilst he was reading
the signals of the needle. The nuisance is prevented by what is termed
joining over or making the short circuit in fact, by providing for the
current a shorter and much more capacious road to the needle coil than
by going through that of the bell-magnet, which is made with very
fine wire; and the control of the short circuit is put in the hand's
of the clerk.

COOKE AND WHEATSTONE'S DOUBLE NEEDLE TELEGRAPH.

The principle of this instrument, as already explained, is involved in
the elementary experiment of Oersted viz., the deflection of a mag-
netic needle from the inside of a coil of wire conveying a
current of electricity, and as it is difficult to give a good de-
scription and drawing of the interior of the instrument that can
really be understood, it may be sufficient to state that the handles
give the operator the power of reversing the current of electricity,
so that the needles are deflected with, the utmost certainty to

224:

BOY'S PLAYBOOK OF SCIENCE.

one side or the other, cither separately or simultaneously. (Eig.
2] 3.)

Fig. 213. The letters of the alphabet, figures, and a variety of conventional signals, are
indicated by the single and combined movements of the needles on the dial. The left-
halid needle moving once to the left indicates the +, which is given at the end of a word.
Twice in the same way, A ; thrice, B ; first right, then left, c ; the reverse, D. Once direct
to the right, E ; twice, F ; thrice, G. In the same order with the other needle for H, i, K,
t, M, H, o, P. The signals below the centre of the dial are indicated by the parallel move-
ments of both needles simultaneously. Both needles moving once to the left indicate E ;
twice, s ; thrice, T. First right, then left with both, u ; the reverse, v. Both moving once
to the right, \v ; twice, x ; thrice, T. The figures are indicated in the same way as the
letters nearest to which they are respectively placed. To change from letters to figures the
operator gives H, followed by the +, which the recipient returns to signify that he under-
stands. If, after the above signs (H and +) were given, c B H L were received, 1845 would
be understood. A change from figures to letters is notified by giving i, followed by the + ,
which the recipient also returns. Each word is acknowledged. If the recipient under-
stand, he gives B ; if not, the +, in which case the word is repeated. Attention to a com-
munication by this instrument is called by the ringing of a bell (of any size), which is
effected through the agency of an electric current. The upper case contains the bell.

Sir "W. O'Shaughnessy, in his excellent work on the electric telegraph
in British India, gives a description of a telegraphic instrument of re-
markable simplicity, which is successfully employed in India, and is

O'SHAUGHNESSY'S SIMPLE TELEGRAPH INSTRUMENT. 225

highly spoken of by Mr. E. V. Walker and other gentlemen practically
acquainted with the working of telegraphs. It consists of a coil of fine
wire on a card or ivory frame, a magnetic needle with a li^ht index of
paper pasted across it ; two stops of thin sheet lead to limit the vibra-
tions of the index ; a supporting board eight inches square, and a square
of glass in a frame of wood, or a common glass tumbler placed over it as
a shade, to prevent the index being moved by currents of air. It is
stated that the office boys, with the assistance of a native Indian
carpenter, make up these telegraphs at a price not exceeding two
shillings each.

In England of course they would be more expensive; but the
simplicity and perfection of the arrangement are so much to be com-
mended that we give the details for the benefit of those boys who might
wish to establish a telegraph on a small scale for amusement.

THE FRAME.

This is a piece of mahogany eight inches square and one inch thick,
with a hollow groove cut in its centre two inches and a half long, half an
inch wide, and a quarter of an inch deep ; a ledge of the same wood
one inch wide and half an inch deep surrounds the frame, leaving the
inner surface seven inches square ; this is stained black with ink to
make the motions of the index more conspicuous.

THE COIL.

This consists of fifty feet of the finest silk-covered copper wire wound
on a frame of card two inches long, half an inch broad, three-eighths
deep in the open part.

An edge or flange of card, three-eighths of an inch wide, is attached
to it at each side to keep the wire in its place. The frame may be of
thin wood or ivory, and the winding of the wire commences at the
lower left corner, and it is coiled from left to right, as the hands of a
watch would move in the same plane. (Fig. 214.)

Fig. 214 ThecoiL

Two inches of each end of the coil wire are now stripped of their silk
covering by being rubbed with sand-paper. The coil is mounted in the
frame by inserting its lower edge or flange in the groove, so that the
lower part or floor of the inside of the coil is level with that of the

226

BOYS PLAYBOOK OF SCIENCE.

frame, as shown below, and it is now ready to receive the magnetized
needle. (Fig. 215.)

Fig. 215. The coil fitted into frame.
THE NEEDLE.

This is one inch long, one-twelfth of an inch wide, of the thinnest
steel, and fitted with a little brass cap turned to a true cone to receive
the point on which it is balanced. These needles are of hard tempered
steel, and are magnetized by a single contact with the poles of an
electro-magnet or other ordinary powerful magnet.

The magnet is now to be balanced on a steel point one-eighth of an
inch high ; these are nipped oif with cutting pliers from common sewing
needles, and soldered into a slip of thin copper three inches long, half
an inch wide. (Fig. 216.)

Fig. 216. A. The needle. B. The point on the slip of copper.

As the north end of the needle will be found to dip, it is advisable to

counteract this by touching the south end with a little shell-lac varnish,

which dries rapidly, and soon restores the needle to a perfect equilibrium.

The needle is completed for use by fixing to it an index of paper (cut

from glazed letter paper) two inches long, tapering from one-eighth of

an inch to a point, and
fastened at rignt angles
on to the needle with
lac varnish, so as to
be truly balanced, and
pointing the sharp end

to the east, when the

J needle placed on the
point settles due north
and south, its north
pole being opposite the
observer's right hand,
the observer facing west.
Fig. 217. The needle with the paper index. (Fig- 217.)

O'SHAUGHNESSY'S SIMPLE TELEGRAPH INSTRUMENT. 227

The coil frame is placed north and south, and the needle is now intro-
duced by sliding the end of the slip of copper into the opening in the
frame.

To limit the vibrations of the pap_er index a stop is placed at each
side. The stops are made of a strip of thin sheet-lead or copper, a
quarter of an inch broad, one inch and a half long, and turned up at a
right angle, so that one inch rests on the board and half an inch is
vertical. For ordinary practice these stops are placed each at half an
inch from the index.

The telegraph is placed in a box, which may have a piece of looking-
glass in the lid, so that the readings can be taken with the needle in the
vertical instead of the horizontal position, if required. (Fig. 218.)

A /

B //

M \\

!C" HI

N \\\

D ////

\\\

E V

P A

'K W

Q AV

e MII

R A\\

H W/

S. M

U \!\

T N

K W

U V /A\

W W

Y W/

X IV

zv////

Fig. 218. Box containing the telegraph, with the looking-glass hi the lid. A small
steel magnet is placed on or near the frame, if required, the south pole of this magnet
oeing opposite to the north pole of the needle in the telegraph coil. The bar is four inches
long, half an inch broad, three-sixteenths of an inch thick, and it is only used to counteract
any local deviation which may arise in using the instrument with miles of wire. It would
not be required under ordinary circumstances. The alphabet used is shown to the left.

The ends of the fine wire of the telegraph coil are joined on to the
wires from the reversing instrument, and this is connected with a voltaic
series of one or more elements, so that by the employment of the
reverser the needle is caused to move right or left at pleasure. The

228 BOY'S PLAYBOOK OF SCIENCE.

white paper index on the black ground can be followed with the greatest
certainty, and Sir W. O'Shaughnessy states that with this instrument a
telegraph clerk may read at the rate of twenty words per minute with a
double needle wire, being equal to forty words per minute.

THE EEVERSEB,

consists of a block of wood, two inches and a half square, in which
four hollows, half an inch deep, are cut, and these hollows are joined
diagonally by copper wires let into the substance of the wood, and most
carefully insulated from each other by melted cement, but exposing
a clean metallic surface in each cell, which is filled with mercury.
(Tig. 219.)

Pig. 219. Block of wood with four holes ; the positive terminal is connected with the
holes A and B, the negative with c and u ; the hollows are filled with mercury. T T are the
wires from the telegraph box, and it is obvious that by dipping them alternately into c B
and A D the current is reversed, and the needle deflected right or left at pleasure.

In practice a more elaborate reverser is employed, but to demonstrate
the principle the simple block above described is quite sufficient.

With the telegraph placed at the top of a house, or in a distant
cottage, and a single cell of Grove's battery, or at most two, for any
short distances, with the reverser, messages may be passed with great
rapidity from the bottom of the house to the top, or from a mansion to
the lodge, it being understood that a battery, reverser, and telegraph,
are required at both places where messages are received and answered;
but if no answers are required, the battery and reverser are placed at
one end of the wire in the house, and the telegraph at the other ex-
tremity in the cottage, and earth plates may be arranged to return the
current, or another wire used for that purpose. *

Whilst lauding to the utmost the invention of the electric telegraph,
we must remember " there is nothing new under the sun," and that
after all Nature claims the principle of telegraphing, and with the silent
gesture, the speaking eye, interpreted and answered by others, she pro-
claims herself to be the originator of communication by signs. Whilst

THE ELECTRIC TELEGRAPH.

229

the language of flowers, and the mournful requirements of the deaf and
dumb in the use of the finger alphabet, show how readily man has
adopted the important principle, till he has brought it to the highest
state of perfection in the electric telegraph.

When the telegraph was first adopted on the Great "Western Railway,
the most ridiculous ideas were formed of its capabilities, and many persons
firmly believed that the wires were used for the purpose of dragging
letters and different articles from station to station. " Wife," said a man,
looking at the telegraph wires, " I don't see, for my part, how they send
letters on them wires, without tearin' 'em all to bits." "Oh, you
stupid!" exclaimed his intellectual spouse ; "why, they don't send the
paper: they just send the writin' in a fluid state."

Fig. 220. One of the ideas of telegraphic communication.

230 BOY'S PLAYBOOK OF SCIENCE.

CHAPTER XVIII.

RUHMKORFF'S, HEARDER'S, AND BENTLEY'S COIL APPARATUS.

IN the course of the popular articles on frictional and voltaic electricity,
it has already been mentioned that whilst the intensity effects such as
the capability of the spark to pass through a certain thickness of air,
or the production of the peculiar physiological effect of the shock
belong especially to the phenomena of frictional electricity, they are
not apparent with the quantity effects, such as may be produced oy an
ordinary voltaic battery, unless the latter consists of an immense
number of elements, such as the famous water battery of the late
respected Mr. Crosse, which consisted of two thousand five hundred
pairs of copper and zinc cylinders, well insulated on glass stands, and
protected from dust and light. If, however, the feeble intensity current
of voltaic electricity, from four or five elements, is permitted to pass into
a coil of a peculiar construction, fitted with a condenser, and manu-
factured either by Ruhmkorff of Paris, or Mr. Hearder of Plymouth, then
the most remarkable effects are producible, which have created quite a
new and distinct series of phenomena, and further established in the
most satisfactory manner the connexion between the electricities derived
from friction and chemical action.

The construction of these coils does not differ very materially, and
great merit is due to Messrs. Ruhmkorff, Hearder, and Bentley, who
have separately and independently worked out the construction of the
most formidable machines of this class. In a letter to the author
Mr. Bentley says :

" I commence the formation of my coil by using as an axis an iron
tube ten inches long and half an inch diameter ; around this is placed a
considerable number of insulated iron wires the same length as the tube,
and sufficiently numerous to form a bundle one inch and three quarters
diameter. This core is wrapped carefully in eight or nine layers of
waxed silk, the necessity of which will be obvious presently.

" My primary helix, which is formed of thirty yards of No. 14 cotton-
covered copper wire, is wound carefully on this core, and consists of
two layers, each layer being carefully insulated one from the other by
waxed silk, for I find that if a wet string or fine platinum wire be con
nected with the two ends of the primary wires ot an induction coil in
action, there is scarcely an indication of an induced current to be
obtained from the secondary wire. That this is not owing to any
decrease of magnetic power is proved by testing the iron core before
and after the experiment, but is simply owing to the central magnet or
coil exerting the whole of its inductive powers upon the nearest closed
circuit ; it therefore follows that if the two layers of primary wire are
connected by the cotton covering becoming moist, the whole of the

THE ELECTRO-MAGNETIC COIL MACHINE. 231

induced current will take this path instead of traversing the secondary
wire.

" Before describing my secondary wire I must again call attention to
the important fact that the magnetism of the iron exerts its inductive
power upon the nearest conducting medium ; and I have constructed
an instrument to demonstrate this fact. It consists simply of an ordi-
nary coil, giving the third of an inch spark, but having the four inner
layers of secondary wire brought out separately. Now, I find that
when I keep the ends of this wire separate 1 obtain nearly the third of an
inch spark, but when I connect them metallically I can obtain no intensity
spark whatever from the seventeen coils which surround them.

" It follows from this that before winding the secondary wire the
striking distance of a single layer must be ascertained, and I find that
with my coil I can get a spark one- tenth of an inch long from one coil
of wire, and sufficiently intense to penetrate with facility six layers of
waxed silk.

" Waxed silk is therefore unsuited for the insulation of large coils,
and I find, after numerous experiments, that there is no substance so
fitted for the purpose as gutta-percha tissue, and I use five layers of
this substance to each layer of wire.

"The secondary helix then consists of three thousand yards of No. 35
silk-covered copper wire, and is insulated in the manner described above ;
but as I do not use cheeks to my coil it assumes the form of a cylinder
having rounded ends.

" For the protection of this instrument I place it in a mahogany box
of the proper size, and it is supported and retained in its position by an
iron rod, which is thrust through the hollow axis of the core and the
two ends of the box, leaving half an inch of the iron projecting to work
the contact breaker, which is fixed to one end of the box, while the
two ends of the secondary wire are brought out of the other through
gutta percha tubes.

" The condenser is contained in a separate box, and is formed of
one hundred and twenty sheets of tinfoil between double that number of
sheets of varnished paper, the alternate sides of the foil being brought
out and connected to appropriate binding screws.

" This condenser forms a convenient stand for the coil, and can be
used for many interesting experiments."

The shock which the condenser gives to the system depends in a
great measure on the size of the coatings. The primary wire alone does
not produce any physiological results, or at least very feeble ones. Mr.
Hearder's coil is wound on a bobbin six inches in length, and four inches
and a half thick, and includes three thousand yards of covered wire
(No. 35). The iron core consists of a bundle of small wires capped
with solid ends, and the sparks obtained from it were five-eighths of an
inch in air when the primary coil was excited by_ four pairs of Grove's
series ; and when connected with the Ley den jar, the most vigorous
and brilliant results were produced. The condenser is made of car-
tridge paper, coated in the proper manner with tinfoil. The secon-

232

BOY S PLAYBOOK OF SCIENCE.

dary coil is quite independent of the primary one, which is laid on in
different lengths, so that the coil can be adjusted to any battery power,
whether for quantity or intensity.

For the successful exhibition of the capabilities of the machine, it is
required to perform the experiments in a darkened room. (Fig. 221.)

Fig. 221. Kuhmkorff's apparatus. A B. The coil, containing more than a mile of in-
sulated wire. The stand it rests upon, and with which it is in communication, contains
the condenser.

In using this apparatus, eight pairs of Grove's battery will be quite
sufficient to produce the effects, and the greatest care must be taken to
avoid the shock, which is most severe and painful, and might do a great

deal of harm to a weakly,
sensitive, and nervous
person. To avoid any
accidents of this kind,
the convenient arrange-
ment at one end shown
in Fig. 222 must be
carefully attended to,
and when manipulating
with any part of the
apparatus, if the bat-
tery is attached, the
contact should first be
Fig. 222. One end of RuhmkorfTs coil. B B. Con- broken by bringing the

nexion to receive the battery wires. A is the cylinder, ivory (the non-COnduct-
one half of which is ivory and the other metal. In this ino^ narf nf tVip rv-
position no shock can be received, because the electricity }?=>/ P, 1 ooo\ ^
is cut off by the ivory from the coil. Under A (Fig. 222) in

communication with the
conductors, B B, where the wires from the battery are attached.

First Experiment.

It is at the other extremity of the coil that the experiments are per-
formed; for instance, if an exhausted globe is connected with the
pillars B B (Fig. 223), and the connexion made with the battery, a
beautiful faint blue light is apparent on one of the knobs and wires, and
by reversing the current the light appears on the other knob and wire.

RUHMKORFF'S INDUCTIVE APPARATUS.

233

This effect is supposed to resemble some
of those magnificent streaks and undu-
lations of coloured light called the Au-
rora Borealis; and,if the globe is removed
from the foot, and screwed onto the air-
pump plate, and a little alcohol, ether,
naphtha, or turpentine placed on wool
or tow is held to the air-pump screw,
where the air usually rushes in, and the
cock turned, so that the vacuum is de-
stroyed, a quantity of the vapour will
necessarily fill the globe ; and if this is
once more exhausted, it presents a
different appearance, being full of co-
loured light (varying according to the
spirit employed) but stratified and of
a circular form. (Fig. 223.)

Fig. 223. End of coil where the experiments are performed. B B. Connecting screws
and wires passing to the exhausted globe, c. The screws are supported on insulating
glass pillars, p p.

Second Experiment.

The appearance of these bands of light is modified by the nature of
the glass tubes employed, and the subject has been carefully investigated
by Mr. Gassiott. At the last meeting of the British Association at
Aberdeen, Dr. Robinson made various experiments, arranged by Mr.
Ladd, for the purpose of showing the connexion between these minia-
ture effects of bands of light in tubes containing various gases, and the
phenomena of the Aurora Borealis. The title of the discourse, which
was specially delivered in the Music Hall by the learned Doctor,
was " On Electrical Discharges in Highly-rarefied Media," and it-
was illustrated by experiments prepared by Mr. Gassiott and Mr.
Ladd.

The kind of tubes employed may be understood from the next figure.
They are made in Germany, and by approaching a powerful magnet to

234:

BOY'S PLAYBOOK OF SCIENCE.

the outside of any of
the glass tubes wliilst
the bands of light are
being produced, the
most remarkable mo-
difications of them are
obtained. Mr. Ladd
has mounted one of
these tubes in a rota-
tory arrangement si-
milar to that de-
scribed at page 186.
When connected with
the coil and battery,
it furnishes one of the
most lovely " elec-
tric fire- wheels" that
can possibly be de-
scribed. (Fie. 224.)
Mr. Grove placed a
piece of carefully-
dried phosphorus m
a little metallic cup,
and covered it with a

Fig. 224. A, B, c, D, B, p. Various tubes of different kinds of jar havin"" a Cap and
glass, and containing gases and vapours. Each tube has a rF. n nrr

platinum wire inserted at both ends, with which the contact is J e - . V re OVm g
made with the coil. The tube A contains mercury, which has the air Irom the re-
been boiled in it, and the air expelled. By moving the con- pojvpr and ra<stnnrr
ducting wire to G or H, the light which otherwise passes ?f 1Ve1 ' 3 ! P assm S
through the whole of the tubes stops at these points. the current of elec-

tricity through it

from the Ruhmkorff coil, he obtained a light completely stratified, and
blended transversely with straight but vibrating dark bands.

Third Experiment.

Fig. 226. Melting of the iron wire.

When two very thin iron
wires are arranged in the
upright pillars (Fig. 223),
and held sufficiently close to
each other, as in Fig. 225,
light passes from one to the
other. The wire from which
the light passes remains
cold, the otner becomes so
hot that it melts into a

little globule of liquid iron, and if paper is held between the wires it
rapidly takes fire. (Fig. 225.)

EXPERIMENTS WITH RUHMKOUFF S COIL.

235

Fourth Experiment.

Remove the break.
Attach two wires to
X X (Fig. 226). Hold
them so as at pleasure
to complete and inter-
rupt the galvanic circle.
Two other wires are at-
tached at P P, their
ends being about three-
quarters of an inch
asunder. When the cur-
rent is closed or broken
at A A, a spark passes
between BB. (Fig. 226.)

Fig. 226. The making and breaking of the circuit.

Fifth Experiment.

A Ley den jar may be charged and discharged with singular rapidity
when connected with the coil, and the snapping noise is so rapid, that it
produces a continuous sharp sound. (Fig. 227.) If a piece of paper

Fig. 227. A B. Leyden jar coated with tinfoil, and standing on any non-conductor,
such as gutta percha or the resinous or glass plate, c.

is held between the ball of the Leyden jar and the wire, it is instantly
perforated, but not set on fire.

236

BOY'S PLAYBOOK OF SCIENCE.

Sixth Experiment.

When the Leyden jar is coated with spangles of tinfoil, a spark
appears at each break, and the whole jar is lit up with hundreds of
brilliant sparks each time it is charged and discharged, and as this
occurs with amazing rapidity, the light is almost continuous. (No. 1.
Fig. 228.) The larger the Leyden jar, the shorter the spark, and vice
versa. By the employment of a nicely-made screw and inch-scale, the
distance between the discharging points connected with a Leyden jar
can be accurately determined ; and Mr. Hearder states that supposing a
Leyden jar has one square foot of charging surface, it will give a spark
of one inch in length, but if a smaller jar is used, with only half a square

Fig. 228. No. 1. Spangled Leyden jar. No. 2. Hoarder's apparatus for measuricg
the length of spark for Leyden jar and coil, r p. Glass pillars. No. 3. Two best forms of
spangles to paste on a Leyden jar.

foot of charging surface, the spark would be about one inch and a
quarter in length. (Fig. 228.)

Seventh Experiment.

The direction and rapidity of the current appear to influence greatly
the heating and fire-giving power of the coil, and the following experi-
ment, devised by Mr. Hearder, furnishes a curious illustration of this fact.

When the current passes in the direction of the arrows (Fig. 229),

HEARDER'S EXPERIMENTS.

237

the platinum wire remains perfectly cool whilst the gunpowder is fired ;
and the contrary takes place if the current is reversed viz., the gun-

Fig. 229. A. The coil. B. Hoarder's discharger, with thin platinum wire, p, hanging
between the points, c. Another discharger, and powder going off between the points
from the little table. The pillars of the dischargers are glass. The arrows show the
direction of the current of electricity.

powder does not blow up, but the platinum wire is heated. In the
second experiment, a Leyden jar is included in the circuit. (Fig. 229.)

Eighth Experiment.

Amongst so many beautiful experiments, it is somewhat difficult to
say which is the most pleasing, but for softness and exquisite colouring,
with the continuous vibrating motion of the flowing current of elec-
tricity, nothing can surpass " the cascade experiment." [This beautiful
experiment is usually termed "Gassiott's Cascade," and is thus de-
scribed by that gentleman. Two-thirds of a beaker glass, four inches
deep by two inches, are coated with tinfoil, leaving one inch and a half
of the upper part uncoated. On the plate of an air-pump is placed a
glass plate, and over it the beaker, covering the whole with an open-
mouthed glass receiver, on which is placed a brass plate having a thick
wire passing through a collar of leather ; the portion of the wire within
the receiver is covered with a glass tube ; one end of the secondary
coil is attached to this wire, and the other to the plate of the pump.
As the vacuum improves the effect is very surprising ; at first a faint
clear blue light appears to proceed from the lower part of the beaker
to the plate ; this gradually becomes brighter, until by slow degrees
it rises, increasing in brilliancy until it arrives at that part which is
opposite, or on a line with the inner coating, the whole being in-
tensely illuminated; a discharge then commences, as if the electric
fluid were itself a material body running over.] This result is ob-
tained by coating the inside of a handsome glass goblet with tinfoil,
and placing it under a jar fitted with a collar of leather and ball, and
arranged in the usual manner on the air-pump. Directly a vacuum is
obtained, the ball is moved down to the inside of the goblet, and the
wires from the coil being attached, a continuous series of streams of

238

BOY'S PLAYBOOK OF SCIENCE.

electric light seem to overflow the goblet all round the edge, and it
stands then the very embodiment of the brimming cup oi' fire, and
emblematical of the dangers of the wine-cup. (Fig. 230.)

If a

on the

Fie. 230. Guiiott'i Cascade.
Ninth Experiment.

piece of wood five inches long and half an inch square is placed
table of the discharger, and one wire brought on to the top edge

and the other ap-
preached to within

Burning tho plcco of wood moistened with tho
strongest nitric acid.

three inches of it,
and touching the
wood, and the
space between ilicm
moistened with UK;
strongest nitric ;idi I,
a curious effect is
visible from the
creeping along of
s the nre,\rhiohgradu-

.illy r;irl)oni/,(:,s and
burns MIC wood.
(Fig. 231.)

HEAUDEB'S EXPERIMENT**. 230

7i?0M Experiment.

A j?lass plate wetted with gain, and then sprinkled with v
filings of iron, zinc, lead, copper, &c., produces a very prettv effect of
ation a on/; of the conducting wires is moved over its surface,
c being in contact with the plate. The gum quickly
dries by putting the plate in a moderately-heated oven,

Eleventh Experiment.

When the continuous discharges from the Leyden jar are made to
pass through the centre of a large lump of crystal of alum, blue vitriol,
or fcrroprussiate of potash, &c,, the whole of the crystal is beautifully

the

Twelfth Experiment.

Thirteenth Experiment.
coil machines have been emloed for a

240

BOY'S PLAYBOOK OP SCIENCE.

by the administration of shocks. These may be so regulated as to be
hardly perceptible, or may be so powerful that the pain becomes abso-
lutely intolerable.

These coils are now made self-acting, and consist of two coils of
covered and insulated wire wound round a bundle of soft-iron wires,
with the necessary connecting screws for the voltaic battery. The con-
tact with the battery is made and broken with great rapidity by a simple
form of break, consisting of a tinned disc of iron held by a spring over
the axis of the bundle of iron wires ; and the continual noise of the
break, which is alternately attracted down to the bundle and brought
back by the spring, when the coil is in contact with the battery, demon-
strates" (without the pain of taking the shock) when the instrument is in
full working order.

The coil machine is not only useful in a medical point of view, but
when properly arranged offers a good reception to a run-away bell-
ringer, ana is an excellent preventive against illicit attempts at cheap
rides by small boys.

Tig. 233. Boy, evidently shocked, behind doctor's carriage provided with a
small coil machine.

241
CHAPTER XIX.

MAGNETO-ELECTRICITY.

Pig. 234. Clarke's magneto-electrical machine.

THE correlation of the physical forces, heat, light, electricity, magnetism,
and motion, is one of the most interesting subjects for study that can
be suggested to the lover of science. The examination of the precise
meaning of the term correlation, so ably considered by Professor Grove,
indicates a necessary mutual or reciprocal dependence of one force on
the other. Thus, electricity will produce heat, and vice versa; motion,
such as friction, produces electricity, and the latter, by its attraction
and repulsion, establishes itself as a source of motion. Electricity pro-
duces light, also magnetism, and contrariwise light is said to possess

242 BOY'S PLAYBOOK OF SCIENCE.

the power of magnetizing steel, whilst magnetism again produces light
and electricity. Such are the intimate connexions that exist between
these imponderable agents, and we may trace cause and effect and its
reversal amongst these forces, until the mind is lost in the examination
of the bewildering mazes, and is content to return to the beaten track
and work out experimentally the practical truths. We have had occa-
sion to notice in another part of this playbook the fact that a current
of electricity causes the evolution of magnetism in its passage through
various conducting media, and the truth lias been specially illustrated by
the various experiments in the chapter devoted to electro-magnetism.
In commencing this portion of electrical science, we have no new terms
to coin for the title of the discourse, as we merely reverse the other
when we examine the nature and peculiarities of

MAGNETO-ELECTRICITY.

The source of the power must necessarily be a bar or horseshoe-
shaped piece of steel permanently endowed with magnetism. If the
former is thrust into a cylinder of wood or pasteboard, around which
coils of covered copper wire have been carefully wound, so that the
extremities communicate with a galvanometer, an immediate deflection
of the needle occurs, which, however, quickly returns to its first posi-
tion, but is again deflected in the opposite direction on the withdrawal
of the steel magnet from the coil of copper wire. (Fig. 235.)

Pig. 235. A B. Coil of copper wire. c. Permanent bar magnet placed inside the
coil, when the galvanometer needle, D, is deflected.

The rapid entrance and exit of the steel magnet in the helix of copper
wire would be insufficient to produce any quantity of electricity, and
the ingenuity of man has been taxed to arrange a method by which a
magnet may be suddenly formed and destroyed inside a coil of insulated
copper wire. The difficulty, however, has been surmounted by several
ingenious contrivances, based on the principles first discovered by
Faraday ; and the one especially to be noticed is the revolution of a
coil of copper wire enclosing a piece of soft iron, called the armature,
before the poles of a powerful magnet. The first machine was invented

THE MAGNETO-ELECTRICAL MACHINE. 243

by M. Hypolyte Pixii, of Paris, and in 1833, Mr. Saxton improved
upon this machine, and three years afterwards, Mr. E. M. Clarke de
scribed a very ingenious modification of the electro-magnetic machine,
which is depicted at page 241 of this chapter. In this picture, the letter
A is the permanent fixed horseshoe magnets, which are very appro-
priately termed the battery magnets, because tney take the position
that would otherwise be occupied by a voltaic battery, and they are
indeed the prime source of the electrical power that is evoked. D is the
intensity armature which screws into a brass mandril seated between
the poles of the magnets A, motion being communicated to it by the
multiplying wheel, E. This armature or inductor has two coils of fine
insulated copper wire of 1500 yards in length, coiled on its cylinders,
the commencement of each coil being soldered to the bar D, from which
projects a brass stem, also soldered into D, carrying the break-piece H,
which is made fast in any position by a small binding-screw in a hollow
brass cylinder to which the other terminations of the coils, p p, are
soldered, these being insulated by a piece of hard wood attached to the
brass stem, o is an iron wire spring pressing against one end of the
hollow brass cylinder ; p is a square brass pillar ; Q is a metal spring
that rubs gently on the break piece H ; T is a copper wire for connecting
the brass pieces with the wood L between them, and out of which p
and o pass ; R E- are two handles of brass with metallic wires, the end
of one being inserted into either of the brass pieces connected with P
and o, and the other into the brass stem that carries the break H, delivers
a most severe shock directly the wheel is set in motion.

In Saxton's electro-magnetic machine, the permanent steel magnets are
placed horizontally instead of perpendicularly, and are composed of six
or more horseshoe-shaped pieces of steel. The armatures, or inductors,
or electro-magnets (for they consist of pieces of soft round iron with
wire wound round them), are two in number, and are adapted to
exhibit either quantity or intensity effects. The quantity armature is
constructed of stout iron, and covered with thick insulating wire. The
intensity armature is made of slighter iron, and covered with from one
thousand to two thousand yards of fine copper wire coated with silk.
The quantity armature is intended for the exhibition of results similar
to those which are procurable from a voltaic battery, such as the mag-
netic spark, inducing magnetism in soft iron, heating platinum wire.
The intensity armature is employed for the chemical decomposition of
water and other bodies, and likewise for the administration of those
terrible blows to the nervous system which cause strong men of the
mildest deportment to become painfully excited, and to make those
ejaculations which are so peculiar to the genus John Bull.

EXPERIMENTS WITH THE MAGNETO-ELECTRIC MACHINE.

First Experiment.

The decomposition of water by the passage of electricity from one
platinum plate to another, has already been illustrated at page 198. The

11 6

244

BOY'S PLAYBOOK OF SCIENCE.

same fact may likewise be displayed by the following arrangement of
the machine. (Fig. 236.)

Fig. 236. A. Apparatus for decomposing water and collecting the gases separately.
B B. Wires proceeding from the machine at M, N. Q, works on the single break, H.

Second Experiment.

The electric light obtained by the passage of the electricity from the
battery through the charcoal points, is also an effect that can be pro-
duced by magneto-electric machines, the wires leading from the points
A B being insulated by glass handles, and placed in the holes M N.
(Fig. 237.)

Fig. 237. The electric light obtained from the magneto machine.

EXPERIMENTS WITH THE MAGNETO MACHINE.

245

Fig. 238. Deflagration of iron wire.

Third Experiment.

The scintillation of iron wire
is one of the most pleasing expe-
riments with this apparatus, and
is performed by pressing gently
one end of a piece of thin iron
wire (attached by means of a
binding-screw to the upright bar A)
against the armature, D. (Fig.
238.)

Fourth Experiment.

The combustion of ether or
other inflammable spirit may
also be demonstrated with the
aid of this powerful appara-
tus, and the arrangement, in
common with the others employed
by Mr. Clarke, is shown in Eig.
2o9.

With the assistance of the mag-
neto-electric machine, telegraphic
communication may be conducted
without the assistance of a battery.
It has also been applied to the art of
electro-plating by Mr. J. P. Woplrich,
of Birmingham ; and whilst visiting
that place, the author had the oppor-
tunity of witnessing the arrangement
employed.

It consists of a very powerful
magneto-electric machine turned by a
steam-engine, and connected with the
large troughs containing the silvering
solution. If it is required to deposit
a thin coating of silver on the article,
a short period suffices for the action of
the machine, whilst a thick deposit of
the precious metal is only obtained by
the constant operation of the magnets
for several hours. At Mr. Wool-
rich's factory, the goods which were
being coated with silver were all kept in motion, moving slowly back-
wards and forwards in the trough by means of an eccentric con-

Fig. 239. The break is removed, and
the double blades, B, fixed in its place.
The brass cup, A, containing mercury is
so adjusted that the points will leave
the surface of the mercury when the
armature is vertical. Ether or alcohol

Hired on the surface is quickly in-
i by the electric spark.

246

BOY S PLAYBOOK OF SCIENCE.

nected with the same steam-engine that worked the electro-magnetic
machine. (Fig. 240.)

Fig. 240. Silvering and plating by the magneto machine,
turned by a steam-engine.

The magneto-electric telegraph patented by Mr. Henley in 1848,
offers another example of the application of the electric current induced
in electro-magnetic coils, when they rotate in close proximity to the
poles of a powerful steel magnet. This telegraph is now in con-
stant use by the English and Irish Magnetic Telegraph Company,
through a distance of more than 2100 miles. The whole length
of wires in use amounts to the astonishing quantity of 13,900 miles,
of which 6350 miles are hidden underground, ana 7500 conducted
above.

This telegraph is considered to be one of the simplest and most
economical yet Drought into practical working.

247

C H A I T E R XX.

DIA-MAGXE1ISM.

AT the end of the chapter devoted to the subject of light, will be found
an experiment devised and carried out by Dr. Earaday, in which it is
shown that if a bar of a peculiar glass (called after the inventor,
Faraday's heavy glass, or sikcated borate of lead) is subjected to the
inductive action of a very powerful electro-magnet, that it has the
power of changing the direction of a ray of polarized light transmitted
through it. This effect is not confined to the poles of an electro-
magnet, but is also perceptible (though in a diminished degree) with
ordinary magnets.

The result of this important experiment was communicated to the
Royal Society by Dr. Earaday on the 27th November, 1845, the enun-
ciation of the fact by this learned philosopher being, " that when ' the
Hne of magnetic force* is made to pass through certain transparent
bodies parallel to a ray of polarized light traversing the same body, the
ray of polarized light experiences a rotation." Now, " the line of mag-
netic force" means that continual flow of the magnetic current which
passes from pole to pole, and is indicated by iron filings sprinkled on
paper placed above the poles of a magnet, and usually termed magnetic
curves, or the curved lines of magnetic force. (Eig. 241.)

Pig. 241. The curved lines of magnetic force.

The heavy glass already alluded to, upon which the magnet exerts u
certain influence, is called

THE DIA-MAGNETIC

and by this term is meant a body through which the lines of magnetic
force are passing without affecting it like iron or steel. At page 212 is
a picture representing (at Eigs. 201 and 202) the direction of the
electricity and that of the magnetic current or whirl at right angles to
it If, then, Eig. 202 be considered as a piece of glass, the arrow A B

248

will show " the line of magnetic force," the point B being the north
pole, and the shaft A the south j)ole of the magnet, and the arrows
traced round will represent direction. This simple drawing expresses
the whole of the law of the action of the magnet on the glass, and if
kept in view, will give every position and consequence of direction re-
sulting from it.

The phenomenon of the affection of the beam of polarized light is im-
mediately connected with the magnetic force, and this is supposed to
be proved by the brightness of the polarized ray being developed
gradually, as the iron coiled with wire requires about two seconds to
acquire its greatest power after being connected with the battery.

In another experiment of Faraday's, where a beam of polarized light
was sent through a long glass tube containing water, and introduced as
a core inside a powerful electro-magnetic coil, the image of a candle
viewed with a proper eye-piece, appeared or disappeared as the battery
connexion was made or broken with the coil ; but this result is not
considered by many philosophers to be conclusive of the action of
magnetism on light, but rather as an alteration of the refracting power
of the medium through which the light passes. These experiments were
the precursors of the other effects of magnetism upon different kinds of
matter which Faraday discovered, and he commenced his examination
with a small bar of heavy glass suspended by a filament of silk between
the poles of an electro-magnet, and when the twisting or effects of
torsion had ceased, the battery was connected. Directly the current
passed, Faraday's keen eye detected a movement of the glass, and on
repeating the experiment, he discovered that the movement was not
accidental, but always took place in a certain fixed direction viz., a
direction at right angles to a line drawn across and touching the two
poles of a horseshoe-shaped magnet i.e., supposing the feeder or bit
of soft iron usually placed in contact with the poles of the horseshoe-
magnet to represent the " axial line" any line drawn across it at right
angles would be called the equatorial line, whilst the general space
included between the poles of the magnet is called "the magnetic
field" The movement of the heavy glass was therefore equatorial, and
it pointed east and west instead of north and south, like iron and steel.

By the use of the apparatus (Fig. 242) Faraday proved that every

Fig. 242. A cube of copper suspended between the poles of a powerful electro-magnet.

PHENOMENA OF DIA-MAGNETISM.

249

substance, whether solid, fluid, or gaseous, was subject to magnetic
influences, assuming either the axial or equatorial position. The appa-
ratus consists of a prolongation of the poles of a powerful electro-
magnet, between which the cube of copper, weighing from a quarter to
half a pound, suspended by a thread, may be set spinning or rotating.
If the electro-magnet is connected with the battery, the cube stops
immediately, and whilst still in the same position or in the magnetic
field, with the magnet in full action, it is impossible to set it spinning
or twisting round again. (Fig. 242.)

A large number of other substances, solid, liquid, and gaseous, were
submitted to the action of the magnet, the liquids and gases being
hermetically sealed in glass tubes, and some of the results are detailed
in the following list :

Bodies that point axially, or are paramagnetic, like a suspended needle.

Iron.

Nickel.

Cobalt.

Manganese.

Chromium.

Cerium.

Titanium.

Palladium.

Platinum.

Osmium.

Paper.

Sealing-wax.

Fluor spar.

Peroxide of lead.

Plumbago.

China ink.

Berlin Porcelain.

Red-lead.

Sulphate of zinc.

Shell-lac.

Silkworm-gut.

Asbestos.

Vermilion.

Tourmaline.

Charcoal.

All salts of iron, when the latter is

basic.

Oxide of titanium.
Oxide of chromium.
Chromic acid.
Salts of manganese.
Salts of chromium.
Oxygen, which stands alone as a

paramagnetic gas.

Bodies that point equatorially, or are diamagnetic, like Faraday's
heavy glass.

Bismuth.

Antimony.

Zinc.

Tin.

Cadmium.

Sodium.

Mercury.

Lead.

Silver.

Copper.

Gold.

Arsenic.

Uranium.

Rhodium.

Iridium.

Tungsten.

Rock crystal.

The mineral acids.

Alum.

Glass.

Litharge.

Common salt.

Nitre.

Phosphorus.

250 EOY'S PLATBOOK OF SCIENCE.

Sulphur. Apple.

Resin. Bread.

Spermaceti.

Iceland spar.

Tartaric acid.

Citric acid.

Water.

Alcohol.

Ether.

Sugar.

Starch.

Gum-arabic,

Wood.

Ivory.

Dried muttoa,

Fresh beef.

Dried beef.

Leather.

Fresh blood.

Dried bloocu

Caoutchouc.

Jet.

Turpentine.

Olive oil.

Hydrogen.

Carbonic acid.

Carbonic oxide.

Nitrous oxide (moaerateiy .

Nitric oxide (very slightly).

Olefiant gas.

Coal gas.

Nitrogen is neither paramagnetic nor diamagnetic, and is equivalent to
a vacuum. Magnetically considered, it is like space itself, which may
be considered as zero.

The term magnetic Faraday proposes should be a general one,
like that of electricity, and include all the phenomena and effects pro-
duced by the power, and he proposes that bodies magnetic in the sense
of iron should be called paramagnetic, so that the division would stand

<ind it is this division which has been observed in the preceding
tables.

All space above and within the limits of our atmosphere may be
regarded as traversed by lines of force, and amongst others are the lines
of magnetic force which affect bodies, as shown in the table of para-
magnetic and diamagnetic bodies, which have the same relation to each
other as positive and negative, or north and south, in electricity and
magnetism.

The lines of magnetic force are assumed to traverse void space with-
out change ; but when they come in contact with matter of any kind
they are either concentrated upon it or scattered according to the
nature of the matter.

The power which urges bodies to the axial or equatorial lines is not a
central force, but a force differing in character in the axial or radial
directions. If a liquid paramagnetic body were introduced into the field
of force, it would dilate axially, and form a prolate spheroid like a lemon,
while a liquid diamagneiic body would dilate equatorially, and form an
oblate spheroid like an orange. Pliicker has demonstrated that if mag-
netic solutions are placed in watch glasses across the poles of the

PLUCKER, S EXPERIMENTS.

251

electro-magnet, they are heaped up in a very curious manner. The
poles of the electro-magnet are pieces of soft iron, which may be drawn
away or approached at pleasure, and according as the poles are nearer or
further asunder, the magnetic liquids, such as solution of iron, are
heaped up in one or two directions, as shown at B and c in Fig. 243.

Fig. 243. Glass dish holding magnetic solution of iron, and placed in the magnetic field.

"The diamagnetic power, doubtless," says Earaday, " has its appointed
office, and one which relates to the whole mass of the globe. For
though the amount of the power appears to be feeble, yet, when it is
considered that the crust of the earth is composed of substances of
which by far the greater portion belongs to the diamagnetic class, it
must not be too hastily assumed that tneir effect is entirely overruled
by the action of the magnetic matters, whilst the great mass of waters
and the atmosphere must exert their diamagnetic action uncontrolled."

Pliicker has also announced what at the time he believed to be true
the highly interesting and important fact that the optic axis of Ice-
land or calcareous spar is repelled by the magnet and placed equa-
torially a fact which Pliicker thought true of many other crystals
when the magnetic axis is parallel to the longer crystallographic axis.
A piece of kyanite, which is a mineral composed of sand, clay, often
lime, iron, water, and is used in India, being cut and polished as a gem,
and sold frequently as an inferior kind of sapphire, will, it is said, even
under the influence of the earth's magnetism, arrange itself like a mag-
netic .needle.

Pliicker believed that he had discovered an existing relation between
the forms of the ultimate particles of matter and the magnetic forces,
and he imagined that the results he obtained would lead gradually to
the determination of crystalline form by the magnet. The experiments
of Tyndal and Knoblauch lead, however, to a very opposite series of con-
clusions, and by ingeniously powdering the crvstals with water, and
making them, into a paste, which was afterwards dried and suspended

252 BOY'S PLAYBOOK OF SCIENCE.

as a model in " the magnetic field ;" also by taking a slice of apple
about as thick as a penny -piece, with some bits of iron wire through it,
in a direction perpendicular to its flat surface, they were found to set
equatorially not by repulsion but by the attraction of the iron wires ; or
instead of the iron by placing bismuth wires, the apple now settled
axially, not by attraction but by the repulsion of the bismuth. Ipe-
cacuanha lozenges, Carlisle biscuits also, suspended in the magnetic field,
exhibited a most striking directive action. The materials in these two
cases were diamagnetic; but owing to the pressure exerted in their
formation their largest horizontal dimensions set from pole to pole, the
line of compression being equatorial ; and it is a universal law " that in
diamagnetic bodies the line along which the density of the mass has been
induced by compression sets equatorial, and in magnetic bodies axial."
Hence they assume, from these and many other conclusive experiments,
that crystallized bodies, such as Iceland spar, take their position in the
magnetic field without reference to the existence of an " optic axis."

At the conclusion of a brilliant lecture at the Royal Institution by
Dr. Tyndal " On the influence of material aggregation upon the
manifestations of force," in which Plucker's experiments respecting the
repulsion of the optic axis were gracefully discussed and his theory
refuted, the learned doctor said : " This evening's discourse is in some
measure connected with this locality; and thinking thus, I arn led to
inquire wherein the true value of a scientific discovery consists ? Not
in its immediate results alone, but in the prospect which it opens to
intellectual activity in the hopes wliich it excites in the vigour
which it awakens. The discovery which led to the results brought
before us to-night was of this character. That magnet* was the
physical birthplace of these results ; and if they possess any value they
are to be regarded as the returning crumbs of that bread which in 1846
was cast so liberally upon the waters. I rejoice, ladies and gentlemen,
in the opportunity here afforded me of offering my tribute to the
greatest workman of the age, and of laying some of the blossoms of that
prolific tree which he planted at the feet of the great discoverer of dia-
magnetism."j'

It was first observed by Father Bancalari, of Genoa, that when the
flame of a candle is placed between the poles of a magnet it is strongly
repelled. The flames of combustible gases from various sources are
differently affected, both by the nature of the combustible and by the
nearness of the poles. Faraday repeated Bancalari's experiments, and
by a certain arrangement of the poles of this magnet he obtained a
powerful effect in the magnetic field, and having the axial line of the
magnetic force horizontal, he found that when the flame of a wax
taper was held near the axial line (but on one side or the other), and about
one-third of the flame rising above the level of the upper surface of the

* Alluding to a splendid magnet made by Logeman, which was sent to the Exhibition in
Hyde-park in 1851. It could sustain a weight of 430 pounds, and was purchased by the
Royal Institution for Dr. Faraday.

t Dr. Faraday.

FARADAY S EXPERIMENTS.

253

poles, as soon as the magnetic force was exerted the flame receded from
the axial line, moving equatorially until it took an inclined position, as
if a gentle wind was causing its deflection from the upright position.

When the flame was placed so as to rise truly across the magnetic
axis, the effect of the magnetism was very curious, and is shown at A,
Eig. 244.

On raising the flame a little more the effect of the magnetic force
was to intensify the results already mentioned, and the flame actually
became of a fish-tailed shape, as at c, Eig. 244 ; and when the flame
was raised until about two-thirds of it were above the level of the axial
line, and the poles approached very close, the flame no longer rose
between the poles, but spread out right and left on each side of the
axial line, producing a double flame with two long tongues, as at B,
Eig. 244.

Fig. 241. Effect of magnetism on candle-flame between the poles of the magnet.

It was these experiments that led to the important discovery of the
paramagnetic property of oxygen, and proved in a decided manner that
gaseous bodies when heated became more highly diamagnetic. Oxygen,
which (tried in the air) is powerfully magnetic, becomes diamagnetic when
heated. A coil of platinum wire heated by a voltaic current, and
placed beneath the poles of Faraday's apparatus, occasioned a strong
upward current of air ; but directly the magnetic action commences the
ascending current divides, and a descending current flows down between
the upward currents.

The discovery, says Silliman, of the highly paramagnetic character of
oxygen gas, and of the neutral character of nitrogen, the two con-
stituents of air, is justly esteemed a fact of great importance in studying
the phenomena of terrestrial magnetism. We thus see that one-fifth of
the air by volume consists of an element of eminent magnetic capacity,
after the manner of iron, and liable to great physical changes of density,
temperature, &c., and entirely independent of the solid earth. In this
medium hang the magnetic needles used as tests, and as this mag-
netic medium is daily heated and cooled by the sun's rays, its power of

254

BOY'S PLAYBOOK OF SCIENCE.

transmitting the lines of magnetic force is then affected, influencing
undoubtedly the diurnal changes of the magnetic needle.

Eor a complete digest of Faraday's discoveries in diamagnetism the
reader is referred to the second edition of Dr. Noad's comprehensive
and learned work entitled " A Manual of Electricity."

Coming always from the highest walks of philosophy to lower and
" common things" one cannot help bein^ reminded of the old-fashioned
method of drawing up a sluggish fire, and the natural query is suggested
whether the poker is to be considered as a weak magnet, and does in-
fluence and draw towards the fire a greater supply of magnetic oxygen
gas? (Fig. 245.)

Fiff. 245.

255

Fig. 246. " The moon shines bright : In such a night as this." The Merchant of Venice.

CHAPTER XXI.

LIGHT, OPTICS, AND OPTICAL INSTRUMENTS.

" To gild refined gold, f o paint the lily,
To throw a perfume on the violet,
To smooth the ice, or add another hue
Unto the rainbow, or 'With taper light
To seek the beauteous eye of heaven to garnish,
Is wasteful and ridiculous excess."

PERFECTION admits of no addition, and it is just this feeling that
might check the most eloquent speaker or brilliant writer who attempted
to offer in appropriate language, the Braises due to that first great
creation of the Almighty, when the Spirit of God moved upon the face
of the waters and said, " Let there be light." If any poet might be
permitted to laud and glorify this transcendant gift, it should be the
inspired Milton; who having enjoyed the blessing of light, and witnessed
the varied and beautiful phenomena that accompany it, could, when
afflicted by blindness, speak rapturously of its creation, in those sublime
strains beginning with

' Let there be light,' said God, zoid forthwith light
Ethereal, first of things, quintessence pure,
Sprung from the deep : and from her native east
To journey through the airy gloom began,
Sphered in a radiant cloud, for yet the sun
Was not; she in a cloudy tabernacle

256 BOY'S PLAYBOOK OF SCIENCE.

Sojourn'd the while. God saw the light was good,
And light from darkness by the hemisphere
Divided : light the day, and darkness iiight,
He named."

There cannot be a more glorious theme for the poet, than the vast
utility of light, or a more sublime spectacle, than the varied and beautiful
phenomena that accompany it. Ever since the divine command went
forth, has the sun continued to shine, and to remain, " till time shall be
no more," the great source of light to the world, to be the means of
disclosing to the eye of man all the beautiful and varied hues of the
organic and inorganic world. By the help of light we enjoy the pris-
matic colours of the rainbow, the lovely and ever changing and ever
varied tints of the forest trees, the flowers, the birds, and the insects ;
the different forms of the clouds, the lovely blue sky, the refreshing
green fields; or even the graceful adornment of "the fair," their beautiful
dresses of exquisite patterns and colours. Light works insensibly, and at
all seasons, in promoting marvellous chemical changes, and is now fairly
engaged and used for man's industrial purposes, in the pleasing art of
photography; just as heat, electricity, and magnetism, (all imponderable
and invisible agents,) are employed usefully in other ways.

The sources from whence light is derived are six in number. The
first is the sun, overwhelming us with its size, and destroying life,
sometimes, with his intense heat and light, when the piercing rays are not
obstructed by the friendly clouds and vapours, which temper and mitigate
their intensity, and prevent the too frequent recurrence of that quick and
dire enemy to man, the coup de soldi.

The body of the sun is supposed to be a habitable globe like our own,
and the heat and light are possibly thrown out from one of the atmo-
spheric strata surrounding it. There are probably three of these strata,
the one believed to envelope the body of the sun, and to be directly in
contact with it, is called the cloudy stratum ; next to, and above this, is
the luminous stratum, and this is supposed to be the source of heat and
light ; the third and last envelope is of a transparent gaseous nature.
These ideas have originated from astronomers who have carefully
watched the sun and discovered the presence of certain black spots
called Macula, which vary in diameter irom a few hundreds of miles to
40 or 50,000 miles and upwards. There is also a greyish shade sur-
rounding the black spots called the Penumbra, and likewise other spots
of a more luminous character termed Faculce; indeed the whole disc of
the sun has a mottled appearance, and is stippled over with minute
shady dots. The cause of this is explained by supposing that these
various spots represent openings or breaks in the atmospheric strata,
through which the black body of the sun is apparent or other portions
of the three strata, just as if a black ball was covered with red, then
with yellow, and finally with blue silk : on cutting through the blue the
yellow is apparent ; by snipping out pieces of the blue and yellow, the red
becomes visible ; and by slicing away a portion of the three silk coverings
the black ball at last* comes into view. On a similar principle it is

THE SOURCES OF LIGHT.

257

supposed that the variety of spots and
eruptions on the sun's face or disc
may be explained. The evolution of
light is not, however, confined to the
sun, and it emanates freely from ter-
restrial matter by mechanical action,
either by friction, or in some cases by
mere percussion. Thus the axles
of railway carriages soon become
red hot by friction if the oil holes
are stopped up ; indeed hot axles
are very frequent in railway tra-
velling, and when this happens,
a strong smell of burning oil
is apparent, and flames come
out of the axle box. The knife-
grinder offers a familiar ex-
ample of the production
of light by the attrition of
iron or steel against his
dry grindstone.

The same result
much grander
scale is produced
by the apparatus
invented by the
late Jacob Per-
kins; thecombus-
tionofsteelensues

on a

under the action,
viz., the friction
of a sof tiron disc revolv-
ing with great velocity
against a file or other
convenient piece of har-
dened steel. (Fig. 247)
The stand has a disc of soft
iron fixed upon an axis, which
revolves on two anti-friction
wheels of brass. The disc, by
means of a belt worked over a
wheel immediately below it, is
made to perform 5000 revolu-
tions per minute. If the
hardest file is pressed against
the edge of the revolving disc,
the velocity of the latter pro-
duces sufficient heat by the
great friction to melt that por-
tion of the file which is brought
in contact with it, whilst some
particles of the file are torn
away with violence, and being

Fig. 247. Instrument for the combustion of steeL

258

BOY'S PLAYBOOK OF SCIENCE.

projected into the air, burn with that beautiful effect so peculiar to
steel. If the experiment is performed in a darkened room, the pe-
riphery of the revolving disc will be observed to have attained a
luminous red heat. Thirty years ago every house was provided with a
" tinder-box" and matches to " strike a light." Since the advent of
prometheans and lucifers, the flint and steel, the tinder, and the matches
dipped in sulphur, have all disappeared, and now the box might be
deposited in any antiquarian museum under the portrait of Guy Fawkes,
and labelled, " an instrument for procuring a light, extensively used in
the early part of the nineteenth century." (Fig. 248.)

Fig, 248. c. The steel. B. The flint. E. The tinder. D. The matches of the
old-fashioned tinder-box, A.

The rubbing of a piece of wood (hardened by fire, and cut to a point)
against another and softer kind, has been used from time immemorial
by savage nations to evoke heat and light ; the wood is revolved in the
fashion of a drill with unerring dexterity by the hands of the savage,
and being surrounded with light chips, and gently aided by the breath
the latent fire is by great and incessant labour at last procured. How
favourably the modern lucifers compare with these laborious efforts of
barbarous tribes ! a child may now procure a light with a chemically
prepared metal, and great merit is due to that person who first devised
a method of mixing together phosphorus and chlorate of Dotash and so

THE SOURCES OF LIGHT.

259

adjusted these dangerous materials that they are as safe as the "old
tinder-box," and have now become one of our domestic necessaries.
Ignition, or the increase of heat in a solid body, is another source of
light, and is well illustrated in the production of illuminating power
from the combustion of tallow, oil, wax, camphine or coal gas. The
term ignition is derived from the Latin (ignis, fire), and is quite distinct,
and has a totally different meaning from that of combustion. If a glass
jar is filled with carbonic acid gas, and a little tray placed in it containing
some gun cotton, it will be found impossible to fire the latter with a
lighted taper, i.e. by combustion (comburo, to burn), because the gas
extinguishes flame which is dependent on a
supply of oxygen; whereas if a copper or
other metallic wire is made red hot or ignited,
the carbonic acid has no effect upon the heat,
and the red hot wire being passed through
the gas, the gun cotton is immediately fired.

Flame consists of three parts viz., of an
outer film, which comes directly in contact
with the air, and has little or no luminosity ;
also of a second film, where carbon is deposited,
and, first by ignition, and finally by com-
bustion, produces the light ; and thirdly, of
an interior space containing unburnt gas,
which is, as it were, waiting its turn to reach
the external air, and to be consumed in the
ordinary manner. (Fig. 249.)

Chemical action and electricity have been
so frequently mentioned in this work as a
source of heat and light, that it will be un-
necessary to do more than to mention them
here, whilst phosphorescence (the sixth
source of light) in dead and living matter,
a spontaneous production of light, is well
known and exemplified in the " glow-worm,"
the "fire-fly," the luminosity of the water of
the ocean, or the decomposing remains of
certain fish, and even of human bodies. Phos-
phorescence is still more curiously exempli-
fied by holding a sheet of white paper, a cal-
cined oyster-shell, or even the hand, in the
sun's rays, and then retiring quickly to a
darkened room, when they appear to be lu-
minous, and visible even after the light has
ceased to fall upon them.

For the purpose of examining the tempo- L of te?me. 2?5r ftS
rary phosphorescence of various bodies, M. which is badly supplied with
Becquerel has invented a most ingenious in- HB^JfflB "the
Strument, called the " phosphorescope." It mterior.contalniifeunburntgas.

260 BOY'S PLAYBOOK OF SCIENCE.

consists of a cylinder of wood one inch in diameter and seven inches
long, placed in the angle of a black box with the electric lamp inside,
so that three-fourths of the cylinder are visible outside, and the re-
maining fourth exposed to the interior electric light.

By means of proper wheels the cylinder, covered with any substance
(such as Becquerel's phosphori), is made to revolve 300 times in a
second, and by using this or a lesser velocity, the various phosphori
are first exposed to a powerful light and then brought in view of the
spectator outside the box.

It is understood that light is produced by an emanation of rays from
a luminous body. If a stone is thrown from the hand, an arrow shot
from a bow, or a ball from a cannon, we perfectly understand how either
of them may be propelled a certain distance, and why they may travel
through space ; but when we hear that light travels from the sun, which
is ninety-five millions of miles away from the earth, in about seven
minutes and a half, it is interesting to know what is the kind of
force that propels the light through that vast distance, and also what is
supposed to be ftie nature of the light itself.

There are two theories by which the nature of light, and its propaga-
tion through space, are explained ; they are named after the celebrated
men who proposed them, as also from the theoretical mechanism of their re-
spective modes of propulsion : thus we have the Newtonian or corpuscular
theory of light, and the Huyghenian or undulatory theory; the first named
after Sir Isaac Newton, and the second after Huyghens, another most
learned mathematician. Many years before Newton made his grand dis-
covery of the composition of light in the year 1672, mathematicians were in
favour of the undulatory iheoij, and it numbered amongst its supporters
not only Huyghens, but Descartes, Hook, Malebranehe, and other learned
men. Mankind has always been glad to follow renowned leaders, it is
so much easier, and is in most cases perhaps the better course, to resign
individual opinion when more learned men than ourselves not only adopt
but insist upon the truth of their theories ; and this was the case with
the corpuscular theory, which had been written upon systematically and
supported by Empedocles, a philosopher of Agrigentum in Sicily, who
lived some 444 years before the Christian era, and is said to have been
most learned and eloquent; he maintained that light consisted of
particles projected from luminous bodies, and that vision was performed
both by the effect of these particles on the eye, and by means of a visual
influence emitted by the eye itself. In course of time, and at least 2000
years after this theory was advanced, philosophers had gradually rejected
the corpuscular theory, until the great Newton, about the middle
of the seventeenth century, advanced as a champion to the rescue, and
stamping the hypothesis with his approval, at once led away the whole
army of philosophers in its favour, so that till about the beginning of the
nineteenth century the whole of the phenomena of light were explained
upon this hypothesis.

The corpuscular theory, reduced to the briefest definition, supposes
light to be really a material agent, and requires the student to believe

THE THEORIES OF LIGHT. 261

that this agent consists of particles so inconceivably minute that they
could not be weighed, and of course do not gravitate ; the corpuscles are
supposed to be given out bodily (like sparks of burning steel from a
gerb firework) from the sun, the fixed stars, and all luminous bodies ; to
travel with enormous velocity, and therefore to possess the property of
inertia ; and to excite the sensation of vision by striking bodily upon
the expanded nerve, the retina, the quasi-mind of the eye. Dr. Young
remarks, "that according to this projectile theory the force employed in
the free emission of light must be about a million million times as great
as the force of gravity at the earth's surface, and it must either act with
equal intensity on all the particles of light, or must impel some of them
through a greater space than others, if its action be more powerful, since
the velocity is the same in all cases for example, if the projectile force
is weaker with respect to red light than with respect to violet light, it
must continue its action on the red ravs to a greater distance than on
the violet rays. There is no instance in nature besides of a simple pro-
jectile moving with a velocity uniform in all cases, whatever may be its
cause ; and it is extremely difficult to imagine that such an immense force
of repulsion can reside in all substances capable of becoming luminous,
so that the light of decaying wood, or two pebbles rubbed together, may
be projected precisely with the same velocity as the light emitted by
iron burning in oxygen gas, or by the reservoir of liquid fire on the
surface of the sun." Now one of the most striking circumstances
respecting the propagation of light, is the uniformity of its velocity in
the same medium. These and other difficulties in the application of the
corpuscular theory aroused the attention of the late Dr. Young, and in
the year 1801 he again revived and supported the neglected undulatory
theory with such great ability that the attention of many learned
mathematicians was directed to the subject, and now it may be said
that the corpuscular theory is almost, if not entirely, rejected, whilst
the undulatory theory is once more, and deservedly, used to explain
the theory of light, and its propagation through space. By this hypo-
thesis it is assumed that the whole universe, including the most minute
pores of all matter, whether solid, fluid, or gaseous, are filled with a
highly elastic rare medium of a most attenuated nature, called ether,
possessing the property of inertia but not of gravitation. This ether is
not light, but light is produced in it by the excitation on the rjart of
luminous bodies of a vibratory motion, similar to the undulation of
water that produces waves, or the vibration of air affording sound.
Water set in motion produces waves. Air set in motion produces waves
of sound. Ether, i.e. the theoretical ether pervading all matter, like-
wise set in motion, produces light. The nature of a vibratory medium
is indeed better understood oy reference to that which we know-
possesses the ordinary properties of matter viz., the air ; and by tracing
out the analogy between the propagation of sound and light, the diffi-
culties of the undulatory theory very quickly vanish. To illustrate
vibration it is only necessary to procure a finger glass, and having
supported a little ebony ball attached to a silk thread by a bent brass

262 BOY'S PLAYBOOK OF SCIENCE.

wire directly over it, so that the ball may touch either the outside or
the inside of the glass, attention must be directed to the quiescence of
the ball when a violin bow is lightly moved over the edge of the glass
without producing sound, and to the contrary effect obtained by so
moving and pressing the bow that a sharp sound is emitted, when im-
mediately the little oall is thrown off from the edge, the repulsive action
being continued as long as the sound is produced by the vibration of
the glass. (Fig. 250.)

Pig. 250. A. The finger glass. B. The violin bow. c. The ebony ball. The dotted ball
shows how it is repelled during the vibration of the glass.

Here the vibrations are first set up in the glass, and being communi-
cated to the surrounding air, a sound is produced ; if the same experi-
ment could be performed in a vacuum, the glass might be vibrated, but
not being surrounded with air, no sound would be produced. This fact
is proved by first ringing a bell with proper mechanism fixed under the
receiver placed on the air-pump plate ; the sound of the bell is audible
until the pump is put in motion and the receiver gradually exhausted,
when the ringing noise becomes fainter and fainter, until it is perfectly
inaudible. This experiment is made more instructive by gradually
admitting the air again into the exhausted vessel, and at the same time
ringing the bell, when the sound becomes gradually louder, until it
attains its full power. The sun and other luminous bodies may be
compared to the finger glass, and are supposed to be endowed
naturally with a vibratory motion (a sort of perpetual ague), only
instead of the air being set in motion, the ether is supposed to be
thrown into waves, which travel through space, and convey the
impression of light from the luminous object. Another familial-
example of an undulatory medium is shown by throwing a stone
into a pool of water ; the former immediately forces down and displaces
a certain number of the particles of the latter, consequently the sur-
rounding molecules of water are heaped up above their level ; by the
force of gravitation they again descend and throw up another wave, this
in subsiding raises another, until the force of the original and loftier

THE THEORIES OF LIGHT.

263

wave dies away at the edge of the pool into the faintest ripples. It
must however Be understood that it is not the particles of water first
set in motion that travel and spread out in concentric circles;

Fig. 251. Boy throwing stones into water and producing circular waves.

but the force is propagated by the rising and falling of each separate
particle of water as it is disturbed by the momentum of the descending
wave before it. When standing at a pier-head, or on a rock against
which the sea dashes, it is usual to hear the observer cry out, if the
weather is stormy and the waves very high, " Oh ! here comes a great
wave !" as if the water travelled bodily from the spot where it was first
noticed, whereas it is simply the force that travels, and is exerted finally
on the water nearest the rock. It is in fact a progressive action, just as
the wind sweeps over a wide field of corn, and bends down the ears one
after the other, giving them for the time the appearance of waves. The
principle of successive action is well shown by placing a number of
billiard balls in a row, and touching each other ; if the first is struck the
motion is communicated through the rest, which remain immovable,
whilst the last only flies out of its place. The force travels through all
the balls, which simply act as carriers, their motion is limited, and the
last only changes its position. Progressive movement is also well dis-

Fig. 252. A B. Series of needles arranged as described, c. The bar magnet, with the
north pole IT towards the needles. The dotted lines show the direction gradually assumed
by all the needles, commencing at D.

played by arranging six or eight magnetized needles on points in a row,
with all their north poles in one direction. (Eig. 252.)

On approaching the north pole of a bar magnet to the same pole of

264 BOY'S PLAYBOOK OF SCIENCE.

one end of the series of needles, it is very curious to see them turn in the
opposite direction progressively, one after the other, as the repulsive
power of the bar magnet gradually operates upon the similar poles in the
magnetic needles. The undulations 01 the waves of water are also perfectly
shown by using the apparatus consisting of the trough with the glass
bottom and screen above it, as described at page 10. The transmission
of vibrations from one place to another is also admirably displayed in
Professor Wheatstone's Telephonic Concert (see page picture), where
the musical instruments, as at the Polytechnic, were placed by the
author in the basement, and the vibration only conducted by wooden
rods to the sounding-boards above, so that the music was laid on like
gas or water. These vibrations or undulations in air, water, and the
theoretical ether, have therefore been called waves of water, waves of
sound, and waves of light, just as if three clocks were made of three
different metals, the mechanism would remain the same, though the
material, or in this case the medium, be different in each.

Any increase in the number of vibrations of the air produces acute,
whilst a decrease attends the grave sounds, and when the waves succeed
each other not less than sixteen times in a second, the lowest sound is
produced. Light and colours are supposed to be due to a similar
cause, and in order to produce the red ray, no less than 477 millions of
millions of vibrations must occur in a second of time ; the orange, 506 ;
yellow, 535; green, 577; blue, 622; indigo, 658; violet, 699; and
white light, which is made up of these colours, numbers 541 millions of
millions of undulations in a second.

Although light travels with such amazing rapidity, there is of course
a certain time occupied in its passage through space there is no such
thing as instantaneity in nature. A certain period of time, however small,
must elapse in the "performance of any act whatever, and it has been
proved by a careful observation of the time at which the eclipses of the
satellites of Jupiter are perceived, that light travels at the rate of
192,500 miles per second, and by the aberration of the fixed stars,
191,515, the mean of these two sets of observations would probably
afford the correct rate. Such a velocity is, however, somewhat difficult
to appreciate, and therefore, to assist our comprehension of their great
magnitude, Sir J. Herschel has given some very interesting comparative
calculations, and coming from such an authority we can readily believe
them to be correct.

" A cannon-ball moving uniformly at its greatest velocity would
require seventeen years to reach the sun. Light performs the same
distance in about seven minutes and a. half.

" The swiftest bird, at its utmost speed, would require nearly three
weeks to make the tour of the earth, supposing it could proceed without
stopping to take food or rest. Light performs the same distance in
less time than is required for a single stroke of its wing."

Dismissing for the present the theory of undulations, it will be
necessary to examine the phenomena of light, regarding it as radiant
matter, without reference to either of the contending theories.

THE KADIATION OF LIGHT.

265

Light issues from the sun, passes through millions of miles to the
earth, and as it falls upon different substances, a variety of effects are
apparent. There is a certain class of bodies which obstruct the passage
of the rays of light, and where light is not, a shadow is cast, and the
substance producing the shadow is said to be opaque. "Wood, stone,
the metals, charcoal, are all examples of opacity ; whilst glass, talc, and
horn allow a certain number of the rays to travel through their par-
ticles, and are therefore called transparent. Nature, however, never
indulges in sudden extremes, and as no substance is so opaque as not
(when reduced in thickness) to allow a certain amount of light to pass
through its substance, so, on the other hand, however transparent a
body may be, a greater or lesser number of the rays are always stopped,
and hence opacity and transparency are regarded as two extremes of a
long chain ; being connected together by numerous intermediate links,
they pass by insensible gradations the one into the other.

If a gold leaf, which is about the one two-hundredth part of an inch
in thickness, is fixed on a glass plate and held before a light, a green
colour is apparent, the gold appearing like a green, semi-transparent
substance. When plates of glass are laid one above the other, and the
flame of a candle observed through them, the light decreases enor-
mously as the number of glass-plates are increased. Even in the air a
considerable portion of light is intercepted. It has been estimated that
of the horizontal sunbeams passing through about two hundred miles of
air, one two-thousandth part only reaches us, and that no sensible light
can penetrate more than seven hundred feet deep into the sea ; conse-
quently, the vast depths discovered in laying the Atlantic telegraph
must tie in absolute darkness.

Light is thrown out on
all sides from a luminous
body like the smokes of a
cart-wheel, and in the ab-
sence of any obstruction, the
rays are distributed equally
on all sides, diverging like the

radii drawn from the centre k^^^-O^-C^CS^^^iX.
of a circle. As a natural ^ **

consequence arising from
the divergence of each ray
from the other, the intensity
of light decreases as the
distance from the luminous
source increases, and vice
versa. Perhaps the best me-
chanical notion of this law
is afforded by an ordinary
fan; the point from which
the sticks radiate, and where
they all meet, may be Fig. 253.

266

BOY'S PLAYBOOK OF SCIENCE.

termed the light; the sticks are the rays proceeding from it. (Kg.
253.)

The fan is held in one hand, and the first finder of the other can be
made to touch all the sticks if placed sufficiently near to A ; and sup-
posing the sticks are called rays of light, the intensity must be great at
that point, because all the rays fall upon it ; but if the finger is removed
towards the outer edge viz., to B, it now only touches some three or
four sticks ; and pursuing the analogy, a very few rays fall upon that
point hence the light has decreased in intensity, or to speak correctly,
"Light decreases inversely as the squares of the distance." This law
has already been illustrated at page 13 ; and as an experiment, the
rays from the oxy-hydrogen lantern may be permitted to pass out of a
square hole (say two inches square), and snould be thrown on to a
transparent screen divided into squares by dark lines, so that the light
at a certain distance illuminates one of them ; then it will be found that
at twice the distance, four may be illuminated, at three times nine, and
so on. (Fig. 254.)

Fig. 254. Lantern at the three distances from the transparent screen, which is
divided into nine equal squares.

Upon this law is based the use of photometers, or instruments for
measuring light, and supposing it was required to estimate roughly the
illuminating power of any lamp, as compared with the light of a wax
candle six to the pound, the experiment should be conducted in a dark
room, from which every other light but that from the lamp and candle
under examination must be excluded.

The lamp, with the chimney only, is now placed say twelve feet from,
the wall, and a stick or rod is placed upright and about two inches from
the latter, so that a shadow is cast on the wall ; if the candle is now
lighted and allowed to burn up properly, two shadows of the stick will
be apparent, the one from the lamp being black and distinct, and the
other from the candle extremely faint, until it is approached nearer the

PHOTOMETRY.

267

wall say to within three feet when the two shadows may be now
equal in "blackness. (Eig. 255.) After this is apparent to one or more

Fig. 255. A. The lamp. B. The oanclle. c. The rod throwing the two shadows, marked
D and B, on a white wall or a sheet of paper.

persons, the distances of the lamp and candle from the wall are carefully
measured, and being squared, and the greater divided by the lesser
number, the quotient gives the illuminating power. For example :

The lamp was 12 feet from the wall
The candle was 3 feet

9)144
16

12 x 12 = 144.
3x3= 9.

Therefore the illuminating power of the lamp is equal to 16 wax candles
six to the pound.

There are other and more refined means of working out the same
fact, but for a rough approximation to the truth, the plan already de-
scribed will answer very fairly.

A most amusing effect can be produced on the principle that every
light casts its own shadow, called the "dance of death," or the "dance of
the witches ;" either of these agreeable subjects are drawn, and the out-
lines cut out of a sheet of cardboard. If a wet sheet is stretched or hung
on one side of a pair of folding doors partly open, and between which
the cardboard is tacked up, and the space left at the top and bottom
closed with a dark cloth, directly the room before the sheet is
darkened and a lighted candle held behind the figure cut out in the
cardboard, one shadow or image is thrown upon the sheet, and these
shadows may be increased according to the number of candles used, and
if they are held by two or three persons, and moved up and down, or
sideways, the shadows follow the direction of the candles, and present
the appearance of a dance. (Fig. 256.)

268

BOY'S PLAYBOOK OF SCIENCE.

Fig. 257. Behind the curtain.

SHADOW ILLUSIONS. 269

Another very comic effect of shadow is that called "jumping up to
the ceiling," and when carried out on a large scale by the author on an
enormous sheet suspended in the centre transept of the Crystal Palace,
Sydenham, it had a most laughable effect, and caused the greatest
amusement to the children of all ages. (Fig. 258.)

Fig. 258. The laughable effect of the shadows at the Crystal Palace.

This very telling result is produced by placing an oxy-hydrogeu light
some feet behind a large sheet, and of course if any one passes between
the two a shadow of the individual is cast upon ^ the sheet, then^by
walking towards the light the figure diminishes in size, and by jumping
over it the shadow appears to go up to the ceiling, and to come down
when the jump is made in the opposite direction over the light and towards
the sheet. The rationale of this experiment is very simple, and is

270 BOY'S PLAYBOOK OF SCIENCE.

another proof of the distribution of light from a luminous source being
in every direction By jumping over the light the radii projected from

the candle over the sheet are
crossed, and the shadow rises or
falls as the figure passes upwards
E x --. or downward. (Eig. 259.)

A beam of light is defined to
be a collection of rays, and it is
a convenient definition, because
it prevents confusion to speak
only of one ray in attempting to
explain how light is disposed of
under peculiar circumstances.

The smallest portion of light
which it is supposed can be se-
parated is therefore called a ray,
and it will pass through any me-
dium of tne same density in a
P^ectly straight line; but if it

gen light. The arrow pointing to the right passes out 01 that medium into

iXh"' ZSSSSSKSg&S. ?*r of a different density, or
ing to the left, shows the reverse. into any other solid, fluid, or

gaseous matter, it may be dis-
posed of in four different ways, being either reflected, refracted, polar-
ized, or absorbed.

The reflection of light is the first property that will be considered,
and it will be found that every substance in nature possesses in a greater
or lesser degree the power of throwing off the rays of light which fall
upon them. Thus if we go into a room perfectly darkened, containing
every kind of work produced by nature or art, such as flowers, birds,
boxes of insects, rich carpets, hangings, pictures, statuary, jewellery,
&c., they cannot excite any pleasure because they are invisible, but
directly a lighted lamp is brought into the chamber, then the rays fall
upon all the surrounding objects, and being reflected from their surfaces
enter the eye, and there produce the phenomena of vision.

This connexion bet ween luminous and non-luminous bodies becomesvcry
apparent when we consider that the sun would appear only as an intense
light in a dark background, if the earth was not surrounded with the
various strata of air, in which are placed clouds and vapours that collec-
tively reflect and scatter the light, so as to cause it to be endurable to vision.
Jt is when the sky is very clear during July or August that the heat
becomes so intense, directly clouds begin to form and float about, the heat
is then moderated.

Many years ago, Baron Alexander "Funk, visiting some silver mines in
Sweden, observed, that in a clear day it was as dark as pitch under-
ground in the eye of the pit at sixty or seventy fathoms deep; whereas, on
a cloudy or rainy day he could even see to read at 106 fathoms deep.
Inquiring of the miners, he was informed that this is always the case, and

THE REFLECTION OF LIGHT. 271

reflecting upon it he imagined very properly that it arose from this
circumstance that when the atmosphere is full of clouds, light is re-
flected from them into the pit in all directions, so that thereby a con-
siderable proportion of the rays are reflected perpendicularly upon the
earth; whereas when the atmosphere is clear there are no opaque bodies
to reflect the light in this manner, at least, in a sufficient quantity, and
rays from the sun itself can never fall perpendicularly in Sweden. The
use of reflecting surfaces has now become quite common in all crowded
cities, and especially in London, where even the rays of light are too few
to be lost, and flat or corrugated mirrors are placed at various angles,
either to throw the light from the outside on the white-washed ceiling
within, and thus obtain a better diffused light through the apartment,
or it is reflected bodily to some back room, or rather dark brick box,
where perhaps for half a century candles have been required at an
early hour in the afternoon. The brilliant cut in diamonds is such an
arrangement of the posterior facets, or cut faces of the jewel, that all
light reaching them shall be thrown back and reflected, and thus
impart an extraordinary brilliancy to the gem.

The intense glare of snow in the Alpine regions has long been noticed,
and the reflected light is so powerful, that philosophers were even
disposed to believe that snow possessed a natural or inherent lumi-
nosity, and gave out its own light. Mr. Boyle, however, disproved
this notion by placing a quantity of snow in a room from which all
foreign light was excluded, and neither he nor his companion could
observe that any light was emitted, although, on the principle of
momentary phosphorescence, it is quite possible to conceive that if the
snow was suddenly brought into a darkened room after exposure to the
rays of the sun, that it would give out for a few seconds a perceptible
light. In trying such an experiment, one person should expose the
snow to the sun, and brin^ it into a perfectly darkened room to a second
person, whose eyes would oe ready to receive the faintest impression of
light, and if any phosphorescence existed, it must be apparent.

The property of reflection is also illustrated on a grand scale in the
illumination of our satellite, the moon, and the various planetary bodies
which shine by light reflected from the sun, and have no inherent self-
luminosity. Aristotle was well aware that it is the reflection of light
from the atmosphere which prevents total darkness after the sun sets,
and in places where the sun's rays do not actually fall during the day-
time. He was also of opinion that rainbows, halos, and mock suns,
were all occasioned by the reflection of the sunbeams in different cir-
cumstances, bv which an imperfect image of the sun was produced, the
colour only being exhibited, but not the proper figure.

The image, Aristotle says, is not single, as in a mirror, for each drop
of rain is too small to reflect a visible image, but the conjunction of all
the images is visible. Aristotle ascribed all these effects to the reflection.
of light, and it will be noticed when we come to the consideration
of the refraction of light, that of course his views must be seriously
modified.

272

BOYS PLAYBOOK OF SCIENCE.

The reflection of light is affected rather by the condition of the
surface than the whole body of a substance, as a piece of coal may
be covered with gold or silver leaf and caused to shine, whilst the
brightest mirror is dimmed by the thinnest film of moisture.

From whatever surface light is reflected, it always takes place in
obedience to two fixed laws.

First. The incident and reflected rays always lie in the same plane.

Second. The angle of incidence is equal to the angle of reflection.

With a single jointed two-foot rule, both of these laws are easily
illustrated. The rule may be held in the hand, and one end being
marked with a piece of white paper may be called the incident ray, i.e.,
the ray that falls upon the surface ; and the other is the reflected ray,
the one cast off or thrown back. A perpendicular is raised by holding
a stick upright at the joint. (Fig. 260.)

Fig. 260. A D. A two foot rule ; the end A may be termed the incident ray, and the end
D the reflected ray. s. The stick held perpendicularly. The angle A B c is equal to the
angle DBF, and the whole may be moved in any direction or plane, either horizontal or
perpendicular. G G. The reflecting surface.

One of the most simple and pleasing delusions produced by the reflec-
tion of light, is that afforded by cutting through the outline of a vase,
or statuette, or flower, drawn on cardboard, and if certain points are
left attached, so that the design may not fall out, all the effect of solidity
is given by bending back the edges of the cardboard, so that the light

THE KEFLECTION OF LIGHT.

from a candle placed behind it, may be reflected from the back edge of
one cardboard on to the design, which is bent back. The liffht reflected
from one surface on to the other, imparts a peculiarly soft and marble-like
appearance, and when the design is well drawn and cut, and placed in
a good position, the illusion is very perfect, and it appears like a solid
form instead of a mere design cut out of cardboard. (Fig. 261.)

Fig. 261. Cardboard design in frame, cut and bent back. The lighted candle is behind.

The leaf at the side of the above picture is intended to give an idea of
the mode of cutting out the designs, and in this case the leaf would be
cut and bent back, and a small attachment slip of cardboard left to
prevent it falling out.

The cardboard design is always bent toward the light, which is
placed behind it. As a good illustration of the importance of reflected
light and its connexion with luminous bodies, a beam of light from the
oxy -hydrogen lantern may be allowed to pass above the surface of a
table, when it will be noticed that the latter is lighted up only when the
beam is reflected downward by a sheet of white paper.

By reference to the two laws of reflection already explained, it is easy
to trace out on paper, with the help of compasses and rule, the effect of
plane, concave, and convex surfaces on parallel, diverging, or converging
rays of light, and it may perhaps assist the memory if it is remembered
that a plane surface means one that is flat on both sides, such as a
looking-glass : a convex surface is represented by the outside of a watch-
glass ; a concave surface, bv the inside of a watch-glass ; parallel rays
are like the straight lines in a copy-book; diverging and converging

BOY'S PLAYBOOK OF SCIENCE.

rays, are like the sticks of a fan spread out as the sticks separate or
diverge ; the sticks of the fan come together, or converge at the handle.
The reflection of rays from a plane surface may be better understood
by reference to the annexed diagram. (Fig. 262.)

Pig. 262. A i, A K. Two diverging rays incident on the plane surface, D. A D is perpen-
dicular, Mid is reflected back in the same direction. A i is divergent, and is thrown off at
i L. The incident and reflected rays forming equal angles, as proved by the perpendicular, H.
Any image reflected in a plane mirror appears as far behind it as the object is before it, and
the dotted lines meeting at G show the apparent position of the reflected image behind
the glass, as seen at &. The same fact is also shown in the second diagram, where the
reflected picture, i M, appears at the same distance behind the surface of the mirror as the
object, A B, is before it.

By the proper arrangement of plane mirrors, a number of amusing
delusions may be produced, one of which is sometimes to be met with
in the streets, and is called " the art of looking through a four-inch deal
board." The spectator is first requested to look into a tube, through
which he sees whatever may be passing the instrument at the time ;
the operator then places a deal board across the middle of the
tube, which is cut away for that purpose, and to the astonishment of
the juveniles the view is not impaired, and the spectator still fancies
lie is looking through a straight tube ; this however is not the case, as
the deception is entirely carried out by reflection, and is explained in
the next cut. (Fig. 263.)

During the siege of Sebastopol numbers of our best artillerymen
were continually picked off by the enemy's rifles, as well as by cannon
shot, and in order to put a stop to the foolhardiness and incautiousness
of the men, a very ingenious contrivance was invented by the Rev. Wm.
Taylor, the coadjutor of Mr. Denison in constructing the first "Big
Ben" bell. It was called the reflecting spy-glass, and by its simple con-
struction rendered the exposure of the sailors and soldiers, who would
look over the parapet or other parts of the works to observe the effect
of their shot, perfectly unnecessary; whilst another form was constructed
for the purpose of allowing the gunner to "lay" or aim his gun in
safety. The instruments were shown to Lord Panmure, who was so
convinced of the importance of the invention, that he immediately

OPTICAL ILLUSIONS.

276

Fig. 263. A A A A. The apertures through which the spectator first looks. B. The
piece of wood, four inches thick, c, D, E, F, are four pieces of looking-glass, so placed that
rays of light entering at one end of the tube are reflected round to the other where the
eye of the observer is placed.

commissioned the Rev. Wm. Taylor to have a number of these telescopes
constructed ; and if the siege had not terminated just at the time the
invention was to have been used, no doubt a great saving of the
valuable lives of the skilled artillerymen would have been effected in
the allied armies. The principle of the reflecting spy-glass may be
comprehended by reference to the next cut. (Fig. 264.)

Fig. 264. A picture of enemy's battery is supposed to be on the mirror, A, whence it
is reflected to B, and from that to the artilleryman at c.

By placing two mirrors at an angle of 45, the reflected image of a
person gazing into one is thrown into the other, and of course the effect
is somewhat startling when a death's head and cross bones, or other

276

BOY'S PLAYBOOK OF SCIENCE.

cheerful subject, is introduced opposite one mirror, whilst some person
who is unacquainted with the delusion is looking into the other. Two
adjoining rooms might have their looking-glasses arranged in that
manner, provided there is a passage running behind them. (Fig. 265.)

Fig. 265. A. A mirror at an angle of 45 degrees. The arrows show the direction of the
reflected image. B. The second mirror, also at an angle of 45 degrees; the face of the
person looking in at A. is reflected at B. o is the partition between the rooms.

One of the most startling effects that can be displayed to persons
ignorant of the common laws of the reflection of light, is called the
" magic mirror," and is described by Sir Walter Scott in his graphic
story of that name. The apparatus for tne purpose must be well
planned and fixed in a proper room for that purpose, and if carefully
conducted, may surprise even the learned. A long and somewhat
narrow room should be hung with black cloth, and at one end may be
placed a large mirror, so arranged that it will turn on hinges like a door.
The magician's circle may be placed at the other end of the chamber in
which the spectators must be rigidly confined, and there is very little doubt
that the arrangement about to be described was formerly used by clever
astrologers who pretended to look into the future, and to hold commu-
nication with the supernatural powers. The credulity of the persons
who consulted these " wise men," is not surprising when we consider
the ignorance of the public generally of common physical laws, and of
the wonders that may be worked without the assistance of the " evil
one ;" moreover, the 'initiated took great care to conceal the machinery
of their mysteries, never imparting the illusive tricks even to their
most faithful dependents except under solemn oaths of secresy, because
they derived in many cases considerable profit by their pretended conju-
rations and juggling tricks, and therefore were interested in keeping the
outer world in ignorance. The wizards were always careful to impress
those who came to consult them with the awful nature of the incanta-
tions they were about to perform, and with such a powerful auxiliary as

THE MAGIC MIRROR. 277

fear, and a well-darkened room, they diverted the thoughts of the more
curious, and prevented them watching the proceedings too closely.
Theatrical effects were not disdained, such as suppressed and dismal
groans, sham thunder, and the wizard usually heightened his own
inspiring personal appearance by wearing of course a long beard and
flowing robe trimmed with hieroglyphics, and with the assistance of a
ponderous volume full of cabalistic signs, a few skulls and cross bones,
an hour-glass, a pair of drawn swords, a black cat, a charcoal fire, and
sundry drugs to throw into it, a very tolerable collection of imps,
familiars, and demons, might be expected to attend without the modern
practice of spirit-rapping. As before stated, the delusion must be care-
rully conducted, and a confederate is necessary in order to use the
phantasmagoria, or magic lantern. The slides of course were painted to
suit the fortune to be unfolded an easy road to riches for the gentle-
men, a tale of love, ending in matrimony, for the ladies.

The spectators being placed in the magic circle, are directed to look
into the mirror ; they may even be ordered singly to fetch a skull off
the mantel-shelf beside the mirror, and whilst doing so to look full
into the mirror, and then return to the circle. Absolute silence is
enjoined, and soft music is now heard ; the darkened room is lit up for
the moment by a little yellow or green fire thrown on to the charcoal
fire, and now looking into the mirror, it no longer reflects surrounding
objects, but a picture, at first small and faint, and then gradually
becoming large and clearer, is apparent. The picture is made visible by
the confederate gently drawing the mirror from its position parallel
with the frame to an angle of 45 degrees, and then throwing on from
the side a picture from a magic-lantern. The picture is small and in-
distinct whilst the confederate holds it near the mirror and out of focus,
but as he moves backwards and focuses the lenses, the picture gradually
increases in size, and the reflecting angles having been well planned
beforehand, only those in the circle will be able to see the picture, and
great fun may be elicited from the magic mirror by pretending to tell
the future fate of a very slim person, and introducing him by a suc-
cession of pictures which gradually assume a John Bull rotundity of
figure, surrounded by dozens of children; whilst to young ladies who are
engaged, a provoking picture of an old maid may be introduced ; indeed,
there is no end to the innocent fun that may be extracted from the
magic mirror, and the whole plan of the delusion may be better understood
by reference to the next picture. (Fig. 266.)

Monsieur Salverte very properly remarks that " man is credulous
from his cradle to his tomb; but the disposition springs from an
honourable principle, the consequences of which precipitate him into

many errors and misfortunes The novelty of objects, and the

difficulty of referring them to known objects, will not shock the
credulity of unsophisticated men. They are some additiona. sensations
which he receives without discussion, and their singularity is perhaps a
charm which causes him to receive them with greater pleasure. Man
always loves and seeks the marvellous. Is this taste natural ?

278

BOYS PLAYBOOK OF SCIENCE.

The magic mirror.

Fig. 266. Plan of room. A A. The frame of the looking-glass. A B. Mirror put back to
an angle of 45 degrees, c. The confederate who manages the lantern and shuts the glass
to the frame after each fortune is told. D. The magic circle, to which the rays are
reflected.

THE CONVEX MTRROK.

279

Does it spring from the education which during many ages the human
race has received from its first instructors ? A vast and novel question,
but with which I have nothing to do. It is sufficient to observe that
as the lover of the wonderful always prefers the most surprising to the
most natural account, this last has been too frequently neglected, and is
irrevocably lost. Occasionally, however (and we shall cite more than
one instance), simple truth has escaped from the power of oblivion.
Credulous man may be deceived once, or more frequently ; but his
credulity is not a sufficient instrument to govern his whole existence.
The wonderful excites only a transient admiration. In 1798, the
French savans remarked with surprise how little the spectacle of

balloons affected the indolent Egyptian But man is led by his

passions, and particularly by hope and fear"

When parallel rays fall upon a convex mirror, they are scattered and
dispersed in all directions, and the image of an object reflected in a
convex mirror appears to be very small, being reduced in size because
the reflected picture i M is nearer the surface of the mirror than the
object A B. No. 1. (Fig. 267.)

No. 2.

Fig. 267. A. B, D H. (No. 2) represent two parallel rays incident on the convex surface
B H, the one (A B) perpendicularly, the other (D H) obliquely, c is the centre of con-
vexity. H E is the reflected ray of the oblique incident one, D H; whilst c H i is the
perpendicular.

Convex mirrors are not employed in any optical deception on a large
scale, although some ingenious delusions are producible from cylindrical
and conical mirrors, ana are thus described by Sir David Brewster :

" Among the ingenious and beautiful deceptions of the seventeenth
century, we must enumerate that of the re-formation of distorted
pictures by reflection from cylindrical and conical mirrors. In these
representations, the original image from which a perfect picture is pro-

280

BOY S PLAYBOOK OF SCIENCE.

duced, is often so completely distorted, that the eye cannot trace in it
the resemblance to any regular figure, and the greatest degree of
wonder is of course excited, whether the original image is concealed or
exposed to view. These distorted pictures may be drawn by strict
geometrical rules, and I have shown a simple method of executing
them. Let M be an accurate cylinder made of tin-plate or of thick

Fig. 268.

pasteboard. Out of the further side of it cut a small aperture, abed, and
out of the nearer side cut a larger one, A B c D (white letters), the size of
the picture to be distorted ; having perforated the outline of the picture
with small holes, place it in the opening A B c D (white letters), so that its
surface may be cylindrical ; let a candle or a bright luminous object the
smaller the better be placed at s, as far behind the picture A B c D (white
letters) as the eye is afterwards to be placed before it, and the light passing
through the small holes will represent on a horizontal plane a distorted
image of the picture at A B c D, which, when sketched in outline with a
pencil, shaded, and coloured, will be ready for use. If we now substitute
a polished cylindrical mirror of the same size in place of M, then the
distorted picture, when laid horizontally at A B c D, will be restored to
its original state when seen by reflection at A B c D (white letters) in
the polished mirror." The effect of a cylindrical mirror on a distorted pic-
ture is shown at No. 2, being copied from an old one seen by Sir D.
Brewster.

By looking at a reflection of the face in a dish-cover or the common
surface of a bright silver spoon or of a silver mug, the latter truly
becomes ugly as the image is seen reflected from its surface, and

PICTURES DISTORTED BY REFLECTION. 281

assumes the most absurd form as the mouth is opened or shut, and
the face advanced or removed from the silver vessel. (Fig. 269.)

Fig. 269. Distorted image produced by an irregular convex surface.

In the writings of the ancients there are to be found certain indica-
tions of the results of illusions produced by _ simple optical arrange-
ments, and the sudden and momentary apparition (from the gloom of
perfect darkness) of splendid palaces, delightful gardens, &c., with
which the concurrent voice of antiquity assures us the eyes of the
beholders were frequently dazzled in the mysteries, such as the evocation
and actual appearance of departed spirits, the occasional images of their
umbra, and of the gods themselves. Erom a passage in " Pausanias,"
(Bceotic xxx.), when, speaking of Orpheus, he says there was anciently
at Aornos, a place where the dead were evoked, veKvop.avrelov, we learn
that in those remote ages there were places set apart for the evocation
of the dead. Homer relates, in the eleventh book of the " Odyssey," the
admission of Ulysses alone into a place of this kind, when his interview
with his departed friend was interruptedly some fearful voice, and the
hero, apprehending the wrath of Proserpine, withdrew ; the priests who
managed these deceptive exhibitions no doubt adopted this method of
getting rid of their visitor, who might become too inquisitive, and dis-
cover the secret of the mysteries.

Of all the reflecting surfaces mentioned, none produce more interesting
deceptions than the concave mirror, and there is very little doubt that
silver mirrors of this form were known to the ancients, and employed in

282 . BOY'S PLAYBOOK OF SCIENCE.

some of their sacred mysteries. Mons. Salverte has industriously col-
lected in his valuable work the most interesting proofs of their use, and
quotes the following passage of " Damascius," in which the results
obtainable from a concave mirror are clearly apparent. (Fig. 270.)

Pig. 270. The picture of a human face, possibly reflected from a concave mirror concealed
below the floor of the temple ; the opening being hidden by a raised mass of stone, and
the worshippers confined to a certain part of the temple, and not allowed to ap-
proach it.

He says: "In a manifestation which ought not to be revealed

there appeared on the wall of the temple a mass of light which

at first seemed very remote ; it transformed itself in coming nearer into
a face evidently divine and supernatural, of a severe aspect, but mixed
with gentleness, and extremely beautiful. According to the institution
of a mysterious religion, the Alexandrians honoured it as Osiris and
Adonis."

Parallel rays thrown upon a concave surface are brought to a focus
or converge, and when an object is seen by reflection from a concave
surface, the representation of it is various, both with regard to its mag-

THE CONCAVE MIRROR.

283

nitude and situation, according as the distance of the object from the
reflecting surface is greater or less. (Fig. 271.) When the object is
placed between the focus of parallel rays
and the centre, the image falls on the
opposite side of the centre, and is larger
than the object, and in an inverted po-
sition. The rays which proceed from
any remote terrestrial object are nearly
parallel at the concave mirror not
strictly so, but come diverging to it in
separate pencils, or, as it were, bundles

No.l.

No. 2.

Fig. 271. No. 1. A B, D H represent two parallel rays incident on the concave sur-
face B H, whose centre of concavity is c. B v and H p are the reflected rays meeting each
other in F, and A B being perpendicular to the concave surface, is reflected in a straight line.
No. 2. A B. The object, i M. The image.

of rays, from each point of the side of the object next the mirror;
therefore they will not be converged to a point at the distance of half
the radius of the mirror's concavity from its reflecting surface, but in
separate points at a little greater distance from the concave mirror.
The nearer the object is to the mirror, the further these points will be
from it, and an inverted image of the object will be formed in them,
which will seem to hang pendant in the air, and will be seen by an eye
placed beyond it (with regard to the mirror), in all respects like the
object, and as distinct as the object itself. No. 2. (Fig. 271.)

Fig. 272. A B represents the object, s v the reflecting
surface, P its focus of parallel rays, and c its centre.
Through A and B, the extremities of the object, draw
the lines o B and c H, which are perpendicular to the
surface, and let A it, A o, be a pencil of rays flowing
from A. These rays proceeding from a point beyond
the focus of parallel rays, will, after reflection, con-
verge towards some point on the opposite side of the
centre, which will fall upon the perpendicular, B c, pro-
duced, but at a greater distance from c than the radiant
A from which they diverged. For the same reason,
rays flowing from B will converge to a point in the
perpendicular K c produced, which shall be further from
c than the radiant B, from whence it is evident that the
image i M is larger than the object A B, that it falls on
the contrary side of the centre, and that their positions
are inverted with respect to each other.

284

BOY S PLAYBOOK OF SCIENCE.

It appears, horn a circumstance in the life of Socrates, that the
effects of burning-glasses were known to the ancients ; and it is pro-
bable that the Romans em-
ployed the concave speculum
for the purpose of lighting the
"sacred fire." This is very
likely to be true, considering
that the priests who conducted
the heathen worship of Osiris
and Adonis were acquainted
with the use of concave metallic
specula, as already described at
page 2 8 2 . The effects that can
be produced with the aid of con-
cave mirrors are very impres-
sive, because they are not
merely confined to the reflec-
tion of inanimate objects, but
life and motion can be well
displayed by them ; thus, if a
man place himself directly be-
fore a concave mirror, but fur-
ther from it than its centre of

Fig. 273. A concave mirror, showing the ap- cnnoavifv hp will <SPP n in
pearlnce of the inverted and reflected image b C 7*^' fle : e( L an "*'
the air. verted image of himself in the

air between him and the mirror

of a less size than himself; and if he hold out his hand towards the
mirror the hand of the image will come out towards his hand and
coincide with it, being of an equal bulk when his hand is in the centre
of concavity, and he will imagine he may shake hands with his image.
(Kg. 273.)

By using alarge concave mirror of about three feet in diameter, the author
was enabled to show all the results to a large audience that were usu-
ally visible to one person only. Whilst experimenting with a concave
mirror, by holding out the hand in the manner described, a bystander
will see nothing of the image, because none of the reflected rays that
form it enter his eyes. This circumstance is well illustrated by placing
a concave mirror opposite the fire, and allowing the image of the flames
projected from it to fall upon a well-polished mahogany table. If the
aoor of the room opens towards the mirror, and a spectator unacquainted
with the properties of concave mirrors should enter the apartment, the
person would be greatly startled to see flames apparently playing over
the surface of the table, whilst another spectator might enter from
another door and see nothing but a long beam of light, rendered visible
by the floating particles of dust. To give proper effect to this experi-
ment the concave mirror should be large, and no other light must
illuminate the room except that from the fire.

On the same polished table the appearance of a planet with a re-

ILLUSIONS WITH CONCAVE MIRRORS.

285

solving satellite may be prettily shown bj darkening the fire with a
screen, and placing a lighted candle before it, which will be reflected by
the concave mirror, and appear on the table as a brilliant star of light,
and the satellite may be represented by the flame of a small wax taper
moved around the large burning candle. The following is the arrange-
ment used by the author at the Polytechnic Institution for the purpose
of exhibiting the properties of the concave mirror. A lantern enclosing
a very brilliant light, such as the electric or lime light, is required for
the illumination of the objects which are to be projected on to the
screw. The lantern and electric lamp of Duboscq was preferred,
although, of course, any bright light enclosed in a box, with a plain
convex lens to project the beam of light when required, will answer the
purpose. (Fig. 274.)

Fig. 274. A B. Portable screen of light framework, covered with black calico, coco.
Square aperture just above the shelf, D D, upon which the object viz., a bottle half full of
water is placed. B. Duboscq lantern to illuminate the object at D D.

By removing the diaphragm required to project the picture of the
charcoal points on to the screen, a very intense beam of light is ob-
tained, which may be focussed or concentrated on any opaque object
by another double convex lens, conveniently mounted with a telescope
stand, so that it may be raised or lowered at pleasure. This lens is
independent of the lantern, and may be used or not at the pleasure of
the operator.

The object is now placed on a shelf fixed to the screen, with a
square aperture just above it. The object of the screen is to cut off all
extraneous rays of light reflected from the mirror, or to increase the
sharpness of the outline of the picture of the object. The screen and
object being arranged, and the light thrown on from the lantern, the
next step is to adjust the concave mirror, and by moving it towards the

286 BOY'S PLAYBOOK OF SCIENCE.

object, or backwards, as the case requires, a good image, solid and quasi-
stereoscopic, is projected on to the screen. (Fig. 275.)

Fig. 275. A. The concave mirror. B. The lantern, c. The portable screen, shelf, and
object. "D. The inverted image of the bottle filling with water, with the neck downwards,
and when thrown on the disc at D producing a most curious illusion.

The act of filling the bottle with water, or better still with mercury,
is one of the most singular effects that can be shown ; and if all the
apparatus is enclosed in a box, so that the picture on the screen only is
apparent, the illusion of a bottle being filled in an inverted position is
quite magical, and invariably provokes the inquiry, how can it be done ?
The study of numismatics, the science of coins and medals, is generally
considered to be limited to the taste of a very few persons, and any
description of a collection of coins at a lecture would oe voted a great
bore, unless, of course, the members of the audience happened to be
antiquaries ; great light, however, may be thrown on history by a study
of these interesting remains of bygone times, and a lecture on this
subject, illustrated with pictures of coins thrown on to the disc by a
concave mirror in the manner described, might be made very pleasing
and instructive.

Coins, or plaster casts of coins gilt, flowers, birds, white mice, the
human face and hands, may all, when fully illuminated, be reflected by
the concave mirror on to the disc. A Daguerreotype picture at a
certain angle appears, when reflected by the concave mirror, to be like
any ordinary collodion negative, and all the lights and shadows are
reversed, so that the face of the portrait appears black, whilst the black
coat is white. On placing the Daguerreotype in another position, easily
found by experiment, it is now reflected in the ordinary manner, showing
an enlarged and perfect portrait on the disc. In using the Daguerreo-
type the glass in front of it must be removed. The pictures from the
concave mirror may be also projected on thick smoke procured from

EXPERIMENTS WITH MIRRORS.

287

smouldering damped brown paper, or from a mixture of pitch and a little-
chlorate of potash laid on paper, and allowed to burn slowly by wetting
it with water.

An image reflected from smoke would be visible to a number of
spectators, just as the light from the furnace fires of the locomotive is
frequently visible at night, being reflected on the escaping column of
steam.

It was probably with the help of some kind of smoke and the concave
speculum that the deception practised on the worshippers at the temple
of Hercules at Tyre was carried out, as it is mentioned by Pliny that a
consecrated stone existed there " from which the gods easily rose."
At the temple of Esculapius at Tarsus, and that of Enguinum in Sicily,
the same kind of optical delusions were exhibited as a portion of the
religious ceremonies, from which no doubt the priests obtained a very
handsome revenue, much more than could be obtained in modern times
by the mere exhibition of such wonders at Adelaide Galleries, Poly-
technics, or Panopticons.

The smoke from brown paper is very useful in showing the various
directions of the rays of light when reflected from plane, convex, and
concave surfaces. The equal angles of the incident and reflected rays
may be perfectly shown by using the next arrangement of apparatus.
(Fig. 276.)

Fig. 276. A. Rays of light slightly divergent issuing from the lantern, and received on
a little concave mirror, which brings the rays almost parallel, and reflects them to E, a
piece of looking-glass, from which they are again reflected, c is the incident, and B the
reflected rays. v. Smoke from brown paper.

A very dense white smoke is obtained by boiling in separate flasks
(the necks of which are brought close together) solutions of ammonia
and hydrochloric acid.

The opposite properties of convex and concave, mirrors the former
scattering and the latter collecting the rays of light which fall upon
them are also effectively demonstrated by the help of the same illumi-

BOY'S PLAYBOOK OF SCIENCE.

nating source and proper mirrors, the smoke tracing out perfectly the
direction of the rays of light. (Fig. 277.)

Fig. 277. The smoke shows the rays of light falling on a convex mirror, and rendered
still more divergent.

The smoke developes the cone of rays reflected from a concave
mirror in the most oeautiful manner, and by producing plenty of

Fig. 278. The smoke shows rays of light falling on the concave mirror. In this ex-
periment attention should be directed to the bright point, E, the focus where the con-
vergent rajs meet.

LORD ROSSE'S TELESCOPE.

289

smoke, and turning the mirror about the position of the focus (focus, a
fire-place), is indicated by a brilliant spot of light, and the reason the
images of objects reflected by the concave mirror are reversed, may be
better understood by observing how the rays cross each other at that
point. (Tig. 278.)

One of the most perfect applications of the reflection of light is
shown in the " Gregorian reflecting telescope," or in that magnificent
instrument constructed by Lord Rosse, at Parsonstown, in Ireland.
(Kg. 279.)

Fig. 279. Lord Rosse's gigantic telescope.

The description of nearly all elaborate optical instruments is some-
what tedious, but we venture to give one diagram, with the explana-
tion of the Gregorian reflecting telescope. (Fig. 280.)

At the bottom of the great tube T T T T, (Fig. 280), is placed the
large concave mirror D TJ v r, whose principal focus is at M ; and in its
middle is a round hole P, opposite to which is placed the small mirror
L, concave towards the greater one, and so fixed to a strong wire M, that
it may be moved farther from the great mirror or nearer to it, by means
of a long screw on the outside of the tube, keeping its axis still in the
same line P m n with that of the great one. Now since in viewing a
very remote object we can scarcely see a point of it but what is at least
as broad as the great mirror, we may consider the rays of each pencil,
which flow from every point of the object, to be parallel to each other,

290

BOY S PLAYBOOK OF SCIENCE.

and to cover the whole reflecting surface D u v F. But to avoid confusion
in the figure, we shall only draw two rays of a pencil flowing from each

Fig. 280. The Gregori an reflecting telescope.

extremity of the object into the great tube, and trace their progress
through all their reflections and refractions to the eye f, at the end of
the small tube 1 1, which is joined to the great one.

Let us then suppose the object A B to be at such a distance, that the
rays E flow from its lower extremity B, and the rays c from its upper
extremity A. Then the rays c falling parallel upon the great mirror at
D, will be thence reflected by converging in the direction D G ; and by
crossing at i in the principal focus of the mirror, they will form the
upper extremity i of the inverted image i K, similar to the lower extre-
mity B of the object A B ; and passing on the concave mirror L (whose
focus is at N) they will fall upon it at g and be thence reflected, con-
verging in the direction N, because g m is longer than g n ; and passing
through the hole p in the large mirror, they would meet somewhere
about r, and form the lower extremity d of the erect image a d, similar
to the lower extremity B of the object A B. But by passing through
the plano-convex glass E in their way they form that extremity of the
image at b. In like manner the rays E which come from the top of the
object A B and fall parallel upon the great mirror at F, are thence re-
flected converging to its focus, where they form the lower extremity K of
the inverted image i K, similar to the upper extremity A, of the object
A B ; and passing on to the smaller mirror L and falling upon it at h,
they are thence reflected in the converging state h o ; and going on
through the hole P of the great mirror, they would meet somewhere
about q, and form there the upper extremity a of the erect image a d,
similar to the upper extremity A of the object A B ; but by passing
through the convex glass R in their way, they meet and cross sooner, as
at a, where that point of the erect image is formed. The like being
understood of all those rays which flow from the intermediate points of
the object, between A and B, and enter the tube T T, all the intermediate
points of the image between a and b will be formed ; and the rays

gassing on from the image through the eye-glass s, and through a small
ole e in the end of the lesser tube 1 1, they enter the eye f which sees

THE BURNING MIRROR OF ARCHIMEDES. 291

the image a d (by means of the eye-glass), under the large angle c e d,
and magnified in length, under that angle, from c to d.

To find the magnifying power of this telescope, multiply the focal
distance of the great mirror by the distance of the small mirror, from
the image next the eye, and multiply the focal distance of the small
mirror by the focal distance of the eye-glass ; then divide the product
of the latter, and the quotient will express the magnifying power.
(Fig. 280.)

"We now come to that much disputed and often quoted experiment of
Archimedes, who is stated to have employed metallic concave specula or
some other reflecting surface by which he was enabled to set fire to the
Boman fleet anchored in the harbour of Syracuse, and at that time be-
sieging their city, in which the great and learned philosopher was shut up
with the other inhabitants. The story handed down to posterity was not
disputed till about the seventeenth century, when JDescartes boldly
attacked the truth of it on philosophical grounds, and for the time
silenced those who supported the veracity of this ancient Joe Miller.
Nearly a hundred years after this time, the neglected Archimedes fiction
was again examined by the celebrated naturalist Buffon, and the account
of his experiments detailed by the author of "Adversaria," in Chambers'
Journal, is so logical and conclusive, that we give a portion of it verbatim.
" For some years prior to 1747, the French naturalist Buffon had
been engaged in the prosecution of those researches upon heat which
he afterwards published in the first volume of the Supplement to his
'Natural History/ Without any previous knowledge, as it woidd
seem, of the mathematical treatise of Anthemius (irepi irapado^cov /LIJJ-
XavrjuaToav), in which a similar invention of the sixth century is de-
scribed,* Buffon was led, in spite of the reasonings of Descartes, to
conclude that a speculum or series of specula might be constructed
sufficient to obtain results little, if at all, inferior to those attributed to
the invention of Archimedes.

" This, after encountering many difficulties, which he had foreseen,
with great acuteness, and obviated with equal ingenuity, he at length
succeeded in effecting. In the spring of 1747, he laid before the French
Academy a memoir which, in his collected works, extends over upwards
of eighty pages. In this paper, he describes himself as in possession of
an apparatus by means of which he could set fire to planks at the distance
of 200, and even 210 feet, and melt metals and metallic minerals at
distances varying from twenty-five to forty feet. This apparatus he
describes as composed of ^68 plain glasses, silvered on the back, each
six inches broad oy eight inches long. These, he says, were ranged in
a large wooden frame, at intervals not exceeding the third of an inch ;
so that, by means of an adjustment behind, each should be moveable in
all directions independently of the rest the spaces between the glasses
being further of use in allowing the operator to see from behind the
point on which it behoved the various disks to be converged.

* See Gibbon's " Decline and Fall," chap, xl., section v., note g.
TJ 2

292 BOY'S PLAYBOOK OF SCIENCE.

" These results ascertained, Buffon's next inquiry was how far they
corresponded with those ascribed to the mirrors of Archimedes the
most particular account of which is given by the historians Zonaras and
Tzetzes, both of the twelfth century.* ' Archimedes/ says the first of
these writers, ' having received the rays of the sun on a mirror, bv the
thickness and polish of which they were reflected and united, kindled a
flame in the air, and darted it with full violence on the ships which
were anchored within a certain distance, and which were accordingly
reduced to ashes/ The same Zonaras relates that Proclus, a celebrated
mathematician of the sixth century, at the siege of Constantinople, set
on fire the Thracian fleet by means of brass mirrors. Tzetzes is yet
more particular. He tells us, that when the Roman galleys were within
a bow-shot of the city-walls, Archimedes caused a kind of hexagonal
speculum, with other smaller ones of twenty-four facets each, to be
placed at a proper distance ; that he moved these by means of hinges
and plates of metal ; that the hexagon was bisected by ' the meridian of
summer and winter / that it was placed opposite the sun ; and that a
great fire was thus kindled, which consumed the Roman fleet.

"Erom these accounts, we may conclude that the mirrors of Archimedes
and Bulfon were not very different either in their construction or effects.
No question, therefore, could remain of the latter having revived one of
the most beautiful inventions of former times, were there not one cir-
cumstance which still renders the antiquity of it doubtful : the writers
contemporary with Archimedes, or nearest his time, make no mention
of these mirrors. Livy, who is so fond of the marvellous, and Polybius,
whose accuracy so great an invention could scarcely have escaped, are
altogether silent on the subject. Plutarch, who has collected so many
particulars relative to Archimedes, speaks no more of it than the former
two ; and Galen, who lived in the second century, is the first writer by
whom we find it mentioned. It is, however, difficult to conceive how
the notion of such mirrors having ever existed could have occurred, if
they never had been actually employed. The idea is greatly above the
reach of those minds which are usually occupied in inventing falsehoods;
and if the mirrors of Archimedes are a fiction, it must be granted that
they are the fiction of a philosopher."

Supposing that Archimedes really did project the concentrated rays
of the sun on the Roman vessels, one cannot help pitying the ignorance
of the Admiral Marcellus. Had this officer been acquainted with the
laws of the reflection of light, he might have laughed to scorn the
power of Archimedes, and by receiving the unfriendly rays on one of
tha bright brazen convex shields of his soldiers, Marcellus could have
scattered the concentrated rays, and prevented the burning of his
vessels.

In these days of learning it therefore appears strange to find any one
advocating the possible use of specula or reflecting mirrors for the
purposes of offence or defence, but M. Peyrard a few years ago proposed

* Quoted by Fabricius in Ms "Biblioth. Grac.," vol. ii., pp. 551, 552.

THE BUKJNING MIRROR OF ARCHIMEDES.

293

to produce great effects by mounting each mirror in a distinct frame,
carrying a telescope so that one person could direct the rays to the
object intended to be set on fire, and he gravely calculated, presuming
on the ignorance of the attacked, that with 590 glasses of about twenty
inches in diameter, he could reduce a fleet to ashes at the distance of
a quarter of a league ! and with glasses of double that size at the dis-
tance of half a mile ! Wbat effect a shell or shot would produce upon
this ancient weapon is not stated ; this we may safely leave our readers
to determine for themselves. The experiment of Archimedes has long
been a favourite one with the boys. (Fig. 281.)

Fig. 281. One of the " miseries of reflection"

The total internal reflection of light by a column of water is an ex-
periment that admits of great variety so far as colour is concerned, and
is one of the most novel and beautiful experiments with light presented
to the public within the last few years. The author had the pleasure
of introducing it in the first place at the Polytechnic Institution, where
the optical novelty excited the greatest attention, and received the
approbation of her Most Gracious Majesty, and his Royal Highness
the Prince Consort, with the Royal Family, who were pleased to pay a
private evening visit to the Polytechnic, and amongst other things
minutely examined the " Illuminated Cascade," which had been erected
by Mons. Duboscq of Paris.

The illumination of the descending columns of water was obtained by
converging the rays from a powerful electric light upon the orifice from

294

BOY S PLAYBOOK OF SCIENCE.

which the water escaped, the Duboscq lantern already explained being
employed, and in front of it were placed three cylinders, each having a
circular window behind and opposite the lens, and an aperture of about
one inch in diameter on the opposite side for the escape of water. The

Fig. 282. Fig. 1. A. The electric light. BCD. The three sides and lenses of the
lantern. E ~s G. The three cylinders of water, each with a circular glass window and
orifices at z z z, from which the water and rays of light pass out. Fig. 2. H. Section of
one side of the Duboscq lantern, i i. Cylinder of water, which enters from below.
K K. The stream of illuminated water, i. L. Bit of coloured glass held between the
lantern and the cistern of water.

lantern used was of a peculiar shape, and had three sides, the electric
light being in the centre of them, and passing through three separate
plano-convex lenses to the three cylinders from which the water escaped.
Attention may be directed to the fact that the light merely passes
out of the orifices as a diverging beam of light until the flow of water
commences, when the rays are immediately taken up and reflected from

THE ILLUMINATED CASCADE.

295

point to point inside the arched column of water, and illuminalingtlie latter
in the most lovely manner, it appears sometimes like a stream of liquid
metal from the iron furnace, or like liquid ruby glass, or of an amethyst
or topaz colour, according to the colours of the plates of glass held
between the mouths of the lantern and the circular windows in the
cylinders of water. The same experi-
ment created quite a furore at the
Crystalralace when it was introduced
in one ci' the author's lectures deli-
vered in that noble place of amuse-
ment. In order that our readers may
understand the arrangement of the
apparatus, we have given at page 294
a ground plan view of it, as also the
appearance of the cascade when exhi-
bited at the Polytechnic to the Royal
party. (Fig. 284.)

Another curious effect observed with
the illuminated cascade, is the descent
of balls of light as the reflection is cut
off for a moment by passing the
finger through the stream of water,
showing that a certain time is occupied
in the reflection' of light from one end
of the cylinder of water to the other ;
indeed the best idea of the rationale

of the experiment is formed by substi- of beamf

tutmg in imagination a Sliver tube light passing down inside the water,
highly polished in the interior, for the

descending jet of water. The reflection of sound takes place precisely
in the same manner, and the vibrations of the air are reflected from plane,
concave, and convex surfaces. It is on this principle that waves of sound
thrown off from different surfaces (as of hard rocks), produce the effect
of the echo. The sounds arrive at the ear in succession, those reflected
nearest the ear being first, and the reflecting surfaces at the greatest
distance sending the waves of sound to the ear after the former. At
Lurley Palls on the Rhine, there is an echo which repeats se^e^teen
times. Whispering galleries, again, illustrate the reflection of sound
from continuous curved surfaces, just as the arched column of water
reflects from its interior curved surfaces the rays of light.

Speaking-tubes are well known in which the waves of sound are
successively reflected from the sides, exactly like the "Illuminated
Cascade" (Fig. 283). The speaking-trumpet is also another and familiar
example of the same principle. Probably when Albertus Magnus con-
structed the brazen head, which had the power of talking, it was nothing
more than a metallic head with a few wheels and visible mechanism
inside, but connected with a lower apartment by a hollow metal tube,
where Albertus Magnus descended, and astonished the ignorant with

Fig. 283. A B.

The sides of the cas-
nes show the re-

396

BOY'S PLATBOOK OF SCIENCE.

same effect occurs in the

THE KALEIDOSCOPE.

frequent occasion to mention the name of Sii D^rid B?ewster a d

THE KALEIDOSCOPE.

297

that will be noticed in another part of this book, but here we shall
describe one of the most original optical instruments ever devised, and
although it is now regarded as a mere toy, its merits are very great.
The title of the instrument is borrowed from the Greek KO.\OS, beautiful,
ei8os, a form or appearance, a-K07re<, to see ; and the public certainly
endorsed the name when they purchased 200,000 of these instru-
ments in London and Paris during the space of three months. It is
said that the sensation it excited in London, throughout all ranks
of the community, was astonishing, and people were everywhere seen,
even at the corners of the streets, looking through the kaleidoscope.
The essential parts of this instrument are two mirrors of unsilvered
black parallel glass, or plate glass painted black on one side, which
should be from six to ten inches in length, and from one inch to an inch
and a half in breadth at the object end, while they are made narrower
at the other end, to which the eye is applied. The mirrors are united
at their lower edges by a strip of black calico fixed with common glue,
and are left open at the upper edges, and retained at the proper angle
by a bit of cork properly blackened. The angles are 36 , 30, 25f,
22i 20, 18, which divide the circumference into 10, 12, 14, 16, 18,
20 parts, thus 36 X 10 = 360, or 18 X 20 = 360, and the strictest
attention must be paid to this part of the adjustment, or the figures
produced will not be symmetrical. After the mirrors are adjusted to

Fig. 285. A u. The tube containing the two mirrors, shown by dotted lines. A. is the
small end where the eye is placed. B. The object end. c D. Another view of the mirrors
arranged to place in the tube; the shaded portion represents the black velvet. E. Double
convex lees. F. Box to contain obieets, and usually fitted with ground glass outside.

298 BOY'S PLAYBOOK OF SCIENCE.

the proper angle, the space between the two upper edges should be
covered across with black velvet and the mirrors placed in a tin or
brass tube, so that the broad ends shall barely project beyond the
end, while the narrow end is placed so that the angle formed by the
junction of the mirrors shall be a little below the middle of that end of the
tube. A cover with a circular aperture in the centre is then to be fitted
to the narrow end of the mirrors, which should in general be furnished
with a convex lens whose focal length is an inch or two greater than
the length of the mirrors. A case for holding the objects, and for com-
municating to them a revolving motion, is fitted to the object end of the
tube. The objects best suited for producing pleasing effects are small
fragments of coloured glass, wires of glass, both spun and twisted, and of
different colours and shades of colours, and of various shapes, in curves,
angles, circles ; also, beads, bugles, fine needles, small pieces of lace, and
fragments of fine sea-weed are very beautiful. M. Sturm, of Prague, has
lately fixed the images of the kaleidoscope, so that they are available for the
production of patterns in every branch of silk, cotton, and mixed fabrics.
Photographs could be taken of the most beautiful of these accidental
designs, which only occur once, and if not copied are lost.

CHAPTER XXII.

THE REFRACTION OF LIGHT.

THIS term appears to be often confounded with that of reflection, and
signifies the bending or breaking back of a ray of light (re, back, and
frango, to break) ; and it will be remembered that when light falls on
the surface of a solid (either liquid or gaseous) body, it may be reflected
(re, back, andjfetfo, to bend), refracted, polarized, or absorbed. In the
previous chapter the property of the reflection of light has been fully
investigated, and in this one refraction only will be considered. It is
a property which has been, and will continue to be, of the greatest
practical utility in its application to the construction of all magnifying
glasses, whether belonging to the telescope, microscope, magic lantern, or
the dissolving views ; or the minor refracting instruments such as spec-
tacles, opera-glasses, &c. ; and it should be remembered that tneir
magnifying power depends solely on the property of refraction.

If substances such as glass had not been endowed with this property,
it would be difficult to understand how the great discoveries in the
science of astronomy could have been made, or what information we
could have gained respecting those interesting truths so constantly
revealed by the aid of the microscope. Numerous instances mi^ht be
quoted of the value of this latter instrument in the detection of
adulteration, and the examination of organic structures. When so
many talented and industrious scientific men are at work with thia

THE REFRACTION OF LIGHT.

instrument, it is perhaps invidious to point to one singly, though we
must make an exception in favour of Professor Ehrenberg, of Berlin, whose
microscope did such good service in procuring undeniable proof of the
Simonides' fraud ; he has made use of it again to detect the thief that
stole a barrel of specie, which had been purloined on one of the
railways. One of a number of barrels, that should have contained
coin, was found on arrival at its destination to have been emptied of its
precious contents, and refilled with sand. On Professor Ehrenberg
being consulted, he sent for samples of sand from all the stations along
the clifferent lines of railway that the specie had passed, and by means
of his microscope identified the station from which the sand must have
been taken. The station once discovered, it was not difficult to hit
upon the culprit in the small number of employes on duty there.

The simplest case of refraction occurs in tracing the course of a ray
of light through the air, and into the medium water ; in this case it
passes from a rare to a dense me-
dium, and the fact itself is well il-
lustrated by the next diagram, in
which the shaded portion repre-
sents water, and the paper that it
is drawn upon the air. The line
A B is a perpendicular ray of light,
which passes straight from the air
into and through the water, with-
out being changed in its direction.
The line c D is another ray, inclined
from the perpendicular, and enter-
ing the water at an angle, does not
rs in the straight line indicated
the dotted line, but is refracted
or bent towards the perpendicular at D E.

This fact reduced to the brevity of scientific laws is thus expressed :
When a ray of light falls perpendicularly on a refracting surface, it does
not experience any refraction or change of direction. When light passes
out of a rare into a dense medium, as from air into water, the angle of
incidence is greater than the angle of refraction. And when light passes
from a dense into a rare medium, as out of water into air, the reverse
takes place, and the angle of incidence is smaller than the angle of re-
fraction.

In order to illustrate these laws, a zinc-worker or tinman may con-
struct a little tank, with glass windows in the front and sides, the
latter being as deep as the half-circle described on the back metal plate
of the tank, which of course rises higher, in order to show the full
circle; this should be japanned white, and a perpendicular and hori-
zontal black line described upon it the whole, with the exception of
the circle, being japanned black. If the Duboscq lantern is arranged
with the little mirror, as described in fig. 276, page 287, the ray of
light may be thrown perpendicularly, or at an angle, through the water,

Fig. 286.

300

BOY'S FLAYBOOK OF SCIENCE.

and the actual breaking back of the ray of light is rendered distinctly
apparent. (Fig. 287.)

Fig. 287. A. Duboscq lantern. B. The mirror. B c. The incident ray. c D. The re-
fracted ray. B p. Tank, containing water up to the horizontal line of the circle.

The refraction of light is also well displayed by Duboscq's apparatus,
with the plano-convex lens, and a brass arrow as an object, with another
double convex lens to focus it. When a good sharp outline of the
arrow is obtained on the disc, a portion of the rays of light producing it
may then be truly broken out or refracted by laying across the brass
arrow a square bar of plate glass. (Fig. 288).

f P

Fig. 288. A. Bays of light from the electric light. B. The cap, with figure of arrow
cut out. c. The bar of plate glass. D. The double convex glass to focus E, the image
on the disc, and portion refracted at B.

There are many simple ways in which the refraction of light is dis-
played, such as the apparent breaking of an oar where it enters the
water, or the remarkable manner in which the bottom is lifted up when
we look, at any angle, through the clear water of a deep river or lake ;
the latter circumstance has unhappily led to most serious accidents, in
consequence of children being induced by the apparent shallowness of

GLASS LENSES.

301

the water to get in and bathe. Fish, again, unless seen perpendicularly
I from a boat, always appear nearer than their true position, and the
Indians, when they spear fish, always take care to strike as near the
perpendicular as possible ; experienced shots know they must aim a
little lower and nearer than the apparent position of a fish in order to
hit it.

Having learnt that light is bent from its course, it might be supposed
that all objects looked at through plate glass should appear distorted;
but it must be remembered that the sides of the glass being nearly
parallel, an equal amount of refraction occurs in every direction so
that, unless the window is glazed with uneven wavy glass, the object,
for all practical purposes, does not apparently change its position, being
neither moved to the right or the left, or upward or downward. In
order to bend the rays of light in the required direction, the glass must
be cut into certain figures called prisms, plane glasses, spheres, and lenses,
some of which are shown in the annexed cut. (Fig. 289.)

Fig. 289.

It would be tedious to trace out, by a regular series of diagrams, the
passage of light through the variety of combinations of lenses ; and as
the plane, convex, and concave
surfaces have been examined with
respect to their effect on the re-
flection of light, they may be re-
ferred to again with regard to
their influence in refracting light.
In the latter it will be found that D-
convex and concave lenses have B

just the opposite properties of Fig. 290. A B. A double convex lens, c is a
mirrnr! tTini n rnnvpv IPTKJ rp ray of light, which falls perpendicularly on A B,

mirroi s , tuns, a convex lens ,- ai / d ther 6 efore s on s ^ ra f ht to & focus ;
ceivmg parallel rays will cause i> D . Kays falling at an angle on AB, refracted
them to converge to a focus, to focus, F.

(Fig. 290.) The case of short-sighted, persons arises from too great a
convexity of the eye, which makes a very near focus; and that of old
people is a flattening of the eye, by which the focus is thrown to a greater
distance. The remedy for the latter is a convex spectacle-glass, whilst
a concave lens is required for the former, to scatter the rays and pre-
vent their coming to a point too soon.

302

BOY S PLAYBOOK OF SCIENCE.

The action of a concave re-
fracting surface is again the op-
posite to a concave reflecting
surface the former disperses
the -rays of light, whilst the latter
collects them. A concave lens,
as might be expected, produces
exactly the contrary effect on
light to that of a concave mirror.
(Eig. 291.)

These facts are well shown
with the aid of the lantern and
electric light. The rays of light
are refracted in a visible manner when received on a concave or convex
lens, provided a little smoke from paper is employed, as in the mirror
experiments. (Tig. 292.)

tfig. 291. A B. A double concave lens, c Is a
ray of light which falls perpendicularly on. A B,
and passes through without any alteration of its
course. D D. Rays falling at an angle on A B, are
refracted and diverged.

Fig. 292. A. The electric light. B. The lens.

Bearing these elementary truths in mind, it will not be difficult to
follow out a complete set of illustrations explanatory of the con-
struction and use of various popular optical contrivances.

303
CHAPTER XXIII.

REFRACTING OPTICAL INSTRUMENTS.

I. The Magic Lantern.

No other optical instrument lias ever caused so mucli wonderment
and delight, from its origin to the present time, as this simple contri-
vance. Eor a long time its true value was overlooked, and only
ridiculous or comic slides painted, but its educational importance is
now being thoroughly appreciated, not only on account of the size of
the diagrams that may be represented on the disc, but also from the fact
that the attention of an audience is
better secured in a room when the only
object visible is the diagram under ex-
planation. The lenses it contains are a
"bull's eye" or plano-convex, nearest
the light, and a double convex glass,
for the purpose of focussing the picture
which is inverted and placed between
the two lenses. (Fig. 293.)

In many books full directions are
given for painting the glass slides, but
this is an art that requires very great
practice and experience. A person may
know how to draw and paint on paper
or canvas, but it is quite a different
thing where glass is concerned, and un-
less the juvenile artist has taken lessons Kg. 293. The magic lantern,
from a regular painter on glass, his or

her efforts are likely to be very unsatisfactory. In many popular works
embracing the subject of optics, full directions are given on the mode of
painting the slides for the magic lantern, or dissolving views ; a new
era, however, has dawned upon this mode of illustration, in the prepara-
tion of photographs on glass of the most lovely description, and now
instead of exhibiting mere daubs of weak colouring, photographic
pictures of singular perfection can be procured of Messrs. Negretti and
Zambra, Holborn, who have turned their attention especially to this
branch, and supply slides of all sizes.

IE. The Dissolving Views.

This very pleasing modification of the ordinary magic lantern is dis-
played with the assistance of two lanterns of the same size, provided
with lamps and lenses wliich are exactly alike. They are best arranged

304

PLAYBOOK OF SCIENCE.

on one board, side by side, and if kept parallel with each other, the
circles of light thrown from the two lanterns would not coincide on
the screen ; it is therefore necessary to place one of them at an angle
which will vary according to the distance from the screen. The task
of making the two circles of light overlap each other precisely on the
disc, is called centering the lanterns, and is the first thing that must
be attended to before exhibiting the slides. The slides for the dissolving
views are all painted of the same size, and supposing a scene such as a
church with a bridal procession and the trees in full foliage, to represent
summer, is first thrown on to the disc, it may be changed to winter by
putting another picture of the same subject, but painted to represent
bare trees, and the church and ground covered with snow, and a grave
open, with a funeral procession. The two pictures must not be pro-
jected on the screen at the same time, and here the dissolving
mechanism is required ; it consists of two fans so arranged that
they may be raised or lowered by a rack- work and handle; one fan
in descending covers one of the nozzles of the lanterns, and the other
leaves the second lantern open, and free to project the picture ; the
dissolving is managed by slowly moving the handle of the rack- work,
so that one quarter of the picture already on the disc is cut off, and one
quarter of the new one thrown on. As the movement proceeds, one
half of the old picture is shut out, and one half of the new slide takes
its place, and so on, till the whole of the original picture is cut off by
the fan and the new one comes into view, ana it is in this way the effect
of the change from summer to winter is produced. (Fig. 294.)

Fig. 294. Nozzle of one lantern, with the fan, A, raised, and in the position to throw a
picture on the disc. B. The other fan shutting off the second lantern.

When two pictures such as those already described, dissolve one into
the other, of course the same building or other marked portion of the
subject, must strictly coincide in each picture on the disc, or else the
two pictures are apparent, and the illusion is destroyed. The pictures
must all be centered, before the exhibition commences. By the arrange-
ment of Mons. Duboscq, one electric light serves to illuminate both lan-
terns by making use of mirrors. The dissolving apparatus is likewise very

THE DISSOLVING VIEWS.

305

simple, and consists of two diamond-shaped openings in a brass frame,
which open and shut alternately by a slide worked with a handle. The
single light is not to be recommended, as it is somewhat troublesome to
manage properly. (Kg. 295.)

Fig. 295. A. The electric light. B B. The two sets of lenses for the two pictures.
c. The dissolving mechanism. D. The picture on screen.

When dissolving views are required on a grand scale, the lenses must
be exceedingly large, and the condenser (corresponding with the " bull's-
eye" of the simple magic lantern) should be at least nine or eleven inches
in diameter, and the front glasses must be of a superior make. The
lenses for a large lantern lit by the oxy -hydrogen light, are arranged
as in the next cut. (Fig. 296.)

Fig. 296. A. The lime light. B. The condensers, c. The picture. D D. The front
lenses for focussing, with rack-work.

At the Polytechnic the author had no less than six lanterns working
at or about the same time, to produce effects, in the views illustrating
the voyages of Sinbad the Sailor ; and in order to obtain the increased

306

BOYS PLAYBOOK OP SCIENCE.

results required for dioramic effects, sucli for instance as the Siege oi
Delhi, showing the bursting of the shells, &c., the four fixed lanterns (the
fronts of which are shown in the next cut) were always employed. The
two upper lanterns are dissolved by discs of brass worked by the hand,
and the lower ones with the fans. (Fig. 297.)

Fig. 297. Fronts of the four lanterns, showing how the dissolving mechanism is arranged.

"Behind the scenes" always has a great attraction for young people ; we
have, therefore, in the frontispiece, with the help of Mr.Hine (who painted
a great number of the photographs shown at the Polytechnic during the
author's management), given a section of the large theatre taken whilst
the effective scene of the Siege of Delhi was in progress. The optical
effects were assisted by various sounds in imitation of -war's alarms, for
the production of which, more volunteers than were required would
occasionally trespass behind the screen, and produce those terrific sounds
that some persons of a nervous temperament said were really stunning.
In a page picture, we have also given a correct drawing of the interior
of the optical box at the Polytechnic, with the four fixed lanterns, and
side cupboards to hold the glass pictures. The four lanterns worked on,
a railway, with wheels and a circular turn-table; they could be removed,
and the microscope arranged in their places.

THE MICROSCOPE AND PHYSIOSCOPE.

307

III. The Oxy-IIydrogen Microscope.

Many persons will recollect the first exhibition of this instrument in
Bond-street, by Mr. _ J. T. Cooper, and Mr. Gary, succeeded by the
Adelaide Gallery exhibition of scientific wonders and an oxy-hydrogen
microscope. The apparatus for this purpose consists of three condensing
lenses and an object glass. The objects, such as live aquatic insects, are
placed in glass troughs containing water; the other objects, ferns,
feathers, butterflies, algse, &c. &c., being mounted on slides in the
ordinary way with Canada balsam. (Eig. 298.)

Fig. 298. A. The lime light, c c c. Condensers. D. The object, such as a tank of water
containing live insects. B. The object glasses.

IV. The Physioscope.

This instrument, brought out at the Polytechnic during the time that
Mr. J. F. Goddard managed the optical department of the institution,
always excited the greatest mirth and astonishment amongst the nume-
rous visitors ; and habitues of the old place may remember the good-
natured inimitable maudlin simper with which poor Mr. Tait (who was one
of the living objects shown on the disc) used to drink off the glass of wine
and then wink at the audience. When we say Mr. Tait used to wink,
of course it is understood that he was personally invisible, and his
apparition or image only appeared on the disc. The countenance is
brilliantly illuminated by the oxy-hydrogen light, and being placed near
the lenses, the rays are reflected from the face into the physioscope, and
being properly focused, and the inversion of the image corrected, the
perfect representation of the human countenance is apparent on the
disc. The lenses and concave reflectors required are shown in the
section of the physioscope. Messrs. Carpenter and Westley, of Regent-
street, have brought the manufacture of magic lanterns to great
perfection ; and Mr. Collins, of the Polytechnic, constructs every kind of
dissolving view apparatus, oxy-hydrogen microscopes, physioscopes,
&c. (Fig. 299.) With this instrument any opaque objects (provided
they reflect light properly) may be displayed to a large audience.
Plaster casts appear with singular beauty and softness, whilst flowers,
stuffed birds, and especially humming birds, are excellent objects for the
physioscope.

x 2

303

BOY'S PLAYBOOK OF SCIENCE.

Fig. 299. A. One or more lime lights, throwing rays reflected by concave mirrors on to
the face B, from whence they are reflected to c c, the first condensers. D D. Object glasses.
This instrument is made by Mr. Collins, who has the tools for making the reflectors with
correct curves. The picture of the face on the disc is covered with black spots if tho
reflectors are not perfect.

V. The Camera Obscura.

A "dark chamber" is the name of a most amusing, and now, in the im-
proved form, extremely valuable instrument for photographic purposes. It
is occasionally to be met with in public gardens, and there is a very good
one on the Hoe at Plymouth. The construction of the camera for
observing the surrounding country is very simple, and merely consists
of a flat mirror placed at an angle, by which the picture is reflected
through a double-convex lens on to a white table beneath. (Fig. 300.)

Fiy. 300. A. The mirror. B. The convex lens. c. The white tablo.

THE ANALYSIS OF LIGHT. 309

The term "focusing," or the art of moving the lenses so that a
sharp image may be obtained, has been frequently mentioned in this
article, and perhaps it may be as well to describe the mode of ascer-
taining the focal distance of a lens by experiment.

Hold the lens opposite the window so that a bright picture of the
window-sash may be obtained on a sheet of paper pinned against the
wall, and the distance of the lens from the paper will be the focal length.

If the lens has a very long focal length, it may be determined as
follows : Measure the distance between the lens and the object, and
also from the image ; multiply these distances together, and divide the
product by their sums ; the quotient will give the focal distance.

VI. The Decomposition of Light "its Analysis and Synthesis"

It is in the Italian language that the bride, the emblem of purity, is
called Lucia (Lux, light) ; and surely if an illustration were required of
beauty and singleness, light would be named
poetically as appropriate ; but physically it is
not of a single nature, it is composite, and made
up of seven colours. The instrument required
to refract a ray of light sufficiently to break it
into its elementary colours is called the prism,
and is a solid having two plane surfaces, called
its refracting surfaces, with a base equally in-
clined to them. (Tig. 301.)

It was in 1672 that Sir Isaac Newton made
his celebrated .analysis ^flight by receiving
a sunbeam (as it passed through a hole in a the refracting surfaces, c A, CB.
shutter) on to the refracting surface of a

prism, and throwing the image or spectrum on to a screen, where he
observed the seven colours, red, orange, yellow, green, blue, indigo, and
violet, and thus proved " that there are different species of light, and that
each species is disposed both to suffer a different degree of refratigibility in
passing out of one medium into another, and to excite in us the idea of a
different colour from the rest ; and that bodies appear of that colour which
arises from the composition of those colours the several species they reflect
are disposed to excite"

Sir Isaac Newton's name would have been immortalized by this dis-
covery alone, even if he had not possessed that transcendent ability
which raised him above all other mathematicians and physicists.
It is at the same time interesting to know that the ancient author
Claudian (A.D. 420) inquires " whether colour really belongs to the sub-
stances themselves, or whether by the reflection of light they cheat the
eye enquires sitve color proprius rerum, lucisne repulsa eludant aciem"

Sir Isaac Newton determined that the spectrum could be divided
into 360 equal parts, of which red occupied 45, orange 27, yellow 48,
green 60, blue 60, indigo 40, violet 80. He also discovered that if the
highly refracted rays, the seven colours, or spectrum were received into

310

BOY S PLAYBOOK OP SCIENCE.

a concave mirror or a double-convex lens, that they again united and
formed white light. In order to demonstrate the properties of the
prism in various positions, the next diagram may be adduced. (Fig. 302.)

Fig. 302. A. The ray of light passing through two prisms B placed base to base. In
this position the light passes through to the second prism, c, without alteration. At c
the decomposition of light occurs, and the spectrum is shown at D . The top prism at B
used singly would reflect the ray to B without decomposing it into the coloured rays.

The rainbow is the most beautiful natural optical phenomenon with
which we are acquainted ; it is only seen in rainy weather when the sun
illuminates the falling rain, and the spectator has the sun at his back.
There are frequently two bows seen, the interior and exterior bow, or
the primary and secondary, and even within the primary rainbow, and
in contact with it, and outside the secondary one, there have been seen
other bows beyond the number stated.

The primary or inner rainbow consists of seven different coloured
bows, and is usually the brightest, being formed by the rays of light
falling on the upper parts of the drops of rain. The exterior bow is
formed by the rays of light falling on the lower parts of the drops of
rain; and in both cases the rays of light undergo refraction and
reflection, hence the opinion of Aristotle, that the rainbow is caused
only by the reflection of light, is not correct.

The first refraction occurs when the rays of light enter, and the
second when they emerge from the spheroids of water in the first bow ;
the refracted rays undergo only one reflection, whereas in the second
the brilliancy of the colours is impaired by two reflections.

The spectrum from the electric light is one of the most gorgeous
exhibitions of colour that can be conceived ; and the instruments re-
quired for the purpose are illustrated in No. 1 (Fig. 303), whilst the

THE ANALYSIS AND SYNTHESIS OF LIGHT.

311

synthesis of the coloured rays and production of white light is shown
at No. 2 of the same figure. (Fig. 303.)

Fig. 303. No. 1. A. The electric light, u. The narrow slit through which the light
passes to the convex lens, c. D. The prism. E. The spectrum. No. 2 is the same for
A B c D ; but F is the convex lens collecting the scattered rays, and forming white light
ate.

VII. Duration oftlie Impression of Light.

If a circular disc is painted with the prismatic colours taken in the
same proportion with respect to each other in which they are exhibited in
the spectrum made by the prism, and the wheel is turned swiftly, then
the individual colours disappear, and nearly white light is apparent.
The cause is due to the same principle that creates the appearance of a
complete circle of fire when a burning squib is moved quickly round
before it is thrown away to burst, and as it is evident that the burning
squib cannot be in every part of the circle at the same moment, there
must be some inherent faculty belonging to the human eye which
enables it to retain for a definite period the impression of images that
may fall upon it ; and this principle has been so far pressed, as it were,
beyond its limits, that it is gravely asserted the image of a man's mur-
derer " might be discovered on the retina of the eye-ball if that could be
examined sufficiently quick after death." The fixture of the picture is
said to be due to a sort of natural photographic process ; but such fanciful
statements often lead the mind into dream-land only, and so we will
return to the fact of the duration of the impression of light on the eye
as evidenced by several ingenious optical instruments, and especially by
the scientific inventions of Dr. Faraday, Dr. Paris, and of Mr. Thomas
Rose of Glasgow.

By careful experiment M. D'Arcy found that the light of a live coal
moving at the distance of 165 feet, maintained its impression on the

312

BOY S PLAYBOOK OF SCIENCE.

retina during the seventh part of a second. Hence the cause of the
reeomposition of white light when the colours on the disc are quickly
rotated. Each colour at any point succeeds the other before the impres-
sion of the last is gone from the eye, and provided the colours move
round within the seventh part of a second, they are all impressed toge-
ther on the eye, and meeting on the retina, produce the effect of white
light.

"VHI. The Phenakistiscope.

This amusing instrument consists of a turning wheel upon which figures
appear to jump, walk, or dance. The disc or wheel is of cardboard,
upon which are painted (towards the peri-
phery) figures in eight, ten, or twelve
postures. Thus, if it is desired to repre-
sent clowns turning round in a circle, twelve
different positions of the figure in the act of
turning are painted on the disc, and above
each of the figures on the wheel a slit is cut
about one inch long, and a quarter of an
inch wide in a direction corresponding with
the radii of the circle. This simple form of
the instrument is used by placing the figured
side towards a looking-glass and then causing
it to revolve at a certain speed, which is
ascertained by experiment ; and as the spec-
tator looks'through the slits into the looking-
Design for the phe- glass, the clowns appear to turn round. At
^ e Polytechnic Institution there are two
of these wheels with looking-glasses, and
supported by a handle through although the same designs have done duty

the centre, round which it is f .-, ,-& ,, , ,-, .

twirled by the other hand. for many years, they still attract the public

attention. (Fig. 304.)

In the "Journal of the Royal Institution" Mr. Faraday has de-
scribed some very interesting experiments and optical illusions produced
by the revolution of wheels in different directions and velocities. The
wheels are made of cardboard, and by cutting out two cog wheels of an
equal size, and placing one above the other on a pin, the usual hazy
tint when the cogs are acting is apparent when they are whirled round ;
but if the two cog wheels are made to move in opposite directions,
there will be the extraordinary appearance of a fixed spectral wheel.
If the cogs are cut in a slanting direction on both wheels, the spectral
wheel will exhibit slanting cogs ; but if one wheel is turned so that the
cogs shall point in opposite directions, then the spectral wheel will have
straight cogs. A number of such wheels set in motion in a darkened
room, and illuminated suddenly with the light from the electric spark,
appear to stand perfectly still, although moving with a great velocity.
An expensive 'instrument has been constructed by Duboscq, for the

Fig. 304.
nakistiscope. The spectator is
supposed to be looking towards
a mirror through the slits. It is

THE PHENAKISTISCOPE.

purpose of showing the usual phenakistiscope effects on the screen
with the magic lantern; a very limited picture, however, is shown, and
there is still great room for the improvement of the apparatus. (Eig. 305.)

No. 1.

No. 3.

No. 2.

Fig. 305. Phenakistiscope made by Duboscq, of Paris. No. 1. Apparatus in elevation
with the condensers. No. 2. Section 1 * of the apparatus. A. The light. B. Condenser, or
plano-convex lens. c. Round glass disc with design painted on it. D. Wooden disc with
four double-convex lenses placed at equal distances from each other, so as to coincide
with c, whilst rotating. Both the latter and c rotate, and the picture is focussed on the diso
by the lenses p. No. 3. Glass plate, with device painted thereon.

314 BOY'S PLAYBOOK OF SCIENCE.

IX. The Thaumatrope.

This very simple toy was invented by the late Dr. Paris, who gave it
an appropriate name, compounded of the Greek words, #av/za, wonder,
rpeVa), to turn. The duration of the impressions of light on the eye
is very apparent whilst using this toy, which is usually made of a
circular piece of cardboard, having on one side a painting of a man's
head, and on the other a hat ; or a picture of a lighted candle on one
face of the cardboard, and an extinguisher on the other ; or a
gate, and a horseman leaping it. Each pair of designs painted on
opposite sides of the cardboard appear to be one when twisted round
by strings tied to the opposite edges of the cardboard circle. The
rationale of this experiment being, that the picture of one design
such as the head and face is retained by the eye until the hat appears,
and being mutually impressed upon the nerve of vision at very nearly
the same instant of time, they appear as one picture.

X. The Kalotrope.

This is an

optical arrangement by Mr. Thomas Rose, of Glasgow,
primarily designed for showing the illusions of the phenakistiscope and
kindred devices to a numerous audience ; but more remarkable for its
presentations of very beautiful spectra, composed of the multiplication,
combination, and involution of simple figures disposed around a disc.
The arrangement consists of a movement for giving considerable
velocity to two concentric wheels, working nearly in contact, and
moving in contrary directions. But the only; part of the apparatus that
requires special explanation and illustration is the device disc and the
disc of apertures ; the first of which is placed on the hinder wheel, and
the second on the front wheel. We give figures of the two discs,
premising, however, that each is capable of an almost infinite variety
of characters. No. 1 (Fig. 306) presents in its four quadrants the
perforations for four distinct discs of apertures ; and No. 2 is a device
disc, consisting of twelve equidistant black balls. Under a the balls
will be presented as twenty-four ovals ; under b, as forty- eight involved
figures, beautifully variegated ; under c, as an elaborate lacework ; and
under d, as a rich variegation of form and colour. Every fresh disc of
devices and disc of apertures of course opens up a new field of effect.
Thus, if we take a disc bearing twelve repeats of a ball in the in-
terior of a ring, each repeat being so painted that its position is ad-
vanced in the ring until it reaches in the twelfth ring the point whence
it started, and place this oh the back disc of the kalotrope, having pre-
viously removed the first one, no effect is observed when ths wheel
is rotated beyond the spreading out of the design and general appear-
ance of hazy black circles. When, however, the disc, with twelve slits
or apertures, is now placed on the front wheel, and the two rotated in
opposite directions, then the whole figure starts as it were into exist-
ence, and each ball apparently moves round the interior of its circle.

MR. ROSES KALOTROPE AND PHOTODRO1IE.

315

The apparatus was produced at the Royal Polytechnic Institution by
the author, and excited much interest. (Eig. 306.)

Fig. 306. Nos. 1 and 2 are the discs. No 3. Kalotrope in elevation. No. 4. Side view
of kalotrppe, showing the multiplying wheels and the perforated and painted discs moving

in opposite directions.

XI. The Photodrome.

This is a second optical arrangement by Mr. Kose for showing spec-
tral illusions ; and it is superior to the last, inasmuch as it offers to the
public lecturer a most effective means of presenting these deceptions to
a large audience. It differs from the kalotrope m several important
points. It dispenses with the discs of apertures, and leaves the device
disc with its face fully exposed to the spectators. The effects are pro-
duced
broken
stands

one a movement for the device discs, and the other for the light. A
wheel four feet in diameter is connected with a train of movement
capable of giving it five hundred or six hundred revolutions per minute.
On this wheel the device disc is placed, in full view of the spectators,
and set in motion. Prom an opposite gallery the light is thrown, and

316 BOY'S PLAYBOOK OF SCIENCE.

broken by a wheel of such diameter and number of apertures as will
admit the velocity of the photodrome (or light-runner) to be at least
six times the velocity of the device disc ; whilst the apertures are of
such width as to restrict the duration of the light- flash to about one-
two-thousandth of a second. The wheel working across the light has a
train of movement for raising the velocity to two thousand revolutions
per second. The management of the apparatus is very simple. The
device- wheel is brought to a steady, rapid rotation, and the operator on
the light then works his wheel with gradually increasing velocity, until
he overtakes the figures of the device, where, by mere delicacy of touch,
he is able to hold them stationary or give them motion, at pleasure.

Theories of light and colour still agitate the scientific world, although
that man must be bold who will assert that his hypothesis is fitted to
explain every difficult point that arises as our experimental knowledge
increases. Mr. G. J. Smith, of the Perth Academy, has propounded a
very ingenious theory of light and colour, supported by some clever
experiments. But, as Solomon says, " there is nothing new under the
sun," and in an able paper Mr. Rose, of Glasgow, lays claim to the
anticipations of Mr. Smith's theory as follows:

" My attention has been directed to a paper entitled ' The Theory of
Light/ by G. John Smith, Esq., M.A., of Perth Academy. I think it
is now nearly two years since I communicated an interesting fact to
Professor Faraday, and to a member of our local Philosophical Insti-
tution, which may fairly claim to have anticipated Mr. Smith's theory.
The fact was this : that if a piece of intensely white card be held in one
hand, with the light of a powerful gas-jet falling upon it, and if the
other hand has command of the gas-tap, as the light is gradually reduced,
the card will assume the prismatic colours down to intense blue, and as
the light is restored the colours will present themselves in inverse
order. The experiment showed, very conclusively to my mind, that light
is homogeneous, and that what we name colour is only the various
affection of the optic nerve by a greater or lesser radiation of light from
a focal point in an imperfect reflector say, in the instance, a white
card. I apprehend that Mr. Smith confuses his theory when he speaks
of alternations of light and shadow-producing colour. Shadow, or
darkness, is mere negation of light. We do not see mixtures of light
and darkness, or blackness and whiteness, but light in its several degrees
of intensity. Mr. Smith's experiments present only what my kalotrope
has done, and what my later device, the photodrome (now nearly three
years old) is doing in a much more perfect manner. It is one of the
mysteries intelligiole only to the initiated, that whilst Mr. Smith's paper
seems to have been received with great favour by the British Association,
my communication relative to the photodrome was voted ' not sufficiently
practical?

" Since I have come before the public with an experiment, which in
any view is an interesting one, permit me to reproduce it under several
distinct conditions, and to add a brief narrative of remarkable presen-
tations of colour that have come before me, and w'hich, so far as I am

ROSE'S EXPERIMENTS. 317

aware, are perfectly novel, or known only through the more recent
experiments of Mr. Smith. Professor Earaday very courteously
acknowledged my communication of the experiment with the card, but
said that it only partially succeeded with him, and added that probably
this was owing to some decay of sensitiveness in his eyes. More likely
I failed to state with sufficient clearness the conditions of the ex-
periment, since I have always found nine persons out of ten perfectly
agreed as to the effects produced when they have been at my side. The
transitions from white to yellow, orange, red, and thence to intense
blue, are, I may say, invariably admitted. Success depends on a very
slow and regular reduction and restoration of the light. I have given
one method of performing the experiment, and will add other two.
Allow the light to remain undisturbed, and begin by holding the card
near to it ; then keep the hand steady and the eye intently fixed upon
the card, and retire gradually with your back to the light, and the
colours will change in the ord'er of the prismatic spectrum from yellow
to intense blue. On returning backwards towards the light the colours
will again present themselves, but in inverse order. In this form of
the experiment we are certain that the light remains precisely the same
throughout. The third method is this : Place a circle of white card,
about three inches in diameter, in the centre of a black board, and let a
spectator stand within twelve inches of the board, with his eyes fixed
upon the card. Let an operator be provided with a light so covered
that it shall not fall on the eye of the spectator ; then, as he retires
with the light or returns with it, the spectator will see the colours as
before. This arrangement evidently subjects the experiment to a severe
test, since the black board enhances the whiteness of the card, and

tends to preserve it Whilst pursuing my principal object,

I frequently noticed most remarkable presentations of colour ; but, as
the conditions were for the most part unsuitable to the lecture-room, I
gave them only a passing regard. Allow me to instance a few of the
experiments.

"The first refers to the kalotrope, which may be briefly described as
an arrangement of two concentric wheels, working nearly in contact and
in contrary directions; Discs of various devices are provided for the
hinder wheel, and a number of perforated black discs for the one
in front. When a disc charged with twelve black radii is placed on
the hinder wheel, the six spokes of the front wheel, in passing rapidly
across it, convert the twelve black radii into twenty-four apparently
stationary white radii upon a tinted ground. Here is a remarkable
presentation of the complementary, inasmuch as it is placed permanently
before the eye by persistence.

" The second experiment is performed with the photodrome, which
consists of an independent wheel to receive the device discs, and an
apparatus (altogether apart, and, if desired, out of sight) by which
flashes of light are thrown upon the disc in rapid and regular succession.
Now, if a disc charged with twelve dark blue balls, nearly in contact,
be placed upon the wheel, and a little natural light be allowed to fall

318 BOY'S PLAYBOOK OF SCIENCE.

upon it, so soon as it is thrown into rapid revolution, and flashes of
artificial light (insulated in a lantern) are duly measured out upon it,
we see twelve apparently stationary light-blue balls upon a zone of
bright orange. Here, again, there is nothing for which we are not
prepared; the complementary is suddenly presented, and it is main-
tained permanently before the eye by persistence.

" A third experiment may prove interesting in its relation to Mr.
Smith's ingenious theory. Place the kalotrope opposite a bright
northern noonday sky, remove the front wheel, and affix to the hinder
wheel one of the perforated black discs used for the kalotropic effects.
The experimentalist stands at the back of the instrument, and can see
the sky only through the apertures in the black disc. Cause these
apertures to pass the eye at intervals varying from one-half to one-sixth
or a second, and very remarkable presentations of colour are seen.
Under the lower velocities the sky flashes, and assumes an unnatural
brilliancy, and the intervals of the fourth and fifth of a second give it
sometimes a crimson, at others a deep purple colour. Now, what are
we to infer from this experiment ? Certainly not that the pulsations
have absolutely produced variety of colour. At every pulsation the
full natural light falls upon the eye, and the intervals between the
pulsations give time for the reaction necessary to the suggestion of
complementary colour, and that under manifold modifications arising
out of the ever-changing condition of the eye during the experiment.
If the apertures pass the eye with a velocity exceeding one-sixth of a
second, the eifect ceases. There is then perfect persistence, and the
eye apprehends nothing but the ordinary light of the sky, reduced in
intensity, with nothing to break its uniformity or give it a chromatic
character.

" A fourth experiment is kindred to the last. Place the kalotrope
under the same adjustment and management as before, in front of a
brilliant sunset, and the spectator will see, with more than a poet's
vision,

' The rich hues of all glorious things.' "

XII. The Kaleidoscopic Colour-top.

This invention by John Graham, of Tunbridge, is designed to show that
when white or coloured light is transmitted to the eye through small
openings cut into patterns or devices, and when such openings are made
to pass before the eye in rapid successive jerks, both form and colour are
retained upon the nerve of the visual organ sufficiently long to produce
a compound pattern, all the parts of which appear simultaneously,
although presented in succession. The instrument forms, therefore, a
pleasing illustration of the law that the eye requires an almost inappre-
ciably short space of time to receive an impression, and that such
impression is not directly effaced, but remains for an assignable though
very limited period. The results are obtained by rotating two discs on
a wheel, the lower disc containing colours, and the upper one the

CHEAP MICROSCOPES AND TELESCOPES.

openings ; this latter disc is made to vibrate as well as to rotate, thus
allowing the eye to receive the coloured light reflected from below,
\ijhich. light assumes, at the same time, the forms of the patterns through
which it has been transmitted. The instrument serves also to illustrate
most of the important phenomena of colour.

XIII. Simple Microscopes and Telescopes.

The Stanhope lenses are now sold at such a cheap rate, and are so
useful as simple portable microscopes, that it is hardly worth while to
detail any plan by which a cheap single-lens magnifier may be obtained.
Eloquent vendors of cheap microscopes are to be found in the streets,
who make their instrument of a pill-box perforated with a pin-hole, in
which a globule of glass fixed with Canada balsam is placed ; and the
spherical form of the drop affords the magnifying power : or a thin
platinum wire may be bent into a small circular loop, and into this may
be placed a splinter of flint-glass ; if the flame of a spirit-lamp is urged
upon the loop of platinum wire and glass by the blowpipe until it melts,
a small double-convex lens may be obtained, which will answer very
well as a magnifying-glass. Practice makes perfect, and after two or
three trials, a good single lens may be obtained, which can be mounted
between two small pieces of lead, brass, or cardboard, properly fixed
together, with holes through them just large enough to retain the edge
of the tiny lens. A prism can be made of two small pieces of window-
glass stuck together with a lump of soft beeswax, and if a few drops
of water are placed in the angle, they are retained by capillary attraction.
The prism is used by holding it against a large pin-hole or small slit in.
a bit of card, and directing them towards the sky, when the beautiful
colours of the spectrum will be apparent if the card and prism are
brought close to the eye.

The most simple form of the refracting telescope is made with a lens
of any focal length exceeding six inches, placed at one end of a tin or
cardboard tube, which must be six inches longer than the focal length
of the lens ; the tube may be in two parts, sliding one within the other,
and when the eye is placed at the other end, an inverted image of the
object looked at, is apparent. By using two double-convex lenses, a
more perfect simple astronomical telescope is obtained. The object-
glass, i.e., the lens next the object looked at, must be placed at the end
of a tin or pasteboard tube larger than its focus, and the second lens,
called the eye-glass, because next the eye, is a smaller tube, termed the
eye-tube ; and if the focal length of the object-glass is three feet, the
eye-glass must have a one-inch focus, and of course the eye-tube and
glass must slide freely in the tube containing the object-glass. An
object-glass of forty feet focus will admit of an eye-glass of only a four-
inch focus, and will, therefore, magnify one hundred and twenty times.
A tube of forty feet in length would of course be verjr troublesome to
manage, and therefore it is usual to adopt the plan originally devised by
Huygens, viz., that of placing the object-glass in a short tube on the

320 BOY'S PLAYBOOK OP SCIENCE.

top of a high pole with a ball-and-socket joint, whilst the eye-glass is
brought into the same line as th,e object-glass, and focused with a tube
and rack-work properly supported. In an ordinary
terrestrial telescope there are four lenses, in order
that the objects seen by its assistance shall not be
inverted; and whenever objects are examined by a
common telescope, they are found to be fringed, or
surrounded with prismatic colours. This disagreeable
effect is corrected by the use of achromatic lenses, in
which two kinds of glass are united ; and the light
decomposed by one glass, uniting with the colours
produced by the other form white light, thus a double
Pig. 307. A com- convex lens of crown glass, c c, may be united with
pound achromatic a plano-convex lens of flint glass, F F, which must
c e c!'thed?uco^ have a focus about double the length of that of the
vex lens of crown- crown-glass lens. The concave lens corrects the
fc^avellsof ^ chromatic aberration of the other and
flint-glass. leaves about one-half of the refracting power of the

convex lens as the effective magnifying power of the
compound lens. The French opticians cement the lenses very neatly
together, and use them in ordinary spy and opera glasses. (Fig. 307.)

XIV. The Stereoscope.

This instrument has now attained a popularity quite equal to, if it
does not surpass, that formerly enjoyed by the kaleidoscope, and without
entering upon the much-vexed question of priority of discovery, it is
sufficient again to mention with the highest respect the names of
Sir David Brewster and Professor Wheatstone as identified with the
discovery and use of this most pleasing optical instrument.

The principle of the stereoscope (meaning, sclid I see) is copied
from nature: i.e., when both eyes are employed in the examination of an
object, two separate pictures, embracing dissimilar forms, are impressed
upon the retinae, and produce the effect of solidity; if the pictures formed
at the back of the eyes could be examined by another person with a
stereoscope, they would come together, and also produce the effect of
solidity.

Stereoscopic pictures are obtained by exposing sensitized paper in
the camera to the picture of an object taken in two positions, or two
cameras are employed to obtain the same result. If the latter mode is
adopted, the stereoscopic pictures must not be taken from positions too
widely separated from each other ; or else, when the two pictures are
placed in the stereoscope, they will stand out with a relief that is quite
unnatural, and the object will appear like a very reduced solid model,
instead of having the natural appearance presented by pictures which
have been taken at positions too distant from each other.

Sir David Brewster says, " In order to obtain photographic pictures
mathematically exact, we must construct a binocular camera which will

WHEATSTONE'S STEREOSCOPE.

321

take the pictures simultaneously, and of the same size ; that is, by a
camera with two lenses of the same aperture and focal length, placed at
the same distance as the two eyes. As it is impossible to grind and
polish two lenses, whether single or achromatic, of exactly the same
local lengths, even if we had the very same glass for each, I propose to
bisect the lenses, and construct the instrument with semi-lenses, which
will give us pictures of precisely the same size and definition. These
lenses should be placed with their diameters of bisection parallel to one
another, and at a distance of 2^ inches, which is the average distance of
the eyes in man ; and when fixed in a box of sufficient size, will form a
binocular camera, which will give us at the same instant, with the same
lights and shadows, and of the same size, such dissimilar pictures of
statues, buildings, landscapes, and living objects, as will reproduce
them in relief in the stereoscope." Thus with a single camera provided
with semi-lenses, or two lenses of the same focal length, stereoscopic
pictures can be obtained.

To bring the images of the two pictures together, and produce
the effect of solidity ; either of two instruments may be employed. The
reflecting stereoscope is the invention of Professor Wheatstone. The
refracting or lenticular stereoscope that of Sir David Brewster.

The former is constructed by placing two upright boards on a wooden
stand at a moderate distance from each other; the stereoscopic pictures
are attached to these boards, which may be made to move up or down,
and if the pictures are held in grooves, they may be pulled right or left
at pleasure, and thus four movements are secured. viz., upward, down-
ward, right, or left. Between the two stereoscopic pictures are placed
two looking-glasses, so adjusted that their backs form an angle of ninety
degrees with each other. (Fig. 308.)

Fig. 308. Wheatstone's reflecting stereoscope.

The pictures are illuminated at night by a lamp or gas flame placed at
the back of the mirrors, which, when fixed together, have the same shape
as a prism ; indeed, Professor Wheatstone substituted a prism for the
mirrors, and thus paved the way for the invention of the lenticular
stereoscope.

3'22 BOY'S PLAYBOOK OF SCIENCE.

The stereoscopic effect is obtained by bringing the eyes close to the
inclined mirrors, so that the two reflected images coincide at the inter-
section of the optic axis ; the coincidence of the images is further secured
by moving either picture a little to the right or left, and if the upright
boards move bodily in grooves to or from the centre mirror, the greatest
nicety of adjustment is procured.

During the last three years of the author's directorship of the Poly-
technic viz., in 1856, 1857, 1858 nearly the whole of the pictures
shown by the dissolving- view apparatus were coloured photographs from
Mr. Hine's original pictures, painted two feet square in blue and white,
and reduced on the glass to about six inches square. The collodion
film being frequently thick and difficult to penetrate with light, was
etched and scratched away where required, and filled in with colour, and
when these pictures were looked at with one eye only, they appeared to
be almost solid or stereoscopic on the disc.

The lenticular stereoscope consists of a box of a pyramidal shape,
open at the base, and provided with grooves in which are placed the
stereoscopic pictures ; if the latter are taken
on glass the base of the box is held directly
against the light, but if they are daguerreotypes
or paper pictures, then a side light is reflected
upon them by means of a lid covered in the
inside with tinfoil, which is raised or lowered
at pleasure from the top part of the box. Two
semi-lenses are now fitted into the narrow part
of the box, and are placed at such a distance
from each other that the centres of the semi-
lenses correspond with the pupil of the eves,
and this distance has already been stated to
amount to ty inches. (Fig. 309.)

The principle of the lenticular stereoscope is
perhaps better seen by reference to the next
diagram, in which the centres of the semi-lenses
(i.e., a lens cut in half) are placed at 2 inches
apart, with their thin edges towards each other,

___ f and marked, A B, Pig. 310. The centres of the

.. , two stereoscopic pictures c D correspond with

Flg iiclr sSseopc ~ the centres of the lenses, and the rays of light

diverging from c D fall upon the semi-lenses,

and being refracted nearly parallel are, by the prismatic form of the semi-
lenses, deflected from their course, and leave the surfaces of the lenses
in the same direction as if they actually emanated from E ; and as all
images of bodies appear to come in a straight line from the point whence
they are seen, the two pictures are superimposed on each other, and
together produce the appearance of solidity, so that a stereoscopic
result is obtained when the spectral images of the two stereoscopic
pictures are made to overlap each other. By taking one of the semi-
lenses in each hand, and looking at the two pictures, the over-lapping

BREWSTERS STEREOSCOPE.

323

of the spectral images becomes very apparent, so that the combined
spectral images, and not the pictures themselves, are seen when \ve look
into a stereoscope. (Fig. 310.)

Fig. 310.

Sir David Brewster says, " In order that the two images may coalesce
without any effort or strain on the part of the eye, it is necessary that
the distance of the similar parts of the two drawings be equal to twice
the separation produced by the prism. For this purpose measure the
distance at which the semi-lenses give the most distinct view of the
stereoscopic pictures, and having ascertained by using one eye the
amount of the refraction producecT at that distance, or the quantity by
which the image of one of the pictures is displaced, place the stereo-
scopic pictures at a distance equal to twice that quantity that is, place
the pictures so that the average distance of similar parts in each is equal
to twice that quantity. If this is not correctly done, the eye of the
observer will correct the error by making the images coalesce, without
being sensible that it is making any such effort. When the dissimilar
stereoscopic pictures are thus united, the solid will appear standing as
it were in relief between the two plane representations."

XV. T-he Stereomonoscope.

M. Claudet, whose name has long been celebrated in connexion with
the art of photography, has described an instrument by which a single
picture is made to simulate the appearance of solidity, and he states that
by means of this arrangement a number of persons may observe the
effect at the same time. The apparatus required is very simple, con-
sisting of a large double convex lens, and a screen of ground glass. The

Y 2

324

BOY'S PLAYBOOK OF SCIENCE.

object A, Fig. 311, is highly illuminated, and placed in the focus of a
double convex lens B, when an image of the object is projected, and will

Pig. 311. The stereomonoscope.

be found suspended in the air in the conjugate focus of the lens at c,
and from this point the rays of light will diverge as from a real object,
which will be seen by separate spectators at D D and E E ; and if the
screen of ground glass is placed at G G, the image will appear with all
the effect of length, breadth, and depth, which belong to solid bodies.

(Kg- 311.)

An image formed on ground glass in this manner can be seen only in
the direction of the incident rays, and the stereoscopic effect is not
apparent when the image is received on a calico or transparent screen, on
account of the rays being scattered in all directions.

XVI. The Stereomoscope.

This arrangement is an important modification of the other, and
consists of a screen of ground glass (A B, Fig. 312), and two convex

Fig. 312. The stcreomoscope.

WHEATSTONE'S PSEUDOSCOPE.

325

lenses (CD, and E F) arranged in such a manner that they will project
images of the stereoscopic pictures, G H, at the same point on the
screen, AB.

It might be thought that a confusion of images would result from
projecting two pictures on one point, p viz., the focus of the two
lenses ; but as each photograph can be seen only in the direction of its
own rays, it follows that if the eyes are so placed that each receives the
impression of one stereoscopic picture, the two images must coalesce,
and a stereoscopic effect will be the result, as is apparent at K K and
L L ; so that several persons may look at the stereoscope at one time.
(Fig. 312.)

XVII. The Pseudoscope.

This curious optical instrument, as its name implies, produces a false
image by the refracting power of prisms, and is the invention of
Professor Wheatstone. When used with both eyes, the same as the
stereoscope, it inverts the relief of a solid body, and makes it appear
exactly as if it were an intaglio, or sunk beneath the line surrounding it.
3?or instance, a terrestrial globe when looked at through the pseudo-'
scope appears to be concave, like Wyld's Globe in Leicester-square,
instead of convex. A vase with raised ornaments upon it looks as if
it had been turned (to reverse the usual expression) outside in, and

Fig. 313. Horizontal section of the pseudoscope, showing at A B two prisms placed
against a block of wood about two inches long and one inch and a half wide, and
cut out in the centre to admit the nose at D. The eyes are supposed to be looking at the
globe, c, in the direction of the arrows. E E. Brass plates blackened, which shut out the
eide light, and assist in keeping the prisms in position.

326 BOY'S PLAYEOOK OF SCIENCE.

the whole of its convexity is turned to concavity ; and of course a face
seen under these circumstances looks very curious. (Pig. 313.) The
cause is perhaps somewhat difficult to understand ; but by taking other
and more simple examples of the same effect, the principle may be
gradually comprehended.

Sir David Brewster, in his " Letters on Natural Magic/' remarks
that " one of the most curious phenomena is that false perception in
vision by which we conceive depressions to be elevations, and elevations
depressions or by which intaglios are converted into cameos, and
cameos into intaglios. This curious fact seems to have been observed
t one of the early meetings of the Royal Society of London, when
one of the members, in looking at a guinea through a compound
microscope of new construction, was surprised to see the head upon
the coin depressed, while other members could only see it embossed, as

it really was The best method of observing this deception

is to view the engraved seal of a watch with the eye-piece of an achro-
matic telescope, or with a compound microscope, or any combination
of lenses which inverts the objects that are viewed through it ; a single
convex lens will answer the purpose, provided we hold the eye six or
eight inches behind the image of the seal formed in its conjugate focus."

After bringing forward various interesting experiments in further
explanation of the cause, Sir D. Brewster states it to be his belief that
the illusion is the result of an operation of our own minds, whereby
we judge of the forms of bodies by the knowledge we have acquired of
light and shadow. Hence, the illusion depends on the accuracy and
extent of our knowledge on this subject ; and while some persons are
under its influence, others are entirely insensible to it. This statement
is borne out by experience, as the author, whilst Resident Director of
the Polytechnic, had four of Wheatstone's pseudoscopes placed in the
gallery, with proper objects behind them ; and he frequently noticed
that some visitors would look through the instrument and see no
alteration of the convex objects, whilst others would shout with delight,
and call their friends to witness the strange metamorphosis, who in
their turn might disappoint the caller by being perfectly insensible to
its strange effects.

The pseudo-effects of vision are not confined to the results already
explained, but are to be observed especially whilst travelling in a coach',
when the eyes may be so fixed as to give the impression of movement to
the trees and houses, whilst the coach appears to stand still. In railway
carriages, after riding for some time ana then coming to a stand still, if
another train is set slowly in motion by the one at rest, it frequently
happens that the latter appears to be moving instead of the former.

327
CHAPTER XXIV.

THE ABSOKPTION OP LIGHT.

THE analysis of light has been explained in a previous chapter, and it
has been shown how the spectrum is produced. Colour, however, may
be obtained by other means, and the property enjoyed by certain bodies,
of absorbing certain coloured rays in preference to others, offers another
mode of decomposing light.

The property of absorption is shown to us in every kind of degree by
innumerable natural and artificial substances; and* by examining the
spectrum through a wedge of blue glass, Sir David Brewster was enabled
to separate the seven colours of the spectrum into the three primary
colours, red, yellow, and blue, which he proved existed at every point
of the spectrum, and by overlapping each other in various proportions,
produce the compound colours of orange, green, indigo, and violet.

Connected with this property is the remarkable effect produced by
coloured light on ordinary colours, and the sickly hue cast upon the
ghost in a melodrama, or the fiery complexion imparted to the hair
of Der Ereischutz, or the jaundiced appearance presented by every
member of a juvenile assembly when illuminated with a yellow light
from the salt and burning spirit of " snapdragon," are too well known
to require a lengthened description here.

If a number of colours are painted on cardboard, or groups of plants,
flowers, flags, and shawls, are illuminated by a mono-chromatic light, and
especially the light procured from a large tow torch well supplied with
salt and spirit, the effect is certainly very remarkable ; at the same time
it shows now completely substances owe their colour to the light by
which they are illuminated, and it also indicates why ladies cannot
choose colours by candle-light, unless of course they propose to wear
the dress only at night, when it is (juite prudent to see the colours in
a room lit with gas ; and this fact is so well known that with the chief
drapers, such as at Messrs. Hailing, Pearce, and Stone's, Waterloo House,
a darkened room lit with gas is provided during the daytime to enable
purchasers of coloured dresses to judge of the effect of artifice. 1 Hght upon
them. Whilst the flowers, &c., are lighted up with the yellow light, a
magical change is brought about by throwing on suddenly the rays from
the oxy-hydrogen light, when the colours are again restored ; or if the
latter apparatus is not ready, the combustion of phosphorus in a jar of
oxygen will answer the same purpose. The light obtained from the
combustion of gas affords an excess of the yellow or red rays of light,
which causes the difference between candlelight .and daylight colours
already alluded M

328 BOY'S PLAYBOOK OF SCIENCE.

CHAPTER XXV.

THE INFLECTION OK, DIFFRACTION OF LIGHT.

IN this part of the subject it is absolutely necessary to return to the
theory of undulations with which the present subject was commenced.
The inflection of light offers a third method by which rays of light may
be decomposed and colour produced. The phenomena are extremely
beautiful, although the explanation of them is almost too intricate for a
popular work of this kind.

The cases where colour is produced by inflection are more numerous
than might at first be supposed ; thus, if we look at a gaslight or the
setting sun through a wire gauze blind, protecting the eye with a little
tank of dilute ink, a most beautiful coloured cross is apparent. An
extremely thin film of a transparent matter, such as a little naphtha or
varnish dropped on the surface of warm water or soap bubbles, or a very
thin film of glass obtained by blowing out a bulb of red-hot glass till it
bursts, or an exquisitely thin plate of talc or mica, all present the
phenomena of colour, although they are individually transparent, and in
ordinary thicknesses quite colourless.

Sir Isaac Newton brought his powerful intellect to bear on these
facts, and as a preliminary step invented an instrument for measuring
the exact thickness of those transparent substances that afforded colour,
and the apparatus displaying Newton's rings is still a favourite optical
experiment. It consists of a plano-convex lens, A. (Eig. 314) a slice,

Fig. 314. The two lenses, with the plate or film of air between them, and producing
seven coloured rings when the lenses are brought sufficiently close to each other by the
screws.

as it were, from a globe of glass twenty-eight feet in diameter, or the
radius of whose convex surface is fourteen feet. This plano-convex lens
is placed on another double convex lens, B., whose convex surfaces have
a radius of fifty feet each, consequently the lenses are very shallow, and
the space (c c) included between them being filled with air, can of course
be accurately measured. (Eig. 314.) It is usual to mount the lenses in
brass rings which are brought together with screws, when the most
beautiful coloured rings are apparent, and are produced by the extreme
thinness of the film or plate of air enclosed between the two lenses ; and

COLOURS OP THIN PLATES.

329

the relative thicknesses of the plates of air at which each coloured light
is reflected are as follows :

Red ,

Orange

Yellow

Green

Blue

Indigo

Violet

133
120

10 millionths of an inch.

105|
98
92|

83^

'By dividing an inch into ten millions of parts, and by taking 133 of such
parts, the thickness of the film of air required to reflect the red ray is
obtained, and in like manner the other colours require the minute thick-
nesses of air recorded in the table above. When the thickness of the
film of air is about TT. 2 opodths ^ an mcn > ^he c l urs cease to become
visible, owing to the union of all the separate colours forming white
light, but if the Newton rings are produced in mono-chromatic light,
then a greater number of rings are apparent, but of one colour only,
and alternating with black rings, i.e., a dark and a yellow succeeding
each other ; this fact is of great importance as an illustration of the
undulatory theory, and demonstrates the important truth, that two rays
of light may interfere with each other in. such a manner as to produce
darkness.

Sir David Brewster remarks that, "From his experiments on the
colours of thin and of thick plates, Newton inferred that they were
produced by a singular property of the particles of light, in virtue of
which they possess, at different points of their paths, fits or dispositions
to be reflected from or transmitted by transparent bodies. Sir Isaac
does not pretend to explain the origin of these fits, or the cause which
produces them, but terms themes of transmission axAfits ofrefiexion"

Sir Isaac Newton objected to the theory of undulations because ex-
periments seemed to show that light could not travel through bent tubes,
which it ought to do if propagated by undulations like sound ; and it was
reserved for the late Dr. Young to prove that light could and would turn
a corner, in his highly philosophical experiments illustrating the inflection
or bending in of the rays of light.

Dr. Young placed before a hole in a shutter a piece of thick paper
perforated with a fine needle, and receiving through it the diverging
beams on a paper screen, found that when a slip of cardboard one-
thirtieth of an inch in breadth was held in such a beam of light, that
the shadow of the card was not merely a dark band, but divided into
light and dark parallel bands, and instead of the centre of the shadow
being the darkest part, it was actually white. Dr. Young ascertained
that if he intercepted the light passing on one side of the slip of card
with any opaque body, and allowed the light to pass freely on the other
side of the slip of cardboard, that all the bands and the white band
in the centre disappeared, and hence he concluded that the bands
or fringes within the shadow were produced by the interference

330

BOY'S PLAYBOOK OF SCIENCE.

of the rays bent into the shadow by one side of the card, with the rays bent
Into the shadow by the other side. (Eig. 315).

c .

In order to show how two waves may interfere so as to exalt or destroy
each other, two sets of waves may be propagated on the surface of a still
tank or bath of water, from the two points A A (Eig. 315), the black
lines or circles representing the tops of the waves. It will be seen
that along the lines B B the waves interfere just half way between each
other, so that in all these directions there will be a smooth surface,
provided each set of waves is produced by precisely the same degree of
disturbing force, so as to be perfectly equal and alike in every respect,
and the first wave of one set exactly half a wave in advance oi' the first
wave of the other, while at the curve in the direction of all the line c c,
the waves coincide, and produce elevations or undulations of double
extent ; in the intermediate spaces, intermediate effects will, of course,
be produced.

Professor Wheatstone has invented some very simple and beautiful
tcoustic apparatus for the purpose of proving that the same laws of
interference exist also in sound, which, as already stated, consists in
the vibrations or undulation of the particles of air.

WOODWARD'S MODELS.

331

The nature and effects of interference are also admirably illustrated
by the following models of Mr. Charles Woodward, President of the
Islington Scientific Institution, and to whom we have already alluded.

Fig. 316. No. 1. A model of waves with moveable rods. No. 2. A model of fixed waves.
No. 3. Intensity of waves doubled by the superposition and coincidence of two equal
systems. No. 4. Waves neutralized by the superposition and interference of two equal
systems, the raised part of one wave accurately fitting into and making smooth the hollow
of the other, Illustrating the fact that two waves of light or sound may destroy each other.

Returning again to the coloured rings, we find that Newton discovered
that at whatever thickness of the film of air the coloured ring first ap-
peared, there would be found at twice that thickness the dark ring, at three
times the coloured, at four times the dark, and so on, tie coloured rings
regularly occurring at the odd numbers, and the dark ones at the even
numbers. This discovery is well illustrated by the models (Fig. 316) ; and
it maybe noticed at No. 3 that the highest and the lowest parts of the wave?

332

BOY'S PLAYBOOK OF SCIENCE.

interfere, but coincide and produce a wave of double intensity ; the little
crosses of the upper model are in a straight line with the numbers 1, 3,
5, 7, and are supposed to represent the coloured rings, whilst in No. i
the upper series of waves is half an undulation in advance of the lower ;
and if the eye is again directed from the little crosses downward, the
figures 2, 4, 6, 8, even numbers, are apparent, and represent the dark
rings, when the waves of light destroy each other. The phenomena of
thin plates, such as colours from soap bubbles, and the films of varnish,
are well explained by the law of interference. The light reflected from
the second surface of the film of air (which must of course, however
thin, have two surfaces, viz., a upper and a lower one) interferes with
the light reflected from the first, and as they come from different points
of space, one set of waves is in advance of the other, No. 4, Fig. 316 ; they

Fig. 317. Appearance of Newton's rings when produced in yellow light, 1, 3, 5, 7, being
the yellow rings, and 2, 4, 6, 8, the dark rings. Light by the odd numbers ; darkness by
the even numbers. The central spot, where the two surfaces are in contact, is dark.

reach the eye with different lengths of paths, and by their interference
form alternately the luminous and dark fringes, bands, or circles.
Bridge's diffraction apparatus, manufactured only by Elliott Brothers,
offers itself specially as a most beautiful drawing-room optical instru-
ment. The purpose of this apparatus is to illustrate in great variety,
and in the most convenient and compact form, the phenomena of the
diffraction or interference of light. This is attained by the assistance
of photography. Transparent apertures in an opaque collodion film are
produced on glass, and a point of light is viewed through the apertures.

ELLIOTT'S DIFFRACTION APPARATUS. 333

The forms of the apertures are exceedingly various, triangles, squares,
circles, ellipses, parabolas, hyperbolas, and combinations of them, besides
many figures of fanciful forms, are included in the set. When an
image of the sun is viewed through these apertures, figures of extra-
ordinary beauty, both of form and colour, are produced ; and of each
of these many variations may be obtained by placing the eye-glass of
the telescope at different distances from the object glass. Many of the
figures produced, especially when the telescope is out of focus, might
suggest very useful hints to those concerned in designing patterns.
Although the phenomena are chiefly of interest to the student of science,
in consequence of their bearing on theories of light, yet their beauty and
variety render them amusing to all. A few words on the mode of using
the apparatus may be of service. (Fig. 318.)

Fig. 318. Elliott Brothers' diffraction apparatus.

Choose a very bright day, for then only can the apparatus be used.
Place the mirror in the sun, and let the light be reflected on the back
of the blackened screen. The lens which is inserted into this screen
will then form an exceedingly bright image of the sun. Then at the
distance of not less than twelve feet, clamp the telescope to a table in
such a position as to view the image thus formed. Put the eccentric
cap on the end of the telescope, clean the glass objects carefully, and
attach them to the cay) so that they may be turned each in order before
the telescope. In this manner, all those which consist of a series of
figures may be viewed. Then detach the eccentric cap, and replace it
by the other. Into it place any of the single objects. In viewing some
of the figures, brightness is advantageous in others, delicacy ; in the
former case, let the lens of long focus be inserted in the screen in the
latter case, that of shorter focus. In every case, let the phenomena be
observed not only when the telescope is in focus, but also when the
eye-glass is pushed in to various distances.

Mr. Warren de la Rue has ingeniously taken advantage of the colours
produced by thin films of varnish, and actually fixed the lovely iridescent
colour produced in that manner on highly polished paper, which is
termed " iridescent paper." A tank of warm water at 80 Eahr., about

334

BOYS PLAYBOOK OP SCIENCE.

six inches deep, and two feet six inches square, is provided, and a highly
glazed sheet of white or black paper being first wetted on a perforated
metallic plate, is then sunk with the plate below its surface, care being
taken to avoid air bubbles. A peculiar varnish is then allowed to
trickle slowly down a sort of tongue of metal placed in the middle of
one of the siaes of the tank, and directly the varnish touches the surface
of the water it begins to spread out in exquisitely thin films, and by
watching the operation close to a window and skimming away all the
imperfect films, a perfect one is at last obtained, and at that moment the
paper lying on the metal plate is raised from the bottom of the tank, and the
delicate film of varnish secured. When dry, the iridescent colours are
apparent, and the paper is employed for many ornamental purposes.

An extremely simple and
pretty method of producing
Newton's rings has been in-
vented by Reade, and is called
" Reade's iriscope*" A plate
of glass of any shape (perhap?
circular is the best) is painted
on one side with some quickly
drying black paint or varnish,
and after the other side has
been cleaned, it is then rubbed
over with a piece of wet soap,
and this is rubbed off with a
clean soft duster. A tube of
about half an inch in diameter,
and twelve inches long, is pro-
vided, and is held about one
inch above the centre of the soaped side of the glass plate, and directly
the breath is directed down the tube on the glass, an immense number
of minute particles of moisture are deposited on the glass, and these by
inflection decompose the light, and all the colours of the rainbow are
produced. (Fig. 319.)

The iridescent colours seen upon the surface of mother-of-pearl, which
Mr. Simonds' excellent commercial dictionary tells us is " the name for
the iridescent shell of the pearl oyster, and other molluscs," are refer-
rible to fine parallel lines formed by its texture, and are reproducible,
according to Brewster's experiments, by taking impressions of them in
soft wax. The gorgeous colours of certain shells and fish, the feathers
of birds, Barton's steel buttons, are not due to any inherent pigment or
colouring matter that could be extracted from them, but are owing either
to the peculiar fibrous, or parallel-lined, or laminated (plate-like) surfaces
upon wnich the light falls, and being reflected in paths of different lengths,
interference occurs, and coloured light is produced.

Fig. 319. Reade's iriscope.

335

CHAPTER XXVI.

THE POLARIZATION OF LIGHT.

THIS branch of the phenomena of light includes some of the most
remarkable and gorgeous chromatic effects ; at the same time, regarded
philosophically, it is certainly a most difficult subject to place in a
purely elementary manner before the youthful minds of juvenile phi-
losophers, and unless the previous chapter on the diffraction of light is
carefully examined, the rationale of the illustrations of polarized light
will hardly be appreciated. We have first to ask, " What is polarized
light ?" The answer requires us again to carry our thoughts back to
the consideration of the undulatory theory of light, already illustrated
and partly explained at pages 262, 330.

After perusing this portion of the subject, it might be considered
that waves of light were constituted of one motion onlv, and that an
undulation might be either perpendicular or horizontal, according to
circumstances. (Fig. 320.)

No. 1.

No. 2.

Fig. 320. No. 1. A wire bent to represent a perpendicular vibration, which if kept
in the latter position, will only pass through a perpendicular aperture. No. 2. A wire
bent to represent a horizontal wave which will only pass through a horizontal aperture.

This simple condition of the waves of light could not, however, be
reconciled theoretically with the actual facts, and it is necessary in
regarding a ray of light, to consider it as a combination of two vibrating
motions, one of which, for the sake of simplicity, may be considered as
perpendicular, and the other horizontal ; and this idea of the nature of

336

BOY'S PLAYBOOK OF SCIENCE.

an undulation of light originated with the late Dr. Young, who while
considering the results of Sir D. Brewster's researches on the laws of
double refraction, first proposed the theory of transversal (cross-wise)
vibration. Dr. Young illustrated his theory with a stretched cord,
which if agitated or violently shaken perpendicularly, produces a wave
that runs along the cord to the other ena, and may be often seen illus-
trated on the banks of a river overhung with high bushes; the bargemen
who drive the horses pulling the vessel by a rope, would be continually
stopped by the stunted thick bushes, but directly they approach them,
they give the horse a lash, and then violently agitate the rope vertically,
which is thrown into waves that pass along the rope, and clear the
bushes in the most perfect manner. (Fig. 321.)

fig. 321. Bargeman throwing his tow-rope into waves to get it over the thick bushes.

Now if a similar movement is made
with the stretched rope from right to
left, another wave will be produced,
which will run along the cord in an
horizontal position, and if the latter
is compared with the perpendicular
B undulation, it will be evident that each
set of waves will be in planes at right
angles to and independent of each
other. This is supposed to be the
mechanism of a wave of common light,
so that if a section is taken of such
an undulation, it will be represented
by a circle A B c D (Fig. 322), with
wave of t wo diameters A B, and c D; or a better
mechanical notion of a wave of com-

Fig. 322. A section of a

THE POLARIZATION OF LIGHT.

337

mon light is acquired from the inspection of another of Mr. Woodward's
cardboard models. (Kg. 323.)

Fig. 323. Model of a wave of common light.

The existence of an alternating motion of some kind at minute intervals
along a ray is, say^s Professor Baden Powell, " as real as the motion of
translation by which light is propagated through space. Both must
essentially be combined in any correct conception we form of light.
That this alternating motion must have reference to certain directions
transverse to that of the ray is equally established as a consequence of
the phenomena; and these two principles must form the basis of any
explanation which can be attempted." A beam of common light is
therefore to be regarded as a rapid succession of systems of waves in
which the vibrations take place in different planes.

If the two systems of waves are separated the one from the other,
viz., the horizontal from the perpendicular, they each form separately
a ray of polarized light, and as Eresnel has remarked, common light is
merely polarized light, having two 'planes of polarization at right angles
to each other. To follow up the mechanical notion of the nature of
polarized light, it is necessary to refer again to Woodward's card
wave model (Kg. 323), and by separating the two cards one from
the other it may be demonstrated how a wave of common light reduced
to its skeleton or primary form is reducible into two waves of polarized
light, or how the two cards placed together again in a transversal position
form a ray of common light. (Kg. 324.)

No. 1.

No. 2.

No. 3.

Fig. 324. No. 1. Common light, made up of the two waves of polarized

a light
light,

Nos. 2 and 3.

The query with respect to the nature of polarized light being answered,
it is necessarv, in the next place, to consider how the separation of these
transversal vibrations may be effected, and in fact to ask what optical
arrangements are necessary to procure a beam of polarized light ? Light
may be polarized in four different ways viz., by reflection, single refrac-
tion, double refraction, and by the tourmaline viz., by absorption.

338 BOY'S PLAYBOOK OF SCIENCE.

Polarization by Reflection, and by Single Refraction.

In the year 1810, the celebrated French philosopher, Mons. Malus,
while looking through a prism of Iceland spar, at the light of the setting
sun, reflected from the windows of the Luxemburg palace in Paris,
discovered that a beam of light reflected from a plate of glass at an
angle of 56 degrees, presented precisely the same properties as one of the
rays formed by a rhomb of Iceland spar, and that it was in fact polarized.
One of the transversal waves of polarized light of the common light,
being reflected or thrown off from the surface of the glass, whilst the
other and second transversal vibration passed through the plate of
glass, and was likewise polarized in another plane, but by single refrac-
tion, so that the experiment illustrates two of the modes of polarizing
light viz., by reflection, and by single refraction. This important ele-
mentary truth is beautifully illustrated by Mr. J. T. Goddard's new
form of the oxy-hydrogen polariscope, by which a beam of common
light traverses a long square tin box without change ; but directly a
bundle of plates of glass composed of ten plates of thin flattened crown
glass, or sixteen plates of thin parallel glass plates used for microscopes,
ave slid into the box at an angle of 56 45', then the beam of common

Fig. 325. No. 1. A is the lime light. B. The condenser lenses, c. The beam of common
light. Here the glass plates are removed. No. 2. A. Lime light. B. The condenser
lenses, c c. The bundle of plates of glass at an angle of 56 45'. D is the ray of light
polarized by reflection from the glass plates, c c, and E is the beam of .polarized light by
.single refraction, having passed through the bundle of plates of glass, c c.

GODDARD'S POLARISCOPE.

339

light is split into two
beams of polarized light,
which pursue their re-
spective paths, one pass-
ing by single refraction
through the glass, and the
other being reflected, and
rendered apparent by
opening an aperture over
the glass plates, and then
again by using a little
smoke from brown paper,
the course of the rays
becomes more apparent.
TKr. cnrnp +rii+li id wpll

ine same truth is well
illustrated by the card-
board model wave and a wooden plane with horizontal and perpendicular
slits, placed at an angle of 56 45', as at Fig. 326.

Fig. 328. A A. Model in *ood of a bundle of plates
of glass at an angle of 56 45'. B. Beam of common
%ht, with transversal vibration. c. Light polarized by

reflection> D> Light po i arized by refraction.

POLARIZATION BY DOUBLE REFRACTION.

The name of Z>ow5/e-refracting or Iceland Spar is given to a very
clear, limpid, and perfectly transparent mineral, composed of carbo-
nate of lime, and found on the eastern coast of Iceland. Its crystal-
lographic features are well described by the Rev. Walter Mitchell
in his learned work on mineralogy and crystallography, and it' is suffi-
cient for the object of this article to state that it crystallizes in rhombs,
and modifications of the rhomboidal system. It must not be confounded
with rock or mountain crystal, which, under the name of quartz, crystal-
lizes in six-sided prisms with six-sided pyramidal tops; quartz being
composed of silica, or silicic acid and calcareous spar of carbonate of
lime. Yery large specimens of the latter mineral are rare and valuable, and
the lion of specimens of calcareous, or double-refracting spar, is now in the
possession of Professor Tennant, the eminent mineralogist of the Strand.
It is nine inches hi^h, seven and three-quarters inches broad, and five
and a half inches thick ; its estimated value being 100/. This beautiful
specimen has been photographed, and its stereograph illustrates in a
very striking manner the double refracting properties of the spar.

If a printed slip of paper is placed behind a rhomb of Iceland spar,
two images of tne former are apparent, and the stereograph already
alluded to shows this fact very perfectly, at the same time illustrates
the value of the stereoscope. Out of the stereoscope the words " Stereo-
scopic Magazine " appear doubled, but seem to lie in the same plane ;
but directly the picture is placed in the instrument, then it is clearly
seen that one image is evidently m a very different plane from the other.
The double-refracting power of this mineral is illustrated by holding a
small rhomb of Iceland spar, placed in a proper brass tube before
the orifice as at Tig. 327, from which the rays of common light are

340

BOY'S PLAYBOOK OF SCIENCE.

passing ; if an opaque screen of brass perforated with a small hole is
introduced behind the rhomb, then, instead of one circle of light
being apparent on the screen, two are produced, and both the rays
issuing m this manner are polarized, one being termed the ordinary and
the other the extraordinary ray. (Fig. 327.)

Fig. 327. A. The condensers. B. The hole in the brass screen or stop. c. The rhomb of
Iceland spar. o. The ordinary, and E the extraordinary, ray, both of which are polarized
light.

The polarizing property of the rhomb is perhaps better shown by
the next diagram, where A B represents the obtuse angles of the Iceland
spar, and a line drawn from A to B, would be the axis of the crystal.
The incidental ray of common light is shown at c, and the oppositely
polarized transmitted rays called the ordinary ray o, and extraordinary
ray E, emerge from the opposite face of the rhomboid. If a black line is
ruled on a sheet of paper as at K K, and examined by the eye at c, it
appears double as at K K and J J. (Fig. 328.)

Fig. 328. Ehomb of Iceland spar.

The cardboard model is again useful in demonstrating the polarization
ct light by double refraction, and if a model of a rhomb of Iceland

THE TOURMALINE.

341

Bpar is made of glass plates, one face of which has an aperture like a
cross, and the other a horizontal and perpendicular slit, as at Nos. 1
and 2 (Fig. 329), the production of the ordinary and extraordinary rays
is demonstrated in a familiar manner, and is easily comprehended.

Fig. 329. No. 1. One face of the model rhomb to admit the transversal vibration, repre-
sented by the cardboard model. No. 2. The opposite face of the rhomb, from which issue
the polarized, ordinary, and extraordinary rays. No. 3. Side view of the model.

In Newton's " Optics" we find the following description of Iceland
spar : " This crystal is a pellucid fissile stone, clear as water or crystal

of the rock (quartz), and without colour Being rubbed on cloth.

it attracts pieces of straw and other light things like amber or glass, and
with aquafortis it makes an ebullition If a piece of this crys-
talline stone be laid upon a book, every letter of the book seen through
it will appear double by means of a double refraction."

POLARIZATION BY THE TOURMALINE.

This mineral was first discovered during the sixteenth century, in
the island of Ceylon, afterwards in Brazil, and since that period at
various localities in the four quarters of the globe. In the Grevijlian
collection purchased many years ago by government for the British
Museum, there is a fine specimen of red tourmaline valued at 500/.
The green tourmaline is named Brazilian emerald, and the Berlin blue
tourmaline is called Brazilian sapphire ; the mineral chiefly consists of
sand (silica) and alumina, with a small quantity of lime, or potash, or soda,
boracic acid, and sometimes oxide of iron or manganese. When light
is passed through a slice of this mineral it is immediately polarized, one
of the transversal vibrations being absorbed, stopped, or otherwise dis-
posed of, the other only emerging from the tourmaline, consequently it
is one of the most convenient polarizers, although the polarized light
partakes of the accidental colour of the mineral. Green, blue, and
yellow tourmalines are bad polarizers, but the brown and pink varieties

342

BOY S PLAYBOOK OF SCIENCE.

are very good, and it is a most curious fact that white tourmaline dees
not polarize. (Fig. 330.)

Fig. 330. Crystal of tourmaline slit (parallel to the axis) into four plates, which when
ground and polished, may be used for the polarization of light.

The mineral crystallizes in long prisms, "whose primitive form is the
obtuse rhomboid, having the axis parallel to the axis of the prism. The
term axis with reference to the earth, as shown at page 10, is an
j^ imaginary single line around

which the mass rotates, but in a
crystal it means a single direction,
because a crystal is made up of
a number of similar crystals, each
of which must have its axis, thus
the whitest Carrara marble re-
duced to fine powder, moistened
with water and placed under a
microscope, is found to consist
chiefly of minute rhomboids, simi-
lar to calcareous spar. The
smallest crystal of this mineral is
divisible again and without limit
into other rhombs, each of which
possesses an axis. (Fig. 331.)
If a plate of tourmaline is held

Upfnro fKo oim -nrln'lcf InnVino- of
k elore th( ; e je whilst looking at

the SUn (like the gay youth in
four other and smaller ones, each of which has Hogarth's picture who IS being

withTth^ Ufc\*jS^to f T l SriS! arrested whilst absorbed with the

axis, consequently the term is employed usually wonders of a tourmaline, which
in the plural number . ^ ^ ^ ^ painte ,> s i[me> a

popular curiosity,) it may be turned round in all directions without the
slightest difference in the appearance of the light, which will be coloured
by the accidental tint of the crystal, but if a second slice of tourmaline
is placed behind the other, there will be found certain directions in which
the light passes through both the slices, whilst in other positions the light
is completely cut off.

Fig. 331 represents a crystal, the axis of
which is the direction A B. The dotted lines
show the division of the large crystal into

THE TOURMALINE.

When the axes of both plates coincide, the light polarized by one
tourmaline will pass through the other, but if the axes do not coincide,
and are at right an-

Fig 1 . 332. A. Model of the first slice of tourmaline into
which the transversal vibrations, B, are passing; the horizontal
wave is absorbed, and the perpendicular polarized one proceeds
to the second shoe of tourmaline, c, where the bars (the axes)
being at right angles to those of A, it is stopped, and cannot
pass through until the bars of c are parallel with A.

gles to each other,
then the polarized
light is entirely
stopped, and the ra-
tionale of this will be
appreciated at once
if a tourmaline is re-
garded (mechanical-
ly) as if it were like a
grating with perpen-
icular bars through
which the polarized
light will pass. Any
number of such grat-
ings with the bars
parallel would not
stop the polarized
light, but if the second grating is turned round ninety degrees, the bars
will be at right angles to those of the first grating, and the perpen-
dicular wave of polarized light cannot pass. (Fig. 332.)

Splendid Chromatic effects produced by Polarized Light.

Having discussed the various modes of obtaining polarized light, the
next step is to arrange an apparatus by which certain double refracting
crystals, and other bodies, shall divide a ray of polarized light, and then
by subsequent treatment with another polarizing surface, the divided
rays are caused to interfere with each other, and afford the phenomena
of colour. Bodies that refract light singly, such as gases, vapours or
liquids, annealed glass, jelly, gums, resins, crystallized bodies of the
tessular system, such as the cube and octohedron, do not afford any of
the results which will be explained presently, except by the influence
of pressure, as in unannealed glass, or a bent cold glass bar. By compres-
sion or dilatation, they are changed to double refractors of light. The
bodies that possess the property of double refraction (though not to the
visible extent of Iceland spar), are all other bodies such as crystallized
chemicals, salts, crystallized minerals, animal and vegetable substances
possessing a uniform structure, such as horn and quill ; all these sub-
stances divide the ray of polarized light into two parts, and by placing
a thin film of a crystal of selenite (which is one of the best minerals that
can be used for the purpose) in the path of the beam of polarized light,
coming either from the glass plates, as in No. 2, (Kg. 325), page 338,
r from a slice of tourmaline, and then receiving it through the ordinary
focusing lenses or object-glasses of the oxy-hydrogen microscope, no
colour is yet apparent in the image of the selenite on the screen, until

344

BOY S PLAYBOOK OF SCIENCE.

another tourmaline, or a bundle of glass plates, is placed at an angle of
56 45', and at right angles to the plane of reflection of the first set of
plates ; then the most gorgeous colours suddenly appear over all parts of
the film of selenite as depicted on the screen, like other objects shown
by the oxy-hydrogen microscope. (Fig. 333.)

Fig. 333. Duboscq's polarizing apparatus. A. The light and the condenser lens.
B. The plates of glass at the proper angle, c. The selenite object. D. The focusing
lens. E. The second bundle of plates of glass called the analyser, r. A stop for ex-
traneous rays of light. G. The image of the film of selenite most beautifully coloured

Goddard's oxy-hydrogen polariscope is one of the most convenient,
because either the reflected or refracted polarized rays can be rendered
available ; it consists of the apparatus shown at Fig. 325, and to
this is added a low microscope power, and stage to hold the selenite
or other objects, with another bundle of sixteen plates of the thin
microscopic glass or mica, called the analyser. A slice of tourmaline,
or a Nicol's prism may be employed, instead of the second bundle of
reflecting plates. When the ray of polarized light reflected from the
first set of glass plates enters the doubly refracting film of selenite,
which is about the fortieth or fiftieth part of an inch in thickness, it is
split into the ordinary and extraordinary rays, and is said to be dipola-
rized, and forms two planes of polarized light, vibrating at right angles
to each other. When the latter are received on another bundle of plates
of glass called the analyser, at an angle of 56 45', but at right angles
to the first set of glass plates, they interfere, because in the passage of
the two rays from the selenite they have traversed it in different direc-
tions, with different velocities ; one of these sets of waves will therefore,
on emerging from the opposite face of the selenite be retarded, and lie

THE POLARIZATION OF LIGHT.

345

behind the other ; but being polarized in different planes, they cannot
interfere until their planes of polarization are made to coincide, which is

Fig. 334. The electric lamp and lantern of Duboscq, showing the projection of the
carbon poles on the disc. This experiment is performed with the help of the plano-convex
lens, A, and the rays pass through a very narrow aperture at B.

Fig. 335. A A. Card model of a beam of polarized light coming from the first bundle of
plates of glass, shown at Fig. 326, p. 339. B. Model of the film of selenite, which divides
or dipolarizes the ray A A into c and D, which, interfering by means of the second bundle
of plates of glass called the analyser z, produce reflected chromatic effects by interference
at B, and refracted effects at p..

346 BOY'S PLAYBOOK OF SCIENCE.

effected by means of the second bundle of glass plates called the analyser ;
and when this is brought into a position at right angles to the first set
of reflecting glass plates, half the ordinary wave interferes with half the
extraordinary wave; and being transmitted through the analyser,
produces, say red and orange, whilst the remaining halves also interfere,
and being reflected, afford the complementary colours green and blue.
(Fig. 334.) The term complementary is intended to define any two
colours containing red, yellow, and blue, because the three combined
together produce white light ; for example, the complementary colour to
red would be green, because the latter contains yellow and blue ; the
complementary colour to orange would be blue, because the former
contains red and yellow. Any two colours, therefore, which together
contain red, yellow, and blue are said to be complementary ; and if this
principle was better understood, ladies would never commit such
egregious blunders as they occasionally do in the choice of colours for
bonnets and dresses, and select a blue bonnet to be worn with a
green dress, or vice versa. By rotating the analyser, the reflected
and refracted rays change colours, and if the former is red and the
latter green, by moving the analyser round 90, the reflected rays change
to green and the refracted to red; at 180 the colours again change
places ; at 270 the reflected ray will be again green, and the refracted
red; to be once more brought back at 360 to the original position, viz.,
reflected rays red, refracted green. The thickness of the films of
selenite determines the particular colour produced.

If the selenite is of a uniform thickness, one colour only is obtained,
and by ingeniously connecting pieces of various thicknesses (in the same
forms as stained glass for cathedral windows), the most beautiful designs
were made by the late Mr. J. T. Cooper, jun., which have since been
manufactured in great quantity and variety by Mr. Darker, of Paradise-
street, Lambeth. The colours of these selenite objects are seen by
placing them in front of a piece of black glass, fixed at the polarizing
angle, and then examining the design with a slice of tourmaline, or still
better with a single-image Nicol prism, when the most brilliant colours
are obtained, and varied at every change of the angle of the analyser.

Selenite, or sparry-gypsum, is the native crystallized sulphate of lime,
which contains water of crystallization (CaO, S0 3 , 2HO). It frequently
occurs imbedded in London clay, and is called quarry glass by the
labourers who find it at Shotover Hill, near Oxford, and also in the
Isle of Sheppey.

At a very early period, before the discovery of glass, selenite was used
for windows ; and we are told that in the time of Seneca, it was im-
ported into Rome from Spain, Cyprus, Cappadocia, and even from,
Africa. It continued to be used for this purpose until the middle ages,
for Albums informs us, that in his time, the windows of the dome of
Merseburg were of this mineral. The first greenhouses, those invented
by Tiberius, were covered with selenite. According to Pliny, bee-
hives were encased in selenite, in order that the bees might be seen at
work.

CHROMATIC EFFECT OF POLARISED LIGHT.

347

The late "Dr. Pereira has placed the phenomena already described in
the form of a most instructive diagram, which we borrow from his
elaborate work on " Polarized Light." (Fig. 336.)

Fig. 336. A. A ray of common or unpolarized light, incident on B. B. The polarizer (a
plate of tourmaline), c. A ray of plane polarized light, incident on D. D. The doubly-
refracting film of selenite. E. The extraordinary ray. o. The ordinary ray, produced by the
double refraction of the ray c. a. The analyser (or doubly-refracting or Nicol's prism).
E o. The ordinary ray. E E. The extraordinary ray, produced by the double refraction of
the extraordinary ray, E. o o. The ordinary ray. o E. The extraordinary ray, produced by
the double refraction of the ordinary ray, o.

The chromatic effects described are not confined to selenite objects
only, but are obtained from glass, provided the particles are in a state
of unequal tension, as in masses of unannealed glass of various forms.
(Fig. 337.) Consequently, polarized light becomes a most valuable

Fig. 337. No. 1. Unannealed glass for the polariscope. Nos. 2 and 3. Appearance of the
black cross and coloured circles in a square and circular piece of unannealed glass in the
polariscope.

means for ascertaining the condition of particles otherwise invisible and
inappreciable. One of the most beautiful experiments can be made

348

BOY'S PLAYBOOK OF SCIENCE.

with a bar of plate-glass, which refracts light singly until pressure is
applied to the centre, in order to bend it into an arch or curve, when

the appearance pre-
sented in Fig. 338 is
apparent.

A quill placed in the
polarizing apparatus is
also discovered to be
in a state of unequal
tension by the appear-
ance of coloured fringes
within it, which change
colour at every move-
ment of the analyser.

Another series of
beautiful appearances

__ o Bar of glass under the pressure of the

screw c, and appearance of bands or fringes of coloured
light, which entirely disappear on the removal of the screw, Jf V^"" H^IUO^IT w,
An effect, of course, only visible by polarized light. when a ray 01 white

polarized light is made

to pass perpendicularly through a slice of any crystallized substance
with a single axis ; if the analyser consist of a slice of tourmaline, a

number of concentric
coloured rings are ren-
dered visible with a
black cross in the cen-
tre, which is replaced
with a white one on
moving the tourmaline
through each quadrant
of the circle.

Crystals of Iceland
spar present this phe-
nomenon in great
beauty; and if the
crystal (such as nitre)
has two axes of double-
refraction, a double-
system of coloured
rings is apparent, with
the most curious
changes and combina-
tions of the black and white crosses with them. (Fig. 339.)

Mr. Goddard has recommended the optical arrangement (Fig. 340) for
showing the rings with great perfection, as also the number of rings
that increase in some crystals (the topaz, for example), with the
divergence of the rays of polarized light passing through them.

Mr. Woodward's table and oxy-hydrogen polariscope and microscope,
made by Smith and Beck, of Coleman-street, is well adapted, from its

Fig. 339. Crystal of nitre with two axes, as seen in
polarized light.

UTILITY OP POLARIZED LIGHT. 34J)

simplicity and perfection, to exhibit all the varied and beautiful effects
of polarized light ; and we only regret that want of space prevents us

Fig. 340. A A A. Polarized light. B B. A lens of short focus, transmitting a cone of
light with an angle of divergence for its rays, c c, of 45. D i>. The crystal of topaz,
Iceland spar, or nitre. E E. The slice of blue tourmaline for analysing.

describing it in detail, although the reader may see the body of the
apparatus at page 123, where the modifications of the oxy-hydrogen
light are described and figured ; and the polarizing apparatus would be
placed, of course, in front of the light issuing from the lantern.

Finally, the question of utility (the cui bond) may be considered in
answer to the query, What is the use of polarized light ?

The value to scientific men of a knowledge of the nature of this
modification of common light cannot be overrated. It has given the
philosopher a new kind of test, by which he discovers the structure of
things that would otherwise be perfectly unknown; it has given the
astronomer increased data for the exercise of his reasoning powers ;
whilst to the microscopist the beauty of objects displayed by polarized
light has long been a theme of admiration and delight, and has served
as a guide for the identification of certain varieties of any given sub-
stance, such as starch.

A tube provided with a polarizer of tourmaline, or a single-image
Nicol prism, is invaluable to the look-out at the mast-head in cases
where vessels are navigating either inland or sea water, where the
presence of hidden rocks is suspected, because the polarizer rejects all
the glare of light arising from unequal reflection at the surface of water,
and enables the observer to gaze into the depths of the sea and to
examine the rocks, which can only be perfectly visible by the refracted
light coming from their surfaces through the water.

Professor Wheatstone has invented an ingenious polarizing clock for
showing the hour of the day by the polarizing power of the atmosphere.
Birt, Powell, and Leeson have each invented instruments for examining
the circular polarization of fluids, by which a more intimate knowledge
of the relative values of saccharine solutions may be obtained, besides
unfolding other truths important to investigators in this branch of
science.

And last, but not least, it was with the assistance of polarized light

BOY'S PLAYBOOK OF SCIENCE,

that Dr. Faraday established the relation that exists between light and
magnetism, and through the latter, with the force of electricity ; and
the next figure indicates the necessary apparatus required to repeat this
highly important physical truth viz., the deviation of the plane of
polarization of light by the influence of the magnetic force from a
powerful electro-magnet. (Fig. 341.)

Fig. 341. A. The light and condenser lens. B. Single-image Nicol prism, c. Eock crystal
of two rotations. D. A double-convex lens. E B. Faraday's heavy glass. F F. The
powerful electro-magnet connected with battery, o. Double-refracting prisms. H.
Image, or screen where the deviation of the plane of polarization by the magnetic force
is shown.

By another and equally beautiful experiment at the London Institu-
tion, Professor Grove demonstrated the production of all the other kinds
of force from light, using the following arrangement for the purpose :

A prepared daguerreotype plate is enclosed in a box full of water
having a glass front with a shutter over it ; between this glass and the
plate is a gridiron of silver wire ; the plate is connected with one ex-
tremity of a galvanometer coil, and the gridiron of wire with one
extremity of a Breguet's helix ; the other extremities of the galva-
nometer and helix are connected by a wire, and the needles brought to
zero. As soon as a beam of either aaylight or the oxy-hydrogen light is,
by raising the shutter, permitted to impinge upon the plate, the needles
are deflected. Thus, light being the initiatory force, we get ~

Chemical action on the plate,

Electricity circulating through the wires,

Magnetism in the coil,

Heat in the helix,

Motion in the needle.

Such, then, are some of the glorious phenomena that we have en-
deavoured to explain in this and the preceding chapters on light.
Here we have noticed specially how completely we owe their appre-
ciation to the sense of sight operating through the eye, the organ of
vision. Well may those who have lost this divine gift speak of their
darkness as of a lost world of beauty to be irradiated only by better

THE LOSS OP SIGHT. 351

and more enduring light; and most feelingly does Sir J. Coleridge
speak on this point when he says :

" Conceive to yourselves, for a moment, what is the ordinary enter-
tainment and conversation that passes around any one of your family
tables ; how many things we talk of as matters of course, as to the
understanding and as to the bare conception of which sight is abso-
lutely necessary. Consider, again, what an affliction the loss of sight .
must be, and that when we talk of the golden sun, the bright stars, the
beautiful flowers, the blush of spring, the glow of summer, and the
ripening fruit of autumn, we are talking of things of which we do not
convey to the minds of these poor creatures who are born blind, anything
like an adequate conception. There was once a great man, as we all
know, in this country, a poet and nearly the greatest poet that
England has ever had to boast of who was blind; and there is a
passage in his works which is so true and touching that it exactly
describes that which I have endeavoured, in feeble language, to paint.
Milton says :-

' Thus with the year

Seasons return ; but not to me returns

Day, or the sweet approach of even, or morn,

Or sight of vernal bloom, or summer's rose,

Or flocks, or herds, or human face divine ;

But cloud instead, and ever- during dark

Surrounds me ; from the cheerful ways of men

Cut ofi, and for the book of knowledge fair

Presented with a universal blank

Of Nature's works, to me expunged and rased,

And wisdom at one entrance quite shut out.

So much the rather, thou, celestial light,

Shine inward, and the mind through all her powers

Irradiate ; there plant eyes ; all mist from thence

Purge and disperse, that I may see and tell

Of things invisible to mortal sight.'

The great poet, when intent upon his work, sought for celestial light to
accomplish it. And this brings me to that part of the labours of our
Blind Institutions upon which I dwell the most and which, after all, is
the greatest compensation we can afford to the inmates for the affliction
they suffer ; and that is, the means we provide for them to read the
blessed Word of God, which they can read by day as well as by night,
for light, in their case is riot an essential."

352

BOY'S PLAYBOOK OF SCIENCE.

Fig. 342. James Watt.

CHAPTER XXVII.

HEAT.

the greater numoer of the preceding chapters it will be
evident that the active properties of matter may be summed up under
one general head, and may be considered as varieties of attraction such
as the attraction of gravitation, cohesive attraction, adhesive attraction,
attraction of composition (or chemical attraction), electrical attraction,
magnetical attraction.

The absolute or autocratic system does not, however, prevail in the
works of nature; and she seems ever anxious, whilst imparting
great and peculiar powers to certain agents, to create other forces
which may control and balance them. Thus, for instance, the
great force of cohesive attraction is an ever-present power dis-
cernible, as nas been shown, in solids and liquids ; but if this agent

THE SOURCES OF HEAT. 353

were allowed to ran riot in its full strength and intensity, it would
tyrannically hold in subjection all liquid matter, and every drop of water
which is at present kept in the liquid state, would succumb to its iron
rule, and retain the solid state of ice. Hence, therefore, the wise
creation of an antagonistic force viz., heat ; which is not provided in
any niggardly manner, but is liberally bestowed upon the globe from that
all-sufficient and enormous source, the sun. And it is by the softening
and liquifying influence of his rays that ne greater proportion of the
water on the surface of the globe is maintained in the fluid condition,
and is enabled to resist the power of cohesion, that would otherwise
turn it all, as it were, to stone.

Cohesion, electricity, and magnetism fully embody the notion of
powers of attraction, or a drawing together ; whilst heat stands almost
alone in nature as the type of repulsion, or a driving back.

Mechanically, repulsion is demonstrated by the rebound of a ball from
the ground ; the parts which touch the earth are for the moment com-
pressed, and it is the subsequent repulsion between the particles in those
parts which causes them to expand again and throw off the ball.

The development of heat is produced from various causes, which may
be regarded as at least four in number. Thus, it was shown by Sir
Humphrey Davy, that even when two lumps of ice are rubbed together,
sufficient heat is obtained to melt the two surfaces which are in contact
with each other. Friction is therefore an important source of heat,
and one of the most interesting machines at the Paris Exposition con-
sisted of an apparatus by which many gallons of water were kept in the
boiling state by means of the heat obtained from the friction of two
copper discs against each other. The machine attracted a good deal of
attention on its own merits, and especially because it supplied boiling
water for the preparation of chocolate, which the public was duly
informed was boiled by the heat rubbed out of the otherwise cold discs
of copper. When cannon made on the old system are bored with a
drill, it is necessary that the latter should be kept quite cool with a
constant supply of water, or else the hard steel might become red-hot,
and would then lose its temper, and be no longer capable of performing
its duty.

Count Rumford endeavoured to ascertain how much heat was actually
generated by friction. When a blunt steel bore, three inches and a
half in diameter, was driven against the bottom of a brass cannon seven
inches and a half in diameter, with a pressure which was equal to the
weight of ten thousand pounds, and made to revolve thirty-two times in
a minute, in forty-one minutes 837 grains of dust were produced, and
the heat generated was sufficient to raise 113 pounds of the metal 70
Fahrenheit a quantity of heat which is capable of melting six pounds
and a half of ice, or of raising five pounds of water from the freezing
to the boiling point. When the experiment was repeated under water,
two gallons and a half of water, at 60 Fah., were made to boil in two
hours and a half.

Chemical affinity has been so often alluded to in these pages, that it

A A

354 BOY'S PLAYBOOK OF SCIENCE.

may be sufficient to mention only one good instance of its almost magical
power in evoking heat. When a bit of the metal sodium is placed on
the tip of a knife, and thrust into some warm quicksilver, or if a pellet
of sodium and a few globules of mercury are placed on a hot plate just
taken from the oven, and then gently squeezed together, a vivid pro-
duction of heat and light is apparent ; and when the mixture of the
two metals is cold, it will be found that the quicksilver has lost its
fluidity, and a solid amalgam of sodium and mercury is obtained, which
gradually, by exposure to the air, returns to the liquid state, thft
mercury being set free, whilst the sodium is oxidized, and forms soda.
Just as an ordinary alloy of copper and gold used by jewellers would
lose its colour and 'brilliancy by the oxidation of the copper ; and when
the rusty, dirty film is removed by rubbing and polishing, the surface is
again brilliant, and remains so until another film of the exposed copper
is attacked : in like manner the sodium is attacked and changed by the
oxygen of the air, whilst the mercury being unaffected retains its bril-
liancy, and at the same time regains its fluidity. The evolution of heat
in the above case indicates that a chemical union has taken place between
the two metals.

Examples of the production of heat by electricity and magnetism
have been abundantly shown in the chapters on these subjects ; and one
of the best illustrations of this fact has been shown on the occasion of
the opening of the telegraphic communication between France and Eng-
land by means of the submarine cable, when cannon were fired alternately
at both ends of the conducting cable by means of electricity, and the
event thus inaugurated in both countries.

That heat is a product of living animal organization is shown, as it
were, visibly by the marvellous phenomena that proceed in our own
bodies. People do not very often trouble themselves to ask where the
heat comes from, or even to think that this invisible power must be
maintained in the body, and that slow combustion, or, as Liebig terms
it, eremacausis, must continually go on inside our frail mortal tenements ;
and more than this, that we cannot afford to waste our heat. If the
body is deprived of heat faster than it can be generated, death must
inevitably occur; and a very melancholy instance of this remarkable
mode of death has lately occurred in Switzerland to a Russian gen-
tleman.

Such another instance of a man being slowly frozen to death within
sight and sound of other beings, through whose veins the blood was
flowing at its accustomed temperature (about 90 Eahr.), it would be
difficult to find, and it stands forth, therefore, as a marked example and
illustration of the statement already made, that living animal organisms
are truly a source of heat, which is as essential to the well-being of the
body as meat, drink, and air.

lleat is of two kinds, and may be either apparent to our senses, and
therefore called sensible heat; or it may be entirely concealed, although
present in solids, liquids, and gases, and is then termed insensible or
latent heat.

EXPANSION OF SOLIDS.

Sensible Heat.

The first effect of this force is a demonstration of its repulsive agency,
and the dilatation or expansion of the three forms of matter whilst under
the influence of heat, admits of very simple illustrations. The expansion of
a solid substance, as, for instance, a metal, on the application of heat,
is apparent by fitting
a solid brass cylinder
into a proper metal
gauge, which is accu-
rately filed so as to
admit the former
when perfectly cold.
If the brass rod is
then heated, either
by plunging it into
boiling water or by
the application of the
flame of a spirit lamp,
its particles are sepa-
ratedfromeach other;
they now occupy
a larger space, and
expansion is the re-
sult, and this is clearly
proved by the appli-
cation of the gauge,
which is no longer capable of receiving it. (Pig. 343.) When, how-
ever, the latter is cooled, the opposite result occurs, the particles of
brass return to their old position, and contraction takes place ; hence it is
stated that " Bodies expand by heat and contract by cold ;" and it is
proper to state here that the term " cold" is of a negative character, and
simply means the absence of heat.

Solid bodies do not expand equally on the application of the same
amount of heat; thus, a bar of glass one inch square and one thousand
inches long would only expand one inch whilst heated from the freezing
to the boiling point of water. A bar of iron one inch square and eight
hundred inches long would expand one inch in length, through the same
degrees of heat ; and a bar of lead one inch square and three hundred
and fifty inches long would also dilate one inch in length. Hence,

Lead expands in volume .

Iron

Glass .

Fig. 343. A B. Cylinder of brass, c D. Iron gauge, admit-
ting A B longitudinally, and also in the hole E when cold, but
excluding A B when the latter is heated and expanded.

Tooo tn -

The unequal expansion of the metals is well illustrated by an experi-
ment devised by Dr. Tyndal, the respected Professor of Natural Philo-
sophy in the Royal Institution of Great Britain, and is arranged as
follows : A long bar of brass and another of iron are supported on the

A A 2

356

BOY'S PLAYBOOK OF SCIENCE.

edges of two pieces of wood placed at an angle, and resting against the
sides of a mahogany framework. The metallic bars only touch one end

of the frame, and are
in metallic commu-
nication with a piece
of brass inserted
there, and forming
part of a conducting
chain connected with
a voltaic battery ;
when heat is applied
to both bars they ex-
pand unequally ; the
brass bar dilates first,
and filling up the mi-
nute space left be-

f wri PTir lc

Fig. 344 A A. The brass bar which has expanded by the
heat from the gas jet B, and making the contact between the ^T

brass plates in connexion with the binding screws c c, the Ot the trame, touches

voltaic circuit is completed, and a coil of platinum wire in the another brass plate
glasstubei), is immediately ignited. The iron bar at E E has not j i-.-fo-.j-i-

expanded sufficiently, which is shown afterwards by removing ana instantly _COm-

the angular wooden supports K K, when the iron falls off, and pletes the voltaic Cir-

the brass remains on the two ledges of the mahogany frame- g^jf, when a coil of
work L i n. i x r

platinum wire be-

comes ignited, showing the fact of expansion ; and secondly, the diffe-
rence in the power of dilatation possessed by each is clearly shown by
removing the two angular supports of wood, when the iron falls away,
whilst the brass remains and still completes the voltaic circuit. (Fig. 344.)

The force exerted by the expansion of solids is enormous, and reminds
us again of the amazing power of all the imponderable agents ; and it is
truly wonderful to notice how the entry of a certain amount of heat into
and between the particles of metals, or other solids, endues them with
a mechanical force which is almost irresistible, and is capable of working
much harm. Kussne made an experiment with an iron sphere, which
he heated from a temperature of 32 Fahr. to 212 Fahr., and he found
that the expansion of the ball exerted a force equal to 4000 atmospheres
i.e. 4000 X 15 on every square inch of surface, or a pressure equal to
thirty millions of pounds ; the entry of only 180 of heat into the iron
sphere produced this remarkable result, just as Faraday has calculated that
a single drop of water contains a sufficient quantity of electricity to pro-
duce a result equal to the most powerful flash of lightning, provided the
electricity of quantity in the drop of water is converted into electricity
of high tension or intensity.

The practical applications of this well-known property of solids with
respect to heat are very numerous ; thus, the iron bullet-moulds are
always made a little larger than the requisite size, in order to allow for
the expansion of the hot liquid lead, and the contraction of the cold
metal. The tires of wheels and the hoops of casks are usually placed on
whilst hot, in order that the subsequent contraction may bind the spokes

EXPANSION OF SOLIDS.

357

and fellies, or the staves, closely together. If an allowance was not
made for the expansion and contraction of the iron rails on the perma-
nent ways of railroads, the regularity of the level would be constantly
destroyed, and the position of the rails, chairs, and sleepers would be
most seriously deranged ; indeed it is calculated that the railway bars
between London

and Manchester p

are five hundred
feet longer in the
summer than in the
winter.

The walls of the
Cathedral of Ar-
magh, as also those
of the Conserva-
toire des Art et Me-
tiers, were brought
back to a nearly
perpendicular po-
sition, by the in-
s ert ion (through the
opposite walls) of
great bars of iron,
which being alter-
nately heated, ex-
panded, and screw-
ed up ti^ht then Fi g- 345 - Tne iron fram e, with c c, wrought-iron bar heated by
,1,J ~ 4- 4- putting on the semicircular piece of irons E, which is first made
COOiea ana contract- re d-hot, and as the heat is communicated to the wroneht iron
ed, gradually COr- rod c c, it is screwed up tight by the nut K. G G. The index
rpp+pd tlip Vmlm'no- attached to the iron frame screwed up when hot ; the arms come

ucu LI. uuapug togetner at P> and separate further to n H as the contraction
OUt 01 tlie walls or takes place by cooling the bar c D.
main supports of

these buildings. The principle of these famous practical experiments is
neatly illustrated by means of an iron framework with a bar of iron placed
through both its uprights, and screwed tight when hot ; on cooling, con-
traction occurs, which is shown by a simple index. (Fig. 345.)

It has often been remarked that there is no rule without an excep-
tion, and this applies in a particular instance to the law that " bodies
expand by heat and contract by cold" viz., in the case of Rose's
fusible metal, which consists of

Two parts by weight of bismuth,
One part lead,

One part tin.

To make the alloy properly, the lead is first melted in an iron ladle,
and to this are added first the tin, and secondly the bismuth; the
whole is then well stirred with a wooden rod, and cast into the shape
of a bar.

358

BOY S PLAYBOOK OF SCIENCE.

"When placed in the pyrometer and heated, the bar expands pro-
gressively till it reaches a temperature of 111 Fahr. ; it then begins to
contract, and is rapidly shortened, until it arrives at 156 Fahr., when it
attains a maximum density, and occupies no more space than it would
do at the freezing-point of water. The bar, after passing 156, again
expands, and finally melts at about 201, which is 11 below the
boiling-point of water. Fusible metal is sometimes made into tea-
spoons, which soften and melt down when stirred in a cup of hot tea or
basin of soup, to the great surprise and bewilderment of the victim of
the practical joke.

Unequal expansion is familiarly demonstrated with a bit of toasted
bread, which curls up in consequence of the surface exposed to the fire
contracting more rapidly than the other ; and the same fact is illus-
trated with compound flat and thin bars of iron and brass, which are
fixed and rivetted together ; when heated, the compound bar curves,
because the iron does not expand so rapidly as the brass, and of course
forms the interior of the curve, whilst the brass is on the exterior.

The experiment with the compound bar is made more conclusive and
interesting by arranging it with a voltaic battery and platinum lamp. One
of the wires from the battery is connected with the extremity of the
compound bar, and as long as it remains cold, no curve or arch is pro-
duced, but when heat is applied, the bar curves upwards, and touching
the other wire of the battery, the circuit is completed, and the platinum
lamp is immediately ignited. (Fig. 346.)

Fig. 346. A B. Compound bar resting on two blocks of wood. The end A is connect
with one of the wires from the battery. The circuit is completed and the platinum lamp
B ignited directly the bar curves upwards by the heat of the spirit lamp, and touches the
wire c o connected with the opposite pole of the battery.

The expansion and contraction of liquids by heat and cold is also
another elementary truth which admits of ample illustration, and
indeed introduces us to that most useful instrument called the ther-
mometer.

If a flask is fitted with a cork through which a long glass tube, open

EXPANSION OF LIQUIDS.

359

at both ends, is passed, and then carefully filled with \vater coloured

with

a little solution of indigo, so that when the cork and tube are

placed in the neck, all the air is excluded, a rough thermometer is thus
constructed, which, if placed in boiling water, quickly indicates the in-
creased temperature by the rising or expansion of the coloured water
inside the flask. (Fig. 347.)

Fig. 347. Expansion of liquids shown at A by the coloured water rising in the tube from
the flask, which is quite full of liquid, and heated by boiling water. B. The expansion of
the water heated by the spirit-lamp is shown by the rising of the piston and rod o c.
i> represents a retort filled up like A to show the expansion of a liquid by heat.

The thermometer embraces precisely the same principle as that
already described in Fig. 347, with this difference only, that the tube is
of a much finer bore, and the liquid employed, whether alcohol or
mercury, is boiled and hermetically sealed in the tube, so that the air is
entirely excluded. To make a thermometer, a tube with a capillary
bore is selected of the proper length ; it is then dipped into a glass con-
taining mercury, so that the tube is filled to the length of half an inch
with that metal. The half-inch is carefully measured on a scale, and
the place the mercury fills in the tube marked with a scratching
diamond ; the mercury is then shaken half an inch higher, and again
marked, and this proceeding is continued until the whole tube is divided
into half inches. The object of doing this is to correct any inequalities

360

BOY S PLAYBOOK OF SCIENCE.

in the diameter of the bore of the glass tube, because if wider at one
part than another, the spaces filled with the mercury are not equal ;
as the bore is usually conical, the careful measurement of the tube
with the half inch of mercury in the first place gives the operator
at once a view of the interior of his tube, and enables him to graduate
it correctly afterwards. (Fig. 348.)

Fig. 348. A B. Magnified view of the bore of one of the thermometer tubes which are
made by rapidly drawing out a hollow mass of hot glass whilst soft and ductile,
consequently the bore must be conical, and larger at one end than the other.

The next step is to heat one extremity by the lamp and blowpipe, and
whilst hot, to blow out a ball upon it ; if this operation were per-
formed with the mouth, moisture from the breath would deposit inside
the fine bore of the glass tube, and injure the perfection of the ther-
mometer afterwards. In order to prevent any deposit of water, the
bulb is blown out, whilst red-hot, with the air from a small caoutchouc

Fig. 349 a. No. 1. First bulb. The intended length of the thermometer is shown at the-
little cross. No. 2 is the second bulb placed above the cross.

bag fitted on to the other extremity of
the tube. The operator now marks off
the intended length of his thermometer,
and above that point the tube is again
softened with the flame and blowpipe, and
a second bulb blown out. (Fig. 349 a.)

The open end of the tube is now placed
under the surface of some pure, clean, dry
quicksilver, and heat being applied to the
upper bulb, the air expands and escapes
through the mercury, and as the tube
cools a vacuum is produced, into which
the mercury passes. By this simple me-
thod, the mercury is easily forced into
the tube, as otherwise it would be impos-
sible to pour the quicksilver into the ca-
pillary bore of the intended thermometer.
(Fig/349.)

The tube is now taken from the glass
containing the mercury, and simply in-
verted; but in consequence of the very
narrow diameter of the bore the air will
not pass out of the first bulb until heat
is applied, when the air expands, and the

Fig. 349 b. Heating and expanding
the air in the top bulb, so that when
cool the mercury in the giass A, may
rise into the tube and fill the bulb B.

THE CONSTRUCTION OF THE THERMOMETER.

361

mercury,, first stationary in tne second bulb, will now displace the air,
and fall into the first bulb when the tube is again cool.

The ball, No. 1 (Fig. 349 a), is now full of mercury, and there is also
some left in No. 2 ; in the next place, the tube is supported by a wire,
and held over a charcoal fire, when it is heated throughout its entire
length, and the mercury being boiled expels the whole of the air, so
that there is nothing inside the bulbs and capillary bore but mercury
and its vapour. (No. 1, Tig. 350.) The open end of the intended ther-
mometer is now temporarily closed with sealing-wax, and the whole
allowed again to cool with the sealed end uppermost, so that the ball
No. 2, Eig. 350, and the tube above it, are quite filled with quicksilver.

After cooling, the tube is placed at an angle with the sealed end
uppermost, and, guided by experience, the operator heats the lower
bulb so as to expand enough mercury into the upper one to leave space
for the future expansion and contraction of the mercury in the tube,
which has now to be hermetically sealed. This is done by dexterously
heating the tube at the cross whilst the mercury in the first bulb is still
expanded ; and by drawing it out rapidly with the help of the heat obtained
from the lamp and blowpipe, the second bulb is separated from the first
at the little cross (B, No. 3, Fig. 350), and the thermometer tube at last
properly filled with quicksilver, and hermetically closed. (No. 4, Fig. 350.)

Fig. 350. No. 1. Boiling quicksilver in the tube with two bulbs. No. 2. Tube cooled,
with the sealed end uppermost. No. 3. Mercury in first bulb expanded by lamp A, and at
the proper moment hermetically sealed by the flame urged by the blowpipe at B. The
upper bulb and tube to the cross being drawn away and separated. No. 4. Thermometer
tube containing the requisite quantity of mercury, hermetically sealed, and now ready for
graduation.

362 BOY'S PLAYBOOK OF SCIENCE.

In order to procure a fixed starting-point, the thermometer tube is
placed in ice, with a scale attached ; the temperature of ice never varies,
it is always at 32 degrees. When, therefore, the mercury has sunk to
the lowest point it can do by exposure to this degree of cold, the place
is marked off in the scale, and represents that position in the graduated
scale where the freezing point of water is indicated.

The tube is placed in the next place in a vessel of boiling water, care
being taken that the whole tube is subject to the heat of the water and
the steam issuing from it, and when the mercury has risen to the highest
position attainable by the heat of boiling water, another graduation is
made which indicates 212 degrees viz., the boiling point of water. This
graduation should be made when the barometer stands at 30 inches,
because the boiling point of water varies according to the weight of the
superincumbent air pressing upon it.

Between the graduation of the freezing and the boiling point of water
the space is divided into 180 parts, which added to 32 make up the
boiling point of water to 212 degrees, being the graduation of Fahrenheit,
who was an instrument-maker of Hamburg. Why he divided the space
between the freezing and boiling point of water nobody appears to know,
unless he took a half circle of 180 degrees as the best division of space.
If the thermometer contains air the mercury divides itself frequently
into two or three slender threads, each separated from the other in the
capillary bore, and thus the instrument is rendered useless until the
threads again coalesce. If the thermometer has been well made, and
is quite free from air, it may be tied to a string and swung violently
round, when the centrifugal force drives the slender threads of mercury
to their common source viz., the bulb containing the quicksilver, and
the whole is again united. The string must be attached, of course, to
the top of the thermometer scale.

When travelling on the Continent it is sometimes desirable to be
able to read the thermometers which are graduated in a different manner
to that of Fahrenheit. In France the Centigrade scale is preferred, and
in many parts of Germany Reaumur's graduation The difference of
the graduation is seen at a glance.

In the Centigrade the freezing point is 0, the boiling point 100.
Reaumur 0, 80.

Fahrenheit 32, 212.

The number of degrees, therefore, between boiling and freezing is
TOO in the Centigrade, 80 in Reaumur, and (212 32, that is) 180 in
Fahrenheit.

If, then, the letters C, R, F, be taken to denote the number of degrees
from the freezing point at which the mercury stands in the Centigrade,
Reaumur, and Fahrenheit thermometers, we have the following pro-
portions :

(1.) 100
(2.) 180
'3.) ISO

80
100

C : R, whence C = f of R, or R = of C.
F : C, whence F = f of Q, or = of F.

F . R, whence F = f of R, or R = $ of F.

EXPANSION OP WATER BY COLD.

3G3

The following examples will show how to apply these formulae :

(l)._Suppose the Reaumur stands at 28, at what height does the
Centigrade stand ? We have C = -f of R (in this case), f of 28 = 35 :
that is, the Centigrade stands at 3&.

(2). Suppose Fahrenheit to stand at 41, what will Reaumur stand
at ? R = f- of (41 32) (that is, the number above freezing in Fahr.)
= |-of9:=4. Reaumur stands, at 4.

(3). Suppose Fahrenheit stands at 23, what will the Centigrade
stand at ? C = f of F = of (32 - 23) = of 9 = 5 below freezing
(or 5).

(4). If Fahrenheit stands at 4 below 0, what will Reaumur indicate ?
R = | of F f of (32 + 4) = -| of 36 = 16 below (or 16). _

The only liquid which has the exceptional property of expanding by
cold is water, and it will be seen presently that this curious anomaly is
of the greatest importance in the economy of nature.

If a box containing a mixture of ice and salt is placed round the top
of a long cylindrical glass containing water at a temperature of 60
Fahr., the intense cold of the freezing mixture, which is zero that is
to say, 32 below the freezing point of water very soon reduces the
temperature of the water contained in the glass, and as it becomes
colder it contracts, is rendered heavier, and sinks to the bottom of the
vessel, and its place is taken
by other and warmer water.
This circulation commencing
downwards, proceeds till the
water has attained a tempe-
rature of about 40 Fahr.,
when the maximum density
is obtained and the circula-
tion stops, because after sink-
ing below 40 the cold water
becomes lighter, and conti-
nues to be so until it freezes,
and of course, being of a
less specific gravity than the
warmer water, it floats (like
oil on water) upon its surface;
so that a small thermometer
placed at the bottom of the
jar indicates only 40 Fahr.,
whilst the solid ice enveloping
the other or second thermo-
meter placed at the top may
be as low as 29, or even

i J- 4- 4V, Fig. 351. A B. Long cylindrical glass containing

lower, according to the quan- wate and two thermometers ; the one at the bottom

titv of ice and salt used in the shows a temperature of 40; the other at the top 32,

W Qurvminrlino- fhp ton of or even lower - c c c c. Section of box containing

box surrounding tne top 01 the ice and Baltjimd sta nding on four legs, two of

the glass. (Jclg. OOi.) which are shown at D D.

!:= mfk

"> T.-V-M:-.-:

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*RLS

: ,; .',- . . x

:! . . .-,' v ,y.
b

M-3b]

,,..,:,,-;..,: , , -,,-;.,-;.

':.; , . : -::""- ,;.

vnonrr

.
tm&*1*fir*eta**m*

x -,',

, ,,,.,,. -,v..- -,,-, vr- ;-,.- v: ,-.-.:, ,, ,,- -.- ,,*

Tf^X^^<fc

v . .-. - -.-. -.- '.H:>n

, >: ;/..-: '.' -' -. ^ :

THE EXPANSION OP GASES.

t as an a

er the name of the
feieata tx>;ri-cu:s vl::: httt

been employed by Sir John

ri:>
sv.. : . i

lire balloons an a good example of the expansion of gases, and the
rity of the air thus increased in bulk was taken advantage of by
Montgolfier in the constitution of his famous baUoon, which, with a
age containing various animals, ascended, in the ptrescMe of the King
and roTalfanu^ of France, at Versailles; and in spite of hiwe rents iu
twoplaoe^ititwetoaheightof 1^10 feet, and after remainW in the
air for eight minute^ foil to the ground at the distance of lttdOO fan
from the place whence it started, without injurr to the aninab.
When it is considered that a rolurnc of air heated no $3* to 491* is
doubled, and tripled nhen heated to 988% it will at once be tadeotood
how great must be the ascending power of such balloons, provided the
air within them is kept sufficiently hot

That gallant aeronaut, Pilate de Boiier, offered himself to be the
rst aerial naTigator; and
successful
eight feet h

oooasion he ascended to a height of ia feet> butm the descent a gust
of wind haTing Mown the machine orer some large trees of an
garden^ the situation of the brave aeronaut was extreme^ da
and if he had not possessed the strongest presence of nuftd, ind it

Oknt aeronaut, Pilate de Bower, ofiered himself to be the
. navigator; and having joined Montgolficr, they made three

asoerta and descents witn a Urge ov%shaped balloon, forty.

in diameter, and seventy-four feet high* On the fourth

BOY S PLAYBOOK OF SCIENCE.

given the balloon a greater ascending power, by rapidly supplying his
stove with some straw and chipped wood, he might on this occasion
have met with that untimely end which subsequently, in another rash
aeronautic adventure, befel this brave but foolhardy Frenchman.

On descending again, he once more, and without the slightest fear,
raised himself to a considerable height by feeding his fire with chopped
straw. Some time after he ascended, in company with M. Giroud de
Vilette, to the height of 330 feet, hovering over Paris at least nine
minutes, in sight of all the inhabitants, and the machine keeping all the
while perfectly steady.

The danger in using this method of inflating the balloon arises from
the possibility of generating gas, which escaping unburnt into the body
of the balloon, may accumulate and blow up, or'burn afterwards.

Fire balloons, as
usually made, are very
dangerous toys, and
may sometimes prove
rather costly to the
person who may send
them off, in conse-
quence of their being
blown by the wind on
a hay or corn rick, or
other combustible sub-
stances. The safest
mode of using fire bal-
loons is to fill them
with hot air from a
lighted gas stove (Wes-
sel's, for instance) ;
the balloons may then
be used in large rooms,
or out in the air, with-
out fear of doing any
harm to neighbouring
property, as of course
the stove and the fire
remain behind, and
will fill any number of

Fig. 353. A. B. Wessel's gas stove, with ring of gas jets air balloons. (Fig. 353.)
lighted inside ; the air rushes in the direction of the arrows, Aftpr nil the fuss
c c, and escaping at the top of the chimney, DD, soon fills the j e f
air or fire balloon, which is usually made of paper. made about the novelty

of the Americanhot-air

engine, it is somewhat amusing to look back to the records of civil
engineering, and in the "Transactions of the Institution of Civil
Engineers," to read Mr. James Stirling's account of his improved air
engine, in which the great expansion of air mentioned at p. 365 has
\>een successfully applied. The engine was constructed about the year

THE HOT-AIR ENGINE.

367

1843, and the principle, discovered thirty years before by Mr. R.
Stirling, will be comprehended by reference to the cut. (Fig. 354.)

Fig. 354 Stirling's air engine.

Two strong air-tight vessels are connected with the opposite ends of
a cylinder, in which a piston works in the usual manner. About four-
ftftns of the interior space in these vessels is occupied by two similar
air-tight vessels or plungers, which are suspended to the opposite
extremities of a beam, and capable of being alternately moved up and
down to the extent of the remaining fifth. By the motion of these
interior vessels, which are filled with non-conducting substances, the air
to be operated upon is moved from one end of the exterior vessel to the
ether, and as one end is kept at a high temperature, and the other as
cold as possible, when the air is brought to the hot end it becomes
heated, and has its pressure increased ; and when it is brought to the
cold end, its heat and pressure are diminished. Now, as the interior
vessels necessarily move in opposite directions, it follows that the pressure
of the enclosed air in the one vessel is increased, while that of the other
is diminished. A difference of pressure is thus produced upon the
opposite sides of the piston, which is thereby made to move from
the one end of the cylinder to the other, and by continually reversing the
motion of the suspended bodies or plungers, the greater pressure is
successively thrown upon a different side, and a reciprocating motion of

368 BOY'S PLAYBOOK OF SCIENCE.

the piston is kept up. The piston is connected with a fly-wheel in any
of the usual modes ; and the plungers, by whose motion the air is heated
and cooled, are moved in the same manner, and nearly at the same
relative time, with the valves of a steam engine.

The pressure is greatly increased and made more economical by using
somewhat highly-compressed air, which is at first introduced, and is
afterwards maintained, by the continued action of an air-pump. The
pump is also employed in filling a separate magazine with compressed
air, from which the engine can be at once charged to the working
pressure. Mr. Stirling's chief improvement consists in saving all or
nearly all the heat of the expanded air after it has done its work, by
passing it from the hot to the cold end of the air vessel through a
multitude of narrow passages, whose temperature is at the beginning
of the tubes nearly as great as that of the hot air, but gradually
declines till it becomes nearly as low as the coldest part of the air
vessel. The heat is therefore retained by these passages, so that when
the mechanism is reversed, the cold air returns again through these hot
pipes, and is thus made nearly hot enough by the time it reaches the
heating vessel to do its work. Thus, instead of being obliged to supply
at every stroke of the engine as much heat as would be sufficient to
raise the air from its lowest to its highest temperature, it is necessary
to furnish only as much as will heat it the same number of degrees by
which the hottest part of the air vessel exceeds the hottest part of the
intermediate passages. This portion of the engine may be called the
economical process, and represents the foundation of all the success to
which it has attained in producing power with a small expenditure of
fuel. No boiler being required, of course the danger of explosions is
much lessened. The higher the pressure under which the engine was
worked the greater was the effect produced. A small engine on this
principle was worked to a pressure of 360 pounds on the square inch;
and perhaps the best popular notion of the novelty in the arrangement
is that suggested by Mr. George Lowe, who compared the economical
part of the machine to a " Jeffrey's Respirator" used by consumptive
patients. The heat from the air expired oeing retained by the laminae,
and again used when cold air is inspired or drawn into the lungs. Mr.
Stirling states that the consumption of fuel as compared to the steam
engine which the air engine had replaced was as 6 to 26 ; the same
amount of work being now performed by about six cwt. of coals which
had formerly required about twenty-six cwt., though he ought to have
stated that the steam engine removed was not of the best construction,
nor had the boiler any close covering. (Fig. 354-.)

Conduction of Heat.

This property of heat with reference to matter, and the consideration
of the curious manner in which it creeps, as it were, through solid sub-
stances, brings the thoughtful mind at once to the bold question of
What is heat ? Is it to be regarded as something real or material ? or

THEORIES OF HEAT.

369

must it be considered only as a property or state of matter ? These
questions are not to be solved easily, and they demand a considerable
amount of experiment and reasoning even to appreciate their meaning.

If a red-hot ball is placed in the focus of a concave metallic speculum,
it gives out certain emanations that are quite invisible, but which are re-
flected from the surface of the mirror in the same manner as visible rays
of light, and may be collected in the focus of another and second con-
cave speculum, when they can be concentrated on to a bit of phosphorus,
and will cause the combustion of that substance. If the air from a pair
of bellows is blown forcibly across the rays of heat as they are being con-
centrated upon the phosphorus, the rays are not moved from their
course, they are no more blown away than a sunbeam darting through
an aperture in a cloud on a stormy, windy day. The heat has, therefore
nothing to do with
the air, and is wholly
independent of that
medium in its pas-
sage from one mirror
to the other. Such
an experiment as that
described would at
once suggest the idea
that heat is a matter
sui generis, a compo-
nent part of all bo-
dies, and given off
from incandescent
matter, the sun, &c.,
and that it may be
propagated through
space much in the
same manner as light.
(Fig. 355.) The me-
chanism may be very
much like the cor-
puscular movement of light as denned by Sir Isaac Newton, and already
explained in another portion of this book. Hence it has been supposed
that heat is propagated through the air, water, and solid substances by
a direct emission of material particles from the heat-giving agent and
that these molecules of heat force their way into, or along, or through
them, according to circumstances.

Certain bodies are almost transparent to heat rays, such as air,
whilst others take an intermedial position, and only stop a certain quan-
tity of the heat molecules, such as rock crystals, mirror glass, and alum
A third class of bodies absorbs the heat plentifully, such as char-
coal, black cloth, &c. ; and a fourth, when polished and placed at the
proper angle, reflects or throws off the heat, as in the case of polished
mirrors. The transparency or opacity of substances (so far as light is

Fig. 355. Heat reflected by mirror, but not blown away by
air from bellows.

370 BOY'S PLAYBOOK OF SCIENCE.

concerned) does not affect the transmission of heat. Light of every
colour and from all sources is equally transmitted by ail transparent
bodies in the liquid or solid form, but this is not .the case with
heat.

The rays of heat emitted by the sun and other luminous bodies have
properties quite different to the rays of light with which they are accom-
panied. From these statements it will be evident that the material
theory of heat is surrounded with difficulties and anomalies that cannot
be reconciled the one with the other, or neatly adapted, fitted in, and
dovetailed with all the puzzling phenomena that arise. Our knowledge
of the theory of heat has been greatly assisted by the researches ^of
Melloni, who has demonstrated that different species of rays of heat are
given off by the same body at different temperatures, which may be dis-
tinctly sifted and separated from each other. Long before the experi-
ments of Melloni philosophers had endeavoured to weigh heat ; trains
of the most delicate levers were exposed, without effect, to the action
of heat rays ; and all attempts, experimental as well as theoretical, to
define heat by the material theory, are imperfect, crude, and unsatis-
factory. We are perforce obliged to adopt another theory, and the one
that obtains the greatest favour, as offering the best definition of heat,
is the dynamical theory, which is more or less analogous to the undula-
tory theory of light. At pages 262, 328, 335, this theory has been partly
explained, and in speaking of it again, great care must'be taken not to
confuse the undulations of heat with those of light. The sun and the
stars swim, in a molecular medium, and 39,180 vibrations or waves must
occur in one inch to produce the sensation of red light, and 57,490
undulations in the space of one inch to produce a violet light. As vibra-
tions of the ethereal molecules affect the eye, so there may be other
nerves in our bodies which are peculiarly sensitive to the waves of heat.
It requires eight vibrations of the air to occur in a second to produce
an audible sound; whilst if the vibrations of the air amount to 25,000
per second they cannot be appreciated by the human ear, although it is
possible to conceive that the ears of certain animals may be so suscep-
tible of rapid vibrations that they may be able, for certain wise purposes
of the Creator, to appreciate sounds which are inaudible to human
ears.

Melloni exhibited a spectrum to a number of persons, and found that
there was more light apparent to some eyes than to others. Lubeck
put a scarlet cloth on a donkey, and found that the two were frequently
confounded together by the eyes of many spectators. These facts indi-
cate that there may be vibrations of molecules that produce the sensation
of heat, but which do not affect the nerves that are sensitive to the
action of light waves, and vice versa; and it is also probable that all these
different undulations, some affording heat and some light, may be gene-
rated and propagated through space, as from the sun ; or through shorter
distances, as from burning lamps and fires, without in any way inter-
fering with or impeding each other's progress.

The dynamical theory seems to offer the best idea of the transmission

THE CONDUCTION OF HEAT. 371

of heat which is carried, conducted, or propagated through solids with
variable rapidity, either by the vibration of the constituent molecules of
the body itself, or by the undulation of a rare subtle fluid which per
vades them. If a copper and iron wire of the same length 'and diameter
are bound together and heated at the point of union, the waves of heat
travel faster through the copper than the iron, and the former is said to
be the best conductor of heat ; and the fact itself is demonstrated bv
placing a bit of phosphorus at the end of each metallic wire, and it will
be found by experiment that the combustible substance melts first and
takes fire on the copper, and that a considerable interval of time elapses
before the phosphorus ignites on the iron.

Fig. 356. c. Copper wire bound at A to i, an iron wire. After the heat of the lamp has
been applied for about five minutes the heat travels to c first, and ignites the bit of phos-
phorus placed there. After some time has elapsed the phosphorus at i also ignites.

The same fact is exhibited in a most striking manner by inserting a
series of rods of equal lengths and thicknesses in the side of a rectan-
gular box, allowing them to pass across the interior to the opposite
side. The rods are composed of wood, porcelain, glass, lead, iron, zinc,
copper, and silver, and have attached to each of their extremities, by
wax or tallow, a clay marble. When the water placed in the box is made
to boil, the heat passes along the different rods, and melting the wax or
tallow, allows the marble to drop off. Consequently the first marble
would drop from the silver rod, the next from the copper, the third
from the iron, the fourth from the zinc, the fifth from the lead,
whilst the porcelain, glass, and wooden rods would hardly conduct (in
several hours) sufficient heat to melt the wax or tallow, and discharge
the marbles.

Conduction of Metals.

Gold . . . . ' 1000

Silver 973

Copper 898-2

Iron 374-3

Zinc 363

Lead - 179-6

BOY'S PLAYBOOK OF SCIENCE.

Fig. 357. A B. Trough containing boiling water,
heated by gas jets below, c. The eight rods and
marbles attached, one of which has fallen. D. The
tray to receive the marbles.

The experiment is made
more striking if the marbles
are allowed to fall on a lever
connected with the detent of
a clock alarum, which rings
every time a marble falls from,
one of the rods. (Fig. ,>57.)

During a cold frosty day,
if the hand is placed in con-
tact with various substances,
some appear to be colder than
others, although, all may be
precisely the same tempera-
ture ; this circumstance is due
to their conducting power:
and a piece of slate seems
colder than a bit of chalk, because the former is a much better con-
ductor than the latter, and carries away the heat from the body with
greater rapidity, and diffuses it through its own substance.

The gradual passage
of heat along a bar of
iron as compared with
one of copper, is well
illustrated by sup-
porting the ends of
the two bars on the
top of the chimney of
an argand lamp, whilst
the other extremities

Fig. 358. A. Section of an argand gas lamp, with a copper are neld in a horizon-
chimney supporting the ends of the bars of copper and iron tal position by little
marked c and i. The balls have fallen from c, the copper ^locjjg O f wood If

marbles are attached

by wax to the under side, they fall off as the heat travels along the
metallic bars, and more rapidly from the copper than the iron, because
the former is a better conductor of heat than the latter. (Fig. 358.)

From the experiments of Mayer, of Erlangen (" Ann. de Ch.," xxx.),
it would appear that the conducting powers of different woods are to a
certain extent to be regarded as in the inverse proportion to their
specific gravities i.e., the greater the density of the wood the less con-
ducting power, and the contrary.

If a cylindrical bar or thick tube of brass, six inches long, and about
two inches in diameter, is attached to a wooden cylinder of the same
size, the conducting powers of the two substances are well displayed
by first straining a sheet of white paper over the brass, and then holding
it in the flame of a spirit lamp. The heat being conducted rapidly away
by the metal will not scorch the paper, until the whole arrives at a
uniform high temperature ; whereas the paper is rapidly burnt when

THE CONDUCTION OF HEAT.

373

strained over the wooden
cylinder, because the heat of
the flame of the lamp is con-
centrated upon one point,
and is not diffused through
the mass of the wood. (Fig.
359.)

In the course of the
highly philosophical experi-
ments of Sir H. Davy, which
led him gradually to the dis-
covery of the construction
of the safety lamp, he con-
nected together, by a copper
tube of a small bore, two
vessels, each containing an
explosive mixture composed
of fire damp and air. When
the mixture was fired in one
vessel he found that the

flnmp Hid Tint armpar in bp Tig. 359. Cylinder, half brass aud half wood. The

name ua not appear t ie pap( 8traine( f over ' the wood is taking ^ The

able to travel, as It were, other extremity, shaded, is the brass portion.

across the bridge viz., the

copper tube and communicate with the other magazine, because it was
deprived of its heat whilst passing through the tube, and was no longer
flame, but simply gaseous matter at too low a temperature to effect the
inflammation of the mixture in the second box.

A mass of cold metal may be suddenly applied to a small flame, such
as that of a night light, and depriving it rapidly of heat (like the case
of the unfortunate Russian described at page 354), it is almost imme-
diately extinguished (fig. 360), not by the mere exclusion of the oxygen

Fig. 360. A. Small flame from night light. B c. Large mass of cold copper wire open at
both ends to place over flame, and by conduction of the heat to extinguish it.

of the air, but on account of the withdrawal of the heat necessary for
the maintenance of the combustion.

Sir H. Davy first thought of making his safety lamp with small tubes,
which would supply fresh air, and carry off the burnt or foul air, at the

37-t

BOY'S PLAYBOOK OF SCIENCE.

same time they were to be so narrow that noflame could pass out of his lamp
to communicate with an outer explosive atmosphere ; and in speaking
of his lamp with tubes he says : " I soon discovered that &few apertures,
even of very small diameter, were not safe unless their sides were very
deep ; that a single tube of one-twenty-eighth of an inch in diameter,
and two inches long, suffered the explosion to pass through it ; and that
a great number of small tubes, or of apertures, stopped explosion, even
when the depths of their sides was only equal to their diameters. And
at last I arrived at the conclusion that a metallic tissue, however thin
and fine, of which the apertures filled more space than the cooling
surface, so as to be permeable to air and light, offered a perfect barrier
to explosion, from the force being divided between, and the heat com-
municated to an immense number of surfaces. I made several attempts
to construct safety lamps which should give light in all explosive mixtures
of fire damp, and after complicated combinations, I at length arrived at
one evidently the most simple, that of surrounding the light entirely by
wire gauze, and making the same tissue feed the fame with air and emit
light."

If a number of square metallic tubes of a fine bore are placed upright
side by side, and a section cut off horizontally, it would represent the
wire gauze which possesses such marvellous powers of sifting away
the heat from a flame, so that it is destroyed in its attempted passage
through the metallic meshes ; and of this fact a number of proofs may
be adduced.

A gas jet delivering coal gas may be placed under a sheet of wire
gauze, the gas permeates the gauze, and may be set on fire at the upper

side, but the flame is cut off from
the mouth of the jet by the cooling
action of the wire gauze. The same
experiment reversed, by holding the
gauze over the gas burning from the
jet, shows still more decidedly that
flame will not pass through the me-
tallic tissue. (Fig. 361.)

Sir H. Davy again says : " Though
all the specimens of fire damp which
I had examined consisted or carbu-
retted hydrogen mixed with different
Fiff.36i. A A. A number of square tubes small proportions of carbonic acid
placed upright. The arrow shows the au( J commoll a i r ye t some pheno-
directionof the section to obtain a figure -, '. J ,, *

like wire gauze. mena I observed in the combustion

of a blower induced me to believe

that small quantities of olefiant gas may be sometimes evolved in coal
mines with the carburetted hydrogen. I therefore resolved to make
all lamps safe to the test of the gas produced by the distillation of coal,
which, when it has not been exposed to water, always contains ole-
fiant gas. I placed my lighted lamps in a large glass receiver through
which there was a current of atmospherical air, and by means of a

THE DAVY LAMP.

gasometer filled with coal gas, I made the current of air which passed
into the lamp more or less explosive, and caused it to change rapidly or
slowly at pleasure, so as to produce all possible varieties of inflammable
and explosive mixtures, and I found that iron gauze wire composed of
wires from one-fortieth to one-sixtieth of an inch in diameter, and con-
taining twenty-eight wires or seven hundred and eighty-four apertures
to the inch, was safe under all circumstances in atmospheres of this kind ;
and I consequently adopted this material in guarding lamps for the
coal-mines, when in January, 1816, they were immediately adopted, and
have long been in general use."

The remarkable conducting power of wire gauze is further shown by
placing some lumps of camphor on a piece of this material, and when
the heat of a spirit-lamp is applied on the under side of the gauze, the
camphor volatilizes, and as the vapour is remarkably heavy, it falls
through the meshes of the gauze, and takes fire ; but the most curious
and further illustration of the conducting power of the wire meshes is
shown in the fact that the fire does not communicate through the thin
film of gauze to the lumps of camphor placed upon it.

The camphor may be ignited by applying flame to the upper side of
the gauze, showing that, although this substance is so exceedingly com-
bustible, it will not take fire even if placed at no greater distance from
flame than the thickness of the wire gauze, provided the latter mate-
rial is interposed between it and the
flame.

A square box made of wire gauze,
with a hole at the bottom to admit a
candle or spirit-lamp, may have a con-
siderable jet of coal gas forced upon
it from the outside, or a large ju^
of ether vapour poured upon it ; and
although the box may be full of flame,
arising from the combustion of the gas
or ether, the fire does not come out of
the wire box or communicate with the
jet or the ether vapour as it is poured
from the jug. (Fig. 362.)

Sir Humphrey Davy's safety lamp
consists of a common oil-lamp, f, with
a wire through the cistern for the pur-
pose of raising or depressing the cot-
ton wick without unscrewing the wire
gauze ; b is the male screw fitting the
screw attached to the cylinder of wire
gauze, which is made double at the top.
The entire lamp, is shown at A, whilst Bfi* fe

the platinum Coil which Sir H. Davy the vapour of ether may be poured on

recommends should be wound rounS ^y-j'^f
s the wick is shown at h. ihe small with that in the jug.

576

BOY S PLAYBOOK OF SCIENCE.

cage of platinum consists of
wire of one-seventieth to one-
eightieth of an inch in thick-
ness, fastened to the wire for
raising or depressing the cot-
ton wick, and should the lamp
be extinguished in an explo-
sive mixture, the little coil of
platinum begins to glow, and
will afford sufficient light to
guide the miner to a safe part
of the mine. With respect to
this platinum coil, Sir H.
Davy gives a careful charge,
and says : " The greatest
care must be taken that no
filament or wire of platinum
protrudes on the exterior of
the lamp, for this wouli fire
externally an explosive mix-
ture?*

Since the invention of the
Davy lamp, a great number
of modifications have been
brought forward, some of
which for a short time have
occupied the public attention, but whether from increased cost or a
sort of inertia that arrests improvement, it is certain that the lamp
originally devised by Sir Humphrey Davy is still the favourite. It was
perhaps unfortunate that the lamp was called the safety lamp, because
it is not so under every circumstance that may arise, unless it happens
to be in the hands of persons who have taken the trouble to study it
and understand how to correct the faults. The lamp might have escaped
the incessant attacks that have been made upon its just merits, if the
name had simply been that of its illustrious inventor " a Davy lamp."
No one could carp at that, whilst " safety" was held to mean perfect
immunity from every possible and probable danger that might arise in
the coal-pits. The lamps are now usually placed under the charge of
one man, who trims them and ascertains that the wire gauze is in perfect
order ; this latter is usually locked upon the lamp, and as it is a penal
offence, and punishable by a heavy fine and imprisonment, to remove the
wire gauze from safety lamps in dangerous parts of the mine, of course
the miners are being gradually brought to a sense of the obligations they
owe themselves and their brother-miners, and the rash, ignorant, ana
foolhardy offences of breaking open safety lamps for more illumination,
or to light pipes, are becoming much less frequent than formerly. One
of the most ingenious "detector lamps" is that of Mr. Symons, of
Birmingham. (Fig. 364.) It consisted of the old-fashioned Davy, but

Fig. 363. Sir Humphrey Davy's safety lamp.

SYMONS DETECTOR LAMP.

377

inside the rim of the wire gauze is
placed a small extinguisher and spring,
which does not move so long as the
gauze is screwed on to the lamp, but
directly the gauze is unscrewed, the
reversed movement releases the detent,
and the extinguisher falls upon the
light. In spite of the manifest inge-
nuity of this lamp, it is not adopted,
because it costs a trifle more than the
ordinary "Davy." To show the re-
markable perfection of the wire gauze
principle, some turpentine may be
poured upon a lighted safety lamp,
when a great smoke is produced by the
evaporation of the spirit, but no flame
passes through to the outside, although
the turpentine burns inside the lamp.
If some coarse gunpowder is laid upon
two thicknesses of fine wire gauze, it
may be heated from below with the
flame of the spirit lamp, and the sulphur
will gradually volatilize without setting
fire to the mass of powder. To show
tne security of the Davy lamp, it may
be lighted and hung in a large box
with glass sides, open at the top, and a
jet of coal gas supplied at the bottom;
as this rises and diffuses in the air, the
mixture becomes explosive, and the
fact is at once evident by the altera-
tion in the appearance of the flame
of the lamp, which enlarges, flickers, and frequently goes out, in conse-
quence of the suddenness with which the explosion of the mixture takes
place inside the lamp, producing a concussion that extinguishes the
flame. In this case the utility of the platinum coil is very apparent,
and it continues to g;low with a red heat until the explosive character
of the air in the box is changed.

If a large washhand-basin is first warmed by some boiling water,
which is then poured away, and a drachm of ether thrown in, a highly-
combustible atmosphere is obtained, and when a lighted Davy lamp is
placed into the basin so prepared, the flame inside the lamp immediately
enlarges and flickers, but is not extinguished, and does not communicate
to the combustible vapour outside. The contrast between the safety
lamp and an unprotected flame is very striking ; if a lighted taper is
thrust into the basin, the ether catches fire, and burns with a very
large flame. The solid conductors of heat, which are said to enjoy this
property in the highest degree, are the metals, marble, stone, slate, and

Fig. 364. Symons' self-extinguishing
Davy lamp.

378 BOY'S PLAYBOOK OF SCIENCE.

other dense and compact solid substances ; whilst the opposite quality
of being non-conductors, or nearly so, is possessed by fur, wood, silk,
cotton, wool, eider and swansdown, paper, sand, charcoal, and every
substance which is of a light or porous nature. The practical applica-
tion of this knowledge is very apparent in the affairs of every-day life.
Thus we rise in the morning, and immediately after the necessary ablu-
tions, if it is winter time, proceed to encase the body in non-conductors,
such as flannel and wool. When we sit down to the breakfast table to
make tea, we may notice the contrivances for preventing the handle of
the top of the urn, or that of the teapot, from becoming too hot for the
fingers, by the interposition of ivory or wood. If asked to place water
in the teapot from the kettle, we instinctively seek for the well-worn
kettle-holder made of Berlin wool, and therefore a bad conductor. As
we cut our meat or fish at the same meal, we may shiver with cold, but
our lingers are not quite frozen by contact with the steel knives, as we
hold them by ivory handles ; and we are agreeably reminded that some
metals are good conductors of heat, by the pleasant warmth of the
silver teaspoons, as we stir our tea or coffee.

Even the polish of the well-rubbed mahogany is protected from the
neat of the dishes by non-conducting mats, and plates are handed about,
if " nice and hot," with a carefully-wrapped non-conducting linen
napkin. Supposing we prefer a bit of fresh-made toast, the fork is
provided with a non-conducting handle; and should we peep out of window
some wintry morn whilst the baker delivers his early work in the shape
of hot rolls, we notice they come out of nicely-wrapped flannel or baize,
which being a bad conductor is employed to retain their heat. We read,
occasionally, in the military intelligence, statements respecting some
newly-constructed shells which are to burst and scatter melted iron (! !);
and of course the idea of the interposition of a good non-conductor of heat
between the bursting charge and the molten metal must be realized in
their construction.

The central heat of our globe is a reality that cannot be disputed, and
after digging beyond a depth of twenty feet the thermometer gradually
rises at the rate of one degree of Fahrenheit's scale for every fifteen
yards. The bad conducting power of the crust of the earth must, there-
fore, be apparent, as it is easy, knowing the diameter of our globe, to
calculate that the increase of heat downwards amounts to 116 for each
mile, consequently at a depth of thirty and a half miles below the sur-
face, there will be a temperature most likely equal to 3500, or a heat
that might easily melt cast-iron, and would help to account for the
earthquakes and eruptions of volcanoes, which still remind us by their
terrible warnings, that we live only on the bad conducting upper crust
of a globe, the inside of which is still, perhaps, in a liquid and molten
state. Monsieur Fourier has demonstrated the non-conducting power
of this shell by calculating that, supposing the globe was wholly com-
posed of cast-iron, the central heat would require myriads of years to be
transmitted to the surface from a depth of 150 miles ; and by inverting
the process of reasoning, we may come to the conclusion that the in-

THE CONDUCTION OP HEAT. 379

ternal heat must be excessive, because it is confined and shut out from
those influences that would carry off and weaken the intensity.

There are no two words, says Tyndal, with which we are more familiar
than matter and force. The system, of the universe embraces two things,
an object acted upon, and an agent ly which it is acted upon; the object
we call matter and the agent we call force. Matter, in certain respects,
may be regarded as the vehicle of force ; thus, the iuminiferous ether is
the vehicle or medium by which the pulsations of the sun are transmitted
to our organs of vision. Or, to take a plainer case, if we set a number
of billiard balls in a row, and impart a shock to one end of the series in
the direction of its length, we know what will take place ; the last ball
will fly away, the intervening balls having served for the transmission of
the shock from one end of the series to the other. Or we might refer to
the conduction of heat. If, for example, it be required to transmit heat
from the fire to a point at some distance from the fire, this may oe
effected by means of a conducting body by a poker, for instance ; thrust-
ing one end of a poker into the fire, it becomes heated, the heat makes
its way through the mass, and finally manifests itself at the other end.
Let us endeavour to get a distinct idea of what we here call heat ; let
us first picture it to ourselves as an agent apart from the mass of the
conductor, making its way among the particles of the latter, jumping
from atom to atom, and thus converting them into a kind of stepping
stones to assist its progress. It is a probable conclusion, even had we
not a single experiment to support it, that the mode of transmission
must, in some measure, depend upon the manner in which those little
molecular stepping stones are arranged. But we must not confine our-
selves to the molecular theory of heat. Assuming the hypothesis, which
is now gaining ground, that heat, instead of being an agent apart from
ordinary matter, consists in a motion of the material particles ; the con-
clusion is equally probable that the transmission of the motion must be
influenced by the manner in which the particles are arranged. Does
experimental science furnish us with any corroboration of this inference ?
It does. More than twenty years ago MM. De la Rive and De Can-
dolle proved that heat is transmitted through wood with a velocity
almost twice as great along the fibre as across it. This result has been
recently expanded, and it has been proved that this substance possesses
three axes of calorific conduction; the first and greatest axis being
parallel to the fibre ; the second axis perpendicular to the fibre and to
the ligneous layers ; while the third axis, which marks the direction in
which the greatest resistance is offered to the passage of the heat, is
perpendicular to the fibre and parallel to the, layers.

If many solids are bad conductors of heat, they are at all events
greatly surpassed by fluids, and especially by water. The conduction of
heat by that fluid is almost imperceptible, so much so, that it has even
been questioned whether liquids do really conduct heat downwards at all.
It has, however, been found that liquid mercury will conduct heat down-
wards, and therefore by analogy it may be assumed that other liquids
must possess a conducting power, although it may be exceedingly limited.

380

BOY'S PLAYBOOK OF SCIENCE.

In order to prove that water is an exceeding bad conductor of heat, a
tube with a large glass bulb blown at one end is partly filled with
tincture of litmus, until it will just sink below the surface of water
placed in a tall cylindrical or open jar. If a copper basin, containing
burning ether, is now floated on the top of the water, so as to leave
about a quarter of an inch between the top of the air thermometer
viz., the bulb containing the coloured liquid and the bottom of the
copper pan, it will be noticed that whilst the water surrounding the
latter almost boils, not the slightest effect arising from the conduction
of heat can be perceived in a downward direction. After the ether has
burnt out of the copper vessel, it may be removed, and the boiling water
stirred down and around the air thermometer, when the air within it
expands, drives out the colouring liquid, and the bulb becoming spe-
cifically lighter, rises to the top of the containing glass. (Fig. 365.)

Fig. 365. A A. Cylindrical glass full of water. B. The glass air thermometer contain'n^
the coloured liquid just standing upright, the mouth of the tube at c being open. D D is
the copper basin containing the burning ether. B shows how the glass bulb and tube
rise after the upper basin is removed, and the hot water comes iu contact with and
expands the air, making the thermometer light, and causing it to rise.

Again, if the tube of an air thermometer is placed through a cork in
the neck of a gas jar, inverted and standing on a ring stand, and the

THE CONDUCTION OF HEAT BY FLUIDS.

381

jar is then filled with
water, and boiled at
the top with a red-
hot iron heater, the
heat does not pass
downwards and af-
fect the thermome-
ter. By introducing
a syphon the water
surrounding the
thermometer at the
bottom of the jar
may be drawn off,
until the hot water
is within a fraction
of an inch of the air
thermometer, and
still no heat is con-
ducted, and the li-
quid in the latter
remains stationary.
(Fig. 366.)

The diffusion of
heat through water
does not take place
like that of solids,
but is effected by the
motion of the parti-
cles of the water.
When heat is applied
to the bottom of a
vessel containing
water, such as an
inverted glass shade,
the first effect is to
expand the layer of
water which is first
affected by the heat;
this expanded layer
being specifically
lighter than the cold

water above, it rises Fig 366t A A A . inverted gas jar supported by the ring
to the upper part of stand. B. The red-hot urn heater, c c. The air thermometer,
thp o-la<!<* shflHp and with the coloured liquid stationary at c. D. The syphon for
tne glass snade, ana drawing off the cold water> ^d bringing the hot down close to
its place is immedi- the bulb of c c.
ately taken by other,

colder and heavier, water, which in like manner moves upwards, and is
again succeeded by a fresh portion. Now, the first and succeeding strata

382

BOY S TLAYBOOK OF SCIENCE,

of water all carry off so much
heat, and thus by the con-
vective or carrying power of
the water the heat is diffused
finally in the most perfect
manner through the whole
bulk of fluid; and indeed,
the movement itself of the
particles of water may easily
be watched by putting a little
paper pulp at the bottom of
the inverted glass shade con-
taining the water. (Fig. 367.)
This bad conducting power
is not merely confined to
water, but is likewise appa-
rent with oil and other fluids,
and if some water is frozen
at the bottom of a long test-
tube by means of a freezing
mixture, oil may then be
poured upon it, and some
alcohol above the latter. If
the flame of a spirit-lamp is
now applied to the alcohol at
the top of the tube it may be
entirelv boiled away, and no
heat will travel down the oil
and communicate with the

tiTo Te^ed wate 6 r7nd th^e King "of [ ce > a ? d even after the alcohol
the cold, in the direction indicated by the arrows. has been evaporated away

the tube can be filled up

with water ; this may also be boiled, and whilst demonstrating the bad
conducting power of the oil, the curious anomaly is observed of a vessel
or tube containing ice at the bottom and boiling water at the top, and
further showing the wisdom of the Supreme Creator in preventing the
freezing of the water of lakes, rivers, and seas, by the exceptional law of
the expansion of water by cold. It is evident from what has been
stated that liquids acquire and lose their heat by means of those cur-
rents and movements of the particles of water which have already been
partly explained. Whatever interferes with this movement must pre-
vent the passage of heat, and consequently thick viscous liquids are
always difficult to boil, and in consequence of their motion being im-
peded they rise to too high a temperature and are burnt. This fact is
remarkably apparent in the manufacture of nice white lump sugar ; as
the syrup is evaporated it becomes very thick, and if boiled over a fire
might frequently be burnt, but it is boiled by the heat of steam, and
under a vacuum produced by an air-pump, and thus the sugar-boiler is
enabled to avert all danger from burning.

Fig 1 . 367. A. A. Inverted glass shade containing
water and some paper pulp. B. Burning spirit lamp
placed under one side of the glass ; the pulp shows

THE CONVECTION OF HEAT.

383

It is, then, by a continual and perpetual motion, involving circulation
of the particles, that heat travels through water ; and the fact already
described .is still further
elucidated by one of Pro-
fessor Griffith's simple but
telling experiments. A
glass tube, about three feet
m length and half an inch
in diameter, is bent as at A
(Fig. 368), and then being
filled with water, is sus-
pended by a string attached
to any convenient support
inside a copper dish con-
taining water, so that the
straight end is at the top
of the water, and the curved
end at the bottom. Just
before it is used some ink
or other colouring matter
is poured into the copper
pan of water; and it
should not be added till
the moment the experi-
ment is to begin, as any
rise of temperature in the
room promotes circulation,
and interferes with the co-
lourlessness of the water
in the tube, which is com-
pared with the inky fluid
in the basin. Directly heat
is applied the hot water
rises to the top of the Fi ^ 368 - A - Thc be f t . ? lass * ube

i j j.1 B B. The copper pan containing coloured water.

Copper vessel, and thence arrows show the circulation of the water.
gradually up the tube ; and

this movement is rendered visible by the hot coloured liquid matter
creeping slowly up the tube, and displacing the colourless water, which
falls gradually into the copper pan. (Fig. 368.)

The principle of the circulation of the particles of water being once
understood, it is easy to comprehend how it is applied to the heating of
buildings by what is called the " Hot Water Apparatus." A coil of
pipe is enclosed in a proper furnace, and the bottom end communicates
with a pipe coming from a second tube or set of coils, placed above it in
another apartment, whilst the top of the latter coil communicates with
the top pipe of the first coil. When the fire is lighted, the circulation
through the first coil of pipe commences, and is communicated to the
second, and from that back again to the first ; so that the " hot water

The

384

BOY'S PLAYBOOK OF SCIENCE.

system" involves an endless chain of pipes of water, provided with
proper safety valves to allow for the escape of any expanded air or
steam ; and serious accidents have occurred in consequence of persons
neglecting to look after the perfection of this safety valve. The fearful
accident which occurred to the hot water casing around one of the
funnels of the Great Eastern offers a painful but memorable example of
the heating of water, and of the dangers that must arise if the pipe,
casing, or other vessel which contains it, is not provided with an escape
or safety valve, which must always be in good working order.

Mr. Jacob Perkins, in 1824, made his name remarkable for experi-
ments with the circulation of water through tubes, and his account of

the invention and im-
provement of the
" Steam Gun," in
which the improve-
ment consists chiefly
in the circulation of
water through coils of
pipe, is so important
that we give it verba-
tim, with a drawing of
the steam gun; and
the author is enabled
to vouch for the accu-
racy of the statements
maile in the description
of the apparatus, as he
purchased one of the
improved steam guns,
and exhibited it at the
Polytechnic Institu-
tion, where it dis-
charged three hundred
bullets per minute.

" The expansive
power of steam has
often been proposed as
a substitute for gun-
powder, for discharging
balls and other pro-
jectiles ; the great
danger, however, which was formerly thought to be inseparably con-
nected with the generation and use of steam, at so extraordinary a
pressure as appeared necessary to produce an effect approximating to
that of gunpowder, prevented scientific men from testing the power of
this new agent by experiment. It was also apparent that the appa-
ratus which was ordinarily used for generating steam for steam-engines
was wholly inadequate to sustain the necessary pressure, and that one

Fig. 369. The charging tube and gun-barrel
of steam gun.

THE STEAM GUN. 385

of a totally different character .must be contrived before steam could
be sufficiently confined to come into competition with its powerful rival.

"In the year 1824, Mr. Jacob Perkins succeeded in constructing a
generator of such form and strength, as allowed him to carry on^his
experiments with highly elastic steam without danger, although sub-
jected to a pressure of 100 atmospheres. The principle of its safety
consisted in subdividing the vessel containing the water and steam into
chambers or compartments, so small, that the bursting of one of them
was perfectly harmless in its effects, and only served as an outlet, or
safety valve, to relieve the rest.

" Although Mr. Perkins' generator was originally intended for working
steam engines (it having long been evident to him that highly elastic
steam used expansively would be attended with considerable economy),
the idea occurred to him, in the course of his experiments, that he had
already solved the problem of safely generating steam of sufficient
power for the purposes of steam gunnery ; and that the steam which
daily worked his engine possessed an elastic force quite adequate to the
projection of musket balls. He therefore caused a gun to be imme-
diately constructed, and connected by a pipe to the generator, the first
trial of which fully realized his most sanguine anticipations. Its per-
formance, indeed, was so extraordinary and unexpected, that it gave rise
to a paradox, which was difficult of explanation viz., that steam, at a
pressure of only forty atmospheres, produced an effect equal to gunpowder ;
whereas it was known that the combustion of gunpowder was attended
with a pressure of from 500 to 1000 atmospheres.

" Mr. Perkins gives the following explanation of this apparent dis-
crepancy, by referring to the small effect produced by fulminating
powder, compared to gunpowder, although many times more powerful ;
he supposes that the action of fulminating powder, however intense,
does not continue sufficiently long to impart to the ball its full power.
The explosion of gunpowder, although not so powerful at the instant of
ignition, is nevertheless, in the aggregate, productive of greater effect
than that of fulminating powder, because the subsequent expansion
continues in action upon the ball (but with decreasing effect), until it
has left the barrel. The action of steam differs from either of these
agents, inasmuch as it continues in full force until the ball has left the
barrel ; and to this is assigned the cause of its superiority.

" In the year 1826, Mr. Perkins had so perfected the mechanism of
the gun and generator that, at an exhibition and trial of its power, in
the presence of the Duke of Wellington and other distinguished officers
of the Ordnance Department, balls of an ounce weight were propelled,
at the distance of thirty-five yards, through an iron plate one-fourth of
an inch in thickness ; also, through eleven hard planks, one inch in
thickness, placed at distances of an inch from each other. Continuous
showers of balls were also projected with such rapidity, that when the
barrel of the gun was slowly swept round in a horizontal direction, a

Elank, twelve feet in length, was so completely perforated, that the line of
oles nearly resembled a groove cut from one of its ends to the other.

c c

3SG

BOYS PLAYBOOK OF SCIENCE.

Fig. 370. Perkins's steam gun..

THE STEAM GUN. 387

" A is an iron furnace, containing a continuous coil of iron tubing, 80 feet in length,
1 inch of external and |th inch of internal diameter, within which the fire is made; the
upper end of this tube, B, called the flow-pipe, is extended any required distance to the top
of the generator.

"The furnace is provided with a very ingenious heat governor or regulator, by which the
intensity of the fire is always proportionate to the temperature which it may be requisite
to maintain in the tubes.

"H is an iron box, containing a series of levers, b I b; c, a nut screwed upon the flow-
pipe, and in contact with the short arm of the lowest of the levers. E. A lever, from one
end of which is suspended the damper f, and from the other end the rod a, which rests
upon the long arm of the highest of the levers, b b b. When the apparatus has arrived at
the required temperature, the nut c is screwed down until it bears upon the lever. Any
farther increase of temperature will expand or lengthen the flow-pipe, and depress the
short arm of the lever, which is in contact with the nut. The combined and multiplied
action of the levers will then elevate the rod g, and the damper f will descend to check
the draught. When the fire slackens, and the apparatus cools, the action of the levers will
be reversed, and the damper will open. The space through which the damper moves, com-
pared with the nut c, is as 200 to 1.

" c is the generator, composed of a strong iron tube, 3 inches diameter and 6 feet in
length, within which are eight smaller tubes, having their ends welded to the ends of the
larger tube. These small tubes communicate at the top with the flow-pipe B, and at the
bottom with the return-pipe D, which is continued to the bottom of the furnace-coil of
tubing. The circulation in the tubes is occasioned by the difference in the specific gravities
of the water composing the ascending and descending currents ; the portion contained in
the flow-pipe and fire coil becoming expanded by the heat, ascends by its superior levity ;
while that contained in the small tubes of the generator, having given off its heat, acquires
increased density, and descends through the return-pipe D to the bottom of the furnace-
coil, to take the place of the ascending current. When the hot-water current has arrived
at a temperature of 212 and upwards, cold water is injected into the generator, and
becomes converted into steam by its contact with the small tubes ; the rapidity of evapo-
ration and the pressure of the steam depending, of course, upon the temperature of the
hot-water current, which at 500 will cause a pressure within the tubes of 50 atmospheres,
or 750 Ibs. upon the square inch. The whole apparatus is proved to be capable of sustaining
a pressure of 200 atmospheres, or 3000 Ibs. upon the square inch.

"G. A force pump for injecting water into the generator.

" i. The indicator for exhibiting the pressure of the steam in the generator, and of the
water in the boiler ; it may be connected with either by means of the valves attached to
the levers.

" J. Valve to regulate the pressure of water.

" J 1. Valve to regulate the pressure of steam.

*' K. The steam pipe.

" L. The gun.

" M. The discharging lever acting upon the valve N.

" o. The discharging cock, by a simple adjustment in which balls are transferred from
the charging tube p to the gun barrel, singly or in a continuous shower.

" As the perfection and introduction of the steam gun was not a field
.for private enterprise, and the British Government having declined to
institute experiments at its own expense, Mr. Perkins was reluctantly
compelled to leave the project, and to engage in others of a more lucra-
tive, although, perhaps, of a less important nature. He did not suspend
"his operations, however, until he had constructed for the French Govern-
ment a piece of artillery which discharged balls weighing Jive pounds at
ihe rate of sixty per minute.

"The gun and generator exhibited at the Polytechnic Institution
during the time that Mr. Pepper was the Resident Director were the
production of Mr. A. M. Perkins, of London, who has invented an
entirely new method of generating steam, which has been successfully
applied to steam engines, and is at once so simple, safe, and economical,
as to leave little doubt that, with its aid, the steam gun will ere long
rank amongst the first instruments of warfare.

c c 2

388 BOY'S PLAYBOOK OF SCIENCE.

"The gun, except in a few -minor mechanical details, does not differ
from that originally constructed by Mr. Jacob Perkins.

"The novelty which distinguishes the generator from all others,
consists in the manner of conveying the heat from the fire to the water,
without exposing the generator to the action of the Jire. This is accom-
plished by means of the circulation, in iron tubes, of a current of hot
water, which is entirely separate from, and independent of, that to be
evaporated in the generator.

" The following are the principal advantages which this generator
possesses over an others : Freedom from all wear or deterioration con-
sequent upon exposure to the Jire, an important quality in a generator that
is to be subjected to great pressure, inasmuch as its original strength
remains unimpaired ; no accident can arise from want of water in the
generator, and the precautions indispensably requisite when a generator
is in contact with the fire are quite unnecessary, as the water may be
drawn off with impunity without producing the least injurious effect,
and the grossest neglect is followed by no worse consequences than an
inefficient supply of steam ; an explosion of the generator is impossible,
as the temperature of the furnace-coil always exceeds that of any other
part of the apparatus, and consequently, being the weakest part, is
invariably the first to yield when the pressure is carried beyond the
strength of the pipes ; economy of fuel is also obtained, icith a small
amount of fre surface. The circulation of the water has likewise the
effect of preserving the fire-coil from the decay to which boilers are
liable ; many such coils, which have been in constant use for eight years,
being apparently as good as when first erected.

" The whole apparatus is exceedingly simple, and will be readily
understood by reference to the accompanying diagram. (Pig. 370.)

" The steam has often been raised to a pressure of 700 Ibs. on the
square inch, but one-third of that pressure is sufficient to completely
flatten the balls when discharged against an iron target one hundred feet
distant from the gun ; and a pressure of 400 Ibs. per square inch, at the
same distance, shivers the ball to atoms, with the production in a dark
room of a visible flash of light. Steam guns are generally mounted
upon a ball and socket joint, which allows the barrel to move freely in
every direction."

The conduction of heat through gases is also very slow when heat is
applied to the upper part of any stratum of air. feat appears to be
diffused through air only by the circulation and rising of the heated and
lighter strata, and the sinking of the colder currents which take their
places ; hence the danger of sitting in a room under an open skylight.
A current of cold air may descend upon the head of the individual,
whilst the warmer air takes some other opening to escape from. No
doubt the movement of heated volumes of air is subject to definite laws,
which apply themselves under every case, but are rather difficult to
grasp when the subject of ventilation is concerned. The philosophical
ventilator is often dreadfully teased by the inversion of all that he had

CONDUCTION OF HEAT BY GASES. 389

planned, or the total failure of his apparatus. No specific mode of
ventilation can be found to suit all rooms and buildings ; they are like
the patients of a physician who cannot be cured by one medicine only,
but must have a treatment adapted properly to each case. If the fires,
candles, gas, or oil-lamps, doors, windows, and chimneys, were always
under the control of the scientific ventilator, his task would be very
simple, but it is well understood that a ventilating system whicn
answers well if certain doors communicating with lobbies are closed,
fails directly they are accidentally opened. The watchful care of the
ventilator must begin with the lowest area door, and in his calculations
he must study the effect of every other door or window that may be
opened, so that if a scientific man undertakes to ventilate a house, he
must have a well-drawn plan hung up in the hall, and it must be
clearly understood by the inmates that any interference with that plan
will prejudice the whole.

There are a few common principles which will guide in ventilation,
and these are, first, the rise of hot and the fall of cold air ; second,
that if an aperture is provided at the top of a room for the escape of
hot air, an equally large aperture must be left for the entry of cola air ;
third, the aperture for the escape of hot air must be adapted in size to
the number of persons likely to enter the room, and the number of gas
or other lights burning in it. During the daytime, moderate apertures
for the exit and entrance of air may suffice, but these must be largely
increased at night, when the room is filled with people and lighted up.
Expanding and contracting openings are therefore desirable, and they
are to be regulated by rules stated on the plan of the ventilating system
(already alluded to as being hung up in the hall) of the house which
has submitted itself to a perfect system of ventilation, and no hall-
keeper, footman, or butler should be allowed to remain in his post
unless he undertakes to comprehend the system and work it properly by
the written rules.

Dr. Angus Smith, in a very able paper " On the Air of Towns," says
" One of the conditions of health, and a most important, if not the most
important of all, is to be found in the state of the atmosphere. As to
the effect on the inhabitants, the question becomes exceedingly com-
plicated ; but the Registrar-General's returns are an unanswerable
reply as to the results of the lethal influences of the district. Pew
people seem clearly to picture to themselves the meaning of a decimal
plan in the per-centage of death, and few clearly see that there are
districts of England where the deaths at least in some years, and when
no recognised epidemic occurs, are three times greater than in others.
When we hear of the annual deaths in some districts being 3 '4 per
cent., and in the whole of England 2 '2, it is simply that 34 die instead
of 22, whilst even that is too slightly stated, as the whole of England
would show a lower death-rate if the towns were not used to swell it."

This quotation is given here to remind our readers of the important
question of a supply of pure air as well as pure water and pure food ;
and if the agricultural labourer, with all his exposure to variable

390

BOY'S PLAYBOOK OF SCIENCE.

weather, can take the first place in the scale of mortality, and outlive
the members of all other trades and professions, it is evident that the
importance of pure air is not overrated.

Every effort ought, therefore, to be made in large schools, hospitals,
and barracks, to enforce a rigid system of supply of fresh air, and a
sewage or removal of the impure ; and in the use of a certain test em-
ployed by Dr. Smith for the detection of organic matter in the air a
number of approximations were obtained, which clearly demonstrated
that 1 grain of organic matter was detected in 72,000 cubic inches of air
in a room, and the same quantity in 8000 cubic inches taken from a
crowded railway carriage.

To show the rising of heated air, a long glass tube, about three-
quarters of an inch in diameter, may be provided and held over the
flame of a spirit lamp at an angle of sixty degrees. As the tube warms,
the heated air rushes past the flame with great rapidity, and pulls it
out or elongates it so much, that the sharp point of the spirit-flame

Pig. 371. A B. The glass tube. c. The spirit lamp, with a very large wick ; if a little
ether is mixed with the spirit in the lamp it increases the length of the flame. . The
effect of the ascension of air, increased by warming the top of the tube with the lamp D.

VENTILATION.

will frequently be seen at the end of a tube ten feet six inches in
length. The flame is, as it were, the sign-post that indicates the path
or direction of the air. (Fig. 371.)

Upon the like principle, heated air may be dragged down the short
arm of a syphon, provided the other arm is sufficiently long to impart a
strong directive tendency to the upward current, and this mode of
setting air in motion has been frequently proposed in numerous schemes
for ventilation. In order to prove the fact that an inverted syphon
will act in this manner, an iron pipe of three inches diameter and
six feet long may be bent round during the construction into the form
of a syphon, so that the short length is about one foot long, and the
long length the remaining four feet, allowing one foot for the bend. If
the interior of the long arm is first warmed by burning in it a little
spirits of wine from a piece of cotton or tow wetted with the latter
(which can be easily done by dropping in such a wetted piece into the
bend of tube, so that it is just under the opening of the long part of
the tube), the air is soon set in motion up the long pipe, and as it must
be supplied with fresh vo-
lumes of air to take the
place of that which rises,
and as the only entrance for
the fresh air can be down
the short arm of the sy-
phon, the circulation soon
commences, and it pro-
ceeds as long as the upper
arm is kept sufficiently
warm. If a flame is held
over the mouth of the
short arm, it is immedi-
ately dragged downward,
whilst, if held at the
mouth of the long pipe,
the motion of the air is
seen by the assistance of
the flame to be in the
contrary direction. (Pig.
372.)

This plan of ventilation
was proposed to be used gsen - the piece of tow mo i ste ned with alcohol, which,

in rooms in connexion With being set on fire, warms the tube B. D. A lighted torch
fhp pViirrmpv inrl nhimnpv f coloured spirit, the flame of which is dragged down

the cnimney ana nimney- the tube at A y ^ descending current> and Spelled
piece, and in order to give upwards by the ascending current B.

it an ornamental appear-
ance, the chimney-piece was supplied with two ornamental hollow
columns, the end's of which were open at the mantelshelf, and the
tubes or columns were continued under the hearthstone, proceeding
up the back of the grate and entering the chimney, in which there
would be a constant. current of heated air, and it was expected that

Fig. 372. A B. Inverted sheet iron syphon. At o la

392

BOY'S PLAYBOOK OF SCIENCE.

the syphon arrangement would keep a current of air always in
motion, and thus help to ventilate the room. (Fig. 373.) This plan,

Fig. 373. A B. Chimney-piece supported on two hollow ornamental pillars corresponding
with the short arm of a syphon, c c c. The dotted line showing the pipes leading from
each pillar under the hearth, and terminating in a long pipe passing into the chimney.
The arrows show the path of the air descending from the chimney-piece and ascending in
the chimney.

However, does not appear to have been adopted, and wisely so, because
half the time the syphon arrangement might invert itself, and vomit
smoky air out of the chimney into the room ; indeed it is surprising what
odd and contradictory freaks are performed by currents of air. The
author remembers a case where two rooms on the same floor, the one
a dining-room and the other a drawing-room, were always exhibiting the
most absurd phenomena of smoke. If the fire in one room was lit, then
the other, in a few moments, began to smell exactly like the inside of a
gas manufactory, and was, of course, more or less filled with smoke,
whilst the room in which the fire was actually burning remained quite
free from this annoyance. The smoke appeared to issue from the
wainscot or moulding which runs round at the bottom of the wall, and
was at first thought to be an escape from the chimney of the kitchen
beneath, the inside of which was duly examined and thoroughly stopped
with cement in every place likely to afford a channel to the smoke, and

VENTILATION OP ROOMS. 393

the crevice whence the smoke issued was also filled in neatly with
cement. But it was all in vain ; the smoke then made its way out from,
another part of the cornice, and at last the roems exhibited a beautiful
reciprocating action. If the drawing-room fire was lighted the dining-
room was full of smoke, and if the latter was lighted the former had the
agreeable visitation. At last the backs of the two grates were ex-
amined, and in each was discovered a hole about one inch in diameter ;
and it was also found that the spaces at the back of the stoves had not
been filled in properly, and, indeed, communicated with the hollow space
behind the cornice. When, therefore, the fire was lighted, and coals
heaped on just above the hole, the gas and smoke distilled through the
orifice and travelled on, where it found the most convenient exit; and
the fact is sadly at variance (apparently] with theory, because it might
be considered that cold air would rush towards a fire, and that the
draught ought to have been from the cornice to the chimney instead of
vice versa. The fact seems to be that the coal in all grates is, in the act
of burning, distilling and giving off inflammable gas ; when the coal was,
therefore, heaped above the orifice, and was, possibly, caked hard at the
top, the gas distilling from it escaped more easily from the little orifice
than elsewhere, and chance determined that the channel or delivery pipe
should be in the direction of the drawing-room when the fire was burn-
ing in the dining-room, and in the contrary direction when the fire was
lighted in the latter chamber. The nuisance was stopped by plugging
the holes at the back of the grate with clay, and putting a sheet of iron
over the orifice.

Before Dr. Earaday was appointed as a scientific counsellor to assist
the deliberations of the Trinity Board in connexion with lighthouses, all
the lamps were burnt in the lanterns with the smallest and most imper-
fect arrangement for carrying off the heated air and products of com-
bustion ; as a natural consequence, and particularly on cold nights, the
windows of the lantern of the lighthouse were covered with ice derived
from the condensation of the water produced by the combustion of the
hydrogen of the oil, whilst the carbon generated such quantities of car-
bonic acid that the light-keepers were unable to stay in the lantern, and
if obliged to visit the latter (whilst looking to improving the light of any
single lamp that might be burning dimly), they were almost overpowered
with the excess of carbonic acid, and stated, in their evidence, that it pro-
duced headache and sickness, and a tendency to insensibility. Earaday
immediately established a system of ventilation ; and by attaching a
copper tube to the top of each lamp-chimney, and centering them all in
one large funnel passing to the top of the lighthouse, the whole of the
water which previously condensed on the glass windows and impeded
the light, besides injuring the brass and copper fittings, was carried off,
as also the poisonous carbonic acid gas ; and thus, as Dr. Earaday ex-
pressed himself, a complete system of sewage was applied to the lamps
of the lighthouses.

If any one of the numerous stories of ships saved by the Eddystone
Lighthouse could demonstrate more than another the value of this beacon

_ "? :
~ SS

The British fleet rounding the Eddystone Lighthouse during the great storm
of October, 1859. p. 394.

FARADAY S LAMP.

395

numerous light-keepers, one of which in plain but striking language
related that " the enemy (alluding to the water and carbonic acid) was
now driven out."

The ingenious invention alluded to was succeeded by another and
equally simple but philosophical arrangement, which Dr. Faraday pre-
sented to his brother, and it was duly patented. It consisted of an
arrangement for ventilating gas burners, and it must be obvious that a
necessity exists for such ventilation, because every cubic foot of coal
gas when burnt produces a little more than a cubic foot of carbonic
acid. A pound weight of ordinary coal gas contains about Y 3 ^ths of its
weight of hydrogen, which when burnt produces two pounds and -^ths
of a pound of water. A pound of ordinary coal gas also contains about
j^ths of its weight of charcoal, which produces when burnt rather
more than two and a half pounds of carbonic acid gas viz., 2'56. In
order to burn this quantity of gas nineteen cubic feet and T 3 oths of a
foot of atmospheric air, containing 4'26 cubic feet of oxygen, are
required.

It is not therefore sur-
prising that as common coal
gas is sometimes purified
carelessly, and contains a
minute trace of sulphuretted
hydrogen, with some bisul-
phide of carbon vapour, that
it should produce the most
prejudicial effects in badly
ventilated rooms, and espe-
cially in some of those
perched up glass boxes in
large places of business,
where clerks are obliged to
sit for many consecutive
hours, lighted by gas, and
breathing their own breath
and the products of combus-
tion from the gas light,
thereby rendering them-
selves liable to diseases of
the lungs, and also to very
troublesome throat _ attacks, pig- 374 A B Gag p . pe and argand b ^

when leaving then: Close air enters, as usual, up the centre of the argand.

glass boxes, and passing into a The fi , rst . glass chimney open at the top. D.

?u 1 A 1,4- ; rnu^/1 Tne second gl a88 chimney closed at the top, with a

the cold night air. The dan- <ji sc of doub i e talc, and fitting over c c, and L leavi

Crerous product of the com- a space between the two glasses, down which the

fnwtirm nf nrdmnrv nnal oi air P ass es, and into the ventilating tube, B E.

bastion ot ordinary coal gas HH . The ground . glass globe closed the ^ Jmd

IS sulphurous acid VIZ., the surrounding the whole.*

Mr. Faraday, of Wardour-street, supplies this ventilating lamp.

396

BOY S PLAYBOOK OF SCIENCE.

same gas as that generated when a sulphur match is burnt ; and if it
will attack the bindings of books, and damage furniture, goods in shops,
curtains, &c., in consequence of the large quantity of water with which
it is accompanied, how much more is it not likely to injure the delicate
organism of the breathing apparatus of the lungs ? Dr. Faraday's lamp
is therefore a great boon, but, like a great many other clever things, it
must be adapted to the currents of air and draught from the room ; and
means must be taken to prevent the draught becoming too powerful in
Faraday's lamp, or else the illuminating power is destroyed by the
thorough combustion of the carbon of the coal gas, and the heat gene-
rated is so intense that the glasses soon crack, and of course become
useless. The lamp will answer very^ well if (as has been already stated)
the draught in the ventilating pipe is not too great.

The system already explained and illustrated is likewise carried
out on a much larger scale in the ventilation of coal pits, where a shaft
is usually sunk into the ground for the admission of air, which, after
circulating through the intricate windings and mazes of the coal pit
workings, escapes at last from another shaft, at the bottom of which is
placed a powerful furnace, and this is kept burning night and day, so

Fig. 375. Section showing the two air-shafts. A. The downcast. B. -The upcast.
c c. One of the working galleries in connexion with the upcast and downcast. D. Tho
furnace at the bottom of the upcast. In this sketch one gallery only has been shown, to
prevent confusion and to show the principle.

THE UPCAST AND DOWNCAST SHAFT. 397

that the movement of the air is maintained in one direction viz., from
the outer air down the shaft called the downcast, thence to the galleries,
where the coal hewers are working, to the second shaft, near which
the furnace is placed, and up this latter the air travels ; the shaft, pit,
or funnel being very appropriately termed the upcast.

Should the furnace at the bottom of the upcast be neglected, the
ventilation may be just balanced, or set slightly towards the downcast ;
under these circumstances the carbonic acid from the fire will begin to
circulate in the galleries, and poison those who are not aware of its
presence and take the proper means to escape. Such accidents, amongst
the host of others that occur in a coal pit, have actually been recorded ;
and the firemen, whose duty it might be to attend to the proper burning
of the furnace, have had to pay the penalty of death for their own careless-
ness in falling asleep and neglecting to maintain the ventilation of the
mine in one direction. (Fig. 375.)

These details are amply sufficient to demonstrate the manner in which
heat is diffused through air, whilst the rarefication of the air by heat
suggests the cause of those frightful storms of wind that rush from
other and colder parts of the surface of the globe, to supply the void
produced by the cooling and contraction of the enormous volumes of
gaseous matter.

The Radiation of Heat.

When rays of heat are emitted from incandescent matter, they are not
necessarily visible, nay, they are generally invisible, and not accom-
panied with a manifestation of light, and pass witli great velocity through
a void or vacuum, also through air and certain other bodies. From
what has been stated respecting the manner in which air, by continually
moving, and by convection, carries off heat, it might be thought that no
proof existed that invisible rays of heat are really thrown off from a
ball filled with boiling water. But this question is set at rest by the
fact, that such a ball will cool rapidly when suspended by a string inside
the receiver of an air pump from which the atmospheric air has been
removed, so that no conduction of the particles of air could possibly
remove the heat.

In the year 1786, Colonel Sir B. Thompson examined the relative
conducting powers of air and a Torricellian vacuum the latter being
used because, as the experimenter stated, it was impossible to obtain a
perfect vacuum, on account of the moist vapour which exhaled from the
wet leather and the oil used in the machine, for at that time carefully
ground brass plates were not used in air-pumps, but plates only, with a
circular piece of wet leather upon them. In a paper which Colonel Sir B.
Thompson read before the Uoyal Society, he stated that "It appears that
the Torricellian vacuum, which affords so ready a passage to the electric
fluid, so far from being a good conductor of heat, is a much worse one
than common air, which of itself is reckoned among the worst ; for when
the bulb of the thermometer was surrounded with air, and the instru-
ment was plunged into boiling water, the mercury rose from 18 to 27

398

BOY'S PLAYBOOK OF SCIENCE.

in forty-five seconds ; but in the former experiment, when it was sur-
rounded by a Torricellian vacuum, it required to remain in the boiling
water one minute thirty seconds to acquire that degree of heat. In the
vacuum it required five minutes to rise to 48-j%ths; but in air it rose
to that height in two minutes forty seconds ; and the proportion of the
times in the other observation was nearly the same.

" It appears, from other experiments, that the conducting power of air
to that of the Torricellian vacuum, under the circumstances described,
is as 1000 to 702 nearly, for the quantities of heat communicated being
equal, the intensity of the communication is as the times inversely. By
others it appears that the conducting power of air is to that of the
Torricellian vacuum as 1000 to 603."

It is therefore very interesting to discover that the attention of

experimentalists was early
directed to the fact that heat
was independent of the air,
and passed either as waves
of heat or molecules of heat
through space. The velo-
city with which heat moves
through a vacuum is very
great, and in an experiment
performed by M. Pictet, no
perceptible interval took
place between the time at
which caloric quitted a
heated body and its recep-
tion by a thermometer at a
distance of sixty-nine feet.
It appears also, from the
experiments of the same
philosopher, to be thrown
off or radiated in every di-
rection, and not to be di-
verted (as shown at p. 369)
by any strong current of air
passing it transversely. Sir
Humphrey Davy ignited the
charcoal points connected
with a battery in a vacuum,
taking care to place the
charcoal points at the top
of the jar, and a concave
mirror, with a delicate ther-
mometer in its focus, at the
Fig. 376. The air-pump and receiver, containing at bottom of the vessel placed
A the electric light in the focus of a concave mirror, 11T . nT1 +],p ai ' r rmmn nlate
and at B a delicate thermometer, also in the focus of a JJP n *

concave mirror. The effect of radiation was

THE RADIATION OF HEAT. 309

ascertained first when the receiver was fall of air, and next when it was
exhausted to xl^th (i.e., 199 parts pumped out, leaving only one part
of air in the receiver). In the latter case, the effect of radiation was
found to be three times greater than in an atmosphere of the common,
density. The greater rise of the thermometer in vacuo than in air is to
be ascribed to the conducting power of the latter ; for this conducting
power, by reducing the temperature of the heated body, has a constant
tendency to diminish the activity of radiation, which is always pro-
portional to the excess of the temperature of the heated body above that
of the surrounding medium. (Fig. 376.)

Count Eumford's experiments with a Torricellian vacuum gives the
proportion of five in vacuo to three in air for the quantities of heat lost
by radiation, and by conduction or diffusion. It is not, perhaps, de-
parting very far from the truth, if it be stated thab one half of the heat
lost by a heated body escapes by radiation, and that the rest is carried
off by the convective power of currents of air.

If the process of radiation was not constantly proceeding, it can easily
be imagined that the temperature of our globe would become so elevated;
by the regular accession of heat from the sun's rays, that the vegetation!
would be parched up and destroyed, and consequently all animals and'
the human race must become extinct. The best time to notice the
radiation of heat from the earth is at night and after a hot summer's
day. If the sky is clear, it will be noticed (with the help of a ther-
mometer,) that the ground is several degrees colder than the air a few
feet above it. (Kg. 377.) It is this reduced temperature that causes

Fig. 377. Negretti and Zambia's terrestrial radiation thermometer. The bulb of this
instrument is transparent, and the divisions engraved on its glass stem, [n use it is placed
with its bulb fully exposed to the sky, resting on grass, with its stem .supported , by .little
forks of wood, and protected from the wind.

the deposition of dew, and produces the earth-cloud which, .so nearly
resembles a sheet of water as to have been occasionally mistaken for an
inundation, the occurrence of the previous night. Mr. Luke Howard
has called this cloud, which is the lowest form of these draperies of the
sky, "The Stratus," or evening mist ; but when permanent, and increased
to a depth so as to rise above our heads, it is then called the morning
fog, so peculiarly agreeable in London when incorporated with the
black smoke, making a fine reddishryellow ochreous mist. By placing a
thermometer, standing at the ordinary temperature of the air, cased

400 BOY'S PLAYBOOK OF SCIENCE.

with a good radiating material, such as filaments of cotton, in the focus
of a concave mirror, and by turning this arrangement towards a clear
sky in the evening, it will be noticed that the temperature falls several
degrees. Good radiators of heat are black and scratched surfaces,
filaments of cotton, grass, twigs, boughs, and certain leaves, especially
those with a rough surface.

Bad radiators of heat are bright and polished metallic surfaces, white
woollen cloth or flannel, hard and dense substances, such as a gravel
path and stone, or those leaves which have a polished surface, such as
the common laurel. It is the frozen dew and mist which produce the
beautiful effect of hoar-frost and icicles on the trees and bushes, the
primary cause being the radiation of heat from the various objects on
the surface of the earth, as well as from the latter itself. When the
wind is high, dew does not deposit, as it is necessary that the air should
be calm, in order to receive the cooling impression of the cold earth, and
to deposit the moisture, which it holds in solution as invisible steam.
When the wind blows, it mixes all parts of the air together, and prevents
that difference of temperature which causes the deposit of dew. Hence
the evening mist will be more generally observed in the bosom of a
valley surrounded by hills and screened from the winds that may blow
from either quarter. The continual presence of moisture in the air is
well shown by the condensation of water on the outside of a glass of
cold spring water, or especially on the outside of a jug containing iced
water. The invisible steam is always ready to bathe the tender plants
with dew, which would otherwise perish and be burnt up during a hot
summer, if they did not radiate heat at night, and thus condense water
upon themselves. The presence of watery vapour in the air becomes
therefore a matter of great importance, and hence the construction of
hygrometers or measurers of the moisture in the air.

Regnault's condenser hygrometer consists of a tube made of
silver, very thin, and perfectly polished; the tube is larger at one
end than the other, the large part being 1'8 in depth by 8'10 in diameter.
This is fitted tightly to a brass stand, with a telescopic arrangement for
adjusting when making an observation. The tube has a small lateral
tubulure, to which is attached an India-rubber tube with ivory mouth-
piece ; this tubulure enters at right angles near the top, and traverses
it to the bottom of largest part. A delicate thermometer is inserted in
through a cork, or India-rubber washer, at the open end of the tube,
the bulb of which descends to the centre of its largest part. A ther-
mometer is attached for taking the temperature of the air ; also a bottle
for containing ether.

To use the condenser hygrometer, a sufficient quantity of sulphuric ether
is poured into the silver tube to cover the thermometer bulb. On allowing
air to pass bubble by bubble through the ether, by breathing in the
tube, an uniform temperature will be obtained ; if the ether continues
to be agitated by breathing briskly through the tube, a rapid reduction
of temperature will be the result. At the moment the ether is cooled
down to the dew-point temperature, the external surface of that portion

HYGROSCOPES AND THE WEATHER.

401

of the silver tube containing the ether will become covered with a coating
of moisture, and the degree shown by the thermometer at that instant
will be the temperature of the dew-point.

The most simple form of the hygrometer was formerly a very favourite
indicator of the state of the weather, and usually consisted of the
figure of a monk with
his hood, which is at-
tached to a bit of cat-
gut; this covering of
paper, painted to re-
present the hood, falls
over the head on the
approach of damp
weather, and inclines
well back during the
period that the air is
dry or contains less
moisture; and simple
as it is, this hygrometer,
in conjunction with the
reading of the baro-
meter, may assist Pa-
terfamilias in deciding
the fate of a pet bon-
net or velvet mantle,
which is or is not to
be worn on a doubtful
day. (Fig. 378.)

A decision on the
possible changes of the
weather requires con-
siderable experience,
and it has been said
that one of the most
celebrated marshals of
France owed his inva-
riable success in mili-
tary combinations and

Fig. 378. The monk hygroscope, in which the Irood, A B,'
covers the head to dotted line c in wet weather, sind takes
various intermediate positions, being quite back and on the
shoulders in dry states of the air. A thermometer, D, is
usually attached.

attacks to his attention to the signs of the weather, as indicated by
the state of the air during the phases of the moon. Inexperienced
persons (and by that we mean young persons) may, however, take a
certain position in the rank of "weather prophets" by consulting the
weathercock, the barometer, and the hygrometer, before committing
themselves to an opinion, if asked to say what the weather will be.

The dry and wet bulb hygrometer (as represented in the next en-
graving) consists of two parallel thermometers, as nearly identical as
possible, mounted on. a wooden bracket, one marked dry, the other wet.
The bulb of the wet thermometer is covered with thin muslin, round the

D D

402

BOY'S PLAYBOOK OF SCIENCE.

neck of which is twisted a conducting thread of lamp-wick, or common
darning-cotton; this passes into a vessel of water, placed at such a
distance as to allow a length of conducting thread of about three inches ;
the cup or glass is placed on one side, and a little beneath, so that the
water within may not affect the reading of the dry bulb thermometer. In

observing, the eye should be
placed on a level with the top
of the mercury in the tube, and
the observer should refrainfrom
breathing whilst taking an ob-
servation. The temperature of
the air and of evaporation is
given by the readings of the
two thermometers, from which
can be calculated the dew-point,
tables being furnished for that
purpose with the instrument.
(Fig. 379.)

The colour of the sky at par-
ticular times affords the most
excellent guidance to doubting
members of pic-nic or other
out-of-door parties. Not only
does a rosy sunset presage fine
weather, and a ruddy sunrise
bad weather, but there are
other tints which speak witli
equal clearness and accuracy.
A bright yellow sky in the even-
ing indicates wind ; a pale yel-
low, wet ; a neutral grey colour
constitutes a favourable sign in
the evening, an unfavourable
one in the morning. The clouds,
again, are full of meaning in
themselves. If their forms are
soft, undefined, and featherv,
the weather will be fine; if
their edges are hard, sharp, and
defined, it will be foul. Gene-
rally speaking, any deep, un-
usual hues betoken wind or
rain, while the more quiet and

delicate
weather.

tints bespeak fine

K , 3ra .

nativesin the neighbourhood of Calcutta for the purpose of obtaining small

THE RADIATION OF HEAT. 403

quantities of ice. In that climate, the thermometer during the coldest
nights does not indicate a lower temperature than about 40 Eahr.
The sky, however, is perfectly cloudless, and as heat radiates with great
rapidity from the surface of the ground, the Indian natives ingeniously
place very shallow earthenware pans on straw, which is a bad conductor
of heat, and hence insulates the pans from communication with the
parched earth. In a few hours, the water in the pans is covered with a
thin sheet of ice, and there can be no doubt of its production by an
absolute loss of heat by radiation, because the plan does not succeed on
a windy night, and succeeds best even when the pans are sunk in
trenches dug in the earth. A windy night prevents that difference of
temperature between one portion of the surface of the earth and another,
which is so essential to a steady and uniform loss of heat, as it must be
evident that the continual mixture of warmer portions of air with that
which is colder would tend to prevent the desired lowness of temperature
being attained.

The manner in which heat is observed to be radiated has suggested
another theory to the fertile brain of philosophical observers, and it has
been supposed that the conduction of heat may be nothing more than a
radiation from one particle of matter to another, as through a bar of
copper, in which the particles, though packed closely together, are not
supposed to be in actual contact, so that it is possible to conceive each
separate atom of copper receiving and radiating its heat to the neigh-
bouring particle, and so on throughout the length and breadth of the
metal. By this theory the radiation of heat through a vacuum is brought
into close connexion with that of the radiation of heat through the air
and other solid and liquid bodies.

Some of the most interesting phenomena of heat are those discovered
by Leslie, who has proved in a very satisfactory manner that the rapidity
with which a body cools, depends (like the reflection of light) more on
the condition of the surface than on the nature of the material of which
the surface is composed. "With a globular and bright tin vessel it was
observed that water of a certain heat contained in it, required 156
minutes to cool ; but when the latter vessel was covered with a thin
coating of lamp-black and size, the water fell to the same degree as that
noticed in the first experiment in the space of eighty-one minutes.

By very careful observations made with a differential air thermometer,
Leslie determined that the power of radiating heat in various sub-
stances was as follows :

Lamp-black 100

Writing paper 98

Sealing wax. 95

Crown glass 90

Plumbago 75

Tarnished lead 45

Clean lead 19

Iron, polished 15

Tin pkte, gold, silver, copper 12

DD 2

40i

BOY S PLAYBOOK OP SCIENCE.

As in the reflection of light, it was noticed that a piece of charcoal
covered with gold leaf, partook of the nature of the precious metal so
far as its power of throwing off or scattering the rays of light was con-
cerned, so a piece of glass covered with gold-leaf appears to possess
the same power of radiating heat as that of any brilliant metal.

Radiant heat, like light, can be propagated through a great variety
of substances, but is stopped by the larger number ; and it can be re-
flected, refracted, polarized, absorbed, or it may undergo a secondary
radiation.

The intensity of radiant heat follows the same law as that of light,
and decreases as the square of the distance from its source. The same
law that governs the reflection of light, also prevails with that of heat ;
and it may be found by experiment that the angle of incidence is equal
to the angle of reflection, so that the heat is disposed of in the same
manner as light when it falls upon bright polished planes, convex and
concave surfaces ; hence the use of bright tin meat screens and Dutch
ovens, and of all those simple pieces of culinary furniture which are em-
ployed in the kitchen for the purpose of arresting the cold currents of
air that set towards burning matter, as also to reflect the heat upon
whatever viands may be cooking before the fire. A bright silver teapot
retains its heat better than a dirty one, and the fact is determined very
readily by pouring boiling water into two teapots, the one being made of
bright tin and the other of black japanned tin. A thermometer inserted
into each vessel will soon show that the latter radiates, and therefore
loses its heat quicker than the former ; the relative radiating powers of
bright and blackened tin being as 15 to 100. Pipes for the conveyance
of hot water or steam should be kept bright, if possible, although this
trouble is avoided usually by packing them in bad conductors of heat,
whilst the polish of the cylinder of a steam-engine is of great impor-
tance as a means of economizing heat.

When the finger is approached within an inch or so of a red-hot ball,
the heat radiated from the latter is so intense that it cannot be held there

Fig. 380. A B. The cone of paper, gilt inside, c. The red-hot ball. D. Stand with
wood supporting a slice of phosphorus, which is brought into the focus of the rays of heat
reflected through the cone.

THE RADIATION OF HEAT. 405

for more than a few seconds. If, however, the finger is coated with
gold leaf it may be kept near the iron ball for some considerable time,
because the radiant heat is reflected from the surface of the gold. If
the word heat is written upon a sheet of paper and the letters after-
wards gilt, the whole of the white surface is rapidly toasted and scorched
when held before a fire, whilst the surface of the paper under the gold
leaf remains perfectly white, which can be ascertained by turning the
paper round and observing the other side. A sheet of paper gilt inside
and turned round as a cone, being left open at both ends, may be em-
ployed as a reflecting surface ; and if a bit of phosphorus, placed on
paper, is held, say at two feet from a red-hot ball of about two inches
diameter, the radial heat from the latter has not sufficient intensity at
that distance to set it on fire quickly ; if, however, the cone of gilt paper
is used between the two, and the phosphorus brought into the focus of
the rays of radial heat, it very quickly takes fire. (Fig. 380.)

Dr. Bache has determined by experiments that the radiation of heat
from a body is not affected by colour, so that in winter all coloured clothes
are alike in that respect, and radiate heat without any appreciable dif-
ference. The power of absorbing heat, however, is greatly dependent on
colour ; and as a general rule, good radiators of heat (such as a black
cloth, or indeed any surface covered with lamp-black), are also excel-
lent absorbents of heat. Dr. Hooke and Dr. Franklin placed pieces of
cloth of similar texture and size on snow, allowing the sun's rays to fall
equally upon them. The dark specimen always absorbed more heat
than the light ones, and the snow beneath them melted to a greater
extent than under the others ; and they both remarked that the effect
was nearly in proportion to the depth of the shade, as in the following
order : After black, the maximum absorbent quality was possessed by,
first, blue; second, green; third, purple; fourth, red; fifth, yellow.
The minimum absorbent power was observed to belong to white.

When radiant heat is allowed to pass through glass, the latter sub-
stance is not found to be transparent to heat rays as it is to those of
light, but a considerable proportion of heat is arrested and stopped;
consequently glass fire-screens are to be found in the mansions of the
wealthy, because they obstruct the heat but do not exclude the cheerful
light and blaze of the fireside.

tMelloni's researches on the nature of the rays of heat, and also on the
media which affect them, would demand and merit a chapter to them-
selves ; want of space, however, obliges us to omit the consideration of
thermo-electricity, and the refined and beautiful experiments of Melloni,
whose labours are a model for the imitation of all original seekers after
truth.

40G

BOY'S PLAYBOOK OP SCIENCE.

Fig. 3S1. Hancock's steam omnibus, which ran on the common roads.

CHAPTER

THE STEAM-ENGINE.

IT must be apparent to those who read popular works on science, that
they possess, at all events, one point of utility viz., that they are
indicative of the various subjects that may be selected in science for
special, searching and exhaustive study. The subject of steam and the
steam engine is not one that could be thoroughly treated of in the
narrow space allowed in this volume, but enough may be said to give
some instruction and to impart common principles, whilst the minute
details are better examined and learnt in the works of Bourne, Rankine,
and other authors who devote themselves specially to the important
commercial question of steam.

The first truth to be comprehended is, that all matter contains within
its substance the power of creating heat or as it may be expressed
more plainly, solids, fluids, and gases contain what is termed latent or
insensible heat, in contradistinction to the heat which is apparent when
we touch a vessel containing warm water or approach a cheerful fire ;
this latter is termed sensible heat, and has formed the subject of the
preceding chapters.

If a cold horse-shoe nail is applied to a thin dry slice of phosphorus
laid on a sheet of paper, no combustion of the phosphorus ensues, be-
cause the temperature of the iron is not sufficiently high to affect that
combustible substance ; but if the horse-shoe nail is vigorously hammered
on an anvil, the particles of the metal are brought closer together, and
if it is applied to the phosphorus, so much heat has been generated,
thrust or squeezed out by the hammering or condensation of the iron,
that it is now sufficiently warm to set fire to it.

LATENT HEAT. 407

The reverse or antithesis to this experiment viz., the production of
cold would be shown if it were possible to expand a mass of metal
suddenly, and this can be effected by first melting together

207 parts by weight of lead.
118 tin.
284- bismuth.

When these metals are in the liquid state and perfectly mixed, they
are poured from a sufficient height into a pail of cold water, for the pur-
pose of granulating or dividing them into small fragments.

If the granulated compound metal is now mixed with 1617 parts by
weight of quicksilver, it becomes suddenly liquefied and expanded :
liquefaction is the reverse of solidification, and hence cold is produced from
the natural heat of the compound metals being rendered latent by the
change from the solid to the liquid state ; so that a small quantity of water
placed in a glass tube, and surrounded with the metals whilst lique-
fying in the mercury, becomes rapidly converted into ice, the fall of
the temperature, as shown by a thermometer, being from 60 Fahr. to
14, which is 18 degrees below the freezing point of water. In the
former case, by hammering the iron the latent heat is made sensible ;
whilst in the latter case, by the liquefaction of the compound metal in
mercury, the sensible heat is rendered latent. The heat rendered latent
by melting different substances is not a constant quantity, but varies
with every special body employed, and the Drs. Irvine have proved
this fact by the following experiments :

Ditto, reduced to the
Heat of fluidity. .specific heat of water.

Sulphur . . . . 143-68 Fahr. . . 27'14.

Spermaceti . . . 145 .

Lead 163 . . 5'6.

Bees'-wax .... 175 .

Zinc 493 . . 48'3.

Tin 500 . .33-

Bismuth .... 550 . . 23'25.

Everjr one of these substances requires more heat to bring them into
the liquid condition than ice, for which 140 of heat are sufficient, or
are rendered latent during its conversion into water.

In coining at the Mint, the cold blank pieces of gold, silver, or
copper become hot directly they have sustained the violent and sudden
pressure of the coining press, and they must be heated again, or an-
nealed, to restore the equilibrium of the heat disturbed by the violent
blow, or else they remain hard and unfit to sustain the finishing process
of milling.

The condensation of water when it assumes a smaller bulk by union
with sulphuric acid, is easily proved by measuring a pint of water and
a pint of acid, and mixing them together, when a very great increase of
temperature may be perceived ; and by placing into the mixture a cold
copper wire that previously could not ignite phosphorus, it becomes

408

BOY'S PLAYBOOK OF SCIENCE.

very hot, and when removed and wiped it will cause phosphorus to fire
directly it touches that substance. When the mixture of sulphuric acid
and water is measured after it has cooled, it has no longer a bulk of two
pints, but is found to have lost bulk equal to one or more ounces by
measure. The heat evolved by a mixture of four parts of strong sul-
phuric acid and one part water is shown by the thermometer to be
300 Fahr., and this mode of obtaining heat has been used by aeronauts
for the purpose of obtaining artificial warmth without the danger of
setting fire to the gas in the balloon.

Fig. 382. Aeronauts in the car warming their hands by a bottle containing
sulphuric acid and water

When alcohol and water are mixed a change of density occurs, and
heat is produced ; and if equal measures of alcohol of a specific gravity
of '825, and water, each at 50 Fahr., are mixed, a temperature of 70
Fahr. is obtained ; if the mixture is made in a glass vessel, as shown in
the annexed cut, the combination is very apparent. To perform the
experiment properly, water is poured into the lower tube and bulb, and
alcohol into the top one ; when this is done, the stopper is inserted, and
the whole thoroughly shaken and mixed together ; the warmth which is

LATENT HEAT.

409

ALCOHOU

WATEF

thus obtained is apparent to the hand, whilst the con-
traction is shown after the mixture is cold, as it no
longer fills the two bulbs of the instrument. (Fig. 383.)

The latent heat of gases is easily shown by suddenly
condensing air in a small syringe or pump, of which the
piston contains a minute fragment of amadou (a species
of fungus, Polyporus igniarius ; this, according to Sim-
monds, after having been beaten with a mallet, and
dipped in a solution of saltpetre, forms the spunk or
German tinder of commerce ; it is also used as a styptic,
and made into razor strops), which takes fire, and before
the invention of vesta and other matches, tobacco-smokers
were in the habit of obtaining a light for their pipes
and cigars in this manner viz., by the latent heat ob-
tained from the contraction or compression of air.
Then, again, an instructive though opposite parallel is
afforded by suddenly expanding or rarefying air in a
glass receiver provided with a delicate thermometer.
By pumping out some of the air, a considerable diminu-
tion of the temperature occurs, and equal to several
degrees of the thermometer. Every child knows that
steam direct from the kettle will scald, but if it issues
from a 1 high-pressure boiler, say at fifteen pounds on
the square inch, thelhand may be held with impunity in
the escaping steam, as it merely feels gently warm, and JjjJjJ the d co-
not scalding. This is due partly to the loss of heat tion in bulk of a
rendered latent by the expansion of the high -pressure mixture of alcohol
steam directly it passes into the air, and partly to the a
currents of air. that are dragged into an escaping jet of steam. This
tendency of the air to rush
into a jet of steam was
discovered by Faraday, and
explains those curious ex-
periments with a jet of
steam by which balls, empty
flasks, and globular vessels
are sustained and supported
either perpendicularly or
horizontally.

If steam at a pressure of W ^^ __ B _^/J^^ B

about sixty pounds per inch
is allowea to escape from

a proper jet, and a large A

lighted circular torch com-
posed of tow dipped in tur-
pentine held over it, the
course of the external air is Fi % 38 U 4 : /; Je * ^barging high-pressure steam
-,. ,. ,. B B. Lighted torch held round the escaping steam

Shown by the direction Ol the flames from the former all rush into the latter.

Fig. 383. Glass

410 BOY'S PLAYBOOK OF SCIENCE.

the flames, which are forcibly pulled and blown into the jet of steam
with a roaring noise, indicating the rapidity of the blast of air moving
to the steam jet. (Fig. 384.)

Egg-shells, empty flasks, india-rubber or light copper and brass balls,
are suspended in the most singular manner inside an escaping jet of high-
pressure steam ; and before the explanation of Earaday, reams of paper
were used in the discussion of the possible theory to account for this
effect ; and what made the explanation still more difficult, was the fact
that the jet of steam might be inclined at any angle between the hori-
zontal and perpendicular, and still held the ball, egg-shell, or other
spherical figure firmly in its vapory grasp. (Eig. 385.)

Fig. 385. A. Ball and socket jet at an angle, and discharging steam. .The egg-shells
are supported by the enormous current of air moving into the jet in the direction of the
arrows.

In consequence of the great rush of air towards a jet of escaping
high-pressure steam, Mr. Goldsmith Gurney has patented the application
of this principle in his ventilating steam jet, which he has already suc-
cessfully applied ; in one case especially, where a coal-mine had been on
fire for several years, and the whole working of the coal-measures in the
pit was jeopardized by the spreading of the combustion to new workings ;
the fire was first extinguished by carbonic acid gas, pulled, as it were,
into the coal-mine bv a jet of steam blowing into the downcast, but
placed in connexion with a furnace of burning coke ; and the circulation
of the carbonic acid, called choke-damp, through the pit workings was
further assisted by a jet of high-pressure steam blowing upwards, and
placed over the mouth of the upcast shaft.

The experiment succeeded perfectly at the South Sauchie Colliery,
near Alloa, about seven miles from Stirling, where a fire had raged for
about thirty years over an area of twenty-six acres in the waste seam
of coal nine feet thick. (Eig. 386.)

Eor the general purpose of .ventilating the coalmine, Mr. Gurnets
plan was tned at the Ebbw Yale Colliery, and very economically, the
waste steam alone being used. Experiments have also been satisfac-
torily made with it for blowing a cupola for smelting iron, and with dry
steam . <?., steam of a very high pressure escaping through a warm
tube, the results were perfectly successful.

With this digression from the subject of latent heat derived from

GURNEY'S STEAM JET.

411

412 BOY'S PLAYBOOK OF SCIENCE.

the compression of air, we return again to the subject with another case
in point, furnished by the Fountain of Hiero, as it is called, at Schemnitz,
in Hungary, described by Professor Brande ; and it may be observed
that all the phenomena related would apply to the great pressure of the
water from the water-towers at the Crystal Palace, if fitted with a
similar air-vessel.

" A part of the machinery for working these mines is a perpendicular
column of water 260 feet high (the Crystal Palace water-towers are
each 284 feet high), which presses upon a quantity of air enclosed in a
tight reservoir; the air is consequently condensed to an enormous
degree by this height of water, which is equal to between eight and
nine atmospheres ; and when a pipe communicating with this reservoir
of condensed air is suddenly opened, it rushes out with extreme velocity,
instantly expands, and in so doing it absorbs so much heat as to preci-
pitate the moisture it contains in a shower of snow, which may readily
be gathered on a hat held in the blast. The force of this is so great,
that the workman who holds the hat is obliged to lean his back against
the wall to retain it in its position/ 5

The best examples of latent heat are furnished by ice, water, and
steam, and we are indebted chiefly to Dr. Black for the elegant and con-
clusive experiments demonstrating the important truths connected with
the latent heat of these three conditions of matter. When various solids
are heated, they frequently pass through certain intermediate conditions
of softness, terminating in perfect liquidity; but ice and many other
bodies change at once to the liquid state on the application of a suffi-
cient quantity of heat. The process of melting ice is very slow, because
every portion must absorb or render latent a certain quantity of heat
before it can take the liquid state hence the difficulty of melting blocks
of ice when they are surrounded with non-conducting materials; and
this fact the author has proposed to take advantage of in keeping water
cool which is to be supplied to the ova of salmon whilst taking them to
stock the rivers of Australia.

In order to prove that heat is rendered latent by the liquefaction of
ice, it is only necessary to weigh a pound of finely-powdered ice and a
pound of water at 212 Fahr. (boiling water), and mix them together ;
when the ice is all melted, the resulting temperature is only 52, there-
fore the boiling water has lost 160 of temperature, of which 20 can be
accounted for, because the resulting temperature of the melted ice is
52; but in the liquefaction of the pound of ice, 140 have disappeared
or become latent, or, as Dr. Black termed it, have become combined.

1 Ib. of ice at 32 -f 20 = 52, the resulting temperature.
1 Ib. of water at 212 - 52 = 160 - 20 = 140, rendered latent.

140 represents the result obtained from innumerable experiments made
by mixing equal parts of ice and boiling water, and it is this large quan-
tity of latent heat required by ice and snow that prevents their sudden
liquefaction, and the disastrous circumstances that would arise from the
floods that must otherwise always be produced.

THE LATENT HEAT OF WATEK. 413

To put the fact beyond all doubt, it is advisable to mix together equal
weights of water at 32 and boiling water at 212, and the result is
found by the thermometer to be the mean between the two, because
half the extremes are always equal to the mean ; and if the two tempera-
tures are added together and divided by two, the result is a temperature
of 122, as shown below :

lib. of ice water at 32 + llb. of water at 212 =244 -^2=122 .

Prom similar experiments Dr. Black deduced the important truth,
" that in all cases of liquefaction a quantity of heat not indicated by, or
sensible to, the thermometer, is absorbed or disappears, and that this heat
is toithdravn from the surrounding bodies, leaving them comparatively
cold." At p. 79 it is shown how the sudden solution or liquefaction of
certain salts produces cold, and hence numerous freezing mixtures have
been devised. In olden times, when officials in authority did what they
pleased, without being troubled with disagreeable returns, and colonels
clothed their men, and were merchant tailors on the grand scale, gun
cartridges were not confined to practice on the enemy, but they did duty
frequently in the absence of ice as refrigerators of the officers' wine, in
consequence of the gunpowder containing nitre or saltpetre ; as a mere
solution of this salt finely powdered will lower the temperature of water
from 50Fah. to 35; whilst a mixture of four ounces of carbonate of
soda and four ounces of nitrate of ammonia dissolved in four ounces of
water at 60, will in three hours freeze ten ounces of water in a metallic
vessel immersed in the mixture during the liquefaction or solution of
the salts.

Fahrenheit imagined he had attained the lowest possible temperature
by mixing ice and salt together, and it is by this means that confectioners
usually freeze their ices, or ice puddings ; the materials are first incor-
porated, and being placed in metallic vessels or moulds, and surrounded
with ice and salt placed in alternate layers, and then well stirred with a
stick, they soon solidify into the forms which are so agreeable, and so
frequently presented at the tables of the opulent. The temperature
obtained is Fahrenheit's zero viz., thirty -two degrees below the freezing
point of water. According to the very wise police regulation observed
in London, all householders are required to sweep or remove the snow
from the pavement in front of their houses, and this is frequently done
with salt ; should an unfortunate shoeless beggar, tramp past whilst the
sudden liquefaction is in progress, the effect on the soles of his feet is
evidently very disagreeable, and the rapidity with which he retires
from the zero affords a thermometric illustration of the most lively
description.

Heat the Cause of Vapour.

Every liquid, when of the same degree of chemical purity, and under
equal circumstances of atmospheric pressure, has one peculiar point of
temperature at which it invariably boils. Thus, ether boils at 96Fahr.,
and if some of this highly inflammable liquid is placed carefully in a

414

BOY'S PLAYBOOK OF SCIENCE.

flask, by pouring it in with a funnel, and flame applied within one inch
of the orifice, no vapour escapes that will take fire ; but if the flame of

a spirit lamp is applied, the
ether soon boils, and if the
lighted taper is again
brought near the mouth of
the flask, the vapour takes
fire, and produces a flame
of about two feet in length.
This fire only continues as
long as the flame of the
spirit-lamp is retained at
the bottom of the flask, and
on removing it the vessel
rapidly cools. The length
of the flame is reduced, and
is gradually extinguished
for the want of that essence
of its vitality, as it were
viz., heat. (Fig. 387.) If
a thermometer is introduced
into the flask, however rapid
may be the ebullition or
boiling of the ether, it is
found to be invariably at

The heat carried off by evaporation is most elegantly displayed by
placing a little water in a watch glass, and surrounded by charcoal
saturated with sulphuric acid, in the vacuum of an air-pump. The rapid
evaporation and condensation of the water by its affinity for the sul-
phuric quickly produces ice; and the pumps and other apparatus of
Knight and Co., Foster-lane, City, are greatly to be recommended for
this and other illustrations.

The illustration of the determination of the fixed and invariable
boiling point belonging to every liquid is further carried out by intro-
ducing some water into a second flask standing above a lighted spirit-
lamp, with a small thermometer, graduated, of course, properly to degrees
above the boiling point of water ; when the water boils, it will be found
to remain steadily at a temperature of 212. And however rapidly the
water may be boiled, provided there is ample room for the steam to
escape, the heat indicated bv the thermometer is like the law of the
Medes and Persians, which altereth not, and it remains standing at the
number 212. The only exception (if it may be so termed) to this law
is brought about by the shape and nature of the containing vessel ;
under a mean pressure the boiling point of water in a metallic vessel is
generally 212 ; in a glass vessel it may rise as high as 214 or 216, but
if some metallic filings are dropped in, the escape of steam is increased,
and the temperature may then drop immediately to 212.
When a thermometer is inserted in a flask containing water in a state

Fig. 387. Heat the cause of vapour.

THE BOILING POINT OF WATER.

415

of ebullition or boiling, so that the bulb does not touch the fluid, but is
wholly surrounded with steam, it will be found that the temperature of
the latter is exactly the same as that of the former ; and if the liquid
boils at 96, the vapour will be 96, if at 212, the steam is 212.
Steam has therefore exactly the same
temperature as the boiling water
that produces it. (Fig. 388.)

Whilst performing the last expe-
riment, it mav be noticed that the
steam inside the neck of the flask is
invisible, and that it only becomes
apparent in that kind of intermediate
condition between the vaporous and
liquid state called vesicular vapour
a state corresponding with the "earth
fog," and called by Howard the
stratus. When a flask containing
boiling water is placed under the
receiver of an air pump (as soon after
the ebullition has ceased as may be
possible), and the air pumped out, it
will be noticed that the water again
begins boiling as the vacuum is ob-
tained, showing that the boiling point
of the same fluid varies under dif-
ferent degrees of atmospheric pres-
sure, and according to the height of
the barometer.

Fig. 388. Thermometer in the steam
escaping from boiling water.

Boiling point
of water.

Height of
barometer.

26 204-91

26-5 .... 205-79

27 206-67

27-5 .... 207-55

28 208-43

28-5 209-31

Height of
barometer.

Boiling point
of water.

29 210-19

29-5 .... 211-07

30 212

30-5 .... 212-88

31 213-76

Alcohol and ether confined under an exhausted receiver boil violently
at the ordinary temperature of the atmosphere, and in general liquid's
boil with 124 less of heat than are required under a mean pressure of
the air; water, therefore, in a vacuum must boil at 88 and alcohol at 49.

On ascending considerable heights, as to the tops of mountains, the
boiling point of water gradually falls in the scale of the thermometer.
Thus, on the summit of Mont Blanc water was found by Saussure to
boil at 187 Fahr. In Mr. Albert Smith's delightful narrative of his
ascent of Mont Blanc, he mentions the violent commotion and escape of
the whole of the champagne in froth directly the bottle was opened at
the summit of this king of mountains.

Dr. Wollaston's instrument for measuring the heights of mountains

416

BOY S PLAYBOOK OF SCIENCE.

by the variations of the boiling point of water has long been known and
used for this purpose.

If a Florence flask is first fitted with a nice soft cork, and this latter re-
moved, and the former half filled with water, which is then boiled over a gas
or spirit flame, the same fact already mentioned and illustrated in the pre-
ceding table may be rendered apparent when the flask is corked and re-
moved from the heat. If it is now inverted, and cold water poured over it,
an ebullition immediately commences, because the cold water condenses
the steam in the space above the hot water in the flask, and producing

a vacuum, the water boils as
readily as it would do under
an exhausted receiver on an
air-pump plate. (Fig. 389.)

Water may be heated con-
siderably higher than 212, if
it is enclosed in a strong
boiler, and shut off from
communication with the air ;
by this means steam of great
pressure is obtained.

Dr. Marcet has invented a
very instructive form of a
miniature boiler, supplied with
a thermometer and barometric
pressure gauge, which can be
purchased at any of the in-
strument makers, and is
figured and described in
nearly every work on che-
mistry.

The reason water boiled in
an open vessel does not rise
to a higher temperature than
212 is because all the excess of heat is carried off by the steam, and
is said to be rendered latent in the vapour. The fixation of caloric
in water by its conversion into steam may be shown by the following
experiment. Let a pound of water at 212 and eight pounds of iron
filings at 300 be suddenly mixed together. A large quantity of steam
is instantly generated, but the temperature of the water and escaping
steam are still only 212 ; hence the steam must therefore contain all
the degrees of heat between 212 and 300, or eight times 88. _When
the water is heated in the hydro-electric machine or other boiler, to
322-7, it very quickly drops to 212 when the steam is allowed to blow
off; yet if the latter is collected, it represents but a very small quantity
of water which constituted the steam, and it has carried off and ren-
dered latent the excess of heat in the boiler viz., the difference be-
tween 212 and 322'7, or 110-7

If steam can carry off heat, of course it may be compelled, as it were,

Fig. 389. The paradoxical experiment of water
boiling by the application of cold water.

THE LATENT HEAT OF STEAM.

117

to surrender it again ; and this important elementary truth is shown by
adapting a tube, bent at right angles, and a cork, to a flask containing
a few ounces of water, and when it boils, the steam issuing from the
end of the pipe may now be directed into and below the surface of some
water contained in a beaker glass ; in a very short time the water in the
latter will be raised to the boiling
point by the condensation of the
steam and the latent heat arising
from it. (Fig. 390.) The amount
of latent heat is enormous, when
it is remembered that water by
conversion into steam has its bulk
prodigiously enlarged viz., 1698
times, so that a cubic inch of
water converted into steam of a
temperature of 212, with the ba-
rometer at thirty inches, occupies
a space of one cubic foot, and its
latent heat amounts, according to
Hall, to 950; Southeron, 945;
Dr. Ure, 967. When we come
to the consideration of the steam-
engine, it will be noticed that the
question of the latent heat of
steam is one of the greatest im-
portance.

Fig. 390. A. Flask for generating steam.
B. Glass pipe bent at right angles to convey
the steam into the fluid containing some cold
water.

Temperature of
Steam.

229 . .
270 . .
295

Elasticity in inches
of Mercury.

. . 40 .

. . 80 .

. 120

Latent Heat.

942

. 942

950

The same weight of steam contains, whatever may be its density, the
same quantity of caloric, its latent heat being increased in proportion as
its sensible heat is diminished ; and the reverse. In consequence of the
enormous amount of latent heat contained in steam, it is advantageously
employed for the purpose of imparting warmth either for heating rooms
or drying goods in certain manufacturing processes. The wet rag-pulp
pressed and shaken into form on a wire-gauze frame or deckle, passes
gradually to cylinders containing steam, and is thoroughly dried before the
guillotine knife descends at the end of the paper machine, and cuts it into
lengths. In calico stiffening and glazing, also in calico printing, steam-
heated cylinders are of great value, because they impart heat without the
chance of setting the goods on fire. The elementary principles already de-
scribed with reference to heat, will prepare the youthful reader for the
application of the expansion of water into steam, as the most valuable
motive power ever employed to assist the labour of man.

E E

418

BOY'S PLAYBOOK OF SCIEXCE.

Fig, 391. The first steam-boat, the Comet, built by Henry Beil, in 1811, who brought
steam navigation into practice in Europe.

CHAPTER XXIX.

THE STEAM-ENGINE continued.

" So shalt thou instant reach the realm assign'd
In wondrous ships, self-mov'd, instinct with mind.

Though clouds and darkness veil the encumbered sky,
Fearless, through darkness and through clouds they fly,
Tho' tempests rage, tho' rolls the swelling main,
The seas may roll, the tempests swell hi vain;
E'en the stern god that o'er the waves presides,
Safe as they pass, and safe repass the tides,
With fury burns ; while careless they convey,
Promiscuous, ev'ry guest to ev'ry bay."

THESE lines, from Pope's translation of the "Odyssey," were very
aptly quoted twenty-five years ago by Mr. M. A. Alderson, in his treatise
on the steam-engine, for which he received from Dr. Birkbeck, the

HERO S-STEAM ENGINE.

419

originator of Mechanics' Institutions, the prize of 20/., being the gift of
the London Mechanics' Institution, and these lines seem to indicate
some sort of rude anticipation by the ancients of that free passage of
the ocean by the agency of steam which has rendered ships almost
independent of wind and weather.

Homer's description, as above, of the Phoenician fleet of King Alcinous,
in the eighth book of the " Odyssey," is certainly an ancient record of
an idea., but nothing more. In a work written by Hero of Alexandria,
about a hundred years B.C., and entitled "Spiritalia seu Pneumatica," a
number of contrivances are mentioned
for raising liquids and producing mo-
tion by means of air and steam, so
that the first steam-engine is usually
ascribed to Hero; and the annexed
cut displays the apparatus. (Fig.
392.)

It is a remarkable circumstance
that Sir Isaac Newton applied the
same principle in a little ball, mounted
on wheels, containing boiling water,
and provided with a small orifice;
and in his description he says : " And
if the ball be opened, the vapours will
rush out violently one way, and the
wheels and the ball at the same time
will be carried the contrary way."
From the time of Hero, there does
not appear to be any record or men-
tion made of steam apparatus till the
year 1002, when, in a work called
" Malmesbury's History," mention is
made of an organ in which the sounds
W ere produced by the escape of air
(query, steam) by means or heated the two apertures, c c. The reaction of
water. It is strafe that in these SSJS T S.*KS5 S gSSA
days or steam application, the Oal- to a centre but hollow axle.
Hope, or steam organ, should be an

important feature at the present moment at the Crystal Palace; and
it only shows how the same ideas are reproduced as novelties in the ever-
recurring cycles of years.

On the revival of classical learning throughout Gothic Europe, the
work of Hero began to attract attention, and it was translated and printed
in black letter, and most likely first from the Arabic character, as in the
year 1543 the first fruits appeared in Spain, where Blasco de Garay, a
sea captain, propelled a ship of 200 tons burden, at the rate of three
miles per hour, Wore certain commissioners appointed by the Emperor
Charles the Fifth. Alas for inquisitorial Spain ! had she 'looked deeper
into the matter, and performed her auto-da-fees on the boilers of steam-

EE 2

Fig. 392. Hero's steam-engine. A. The
boiler in which steam is produced, and

BOYS PLAYBOOK OF SCIENCE.

engines instead of the bodies of poor human beings, what lasting glories
would have been her reward. The invention made its debut in "Spain,
the commissioners reported, the worthy inventor was rewarded, but the
mighty giant invoked was put to sleep again for at least 150 years.
The steam giant was disturbed with dreams; one Mathias, in 1563,
gave him a nightmare ; Solomon de Cans, in 1624, nearly woke him up ;
Giovanni Bianca, in 1629, did more ; and the Marquis of Worcester, in
the middle of the seventeenth century, as the evil genius of Spain,
carried off the giant bodily and made him the slave of England; at least, he
experimented, and wrote such wondrous tales of his new motive power,
that in 1653 we read of steam being fairly tethered to its work, and set
to draw water out of the Thames at Vauxhall ; and Cosmo de Medici,
a foreigner who inspected the apparatus in 1653, says, "It raises water
more than forty geometrical feet by the power of one man only, and in a
very short space of time will draw up full vessels of water through a
tube or channel not more than a span in width, on which account it is
considered to be of greater service to the public than the other machine
near Somerset House, which last one was driven by two horses"

What would the Marquis of Worcester and Cosmo de Medici have
thought of Blasco de Garay on the ocean, and ruling 12,000 steam
horses ? Write the name of the brave and prudent Captain Harrison, in
the good ship Great Eastern, date 1859, instead of that of the gallant
Spaniard, and our brief history is finished.

The first really useful steam-engine was made, not by a plain Mr.,
but again by a captain namely, Captain Savery, who appears to have
been the first inventor who thoroughly understood and applied the
vacuum principle. (Eig. 393.)

A A. The furnaces which contain the boiler. B 1 and B 2. The two fireplaces, c. The
funnel or chimney, which is common to both furnaces. In these two furnaces are placed
two vessels of copper, which I (Savery) call boilers the one large as at L, the other small
as D. D. The small boiler contained in the furnace, which is heated by the fire at B 2.
E. The pipe and cock to admit cold water into the small boiler to fill it. F. The screw that
covers and confines the cock B to the top of the small boiler. G. A small gauge cock at
the top of a pipe, going within eight inches of the bottom of the small boiler. H. A large
pipe which goes the same depth into the small boiler, i. A clack or valve at the top of
the pipe H (opening upwards). K. A pipe going from the box above the said clack or
valve in the great boiler, and passing about one inch into it. t L. The great boiler con-
tained in the other furnace, which is heated by fire at B 1. M. The screw with the regu-
lator, which is moved by the handle z, and opens or shuts the apertures at which the
steam passes out of the great boiler at the steam-pipes o o. jr. A small gauge cock at the
top of a pipe, which goes half way down into the great boiler, o 1, o 2. Steam pipes, one
end of each screwed to the regulator ; the other ends to the receivers p p, to convey the steam
from the great boiler into those receivers, p 1, P 2. Copper vessels called receivers, which
are to receive the water which is to be raised. Q. Screw joints by which the branches of
the water-pipes are connected with the lower parts of the receivers. B 1, 2, 3, and 4. Valves
or clacks of brass in the water-pipes, two above the branches Q and two below them ; they
allow the water to pass upwards through the pipes, but prevent its descent ; there are
screw-plugs to take out on occasions to get at the valves B. s. The forcing-pump which
conveys the water upwards to its place of delivery, when it is forced out from the receivers
by the impelled steam. T. The sucking-pipe, which conveys the water up from the bottom
of the pit to fill the receivers by suction, v. A square frame of wood, or a box, with holes
round its bottom in the water, to enclose the lower end of the sucking-pipe to keep away
dirt and obstructions, x is a cistern with a bung cock coming from the force-pipe, so as it
shall always be kept filled with cold water. T T. A cock and pipe coming from the bottom
of the said cistern, with a spout to let the cold run down on the outside of either of the re-
ceivers, P P. z. The handle of the regulator to move it by, either open or shut, so as to let
the steam out of the great boiler into either of the receivers.

THE FIRST USEFUL STEAM-ENGINE.

421

Fig. 393. Savery's engine.

422 BOY'S PLAYBOOK OF SCIENCE.

This is Savery's own description (taken from the " Miner's Friend,"
printed in 1702)" of his water-engine, which differs from that suggested
uy the Marquis of Worcester, in the fact that he made the pressure of the
air carry the water up the first stage. Savery's patent was " for raising
water and occasioning motion to all sorts of mill-work by the impellant
force of fire;" and the patent was granted in the reign of King
William the Third of glorious memory.

Thus Savery overcame, as he remarks, the "oddest and almost
insuperable difficulties," and introduced a steam apparatus or engine, a
good many of which were constructed, and employed for raising water.
The mechanical skill required to construct the boiler, the very heart (as
it were) of the iron engine, had not been acquired in the time of Captain
Savery, and hence the weakness of the boilers, and the danger of working
them. As the pressure required was very considerable to overcome the
resistance of a lofty column of water, these engines were gradually
relinquished for those of another clever mechanician viz., for those of
Thomas Newcomen, an ironmonger of Dartmouth, who, about the year
1705, constructed and introduced the cylinder, from which the transition
was gradually made to the mode of condensing by a jet of cold water,
the use of self-acting valves, and the construction of self-acting
engines by Smeaton, Hornblower, and finally by the illustrious Watt,
whose portrait heads the first chapter on Heat in this book.

Newcomen was assisted in his work by one Cawley, a glazier ; and
their persevering labours were crowned with a successful result of the
most memorable importance in the history of the steam-engine.

In the engine by Savery, the operation of the steam was twofold
namely, by the direct pressure from its elasticity, and by the indirect
consequence of its condensation, which affords a vacuum. This last
may be said to be the only principle used by Newcomen, who employed
a boiler for the generation of steam, and conveyed it by a pipe to the
bottom of a hollow cylinder, open at the top, but provided with a solid
piston, that moved up and down in it, and was rendered tight by a stuffing
of hemp, like the piston of a boy's common squirt. It can readily be
understood, that if the jet of the latter was connected with a tight little
boiler, and steam blown into it, that the piston of the squirt would rise
to the top of the barrel in which it works, being thrust up by the
pressure or force of the steam ; but unless the steam was cut off, and
cold water applied to the interior of the barrel, the piston could not
descend again. As soon, therefore, as Newcomen had thrust up the
piston by the action of steam, he introduced a jet of cold water, sup-
plied from an elevated cistern beneath the piston, when the steam was
condensed into water, and a vacuum or void space obtained^ The piston
being free to move either up or down, was now forced in the latter
direction by the pressure of the air, which is a constant force equal to
fifteen pounds on the square inch ; and thus the piston in Newcomen's
engine was raised by heat viz., by steam, and thrust down by cold
i.e., by the condensation of the steam producing a vacuum. The void
obtained in this manner was very considerable, because one cubic foot of

NEWCOMEN'S STEAM-ENGINE. 423

steam at 212 condenses into one cubic inch of water. The production
of a vacuum with the aid of steam is quickly effected by boiling some
water in a clean camphine can, and when the steam is issuing freely from
the mouth of the latter it is then corked, and cold water thrown over the
exterior. Directly the temperature is lowered, the steam inside the tin
vessel is condensed suddenly into water, and a void space being suddenly
obtained, the whole pressure of a column of air of a breadth equal to
the area of the vessel, and of a height of forty miles, is brought sud-
denly down like a sledge-hammer upon the sides of the tin vessel, and
as they are not sufficiently strong to offer a proper resistance, they are
crushed in like an egg-shell by the giant weight which falls upon them.
The barometer, or measurer of the weight of the air, consists of a glass
tube about thirty-three inches in length, hermetically sealed at one end,
and containing mercury that has been carefully boiled within it, and
being perfectly filled the tube is inserted in a cistern of clean mercury,
when it gravitates to a height equal to the pressure of the air, leaving
a space at the top called the torricellian vacuum. As the atmospheric
air decreases in density by admixture with invisible steam or vapour, any
given volume becomes specifically lighter : hence the column or mercury
falls to a height of about twenty-eight inches ; whilst if the aqueous
vapour diminishes, the weight of the air becomes greater, and the baro-
meter may rise to a height of about thirty-one inches.

Having thus secured a " reciprocating motion," Newcomen applied it
to the working of a force-pump by the intervention of a great beam or
lever suspended on gudgeons (an iron pin on which a wheel or shaft of
a machine turns) at the middle, and suspended like the beam of a pair
of scales; and, in fact, he invented that method of supporting the
beam which is in use to the present day. Supposing we compare
Newcomen's beam to a scale beam, he attached to the extremities
(instead of scale pans) a water pump and his steam cylinder the latter
being at one end, and the former at the other. The beam played at
" see-saw :" by the primary action of the steam on the bottom of the
piston in the cylinder it was pushed up at this end, and of course
suffered an equal fall at the other, to which the pump piston was
attached ; and when the motion was reversed by the condensation of the
steam, down went the piston again by the pressure of the air, whilst
that of the water pump was again raised, and being provided with
proper valves, the water was pumped slowly out of the mine, although
the steam power used was very moderate, and only just sufficient to
counterpoise the weight of the atmosphere. Newcomen made the end
attached to the water pump purposely heavier than the steam piston of
the other end of the beam, and by this means the work of the steam,
by its elasticity, was very moderate, whilst the actual lift of the water
from the mine was performed by the pressure of the air, equal (as
already stated) to fifteen pounds on every square inch of the surface of
the steam piston. This engine is called the atmospheric engine, and in
the next cut we have a picture taken from a photograph by the " Watt
Club 35 of the actual model of the Newcomen engine in the Hunterian

424: BOY'S PLAYBOOK OF SCIENCE.

Museum of the University of Glasgow : the dimensions being length,
27 in.; breadth, 12 in.; height, 50^ in.; from which, "in!765, James Watt t

Fig. 394. Model of the Newcomen engine, in which the furnace and boiler, the steam
cylinder, beam, water-pump, and elevated cistern of water, are apparent.

in seeking to repair this model, belonging to the Natural Philosophy Class
in the University of Glasgow, made the discovery of a separate condenser,
which has identified his name with that of the steam-engine." (Fig. 394.)

In Newcomen's engine, the opening and shutting of the cocks re-
quired the vigilant care of a man or boy, and it is stated on good
authority that a boy who preferred (like nearly all other boys) play to
work, contrived, by means of strings, a brick, and one or two catches on
the working beam, to make the engine self-acting.

This poor boy's ingenious contrivance paved the way for the improved

WATT'S STEAM-ENGINE. 425

methods of opening and shutting the valves, which were brought to a
great state of perfection by Beighton, of Newcastle, about 1718.
Between that time and the year 1763, we find honourable mention made
of Smeaton in connexion with the steam-engine, but the name of the
great James Watt at this time began to be appreciated, and by a series
of wonderfully simple mechanisms, he at last perfected the machine
whose origin could be traced back not only to the time of Blasco de
Garay, in 1543, but even to the days of the ancient mechanicians, such
as Hero, who lived 130 B.C.

In 1763, James Watt was a maker of mathematical instruments in
Glasgow, and his attention was drawn to the subject of the steam-
engine by his undertaking to repair a working model of Newcomen's
steam-engine, which was used by Professor Anderson, who then filled
the Chair of Natural Philosophy, and subsequently founded the Ander-
sonian Institution. The repairs required for this model induced Watt
to make another, and by watching its operation, he discovered that a
vast quantity of heat, and therefore fuel, was wasted in the constant and
successive heating and cooling of the steam cylinder. About two years
after, when Watt was twenty-nine years of age, he had made so many
experiments, that he was enabled to put into a mechanical shape his
original ideas, which are embodied in his patent of 1769, as follows :

" My method of lessening the consumption of steam, and consequently
fuel, in fire-engines, consists of the following principles :

" First : That vessel in which the powers of steam are to be employed
to work the engine, which is called the cylinder in common fire-engines,
and which I call the steam-vessel, must, during the whole time the
engine is at work, be kept as hot as the steam that enters it first, by
enclosing it in a case of wood or any other materials that transmit heat
slowly ; secondly, by surrounding it with steam or other heated bodies ;
and thirdly, by suifering neither water nor any other substance colder
than steam to enter or touch it during that time.

" Secondly : In engines that are to be worked wholly or partially by
condensation of steam, the steam is to be condensed in vessels distinct
from the steam-vessels or cylinders, although occasionally communi-
cating with them ; these vessels I call condensers ; and whilst the engines
are working, these condensers ought at least to be kept as cold as the
air in the neighbourhood of the engine, by application of water or other
cold bodies.

" Thirdly : Whatever air or other elastic vapour is not condensed by
the cold of the condenser, and may impede the working of the engine, is
to be drawn out of the steam-vessels or condensers by means of pumps
wrought by the engines themselves, or otherwise.

" Fourthly : I intend in many cases to employ the expansive force of
steam to press on the pistons, or whatever may be used instead of
them, in the same manner as the pressure of the atmosphere is now
employed in common fire-engines. In cases where cold water cannot be
had in plenty, the engines may be wrought by this force of steam only,
by discharging the steam into the open air after it has done its office.

" Lastly : Instead of using water to render the piston or other parts

426 BOY'S PLAYBOOK OF SCIENCE.

of the engines air and steam-tight, I employ oils, wax, resinous bodies,
fat of animals, quicksilver, and other metals in their fluid state.

"And the said James Watt, by a memorandum added to the said
specification, declared that he did not intend that anything in the fourth
article should be understood to extend to any engine when the water to
be raised enters the steam-vessel itself, or any vessel having an open
communication with it."

"About the time he obtained his patent, Watt commenced the con-
struction of his first real engine, the cylinder of which was eighteen
inches in diameter, and after many impediments in the details of the
work he succeeded in bringing it to considerable perfection. The bad
boring of the cylinder, and the difficulty of obtaining a substance that
would keep the piston tight without enormous friction, and at the same
time resist the action of steam, gave him the most trouble, and the em-
ployment of a piston rod moving through a stuffing-box was a new
feature in steam-engines at that time, and required great nicety of
workmanship to make it effectual. While Watt was contending with
these difficulties, Roebuck's finances became disarranged, and in 1773
he disposed of his interest in the patent to Mr. Boulton, of Soho.
As, however, a considerable part of the term of fourteen years, for
which the patent was granted, had already passed away, and as several
years more would probably elapse before the improved engines could be
brought into operation, it was judged expedient to apply to Parliament
for a prolongation of the term, and an Act was passed m 1775 granting
an extensipn of twenty-five years from that date, in consideration of
the great merit of the invention." (Bourne's " Treatise on the Steam-
engine.")

In Fig. 395 (p. 427) we give an illustration of a low-pressure con-
densing engine and boiler of eight-horse power, constructed on the prin-
ciple of Boulton and Watt, as the latter had fortunately united his skill,
learning, originality, and experience with Mr. Boulton, of Soho, near
Birmingham, whose metal manufactory was already the most celebrated
in England.

During the explanation of this eight horse-power engine, the oppor-
tunity may be taken to discuss occasionally the special improvements
effected by Watt. The steam-pipe A. conveys the steam generated in
the boiler B to the slide-valve c, which is kept close to the surface,
against which it works by the pressure of the steam.

Here we notice some of the valuable improvements of Watt in the
admission of steam above as well as below the piston, by which he
increased the power of his engine, and no longer confined it to the force
of the atmospheric pressure. It is also necessary to remark the beauti-
fully simple mechanism of the slide-valve, by which steam is admitted
alternately above and below the piston. Want of. space prevents us
tracing out the gradual improvements effected by Watt, and therefore
we take his invention as it stood in the year 1780, and refer our readers
to Bourne's " Treatise on the Steam-engine" for the full and rninutf-
particulars of the improvements to that date.

WATT'S STEAM-ENGINE.

427

Fig. 395. An eight-horse power condensing steam-engine, after the principle cf
Boulton and Watt, and explained in pages 426 to 432.

428

BOY'S PLAYBOOK OF SCIENCE.

At that time it occurred
to Watt that the conden-
sation of the steam from
the cylinder after it had
done its work, might be
made more perfect if a
perpetual vacuum was
maintained beneath the
piston, while an alternate
steam-pressure and vacu-
um were produced above
it. (Fig. 396.)

Instead of obtaining a
specific advantage the
contrary occurred, and
Watt was obliged in this
case to return to the
ponderous Newcomen
counterweight to balance
the difference in the va-
cuum above and below
the piston, consequently
this form of the cylinder
and valves was abandoned.
The juvenile reader will
perceive in the above
drawing that the superior
arrangement of Watt's
cylinder to that of New-
comen arises from the
steam operating above
and below the piston,
and that the piston

_ __

rod works air-tight in a

Fig. 396. "B Bis the cylinder, j. The piston, a. The , /* /
am-i h stun box *t the to ot

steam-pipe. 6. The regulating or throttle valve, e. The sung ox * e top

eduction and equilibrium single valve, performing the the Cylinder. A most im-

functionsofboth. c. The upper, and /the under, port- r^rta'tit irrmrrwpmpnf in

holes, by which passages only the steam can enter and POrtant improvement 11

pass away. d,j, g. The eduction-pipe by which the steam the employment 01 Steam

passes from above the piston during every returning as a motive power has

stroketothecondenser,aperpetualexhaustionbeingmain- ,

tained beneath it."-From BOUENE on the Steam-engine. been discovered in the

mode of using it "expan-

sively," by which the steam, at a pressure say of sixty pounds on the
square inch, is admitted below the piston, and then cut off and allowed to
expand and drive up the latter without the expenditure of any more
fuel, and leaving, after lifting the piston to a height say of three feet,
an average or mean power of thirty pounds on the square inch.

Returning to the eight-horse condensing engine, D is the steam cylinder
surrounded by a case to prevent the steam cooling and to maintain in the

WATT'S PARALLEL MOTION.

429

cf Watt's Patent,

cylinder the same, or nearly the same, temperature as that of the steam

in the boiler, according to the condition of Art. T ~ f wtt Pnfpnt

quoted at p. 425 of this

book. The same outer

case is apparent around the

cylinder in Fig. 396 ; E, the

piston, which, by stuffing

with hemp or other proper

material, fits the interior of

the cylinder in the most

accurate manner, and pre-

vents the escape of steam

by its sides : e is the piston

rod attached to the parallel

motion. This clockwork-

like piece of mechanism has

often been quoted as one of

the masterpieces of Watt,

and in its greatest perfection Fig 397 A B ig half the beam> A behlg the maill

centre. B E. The main links connecting the piston-
rod F with the end of the beam. G D. The air-pump
links, from the centre of which the air-pump rod is
suspended, c D and E D produce the parallelism,
because c D is moveable only round the fixed centre

c, whilst B D is not only moveable round the centre
D, but the centre itself in the arc described by o D,
and by this action E D corrects the distorting in-
fluence of its own radius. The dotted lines and
letters above enable the observer to see the eflect of

is called the complete parallel
motion, and may be found
in all the best land beam
steam-engines. The object
of the parallel motion is to
cause the piston and pump
rods to move always in

. ,, ,. j f . , letters above enable the observer to see tne etrect

Straight lines, never deviat- the movement of the beam on the parallel motion,
ing to either side. (Fig. 397.)

In the eight horse-power engine shown in page picture, e is also
attached to the piston E, which moves the beam r, and the other end
of this beam, by the connecting rod^, gives motion to the heavy fly wheel
G, by means of the crank h.

H is an eccentric circle on the axle of the fly wheel G, it gives motion
to the slide valve, which admits the steam alternately above and below
the piston. The slide valve and its seat are contained within an oblong
box or case, large enough to permit the easy motion of the valve within
it, and usually forming an enlargement in the course of a pipe.

The valve rod by means of which the valve is opened and shut,
passes out through a stuffing box ; or, instead of such a rod, a valve
of moderate size often has a nut fixed to it, within which works
a screw on the end of an axle which passes out through a bush, and
has shoulders within and without to prevent it from moving lon-
gitudinally, and a square on the outer end on which the key fits that
is used in turning it. I is the throttle valve inside the steam pipe and
lever connected with a governor for regulating the admission of steam
into the cylinder.

Here, again, we pause in the description of our eight horse-power
engine to illustrate more particularly this admirable contrivance of

430

BOYS PLAYBOOK OF SCIENCE.

Watt, which remains to the present day without any material alteration
even in the best steam-engines. (Eig. 398.)

Fig. 398. A. The seat of the throttle valve, z. The valve itself turning on a spindle,
which passes through its centre, a is the steam pipe. ic. The throttle valve lever on
which the rod H, proceeding from the governor, acts. D D. The spindle of the governor
revolving by a belt acting on the pulley d. E E. The balls hung on the ends of the arms,
which cross each other at e like a pair of scissors. When D D is set in motion, the balls fly
out by centrifugal motion, and in doing so draw down the collar into which the lever v
works by means of the links/" h. When F is depressed, of course H rises, and the valve z is
partly closed, and the supply of steam reduced.

In the eight-horse engine already partly explained, k is the cylinder
of an air-pump to remove any air, and the water which condenses the
steam, from the condenser L. There is also the eduction pipe, which
conducts the steam from the cylinder to the condenser L. o is the
pump that supplies cold water to the cistern s, in which the condenser
and air-pump stand, p is a rod connected with the injection cock for
admitting a jet of water into the condenser from the cistern, and which
is continually flowing during the working of the engine. Q Q, cast-iron
columns, four of which support the principal parts of the engine.

We now come to the boiler of the steam-engine, which is of course
of almost equal importance with the engine itself; and the one in our
page-picture is a good type of one of the favourite boilers used by
Messrs. Boulton and Watt, and is called the " Wagon boiler." The
boiler is made of wrought-iron plates rivetted together, and properly
strengthened where necessary; and the steam-pipe A conveys the
steam to the engine. It may be remarked here that the cylindrical

'i'HE BOILER OF THE STEAM ENGINE. 431

boiler consisting of two cylinders, one within the other, of which the
former contains the fire, whilst the furnace-draught circulates outside the
latter, and the space between the two cylinders being filled with water
is the form of boiler which is most highly approved of, and is employed
in the famous economical steam-engines of the Cornish mines.

As the water evaporates in the form of steam, the boiler must be con-
tinually supplied with fresh water, which comes (as will be noticed by
inspecting the page picture) from the hot well s, by means of the hot-
water pump r, attached to the beam F. The water is pumped to the top
of a column rising above but connected with the boiler. There is a
cylindrical float, inside the column of water, connected with the boiler,
suspended ever a pulley by a chain passing to the damper of the furnace.
The damper and float balance each other, and when the water in the
boiler rises to too high a temperature, it causes the float to rise in the
column of water, which lowering the damper or shutter that stops the
draught of the chimney of the furnace T, diminishes the intensity of the
heat, and reduces the formation of steam. On the other hand, as the
temperature diminishes, the float descends and the damper rises, and
permitting more air to rush to the burning fuel in the fire, a greater
quantity of steam is generated.

There is likewise a stone float inside the boiler, for regulating the
supply of water by the feed pipe, or column of water, which latter must
always be sufficiently lofty to press with greater force than the steam
produced in the boiler, or else the power of the steam might, under cer-
tain circumstances, eject or blow out the water from the top of the
column. The stone is suspended by a brass wire which works through
a stuffing box, and is connected with a lever, to which is attached a
heavy counterpoise, so adjusted that when the stone is immersed to a cer-
tain depth in water (according to the principle of a solid body losing weight
in a fluid, explained in the article on specific gravity, page 48), it shall
exactly balance the latter, but when the water sinks in the boiler, and
the stone is no longer surrounded with water, it becomes heavier, and
sinking down opens a conical plug, ground so as to fit water-tight into
a hole in the bottom of the column of water or feed pipe, and directly
the plug opens, water rushes into the boiler; being cut off again as
the stone rises when immersed or surrounded with the proper height of
water. Unless our juvenile readers refer to the article on specific
gravity, they will not understand the otherwise seeming anomaly of a
stone float.

A large hole, called the man-hole, covered with an iron plate and
securely fastened with screws, is provided for the purpose of allowing
the engineer to enter the boiler, when cold, for the purpose of clearing
out the incrustation and dirt arising from the water. To prevent the
incrustation of lime and other earthy matters, it is sometimes usual, on
the principle " that prevention is better than cure" to put a large log of
"logwood" inside the boiler, as it is found that the colouring matter

nn*n/%***l*P YVT OTTO iff o "fl>o Aflf*nv m f i". A l* CA TurAll VnrTTtm QCJ flia ** Pni*" -iv*

curiously prevents the earthy matter, so well known as the
iron " tea-kettles," sticking to the sides of the boiler. Sal

the " fur" in
ammoniac

432 BOY'S PLAYBOOK OF SCIENCE.

and other salts also have the same property, but neither are much used,
the mechanical labour of chipping out the boiler and stopping its work
for a day or so, being preferred to the prevention plan already
described.

There is also a valve opening inwards to prevent the consequences of
a sudden condensation in the boiler, and also a safety valve and lever
with weights opening outwards, and allowing the steam to escape when
it reaches a dangerous excess, and in order to look as it were at the
state of the pressure inside the iron boiler, a proper steam gauge is pro-
vided, also two cocks viz., a water and steam cock, to enable the en-
gineer to ascertain if the water is up to, and does not exceed, the
proper height, because when turned, supposing that all is going on pro-
perly, the former, No. 7, should eject water, the latter, No. 8, steam.

It is truly wonderful, considering the number of safeguards and
warnings provided, that accidents ever happen to boilers, but the
statistics of deaths and annual destruction of property show that science
is powerless, nay, absolutely dangerous, when handled by ignorant and
careless persons. The great fly-wheel, which is usually such an awe-
inspiring and marvellous exhibition of strength in an engine of any great
power, is employed for the purpose of storing up force, so that if any
parts of the engine work indifferently (they all work with resistance), it
shall equalize the wants of the whole, and by its inertia it will continue
to move until its motion is stopped by a resistance equal to its mo-
mentum.

In starting an engine, the engineer may sometimes be observed la-
bouring to move the " fly-wheel," and when once he succeeds in getting
it to move, the resistance of the other parts of the machinery is soon
overcome. Mr. Alderson, in his prize essay, remarks that "it is in the
property which the steam-engine possesses of regulating itself, and pro-
viding for all its wants, that the great beauty of the invention consists,
It has been said that nothing made by the hand of man approaches so
near to animal life. Heat is the principle of its movement ; there is in
its tubes circulation, like that of the blood in the veins of animals,
having valves which open and shut in proper periods ; it feeds itself,
evacuates such portions of its food as are useless, and draws from its
own labours all that is necessary to its own subsistance. To this may
be added, that they are now regulated so as not to exceed the assigned
speed, and thus do animals in a state of nature. That the safety valves,
like the pores of perspiration, open to permit the escape of superfluous
heat in the form of steam. The steam gauge, as a pulse to the boiler,
indicates the heat and pressure of the steam within; and the motion of the
piston represents the action and the power of which it is capable. The
motion of the fluids in the boiler represents the expanding and collapsing
of the heart ; the fluid that goes to it by one channel is drawn off by
another, in part to be returned when condensed by the cold, similar to
the operation of veins and arteries. Animals require long and frequent
periods of relaxation from fatigue, and any great accumulation of their
power is not obtained without great expense and inconvenience. The

THE LOCOMOTIVE STEAM-ENGINE. 433

wind is uncertain ; and water, the constancy of which is in few places
equal to the wants of the machinist, can seldom be obtained on the spot
where other circumstances require machines to be erected. To relieve
us from all these difficulties, the last century has given us the steam-
engine for a resource, the power of which may be increased to infini-
tude : it requires but little room ; it may be erected in all places, and
its mighty services are always at our command, whether in winter or
summer, by day or by night, on land or water ; it knows no intermission
but what our wishes dictate."

The high-pressure steam-engine appears to have been first brought
into general use by Trevethic and Vivian, although the primary notion
of such a modification of the Newcomen or water-engines did not ori-
ginate with them. As the name implies, the steam is brought to a
much higher temperature and pressure than is required in the con-
densing engines of Boulton and Watt. It consisted, in the first place,
of a cylinder open at the top, and provided with a piston. To save
heat the cylinder was fixed inside the boiler, and was provided with a
two-way cock worked by a crank, for the purpose or supplying and
cutting oft 7 the steam. The downward stroke was produced by the
atmosphere, and the steam having done its work, was simply blown away
and wasted in the air.

The engine was provided with a fly-wheel, to which the piston-rod
was at once attached, producing a continuous rotatory movement
without the assistance of the heavier parallel motion, or not and cold
water pumps.

This form of engine was soon adopted for pumping work such as
that of draining fens ; and in 1804 Mr. Richard Trevethic used it for
propelling the first carriage on the Merthyr Tydvil rail or tram way,
and it was then speedily adopted in all the coal districts where the levels
were moderate. Stephenson the elder, succeeded by the late lamented
Robert Stephenson, followed with inventions and improvements of the
locomotive steam-engine ; and we are told in " Once a Week" that,

" One of those best qualified to speak to the latter 's contributions to
the development of the locomotive engine, states that from about five
years from his return from America, Robert Stephensori's attention was
chiefly directed to its improvement. * None but those who accompanied
him during the period in his incessant experiments can form an idea of
the amazing metamorphosis which the machine underwent in it. The
most elementary principles of the application of heat, of the mode of
calculating the strength of cylindrical and other boilers, of the strength
of rivetting and of staying flat portions of the boilers, were then far
from being understood, and each step in the improvement of the engine
had to be confirmed by the most careful experiments before the brilliant
results of the Rocket and Planet engines (the latter being the type of
the existing modern locomotive) could be arrived at/

" Stephenson's time was not, however, so fully taken up during the
above interval as to preclude attention to his other civil engineering
business, and he executed within it the Leicester and Swanoington,

p r

434 BOY'S PLAYBOOK OF SCIENCE.

Whitby and Pickering, Canterbury and Whitstable, and Newton and
Warrington Railways ; while he also erected an extensive manufactory
for locomotives at Newton, in Lancashire, in partnership with the
Messrs. Tayleur. About the middle of the above period, also, the first
surveys and estimates for the London and Birmingham Railway were
framed, leading eventually to the obtaining of the Act. Then followed
the execution of that line, and here Robert Stephenson had an oppor-
tunity of showing his great talent for the management of works on a large
scale. This was the first railway of any magnitude executed under the
contract system ; perfect sets of plans and specifications (which have
since served as a type for nearly all the subsequent lines) were prepared
no small matter for a series of works extending over 112 miles,
involving tunnels and other works of a then unprecedented magnitude.

" Many other railways in England and abroad were executed by him
in rapid succession; the Midland, Blackwall, Northern and Eastern,
Norfolk, Chester and Holyhead, together with numerous branch lines,
were executed in this country by him ; and among railways abroad may
be enumerated as works either executed by him or recommended in his
capacity of a consulting engineer, the system of lines in Belgium, Italy,
Norway, and Egypt, and in France, Holland, Denmark, India, Canada,
and New Zealand.

" Robert Stephenson first saw the light in the village of Willington,
at a cottage which his father occupied after his marriage with Miss
Eanny Henderson a marriage contracted on the strength of his first
appointment as "breaksman" to the engine employed for lifting the
ballast brought by the return collier ships to Newcastle. Here Robert
was born on the 17th of November, 1803. As the cottage looked out
upon a tramway, the eyes of the child were naturally familiarized from
infancy with sights and scenes most nearly connected with his future
profession."

In locomotive steam-engine boilers, the principal object is to generate
steam with the greatest rapidity ; hence the boiler consists of two parts
viz., a square box containing the fire, and around which a thin stratum
of water circulates, whilst the draught for the fire rushes through a
number of copper tubes placed in the second or cylindrical part of the
boiler. By the use of these tubes an immense surface of water is
exposed to the action of the fire, and the steam is not only generated
with amazing rapidity, but is also maintained at a very high pressure.

Within the last few years " superheated steam" has been favourably
mentioned, and employed economically for driving certain engines.
The principle consists 'in first generating steam, and then passing it
through coils of strong wrought-iron pipe, by which it acquires addi-
tional heat, and we have therefore combined in steam the ordinary
Srinciple of evaporation of water with the heated-air principle of
tirling, described at p. 367. We give a drawing of Scott's patent
generator and superheated steam engine. (Fig. 399.)

The apparatus is used as follows : A fire is made in the furnace, and
so soon as a pyrometer connected with that indicates about 800 degrees,

SUPERHEATED STEAM.

435

a little water is pumped into the coils by hand, which is immediately
converted into steam. The donkey engine is then started, which

Fig. 399. Scott's patent generator, or new versus old steam.

maintains the necessary feed of air and water. The generator produces
a copious supply of elastic mixed gaseous vapour, at a pressure of
250 pounds on the square inch ; and it is stated that this engine works
satisfactorily, and is started in the incredibly short time of from three
to five minutes, so that for marine engines in war vessels, expecting to
to be ordered out suddenly, no fuel need be burnt till the moment
required.

Experiments with superheated steam have already been tried most
successfully on board the Peninsular and Oriental Company's ship the
Valetta, whereby it is stated that a saving of thirty per cent, in fuel

436 BOY'S PLAYBOOK OF SCIENCE.

is obtained. The engine to which the superheated steam was adapted
was constructed by Penn and Sons, and the vessel attained a speed of
nearly sixteen knots per hour, and under the most adverse circum-
stances had an abundance of steam to spare.

" A most important experimental improvement in steam machinery
was on Thursday last triea for the first time down the river, on board
the Peninsular and Oriental Company's ship, the Valetta. The actual
nature of the improvement may be described in a few words as con-
sisting of a simple apparatus for working marine engines by means of
superheated steam ; but it is not too much to say that in the success or
failure of this experiment are involved results so important as to affect
materially all ocean-going steamers, and, indeed, steam machinery of all
kinds. To be able to work machinery with superheated steam, means to
command increased power with a thirty per cent, reduction in the con-
sumption of fuel. A principle which can effect such important changes
in the universal application of steam has not remained undiscovered to
the present day. The want of superheated steam has long been felt,
and the enormous comparative advantages of working engines on such
a plan have long been known. A simple and effective working of the
principle, however, has been an engineering difficulty which various ex-
pedients all, however, sufficiently successful to show the value of the
improvement have failed to obviate entirely. This obstacle has now,
we believe, been effectually overcome by Mr. Penn, and the value of the
improvement so clearly demonstrated, that the general application of
the principle to steam machinery of every kind may now be regarded as
certain.

" The idea of working engines by superheated steam, and the immense
saving of fuel and increase of power it would effect, was, we believe,
first started many years ago by Mr. Howard, and subsequently by Dr.
Haycraft. The difficulties, however, in the way of its adoption at' that
time, and the undue estimate of the importance of the principle, pre-
vented those gentlemen from realizing very great practical results. At
a later period the matter was again taken up by an American engineer
Mr. Weatherhead who, however, only superheated a portion of ^he
steam and mixed it with common steam in its way to the cylinders. The
success which attended even this partial application of the process again
revived the idea, and encouraged other engineers to turn their attention
to the subject. The result of these renewed efforts is that several
methods of securing the great economy to be effected by superheating
the steam are now under trial, and there is no doubt that a most im-
portant step in the progress of steam, especially as applied to ocean
navigation, is now at last on the point of being successfully accom-
plished.

" The value of the improvement on the score of economy in working
may be best illustrated oy a single fact namely, that the Peninsular
and Oriental Company's b'ill for coal annually amounts to the enormous
sum of 700,OOOZ., and that by working their vessels with superheated
steam properly applied, it is become almost certain that, without any

SUPERHEATED STEAM. 437

detriment to the machinery, from 28 to 30 per cent, of this gigantic
outlay can be saved. As to the various proposed methods of super-
heating steam, it may be briefly explained, that the conditions required
to be fulfilled are perfect simplicity of arrangement with ready control
over the apparatus ; that it should be so placed as not to be liable to
accidental injury in the engine-room; and that the heat employed for
superheating the steam should be waste heat which has already done its
duty in the boilers and is passing away.

" All these conditions have been most satisfactorily fulfilled by Mr.
Penn in the new engines on board the Valetta, which were tried down
the Thames for the first time on Thursday. The Valetta, as our readers
may remember, was for many years the mail-boat between Marseilles,
Malta, and Constantinople. While thus employed, she had Penn's
engines of 400 horse-power, and to work these up to an average speed
of 15 miles an hour required a consumption of fuel of from 70 to 75
tons of coal per day. At no time was it less than from 45 to 55 tons.
These engines have now been removed to a vessel nearly double the
tonnage of the Valetta, and the latter fitted with engines by Mr. Penn
on the superheating principle. We may mention that, besides this
alteration, the Valetta has been considerably improved. A poop and
forecastle have been added, increased accommodation given to passengers,
and the whole vessel fitted up in the richest style. The saloon is one
of the simplest and handsomest things of the kind we have seen, suffi-
ciently lofty and capacious, and above all, admirably ventilated on the
system which is now being adopted on all sea-going steamers, and the
merit of devising which belongs to Mr. Ilobinson, of the Peninsular and
Oriental Company.

"To return, however, to the engines. Mr. Penn, at the repeated
request of Mr. Allen, the Managing Director of the Peninsular and
Oriental Company, undertook to apply to them the principle of super-
heating, to which his attention had many years before been seriously
directed by Dr. Haycraft. His method of doing this is to place in the
smoke-box of the boiler, through which the hot air from the furnace
first passes, as large a number of small pipes as is consistent with
allowing a free draught from the furnaces. Through these all the steam
from the boilers passes in its way to the cylinders. By this plan an
immense heating surface in the pipes is secured, the steam is in a
subdivided form, so as to be readily acted on, and the waste heat from
the furnace is utilized at the point where its intensity is greatest, and
where the greatest conveniences exist for applying the apparatus. By
means of three ordinary stop-valves, the whole contrivance can be
shut in or off from the engines at pleasure. In ordinary engines steam
leaves the boilers at about 250, but declines from this temperature in
its way to the engines to 230, undergoing from condensation a still
greater and more serious diminution of heat in the cylinders. From
these causes, and also from the immense quantity of waste heat which
escapes through the smoke-box and up the funnels, there has always
been a theoretical loss of steam power amounting to forty per cent., ar

438 BOY'S PLAYBOOK OF SCIENCE.

compared with the coal consumed. It is this loss of power and waste
of heat which the superheating process is intended to prevent, and
which will, of course, allow a reduction of from twenty-eight to thirty
per cent, on the fuel now consumed. By the superheating process the
steam is raised in passing along the pipes in the smoke-box (where the
heat is about 650) from a temperature of 250 to 350, and so enters
the cylinders at 100 in excess of the temperature due to its pressure.
This extra heat is, of course, rapidly communicated to the metals, and
prevents the condensation in the cylinders or other parts of the engines,
which would otherwise, of course, take place. Singularly enough, a
smaller amount of cold water is required to condense the steam at this
high temperature of 350 than when at the ordinary heat of common
steam.

" The trial trip of the Vuletta on Thursday was most satisfactory, not
only as regards the engines, but still more so as to the application for
the superheating process. At the measured mile at the Lower Hope,
near the Nore, the result of repeated runs gave an average speed of
nearly 14|- knots per hour, thus realizing with engines of 260 horse-
power, and a small consumption of fuel, the same rate of speed as had
been gained with her previous engines of 400 horse-power, and a con-
sumption of seventy-five tons of coals per day. The superheating
apparatus evidently effected a most important saving in fuel, but until
an average of many days' working can be obtained, it would be difficult
to estimate the exact amount economized. There seems, however, every
*eason to believe that an average of fourteen knots an hour can be
obtained with a consumption of only from twenty-four to twenty-six
tons per diem. The thermometer during the trial indicated in the steam
pipes an addition to the ordinary temperature of 100, which Mr. Penn
believes to be enough for all practical purposes of superheating. Even
when making from thirty-three to thirty-four revolutions per minute,
and driving the vessel against a strong head wind and tide, it was
impossible to consume all the steam generated, which was blowing off
from both boilers all the trip. The engines are remarkable for the
extraordinary beauty and simplicity of their proportions, qualities well
known in all engines from Penn and Sons, and which, combined with
the strength of the materials and perfection of the workmanship, make
this firm the foremost in the world for machinery of this description.
Both cylinders are oscillating, of sixty-two inches diameter, and with a
stroke of four feet six inches. The paddles are on the feathering
principle, and the boilers of Lamb and Co.'s patent. During the whole
course of the trials, and when going at one time nearly sixteen knots,
there was no perceptible vibration, even at the end of the saloon nearest
to the engines. When it is remembered that the superheating process
which can effect such important results is capable, as we have said, of
application to steam machinery of every kind, including even loco-
motives, it cannot be doubted that the trial of Thursday and its great
success is one of the most important events for the progress of steam
which we have had to chronicle for many years." (The Times, April 23rd
1859.

STEAM VESSELS. 439

Whilst speaking of the application of this somewhat novel condition
of steam, it may be observed that many inventors, who have paid little
or no attention is first principles, have proposed to apply the vapours of
alcohol, ether, or turpentine, instead of that of water ; and they have
founded their notions on the idea that in consequence of the less latent
and sensible heat of alcohol, ether, and turpentine vapour, and of the
small quantity of fuel required to boil them, that they would compete
advantageously with steam. This view of the case, however, is soon
proved to be a very shortsighted one, because the amount of expansion.
has been quite overlooked ; and if it was desirable, by way of com-
parison, to produce a cubic foot of steam, alcohol, ether, or turpentine,
the steam would stand first for cheapness, and would require the least
quantity of fuel to produce it, so that if the more expensive of com-
bustible liquids could be obtained for nothing, it would still be cheaper
to employ water.

Latent heat, or
equivalent for fuel.

A cubic foot of water yields 1700 cubic feet of steam . = 1000
A cubic foot of alcohol produces 493 cubic feet=457.

Then, by rule of proportion, 493 cubic inches : 457

:: 1700: . . . . ; . . . 1575

A cubic foot of ether yields only 212 cubic feet of

vapour=312, and 212 : 312 :: 1700 : . . . . . 2500
A cubic foot of the oil of turpentine affords 192 cubic

feet of vapour=183, and 192 : 183 :: 1700 : . . . 1620

It will therefore be seen that water, when converted into steam,
expands eight times as much as sulphuric ether, and nearly three times
and a half as much as alcohol.

The application of steam for the purpose of propelling vessels has
already been mentioned in connexion with the Spanish inventor, Blasco
de Garay, in the year 1543. The first patent in this kingdom granted
for that' purpose was that of Mr. Jonathan Hull in 1773. In 1787,
Mr. Miller tried a number of important experiments in the propulsion
of vessels by steam-engines, and it would appear that Lord Cullen
advocated his ideas, and endeavoured to secure the co-operation of the
great firm of Boulton and Watt, who, occupied with their land engines,
could not pay attention to it ; and twenty years elapsed after the reply
of Watt to Lord Cullen's application, before the real novelty appeared
of a first successful experiment with a steam-boat in " the open sea,"
by Henry Bell, in 1811. A picture of this boat, called the Comet, which
was afterwards wrecked, is shown at p. 418. Henry Bell's novelty was
success, and he is fairly entitled to the merit of first introducing steam
navigation into Europe.

In 1811, the public stared with mingled astonishment and satisfaction
at the realization of that which was called a fable. Only forty-seven
years afterwards another generation spontaneously exhibits the liveliest
interest in the gigantic private speculation of the Great Eastern. Henry

440

BOY S PLAYBOOK OF SCIENCE.

Bell's vessel of 1811 was 40 feet keel, 10 feet 6 inches beam, and
25 tons burthen ! The Great Eastern of 1859 is 692 feet long, 83 feet
wide, GO feet deep, and 24,000 tons burthen ! ! The whole nation with
one voice wish her God speed in her projected voyage across the
Atlantic, as the embodiment of that great goodwill which every generous-
hearted Englishman feels towards the enlightened free-born people of
the United States.

Should the author's little vessel, with its humble freight of science,
meet with the approbation of his good friends, the boys and their
advisers, another and another, if health permits, shall be launched or
their benefit. Vale.

THE END.

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