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B05TON PUBLIC LIBRARY.

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PHILOSOPHICA L

TRANSACTIONS,

OF THE

ROYAL SOCIETY

O F

LONDON

VOL. LXXV. For the Year 1785.

Sa^m/f .

LONDON,

tOtr> BY LOCKYER DAVIS, AND PETER ELMSLYj
PRINTERS TO THE ROYAL SOCIETY.

MDCCLXXXV,

i....i.^3?mJ■

AOAM8/03.I3

t i" ]

ADVERTISEMENT.

TH E Committee appointed by the Royal Society to direcl: the pub-
lication of the Philofophical Tranfa^lom, take this opportunity to
acquaint the Public, that it fully appears, as well from the council-books
and journals of the Societ}^, as from repeated declarations which have
been made in feveral {ovmcr Tranfactions, that the printing of them was
always, from time to time, the fmgle act of the refpeftive Secretai-ies, till

x

the Forty-feventh Volume : the Society, as aBody, never interefling them-
felves any further in their publication, than by occafionally recommending
the revival of them to fome of their Secretaries, when, from the particular
circumftances of their affairs, the TraJtfadions had happened for any
length of time to be intermitted. And this feeras principally to have
been done with a view to fatisfy the Public, that their ufual meetings
were then continued for the improvement of knowledge, and benefit of
mankind, the great ends of their firfl: inftitution by the Pvoyal Charters,
and which they have ever fmce (leadily purfued.

But the Society being of late years greatly inlarged, and their com-
munications more numerous, ft was thought advifable, that a Committee
of their members mould be appointed to reconfider the papers read be-
fore them, and feleft out of them fuch, as they iliould judge raoft pro-
per for pubHcation in the -future Tranfadions ; which was accordingly
done upon the 26th of March 1752. And the grounds of their choice
are, and will continue to be, the importance and fingularity of the fub-
jefts, or the advantageous manner of treating them ; without pretending
to anfwer for the certainty of the fafts, or propriety of the reafonings,
contained in the feveral papers fo publifhed, which mult ftill refl on the
credit or judgment of their refpeftivc authors.

A 2 fe

C iv ]

It is likewife necclTary on this occafion to remark, that it is an cfta*
bliihed rule of the Society, to which they will always adhere, never tO'
give their opinion, as a Body, upon any fubjeft, either of Nature or Arty
that comes before them. And therefore the thanks, which are fre-
quently propofed from the chair, to be given to the authors of fuch pa-
pers as are read at their accuflomed meetings, or to the perfons through
whofc hands they receive rhem, are to be confidered in no other light
than as a- matter of civility, in return for the refped fhewn to the Society
by thofe communications. The like alfo is to be faid with regard to
the feveral projefls, inventions, and curiofities of various kinds, which.
^re often exhibited to the Society ; the authors whei^eof, or thofe wh»
exhibit them, frequently take the liberty to report, and even to certify
in the public news-papers, that they have met with the higheft applamfe
and approbation. And therefore it is hoped, that no regard will here-
Efter be paid to fuch reports, and public notices ; which in fome in(lanc§3
have been too lightly credited, to the diflionour of the Society,. .

■*.i'Ti ■w^*»»— »ni*»wii>*i4i>M«*»«Mifc<— fc^**

CONTENTS

O F

VOL. LXXV. Part I.

L yf^ Account of an artifcial Spring of IVater^ By Eraf-
mus Darwin, M. D. F, R, S, page i

II. An Account of an Englifh Bird of the Gejius Motacllla,

fuppofed to be hitherto unnoticed by Britifli Ornithologijis ;

obferved by the Rev. John Lightfoot, M. A. F. R. S. In a

Letter to Sir Jofeph Banks, Bart, P. R. S. p. 8

m. An Account of Morne Garou, a Mountain in the Ifand of
St. Vincent, with a Defcription of the Volcano on its Summit.
In a Letter from Mr. James Anderfon, Surgeon, to Mr.
Forfyth, His Majejlfs Gardener at Kenfington ; communi-
cated by the Right Honourable Sir George Yonge, Bart.
F. R.S. p. i6

IV. A Supplement to the Third Part of the Paper on the Sum-
mation of infinite Series ^ in the Philofophlcal Tranfadlions

for
2

VI CONTENTS.

for the Tear 1782. By the Rev. S. Vince, M, A;
communicated by Nevii Malkelyne, D. D. F, R. S, and
Aftronomer Royal. P* 32

V. Defcrlption of a Plant yielding Afa foetida. In a Letter
from John Hope, M. D. F, R. S. to Sir Jofeph Banks,

Bart, P, R,S, p. 36

VI. Catalogue of Double St^rs. By William Herfchel, Ffq.
F, R. S, p. 40

VII. Obfervations of a new Variable Star, hi a Letter from
Edward Pigott, £/^. to Sir H. C. Eiiglefield, Bart.F, R, S.
and A. S. p. 127

VIII. Aftronomical Obfervations, In two Letters from M,
Francis de Zach, Prof ef or of Mathematics^ and Member of
the Royal Academies of Sciences at Marfeilles, Dijon, and
Lyons, to Mr. Tiberius Cavailo, F. R, S, p. 137

IX. Obfervations of a new Variable Star. By John Goodricke,
Efq. ; communic-ated by Sir H. C. Englefield, Bart, F. R. S^
and A. S. p. j 53

X. On the Motion of Bodies affeSled by FriBion. By the Rev.
Samuel Vince, A. M, communicated by x^nthony Shepherd,
JD. Z). F. R. S. Plumian Profejfor of Aftronomy and experi^
mental Phllofophy at Cambridge. p. 1 6^

XI. Obfervations and Experiments on the Light of Bodies in a
State of Combujlion. By the Rev, Mr, Morgan ; communicated
by the Rev. Richard Price, LL.D. F.R.S, p. 190

XII. On the Cnnfru5iion of the Heavens, ^j William Herfchel,
Ffq, F.P^.S. p. 213

XIII. Remarks on fpecifc Gravities taken at different Degrees of
Heat, and an eafy Method of reducing them to a common StaU'
Jard, i?y Richard Kirwan, E/q. F.R.S. p. 267

Q ' ' XIV,

CONTENTS. vli

"XIV. Elecirical Experiments made m order to afcertam the non^
condudling Power of a perje^ Vacuiwi^ &c. By Mr, Wil-
liam Morgan ; communicated by the Rev. Richard Price,

LL,B. FM.S,

272

XV. Experiments and Ohfervations relating to Air afid Water,.
By the Rev, Jofcph Prieilley, LL,D, F.R.S. p. 2yg,

THE Prefident and Council of the Royal Society adjudged,
for the Year 1784, the Medal on Sir Godfrey Copley's

Donation, to Edward Waring, M. D. Lucafian Profeflbr
of the Mathematics at Cambridge, for his Mathematical
Communications to the Society,

PHILOSOPHICAL

TRANSACTIONS.

L Aft Account of an artificial Spring of Water, By Bfafmus.

Darwin, M. D. F. R. S.

Read November 4, 1784.

c

To the Prefident and Fellows of the Royal Society.

iNTLEMEN, Derby, July 16, 1784.

ONFIDENT that every atom which may contribute to
increafethe treafury of ufeful knowledge, which you are
fo fuccefsfuUy endeavouring to accumulate, will be agreeable
and interefting to the Society, I fend you an account of an
artificial fpring of water, which I produced laft fummer near
th-e fide of the river Darwent in Derby, i-^,^ 3^-^ ],a-t .

VoL.LXXV. B ' Near

i £)r\ T)ARWrN*S^^CCCU/lt of

Near my hftufe was an old welj, about one hundred yards
from the river, and about- four yards deep, which had been
many years difufed on account of the badnefs of the water,
which I found to contain much vjitriohc acid, with, at the
fame time, a fliglit fulphureous fmell and tafte ; but did not
carefully analyle it. The mouth of tliis well was about four
feet above the furface of the river ; and the ground, through
which it was funk, confiited of a black, ioofe, moid: earth,
\vhich appeared to have been very lately a morafs, and is now
covered with houfes buiit upon piles. At the bottom was
found a bed of red marl, and the fpring, which was fo ilrong
as to give up many hogfheads in a day, oozed from between
the morafs and the marl : it lay about eight feet beneath the
furface of felie river, and the Water rofe within two feet of the
top of the well.

Having obferved that a very copious fpring, called Saint
Alkmund's well, rofe out of the ground about half a mile
higher on the fame lide of the Darwent, the level of which I
knew by the height of the intervening wier to be about four or
£ve feet above the ground about my well ; and having obferved,
that the higher lands, at the diftance of a mile or two behind
thefe wells, confifted of red marl like that in the well ; I
concluded, that, if I fhould bore through this flratum of marl,
I might probably gain a water fimilar to that of St. Alkmund*s
well, and hoped that at the fame time it might rife above the
furface of my old well to the level of St. Alkmund's.

With this intent a pump was firft put down for the
purpofe of more eafdy keeping dry the bottom of the old well,
and a hole about two and an half inches diameter was then
bored about thirteen yards helow the bottom of the well,
till feme fand was brought by the auger. A wooden pipe,
4 • ' which

iin at'lifichil Spring of W'aier. |

which was previoufiy cut n\ a coaical form at oWe end, and
armed v^ith an iron ring at the other, was driven into the top of
this hole, and ftood up about two yards from the bottom of
tlie well, and being furrounded with well-rammed ckiy, the
new water afcended in a fmall ftream through tiie wocden

)e.

Our nextroperation was to build a wall of clay againil: the
morally lidos of the well, with a wall of well'bricks inter-
nally, up to the top of it. This completely flopped out every
drop of the old water ; and, on taking out the plug which
had been put in the wooden pipe, the new water in two or
three days rofe up to the top, and flowed over the edges of the
welk

Afterwards, to gratify my curiofity in feeing how high the
new fpring would rife, and for the agreeable purpofe of pro-
curing the water at all times quite cold and frefh, I directed
a pipe of lead, about eight yards long, and three-quarters of
an inch diameter, to be introduced through the wooden pipe
defcribed above, into the ftratum of marl at the bottom of the
well, fo as to fliand about three feet above the furface of the
PTound. Near the bottom of this leaden pipe was lewed, be-
tween two leaden rings or flanches, an inverted cone of ftiff
leather, into which fome wool was fluffed to ftretch it out, fo
that, after having pafled through the wooden pipe, it might
completely till up the perforation of the clay. Another leadeiy
ring or flanch was foldered round the leaden pipe, about tv/o
yards below the furface of the ground, which, with fome dou-
bles of flannel placed under it, was nailed on the top of the
wooden pipe, by which means the water Vv^as perfedly pre-
cluded from rifing between the wooden and Uie leaden pipes.
' ' B 2 This

4 Dr. Da-kw^i^^s Account of

This being accomplifhed, the bottom of the well remained
quite dry, and the new water quickly rofe about a foot above
the top of the well in the leaden pipe ; and, on bending the
mouth of this pipe to the level of the furface of the ground,
about two hoglheads of w^ater tiowed from it in twenty- four
hours, which had hniilar properties with the water of St. Alk-
niund's w-ell, as on comparifon both thefe waters curdled a
folution ot fonp in fpirit of wine, and abounded with calca-
reous earth, which was copioufly precipitated by a folution of
fixed alkali; but the new water was found to poflHs a greater
abundance of it, together with numerous fmall bubbles of
aerial acid or calcareous gas.

The new water has now flowed about twelve months, and, as
far as I can judge, is already increafed to almofl: double the quan-
tity in a given time ; and from the rude experiments I made, I
think it is now lefs replete with calcareous earth, approaching
gradually to an exad correfpondence with St. Alkmund's well,
as it probably has its origin between the fame ftrata of earth.

As many mountains bear Inconteftible marks of their having
been forcibly raifed up by fome power beneath them ; and
other mountains, and even iflands, have been lifted up by fub-
ferraneous fires i^ our own times, we may fafely reafon on the-
fame fuppolition in refpe£t to all other great elevations of
ground. Proofs of thefe circumftances are to be feen on botli
tides of this part of the country ; whoever will infpe<£l:, with
the eye of a philofopher, the lime-mountain at Breedon, on
tlie edge of Leicefterfhire, will not hefitate a moment in pro-
iioijncing, that it has been forcibly elevated by fome power
beneath it ; for it is of a conical form, with the apex cut off,

and

an artificial Spring of Water. ^•

and the llrata, which compofe the central parts of it, and
which are found nearly horizontal in the plain, are raifed
almofl perpendicularly, and placed upon their edges, while
thofe on each fide decline like the furface of the hill ; fo that
this mountain may well he reprefented hy ahur made hy forc-
ing a bodkin through feveral parallel fheets of paper. At Rou-
ter, or Eagle-ftone, in the Peak, feveral large maflTes of grit-
ftone are feen on t'^e fides and bottom of the mountain, which
by their form evince from what parts of the fummit they were
broken off at the time it was elevated ; and the numerous loofc
flones fcattered about the plains in its vicinity, and half buried
in the earth, muft have been thrown out by explofions, and
prove the volcanic origin of the mountain. Add to this the.
vaft beds of toad-ftone or lava in many parts of this countyv
fo accurately defcribed, and fo well explained, by Mr. Wpiite-
HUKST, in his Theory of the Formation of the Earth.,

Now as all great elevations of ground have been thus raifed
by fubterraneous fires» and in a long courie of time their lum-
mits have been worn away, it happens, tl^at fome cf the mors
interior jftrata of the earth are expoled naked on the tops cf
mountains ; and that, in general, thofe flrata, which lie up-
permoft, or neareft to the fummit of the mountain, are th«
lowefl in the contiguous plains. This will be readily con-
ceived if the bur, made by thrufting a bodkin, through feveral
parallel Iheets of paper, had a part of its apex cut off by a pen-
knife, and is fo well explained by Mn Michell, in an inge-
nious paper on the Phicnomena of Earthquakes, publifiied a few.
years ago in the Philofophical Tranfaclions.

And as the more elevated parts of a country are fo much
colder than the vallies^ owing, perhaps, to a concurrence of

tv;o

Z T)r. Darwin's Account of

two or three caufes, but particularly to the lefs condenfed flate
■of the air upon hills, which thence becomes a better conduclor
of heat, as well as of eleclricity, and permits it to efcape the
fader; it is from the water condenfed on thefe cold furfaces of
mountains, that our common cold Iprings have their origin ;
and which, fliding between two of the ftrata above defcribed,
defcend till they find or make themfelves an outlet, and will in
.confequence riie to a level with the part of the mountain where-
they oripinated. And hence, if by piercing the earth you gain
a fpring between the f^cond and third, or third and fourth
flratum, it mull: generally happen, that the water from the
loweff ftratum will rife the higheff, if confined in pipes, be-
'raufe it come6 originally from a higher part of the country in
its vicinity.

I'he increafing quantity of this new fpring, and its increafing
purity, I fuppofe to be owing to its continually diflblving a
part of the earth it pallies through, and hence making itfelf a
wider channel, and that through materials of lefs folubility.
Hence it is probable, that the older and ftronger fprings are
generally the purer ; and that all fprings were originally loaded
with the foluble impurities of the llrata, through which they
tranfuded.

Since the above- related experiment was made, I have read
with pleafure the ingenious account of the King's wells at
Sheernefs, in the laft volume of the Tranfadions, by Sir
Thomas Hyde Page, in which the water rofe three hundred
feet above its fource in the well ; and have alfo been informed,
that in the town of Richmond, in Surrey, and at Infhlp near
Frefton in Lancafhire, it is ufual to bore for water through
a lower flratum of earth to a certain depth ; and that when it

is

an art ificial Spring of Water, y-

is found at both thofe places, it riles fo high as to overflow the
furface of the well : all thefe fa6ls contribute to eftabliili the
theory above-mentioned. And tliere is reafon to conclude,
that if fimilar experiments were made, artificial fprings,
rifing above ground, might in many places be thus produced
at fmall expence, both for the common purpofes of life,
and for the great improvement of lands by occafionally water-
ing them.

[ 8 ]

Ti. An -Acmmt of an Englifli Bird of the Genus Motacilla,

fuppofd to be hitherto tmnotked by Britifh OrnlthrAogijls ;

ohfervsd by the Rev. John Lighttbot, M. A. F. R. S. In. a.

Letter to Sir Joieph Banks, Bart. P. R. S. -^ ^

Rejid November 1 8, i}-84.

S I R, Uxbridge, Nov. 20, 1783.

AS every difcovery In natural hiftory is efleemed worthy the
notice of that Society which was inftituted on purpofe to
iniprove natural knowledge, I have taken the liberty to fend
you a defcription and drawing of a bird which haunts the
reeds of the river Coin, in the neighbourhood of Uxbridge,
and which feems to have hitherto efcaped the notice of writers
on Britifli Ornitiiology ; and therefore fome account and de-
fcription of it will not, I trud, be unacceptable to the Society
over which you fo laudably prefide.

The neft and eggs of the bird I am about to defcribe firft
attra£ted my attention, and led to the difcovery of the bird
itfelf. They were repeatedly brought by a fifherman on the
Uxbridge river, in the parifh of Denham, to her grace the
Duchefs DowMger of Portland, who firfl communicated them
to me. They were fuppofed by the fiflierman to belong to the
Sedge-bird of Pennant, or Motacilla Salicaria of LiNNiEUS ; but
being well acquainted with the neft and eggs of this, I was very
fure he was miftaken, though he adually produced this bird as
the true proprietor of the fubje£ls in queftion. The flru£ture
and pofition of the nefl: having a lingular appearance, and both

that

Mr, Lightfoot's Account of a new Englifh Bird, ^
that and the eggs belonging to a bird unknown to me, I became
defirous of finding out the fecret architeft, and to that end made
life of fuch means as I thought moft likely to promote the
difcovery.

In a fliort time my expectations were gratified ; for on the
26th day of July, 1783, intelligence was brought me, that
fuch a neft as I wanted was found. I had given pre-
vious direction, that it fhould not be difturbed before I had
feen it. Upon examination, I inflantly perceived it to be of
the fame kind and ftrudure with that under enquiry, contain-
ing two eggs, and two young ones juft excluded from the fheli.
One of the old birds was fitting at this time upon the neft,
which a perfon in company attempting to feize, it flew at him
with fo much refentment and acrimony, as to draw blood from
the hand that dared to molefl its inllindive operations. Both
the parent birds continued hovering about their neil: with much
watchful care and anxiety, while I made feveral attempts to
take them alive ; but, finding all endeavours in vain, left I
ihould lofe the opportunity of examining them w'ith accuracy,
I at length, with relu6lance, caufed them to be fliot. From
thefe fpecimens the following defcriptions were made, which,
with an accurate drawing of one of them, together with its
nefl and egg, are humbly fubmitted to your notice.

From the generic chara«£lers delivered by Linnaeus, our bird
muft evidently be reduced to the family of his MotacUla^ for it
has a weak, flender, fubulate bill, almoft ftraight ; the man-
dibles nearly equal; the noftrils oval and naked, or not covered
with briftles ; the tongue lacerated at the extremity ; the legs
flender ; the toes divided to the origin, except that the exterior
one is joined, at the under part of the lafl joint, to the middle
toe ; the claws of nearly equal length.

Vol. LXXV. C The

lo 34^* Lighttoot's Account of

? The male and female have the fame coloured plumage, fo
that one defcription will ferve for botli. They differ a little in
fze, but their external appearance is the fame. They are both
larger than the Pettychaps defcrlbed by Willougiiby ; fmaller
than the JVhite-throat, and nearly of the fame frze with the
JViUow-wren ; but to be more particular.

The cock-bird weighed, when jufl: killed, exa6lly feven
pennyweights and nine grains ; the hen fix pennyweights and
nine grains, or one pennyweight lefs.

The males meafured, from tip to tip of the extended wings,
feven inches and a half; the female fix and three-quarters.

From the end of the bill to the extremity of the tail, the,
cock meafured five inches and a half; the hen only five
inches.

The bill in both meafured half an inch, which is longer
in proportion than in mofl: of this genus. The upper mandi-
ble is of a dark horn colour, (lightly incurved near the extre-
mity, with a minute indenture on either fide near the point ;
the lower is pale red or flefh- coloured, with a fhade of yellow ;
the infide of the mouth deep orange-coloured ; the tip of the
tongue cloven and ciliated ; thenofirils oval, and deftitute of a
briftly covering; but at the bafe of the upper mandible, on
either fide, near t4ie angle of the mouth, arife three fliort ^'/-
brid'cs pointing downwards, black at their fummits, white at
their bafes ; a circumfiance common to many others of this
genus. The /m of the eye is olive-brown; the pupil'black.
The ihort feathers of the orbits or eve-laflies are of a dirtv
white colour. From the corner of each eye to the nofiril is a
broad ftroke or band of tawny-white feathers, lying over each
other, and running narroweft towards the bill; this affords an
excellent mark to diftinguifli the fpecies.

The

^ new Englifh Bird, j, i

The feathers of the head, neck, back, coverts of the wings and
rump, are of an oUve-brown, with a flight thige of green. The
quill and tail feathers are all of a darker hue, or fimply bro'vvn ;
their outwaid. edges of a paler fhadc. The tail is two inches
lonp-, {lightly cuneated, the middle feathers being a little loxiger
than the reft, the others gradually fhorter ; all of one uniform
dun-brown colour edged with paler brown, and a little we4ge-
fhaped at their ends.

The chin is white ; the throat, breail, belly, and parfes about
the vent, are white with a flight fliade of buff or tawny -,
but all thefe feathers (as in feveral others of this genus) when
blown afnnder, or clofely examined, are found to have their
tafe or lower half black, except the fliafrs, which are
.white throughout.

The rid2:e and under coverts of the exterior ang:le of the
wing are of a yellowifli- tawny colour, as are alfo the feathers
of the thighs ; but thofe of the knees are a fliade darker, or a
.pale yellowifli brown.

The legs arc a light olive ; the foles of the feet bright yel-
low, with a tinge of green, which foon fades after the bird Is
dead. The inftep is covered with feven large imbricated fcales,
snd five fmaller on the toes, as in others of the genus. The
toes fland three before, and one behind ; the claws are nearly
of equal length and curvature; but the hindmofl: is thick eft
and fl:rongefl:.

From the foregoing remarks it is evident, that the bird men-
-tioned is a fpecies of MotacUla^ which, as I can fipd no fuch
defcribed by any fyflematic writer, I fliali- venture to name,
after the Lin NiE AN manner,

Motacilla {arimdmacea) fupra olivaceo-fufca, fubtus aiblda,
Joris et o;-biti^ fufco-albefcentibus, angulo carpi fubtus

C 2 luteo-

12 Mr. Lightfoot's Account of

]uteo-fulvo, Cauda fubcuneata fufca, plantis luteo
virefcentibus.

In regard to fynonyms, the only author I can find who can
be fufpedted of having noticed this bird is Sepp, who, in a late
fplendid work, in the Dutch language, intituled, Nederlandfche
Vogelen ffol. chart, max,) p.. i o i . has defcribed and figured a bird,
under the name of Turdus arundinaceus minimus^ called in Hol-
land Karrahietje^ which in many refpe6ls agrees with our bird ;
but as the colour of the wings in that figure is made a reddifti
brown, inftead of an olive-brown, and the tawny-white Lora
(a moft eifential chara6ler to diftinguifli the fpecies) are not at
all exprefled ; and the eggs are made to be of a pale-blufli colour
with dark fpots, inllead of a dirty-white with olive fpots ; I
cannot pronounce for certain, that the bird there intended by
that writer is the fame which we have now defcribed ; though,
if fome allowance be made for ill- colouring and other omif^
fions, it may pofi^bly have been defigned for the fame fpecies.

As we have already a bird, called in Engliih the Willow^
*ivren ; ours, being nearly of the fame fize and fliape, as well as.
the fame genus, may, from its haunts, not improperly be
denominated the Reed- wren.

It frequents the banks of the river Coin near Uxbridge, as
far as from Harefield-Moor down to Iver, about the fpace of
five miles, and very probably mofl: other parts of the fame
river, though not as yet obferved.

It is alfo certainly found in the neighbourhood of Dartford
in Kent, from whence a nefi: and eggs were communicated by
the ingenious Mr. Latham of that place, but without know-
ledge of the bird to which they belonged ; fo that there is
little doubt but that it may be found in many parts of the
kingdom.

Its

a fiew Engllfh Bird, 12

Its food is infects, at leaft in part, for I obferved it catching
flies. It hops continually from fpray to fpray, or from one
reed to another, putting itfelf into a ftooping pofture before it
moves. I heard it make no other than a fmgle note, not un-
like the found of the word peep, uttered in a low plaintive
tone; but this might probably be only a note of difrrefs, and
it may have, perhaps, more pleafing and melodious ones at
other times, with which I am unacquainted.

The neft of tliis bird is a mod: curious ftrudlure, unlike that
of any other I am acquainted with, enough to point out the
difference of the fpecies, if every other charader was wanting.

It may not be amifs here to obferve, that there is fuch a
manifeft diverfity in the materials, locality, and formation of
nefts, and fuch variety of colours in the eggs of many birds
(in other refpeds hard to be diftinguiflied), that it is pity this
part of Ornithology has not been more attended to. I am well
convinced, that as many fpecies of i?ife5is, nearly allied to each
other in colours and (hape, and reputed loht only varieties, are
frequently, from a due attention to their larv{£ (which are often
extremely different), difcovered to be fpecies totally dijlinSl ; fo,
amongft birds of fimilar genus and feather, their true differences
may be often found by carefully obferving their nefts and eggs,
when other charafters are fo minute, in the birds themfelves,,
as to be diftinguifhed with difficulty. By experience I have
found this to be remarkably verified in feme of the Lark kind.

But to return to the neft I was going to defcribe. It is com-
pofed externally of dry ftalks of grafs, lined, for the mofl
part, with the flowery tufts of the common reed, or Arundo
vallatoria, but fometimes with fmall dead graffes, and a few
black horfe-hairs to cover them. This neft is ufually found

fufpcnded-

14 Mr, luiG-ii'vvoo'v^s Account of

fufpended or faftened on; like a hammock, between three or
four ftalks of reeds, below the panicles of flowers, in fuch a
manner that the ftalks run through the fides of the ncfts at
nearly equal diftances ; or, to fpeak more properly, the neft
is tied on to the reeds with dead grajs^ andfometimes (as being
more eligible when it can be had) even with thread and pack-
thread, emulating the work of a fempftrefs, as was the cafe of
the nefl exhibited in the drawing. The bird, 'however, though
generally, does not always confine her building to the fupport
of reeds ; fometimes fhe fixes it on to the branches of the
Water-dock; and, in one inftance only (that here delineated),
it was found faftened to the trifurcated branch of a Syringa
bufh, or Fhiladeiphus, growing in a garden hedge by the rivet
fide.

She lays commonly four eggs ; the ground colour a dirty
white, flained all over with dull olive-coloured fpots, but
chiefly at the greater end, where are generally feen two or
three fmall irregular black fcratches ; but thefe are fometimes
"fcarcely vifible.

I mufl not omit, that both the nefl and eggs which I have
now defcribed, whether defigned for the fame Or not, are well
expreffed by Sepp, in the work above cited, under the article
'Turdus Calamoxenus^ or Rietvinck, p. 97, ; but as the bird there
reprefented is evidently the Motacilla Sylvia^ Lin. or common
White-throat (which is known to make a very different neft), I
am inclined to believe, that the author, by miflake, placed a
bird and nefl in the fame plate which do not belong to each
other.

1 have reafon to think, that the bird I have been charac-
terizing is a bird of migration; for the inhabitants on the fides

2 of

/'/«/,... rrniLrlMLXXV ■Ub.\.,,. (4.

a new Englifli Bird, 1 5

of the Coin do not recollea ever to have feen It In the winter
months ; and its food being infeds, it is probable, it muft be
oblioed to fhift its quarters for a warmer climate at the ap-
proa'^ch of a fevere feafon ; but this at prefent is only matter of
Gonjeaure, and not certainty.

I am, &;c,

JOHN- LIGHTFOOT,

ifi :iV'

[ '6 ]

fit. An Acpoiint of Morne Garoii, a Mountain in the IJland ef
St. Vincent, with a Defcription of the Volcano on its Summit,
In a Letter from Mr, James Anderfon, Surgeon^ to Mr,
Forfyth, His Majejlfs Gardener at Kenfington ; cofnmuni"
cated by the Right Honourable Sir George Yonge, Bart,
F, R, S,

Read November i8, 1784.

THE many ridges of mountains which interfe^l this ifland
in all direction s, and rife in gradations, one above the
other, to a very great height, with the rivers tumbling from
their iides over very high precipices, render it exceeding difficult
to explore its interior parts.

The moll: remarkable of thefe mountains is one that termi-
nates the N.W. end of the ifland, and the higheft in it, and
has always been mentioned to have had volcanic eruptions from
it. The traditions of the oldefl inhabitants in the ifland, and
the ravins at its bottom, feem to me to vindicate the aflertion
As I was determined, during my flay in the ifland, to fee as
much of it as I could ; and as I knew, from the altitude of
this mountain, there was a probability of meeting with plants
on it I could find in no other part of the ifland ; I fliould
have attempted going up if I had heard nothing of a volcano
being on it. But viewing the mountain at a diftance, the
ilrudture of it was different from any in the ifland, or any I had
feen in the Weil Indies. I could perceive it divided into many
3 different

Mr, Anderson's Account of a Volcanic MouniaiTi^ Scq, i 7

different ridgeSj feparated by very deep chafms, and its fum-
mk appeared quite deflitute of any vegetable produdtiou. On
examining fe vera! ravins, that run from the bottom a great way
up the mountain, I perceived they were quite deftitute of water,
and found pieces of puniice-flone, charcoal, feveral earths and
minerals, that plainly indicated there muft be fome very lingu-
lar place or other on fome part of the mountain. I alfo recol-
levied a ftory told by fome very old men hi the ifland, that
they had he^rd the captain of a (hip fay, that between this
ifland and St. Lucia he faw, towards niaht, flames and fmoke
ifluing from the top of this mountain, and next morning his
decks were covered with aflies and fmall ftones. This, you
may readily imagine, was excitement enough to examine it, if I
poffibly could ; but I was much difcouraged upon being told,
it was impofiible to gain the fummit of it; nor could I get
either white men, Carribbee, or Negro, that would undertake
to conduct me up for any reward I could offer ; nor could I get
any information relative tq it, But as difficulty to attain in-
hanc€s the value of the obje<£l, fo the more I was told of the
impoffibility of going up, the more was I determined to
attempt it»

After I had examined thetjafis of it, as far as I could for the
fea ,aud other mountains, to find the moft probable place to
commence my journey, I obferved an opening of feveral large
and dry ravins, that feemingly ran a great way up ; but I was
not fure if they wera not interfe£led by fome rocks or preci-
pices I could not get over. I came to Mr. Maloune's, about
a ofiile diffant from the mountain, but the nighefi: houfe to it
I could fi:ay at all night. Here I met with a friendly recep-
tion and great hofpitality. After communicating my inten-
tions to him, he tol<i me, he would give me every afliffance
Vol. LXXV. D he

18' Mr. Anderson's Account of a

he could, by fending fome trufty negroes with me, and wiihed
he was able to go with me himfelf. This was a kind offer to
me, in my then fituation, as negroes were what I only wanted,
having only one boy belonging to Dr. Young with me. I
kneWj if I had great difficulties in the woods, he and I both
ihould be inadequate to the talk, as in a fliort time we fiiould be"
io wearied as to be unable to proceed : from what I had feen of
the mountain, I knew I muft be under the neceflity of carrying-
water with me; and from the great diftance- to the top, and
obftru6lions we might naturally expedt, I -fhould -at leaft
require two days to accomplifh it. , ■ i

Yij examining the fide of the mountain towards me with a-
good glafs, I imagined I faw two ridges Imight get up. I per-
ceived they were covered great part of the way W'ith. thick
wood ; yet 1 hoped, with a little cutting, I fliould be able tO'^
fcramble through them. I appointed next mornings to begin
my route by one of thefe ridges.

February 26, 1784, I left Mr. Maloune's about fun- rife,
with two ftout negroes and Dr. -Young's boy ; each of us hav--
ihg a good cutlafs, as well to-clear our way through the woods,
as to defend us in cafe we fliould be attacked by Caribbees or*
run-away negroes. We arrived at the bottom of the mountain
a little before feven in the morning. To get to either of-the^
ridges, we found we had a rock to olimb above forty feet'
high: it was with great difficulty we fcrambled up, affift^^
ing one another in the beft manner we could ; here we. found iti
necefiary to contrail: our baggage* After gettjngup this rock,i
I foiind myfelf in the bottom of a narrovv and deep ravin.
Having afcended this ' ravin a little way, I faw fome cleared'.,
ground on its fides, with tobacco grovi^ing. ' This I conjee* •'
tured was the -habitation- of fome Caribbees; but I wasmuchi

ilhrprlfed

Volcanic Mountain in St. Vincent's. iq

fiirprlfed when one of the negroes I had with me told me, it
w^as the habitation of a Mr. Gasco, a Frenchman. What
could induce a ftout healthy man in the prime of life, and a
good mechanick, w-irh feveral negroes, to take up his relidence
among rocks and precipices, excluded from the wdiole world,
is a mvfterv to me. Befides, by every torrent of rain that
happens, he may expert himfelf and all his habitation to be
wafhed over the rocks into the ocean. Notwithflanding his
lingular fituation, I found him an intelligent man, and I expe-
rienced every hofpitality his poor cottage could afford.

The difficulty of going through woods in the Weft Indies,
where there are no roads or paths, is far beyond any thing an
European can conceive. Befides tall trees and thick under-
wood, there are hundreds of different climbing plants tw^iftcd
together like ropes, and running in all diredlions to a great ex.-
tent, and even to the tops of the higheif trees ; by pufhing on
they cannot be broke, and many of them with difficulty cut ;
beiides a fpecies of grafs, the Scboenus Lithofpermos^ with fer-
rated leaves, that cuts and tears the hands and face terribly.
With fuch obftruclions as thefe it was above two hours before
wx got on the ridge, where I was in hopes our pafl'age would
have been eafier ; but I foon found my miflake, for I was fur-
rounded with a thick foreft, much more difficult to. get through
than before, on account of the large piles of trees broken down
by the hurricanes, to pais which in many parts we were obliged
to creep on our hands and feet to get below them, and in other
places to climb a great height above the furface of the ground,
to get over large trunks lying on one another, and thefe being
frequently rotten, occafioned us to tumble headlong dov/n to a
great depth, among rotten wood and grafs, fo that it was with
great difficulty I and the negroes could extricate ourfelves. B}'-

D 2 con-

20 Mf\ Anderson's Account of a

corifbiiitly cutting to clear our way, I, as well as my compa-
nions, grew much fatigued, and they \'v'iliied much to return
back. A'bout four in the afternoon 1 couW not prevail upon
them to pi'oceed farther ; if tliey did, they could not return
before v3^rk, and they would not fieep all night in the woods;
but faid, if I ftayedthey would return to me next morning. I
faW it was impofiible to gain the fummit of the mountain with
the boy only by that route : 1 likewile faw t!:c woods
growing more difEcult, m.y water alfo totally expended :
from thefe confiderations I intended to go down to the French*
man's, and remain there all night, and try another route with
my boy next morning, hoping I might be fortunate enough to
find an eaher pafiage. I arrived at Mr. Gasco's a little after
fun-fet, being much fatigued and thirfry, and never expe-
rienced more hofpitality and kindnefs than from this man in
his miferable cot ; for we ought not to judge of the value of the
things received, but of the difpohtion of the heart with which
they are given. He parted with his hammock to me, and fiept on
aboard himfelf. This I at firft refufed; but he infifted on it,
telling me, from my hardfhips of the day 1 was much more
tired than he. I took the hammock, but I found it was impofiible
to clofe my eyes during the night with cold. His hut was
built of rojeaux or large reeds, between each of which a dog
might creep through, and the top was covered with dry grafs.
It is fituated in the bottom of a deep gully, where the fun
does not £hine till nine in the morning, nor after four in the
afternoon. It is furrounded by thick wood, and during the
night the whole of the mountain is covered with thick clouds^
from Vv^hich it frequently rains ; tliis makes the night air ex-
ceedingly cold. I got ready to renew my journey next morn-
ing, having only Dr, Young's boy with me, who continued

I very

P^olcavk Motini<.vn in St. Vincent's. 21

very faithful to me during -tkis excurlion^ being very active and
hardy: 1 do not know if i could have gone throuigh this, fa-
tigue had it not been for his afiti^ance. 1 aaow determined to
commence this day's route up the ravin, as it icemed to- widen
a^iid apparently run a confiderable way up in the direction I
wiflied for; and if I could get out of it upon the other ridge,,
it would at kail be two miles nearer than the way I had at-
tempted yefterday, and probably, after getting out of it, I
might £nd wood eafier of accefs. In this ravin I got up about
a mile and a half, without meetkig with any contiderable ob-
flruttion. Encouraged by getting fo far, aUhough the jraviii-
was narrowing fail, with numbers of rocks and precipicss^ to>
climb over, with vines and bufties difficult to get tlnough, I
was reiblved to perfifb m this route, and determined by every:
poffible means to get to the Qbje(£l of my wifbes^ well knowing
if I could not perform it this way, I might abandon it entirely*
After climbing over a number of difficult paffes,, tihe raviii ter-
minated at the bottom of a very high precipice ; how far it-
was to the fummit I did not know, being covered toward tlie-
top with thick wood ; but from the bottom upwards it
was loofe fand as far as 1 could fee, with ferns and tufts of
grafs, which, as feon as I took hold of them, came our
at the roots. The precipice being fo very fteep, with no trees
or buffies on it to affift me in getting up^ I plainly faw the at-
tempting to climb it was at the riik of my life : however, I
was refolved to try it, and telling the boy to keep fome diflance
behind me, in cafe I fhould tumble and drive him down along
with me, I began to afcend, holding the tufts of grafs as
lightly as poffible, and digging holes with my cutlafs to put
my feet in ; but I often lofl: my hold, and frequently flipped.
down a confiderable diftance ; however, as it was nothing but

loQfe

J.^

Mr. x^NDER son's Account of a- \

loofe fiind, I could eafily pufli my cutiafs into it to the handle-,-
and hy grafping it could recover myfelf again. Had I not!
taken the relolution before! began to afcend to diveft myfelf of
fear, I could not poffibly have gone, for the terror of falling
would ; have; been the means of it every inftant. I got up to
fome wild plantains., which I law continued all the, way to
the place where; the bullies and trees began to grow. 1 here;
refted myfelf, and waited for the boy's getting to me, which
he did much eafier than I, although he had the provifions and
water, owing to the track I had made, and becaufc, being
much lighter, he could better trufl: himfelf to the grafs and.
lerns.. After fome labour we arrived at the top of the preci-
pice. I found myfelf on a very i>arrow ridge, thickly covered,
with wood, and bounded by two ravins, the bottoms of. .which
I could not fee ;. the defcent to them feemed to be nearly per-
pendicular, yet all the way covered with thick wood. After re-
frelhing ourfelves,. we began our fatigue, the boy and 1 cutting,
and carrying our water and provifions, alternately. When we.
.had got fome way, I found I was on an exceeding narrow ridge,
in m.any parts not fix feet broad; on each fide a tremendous
gulf, into one or other of which J was often in danger of fal-
ling, fo that with great caution I was obliged to lie down on
my belly, to fee through the buflies hov/ the ridge tended. Here
I began to Imell fulphur, or rather a fmell like gunpowder.,
As I knew this fmell mull; come from the top of the mountain, ,
being in the direction of the wind, I was in hopes we could-
not be far from it, as the fmell grew Wronger and flronger as I
afcended. I law a rihng before me, and thought if I was once-
on it, if the top of the mountain was near I could have a view
of it ; but having got on this riling I could only fee a high peak
^n the N.W. end of the mountain, and bvapnearance I thought,
6 myfelf

Volcanic Mountain in St. Vincent's. 2:3,

myfelf very little nearer than when I. was at the bottom. The.
woods now became very difficult to get through ; great quan-
tities of fallen trees lying buried under long grafs and being
rotten, when T thought myfelf walking on the ground, I was-
frequently buried a great depth among them. Being now
about noon, and my turn to carry the baggage, and confe-
quently my turn of reft, I was furprifed to hear a ruftling
among the buflies, and fomething like a human voice behind'
me. As we- were now in a place where I" had little reafon to
fuppofe there had been a human foot before, and could not
i'magine there could be habitations of Caribbees or run- away
negroes, fmce from the barrennefs of the mountain they
could notpoffibly findany proviiions to fubfiil on, 1 told the boy
to fliand flill, and let us' wait their coming up ; for if they were.
Garibbees advancing with an intention ta hurt u«, there was no
alternativ^e but to defend ourfelves. You may imagine my fur-
pTife wheil I faw one of the negroes who had B^en with me the
day before, with three others, which Mr. Maloune had fen t
to my affiftance, with plenty of provifions. After refrefli-
menti with this afliftance, I renewed my labours with freflr
fpirits, and thought 1 was- fure of 'Teaching the top before
night. Having proce-ededa^- little, I.^iad a fair viev/ of the;
ravin on my left, whicH wa§ of prodigious depth, and ran
from near the top 'of the mountain to the fea ; its . bottom
feemed to-be a rock of a colour nearly refembling lava, and
appeared as if there had be^n vail: torrents of fulphureous mat-
ter running in it feme time. - I regretted much I knew 'not of
this ravin before I' commenced my excurfion, "as by. paffing a
head-land in a canoe, and getting into the ravin, I might have;
gained the fummit of the mountain, without experiencing, ths:
dfekys and difficulties I here encountered. It was now about

24 Mr, Anderson's Account of a

4 P.M. and I had no profpe<5t of the mountain's top ; but from
the afcent of the ravin below, I knew it was a-gi-eat way off. I
thoup-ht if I could get into the ravin before niglit, I could get
cafrly up next morning. After cutting a great way through
wild plantains, the fun near fetting, I found myfelf almoll:
-over the verge of a precipice; by catching hold of fome fhruba
I prevented myfelf from falling. We were now about; -half-
Vv.ay down ; but all the way below us, i^s far as we could fee,
wna a perpendicular precipice of rock, feveral hundred feet
hi2,h, to pafs whicii wis impoffible. I had a view of fom&parE
of the top of the mountain, which I faw was yet far from me ;
nor could I attempt any other way than the ridge I had left.
Being now fun-fet, and the negroes very difcontented, becaufe
they could not return that night, I found we mufl take up our
night's refidence in the place where we were. It was a very
unfavourable one, there being nothing but plantains growing,
which retaining the rain long in their leaves, and being frequently
agitated by the wind, were conflantly dropping, and kept the
ground always moifi:. Being almoft dark, we had time to make
us no other habitation,, than placing two or three flicks againft
an old ftumpof atree, and flightly covering them with plantain
leaves. After getting together fome little wood to make a fire;
to keep lis comfortable, it began to blow and rain violently*
which continued all night. We loon found our building;
afforded us no flielter, and <he wood would not burn, io that
we could not get any fire ; and the ground on which we were
fituated would not allow the leaft exercife to keep us warm..
From fuch a miferable night I experienced no mitigation for
^tiie fetigues.ef the day. 1 wiflied for the rifing fun, to renewi
.i^y labours^ whidi I at lafl beheld with inexprefiible joy.

As

Vokantc Mouniain in St. Vincent's. 25

As loon as we could fee, wc returned to the ridge we left
the night before, and began to work with alacrity, as we were
idmofl chilled with cold. I pufiied on as fail as pofTible, and
about ten o'clock found the woods began to grow thin. 1
could not fee the top of the mountain, but had a view of fe-
veral ridges that joined it. From the wind falling, and the
heat growing inttufc, I thought we mull: then be under the
cover of the lummit : I here found i*nan.y new plants. About
eleven A.M. I was overjoyed to have a full view of thefummit
oi the mountain, nearly a mile diftant from us, and that we
were nearly out of the woody region. The top feemed to be
compofed of fix or feven different ridges, very much broken in
the fides, as if they had fuffered great convulfions of nature ;
they were divided by amazing deep ravins, without any water
In them. I obferved where the ridges meet the edge of a large
excavation, as it feemed to be, on the highefl: part. 1 imagined
this might be the mouth of the crater, and directed my courfc
to a high peak which overlooked It. I found here a moft
beautiful tree which compofed the lafl: wood. After that I en-
tered into a thick long grafs, intermixed with fern, which
branched and ran in every dire6lion. To break it was Impof-
fible, and with great difficulty I could cut it ; {q that in clear-
ing our way through this grafs, eight or ten feet high, there was
equal difficulty as In the woods, and it feemed to continue
very near to the top of the mountain. Being now about noon, I
and the negroes were fo fatigued as hardly to be able to ftand ;
our thirfl very great, to allay which, as much as poffible, we
chewed the leaves of the Begonia obliqua. Two of the negroes
returned, and the others faid they would go no" farther with '
me, as they muft perifh for want of water, and it would be
impoffible to get to the bottom before night, and they mull: all

VaL. LXXV. E dift

2 6 Mr. A'i^'DBRso^''s Accotmt of a

die in tlie woods. The propriety ot" their reafoning was evi-
dent to me ; vet I thought it hard, after the fatigues of three
days and two nights, to be within half a mile of the top,
and not be able to get up, and to know little more about it than F
did at the bottom. As the negroes had not the fame motive
for going up as I, all my reaioning was to them ineffe6lual ; I
found I was obliged to return myfelf, as I could not perfifl
alone. At half pafl twelve we began to defcend the fame way
we came. As there was nov/ a clear path all the way to
the bottom, we got down to Mr. Gascons by funfet. After
fitting fome time here, I was hardly able to rife again, I wasfo
tired ; and my feet were fo fore I could hardly ftand on them,
for, my fhoes being torn to pieces, I came down the whole way
bare-footed. I continued my journey, however, to Mr. Ma-
loune's, where I arrived between fix and feven at night.

March 4th, being the day I had fixed to finifh my excurfion^
about four in the morning, I left the houfe of Mr. Fraser,,
who out of curiofity agreed to accompany me, of which I was-
very glad, as he was a fenfible young man ; and with the aflifl-
ance of two negroes we purfued our journey. We found very
little obfi:ru£lion in our way up, until we got to the place where
I returned ; and there, for about a quarter of a mile, wc had
confiderable difficulty to clear our way through grafs and ferns*.
After we came within a quarter of a mile from the top, we
found ourfelves in another climate all at once, the air very cold,,
and the vegetable productions changed ; here was nothing but
barrennefs over the whole fummit of the mountain. On the
confines of the grafiy region and the barren I found fome beau*
tiful plants. Mofs grows here in fuch plenty, that I frequently
funk up to my knees in it. This is the only place in the Weft
Indies that produced any mofs that I have feen. About noon
t we

P'okanic Mounl^in in St. Viiice*it*;3. ±*j

we gained the top of the peak I had dire£ted my co\3iTe to be-
fore ; when, in an hiftant, we were furprlfed with one of the
grandeil and moft awful fcenes 1 had ever beheld* I wnsflruck
with it amazingly, as I could not have conceived fuch a vtry
large and fo fingularly formed an excavation. It is lituated on
the center of the mountain, and where the various ridges
unite. Its diameter is fomething more than a mile, and its cir-
cumference to appearance a perfefc circle. Its depth from the
furrounding margin is above a quarter of a mile, and it nar-
rows a little, but very regularly, to the bottom. Its fides are
very fmooth, and for the moll: part covered with {liort mofs'^>
except towards the fouth^ where there are a number of fmall
holes and rents. This is the only place where it is poffible to
jgo down to the bottom : it is exceedingly dangerous, owing to
the numberlefs fm^il chafms. On the weft fide is a fedion of
red rock like granite, cut very fmooth, and of the fame decli-
.. ■ vity with the other parts. All the reft of the furrounding fides
feems to be compofed of fand, that looks to have undergone
the a(flion of intenfe fire. It has a cruft quite finooth, of
about an inch thick, and hard almoft as rock ; after breaking
through which, you find nothing butloofe fand. In the center,
of the bottom is a burning mountain of about a mile in cir-
cumference j of a Gonic form, but quite level. On the fum-
mit, out of the center of the top, arifes another mount, eight
or ten feet high, a perfe*5t cone ; from its apex iflues a column
of fmoke* It is compofed of large maffes of red granite-like
rock of various fiies and fllapes, which appear to have been
fplit into their prefent magnitudes by fome terrible convulfion
of nature, and are piled up very regular. From moft parts of
the mountain iffue great quantities of fmoke, efpecially on the
iiorth fide, which appears to be burning from top to bottom j

E 2 and

28 M'. Anderson's Account of a

and the heat is lb intenfe, that it iS impoffible to go upon it.
Gouig round the bafe is very dangerous, as large mafies of rock
are conftantly fpUttlng with the heat, and tumbhng to the bot-
tom. At the bottom, on tlie north fide, is a very large rock
iplit in two ; each of thefe halves, which are feparated to a
confiderable dillance from each other, is rent in all dire(5tions, and
from the crevices iflue efflorefcences of a glofly appearance, which
tafte like vitriol, and alfo beautiful cryftallizations of fulphur.
On all parts of the mountain are great quantities of fulphur in all
f^att^s; alfo alum, vitriol, and other minerals. From the external'
jippcarance of this mountain,. I imagine it has only begun to
burn lately, as on leveral parts of it I faw fmall ihrubs and"
grafs, w^hich looked as if they had been lately fcorched and'
burnt. There ane feveral holes on the fouth, from which iffues
fmoke, feemingrlv broken out lately, as the bulhes round are but
lately burnt. On two oppofite fides of the burning mountain,
caft and wtft, reaching from its bafe to that of the fide of the
crater, are two lakes of water, about a tone's throw in breadth ;
they appear to be deep in the middle ■; their bottom to be co-
vered with a clay-like fubfl^ance. The water feems pleafant to
the tafte, and is of a chalybeate nature. I fuppofe thefe lakes
receive great in creafe, if they are not entirely fupported, by the
rain that tumbles down the fide of the crater. I obferved on:
the north fide of the bottom traces of beds of rivers, that to
appearance run great quantities of water at times to both thelc
lakes. By the ftones at their edges, 1 could perceive that either
abforption or evaporation, or perhaps both, go on fail. Tb^
greater part of the bottom of the crater, except the mountain
and two lakes, is very level. On the fouth part are feveral
fhrubs and fmall trees. There are many ftones in it that feeni
to be impregnated with minerals : I faw feveral pieces of pu-
J niice-

*■ 1

V$!cmic Mountain in St. Vincent's. 29

mice-ilone. I alfo found many flones about the ilze of a man's
fill, rough, on one fide blue, which appearance, I imagine,
they have got from heat, and being in contad with fome
mineral. Thefe ftones are fcattered over the whole mountain,
one or two of which 1 have fent you, with fome others.

After I had got up from the bottom of the crater, 1 could not
help viewing it with admiration, from its wonderful flrudure
and regularity. Here I found an excavation cut through the
mountain and rocks to an amazing depth, and with as muck
regularity and proportion of its conftituent parts, as if it had
been planned by the hand of the moft Ikilful mathematician. I
wifhedmuch to remain on the mountain all night, to examine
its feveral ridges with more attention next day ; but 1 could not
prevail on my companion to ftay, and therefore thought it
advifable to accompany him.

' I obferved the motion of the clouds on this mountain to be
very lingular. Although there are feveral parts on it higher
than the mouth of the crater, yet I faw their attradion was
always to it. After entering on its eaft or windward fide, they
funk a confidcrable way into it ; then, mounting the oppofitc
lide, and. whirling round the north-w^eft fide, they ran along a
ridge, which tended nearly north-eaft, and afterwards funk
nito a deep ravin, which divided this ridge from another on the
north-weft corner of the mountain, and the highefton it, lying
in a direction nearly fouth and north. They keep the courfe of
this ridge to the fouth end, and then whirl off weft in their
natural courfe.

1 took my departure from the mountain with great relu£lance.-
Although I encountered many difficulties to get up, yet it
amply rewarded me for all my toil ; but I had not time to^
examine it with, that attention. 1 wiftied. When I got on tha

peak

^d Mr, ht^-Qm^o-ti^s Account of a

peak \mm which I had my firft view of It, and fromVwhlch 1

could fee its dit!t*rcnt parts, I eauld not help rcviewius; it
feveral times. After Imprinting its flru(5tute on my mind, I
took my final adieu of it, and returned down, and got to Mr«
Fji A3E?.\s houfe about {^vcn at nighty much fatigued.

I am forry I had no inftruments, to take the flate of the air,
nor the exacl dimenfions of the different parts of the moua-
tain ; but, I believe, on meafurement, they will be more than,
I have mentioned.

From the iituation of thefe illauds to one another^ and to the
continent of South America, I imagine there are fub-marine
communications between the burning mountains or volcanoes
\n each of them, and from them to the volcanoes on the high
mountains of America. The iflands, which are fituated next
the continent, feem to tend in the diredlion of thofe moun-
tains I and I have obferved, that the crater in this ifland lies
nearly in a line with Soufriere in St. Lucia and Morne Pelee in
Martinique, and I dare fay from ^lorne Pelee to a place of. the
fame kind in Dominique, and from it to the others ; as it is cer»
tain there is fomething of this kind in each of thefe iflandsj
Sarbadoes and Tobago excepted^ which are quite out of the
range of thfe reil.

There rs no doubt but eruptions or different changes in fonie
of thenfi, although at a great diftance, may be communicated
to and affed'the others in various manners. It is obferved by
the inhabitants round thefe burning mountains, that fhocks of
'earthquakes are frequent near them, and more fenfibly felt
than in other parts of the ifland, and the fhocks always go in
the diredion of them.

I cannot omit mentioning the great affiftance I received iii
■the above excurfion from Dr. Young, Mr. Maloune, and Mr.

Fraserj

Volcanic Mountain in St. Vincent^s. 3 1

Eraser; for, without the aid of their negroes, I could not
have poffibly gone through with it.

References to the figure, tab. II.

A I. The fummit that overlooks the crater, from which the

drawing is taken.
A AAA. The circumference of the crater.
BBBB. The circumference of the bottom.

C. The burning mountain.

D. The fmall one on its fummit.
EE. The two lakes of water.

F. The fedion of the rock on the weft fide of the crater,

G. The large ravin.
HHHH. Ravins of great depths

i. Efflorefcence on the north end of ths rocky which at St
diftance looks like alum or nitrcr

1.2.3.4.5.6. The different ridges on the fummit of the moun-
tain, as they join the crater,

7.. Woods deftroyed by the hurricane*-

S.8, The clouds going to the fouthward of the weft ridge^
after paffing north on the weft fide of the crater.

9.9.9. Where I defcended into the bottom of the crater.

t and 10. The fummit and bafe of the ridge on which S
afcended the mountain.

C 32 ]

IV. A Supplement to the Third Part of the Paper on the Sum*

mation of infinite Series^ in the Philofopliical Tranfa6tions

for the Tear 1782. By the Rev, S. Vince, M ^. ;

communicated by N^evil Maikelyne, D. D. F. R, S, and

AJironomer RoyaL

Head November 25, 1 784.

1'^HE reafoning In the third part of my paper on the Sum-
. mation of infinite Series having been mifunderftood, I
have thought it proper to offer to the Royal Society the follow-
ing explanation. When I propofed, for example, to fum the
feries I - 4^+ I -" Sec, Jine fine, I wanted to find fome quantity
which, by its expanfion, would produce that feries, and that
quantity I called its fum ; not (as I conceived muft have been
evident to every one) in the common acceptation of that word,
that the more terms we take, the more nearly we fhould
approach to that quantity, and at lafl arrive nearer to it than.
by any affignable difference, for there manifeflly can be no fuch
quantity ; but as being a quantity from which the feries muft
have beeti deduced by expanfion, which quantity I found to be
— I +H. L. 2. If therefore in the folution of ^ny problem,
the conclufion, whofe value I want, is exprefled by the above
feries, and which arofe from the neceflity of expanding fome
<juantity in the preceding part of the operation, furely no one
can deny but that I may fubflitute for it - i -f H. L. 2. For
^whatever quantity it was? which by its expanfion produced at

firfl

n,l„j.Tr,„u. V„/.LXX7. TabJ! o . J1 .

Mr, Vince's Supplement, See. 33
firfl a feries, the fame redudion which, from that feries, pro-
duced the feries |-i--{-|-&c. muft alfo have produced
— I + H. L. 2. from the qiiantitv which was expanded. This
value of the feries I obtained in the following manner, i fup-
pofed the feries | — .1 -f-f - &c. to be divided into two parts ;
the firft part to contain all the terms till we come to thofe
where the numerators and denominators become both infinitely"
great, in which cafe every term afterwards m.ay be fuppofed to
be equal to unity : the fecond part, therefore, would neceflarily
be (fuppofmg the firft part to terminate at an even number of
terms) i - i + i - 1 -\- ^z. fine fine , The firfl: part, by collect-
ing: two terms into one, becomes - — ~- &;c.

^ 2 .3 4- S 6 • 7

which feries, as it is continued till the terms become infinitely
fmall, is equal to - i + H. L. 2. The fecond part i •- i + i —
&c.has not, taken abftradedly of its origin, any determinate value
(as will be afterwards obferved), but confidered as part of the ori-
ginal feries it has, for that feries muft have been deduced from the

expanfion of the binomial i + x\ , or 7—; and hence, when

x—\y I - I + I - &c. can in this cafe have come only from

-^— , which, therefore^ mull: be fubftituted for it ; confe-
I + 1

quently the two parts together give — | + H. L. 2.

Having thus explained the nature of the feries which I pro-
jDofed to fum, and the principle upon which the corredlioii
depends, I muft beg leave to acknowledge my obligations to
my very worthy and ingenious friend George ArwooD-Efq.
F.R.S. who firfl obferved that the feries i - i + i - i -f &c. has
no determinate value in the abfira6t, as it may be produced^ by

^ r— whatever be the numiber of units in the denomi-

I + I + I + (N-C.

Vol. LXXV. F iiator^

34 ^^* Vince's Supplement on the

iiator * ; ^nd it may alfo be added, that the fame feries arlfo'^

from — — -~ — - — r-T— > provided the number of units be greater iii
the denominator than in the numerator. The ccrrecSlion will
therefore be different in different circumflances, and will depend
on the nature of the quantity which was at firft expanded. la
the third part of my paper, I applied the corredion to thofe cafes
where the original feries arofe from the expanlion of a binomial,
where the correftion is in general as I there gave it ; but as I
did not apply my method to any other feries, I confefs that it
did not appear to. me, that the correction would then be dif-
ferent, which it neceflarily would had I extended my reafon-
ing to other cafes. I (hall therefore add one example to (hew
the method of correction in other inftances, where the value
of the corredion will be found to be different, according as w^e
begin to colleCl at the firft or fecond term. Let the feries be
_*__l + l-^-}-l- &c. fine finey which came originally from

\ ^ : now if v/e berin to colle6l at the firfl term, the feries

becomes — — -1 — — +&c. and for the fame reafon as before, the

1.2 4.5

correaion, to be added, is 4 ; but — — + — - + &c. = i of a

1 • - 4 • 5

circular arc (A) of 30° to the radius — ^ ; hence the fum re-

quired = 4-A + -i. If we begin to colle£l: at the fecond term the

feries becomes 2 -" ? &c. ; and the correftion to be

2.4 5-7

fubtracled is -| ; for the fecond part of the original feries is now
_ I _i- 1 _ I 4. 1 _ &c. which was produced by - ]_ 2 , ; hut

* I have been fince informed by Mr. Wales, F. R. S. that a pupil of his, Mr.
»;OND, made the fame obfervation*

3 ^—

Summation of infinite Series,

2 -— . T &c. = I + -i A ; therefore the fum required =

2 .4 5 • 7 ■ ^

i. + -t A as before. In the fame manner we may apply the cor-
rection in ail other cafes. Although, therefore, the ieries
I - I 4- I — I + &c. or - I -f I - I -f I _ &c. have no determi-
nate value in the abftraci:, yet the given feries will fix its value
by pointing out the quantity from which the feries muft have
been originally produced.

F z

[ 36 ]

V. Defcripiion of a Plant yieUing A fa foetlda. In a Letter
Jrom John Hope, NJ. D. F. R. S\ to Sir Jofeph Banks,
Bart. P. R, S.

Read December 9, 17B4.

TO SIR JOSEPH BANKS, BART. P. R. S.
SIR, Edinburgh, Auguft i8, 1784.

I BEG you will do me the honour of prefentlng the inclofed
account of the Afa foetida, and the botanical defcription of
the plant, with the drawings, to the Royal Society.

I have the honour of being, with much refpe6l andefleem, &c.

JOHN HOPE.

ASA F OE T I D A.

Planta umbellifera, tripedalis, ere61:a, ramofa, glauca,
flore luteo.
Radix perennis.

Folia radicalia fex, procumbentia, trilobo-ovata, multoties
pinnatim divifa ; follolis incifis, lubacutis, fub-
decurrentibus ; petiolo communi fuperne piano, linea
«levata longitudlnaliter per medium dccurrente.

2 CaiiUs

Dr. Hope's Defer iption^ &c. 27

Caulis blpeclal'is, ereclus, teretiufculus, annuus, leviter ftria-
tus, glaber, nudus praeter unam circa medium fo-
lioi'um imperfeclorum conjugationem ; petiolo mem-
bran aceo, concave.
Rami nudi, patuli ; quornm tres inferi, altcrnl,, fuftlnentur
linguli folii imperfedi petiolo membranaceo cou-
cavo.
Quatuor intermedii verticillati funt. Supremi ex apice

caulis ofto, quorum interni ertQCi.
Omnes hi rami fummitate fuftinent umbellam com-
pofitam feffilem terminalem, et prasterea 3 — 6 ramulos
externe pofitos, umbellas compofitas ferentes.
Hoc modo, rami inferiores luftinent 5, raro 6 ramulos ;
intermedii 3 vel 4; luperiores i et 2.
Cal. TJmbella univerfalis radiis 20 — 30 conftat.

' — partialis flofculis fubfeliilibus 10 — 20.

Umbella compofia feiHYis convexo -plana.

. pedunculata hsemifpherica.

Involucrum univerfale nullum.

partiak nullum.

Perianthium proprium vix notabile.
CoR. univerfalis uniformis.

Flofculi umbellae feffilis fertiles.

• pedunculatae plerumque abortlunt.

propria petalis quinque asqualibus, planis, ovatis : prim.o
patulis, dein reflexis, apice afcendente.
St AM. Filamenta 5, fubulata, corolla longiora, incurvata. u4n~-

thera fubrotundae.
PiST. Gennen turbinatum, inferum.
Styli duo, reflexi.
Stigmata apice incraffata.

Per.

^8 Dr, Hope's Defcrlptkn of a

p£:R. nullum : frucliis obiongus, plaiio-compreflus, utrlnqiie 3

liiieis eleva'ds iiotatus eft.
S-EM. duo, oblonga, magna, utrinque plana, 3 lineis elevatls

notata.
Flanta odorem alliaceum diffundlt. Folia, rami, pedun-

cull, radix, triincus, feci! luccum fundunt latleum,

lapore et odore A fa; foetidi.e.

THOUGH x^fa foetida has been ufed in medicine for many
ages, having been introduced by the Arabian phyficians near a
thoufand years ago ; yet there was no fatisfadlory account of
ihe plant which yielded it, tillK.EMPFER publiihed his Amoeni-
tates Exoticas about feventy years ago.

K^MPFER, towards the end of the laft century, travelled
over a great part of Alia, and was in Perlia, and upon the fpot
where the Afii foetida is coilecled. He gives a full account of
the manner of collecting it. He defcribes the plant ; and alfo
gives a figure of it, differing in many refpedts from thofe which
I now prefent to the Society *.

Six years ago, I received from Dr. Guthrie, of St. Peter{burg,
F. R. S. two roots of the Afli foetida, with the following card
from Dr. Pallas, addreffed to Dr. Guthrie :

" Dr. Pallas's compliments to Dr. Guthrie ; he fends
*' him two roots of the Ferula Afa foetida, a plant which he

* Probably KjEmpfer's Afa fcetida Plant is a different fpecies from that
defcribed by Dr. Hope in this paper. K^^mpfer was himfelf upon the mountains
where the drug is coUefted, and his fidelity in defcribing, as well as delineating, has
not hitherto been impeached. Sanguis Draconis, and ibme other gums, are
indifferently the produce of various fpecies of plants ; aiid why may not Afa
foetida be iimiUrly circumftanced ? Jos. Banks,

^' thinks

Fhihi . Tnjv. m.LXXVttbM.p.3'-

^'^mmM^^

■ I

Pt,-ht Tr..,,^ V'l I XXi- Tji». iV I

PIa?ii yielding Ala fcstlda. -^^

**' thinks never was cultivated in any European garden, and
*' which nobody has been fo fortunate as to raife from feed but
*' himfelf, though the feeds fent to the Academy from the
** mountains of Ghilan in Perfia had been diftributed among
** feveral curious perfons."

Both thefe roots were planted in the open ground, in the
Botanic Garden at Edinburgh ; one died ; the other after fome
time did well, and lafl fummer flowered and produced feed. I
had an accurate drawing of the plant made by IVIr. Fife, which
I now have the pleafure of laying before the Society. It ex-
preifes very well the general habit of the plant, which was of
a pale fea-green colour, and grew to the height of three
feet. The ftem is deciduous, but the root is perennial.
Every part of the plant, when wounded, poured out a rich
milky juice, refembling In fmell and tafte Afa foetlda ; and at
times a fmell refembling garllck, fuch as a faint impregnation
of Afa foetida yields, was perceivable at the diftance of feveral
feet.

In Perfia, at the proper feafon, the root is cut over once and
again ; from the incifions there flows a thick juice like cream,
which, thickened, is the Afa foetida.

I have only further to obferve, that as the plant grows in
the open air, without protedion, and even in an unfavourable
feafon produced a good deal of feed, and as the juice feems to
be of the fame nature with the officinal Afa foetida, there i»
fome reafon to hope, that it may become an article of cultiva*
tion in this country of no inconfiderable importance,

Edinburgh, Jan. 1783.

[ 40 ]

VI. Catalogue of Double Stars,
V/illiam Herfchel, Efq, F. R. S.

Read December 9, 1784.

INTRODUCTORY REMARKS,

t I "^HE great life of Double Stars having been already pointed
jL out in a former paper, on the Parallax of the Fixed Stars^
and in a latter one, on tlie Motion of the Solar Syftem, I have
now drawn up a fecond colle6lion of 434 more, which I have
found out fince the firfl was delivered.

The happy opportunity of giving all my time to the purfuit
of aftronomy, which it has pleafed the Royal Patron of this
Society to furniih me with, has put it in my power to make
the prefent collection much more perfect than the former ;
almoft every double flat in it having the diftance and pofition
of its two ftars meafured by proper micrometers ; and the
obfervations have been much oftener repeated.

The method of claffing them is in every refpeCl the fame as
that which has been ufed in the firft colle6lion ; for which rea-
fon I refer to the introdudlory remarks that have been given
with that colle6lion * for an explanation of feveral particulars
neceflary to be previoufly known. The numbers of the flars
•are here alfo continued, fo that the firfl clafs ending there at

* See rhilofophical Tfanfa6tions, vol. LXXII, p. II2.

24

Mr. Herschel's Catalogue of Double Stars, 41

14. begins here at 25, and the fame is done with the other
clafles.

Mofl of the double flars in my fird.colleclion are among the
number of thofe ftars which have tlieir places determined in
Mr. Flamsteed^s exteniive catalogue ; but of this colledtion ^
many are not contained in that author's work, I have therefore
adopted a method of pointing them out, which it will be proper
to defcribe.

The finder of my reflector is limited, by a proper diaphragm,
to a natural field of two degrees of a great circle in diameter.
The interfeclion of the crofs wires, in the center of it, points
out one degree ; and by the eye this degree, or the diitance
from the center to the circumference, may be divided into |,
I, I, 4, and f. Thus we are furnifhed with a meafure which,
though coarfe, is however fufficiently accurate for the purpofe
here intended ; and which, if more than two degrees arc
wanted, may be repeated at plealure.

In fuch mcafures as thefe 1 have given the difbance of a dou-
ble flar, whofe place I wanted to point out, from the nearefl
ftar in Flamsteed's Catalogue. And fince, befides the
diftance, it is alfo required to have its poiition with regard to
the flarthus referred to, I have ufed the neighbouring liars for
the purpofe of pointing it out.

The ufefulnefs of this method is fo extenfive, that I fliall be
a little more particular in defcribing its application. When a
ilar is thus pointed out, as forinftance the32d in the firfl clafs,
where it is faid, '* About Ci degree f. preceding the 44th Lyncis,
*^ in a line parallel to ^Urfae majoris ao^ the 39th Lyncis ;" we
are to apply one eye to the finder, and placing the 44th Lyncis
into the center of the field, we are to look at 5 Urfae majoris
and the 39th Lyncis in the heavens with the other eye by the
Vol. LXXV. G fide

jf% Mr. Hersckel's Catalogue

lide of the Wilder. The naked eye then will immediately dire£t
us, by means of the two ftars juft mentioned, towards the
place where, in the finder, the armed eye will perceive the
double flar in queftion about | degree from the 44th Lyncis. I
need hardly obferve, that we mull: recoiled the invcrfion of the
finder, as thofe who are in the habit of ufing teiefcopes with
high powers, always fnrnifhed with inverting finders, will of
courfe look for the fmall ilar in the upper part of the field, as
in fig. I. ^

At the 45th ftan, in the fird clafs, the defcription fays,
*^ About I \ degree f. preceding ^ti, towards ; Aurigse.'* This
double flar will accordingly be found by placing ^ Aurigae firft
into the center of the finder ; then, drawing the telefcope
towards/, which the naked eye points out, the ftar we look for
will begin to appear in the circumference as foon as jtt is about-
I degree removed from the center, as in fig. 2.

It will fometimes happen, that other flars are very near
thofe whvich are thus pointed out, that might be miftaken for
them. In fuch cafes an additional precaution has been ufed by
mentioning fome circumftance either of magnitude orfituation,
to diiKnguifh the intended fi:ar from the refl. After all, if any
obferver fhould be ftill at a lofs to find thefe flars without having
their right afcenfion and declination, he may furnifh himfelf
with them by means of F.lamsteed's Atlas Cceleflis ; for my
defcription will be fufficiently exa6t for him to make a point in
the maps to denote the flar's place; then, by means of the gra-
duated margin, he will have its A and declination to the time
of the Atlas, which he may reduce to any other period by the
ufual computations.

Before I quit this fubje£l: I muft remark, that it will be found
en trial, that this method of pointing out a double ftar is not

only

of^ Douhk Stars. 4_^

^nly equal, but indeed fuperior, to having its right afcenfion
and declination given : for, fince it is to be viewed with very
high powers, not fnch as fixed inilruments are generally fur-
nifhed with, the given right afcenlion and declination would be
of no fervice. We might, indeed, find the iliar by a fixed or
equatorial inftrument ; and, taking notice of its (ituation with
regard to other neip;hbourinp fiars, find, and view it after-

O O CD ' ' ^

Wards, by a more powerful telefcope ; but this will nearly
ftmount to the very fame way which here is purfued, with more
deliberate accuracy than we are apt to'ufe, while we are em-
ployed in feeking out an obje6l to look at.
' It will be required, that the obferver fhould be furnidied
with Flamsteed's Atlas Cceleflis, which muft have the fliars
marked from the author's catalogue, by a number eafily added
to every flar with pen and ink, as 1 have done to mine. The
catalogue fhould alfo be numbered by an additional column,
after that which contains the magnitudes. I hope in fome
future editions of the Atlas to fee this method adopted in print,
as the advantage of it is wtty confiderable, both in referring to
the catalogue for the place of a ftar laid dow^n in the Atlas, and
in finding a ftar in the latter whofe place is given in the
former.

I would recommend a precaution to thofe who wifh to exa-
mine the clofeft of my double ftars. It relates to the adjufl
ment of the focus. Suppofing the telefcope and the obferver
long enough out in the open air to have acquired a fettled tem-
perature, and the night fufficiently clear for thepurpofe; let
the focus of the Inftrument be re-adjufted with the utmofl
delicacy upon a ftar known to be fingle, of nearly the
fame altitude, magnitude, and colour, as the ftar which is to
be examined, or upon one ftar above and another - beloW the

G 2 • fame.

44 Mr. Herscheis^s Catalogue

fame. Let the phaenomena of the adjufting fiar be w^ll
attended to ; as, whether it be perfe<flly round and well de*
fined, or affeded with little appendages that frequently keep
playing about the image of the ftar, undergoing fmall altera-
tions while it pafles through the field, at other times remain-
iiig fixed to it during the whole paliage. Such deceptions may
"fee detected by turning or unfcrewing the obje6t-gl.ils or fpecu-
lum a little in its cell, when tliofe appendages will be oblerved
to revolve the fame way. Being thus acquainted with the
imperfections as well as perfections of the inflrument, and
going immediately from the adjufting ftar, which for that
reafon alfb fhould be as near as may be,, to the double flar which-
is to be examined, we may hope to be fuccefsful. The afire*
nomical Mr. Aubert, who did me the honour to. follow this,
method with y Leonis, which he did not find to be double
wheathe tekfcope was adjufled by y itfelf, foon perceived the
fmall ftar after he had adjufted it upon Regulus. The inftru-
ment, being one of Mr. Doi.lond's befl 3! feet achroma-
tics, fhewed Mr. Aubert the two ftars of y Leonis in very
clofe conjundion, or rather one partly hid behind the other.
On comparing thefe appearances with my obfervations of that,
double flar, we mufl not be furprifed to find that I place them,
at a vilible diftance' from each other: for the Newtonian re-
fle<5lors, on the plan of my 7-feet one, as I have found, will
give a much fmaller image of the liars than the 3I feet achro-
matic refractors; wherefore the two ftars, which in refradtors-
as it were run into each other, will in the reflector remaia.
feparate. For this reafon alfo, thofe who only ufe fuch re-
fractors muft not be difappointed if they cannot perceive the
26th, 30, 31, 36, 41, 44, 46, 47, 60, -j^^ 82, 86, and 87th.
flars of my firfl clafs to be double,

A.

of Douhle Stars. ^c

Ali the obfervations in the following catalogue on the rela-
tive magnitude, colour, and potition of the (tars, are to be
underflood as having been made with a power of 460, unlels
they are marked otherwife. This will account- for the dif-
ference wliich obfervers may find in the relative magnitude ; for
fhould they ufe only a power of about 200, many of the
fmall ftars that are faid to be very unequal and extremely une-
qual, mull: appear to them perhaps a degree lower in the fcale,
and become extremely and exceffively unequal : and this will
happen, though the quantity of light fhould be the very fame
which the reflector has that ferved me to fettle thefe particulars.
I need not fay, that on other accounts, fuch as a real difference
in the light of the telefcope, the prefence of the moon, twi-
lights, auroras boreales, or other caufes,, many of the fmall
flars may be found to be of a different comparative luflre from
what is alligned to them in the catalogue. The fmall ftar near
Rigel, for inflance, appears of a beautiful pale red colour, full,
round, and well defined, with my 20-feet reflector; the lo-feet
inftrument fhews it alfo very well in fine evenings ;. the ^-feet
requires more attention, nor is the fmall flar defined, but of a
dulky pale red colour. A good 3I feet achromatic, of a large
aperture, when Rigel is on the meridian^ tT^^Y? perhaps, alfo
ihew the fmall flar, although I have not been able to fee it
with a very good initrument of that fort, which fhew^s the
fmall ftar that accompanies the pole-flar ;, but the evening was.
not very favourable.

The meafures of the diftances were all taken with a parallel
filk-worm'^s- thread micrometer, and a power of 227 only..
They are not, as in the former catalogue, with the diameters
included, but from the center of one flar to the center of the

othcr^

^6 Mr. Herschel's CcUaloguc

other. I l^ave adopted thefe meafures on finding that I could
procure threads fine enough to fubtend only an angle of about
\" ix''-^ and that by this means there was no longer any
great difficulty of judging when the flars were centrally co-
vered by the threads. However, I do net know whether thefe
meafures, with flars at a confiderable diflance, may not bs
liable to an additional error of perhaps one fecond, owing to
the remaining uncertainty in judging of their exad central
pofition while the meafure is taking.

The pofitions have ail been meafured (unlefs marked other-
wife) with a power of 460, adapted to an excellent microme-
ter, executed by Mefl'. Nairn e and Blunt, according to
the model given in the PhilofophicalTranfacSlions, vol. LXXI.
page 500. fig. IV.; but with a great and neceffary improve-
ment of making the wheel d^ d^ of that figure perform its
whole revolution ; by which means the two filk- worms-
threads may be adjufted to a greater degree of exa^lnefs ; for if
they are not placed fo as perfedlly to bife6l the circle, the two
threads will not coincide exactly after having performed one
femi- revolution, which they muft be made to do with the
utmofl rigour. I found the abfolute neceffity of this precau-
tion when I came critically to examine the pofitions of the
Georgium Sidus, as they are given in table III. Phil. Tranf. vol.
LXXI. p. 497. The meafures were afFe6led with a fmall and
pretty regular error, which I was at a lofs to account for ; and
the diflance oi this ftar being then totally unknown, I looked
for the caufe of the deviation at firft in a diurnal parallax of
that heavenly body ; but foon found it owing to the incon-
venience before-mentioned, of not being able experimentally
TO adjufl the moveable thread to that critical nicety which I

have

oj Double Stars, 4-

have now introduced and ufed in all the angles of the following

catalogue*.

Datchet nearWindfor, Nov. i, 1784. W. HERSCHEL.

CATALOGUE OF DOUBLE STARS,
FIRST CLASS.

I, 25. A Orionis. Fl. ^2. Sub humero in confequentia.

Jan. 20. Double. Confiderabiy unequal. L. fine w. ; S. w,
1782. inclining to pale rofe colour. The diftance or black
divifion between the two flars with 278 is about I dia-
meter of L. ; with 460, near | diameter of I^. Pofi-
tion with 278, 52® lo'f. preceding.

26. u Leonis. Fl. 2. Anteriorem pedem dextrum praecedens.

Feb. 8. A very minute double fl:ar. Confiderabiy unequal.
1782. Both r. With 227 there is not the leafi: fufpicion of
its being double ; with 460 it appears oblong, and,
when perfe6i:ly dillind:, we fee i of the apparent dia-
meter of a fmall flar as it were emerged from behind a
larger ftar ; with 932 they are more clear of each other,
but not feparated ; the focus of every power adjufted
upon the 3d and 6th Leonis. November 6th, 1782^ I

* The divilions on the moveable circular index {a) of this micrometer fliould
be read off by means of a line drawn on a fmall plate faftened to the fide /, and
projefting with a proper curvature againft the plane of the divifions towards r, fo
as to be nearly in contad ; a coincidence of lines being by far the beft method of
afcertaining the fituation of the index. A nonius of four fub-divifions may alfo
be ufed, whereby the 60 divifions, already divided into halves upon the index-
plate, will be had in eighths, each of which, on the conftrudtion of my prefent

ene, will be equal to three minutes of a desree of the circle.

7 firft

4"^ Mr. PIerschel's Catalogue

L fiiil: ful^dled a feparation ; and November 13th, fairly

favv a divlfion between them. April 4, 1783, with an
improved refle<Slor of 20 feet 3 inches focal length and
1 2 inches aperture, I faw them evidently divided. Pofi-
tion 20° 54^ f. following*.

27. Fl. 90 Leonis. Infra edu6lion?^m can die.

Feb. 9. Treble. The two nearefl: — very unequal. L. w. ;

1782. S. rw. With 278, 1^ diameter of L; with 460, \\
diameter of L. Pofition with 278, 61° 9' f. preceding.
The two farthefi: — very unequal. S. dufky r. Dif-
tance from L. 53'^ 43^'^ Pofition 2,S^ ^'^' ^- preceding.

28. y Leonis. Fl 41. In coUo lucida.

Feb. II. A beautiful double fl:ar. Pretty unequal. L. w. ;

1782. S. w. inclining a little to pale red. With 227 and 278

dillincVly feparated ; with 460, ~ diameter of S. j with

625, I diameter; with 932, full \ diameter, or when

* I fufpeft thefe ftars to recede from each other. It is, however, very
pofTible, that the opening which I obferved between them, at the latter end
of the year 1782 and beginning of 1 783, may be owing to very iavoura-
bb weather, or to my being better acquainted with the object:. Could we
increafe our power and dillinftnefs at pleafure, we might undoubtedly fcparate
any two ftars that are not abfolutely in a dired line palnng through the eye of the
obferver, and the centers of both the l^ars. This will appear when we confidcr
that perhaps 59 thirds out of one fecond, which the diameter of the liar may
fubtcnd, are fpurious ; fo that a double ftar feemingly in conta«5l, or even partly
hiding each other in appearance, may ftiil be far enough afunder to admit of a fair
and confiderable feparation by applying an adequate magnifying power. It would
hflve besn curious, if a confiderable diftercnce in the colours could have led us to
<li!ic.over which of the two ftars is before the other ! But the far greatelt part of
their apparent diameters being, as we have obferved, fpurious, it is probable, that
a different coloured light of two l^ais would join together, where the rays of one
extend into thofe of the other; and lo, producing a third colour i^y the mixture
of it, ftill leave the qneilion undecided.

befl

of Double Stars, 4^

I^ befl 1 diameter of S. ; with 1504, I diameter, we!l-
defuied, and the difference of colours fllll vifible; with
2176, not quite a diameter of S, pretty well defined,
but exceedingly tremulous; w^ith 2589, lefs than i
diameter; with 3168, ftill pretty diflincl, and about
f diameter of S ; witii 4294,, more than a diamf.ter of
S, but attended w'lth the utmoft difficulty of managing
the motions ; with 5489, the interval ftill fomewhat
larger, and if the obje6l could be kept in the center of the
field, the eye might adapt itfelf to the focus, and
get the better of the violent aberration y but the edges
of the glafs being of a different focus, the eye is con-
ftantly difappointed in its endeavours to define the,ob-t
je6: ; with 6652, I had but a fingle glimpfe of the ftar
quite disfigured ; however, I afcribe it chiefly to the
foulnefs of the glafs, wdiich, on account of its fmall-
nefs, is extremely difficult to be cleaned ; with a lo-feet
reflector, 9 inches aperture, power 626, above f dia-
meter of S. very difl:in£t ; with a 20-feet refledtor,
power 350, too bright an objedt to be quite diftind,
though I fee it very well. Polition 5" 24' n. following.
A third ilar preceding. Dift. i'5i'^23''", pretty accurate
for fo great a diftance. Pofition 31° o^ n. preceding. A
fourth flar preceding the third, and fomewhat fmnller.

29. Parvulajuxta Fl. 44^"^ :Leonis,

Feb. 17. Double. About 4' following the 44th Leoaiis, which
1782. being double in the finder; this is the leafl: of the two.
Extremely unequal. L. w. S. d. With 227, 14- dia-
meter of L. ; with 460, 2 diameters of L. Polition
26° 32' n. following.
Vol. LXXV. H 30. Secunda

CO Mr. Herschel*s Catalogue

I. ^o. Secunda ad t Cancii. Fl. 57.

March '. Double. Pretty unequal. Both pr. With 227,
I'^Sa. about |- diameter; with 278, | diameter; with 460,

about I diameter or lefs. Pofition 68'' iz' n. preceding.

A beautiful minute obje6l.

31. Inter Fl. 41^"^ et 39'" Lyncis.

March 5. Double. Near i| degree n. preceding the 41ft Lyn-
17^82. cis J towards « Urfae majoris. A little unequal. Both
w. With 460, I or at moft i diameter, Poiition 51®
2i' f. preceding.

32. Fl. 44^ Lyncis auflralior et prjecedens.

April 3. Double. About | degree f. preceding the 44th Lyn-
1782. cis ; in a line parallel to 5 Urfse majoris and the 39th
Lyncis. Very unequal. L. r. ; S. bluifh r. With
227, I diameter of L or i| when beft; with 460, i|
1 diameter, or when beft, near 2 diameters of L. The
diameters are fo fmall that the length of the time, and
attention of looking, makes a con fide rable difference in
, - the eftimation of - the diftance. Pofition 8*^^ 27' f. pre-
ceding.

33. I Librae. Fl. 51. Primam'chelam Scorpil attingens.

May 12. Treble. Without great attention, and a confiderable
1782. power, it may be miftaken • for a double jftar ; but the
largefl: of them confifts of two. Very little unequal.
Both w. With 460, \ or at moft 4 diameter afunder;
1 with 932, full i diameter of L. or near | diameter of

S. Pofition, with 278, 82° 2' n. following. For
meafures of the third ftar fee the 20th of the fecond
clafs.

34. Fl. 55, Cailiopeiae. ; Ptolemaei. In pedis extremitate.

Treble

of Double Stars, ^i

I. Treble. The two neareft very unequal. L. w. ; S.

June ir, colour of pale red blotting paper. With 278, | diame-
1782. ter of S. Pofitlon with 227, 20^ '^o' n. preceding. For
meafures of the third ftar fee the fourth in the third
clafs.

35. Fl. 38. Serpentarii. Dextrum infra pedem.

June II, Double. Very unequal. L. w. ; S. d. With 460,
1782. 1 1 diameter of L. As the fituation Is too low for 460,
I tried 227, but it only (hewed the ftar wedge- formed.
Pofition 60° 48^ n. preceding.

06. f Herculis. Fl. 40. In dextro latere.

July 18, A fine double ftar. Very unequal. L. w, ; S. afii-

1782. colour. With 460, lefs than § diameter of S. ; with
932, I full diameter of S. *. Pofition with 811,
20° 42' n. following.

37, (P(Fl. 11^.) Herculis borealior et fequens.

July 22, Double. About f degree n. following (p ; in a line

1782. parallel to the 35th and 42d Herculis ; the moft foutii
of two very fmall telefcopic flars. Confiderably une-
qual. Both reddifti. With 227, they can but juft be
feen as twoftars; with 460, near i diameter; with
932, not lefs than i| diameter of L. Poiiti'on ^9^48^
f. following.

* The inten^al between very unequal flars, eftimated in diameters, generally
gains more by an increafe of magnifying power than the apparent diftance of thofe
which' are nearer of a fize. Inllances of the former may be found in the firft
clafs, the ift, 7, 29, 35, 37, 39, 53, 59, 63, 64, 72dlT:ars; of the latter, the
i6th, 28, '^'^<, 45, 46, 73, 8111 liars. However, this only feems to take place
when there is a difficulty of feeing the objed well with a low power, which being
removed by magtiifying more, the diitance is, as it were, laid open to the view. '

H 3 38. Fl.

52 iV/r. Herschel's Catalogue

I. 38. Fl. 1 8^"^ Perfei prarcedens ad boream. In caplte.
Aug. 20, Double. About § degree n. preceding the i8th; in
1782. a line parallel to c and r Perfei; of two ftars that
next to the 18th. A little unequal. Both pr. With
278, a mofl: minute and beautiful obje6l ; with 460,
I diameter of either. Pofition with 278, p° 42' n^
preceding.

39. /3 (Fl. 11"''^) CaffiopeiiE praecedens ad auftrum.

x\ug. 25, Double. Aibout I degree f. preceding /3 ; in a line
1782. parallel to 17 and a. CafliopeiiC ; the following and largeft
of two very confiderable ftars. Very unequal. L»
pr. ; S. r. , With 278, | diameter of S. ; with 460,
I, or when beft, -| diameter of S. Pofition 50° 42^ n.
preceding. is

40. Fl, 25^"" Cafiiopela3 pra^cedensad boream.

Aug. 28, Double. About I degree n. preceding the 2«^th;.
1782. towards cz Caffiopei^e; the hrft telefcopic flar in that
direction. • Very unequal. Both r. With 460, | dia-
meter of S. ; difficult to be feen. Poilticn 50° 30' f,
following.

41. Fl. ^i^Draconis boreallor.

Aug. 29, A very minute double ftar. About | degree n. of the
1782. 31ft* ii^ a lii^e parallel to y and J Draconis; the mofl
Ibuth and preceding of two. Coniiderably unequal.
Both pr. or r. With 227, they appear only as a
lengthened or diftorted flar ; with 460, | diameter of
S. ; or in very fine nights | diameter of S. ; with a
new Ipeculum and foo, near | diameter, when beft;
with 932, i diameter. Pofition 84° 2'/ n. preceding.
Requires every favourable circumftance to be feea
double.

42

7»

of t)ouble Stars, 5j

I. 42. ^ Serpentis. Fl. 13. In primo flexu colli.
Sept. 3, A beautiful double ftnr. Confiderably unequal. L*
1782. w. ; S. greyifh. With 227, J- diameter of S. ; with
278, not quite \ diameter of S. ; with 460, near t
diameter of S. ; with 932, near i diameter of S. ;
with i;§045 above 1 diameter of S, Pofition 42° 48^ f.
preceding, ■

43. AdFL. 48^"^ Draconis.

Sept. 3, A very minute double ftar. The mofl north of
1782. three, forming an arch ; or that which is towards 0
Draconis. Confiderably unequal. Both pale pink. In
fine nights, with 460, it has the fhape of a wedge ;
with 932, a fine black divifion juft vifible j in a very-
clear dark night a divifion may be feen with 500, and
wath 932, it will be about \ diameter. Pofition with
500, 88° 24' n. preceding.

44. Fl. 4. Aquarii. Supra veftimentum manus finiflrce.

Sept. 3, A minute double ftar. Very unequal. Both pr*
1782. With 460, almoft in conta£t, or at moft i. diameter
of S. Pofition 8r 30^ n. preceding. A,third fiar of
the fixth clafs in view, n. preceding.

45. \JL Aurigae (Fl. i i^™) pr^ecedensad auftrum.

Sept. 5, Double. About i \ degree f. preceding ^u, towards
1782. < Aurigaj ; a pretty confiderable ftar in a minute tele-
fi:opic conftellation. A little unequal. Both pr. or r.
With 227, \ diameter of S. ; with 27S, near \ dia-
5i:ieter of S. ; witli 460, about \ diameter, or near |
Jiameter of S. Pofition 47° ^i?! ^- preceding,

46. V (Fl. 13''") Aquarii fequens ad boream.

Sept. 7. Treble. About 1 1 degree n. foUovvlng y, in a line
1782. parallel to j3 and « Aquarii; the middle of three that

are

54 ^^1^' Herschel's Catalogue

^I. are in the lame clire(5lion. The two neareft very une-

qual. L. rw, ; S. pr. With 460, about i diameter
of L. or more. Polition 62° 27^ n. preceding. The two
fartheft very unequal. S. pr. Diftance with 227,
1' 22'' 42^'^ Pofition 35° 51' n. following.
■ 47. Fl. 29^"* Capi-icorni priEcedens ad boream.
Sept. 27, A minute double flar. About | degree n. preceding
.1782. the 29th, in a line parallel to y and a. Capricorni. A
^'little unequal. Appears diftorted with 227 and 278;
nor will 460 fhew it feparated ; with 657, two ftars
viiible ; 932 confirms it. Difficult to be feen diftindly
on account of its low fituation. Pofition 84° 48' n.
preceding. 20-feet refledor, 200. Both w.

48. Fl. 6*'" Cephei praecedens. In dextro brachio.

Sept. 27, A very minute and beautiful double flar. Near | de-

^1782. gree preceding the 6th towards 1? Cephei ; a pretty

' confiderablc telefcopic ftar. A little unequal. Both pr.

Almoft incontaft with 460; with 625, better divided;

with 6^7 ftiil better. Pofition 14^9' f. preceding.

49. X Cephei (Fl. 22'''') fequens ad boream.

Sept. 27, Double. About i\ degree n. following A, in aline
1782. from ^through X Cephei continued.. Extremely une-
qual. Both dw. Cannot be feen with 278, except
with long attention; with 460, if diameter of L.
Polition 85° 48' n. following; perhaps a little inac-
curate.
^o. A Aquarii (Fl. 73'"^') praecedens.

Sept. 30, Double. About 2| degrees preceding, and a little

1782. fouth of •A Aquarii; a confiderable ffar. Very unequal.

I'L. w; ; S. dw. With 278, lefs than i diameter of

L; with 460, 1 1 diameter of L. Pofition with 227,

6

41

o

of Double Stars. ^t

I, 41^ 12' n. preceding. The meaiure inaccurate on

account of the low power, and probably 3'' or 4° too
fmall.

51. Quae iequitur / (Fl. 52"") Cephei.,

Sept. 30, Double. About 2I degrees n. foUov/ing ;, towards
1782. 7 Cephei ;. a confiderable ftar. A httle unequal. Both
pr. A pretty objed with 227 ; with 460, i| diameter
nearly. Poiition 3° 36' f. preceding.

52. ParvTula Fl. 25'"" Orionisadje^la.

oa. 2, Double. A few minutes n. following the 25th.
1782. Orionis, in a line parallel to b Eridani and s Orionis,

Very unequal. L. afli w. ; S. dw,. With 460, i dia- .

meter of L. Pofition 52° 48' n. preceding* .

53. Parvula Fl. 30™"^ Orionis adje£la.

oa. 2, Double, About 10' preceding the 30th, in a line
1782. parallel to X and -y Orionis. Very unequaL L. w. ;
S. d. ; with 460, i diameter of L. Pofition 43° 24' 11,.
; following.

54. r (F:L, 20'"") Orionis praecedens. In malleolo liniflri cruris*
oa..4, Double. Near | degree preceding r, in a line fronx
1782. ^ through T Orionis continued. Very unequal. L. r. ;

Si dr. With 227, about 1 diameter of L. ; with 460^
about 2 diameters of L. Pofition 35° 42^n.. preceding.; ,
a. little inaccurate.
^^, Fl. S-*"" Tauri praecedens ad boream. ^
oa. g. Double. About i| degree n. preceding the 8th
1782. Tauri, or near 2 decrees f. following the 65th Arietis,
in a line parallel to the Pleiades and e Tauri ; a fmall
telefcopic ftar not eafily found. A little unequal.
L. r.; S, d. With. 227, lefs than i diameter of S. ; .

■ with

56 Mr. Herschel*s Catalogue

I. with 460, near two diameters. Pofition 82*^ 48' C

following.

^(). Fl. 54*'"Ceti fequens adauftrum.

Oft. 12, Double. About | degree f. following the 54th,
1782. towards J' Ceti. Nearly equal, Both r. With 227,
about I diameter; with 460, about \\ diameter. Po-
fition 87° 39^ n. following.

57. Fl. 70^"" et 67"" Orionis priciens.

oa. 12, Multiple. In a fpot wriich appears nebulous in th&
1782. finder, and is about 50' from the 67th, and 45^ from
the 70th Orionis. More than 12 ftars in view with
460 ; among them is a double ilar. The largeft of the
bafe of an ifofceles triangle, n. preceded by four ftars in
a line. Confiderably unequal. With 460, i full dia-
meter of L. Pofition 19° 48^ f. following..

58. 5 Lyras (Fl. 12*"") fequens. Inter educlionem cornuum.
0<a. 24, Double. About | degree following the 1 2th, in a

1782. line continued from the 11 through the 12th Lyrae;
the laft of a fmall telefcopic triangle. Extremely une-
qual. L. r. ; S. d* Not eafily feen with 227 ; with
460, near 2 diameters of L. Pofition 13° o' n. pre-
ceding.

59. Ab I (Fl. 18') Lyrse jG verfus.

oa. 24, Double. The moft fouth of two very fmall tele-
1782. fcopic ftars, which are the fecond pair fituated in a line
from i towards. /2 Lyrae. A little unequal. Both d. ;
the fainteft obje6: that can be imagined. With 460,
about I diameter. Pofition 75° o^ f. preceding; the
meafure is liable to fome error from the obfcurity.

60. E telefcopicis y tX.7< Lyr« auftralioribus et fequentibus.

Double

I.

oa. 24, Double. About I degree f. following A, lu a Hue

1782. parallel to « and y Lyr«; a very fmall telefcopic ftar.
Extremely unequal. Both dr. With 227, i full dia-
meter of L ; with 460, near 2 diameters of L. Poii-
tion 16^ 48' D. preceding.

61. Praeiens Fl. i^^ Equulei.

oa. 26, A minute double flar. About I degree n. p'receding
17S2. the 111: Equulei, in a line parallel to a Equulei and
y AquiliE ; a large ll:ar. Very unequal. Both pr.
With 460, i diameter of S. Pofitlon 18^ 24' n. pre-
ceding. A pretty objeQ:, but requires fine weather.

61. Sequitur Fl. 2"" Equulei.

OSt. 29, Double. About | degree f. following the 2d Equulei,
1782. in a line parallel to I Delphini and ^Equulei. Conii-
derably unequal. Both r. With 460, i| or i| dia-
meter of S. Pofition ^^"^ ()' f. preceding.

(^2^, y Equulei (Fl. 5^) auftralior.

oa. 29, Double. Full \ degree f. of 7, in a line from the
1782. 5th through the 6th Equulei continued. Equal. Both
dr. With 227, about \ diameter fcarce viiible ; with
460, about I diameter. Pofition 5° ^^' f. preceding.

64. <77 Arietis. Fl. 42. In poplite.

oa. 29, Treble. Excefiively unequal. L. w; S. both mere.
1782. points. With 227, neither of the fmall ftars can be
{^z\\^ except with confiderable and long continued atten-
tion, when they alfo appear ; the nearefh with this
power is | or _} diameter oi L. ; with 460, 1 1 or 1 1
diameter of L. The third is about ^^" or 26'^ diftant
.from E, by exact eflimation. >Po.0tion of both, being
all three in a line 19° 19' f. following; as exadl: as the
obfcurity will permit.
Vol. LXXV. I (>s^

rS Mr. Hekschel's Catalogue

I. 6^. In Nubecula /3 Sagitta: adje£la et fequenti.
Nov. A. Double, t degree n. following /3 Saglttie, towards
1782. 29th Vulpecula3 ; the largeft and mod fouth of a clufler
^ of fmall ftars that appear cloudy in the finder. Very
unequal. L. rw. ; S. pr. With 2 2J-, full i diameter
of L. ; with 460, about 1 1 or 2 diameters of L. Po-
rtion 14° o^ n. preceding. A third ftar in view, of the
5th or 6th clafs.

66. /3 (Fi.. 23^) Draconis auftralior et prsecedens.

Nov. 4, Double. About 1 1 degree f, preceding /?, in a line
1782. from V continued through jG Draconis. Pretty une-
qual. Both pr. With 460, if or 1$ diameter of L.
Polition 2° 24^ f. preceding,

67. Nebulam AurigcC pedem dextrum fequentem, priccedens.
Nov. 4, Double. About ^c^' from the 37th Nebula of M.

1782. Messier ; the largeft and moft preceding of two ftars.
Very unequal. Both pr. With 460, near 2 diameters
of L. Polition 23° ^Y n. following.

68. Parvula Fl. i o* Orionis quam proxime adje61:a.

Nov. 5, Double. The fmall ftar not many minutes from the
1782. icth Orionis. A little unequal. Both Vv^hitifh. With

460, near i diameter. Polition 84° 54' f. following;

a little inaccurate on account of the difficulty of feeing

the ftars well,

69. In Lyncis pe£lore.

Nov. 13, Double. About 3 degrees f. preceding the 19th

1782. Lyncis, in a line drawn from the 19th Lyncis to r Au-

rigte ; the 24th and 19th Lyncis alfo point to it nearly :

in a very clear evening it may juft be feen with the

naked eye. A little unequal. Both rw. With 227,

I dia-

^ Double Stars. ^c^

I. i diaaieter ; with 460, 1 1 or near i i diameter. Pofi-

tion 77° o' f. following.

70. s (^^* ^23*) Tauri borealior et praecedens.

Nov. I-', A very pretty double ftar. Near i degree n. pre-
i-'82. ceding f Tauri towards Capella ; the corner of a rhom-
boid made up of f, this, and two more, and oppofite
to ^. Confiderably unequal. L. pr. ; S. a little deeper
r. With 227, almoU: i diameter of L. ; with 460,
1 1 diameter of L. Pofition 36^ 24' f. preceding.

7^. Fl. 44'"" UrfaD majoris prascedens ad auftrum.

Nov. 19, Double. Nearly in the interfe6llon of a line from
1782. /3 Urfae majoris to the 39th Lyncis, croffed by one from
if/ to t; Urfae majoris ; the lafl; line (hould bend a little
towards ^ Urfas majoris. A little unequal. Both
whltifh. With 460, near 2 diameters of S. Pofition
2" 6' n. following.

72. Fl. 6^. Urf^e majoris.

Nov. 20, Double. Exceflively unequal. L. pr. ; S. a point.
1782. Notvifible with 227, nor hardly to be fufpecled unlefs
it has been firft feen with a higher power ; with 460,
1 1 diameter of L. or, when long viewed, full 2 dia-
meters of L. Pofition S3° 45' ^^' following. A third
flar in view. Equal to L. Colour rw. Diftance
I'o'^ 2^'", Pofition 22° 31' f. following.

y^. f2 (Fl. 6^) Arietls borealior et praecedens.

Nov. 22, Double. About 1 1 degree n. preceding /3 Arietis,
1782. towards (3 Andromed^e ; a confiderable ftar. Very une-
qual. L. r. ; S. deeper r. With 227, about | dia-
meter of L. ; with 460, full i^ or almofl: i| diameter
of L. when beft. Pofition jf 24' f. following.

I 2 74.

6o Mr. Ker^chel's Catalogue

I 74-, Fl. 39^ Arietis borealior et praecedens.
Dec. 22, Double. About | degree n. preceding 39 Arietis,

1782. towards y Trianguli ; a pretty large telefcopic flar. A
little unequal. Both pr. With 227, near i diameter
of L. ; with 460, about il diameter of L. Pofitloa
20° 36' n. preceding.

yc. Fl. 26'"' Orionis priEcedens ad aufrrum.
Jan. 9, Double. About I degree f. preceding the 26th, iii-

1783. a line parallel to <5^and /S Orionis ; the fartheft of two ;
or I degree f preceding the 30th in the fame diredlion.
Nearly equal. Both w. or rw. With 460, perhaps a
diameter. Pofition 89^ 36^ n. preceding ; but not very
accurate.

^6. In pedore Lyncls.

Tail. 2-^, Double. Not eafy to be found. A line from the I9tb
178-2. Lyncis to v Geminorum eroded by one from Q Urfe
majoris to s Auriga;, points out a ilar but jufl: vifible in
a fine evening ; it is perhaps about three degrees from
the 19th Lyncis ; when that flar is found, we have the
double flar about i degree n. following the fame, in a
line parallel to t Geminorum and the 19th Lyncis..
Confiderably unequal. Both afh w. With 460, I
diameter of S. Pofition o' o' preceding. A third
large ftar in view. Diflance 1' •]" \(y"' * Pofition
3° 42' f preceding.

77. a (Fl. 7^) Crateris borealior.

Tan. 9 1 Double.. Near 2| degrees north of a Crateris; a^

178-. fmall telefcopic ftar, about | degree following the
moft north of two large ones. Pretty unequal. Both
whitlfli. With 227, lefs than half diameter of S. ;

with

cf Double Sfars^ 6r

I. with 460, near i diameter; with 625, a little more

than I diameter. Poiition 82° 24.^ n. following.
'78. Fl. I i^ Libras borealior.

Jan. 31, Double. Near 2§ degrees north of the i ith Libr^e^

1783. in a line parallel to f/. Virginis and the 109th of the

fame conftellation. Equal. Both inclining to r. With

460, full I diameter. Pofition 58'-' 24' n. preceding,

or f. following.

yg. Fl. 46 Herculis, In dextro latere.

Feb. 5, Doabje. Extremely or almofl: exceffively unequal.
1783. L. w. ; S. d. With 227, it is hardly vifible; with
460, near i diameter of L. Poiition 66^ 36' f. fol-
lowing.

80. Fl. 81 Virginis.

Feb. 7, Double. Equal. Both pr. With 227, near | dia-
1783. meter; with 460, f diameter. Poiition 41^ 12' n. fol-
lowing or f. preceding.

81. rr Serpentis (Fl. 44"'^) pra3cedens ad auilrum.

Mar. 7, Double. About 1 1 degree f. preceding tt, towards
1783. Jt; the moft north of two. A little unequal. Both
r. With 460, 1 1 diameter of L. Poiition 49^ 48' f.
preceding. A third large flar in view ; paler than the
other two. Diftance from the two taken as one ftar
56'' 28^'^ Pofition, with L. of th^ two, 31^ 48' f^
preceding.

82. Fl. 49 Serpentis.

Mar. 7, Double. The mofl north and following of two
1783. ftars. A little unequal. Both pr. With 227, | qr |

diameter, and a very minute and beautiful obje6t ;

with 460, I diameter. Pofition 21° ^^^ n. preceding.

3 83,

62 Mr. Herschel's C^/a/ogue

I. 83. X Ophiuchi. Fl. 10. In ancone fmiftrl brachll.
Mar. 9, A very beautiful and clofe double flar. L. w. ; S.
1785. blue; both fine colours. Confiderably or almofl: very
unequal. With 460, :| or j diameter of S. ; with
932, full } diameter of S. Pofuion 14° 30' n. fol-
lowing.

84. Fl. ^o^ Aurlgse auftrallor.

Mar. 18, Double. Near i degree f. of the 50th Aurigce, m

1783. a line parallel to (3 and d. Very unequal. L. r. ;

S. dr. With 227, about | diameter. of L. 3 with

460, almoftj 1 1 diameter of L. Pofition 14° o' n.

following.

2^. Fl. 36^"" Lyncls fequens ad auftrum.

Mar. 24, Double. Near f degree f. following the 36th Lyn-

1783. CIS, in a line parallel to the 31ft Lyncis and n Urfas
■majoris ; of two the neareft to the 31^ Lyncis. Con-
fiderably unequal. Both w. With 227, I diameter of
L. ; or when long kept in view, 1 1 diameter of L. ;
with 460, and after long looking, 2 diameters of L ;
otherwife not near fo much. Pofition 88° 57' n. fol-
lowing.

86. Fl. 105^ Herculis borealior.

Mar. 27, Double. One full degree n. of the 105th Herculis,

1783, in aline from the 72d Serpentarii continued through the

I octh Herculis ; a fmali telefcopic /lar. Confiderably

unequal. Both dr. With 460, a little more than i

diameter of L. Pofition 79° 24' n. preceding.

87. q Ophiuchi. Fl. 73.

/ April 27, A very minute double flar. Confiderably unequal. L. r.

1783. S. r. With 227, not to be fufpeded unlefs known to

be double, but may be {een wedge-formed, and with

6 long:

of 'Double Stars, 63

L long attention I have alfo perceived a mo{l minute divi-

fion ; with 460, about \ ox ^ diameter of S. Pofition
2° 48' f. preceding.

88. T Ophiuchi. Fl. 69. In dextra manu fequens.

April 28, Theclofefl of all my double ftars ; can only be fuf-
i-S-^. pefled with ^60; but 932 confirms it to be a double
ftar. Pretty unequal. Both pr. or wr. It is wedge-
formed with 460; with 932, one-half of the fmall
ftar, if not three-quarters feem to be behind the large
ftar. Poficion of the wedge 61° 36' n. preceding.
V Ophiuchi, juft by, is perfedly free from this wedge-
formed appearance.

89. Illas ad Fl. 56*"' AndromediE praecedens ad boream.

July 28, Double. About f degree preceding, and a little north
1783. of the two ftars that are about the place of the 56th An-
dromeda?, in a line towards ^; a confiderable ftar; and of
two in a line parallel to /3 and y Trianguli that which
is nearefl: to the 56th Andromedae. Pretty unequal.
L. drw. ; S. dpr. With 227, near i diameter of L. ;
with 460, about \\ diameter of L. Pofition 75" 30'
f. following.
90. jQ Aquarii (Fl. 22^^") praecedens ad auftrum.
July 31, Double. About 4i degrees from /3 towards ^ Aquarii.
1783. A little unequal. Both dw. or pr. With 460, i\
diameter or near 2. Pofition 77° 36^ f. following.
91.7/ Aquilae (Fl. 50^"") prascedens ad boream.
Aug. 7, Double. About \ degree n. preceding y, in a line
1783. parallel to y and ^Aquilae; of two that nearefl to y.
Very unequal. L. dpr. ; S. d. With 227, hardly
vifible, and like a ftar not in focus ; with 460, appears

nebulous

64 Mr, Herschel's Catalogue

I. nebulous on one fide, but is a double flar; with 932,

about 1 1 diameter of L» Pofition 8° 18' 11. preceding,

92. TT Aqully?. Fl. 52. Duarum in liniilro humerofequens.
Aug. 27, A minute pretty double fiar. A little unequal.

1^83. Botli pr. With 460, | diameter of L. or near | dia-
meter of S. Pofition 3-}-'^ 24^ f. following.

93. Fl. 62""" Aquil;^ praecedens ad boream.

Sept. 12, A minute double fl:ar. About | degree n. preceding
.1783. the 62d, in a line parallel to Q and f Aquili£; a pretty
confiderable ftar. Very unequal. Both inclining to pr.
With 278, almofl in contadl ; with 460, near | dia-
meter of S. ; when in the m.eridian, and the air fine,
near i diameter of L. Pofition 19" 9' n. preceding.

94. 5 Cygni. Fl. 18. In ancone alae dextne.

Sept. 20, Double. Very unequal. L. fine w. ; S. afli colour
1783. inclining to r. With 278, about | diameter of L. ;
with 460, I diameter of L. ; with 932, full i| dia-
ineter of L. in hazv weather, which has taken off the
rays of L. and and thereby increafed the interval.
Pofition 18'' zi' n. following; perhaps a little inac-
curate.

95. Fl. QiT"^ Cygni fequens ad auftrum.

Sept. 22, Double. Full 1} degree f, following the 33d,

1783. towards | Cygni ; a pretty confiderable flar. Very une-
qual. L. w. ; S. inclining to r. With 460, at firfl
about f diameter of L. ; but, after looking a confidera-
ble time, and in a fine air, near i| diameter. Pofition
72° 15^ n. preceding-

<)(^, 7} (Fl. 21'"') Cygni fequens ad auftrum.

Sept. 23, Treble. Full 1 1- degree n. following ij, in a line
57^3- parallel to ,/3 and K Cygni. The two neareil confiderably

unequal.

of Double Stars, 65

I. unequal. Both pr. With 460, i diameter of S. or |
diameter of L, Pofitloii 89° 18^ f. following. The
two farthefl: coniiderably unequal ; the colour r. Difi:.
Polition 56*^ 3' n. preceding.

97. Fl. 51"" Cygni fequens.

Sept. 24, A minute double flar. About zf degrees following
1783. the 51^^, in a line parallel to I and u Cygni ; the largeft
and moil fouth of an obtufe-angled triangle ; a very
confiderable ftar. Pretty unequal. Both rw. ; but S.
a little darker r. With 278, | diameter of S. and
beautiful ; with 460, | diameter of S. Pofition 46'
24' n, following.

SECOND CLASS OF DOUBLE STARS.

11.39. Procyonem juxta.

Feb. 2, Double. About 2 degrees f. following Procyon, In

1782. a line from X Geminorum continued through Procyon.

ExcefTively unequal. L. pr. ; S. not vifible with 278 ;

with 460, more than 3 diameters of L. Pofition, by

the affiftance of a wall * and micrometer 54" 28' f.

following.

40.

* When the fmall ftar is fo faint as not to bear the leaft illumination of the
wii;es, its pofition may ftill be mcafured by the affiftance of fome wall or other objea ;
for an eye which has been fome time in the dark, can fee a wall in a ftiir-light
evening fufficiently well to note the projeaion of the ftars upon it, in the manner

VOL. LXXV K which

%

55 Mr. Herschel's Catalogui

11. 40. * Seen nek ad (p Cancri. Fl. 23.

Feb. 2, Double. K little unequal. Both rw. With 227,
J782. near 2 diameters; with 460, 2| diameters of L. Po-
{ition 56" 42^ n. followiug.

41. * Prima ad u Cancri. Fl. 24.

Feb. 2, Double. Confiderably unequal. Both pr. With
J782. 227, 1 1 diameter of L. ; with 460, 4 diameters of L.
Poiition 32'' 9' n. following.

42. E telefcopicis ^ Virginis precedentibus-K

Feb. 6, Double. About il degree f. preceding i Virglnis^
1782. in a line parallel to ^ and /5 ; the moft fouth of three

forming an arch. Extremely unequal. L. vv. ; S.

hardly vifible with 227 (but with a ten-feet refle£tor

S. b.) ; with 460, above 2 diameters of L. Pofitioa

52° 24^ f. following.
4.9. Fl. a 2^"" Leonis priEcedens ad auftrum. In dextro genu.
Feb. 17, Double. Near f degree f. preceding the 43d, in 3
1782. line parallel to c. and the 14th Leonis. Very unequal.

L. w. ; S. d. With 227, near 2| diameters of L*

when beft. Pofition 85° 2' n. following.
44. 0 Virginis. Fl. 84. Verfus finem alas dextro.
Feb. 17, Double. Extremely unequal. L. w. inclining to r. ;
1782. S. d. Requires attention to be feen with 227; with

460, 2§ diameters of L. Pofition, with 278, 29° 5'

f. preceding.

which has been defcribed with the lamp -micrometer, Phil. Tranf. vol. LXXIT. p.
169 and 170. Then, introducing fome light, and adapting the fixed wire to
the obferved direftion of the ftars on the wall, the moveable wire may be fet to
the parallel of the large ftar, which wiU give the angle of poiition pretty
accurately.

t See note to IV. 5 r»

45*

of Double Stars, 67

11. 45. Fl. 54 Virgials,

April 3, Double. A little unequal. Both w. With 227,
1782. 1 1 or near i| diameter. Pofition 57^ o' n. following.

46. Fl. 42^"^ Comae Berenices fequens ad auflrum,

April 15, Double. About i| degree from the 42d Coma:
1782. towards v Bootis ; the moft louth of a telefcoplc equi-
lateral triangle. Exceflively unequal. L. pr. ; S. d.
With 278, 2| diameters of L. ; not fo well to be feeu
with higher powers. Poiition 6^ 42^ f. following. A
third flar preceding, above i '.

47. Fl. 2 Comas Berenices.

April 18, Double. Confiderably unequal. L. rw. ; S. pr.
1782. With 278, 2 diameters of L ; with 460, above 2 dia-
meters of L. Pofition 27° 42' f. preceding.

48. Prope Fl. i6''",Aurigce.

Aug. 28, A minute double ftar. Lefs than I degree f. pre-
1782. ceding the i6th, in a line parallel to the 10 and 8
Aurigae ; the preceding ftar of a fmall triangle of which
the 1 6th is the largeft and following. A little unequal.
Both pr. With 227, i| or, when beft, i| diameter
of L. Pofition 15° 48' n. following.

49. 0 (Fl. iio*)Pifcium borealior. In lino boreo.

Sept. 3, Double. About | degree n. of, and a little pre-
1782. ceding iioth, towards 71 Pifcium. A little unequal.
Both wr. With 460, about 3 diameters of L. Pofi-
tion 59° 6' n. preceding. A third flar iii view, about
1 1 min.

50. Fl. 38. Pifcium. In auftrino lino.

Sept. 4, Double. Pretty unequal. Both pr. With 227,

1782. full 2 diameters of L. ; with 460, about 4 diameters
of L. Pofition 25° 3^ f. preceding.

K z S^'

68 Mr. IIerscuel* s Catalogue

II. 51. /i Capiicorni. Fl. ii, Trium in roftro fequens.
Sept. 5, Double. Very unequal. Both rw. With 460, if
1782. diameter of L. Pofition 84° o^ f. following. A thitd
ftar in view.

52. 0 (Fl. 40*"") Perfei prsecedens ad boream.

Sept. 7, Double. Almofl: | degree preceding the 40th, in 3
1782. line parallel to f and the 38th Perfei. Equal. Both w.
With 227, nearly 2 diameters. Pofition S'' 24^ n. pre-
ceding.

53. Fl. 12*"* Camelopardali praecedens.

Sept. 7, Double. Lefs than | degree preceding the i rth and
1782. 1 2th, in a line from the ift Lyncis continued through
the 1 2th Camelopardali. Extremely unequal. Both
dr. With 227, it appears like a ftar with a tail; but
932 fhews it plainly to be only a double ftar ; with
227, not much above i diameter of L. ; with 932,
about 3 1 diameter of L. Pofition 1 8^ ^^^ f. following ',
a little inaccurate.

54. Quae praecedit e (Fl 74^™, oculum boreum) Tauri;

Sept. 7, Double. Near | degree f. preceding s, m a line
1782; parallel to a and y Tauri; a f mall ftar. Extremely
unequal. L. rw. ; S. d. With 460, above 3 diameters
of L. Pofition 68° 42' f. preceding.
^^. Fl. 4^ Ceti auflralior et fequens.

Sept. 9, Double. About i degree f. following the 4th and

1782. 5th in a line parallel to ^ and r Ceti ; in the fhorter leg

of a redbangular triangle. Very unequal. L. r. ; S.

d. With 278, rather more than 2 diameters. Pofi*

tion 21° 42'' n. preceding.

56. /3 (Fl. 6"") Arietis ptiCcedens ad boream.

7 Double

of Double Shirs. 69

II. Double. Almolt i degree n. preceding 13 Arietls,

Sept. 10, towards f Andromeda; a fmall ftar. A little unequal.

1782. Both reddifh. With 227, full 2 diameters of L. Pofi-

tion 23° 12' n. preceding. A third ll:ar 2^ or 3' preceding,

in the fame diredioii with the two flars of the double ftar.

57. Ad Fl. 72^"" Aquarii.

Sept. 27, Treble. About 2I degrees following x, in a line parallel

1782. fo cc and V] Aquarii. The neareil: a little unequal. Both

r. With 460, 2| diameters of L. Pofition 25° 51' f.

preceding. The two farthefl a little unequal. Of the

5th clafs. About 50" or 55° f. following.

58. Fl. 56^Ceti auilralior et fequens.

Sept. 27, Double. About | degree f. following the 56th, in a
1782. lin-e parallel to ^ and r Ceti. Confiderably unequal.
Both dw. With 278, li diameter of L. Pofition
25'' 12' u. preceding ; too low for accuracy.

59. ^ (Fl. 46*"") Aquarii fequens adauifrum.

Sept. 30, Double. About 2 degrees f. following ^, in a line pa-
1782. rallel to (3 and ^i\quarii ; there is a very confiderable ftar
between this and ^, not much out of the line. Pretty
unequal. Both dr. With 227, 2| or 2| diameter of
L. Pofition 61° 12' n. preceding.
■60. I (Fl. 5'") Canis majoris fequens ad bore'am.
Sept. 30, Double. About i degree n. following the 2d ad J,
1782. ii"^ a line from the 4fth continued through the 5th
Canis majoris nearly. Very unequal. L. rw. ; f. d.
With 227, 1 1 diameter. Pofition 67° 36' n. preceding.
61, ^ (Fl. 47^"") Orionis fequens ad auftrum.
oa. 2, Treble. About i| degree f. following -zer in a line
i/S^' parallel to (p and a Orionis ; the fmallefi: and moll: fouth
of three forming an arch. The two nearefl extremely

unequal.

^D M)\ Herschel*s Catalogue

^J. unequal. L. dw. ; S. a mere point. With 227, 1 1 or

i| diameter of L. Pofition 4*^ 54' n. following; too
obfcure for accuracy. The two farthefl: extremely une-
qual. S. a mere point. Of the foiirth clafs. Pofi*
tion about 50" f. following.
•62. Fl. 2r P^g3^ adjedla.

oa. 4, Double. In a line with, and north of, the two flars
3782. that are about the place of the third Pegafi. A little
unequal. Both duiky r. With 227, about 3 dia-
meters of S. Pofition 88'^ 24' n. preceding; perhaps a
little inaccurate.
€3. Fl. 2"" et 4^"" Navis praecedens.
oa. 12, Multiple. Near 2 degrees preceding the 2d and 4th
1782. Navis; the middle one of three. One of the multiple
is double. Nearly equal. Both w. or afh colour.
With 227, about 2I diameter, and not lefs than 20
fliars more in view ; with 460, about 3 diameters. Po-
rtion 30° 12^ n. preceding.
^4. g (Fl. Si'"") Geminorum ad auftrum fequitur.
oa. 13, Double. About f degree f. following^, in a line from
1782. ^continued through g Geminorum nearly; the neareft
and largefl: of two. Very unequal. L. r. ; S. bluifli
r. With 227, above 3 diameters of L, Pofition
4° 9' n. preceding.
65, PoUucemfequens ad boream.

oa. i^,, Double. Full | degree n. following /3, in a line from
2782. ^ continued through /3 Geminorum; the flar next to
the middle one of three, nearly in a line. Exceffively
unequal. L. rw. ; S. d. With 227, above 2 1 or near
3 diameters of L. and 5 other ftars in view ; with 460,
^ibove 3 diameters of L. Pofition 89'' iz' n, following.
1 66.

of Double Stars^ js^

II. 66, Juxta ^ Delphini.

oa. 19, Double. Fnll | degree f. preceding y^ towards ^
1782. Delphiiil. Confide rably unequal. L. pr. ; S. r. With
227, l| diameter of L. Pofitioii 78'' 4.2' n. preceding.
67. /3 (Fl. 10^"*) Lyr^ priEcedejis ad boream.
oa. 19, Double. The 4th telefcopicftar about i§ degree n*
17S2. preceding /3, in a line parallel to y and a. Lyrae. Ex-
tremely unequal. L. r. ; S. ,dr. With 227, i| or
almofl: 1 1 diameter of L. With 460, above z. diame-
ters of L. Pofition 68° 6' f. following.
6^. Proxime ^ Lyrae.

oa. 24, Treble. About 2| minutes f. following ^ Lyrse.
1782. The two neareft, a little unequal. Both dr. With.
460, 3 full diameters. Pofition 8° 24' n. following.
The fartheft as large as L. of the two nearefl at leafl.
Colour dr. Pofition with L., 25° 57' f. preceding*
Diftance of ^ Lyras, which is in view, from the two
neareft 2' if 30'''. Pofition d^"" 12^ ^ being n. pre*
ceding, or the double ftar f. following.
6p. Fl. 4^"" Cygni fequens ad boream.

oa. 24, Double. Near I degree n.. following the 4th Cygni,

1782. in a line from y Lyras continued through the 4th

Cygni. A little unequal. Both w. With 227, about

2 diameters of L. or 2| when beft. Pofition 29° 12'

n. following.

7-0. Twv 8 telefcopicarum % (Fl, 15.) Sagittas fequentium

ultima.
Nov. 6, Double. About i \ degree f. following % Sagittse, in
J78;ji, a line parallel to y Sagittas and y Delphlni. Extremely
xjnequaU Both r. ; S. deeper r. With 227, il dia-
meter

«i Mr, Hkrscuel^s Catalogue

II. meter of L. ; with 460, above 2 diameters of L. Po-
fition 72° 57' n. following.

71. Fl. 58* Aurigae auftralior.

Nov. 6, Multiple. About | degree f. of the 58th Aurigae, in
iy82. a line parallel to /3 and Q, A clufter of ftars containing
a double ftar of the fecond, and one of the third clafs.
That of the fecond very unequal. Both r. With
460, about 2 1 diameter of L. Pofition 44° 36' n.
following ; that of the third equal. Both r. With
227, above 20 ftars in view. Diftance 17''' 41'^''. The
two double ftars are in the following lide of a fmall
telefcopic trapezium*

72. Fl. 13^ L.yncis auftralior.

Nov. 13, A pretty double ftar. About 1 1 degree f. of the 13th
1782. Lyncis, towards 9 Geminorum ; a coniiderable flar.
Nearly equal. Both pr. With 227, full 2 1 diameters;
with 460, almoft 4 diameters. Pofition 11° of. pre-
ceding.

73. Fl. 2i*Urfi£ majoris.

Nov. 17, Double. Very unequal. Both rw. With 227, 2I
1782. diameter of L. ; with 460, above 3. Pofition 36^45'
n. preceding.

74. V (Fl. 4*)Crateris borealioF.

Nov. 20, Treble. Near i degree n. preceding v Crateris,
1782. towards a Leonis. The two nearefi: equal. Both dw.
With 227, 2-i or 3 diameters. Pofition 71° ^^^ n. fol-
lowing. The fartheft larger than either of the two
other flars. Of the fixth cla-fs. Pofition. about 68 or
69** f. preceding the double ftar.

75'

tf Double Stars, ^r^

II. 75. Fl. t 18 Taurl.

Pec. 7, Double. A little niiequal, L. w. ; S. w. Inclining
1782. to r. With 278, i\ diameter of L- ; with the fame
power by the micrometer 4'^ \^'" ', more exadlly with
625, 5'' "2.' ' . Portion 77° 15'. I could jud: fee it
with an 18-inch achromatic, made by Mr. Nairne ; it
was as clofe as poffible, and a pretty objesfl:.

76. T (Fl. (y-^^^ i^rietls auftralior et prj^cedens.

Dec. 23. Double. About i degree f. preceding r Arietis,

17S2. towards ^a Ceti ; the mofr fouth of two fmall telefcopic

flars. Nearly equaL Both w. With 227, above 3

diameters; by the micrometer ^" ^q'". Pofition ly

24' f. preceding.

77. *Fl. 17 Hydrse.

Dec. 28, Double. The largefi: of two. A little unequal.

1782. Both w. With 227, 2 1 diameter of t«. ; with 460, i f
diameter. Pofition 90° o' north.

78. % (Fl. 63"'") Leonis fequens ad auftrum.

Jan. I, Double. About | degree f. following p(^, towards r
J 783. Ivconls; the fmalleft of two. Very or extremely un-
equal. L. r. ; S. d. With 227, 3 full diameters of
Iv. Pofition 75° 2\' f. following.-

79. Fl. 39 Bootis.

Jan. 8, A pretty double ilar, A little unequal. Both pr.

1783. With 227, near \\ diameter of L. ; with 460, near 2
diameters of L. Pofition 33^ 21^ lu following.

.80. d (Fl. 40^^) Eridanl adjecla*

Jan. 31, Double. About i :^ min. f. following d Eridanl.
1783. Very unequal. Both dr. With 227, hardly vilible ;
with 460, very obfcure. Pofition 56^ 42^ n. preceding.
Vol. LXXV. l^ Diftancc

74 -^^^^- Herschel's Catalogue

II. Diftance of L. from J Eridanl, with 227, i' z\" ^i^'i"^*

Poiitioii of L. 17° 53' f. following ^ Eridaiii.

81. Fl. 49^"" Eridani fequens.

Jan. 31, Double. Near i degree following the 49th Eridani^,
1783. towards § Orionis. Very unequal. Both dw. With.
227, full I diameter of L. ; with 278, 1 1 or i| dia-
meter of L. ; with 460, 2| or 3 diaiTieters of L. Po-
rtion 51° 36' n. preceding.
82.. Fl. 31^'" Bootis fequens ad auftriim,

Feb. 3, Double. Near i degree 1'. following the 31 ft, in a
1783. line from u continued through the 3 i ft Bootis ; the moft
Ibuthoftwo. A little unequal. L. w. ; S. dw. With
227, about 1 1 diam.eter of L. ; with 460, about 3 dia-
meters of L. Pofition \° o' i. following. A third ftar
in view, 20° or 30° n. preceding.

82. Fl. 22^ Andromedas borealior.

Feb. 26, Double. Within | degree north of the 22d, In a
1783. line parallel to the 19th and i6th Andromeda; the folt

lowing and fmalleft of two. Confiderably unequal. L.w.;

S. d. With 227, 1 1 or i| diameter of L. ; with 460,.

more than 2 diameters of L. Pofition 5° 48^11. following.

84. Fl. 65 Pifcium.

Feb. 27, Double. Nearly equal. Both pr. With 227, near
1783. i§ diameter of L. ; with 460, full 2 diameters. Pofi-
tion 30° ^7' n. preceding.

85. h (Fl. 36') Serpentis borealior et fequens.

iMar. 4, Double. About 1 1 degree n. following hy nearly in
1783. a line from the 3 2d continued through the 36th Ser-
pentis. Extremely unequal. L. w. ; S. dw. With
227, I full diameter of L. ; S. hardly to be feen ; with
460, full 2 diameters of L. Pofition 46° 9' n. preceding.

86.

of Jjonhle Sictru y^'

IJ. 86. Fl. 49**" Serpentis prsecedens ad auftrum.
Mar. 7, Double. About if degree f. preceding the 49tli, in
1783. a line with the 49th and another between this and the
49th Serpentis, each nearly at | degree didance. Very
unequal. L. dw. ; S. d. With 227, 2 diameters, or
2 1 when befl:^ Polition 53^ 9' i'. following.
%y. Fl. 29^et30^ Monocerotis auftralior.
Mar. 8, Multiple. It makes nearly an equilateral triangle
1783, with the 29th and 30th Monocerotis towards the fouth.
Among many, the fourth from the fouth end of an
irregular long row is double. A little unequal. Both
pr. With 227, 1 diameter of L. and 16 more in
view. Polition 86° 12' f. following. *

^8. b) (Fl. 51^"") Serpentis prcecedens ad auftrum.
Mar. 8, Double. About | degree f. preceding the 51 ft,
1783. towards the 13th Serpentis. Very or extremely une-
qual. Both t. With 227, 2 1 diameter of L. when
beft; with 460, near 3 diameters of L. Pofitioa
44° 45^ n. preceding.
(89. Ad Genam Monocerotis.

Mar. 26, Double. About i degree n. preceding the 1 2th Mo*
1783. nocerotis, in a line parallel to cc and x Orionis ; the
fmalleft arid moft north of two. Confiderably une*
qual. L. r. ; S. bluiih r. With 227, near 4 diame-
ters of L. when heft. Polition 50° 5^' n. following.
i^o. Fl. ioo^"" Herculis prsecedens ad boream,
i^t^vAjf Double. About r| degree iV. preceding the locth,
^^83. towards {/, Kerculis ; a very fmall telefcopic flar; the
moH: towards ^ and fmalleft of three forming an arch.
Conliderably unequal. Both dw. With 227, about
2 drameters of L. Pofition -j^'^ 9' f following.

L 2 51.

id .Mr, Herschel^ s'C^Ui/ogue

II. 91, s (Fl. 15') Sagittal auftralior.

Apr. 5, Treble. About twice as far louth of 2- Sagltta?, as z
fjB%. and the ftar near it are from each other ; a fmall ftar.
The two neareft very unequal. L. pr. ; S. r. With
227, 1^ diameter of L. Pofitiou 74° 54' f. preceding.
The third with L. extremely unequal. S. d. With
227, about 2 diameters of L. or more. Poiition about
40*^ or 50° n. preceding. With more light this would
be a fine object.
^z, lu Camelopardall clune.

Apr. 30, Dfcuble. About four times the diftance of the i oth
1783. and 1:2th Camxclopardaii, north of the loth, and almof^
in the fame direction with the loth and 12th, is a ftar
of between the 5th and 6th magnitude not miarked in
Flamsteed ; naming that ftar A, we have the fol-
lowing dire6lion. About I degree preceding A Came-
lopardall, in a line from the 2d Lyncis continued
through A ; the fecond from A. Very unequal. L;
w. ; S. d» With 227, li or 2 diameters of L. Po-
fttion 22° 42^ f. following. Very inaccurate.
^3. £ (Fl. 13') AquiliE auftralior.
May 25, Double. Near I degree fouth of, and a little fol*
37S3. lowing e, towards X Aquilas, a very fmall ftar. Very
luiequal. L. dw. ; S. dr. With 460, above 2 dia-
meters of L. Pofition 16" o' n. preceding.
94. i (Fl. 17^"") Andromed^e pra:cedens ad boream.
Aug. 19, Double. About if degree n. preceding; Andromeda
1783. iii a line parallel to cc and (3 Caffiopeia;^ ; in the ftde of a
trapezium of four fmall ftars. Pretty unequal. Both
r. With 460, 24 diacneters of L» Poiition 34° 24'
11. preceding. <

95-

of Double Stars. yj

II. pj. VI (Fl. ^5') AquiliE auftralior.

Sept. 12, Double. About I degree ibuth of ?;, in a line from
17S3. « continued through i; Aquilic ; a fmall liar. A little

unequal. Both duiky a(K-coloured. With 460, near

3^ diameters of L. ; with 278, near 2 diameters of L.

Pofition 29° 3^ n. preceding.
96. 5 (Fl. 65^) Aquilae borealior et fequens.
Sept. 12,. Double. About i| degree n. following Q Aquilic.,
J783. towards e Delphini ; more accurate towards 29 Vulpe-

culi£ ; a very conflderable flar. Nearly equal. Both

rw. With 278, about if diameter of L. ; with 460,.

full 2 diameters. Pofition 56" 12' f. preceding.
97' f (Fl. 64^"") Cygni praecedens.

Sept. 15, Treble. About i degree, preceding f, towards the
^1783. 4iftCygni^, alargeftar. The two neareft extremely

unequal. L. w. ; S. pr. With 460, 2| diameters of

L. Pofition 45° 15^ n. preceding. The third with L.

extremely unequal. Of the 5th or 6th clafs; about-

^0° f. preceding.

98. Fl. 49 Cygni.

Sept. 15, Double. Very unequal. L. r. ; S. bluifli r. Witk
1783. 278, 1 1 diameter of L. ; with 460, 2i diameters of
L. Pofition 31° 48^ n. following.

99. /3 (Fl. 6"") Cygni fequens ad boream.

Sept. 15, Double. Near | degree n. following /2, towards ^
1783. Cygni. Very unequal. Both dw. With 27S, if

diameter of L. ; with 460, about 2 diameters of L.

Pofition 87° 48' n. following.

100. Fl. 51^ Cygni borealior et fequens.

Sept. 24, Double. Near two degrees n. following the 51 ft

1783. Cygni, in a liiie parallel to 0 Cygni and a Cephei ; a.

4 pretty

y8 'Mr. Herschel's Catalogue

II. pretty confiderable ftar. Very unequal. L. w. ; S.

inclining to blue. With 2^8, extremely unequal,
and li diameters of L. when befl ; requires attention to
be feen well with this power; with 460, full 2 diame-
ters of L. or 2i when beft, otherwife much lefst Poii-
tiori 15° 51^ n. following.

101. T'L. 57^™ :: Camelopardali prsecedens ad boream.

Sept. 26, Double. About 2 degrees n. preceding the 57::,
1783. towards the 42d Camielopardali ; a confiderable flar
near three fmaller, forming an arch. About i degree
from the double ftar V. 135. Conliderably unequal.
Both pr. With 278, i| diameter of L. ; with 460,
2| diameters of L. Pofition 67° 15' n. preceding. '

102. e (Fl. 29^) Orionis auftralior et prascedens.

Sepr.^27, Double. About | degree f. preceding e, in a line

1783. parallel to ^ and /3 Orionis ; the largeft of feveral. Very

imequal. L. pr. ; S. inclining to garnet. With 278,

near 2 diameters of L. With 460, 2I diameters of

L. Pofition 52^ 24^ f. following.

THIRD CLAsS of DOUBLE STARS.

III. 47. e Pollucis; Fl. 38 Gekmdfli^m.^ In cake.
Dec. 27;^- Double. Extremely viiiequal. ' L. rw. ; S. r. Dif-
1781. tance, with 460, y'' 48''''. . Pohtion 89° 54' f. follow-
ing. Two more in view, the neareft of them perhaps
%o" ■', they for\ii a redanglc nearly.

4§.

of Double Stars, hg

lit. 48. /■ (Fl. 61*"") Geminorum praecedens ad boream.
Dec. 27,- Double. About § degree n. preceding r, in a line

1781. parallel to it and the 60th Geminorum; near two de-
grees from ^. A little unequal. Both pr. Diftance
6'^ 15^^' Pofition 43° 54^ n. following.

49. ^ (Fl. 4'^") Hydri£ praecedens ad boream.

Jan. 20, Double. About 1 1 degree n. preceding ^, in a line

1782. iiom 7] continued through ^ Hydrae. Pretty unequal.
L. r. ; S. garnet. Diftance 12'' 30''". Pofition 62'^
48' n. following.

50. & Virginis. Fl. 51. De quatuor ultima et fequens;
I;eb.6, Treble. The two neareft extremely unequal. L. w. ;
17S2. S. d. Diftance 7'^ 8'^^ ; but inaccurate on account of

the obfcuritj of S. Pofition 69'^ 18' n. precedingw
For meafures of the two fartheft fee VI. 43.

51. Fl. 88 Leonis. In dextro clune.

Feb. g, Double. Extremely unequal. L. rw. ; S. r. Dif-
J782. tance 14^^38^^^; a little inaccurate. Pofition 47° 33'
n. preceding.

52. Fl. 10'"* Orionis fequens.

Feb. 17, Double. Above | deg. n. following the loth, towards
1782. w Orionis. Confiderably unequal. Both pr. Difbance

with 278, 13^' 40^'^ Pofition ^7° 3' n. following.
^^. y Virginis borealior et fequens.

Feb. 17, Double. Near 2! degrees n. following y, in aline
1782. parallel to e and u Virginis ; a confiderable flar; a line

from y to this pafies between two of nearly the fame

magnitude with this frar. A little unequal. Both d,.

Diftance 12'' 58'''. Pofition 79° o' n. preceding.

2, 54*

8(S M}\ Herschel's Catalogue

III. 54. Secuncla ad cr Urfae majoris. Fl. 13, In fronte.
June 2, Double. Extremely unequal. L. w. ; S. r. Dif-
1782. tance j'^ 56^'^ Polition 13" o'n. preceding.
55. V (Fl. 18'™) Coronas borealis fequens ad boream.
June 14, Double. Confiderably unequal. L. dr. ; S. d.
1782. Diftance with 227, about 3 or 4 diameters of I^. being
too obfcure for the micrometer. Pofition 2)3^ A^' ^'
preceding. Dlftance of the largeft of the two from u
Coronas I ^ 18^' V. Pofition of the fame with u, 64''
24' n. following.
s^6, S (Fl. 72^) Serpentarii borealior.

June 16, Double. About 2i degrees n. of the 72d Serpen-
1782. tarii ; a confiderable ftar. A little unequal. Both r.
Diftance 7'' 3y'^^ Pofition 9° 42'' f. preceding. A third
flar about i^ preceding.
57. In Anferis corpore.

Aug. II, A pretty double ftar. About I degree n. of a clufter
1^82. of flars formed by the 4th, 5th, 7th, 9th Anferis; in
a line parallel toithe 6th Vulpeculas and /3 Cygni ; that
of two which is fartheft from the clufter. A little
'Unequal. Both r. Diflance f 1^'', Pofition 58^ 36'
f. following*
-58. 0"Perfei. Fl. 13. In finiftro humero.
Awg. 20, Double. Extremely unequal. L. w. Inclining to r. ;.
■1782. S. d. Diftance with 932, 13'' j'^'" - Pofition 20" o'
n. preceding. A third 'ftar, very unequal, within i^;
towards the fouth.
5.9. Ad Fi,. 19^'^Perfei. In capite.

JVug. 20, Double. It is perhaps the 19th Perfei removed, or
'?.782. more likely a flar not marked in Fla.msteed's Cata-
logue;, the 19th being either vanilhed, or mifplaced by

Flamsteed.

of Double Stars. . « *§i'

III. Flams TEED. Pretty unequal. L. bw. ; S. br. Dif-
taiice 1 1'^ ^"' , Pofitioii o° o' following.

60. Secunda ad p Perfei. Fl. 20. Illas in larva prsecedit.

Aug. 20, Double. Extremely unequal. L. rw. ; S. d. Dif-
1782. tance 14'' ^"'. Pofition 30° 30' f. following.

61. Sub finem caudi£ Draconis.

Aug. 29, Double. Of two conliderable ftars, about half-way

17S2. between a and i Draconis, that which is towards ;.

The two ftars are parallel to f and g Urfc majoris.

Very unequal. L. pr. ; S. db. Diil^nce 12'^ 30'''^

• perhaps a little inaccurate. Pofition 87° 42' n. preceding.

62. Fl. 35 Pifcium. In lino auflirino, ,

Sept. 4, Double. Confiderably unequal. L. rw. ; S. pr.

1782. Diftance \z" 2p"' - Pofition 58° 54' f. following.
(iOf, Prope Fl. (^^'^'^ Sagittarii. Ad extremum paludamentum.

Sept. 5, Double. Near f degree f. following the 65th Sagit-

1782. tarii towards f Caprrcorni. Very unequal. Too low
for colours; perhaps dw. Diftance 14'^ ^o'". Pofi-
tion 73° 48' n. following.

64. Fl. 26 AurigiE. In dextrl cruris involucro.

Sept. 5, Double. Very unequal. L. rw. ; S. r. Diflance
1782. 13 ' 25'^'. Pofition 2° 36' n. preceding^'

65. e (Fl. 58^) Perfei auftralior. In dextri pedis talo.

Sept. 7, Double. About 10' fouth of the 58th Perfei, in a
1782. line parallel to ^and < Aurigas; a fmall telefcopic flar.
Very unequal. L. r. ; S. d, Diftance with 625, iii'^'
22^^'. Pofition 48° "^P in. folio wing. Vert inaccurate :
: windy. ^ .' .,^^^

66. e Tauri, Fl. 30. In dextri humeri fcapula. .

Sept. 7, Double. Extremely unequal. L. W4 ; S. r. Dlf-
1782. tance 11'' id'" \ inaccurate on account of obfcurity.
• : Pofition 17° 15' n. following.
Vol. LXXV. M .(^^^

1-11.67- J Leporis. Fl. 3.. Bgrea priecedentl,>ktensquri<]rilatcri

ad aures.
Sept. 7, Double. Excefiively unequal, L. w. ; S. d. Wltli
5782. 227, there was not a poffibility of meafuring the dif-
t^nce, though the glafs was carefully cleaned ; on try-
ing 625, 1 found the flar fo firong that it bore a very
■ tolerable good light '^. Diftance with this power 12"
20'^'. Pofition. 8w° 21' n. preceding.
€8. tj (Fl. i-7^).Arietis auftralior et praecedeus.
Sept. ic, Double. . Full I degree fouth preceding 5j, in a line
1,7^2. parallel to a and^^ Arietis. Very unequal. L. pr. ;
''' S. d. Diftance 8/',5;;^., Pofition 55° 42^ f. following.

69. Prope Fj.. 64'"' Aquarii. In dextro femore.

Sept. 27, Double. Full i\ degree n. following the 64tli :i ,
1782. in ^ ^ii^s parallel to X and <p Aquarii ; -the largefl of rtwo*
that follow a very obfcure triangle in the finder. Ex-
trenaely unequaL , L.;r,w..;.S. db. Difbnce 12^-' 46''^
Pofition 20^3' f.- following.

70. « Cephel. Fl. i. In dextro crure,

Sept. 27, A beautiful double flar. Extrertiely unequal. L..
j-,82. fine w, ; S. r- Difl:ance..5''' 4^'^^ Pofition 32° 30' f.
following. , , . u;.;.r. . ^

* With regard to fmall fiars, that become vlfible ty an increafe of* magnifyiBg
prower, vf^ msy fnrmife, t'hat it is partly owing to the greater darlcnefs of the
field of view, arifing from the increafed power, and partly to the real efFeft of
the power; for, though the real diameter of a ftar, notwithftanding it he magnified
a.thoufand times, fhould ftill remain faialler than the minimum vifibile, yet fince a
Irar of the feventh magnitude maybe feen by the naked eye, we may conclude, that
the light of a ftar fubtends iincomparably a larger angle than its luminous body ;
and this may be in fuch a proportion, with very fmall ftars, that the power of
the telefcope fliall be jufl fufiicient to magnify the real diameter fo a« to bring it
'^vithin the limits pf this proportion, wherel?;^, U>e flar will become vilible.,

if. . / /

of Dot! oli^' Star-. 8^

III. 71. Tiaram Cephtl pra?ceden3,

Sept. 27, Treble. iVboutii degree preceding the ^vj/v/f/y/.'zr*,
J082. ii^ a lii^6 parallel to ; and f Cephei. The two nearefi:
^'ery unequal. Iv. w. ; S, db. Diftance 11" 35'''.
Politlon ^^"^ 24' f. following. The two fartheft confi-
derably unequal. S. db. Diftance 18^' 37'" - Pc){i-
tion J^"" S7^ ^^' pi"cceding. The place of t\\Q gar?2et
jiar, reduced to the time cf Flamsteed*s Catalogue, is
about 7B. 21 h. 45^ P.D. 32°!.

72. Tiaram Cephei prsecedens.

Sept. 27, Double. Within \ degree of the foregoing treble-
1782. ftar. Confiderably unequal. L. rw. j S. pr. Diftance
13^'' ^"\ Pofition 32^0^ n. following.

73. Fl. 25^ Ceti auftralior et fequens.

06t. 2, Double. About | degree f. following the 25th, in a
1782, line parallel to ^ and r Ceti, Pretty unequal. Diftance

with 278, 14''' S^"^' Pofition 89^^12'' i. preceding ; ^

perhaps a little inaccurate.

74. Fl. 1 8^ Pegafi auftralior. Ad oculum finiftrum.

oa. 4, Double. About \ degree f. preceding the i8, in a
1782. line parallel to y\ and e Pegafi ; the moft north and largeft:
of two. A little unequal. Both rw. Diftance 14''^
^()"' full meafure. Pofition 31^ 2>o "• following.

75. Ad Genam Monoccrotis.

oa. 4, Double. About 1 degree n. of, and a little preceding
1782. the fix telefcopics in the place of the 12th, in aline
parallel to the 12th Monocerotis and ^ Geminorum.

76. rm quatuor tclefcopicarum, I Orionis fequentium, penultima.
oa. 4, Double. About | degree n. following ^, in a line
J 782, parallel to t and ; Orionis. Extremely unequal.

^* Pfeil. Tranf.vol.LXXIII. p. 257,

M 2 L.

84. Mr, Herschel's Catalogue

III. JL. r. ; S. d. Diftance with 278, 9'' 12'^^ Pofidoa
13^ 6' n. preceding.

77. Fl, 65^"" Arietis fequens adauflrum.

oa. 9, Double. About | degree f. following the 65th Arie-
1782. tis, in a line parallel to the Pleiades and e Tauri ; the

preceding of two. Very unequal. L. r. ; S. bluifh.

Diflance 8'^ yJ^'. Pofition 73° 1 8^ f. following.

78. Fl. 13*":* Tauri prsecedens ad auflrum.

oa. 9, Double. About i| degree f. preceding the 13th
1782. Tauri, in a line parallel to e Tauri and I Ceti. Nearly
equal. Both pn Dillance Y' io'''\ Pofition 87*^ 57'
n. preceding.
.79. £ (Fl. 83^) Ceti borealior.
oa. 13, Double. About f degree n. of e Ceti ; the neareft of
1782. three forming an arch. Extremely unequal. L. rw. ;
S. darkifh red. Diftance with 278, 10^^ 48'^^ Pofi-
, tion 45° 1 2^ C preceding.
80. (T (Fl. 76"") Ceti prascedens. In finiflro crura,
oa. 13, Double. Full i| degree preceding 0-, towards r Ceti.
1782. Extremely unequal. L. rw. ; S. br. Diftance 11^''

i6^^\ Pofition 22° 24^ n. preceding.
Sir Parvula a f Lyrae e verfus.

oa. 19, Double. Above | degree frona ^ towards e Lyrse.
1782. Extremely unequal. L. r. ; S. dr. Diflance 9^^ 27^^''

full meafure. Pofition 66° 18' n. following.
82. Fl. 41 Aurigae.

Nov. 6, A pretty double ftar. Confiderably unequal. L. w. ;
1782. S. grey incrming to r. Diflance 8^^ 32"'% Pofition
80° o^ n, preceding,

■85.

of Double Stars* 8^

III. 83. Fl. 19 Lyncls.

Nov. 13, Double. A little unequal. L. rw. ; S. bw. Dii-
1782. tance 14^^ 1 1^^''. Pofition 46° 54'' f. preceding.

84. Fl. 40 Lyncis. In Urfae majoris pede.

Nov. 13, Double. Very or extremely unequal. L. wr. ; S. r.
1782. Diflance 7'^ ii^^\ Poiition 48^ 12' n. preceding.

85. Fl. 2 Canum Venaticorum.

Nov. I--, Double. Very unequal. L. r. ; S. bluifh. Dif-
1^82. tance 12^^ i2^^\ Pofition 11° o^ f. preceding.

86. Fl. 57 Urfas majoris.

Nov. 20, Double. The largeft of two ftars. Exceffively un-
1782. equal. L. w. ; S. a red point without fenfible magni-
tude. With 227, S. is but juft vifible. Pofition 75°
36^ n. following.

87. Fl. 59* Urfe majoris borealior.

Nov. 20, A pretty treble ftar. Near i| degree n. of the 59th,
J782. ill ^ line parallel to ^ and jS Urfae majoris nearly. The
two neareft confiderably unequal. L. pr. j S. r. Dis-
tance 12^^ 30^^^ Poiition o'' o^ preceding. The two^
fartheft very unequal. S. dr. Diftance 32^^ 21^^^,
Politioi} 4° o^ n. following.

88. Fl. ii^ Tauri borealior et fequens*

Nov. 25, Double. About | degree n. following the nth'
1782. Tauri, towards / Aurigae. Very unequal. L. w. ; S.

pr. Diflance with. ^78, 13'' 37'''. Pofition 89'^ 51'

n. following.

89. Ad 63*'" Herculis. In llnea per ^ et e du£la.

Nov. 26, Double. About 4 degrees from ^towards £ Herculis,.
1782. near the 63d. Very unequal. L.,r. ; S. r. DIftance
1 1'' ^2l"* Pofition 47^ 48' n. following.

90*

^^^> Mr. HEtisCKFT/vS Ctitahgue

III. 90. Fl. 103^ Taiiri boreal ior.

\

Nov. 29^ Double. About three deg'rees diredly n. of the ic^.
1782. Taurl ; the largeft of three, forniing an obtiife angler

Confiderablj unequal. L. rw. ; S. pr. Diftance with

278, 13''^ 6^'\ Pofitlon 64^ o' n. followmg.
^r, Fl. 62^ Arietl-sborGallor et fequeus,
Dec. 23, Double. Near i degree n. followhig the 62d Ari-
1782. etis, towards e Perfci. Nearly equal. Both dw. Dif-

tance ii'^ 17^^^; not very accurate. Pofition 12° 24'

n. preceding or f. followmg.

92. f (Fl. 77^™) Cancri prsecedens ad boream.

Dec. 28, Double. About i degree n. preceding | Cancri, in a
i>S2. line parallel to « Leonis and the 41 ft Lyncis; a confi-

derable ftar. A little unequal. Both r\v. Diftance

8'" 50'"^ Pofition 65° 12' f. preceding.

93. Fl. 1 1 7 Tauri.

Dec. 31, Double. Almoft equal. Both rw. Diftance la'"'
1782. 12'"'^ Pofition 5:^° 27^ f. following.
^4^ V (Fl. 7^"^) Leporis praecedens ad boream.
Dec. 5i, Double. About i f degree n, preceding v Leporis, in
1782. a line parallel to >i and £ Orionis; the fecond in that
line. Equal. Both rw. Diftance ii'^ 44^^^ Pofi-
tion 4'' o' f. following or n. preceding.
95. V (Fl. 48*'") Eridani praecedens ad auftium.
Jan. 2, Double. Near | degree f. preceding v^ m a line from
2783. the 5 1 ft continued through the 48th Eridani. Extremely
unequal, L. rw. ; S. d. and hardly to be feen with
227. Diftance with 278, 15'' 21'''; very inaccurate
«ii account of obfcurity. Pofition 9° 18' f, preceding*

* ^6,

of Double Stars » ' ^y

III. 9^. Fl. 17 Craterls.

Jan. 10, Double. Nearly equal. Both iw. Diflaiice 9'*"
1783. 46^^^ Pofition 64'' 27' f. preceding.

97. Fl. 54 HydriE.

Jan. 10, Double. Very unequal. L. w. ^ S. bluidi r. Dif-
1783. tance ii"" 17'''; too low for great accuracy. Pofitiom
^8° 1 5^ r. following..

98. Ad Genam Monocerotis.

Jan. 13, Double. About f degree f. preceding the mod f. of^
1^83. a clufter of fix telefcopics in the place of the 12th, in a
line parallel to the 15th and 12th Monocerotis. Ex-
ceffively unequal* Pofition 61° 57' f. preceding.,

pp. Fl. ^^ Eridani.

Jan. 31, Double. A very little unequal. L. pr. ; S. rw»
/17S3. Diftance 9^^ 9^^^. Pofition 44° 9^ n. preceding.

LjOo. Fl. ^^'''^ Eridani praccedens ad auflrum.
Jan. 31, Double. About 2| degrees f. preceding the 55th.
1783. Eridani, iu a line parallel to Rigel and y Eridani. Con*-
'], fiderably unequal. L. pr. ; S. db. Diftance 1 1^^ S3^'^'

: ;: . Pofition 16° 24M'. preceding.

ipi«;^ Centauri. Fl. 3.

Jan^3i, Double. Confiderably unequal.. L. dw. ;, S. dpi,
1783. Diftancc 1 1^^ 35^^^ Pofition 22° o^ f. following.

1 02. h (Fl. 29*"*) Herculis praecedens ad auftrum.,

Feb. 3, Double. About 1 1 degree £ preceding h Herculis-
$-783, towards s Serpentis ; a fmall ftar. Very unequal. Both
J. Diftance 14''^ 2^''^ Pofition 67® i^' n# following.

103. 6 (Fl. 37^) Serpentis borealioret fequens.

March 4, Double.. Near two degrees f. following e, in' a line

1783. parallel to the 13th Serpentis and 10th Serpentarii.

Very unequal. L. pr. ; S. r. ; but a dry fog, if I may

83- Mr. H£RSCHEL*3 Catalogue

ill. fo call it, probably tinges them too deeply. Dlftance

with 278, 12'^ 34'''; with 625, 12'' 2^"\ Pofition

50"^ I 2'' n. preceding.
104. Fl. 83'"' Herculis priEcedens.

Mar. 26, Double. About } degree preceding the 83 ; the fe-
1783. cond ftar towards the 79th Herculls. Very unequal.

L. r. ; S. darker r. Diftance 14'' 20'''. Pofition 83^

48^ n. preceding.
1435*" y (Fl.'I*2^) Sagittae boreailor et pr^cedens.
April 7, 'Double, About 2^ preceding the double ftar V. 106.
1783. Pretty unequal. L. r. ; S. d. Diftance 14^^29^^^;

very inaccurate, on account of obfcurity. Pofition

50° 24' f, preceding.
ro6. Fl. 5 Serpentis.

May 21, Double. Excefiively unequal. L. rw. ; S. db. Too
1783. obfcure for mealures. Of the thir<l clafs, far. Pofi-

fition about 30° or 40° n. following,
107. Congerie Stellularum Sagittarii boreal ior.
Tune 6, Double. Abave i| degree n. of the 20th clufler of
1783. ftars of the Connoijfance des ^€mps^ in a line parallel

to y Sagittarii and the clufter : the moft fouth of many.
'Cofifiderably unequal. Diftance with 278, 15'' lo^^^

As accurate as the prifmatic poW€r of the atmofphere,

which lengthens the ftars-, will permit. Pofition K^d^'

48 M. preceding ^,

" '■•''.' ^ . 108.

* What I call the prilmaric power of the atmofphere, of which little notice
has been taken by artronomers, is that part of its tefraftive quaHty whereby it
difperfes'the rays of light, and gives a lengfliened and coloured image of a hicid
point. It is very vifibie in lowitars; Fomalhanp, forinftance, affords a beau-
tiful prifmatic fpedtrum. That this power ought not to be overlooked in delicate
4 and

r.f Double Stars, ^q

HI. loZ. Fl. i^'^ AquiliE pra?cedens ad boream.
July 7, Double. Above | n. preceding the ipth, in a line
1783, parallel to jG and ^ Aqullae. Very unequal. L. r. ;
S. dr. Diftance 12^' 58^^^ PoUtion 58^ 27^ f. fol-
lowing.
109. Fl. ip^'^Aquilae praecedens ad Boream.
July 7, Double. About If degree n. preceding the 19th, in
1783. a line parallel toe and (J'Aquihr. Pretty unequal. Both
rw. Diftance lo'" 13'''. Poiition 22'' 6^ n. preceding.
no. Fl. 77^ Cygni borealior et prcTcedens.
Sept. 17, Quadruple. Full | degree n. preceding the 17th, in
1783. a line parallel to a- and « Cygni ; a fmall ftar. The
two nearefl: extremely unequal. L. r. ; S. d. Diftance
with 625, 13''' 54'''. Politlon 6f 36' f. following.
The two largeft a very little unequal. Both r. Dif-
tance with 278, 25'' 58''". Pofitioa 40'' 33^ n. fol-

and low obfervations, is evident from fome meafures I have taken to afccrtain its
quantity. Thus I found, May 4, 1783, that the perpendicular diameter of e,
Flamsteed's 20thSagittarii, meafured 16" 9' ', while the horizontal was 8"35'" ;
which gives ']" 34'" for the prifmatic effeft : the meafures were taken with 460,
near the meridian, and the air remarkably clear. And though this power, which
depends on the obliquity of the incident ray, diminifhes very fall in greater alti-
tudes, yet I have found its effcfts perceivable as high, not only as « or y Corvi in
the meridian, but up to Spica Virginia, and even to Regulus. Experiments on
thefe two latter flars I made November 20, 1782 ; when Regulus, at the altitude
of 4g°, fliewed the purple rather fuller at the bottom of the field of view than
when it was at the upper tdge ; which fliews that the prifmatic powers of the edges
of the eye lens were affifted in one lituation by the power of the atmofphere, but
counterafted by it in the other. I turned the eye lens in all fituations, to convince
myfelf that it was not in fault. This experiment explains alio, why a ftar is nor,
always befl in the center of the field of view ; a fad I have often noticed before I
knew the caufe.

Vol, LXXV. N lowing.

9& Mr. Hekschel's Catalogue

III. lowing. The fartheft very unequal, S. d. Pofitlon
almoft in a line with the two largeft.

1 1 r. £ (Fl. 46') Orionis borealior et fequens.

Sept. 20, Treble. About i| degree n. following c, towards
1783. o^ Orionis. The two neareil; of the third clals.

112.^ (Fl. 18'"') Cygni fequens ad auflrum.

Sept. 22, Double. About i degree f. following §, towards the 1
1783. 47th Cygni; a pretty con fiderable ftar. Equal, or per-
haps the fouthern ftar the fmalleft. Both pr. Dif-
tance with 278, 10'" 8'''. Pofition 71° o'. f. fol-
lowing.

1 13. Fl. 27*"" Cygni praecedens ad auftrum.

Sept. 23, Quadruple and Sextuple. About | degree f. prc-
i-y8'>. ceding the treble ftar I. 96.; the middle of three, the
moft north whereof is the 27th Cygni. In the qua-
druple or n. preceding fet, the two neareft very une-
qual. Diftance with 278, 11^^ i6'^ Pofition 26° o^ 1
n. preceding; the two largefl almofh equal. Both r.
Diftance with 278, 29^^ 27^^'. Pofition 57° 12^ n. fol-
lowing. In the fextuple or f. following fet, the two
largeft pretty unequal. Both r. Diftance with 278,
19'^ 20^'^ Pofition 27° 36' f. preceding. All the
other flars are as fmall as the fmalleft of the quadruple
fet, and fome of them much fmaller.

J 1 4. Fl. 16"" Monocerotis praecedens ad boream.

Jan. 23, Double. About J k degree n. preceding the 1 6th»
1284,

FOURTH

of Double Stars, 9 1

FOURTH CLASS OF DOITBI, E STARS.

IV. 45. In pedoris crate Ononis.

Dec. 27, Double. About f degree following i{/, towards n
1781. Orionis. Extremely unequal. L. pr. ; S. dr. Dif-
tance with 278, %q" 3". Pofition 62° 24 f. fol-
lowing.

46. Fl. 21 :: Geminorum *.

Dec, 27, Double. A little unequal. Both pr. Diil:ancc

1781. about 25^^. Pofition

47. Fl. 3 Leonis.

Feb. 2, Double. Exceffively unequal. L. r. ; S. d. ; not
iTSa. vifible with 227. Diflance eftimated with 460, about
24'^ Pofition a little n. following. A third ftar in
view. Diftance perhaps 2'. Pofition about 1 5** f . fol-
lowing.

48. H (Fl. i="") Geminorum praecedens ad boream.

Feb. 6, Quintuple. In the form of a crofs. About f degree

1782. n. preceding H Geminorum, in a line parallel to the
65th Orionis and ^ Tauri ; the middle of three. The
two nearefl or preceding of the five extremely unequal.
Diflance 2.0" Sl'^' ' Portion 7° 27' f. preceding. The
lafl of the three, in the fhort bar of the crofs, has an
excefUvely obfcure ftar near it of the third clafs. Five
more in view, differently difperfed about the quintuple.

* The 2ift and 20th Geminorum are not in the heavens as they are marked ia
Tlamsteed's Atlas, fo that it becomes doubtful whether the N" 21. is right.

N % 49-

92 Mr. He RSCH el's Catalogue

IV. 49. f (Ft. 4^"") Virglnls fequens adboream.
Feb. 6, Double. I full degree n. following | Virginis, in a
1782. line parallel to i and /3 Leonis. A little unequal. L.
pr. ; S. dr. Diftance 27'' 28""^ Pofition 56° 30'f,
preceding.

50. Fl. 17 Virginis. In pe£lore.

Feb. 6, Double. Confiderably unequal. L. w. ; S. bluilh.
• 1782. Diftance 20^^ 9''^ Pofition 58" 21^ n. preceding.

51. it Virginis :*. Fl. 44 :: -f-. In ala auflrina.

Feb. 6, Double. A ftar fouth of three forming an arch, and
J 782. of the fame magnitude with the middle one of the arch.
Extremely unequal. L. w. ; S. db. Diftance 22''
17^^''; inaccurate. Pofition 32^ 3^^ i^- following.

52. * i Cancri. Fl. 48. In boreali forfice.

Feb. 8, Double. Confiderably unequal. L. rw. ; S. d. gar-
2782. net. Diflance 29^^ 54^^^ Pofition 39° 54^ n. preceding;;
a little inaccurate.

53. crGeminorum. Fl. 80. Supra capita.

Feb. 9, Double. Exceffively unequal. L. garnet; S. d#,
3782. Diftance with 460, 21^^ 30^^^ Pofition
Other very fmall ilars in view.

54. I (Fl. 4^"") Hydras fequens.

Feb. II, Double. About i degree following \ towards ^
J782. Hydr^e. Pretty unequal. Both pr. S. deeper. Dif-
tance 25^^ 43''''^. Pofition 59° 24^ n. following.
^^. Fl. 41'" Lyncis fequens. In caudaefine.
Mar. 5, Double. About 3$ minutes n. following the 41ft
3782. Lyncis. Extremely unequal. L. r. ; S. dr. Diftance
15'^ 52^^^; a little inaccurate. Pofition 50° 48' n,
preceding; inaccurate.
t Perhaps the 45th j reqwjFes fibsed inftrumcnts to determine,

^6.

of Double Stars'^ ^^

17. 56. Fl. 18 Librae.

April 3, Double. The following of two. Extremely unc-
J782. qii^l- L. r. ; S. b. Diftance 17'^ ^^''\ Pofuioiii
44^" 45^ n. following.
57. Fl. 42^"" Comie Berenices fequens ad auftrum^
April 15, Double. About 3 degrees f. following the42d Com^
1782. Berenices towards u Bootis ; the vertex of an ifofceles>
triangle. Extremely unequal. Diftance with 625,.
16'' 42^^^ Pofition 46° 31^ f. preceding.
c8. Fl. 2(>^'^ Comse Berenices praecedens ad boream.
April 18, A pretty double ftar. About 2i degrees n. preceding;
1782. the 36th, in a line parallel to the 42d and 15th Com^
Berenices % the following of two unequal ftars. A little
unequal. Both rw, Diftance 15^^ S^^''- Pofitioii.
67° 57^ f. preceding.

59. Prope a Lyrse,

May 12, Double. About 2 or 3 minutes f. preceding a Lyrae^
1782. Very unequal. Bothd. Diftance with 278, 22^'' 20^^''.
Pofition 2,3^ S7^ ^* preceding. Pofttion of the largeft
with regard to a, Lyrae 59° iz' f. preceding,

60. Fl. 4'*'° Urfge majoris fequens ad boream.

June 6, Double. Near i degree n. following the 4th, In a
1782. line parallel to 0 and h Urfae majoris; a pretty large

ftar. Extremely unequal. L. r. ; S. d. Diftance

near 30^^ ; but too obfcure for meafures.
di. Z^^' T) Coronae auftralior et praecedens.
July 18, Double. Near f degree f. preceding f, towards vi
1782. Coronse bor. Nearly equal. Both pr^ Diftance

16'' 46'''. Pofttiou 4° sf li' following.

0

94- Mr. Herschel's Catalogue

IV. 62. r (Fl. 22^) Herculis aujftralior et fequens.
Aug. II, Double. About 2f degrees f. following r Herculis,
1782. in a line parallel to < and y Draconis ; a confiderable

ftar. Very or extremely unequal. L. w. ; S. br.

Diftance 16^^ S"^^^^- Pofition 72" 15^ f. preceding.

63. Fl. 42 Herculis. Dextrum fupra genu.

Aug. II, Double. Very unequal. L. r. ; S. rvv. Diflancc
,782. 21'' 31^^''. Pofition 3° 42^ f. following.

64. Prope ^ (Fl. 12*''") Perfei.

Aug. 20, Double. Vv^ithin a few minutes of 5^ Perfei. Pretty
1782. unequal. Both pr. ; but S. a little darker. Diftance

2i'' S9^''' Poi^ition sT SY ^- preceding.
6^. Prope Fl. :;^'" CafTiopeiis.

Aug. 25, Double. Within 10 minutes of the 3d CafliopeliB.
1782. Very unequal. L. pr. ; S. r. Diflance 20''' 46^^^ ;
very inaccurate. Pofition 41° 12' f. following.

66. Q (Fl. 2,3''"'^ Cafliopeias praecedens.

Aug. 28, Double. About i| degree f. of, and a little pre-
J782. ceding^, in a line from I continued through Q Callio-
pei^je. Extremely unequal. L. r. ; S. db. Diflance
24^^ 2''^^; very inaccurate. Pofition 13° 12. n. fol-
lowing ; inaccurate.

67. -f Fl. 40 et 41 Draconls.

Aug. 29, Double. A little unequal. L. rw. ; S. pr, Dif-
1782. tance 20'' 39^''^ mean meafure; very accurate. Pofition
35° ^5^ ^- preceding*. There is a third, much fmallcr
ftar. Diflance 3' 16'' 33'''. Pofition about 30° f,
following .
* The proper motion of one of thefe ftars at leaft fince the time of Flam-
steed is evident, as he gives us their difference in J^ 2', and in PD 3' 5". Pofi-
tion f, preceding. Hence we have the hypotenufe or diilance above 3' 40",
inftead of 20" 39'"; and the angle 86° 17' inilead of 35° 15'.

4 68.

of Double Stars, or

IV. 68. Fl. 77 Plfcium. In lini flexu.

Sep- 3, Double. A little unequal. L. vvr. ; S. pr. Dlf-
1^82. tance 29^' 3^^'^ Pofition 4° 48^ n. following. In both

meafures the weather too windy for accuracy.
69 Fl. 23*"" Andromed^e praecedens.

Sept. 4, Double. Full I i degree preceding the 23d, in a line

1782. pai'aliel to V and 1, Andromedas. Of two double ftars

in the finder the largeft of the preceding fet. Verv

unequal. L. r. ; S. d. Diftance with 278, 21^'' 58^^^.

Poiition 70° 36' n. preceding.

70. Fl. 51 Pifcium. In auftrino lino.

Sept, 4, Double. Very unequal. L. rw. ; S. d. Didance
1782. with 278, 22^' Z()''\ Pofition 0° 36^ n. following..

71. * (9 Capricorn i. Fl. 12. Trium in roftro auflrina.

Sept. 5, Double Pretty unequal. Both rw. Diftance 23''^
1782. Z^'"* Pofition 3^° 45^ f. preceding.

72. Fl. 55^ Perfei borealior.

Sept. 7, Double. About \ degree n. of the 55th Perfei ; of
1782. three in a line the moft north. Pretty unequal. L.,

rw. ; S. pr. Diilance with 278, 16'^ 51^''^ Pofition.

27° 24^ n. following.

73. In Conftellatione Camelopardali.

Sept. 7, Double. Between Fl. 2 and 8 Cam. ; the fmallefl
1782. of two that are within | degree of each other, Confi-

derably unequal. Diftance 19'^ 32''^ Pofition 85^0'

f. preceding.

74. ^ (Fl. 68*"^) Tauri fequens ad boream.

Sept. 7, Double. Near \ degree n. following^, toward &^^ *
1782, Tauri. Very unequal. L. pr. ; S. r. Diflance 16''
31/'^ Pofition 2-5° 45' n, following,

75-

<)6 il/r. Her? CITE T.\i G?/^%?/f

IV. 75. r (Ft. 66*^) Taurl fequens.

Sept. 7, Double. About 1 1 degree 11, following r, in a line
1782. parallel to i^. Tauri and the 9th Orionis. Very une-
qual. L. r. ; S. dr. Diftance zz^' 35^^'' Pofitioii
61° 36' i'. following.
*76. Fl. 13''"' Ceti praecedens ad auftrum.
Sept. g, Double. i\bout I degree f. preceding the ijth,
1782. towards the 8th Ceti. Confiderably unequal. L. rw. ;
S. br. Diftance with 278, 18'' ^^"\ Pofition 40° 24'
11. following,
^-y. Fl. 37^ Ceti borealior. In dorfo.

Sept. 22, Double. About | degree n. preceding the 37th,

1782. towards the 36th Ceti. Very unequal. L. r. ; S. dr.

Didance 19'^ 6''\ Pofition 63'^ 24' 11. preceding*

78. y] (Fl. 3'™) Cephei praecedens.

Sept. 27> Double. About i? degree preceding 1;, in a line
1782. from 6 continued through yj Cephei. Very unequal.
L. r. ; S. d. Diftance 19'' 32''^ Pofition 40'' 36' lu
following.

79. p Cephei. Fl. 13. Ad coronam.

Sept. 27, Double. A little unequal. L. w. ; S. rw. Dif"
1782. tance 21^^ 3^"^ Pofition 77° 48^ f. preceding.

80. jG (Fl. 2^) Canis majoris borealior.

Sept. 30, Double. About 1 1 degree n. of /3 Canis majoris

1782. towards the nth Monocerotis ; the moft n. of two.

Confiderably unequal. Diftance 17^^ 59'^^^? difficult

to take, and perhaps a little inaccurate. Pofition 2° 24'

n. following. ,

81. V Canis majoris. Fl. 6. In dextro genu.

Sept. 30, Double. Confiderably unequal. L. rw. ; S. pr. Dift.
1782. 18'' 19'''. Pofition very near diredly preceding.

I 82.

JV. 83. Prope Fl. r6'"'' Cephei, In eingulo,
^ept. 30, Double. Above | degree following tlic i6rh C<.^phei,
J 7^2. in a line parallel to fl and *j, Caffiopeiie, Coniidcrably

unequal. L. orange, S. r. Diftauco 28^'' 5''^ Poli-

tloii ^9° 18' n. preceding.

83. Fl. 2.6 Ceti. Supra dor fura. ,
oa. 2, Double. Yeiy unee^iiaL L., .rw. S. db. Dlilanee
1782. 17'^ 2'''^ mean meafure. Pofitlon 14'' 36' f. preceding.

84. ;w OfionLs. FL.23 In crate pectoris

Oft, 2> Double. Conliderably unequal. L. w. ;''S. pr.
J782. Diflance with 278, 26" 9'''''» Pdltlon 59"^ 33' n. fal«
lowing.

85. Fl. ultima Lacerti^.

06ir. 4, Treble. The two nearefl: extremely unequal. Lr»
»7Ba. rw. ; S. d. Dill:ance 10" 7.^" \ Pofition 79"^ ^3' n,

preceding. The next very unequal ; S. r. Diftancc

54^^ S7''^ ^ inaccurate. Pofition 44° 24' n. following*

A fourth and fifth ftar In view*
$6. Fl. 8 LacertJE. In media cauda*
oa, 4, Quadruple. The two largeft and neareft a little unc-
1.782. qual. Both rw. Diftance \f^ 14'"^ Pofition 84®

30' f. preceding. The two next very unequal, of the

fourth clafs. The two remaining conftderably unequal,

of the fifth clafs. They form an arch.
%1» e (Fl. 29"") Orionis praecedens. In finlftro calcaneo.
0(^.4, Double. About i degree preceding ^, in a line pa-
1782. rallel to o- Orionis and b Eridani nearly. Confiderably

unequal. Both pr. Diftance ap^MS'^^ Pofition 82**

18' n. following.

Vol. LXXV. O S5.

9 3 Air. Herschel's Catalogue

IV. 88. Fl. 7 Taurl. In dorfo.'

ca. 9, Double. Very unequal. L. pr. ; S. dr. Diflance
1782. 19^^50^^^' Pofition 23° 15^ n. following.

89. E telelcopieis caudam Arietls fequentibus.

oa 9, Double, The vertex of an ifofceles triangle follow-
178a. ing T Ariem ; a very fmall ftar. Very unequal. L.

r. ; S. d. Diftance with 278, 20^^ ^'^\ Pofitioa

62° o^ f. following.

90. Ad Fl. iS^"" Urfae minoris. Prope edu6:ionern caud^.

0£t. 12, Double. The largeft of fix or feven ftars, and moft
,y82. fouth of a triangle formed by three of them. A little

unequal. L. pr. ; S. deeper pr. Diftance 26^^ 24^^^.

Pofition 3" 12' n. following,

91. Fl. 2 Navis.

oa. 12, A pretty double flar. A little unequal. L. w. ; S.
1782. w. inclining to r. Diftance 17^' 23'^'. Pofition 6^^
11' n. preceding.

92. (Q inter et J" Delphini.

oa. 17, Treble. Between /3 and ^, but nearer to jG Delphinu
1782. All three nearly equal. All wr. Diflance of the two
nearefl with 278, zi" 2>?l''* Pofition 18^ 27' n. pre-
ceding.
93.- 1 (Fl. 4*'*) Lyrae fequens.

oa. 19, Double. About 3 degrees following e, in aline pa-

1782. rallel to « and 5 Lyn^; the largefl of two. Extremely

unequal. L. w. ; S, r. Diflance 19'^ 50'", Pofition

24° o^ f preceding.

94. E borealibus telefcopicis |Q Lyr^e praecedentibus.

oa. 19, Double. Full 2 degrees n. preceding jS Lyrae, In a

1782. line parallel to the 18th and t ; the fixth telefcopic ftar.

• Confiderably

of Double Stars* gg

IV. Confiderably unequal. L. rvv. ; S. pr. Diilancc 22'''

Ss'^^' Pofition 5° 24' n. following.
^5. Fl. 35"" Monocerotis pr:£cedcns.

0<a. i9» Quadruple. About 2 1 degrees precedijig, and a little
1782. n. of the 35th Monocerotis. Two large (tars always to
be feen, and two more only vifible in dark nights. The
neareft which is that to the fmalleft of the two largs
ones, extremely unequal, Diflance 20" ly^ \ Pofi-
tion following.
p6. Fl. 25^*^ Monocerotis fequens. In latere,
oa. 19, Double. About 1 1 n. following the 25th, in a line
1782, parallel to the 21ft Monocerotis and Procyon. A little
unequal. Both dr. Diflance i8'^ 19^'^ Pofition
, 24° o^ f. preceding.
P7. Fl. 29 Monocerotis. In femore.

oa. 19, Double. Extremely unequal. L. wr. ; S. d. Dif-
1-782. tance 29''' 54^^^ Pofition 15° 12' f. following. Six
more in view.
98. w (Fl. 58^"") Orionis ad auflrum praeiens.
oa. 29, Double. About | degree preceding a, towards ^
3782. Orionis. Equal. Both r. Diftance 17^' 59'^'; alittle
inaccurate.
59. Duarum telefcopicafum ^ Sagitt^ ad auftrum fequentium
borea.
Kov. 6, Treble. Of a trapezium, confifting of this treble
3782. il:ar, ^, f, and the 9th Sagittae, it is the corner oppolite
to f ; the nearefl to ^of two. The two neareft very
unequal. L. pr. ; S. db. Diftance 21^^ 22'^^; inac-
curate. Pofition 0° o^ following. The two largefl a
little unequal ; of the fifth- clafs. Pofition 10° 36' f.
preceding.

O 2 100.

loo Mr. HtKsciiEi/s Catah^ue

o

IV. ICO. ;)k; Sagittae Fi.., t^. Intra mediam aruiulinem.
Nov. 6, Treble. Hie. largeft of three. The two iiearefl
1782. equal. Both r. Diiuince23^^ 2^''^. Pofitloii io^i2^f.>
preceding. The third is a large ftar. Diftance ahovG
1 minute. Foiitiou about 10" or 1 5° n. preceding the
other two.
10 1, ^ (Fl. 24*) Aurlgae borealior et pra^cedens.
Nov. 6, Doubk, Near | degree n. preceding (p, in a line
1782. parallel to the 2 1 ft and 8th Aurigse. Pretty unequaL
L. rw. S. bluifh. Diftance 25^^ 2^''\ Pofitioit
76° o^ n. preceding.
IC2. Fi. 59 Aurigae.

N:ov. 6, Double. The apex of an ifbfceles triangle. Ver}^
1782. or extremely unequal. JL. rw. ; S. Diftance

23''' 30^^^ Pofition 50° 3^ f. preceding..

103. Fl. 77^'" Draconis fequitur,

Nov. 13, Double. Near | degree following the 77th Dra-v

3782. conis, in a line parallel to x Cephel and the 76th Dra-

conis nearly; of a rectangular triangle the leg neareft'

the 77th. Very unequaL L. r. j S. blui(h r. Dif--

tance 22'" 35^^^ Polition 45^ 48' n. following.

104. Inter y et 55^"' Andromeda^.

Nov. 13, Double. A little more than i degree n. folIowing^

1782. the 55th Andromedae, in a line parallel to jS Trianguli

and Algol. Confiderably unequal. L. r. ; S. d. Dif-

tance with 278, 18'^ ^y'\ Pofition 22° ^^' n. fol-<

lowing.

105. ^ Corvi. Fl, y. Duarum In ala fequente piaecedens.
Nov. 13, Double. Extremely unequal. L. w. ; S. r. DiA

J7«2. tance 23^^ 30'^^. Polition 54"^ o' f. preceding.

106,

of Double Stars, iqi

IV. lo6. a (Fl. jC") Urf^e majoris fequens ad boream.
Nov. 17, Double. About li degree n. following «, in a line-
1782. parallel to (^ Urfas et y, Draconis ; the lafl: of three in a

Fow. Extremely unequal. Both r. Dlftance i8''~

^c^^^^ ; very inaccurate. Pofitioa 44° 33' f. following..

A third fmall ilar in view.
107. Fl. 79'Pegari auftraiior et praeced'ens..
Nov. 20, Double. About | degree f. preceding the 79th,
17:82.. ta^vard3 r Pegaii ; at the center of a trefoil. Very

•anequal. L. r. ; S. d. Diflance with 378, 2.6,'' 12/'*,

Polltion 50° 21' n. following..
i;o8. Fl. 69* UrfiEiTjajoris auftralior..

Nov. 20, Double. Near 2 degrees f. of the 69th, towards -
1782. the 63d^Urf<£ majoris. A very little unequal. Both r»,

Diftance 19^'' 15''' ; very inaccurate. Pofition 10° i^

n. following.

109. Fl. 6aTauri.

Nov. 25, Double. Confiderably unequal. L. w. ,; S. r. Dif-
1782. tance 28^' ^"\ Pbfitionai" 12' n. preceding.

110. /S (Fl. 1 1 2")- Tauri borealior et fequens.

Dec. 24, Double. About i| degree n. following jQ Tauri,,
1782. towards ^ Aurigae ; the fecond in that direction. Very^
\inequal. L. r. ; S. d. Diftance 16'^ \"\. Pofition
74° 54'' n. preceding..
XXI. Fl. 54 Cancri.

Dec. 28, Double. A little unequal. Both rw. S. a little
1782. darker. Diftance \f i/^" . Pofition 29° o' f. fol ^

lowing.
112. y (Fl. i5*">) Crateris fequens ad boream.
Jan. I, Double. About i degree n. following y Crateris, in
1783* a line parallel to I Corvi and Spica. Equal. Both pr.

Diflance

!0i Mr, Heiischel*s Catalogue

IV. Diilancc 26^^ 15''''^; too low for accuracy. Politioa

58° 42^ n. preceding or f. following.
113. Fl. 61^ Cygni'borealior et praecedens. ' •

Jan. 6, Double. About \\ degree n. preceding the 6ifl, in
1783. 'a line parallel to u and a Cygni. Very or extremely
unequal. L. r. ; S.db. Diftance with 278, i 7'' 30'^'.
Pofition 28° 24.' n; preceding. A third ftar in view.
1-14. 7 (Fl. 12') Virginis auftralior. ^

•Jan. 8, Double. About i \ degree f. of t Virginis. Very
1783. unequal. L. pr . ; S. d. Diitance 23'^ ai^^^ Pofition

15° 54^ n. preceding.
1 15. (p (Fl. I H"^) Herculis praecedens ad auftrum.
Jan. 10, Double. About 2i degrees f. of, and a little pre-
1783. ceding (p, in a line parallel to y^ and f Herculis; the
largeft of three or four. Extremely unequal. L. r. ;
S. b. Diftance ^o'' 54"^ Pofition 43° 48' n. fol-
lowing.
116*. Fl, 83"" Pegafi fequens ad boream.
Jan. 13, Double. Equal. Both w. Diflance 28^^ 59'^''.
J783. Pofition 68° 2 1^ Mr. C. Mayer, in 1777, fettled its
place ^o\ 52^ ^^'' in tinae, and 20" 17' ^2!' '^"^ de-
clination N.
1 17. Fl. 42' Erldani auftralior.

Jan. 31, Double. About i \ degree f. of the 42d Eridani, in

1783. a line parallel to Rigel and \jl Leporis; the moft fouth

and following of three. Very unequal. L. r. ; S. n

Diftance 1,9^^ 3 2^''^ Pofition 31° 48'' f. preceding.

-^18. i (Fl. 48"") Cancrl fequens.

Feb. 5, Double. Full I degree following the 48th, in a line

1783. parallel to ^^ Cancrjand e Leonis; a very fmall flar,

next to" two more which are nearer to *. A little une-

7 qual.

cj Double Stars, \ q ^

IV. qu.il. Dlflance 24^' 6''\ Pofition about 23'' n. fol-
lowing.

1 19. i (Fl. 68*"") Virginis praecedens ad auftrum.

• tdb. 7, Double. About 1 degree f. preceding the 68th, in a
V783. line parallel to the 99th and a, Virginis. Extremely
unequal. Diflance 2.1'' 49"^^ Pofition 36"* 54' n.
preceding.

120. Fl. Si*"" Pifcium fequens ad boream.

Feb. :^7, Double. About | degree n. following the 82d Pif-
J783. cium, in a line parallel to « and /Q Trianguli ; the
largeft of two. Confiderably uiiequal. L. rw. ; S pr.
Diftance 18'' 19''^. Pofition 2 r° o^ f. preceding. A
third ftar in view.
.121. 0- Scorpii Fl. 20 priecedens trium lucidarumln corpore.
Mar. I, Double. Very unequal. L. whitifli ; S. r. Dif-
J783. tance 21^^40'''''. Pofition o*^ o'' (or perhaps 1°) n. pre»
ceding.
122. Fl. 32^ Ophiuchl borealioret prascedens.
Mar. 7, Double. Near I degree n. of, and a little preceding
1783. the 32d Ophiuchi, in a line parallel to m and ri Herculis*
Very unequal. Diflance 21'' 3'''^ Pofition 25° 3 f.
preceding.
223. Fl. 19 Ophiuchl.

Mar. 9, Double. The mofl: Touth of two. Very unequal-
3783. L. pr.; S. d. Dlllance 20'^ Ti'f^/, Pofition 3^ 9' f,

following.
1 24. ^ (Fl. 4="") Ophiuchl pfse^edens ad auftrum.
Mar. 24, Double. About I degree preceding and a little f, of if/,
1783. in a line parallel to if; Ophiuchi and u Scorpii; in the
bafe of a triangle, the neareil to ^* A little unequal.

, ^ Both

104 Mr, hlET.zcnRLh Ci-iHakgi^e

W. Botli inclining to r, Didance 15''' 2^^^\ PoCitms

Ci'^ 54'' n. following.
12 p Ft.. 29 Camelopardali,

April 2, Double. Very unequal. L. pr. ; S. d. Diflancc
jysij. 22^'' 26^^^; very inaccurate. Pofitioii 47° 36'. f. fol- \

lowing; a little inaccurate.
■126. X (Fl. 22^ Cephei borealior et pryecedens.
April 20, Double. Lefs than i degree n. preceding A, In a
1783. line almofl: parallel to I and ^ Cephei; a confiderablc

ftar. A little unequal. Bothdvv. Diftance 1 8'^ 50'^''.

Pofitlon 45° 39^ n. preceding.
127-I-. A (Fl. 16*°") Aquilae fequens adboream.
^lay 21, Double. About 2| degrees n. following the fartheft
5783. of two which are about if degree from A, in a line

parallel to K and J Aqull«. Very unequal. L. rw. ;

S. dr. Diflance 1 7^^ 14'^''; more exa6t with 932, 15''

52^^''. Pofitlon 69"* 54'. n. preceding. Mr. Pi got t,

who favoured me with it, gives its place J^ x8'

52^1 ±, Declination 1° o' S.
iiS. y (Fl. 57*"*) Andromedae praecedens ad auftnim.
July 2^, Double. About if degree f. preceding y almoft
J7S3. towards jS Andromedae; moreexad towards o-Pifcium;

one not in a row of ftafs which are near that place.

Confiderably unequal. L. pr. ; S. dr. Diftance 1 5^',

42 '''^ Pofitlon 24° 12' n* following.
129. Fl. 59 Andromedae.

July 28, Double. A little unequal. L. rw. ; S. pr. Dif-
1783. tance 15'^ 15^^^ Pofitlon 55° 9' n. following. A third

Ihr in view about 58*' or 60'' f. preceding.

df Double Stars, lo^

JV. 130. jj (Fl. 99^) Plfcium borealior et fequens.
Aug. 2, Double. About i| degree 11. of, and a little fol-
^,7,83. lo>ving 77 Pifcium, in a line parallel to /3 Arietis and j3
Trianguli ; the lail of four in a crooked row. Very
,un.ec[ual. L. r. ; S. darker r. Diftance with 278,
15'' 49^''' Pofition 62° 15' n. fc)llowingi
.m^ f.h (1°^ Pii*cium.
Aug. 2, Double. Pretty unequal. L. pr. ; S. r. Diftance
1783. ^s" S'^"'* Pofition 5° o' n. following.
,jf22. F.L. 46*'" AquiliE fequens ad boream.
Aug. 6, Double. About \ degree n. following 46 Aquilae, in
1783. ^ 1""^^ parallel to cc and y Sagittae. Very unequal.
L. r. ; S. db. Diftance 22'' 44^^^. Pofition 41"^ 24'
n. preceding.

FIFTH CLASS OF DOUBLE STARS.

V. 52. Secunda a v Geminorum ^ verfus. ,
Dec. 27, Double. The fecond ftar from v towards ^ Gemino-
1781. rum. Pretty unequal. L. r. ; S. b. Diftance 35'^;
inaccurate.

53. p Geminorum. Fl. 63. In inguine fequentis !!'•

Dec. 27, Double. The brighteft of two. Extremely une*

1781. qual. L. pr. ; S. d. Diftance 44'^ ^s'^^'

54. 5 HydrjE. Fl. 22. Duarvina in edudione cervicis fequens.
Jan. 20, Double. Exceffively unequal. L. w. ; S. a point.

1782. Diftance near 1 minute, too obfcure for meafures, and
Vol. LXXV. P not

io6 Mr. HtiRsCHEL's Cafalogtie

V. not vifible till after having looked a good while at B,

Pofition about 75° f. following.
K^. i\d F:.. 1 2*"" Geminorum. In pede ![' praecedentls (iniflro.
Jan. 30, Treble. A fmall flar near the place of the 12th
1782. Geminorum. The two neareft a little unequal. Dif-

tance lefs than i\
56. Fl. T5 Geminorum. Dextrum prioris Ifi pedem attingens.
Jan. 30, Double. Confiderably or very unequal. L. r. ; S. d,
1782. Diftance 32^^ 39^^^- Pofition near 60'' f. preceding.
K^j, Fl. 9^ Orionis borealior et fequens. In exuviarum

fummo.
Feb. 4, Treble. More than i degree n. following the 9th
1782. Orionis, towards the 1 1 3th Tauri ; the largefl of two*.
The two neareft confiderably unequal. L. rw. ; S. rw.
Diftance with 278, 36'' 26''^ Pofition ^2!" 3^'- The
farthefl very unequal. S. r. Diflance Vth Clafs. Po.^
iition following.

58. Fl. 7 Leonis. Supra pedem borealem anteriorem,
Feb. 4, Double. Very unequal. L, rw. ; S. r. Diftance
1782. 42'' 25'^^ Pofition 8° 36' n. following.
^g, ^ Cancri. Fl. 31. In quadrilatero circa Nubem..
Feb. 6, Double. Extremely unequal. L. r. ; S. d. Dif-
1782. tance 44^^ 52^''^. Pofition n. following.

60. 0 (Fl. 95'") Leonis prascedens ; ad caudam.

Feb. 9, Double. Near | degree i\. preceding the 95th, in. a
3782. line parallel ta/3 and ^ Leonis. Very unequal. L. rw. ;.
S. d. Diftance 37'' 15'''. Pofition 70" 48' n. fol-
lowing.

61. Fl. 81 Leonis. In clune.

Feb. 9, Double. Extiemely unequal L. rw. ; S» r. Dif-
1782. tance ^y'^ 23'^'. Pofition

2 62.

(yf Double Stars, loy

T. 62. Fl. 57 Leonis. E pofleriores pedes pra?cedentI'oiis.

Feb. II, 1782. Double. Very unequal. Diflaiice 33^^ 16'''".
6^, Fl. 25 Leonis. In infimo pedore.

Feb. 17, Double. The largeil of two. Extremely unequal.

1782. L. pr. ; S. d. Diftance 52'^ 46^^^ Pofition
64. Fl. 43^ Leonis auflralior. Ad finiftrum anteriorem cu-

bitum.
Feb. 17, Double. Near i degree f. of the 43d, in a line pa-
1782. rallel to vj and a. Leonis. Extremely unequal. L. w.

inclining to r. ; S. db. Dlftance 59^^ 40^^^ Pofitioa
6^» Secunda ad tt Canis majoris. Fl. 17. In pe£lore.
Mar. 3, Treble. The two neareft very unequal. L. rw. ;
1782. S. r. Diftance 44^'' 52''^'. Pofition 64° 1 2^ f. following.

The two farthefl very or extremely unequal. S. r.

Diflance Vth Clafs. Pofition about 85° f, preceding.

The three flars form a redangle, the hypotenufe of

which contains the largeft and fmallefl.

66. p (Fl. 63^) Geminorum borealior.

Mar. 3, Double. About | degree n. of, and a little pre-
1782. ceding />, in a line parallel to v and a Geminorum.

Very unequal. L. pr. ; S. d. Diflance 34'' ^^"^-

Pofitlon 1° or 2° n. preceding.

67. Pollucem prope. In capite fequentis "][}.

Mar. 3, Double. Near i degree n. following /3, m a line
J782. from ^ continued through /3 Geminorum nearly; the

fartheft and fmalleft of three. Confiderably unequal.

L. r. ; S. dr. Diflance 47'' 37'''.

68. Fl. 75^"* Leonis prsecedens ad borcam.

Mar. 5, Treble. One of two n. preceding the 75th, in a
5782. line parallel to the 84th and 59th Leonis. The two

P 2 nearefl

io8 Mr. Hersciiel's Catalogue

V. neareft very unequal. Diriance 54^' 3Y'^* The fat-

thefl: extremely unequal.
69. Fl. 7 Leonls minoris. In extremo anteiiore pede.
Mar. 12, Double. The largefl: of two. Extremely unequal*
3782. L- pr. ; S. r, Diftance 58'^ i6"\
*jo. Fl. z^^ Bootis praecedensad borearli.

Aprils, Double. Near 3 degrees n. preceding the 2d Bootis^
1782. towards the 43d Comas Ber. ; the preceding of three in

a line parallel to u and -^ Bootis. A little unequal.

L. r. ; S. darker r. Diftance 56'^ S^'"* Polition 7° o'

f. preceding.

71. Prope y (Fl. 24*™) Geminorum.

April 15, Double. Three or four minutes li. preceding yQt*
1782. minorum. Of the Vth Clafs. More in view.

72. -f* /;;Herculis. Fl. 36 et37. In liniftro Serpentarii brachio.
May 18, Double. A little unequal. L. bluifli w. S. reddilh
1782. w. Diflance 59^^ ^<)"\ Polition 36'' 57' f. pre-
ceding *.

'j^, T Urfae majoris. Fl. 14. Duarum in coUo praecedens.
June II, Double. Extremely unequal. L. w. ; S. d. DH^
1782. tance 54'' 46^'^ Pofition about 45° n. following.
74. S (Fl. 72^) Serpentarii borealior.

June 16, Double. More than i degree n. following the 5'6th

1782. double ftar of the Illd Clafs ; nearly in a line parallel to

the62dand 72d Serpentarii, Very unequal. L. rw. ;

S. r. Diftance 40^'' 54'^', Pofition 39° 15' ; inaccurate..

* One of thefe ftars, at leaft, feems to have changed its place fince the tkn?
of Flamsteed, who makes their difference in R.A. 45", and in P.D. 1' 35"»
Pofition f, preceding; hence we have the hypotenufe or diftance above i'45'%
Inftcad of 59" 59'", and pofition 69° 46' inftead of ^° 57'.

7 75-

of Double Stars, * loo

V. JS' -^ telefcopicls f Coronas borealls fequentibus.
)uly 18, Double. About i degree f. following e, in a line
'1782. parallel to 5 and e Corona ; the preceding of three
forming an arch. Extremely unequal. L. r. ; S.
darker r. Diftance 41'' i2"\ Pefition i6''o'f. fol-
lowing.
^6. /3 Aquarii. Fl. 22. In finiftro humeroi
July 2a, Double. Exceffively unequal. L. w. ; S. d. Dif-
1782. tance about 33'' 16'^^; very inaccurate. Pofition

55° 48;.
^7. d(FL. 43^) Sagittarii borealior et fequens..
Aug, 4, Double. A few minutes n. following the 43d, in z
1782. line parallel to 0 and tt Sagittarii ; the neareft of two.

Extremely unequal. L. w. ; S. d. Diftaiice with 278,

36'' f\ Pofition 78° 45' f. following.
^8. ^Sagittarii. Fl. 38. Trium fuper coftis fub ^axilla*
Aug. 4, Double. Extremely unequal. L. r. ; S. d» Dif-
1782. tance VthClafs. Pofition 28° 6' n. preceding. A

third ftar. Diftance about four times as far as the

former. Pofition alfo n. preceding.

79. Fl. 9 :: Caffiopelcc.

Aug. 25, Double. Of two in a line parallel to (3 and y, that
1782. towards y Caffiopeiae. Very unequal. L. w. ; S. pr*
Diftance 52'' 39^^' Portion 50° 36' n. preceding.

80. T Aquarii. Fl. 69. Duarum in dextra tibia borealior.

Aug. 28, Double. Very unequal. L. rw. ; S» d^ Diftance
1782. 36'' 47'''. Pofition 19° 54' f. following.
Zi. Fl. 35 :: Caffiopeiae. In finiftrocrure.
Aug. 28, Double. Confiderably unequal. L. rw. j S. br..
li^Sz. Diftance 42'' 25^^^^^ Pofition 85° 12' n. following.

82.

no ~ Mr. Herschel''s Ca/alogue

V. 82. V (Fl. 25''") Calliopeias pr^ecedens. In fialflra manu.

Aug. 28, Double. Near I degree 11. preceding v, in a line pa-*

J 782. raliel to a and /3 Cafliopeias. Nearly equal. Both pr,

Diftance 43^^ 26^''. Pofition 7° 48' n. following.
8 J. iJ/Caffiopeice. Fl. 36. Sub pede finiftro.
Aug. 28, Double. Very unequal. L. pr. ; S. r. Diflancc

iy82. ^3^^ '^S' ' ' Pofition 10° 12' f. following.

84. Fl. .47 :: Calliopeise. Ex obrcurioribus infra pedes,

Aug. 29, Double. The largefl of three forming a rectangular
1782. triangle on, or near, the place of the 47th CafTiopeiae. A

little unequal. L. rw. ; S. pr. Diftance 50^'' ^V*

Pofition 3° ^53^ n. preceding.

85. f (Fl. 27') borealior et prsecedens. In dextro brachio.
Aug. 29, Double. About | degree n. preceding ^ Andromedae

1782. ^verfus. Very unequal. L. rw. ; S. r. Diftance 30''
^^'^' • Pofition 79° 24' n. following. ^

86. Fl. . I % Urfaj niinoris.

Sept. 4, Treble. Extremely unequal. All three r. The
1782. neareft is the fmalleft. Pofition fome degrees f. follow-
ing. The farthefl alfo fouth, but more following.

87. (T Capricorni. Fl. 7. Sub oculo dextro.

Sept. 5, Double. Very, or almofl: extremely unequal. L. r. ;
,782. S. d. bluiOi. Diflance 50'' -j"'. Pofition 85" \z f.

following.
^8. X (Fl. 15^) Aurlgae borealior. Infmiftra manu.
-Sept. 5, Double. About 3' or 4^ n. following the 15th Au«
1782. i*ig«* Very unequal. Diftance 34'^ 15''^, meanmea-

fure. Pofition 54'' 6' f, precedilig*

m

of Double Stars. 1 1 1

V. 89. ^Aurigae. Fl. 37, In dextrocarpo.
Sept. 5, Double. Exceffively unequal. L. line w. ; S rcd-
1782. difh. Diftance with 460, 35^^ i%^^\ narrow nieafure.

Pofitlon i6°o''n. preceding. A third ftar in view.
90. V Aurigae. Fl. 32. In dextri brachii ancone.
Sept. 5, Double. .Exceffively unequal. L. orange w. ; S. r.
1782. Diftance 53'^ 43^^^ Pofition 61^ 48' f. preceding. S.
not vifible till after fome minutes attention.
01. jG (Fl. ^4=^) AurigiE adje<5la. In dextro humero.
Sept. 5, Double. Near | degree f. following /3, in a line
1782. from the 27th continued through /3 Auriga^; a confi-
derable liar. Very or extremely unequal. L. pr. ; S.
d. Diftance 30^^ 3^^^ Pofition ^45° 6^ n. preceding
p2. Fl. 3* Arietis borealior.

Sept. 10, Double. Full 4 degree f. following the 3d Arietis^
1782. in a line parallel to a Arietis and (J^Ceti ; the mofl: fouth
of two. Equal. Both reddifh. Diftance 51^^ i6^^\
Pofition 52° 45^ H. preceding or f. following.
93. Fl. 103'™ Herculis fequens ad auftrum.
Sept. 19, Double. About i| degree f. following the 103d
1782. Herculis, in a line parallel to the ift and loth Lytic;
the neareft of two. Equal, perhaps the following the
fmalleft. Both r. Diftance 47'^ 46''^ Poiition 45"
42'' f. following.
^4. Duarum Fl. 31^"" Cephei fequentium auftiina.
Sept. 30, Double. About I degree n. of the 31ft Cepliei,
1782. towards ix Polaris. Pretty unequal. Both pr. Diftance

41^^ 40^''^ Pofition 45° 15^ f. following.
95. Fl. 51 x^quarii. In dextro cubito.

O^. 2, Double. Exceffively unequal. L. rw' ; S. d. Dif-
1782. tance Vth Clafs. Pofition n. preceding. Two

other

112 Mr. IIeb.schei*5 Cata/ogue

V. other flars in view; tfie neareil: of them exltremely
unequal. Polition about 80 or 90° f. preceding. The
fartheft very unequal. Pofition about 30° f. following.

96. V (Fl. 59"") Aquarii fequens ad auftrum.

oa. 2, Double. About | degree f. following u, in a line
1782. parallel to S and c Aquarii. Extremely unequal. Dif-^
tance Vth Clafs near. Pofition 15 or 20^" f. pre-
ceding.

97. Fl. loLacertae.

Oft. 4, Double. Very unequal. L. w. ; S. r. Diftancc
1782. with 278, 52'' 34'^^ Pofition 38° 45^ n. following.

98. Fl. 3 Pegafi.

Oft. 4, Double. Pretty unequal. L. wr. ; S. dr. Diftancc
1782. 34'' 43^^ • Pofition 82*" 48' n. preceding. Befides IJ.
62. another flar in view. Pofition following.

99. Fl. 33 Pegafi.

Oft. 4, Double. Confiderably unequal. L. pr. ; S. r. Dif-
1782. tance with 278, 45^^ 3^^^ Pofition 89'' 12' n. fol-
lowing.

100. Fl. 59 Orionis.

Oft. 4, Double. The following of two. Extremely une-
1782. qual. L. w. ; S. a point requiring fome attention to

be feen. Diftance ^y'^ 15^^^* Pofition about 65° f.

preceding,
loi. V (Fl. 36"'") Orionis pr^Ecedens.

Oft. 4, Double. About f- degree preceding u, nearly .in a
1782. line parallel to k and (3 Orionis; the fecond from u.

Extremely unequal. L. w. ; S. r. Diftance 44

15^'^. Pofition about 15° f. following.

IQ2.

//

of Double Siaru 113

V. 102. Ft. 61 Ceti.

0<^. 1-2, Dt>uble. Extremely unequal. L. r\v. ; S. dr. Dil-
J782. tancc with 278, -^-j" $3''' P^^^itlon 76^ 21' f. pre»
ceding. A third liar at fome dlfiance. A little une-
qual. Poiition n. tollowing.

103. Ah ; (Fi, 18^) Lyrct /S verfus.

oa. 24, Double. Full \ df-gree 1. preceding <, ncnrlv rewards
1^82. /S LyriE. Extremely unequal. L.w. ; S. r. Dllhuice
with 278, 45'^ 3-^'^- Portion 29^" 12' a. following.

104. g (Fl. 4^) SagittcC aullralior et priecedens.

Nov. 6,. Double. Full I degree f. preceding s, in a line pa-
1782. rallel to y Sagittae and y Aquila^ ; the neareil: ot two.
Extremely unequal. L. pr. ; S. d. Diflance Vth Clafs,
Poiition 16'' 18^ f. following.

105. y (Fl. 14'') Sagitta; auftralior et fequens.

Nov, 6, Double. About \ degree f. following)' Sagitta% in a
1782. line parallel to Sagitta and Delphinus. Confiderably

unequal. L. pr. ; S. r. Diftance 38^^ 3^^' Pofition

74" 15' f. following.

106. ^(Fl. 12^) Sagittal bo realior et prsecedens.

Nov. 6, Double. About i^- degree n. preceding y Sagittit,
1782. towards the 6th Vulpecula* ; a confiderable ftar.

Equal. Both rw. Diftance 38'' 54'''. Pofition 60^

42^ n. preceding or f. following.

107. Fl. 56 Aurigae.

Nov. 6, Double. Confiderably unequal. L. w. ; S. pr.
1782. Diflance 52'' sY^'- P^^'^tioii 7-° 36^ n. following.

108. X. (P"l. I :^^) Canis majoris borealior.

Nov. 6, Double. iVbout | degree n. of y. Canis majoris. A
1782. little unequal. L. dw. ; S. d. Diftance 42'' S3''^^-
Policlon 23^ 18' n. following.
Vol. LXXV. Q 10;.

114 Afr. 11^ nsciJEL^s Ciifalogtfg'

V. 109. Inter G Cnnci 1 et a Hydrx.

Nov. 6, Double: A large flar not in Flamstef.d, beUveen'.
1782. /S Cancri and 5 Hydrtis. Exceiilvely unequal. Diflancer

35^^ 24^'^ Pofition 5 ^^ o'' n. preceding.
1 10. Fl. I 1 I Tauii.

N')\'. !•;, Doiihlc. Very unequal. L. r\v. ; S. r. DIftance
1782. 46'^ 4-''^- PoiHion j^ 48' n. preceding.
HI. Fl. 42' Urte mnjoris auih-alior et fequens.
Nov. 20, Double. Full 1 degree 1. following the 42d, in a^
1782. line parallel to the 29th and 48tli Urfae m^ijoris ; the
middle of three forming aii .arch. Conliderably une-
qual. L.. wr. ; S. r. Diftanee 30''^ 40:'^^- Pofitioii:
51° 27^ n. following.

I I 2. *Ex oblcurioribus ^u, and v Geminorum fequentibus-.

Dec. 1, Doul)le. Forms almolt an iiofceles triangle with jx.
1-82. and V Cscminorum. Nearly equal. The precediiig pr.
the following wr. Diltance Vth Clals far.

113. * Fl. 9^"" inter et i i*"" Ononis,

Dec. *?, Treble. i\bout i| degree f. preceding the iitb
1-S2, Oiionis, towards i Tauri. The two largefl. coniidera-
bly unequal. L. w. ;; S. pr. Diftance 37^^ 5 r^'^ Po-
rtion ^.^"^ 54' n. preceding.- The third farther oft and.
fmaller. S. r. Poiitioii n. following.

1 14. Fl. 103 Tanri.

Dec. 7, Double. Exceflively unequal. L. rw. ; S. d. Dlf-
5^,82. tance with 278 and 625, 30''' 2^'", mean meafure. Po'
fition 72 24'.

I I 5. 0 Tauri. Fl. 114.

Dec. 7, Double. Exceflively unequal. L. w. ; S. a point.

iT82. Dillancc 5.''' 34'''. Pofition 77' 54' f. preceding.

■2 l\vo

V. Two other fmall ftars follo\vi]ig, aiulra thi-rd to tjxe

nortiv
1 1 6. Fl. 41 Arletis.

Dec. 23, Treble. The two ncarefl- exceilivciy unequal. L. w.;
1782. S. a point, Diliaiice with 278, 39" 20'". j^oiitioii
So'' 48'' r. preceding. For the diR'ancc of the iaithcil,
lee VI. 5.*,
1 1-7. f (Fl. 58"") Arietis nraeceitens ad hoicam.
Ddc. 23, Double. About 1 1- n. preceding (^, towards the 41 il
1782. Arietis; the following of four forming an arch. Very
unequal. Both dr. Diilance 34'' 48"^ rofitiou 47'
21' n. preceding.

118. £ (Fl. 46-') Orionis borealior et pra^cedcn.-^.

Dec. 28, Double. The moll n. of three preceding e Orionis,
.1782. towards ;x Tauri. More north is another let of three;
care mull: be taken not to miilak'e one of rhiem for this'.
Extremely unequal. L. rw. ; S. d. Diftance Vth
Clafs. Pofition 13° 6' f. preceding. Two more fol-
lowing, exceilively unequal; one about i', the other
about 1 1 minute.

119. e (Fl. 46') Orionis aullralior et praecedens.

Dec. 28, Double. Full | degree C preceding e, in a line pa-

1782. rallel to s Orionis, a«d b Eridani ; the fmallefl: and moil:

f. of two. Very unequal. L. w. ; S. r. Diftance 30^'

12^^''; a little inaccurate. Pofition 2i''33r preceding.

A third ftar 2 or 3'' f. following.

* The ftar Vl. 5. in the plsce referred to is called Flamsteed's Q5rh
Arietis. With lo many liars and me^fiires it was hardly poffible to avoid leveral
■errors, I have therefore now added to the errata already given at the end of vol.
LXXII. and LXXIII. ef the Phil. Tranf. foroe others, that have fini:ebeen detected
by a careful review of the double liars, and believe that no more will be found.

0^2 120.

1 1 6 Mr. Herschel's Catalogue

V. 120. Fl. i5llydrae.
Dec. 2S, Double. Extremely unequal. L. w. ; S. r. Dif-

1782. tnnce 43'^ i^^\ Pofition about 70'^ n. preceding.
121.^ CoiiKt Berenices. Fr.. 12.

J.in. I, Double. Confiderably unequal. L. rvv. ; S. pr,
17S3. Dillance 58'' ^s'^'' Poiition alK>ut 77*^ 1". following.
122. Fl. 44'' Booris auilralior et praxedcns.
J:in. 8, Double. Near f degree i. preceding the 44tli,

1783. towards tlie 38th Bootis. Very unequal. L, bw. ; S. .
pr. Dillance 34^' ii'-\ Poiition 67' 6' f. preceding.

223. *■ In Andromedae pe<5lore,

Jan. 8, Double. Equal. Both rw. or pr. Diftance 45/' i'^^.
i-8^. Poiition 32" 24' f. preceding. Its place, as determined

in 1777 byC. Mayer, is ^ ^^ 2,^' 33' "^ time, and |

29^4^'^ 3'' declination north.

124. g (Ff.. 2'") Centaurl fequens ad auflrum. \
Jan. 37, Double. About 1 1 degree f. following ^ Centauri,
J783. in ^ liiie parallel to y Serpentls and 5 Centauri; the

mofi; 1^ of two. Confiderably unequal, Diftance 54'^'
I '^' ; too low for accuracy.

125. Fl. 46*"" Bootis fequens ad boream.

,reb. 3, Double. Near 2 degrees n. following the 46th, m a

T^Sj. line parallel to ^Bootis and /2 Coronas; the third flar

about that dire(5lion. Confiderably unequal. L. r. ;

S. darker r. Diftance 33^" ^^'. Pofition 37° 33' f.

preceding.

126. r (Fl. 5"") lierculis praccedens ad auftrum.

I'eb. 3, Double. Near | degree f. preceding r Herculis, 111
1-83. iv liue parallel to y and I Serpentis ; a fmall ftar. A
little unequal. Both pr. Dlflance ^j'' 51% rather
fvill mcafure. Pofition 5 a'' 6' f. preceding. .

127

cf Double Si an, iij

V. 12 7. (Fl, 41*"') Herculls praecedens ad boream.
Feb. 5, Double. About I degree n. preceding the 41 fl Her-
1^83. culis, in aline parallel to k. Serpentarii and /3 Herculis.
Pretty unequal. Both r. Diftance 48'',^ ^o"\ Poiition
19- 45' n. preceding.
128. , (Fl. 63"") Virginis iequens.

Feb. 7, Doiihle. About i| degree following / Virginis,
1783. Jn a line par ulel to Spica and (o Librae. A little une-
qual. L. pr. ; S. r- Diitanc3 4r' 58^^^
l29.y(FL. 25"^) Virginia fequens ad boream.
Feb. 7, Double. About i' ceg-'ee n. following/, in a line
1783. P^r^ll-1 to y and t Virgin::, a b-^ge ftar. Very une-
qual. L. r. ; S. dark r. Di(bnce 46 42"^ Poiition
6 or 7° f f >llowing^ A rouble fiar of the Vth Ciafs
in view, preceding.
I JO. Fl. 35 Comas Berenices.

Feb. 26, Double. Very unequal. L. r. ; S. d. Didancc
1783. 31^^ 17^''. Pofition 36" 51 f. following.

131. Fl. 24*"' Librae fequens ad boream.

Mar. I, Double, About i{ degree n, following the 24th
1783. Librae, in aline parallel to tt and /S Scorpii. Conlidera-
bly unequal. L. rw. ; S. r. Diftance 47'^ 46^".

132. Fl. 29"" inter et jC" Librae.

Mar. I, Double. Of two between the 29th and 30th Librae
1783. that nearefi: to the 3ath. Very unequal. L, w. ; S. d.
Diftance 39'' 59'^' i very Inaccurate.

133. Fl. 60 Herculis.

Mar. 7, Double. Extremely unequal. L. w. ; S. d. Dif-
1783. tance 48' 40'^'. Pofition ^'^'^ o^n. preceding.

154.

Il8 Mr', IlERSCIIEr/s Cc//.7%7//?

V. 134. ip (Fl. 4^"") Ophiuchi prir:^ceclens ad aullriiin.
Mar. 24, Double. About i degree preceding and a little f. of
1783. 4^? ^^^ '^ ^^'^^ parallel to ij/ Ophiuchi and u Scorpii ; the

fartheft of two in the bafe of a triangle. Equal. DiLf-

tance 45'^ A-j"^'

1 35. Ad Fl. 49*"* Camelopardali.

April 4, Double. The fmalleft and mofl: f. of two that arc

1783. about 20^ afunder. A little unequal. Both r. Dii-

tance with 278, 38'' 1 8'"', Pofition 85° o' f. preceding.

136. 5 (Fl. 65^) Aquilae borealior.

Sept. 12, Double. About | degree n. of ^, in a line parallel
1J83. to ij and /3 Aquilic; a conliderable ftar. Confiderably
unequal. L. pr. ; S. r. ; Diilance with 278, 47'' 5''^'.
Pofition 6^^ 48^ f. preceding,

137. % (Fl. 17') Cygni borealior.

Sept. 22, Double. About i j degree n. oi x-> towards (JCygni^;
1783. a confiderable flar. Confiderably unequal. L. garnet ;
S. r. Diftance with 278, 35^^ i''\ Pofition sf 3' "•
following.

SIXTH CLASS OF DOUBLE STARS.

VI. 6y. lyOrlonis. Fl. 28. In extremo enfis manubrlo.
Dec. 27, Double. Exceffively unequal. L. w. ; S. d. Dii-
1781. tance i' 50^' $Y^'' I^ofitio^^ 35° ^^' i^- following.

6S.

of Double Stars, irp

VI. 68. 7? (Fl. 28'^ Orionls auftralior.

Dec. 27, Double. About | degree f. of, anc^ a little follow-

v--%i. ing 7j, In a line nearly parallel to J" and ^ Orionls. Very

unequal. L. r. ; S. d. Diftance 2' o'^ 1 1''''. Polition

7° <J4' n. preceding.

69. Fl. 14 Arietis. Supra caput.

Dec. 27, Double. Very unequal. L. pr. ; S. dr. Dlilance

1781. -i^ 29" 28"'. Potitlon 11° 12' n. preceding.
'JO, (9 Geminoruni. Fl. 70. Supra caput prioris If '.

Dec. 27, Treble. Or two fmall ftars In view ; the neareft a
1^81. little more than i n^inute ; the other not much farther.

71. T Hydra.^ Fl.^i. Trium in fiexu colli auflraliffima.

Jan. 20, Double. Pretty unequal. L. w. inclining to rofe

1782. colour. S. pr. Dlilance 1/ i" ^o"\. Pofition 88° 36'
n. preceding.

72. Ad Fl. 68'"^ Orionls. In fufte-

Jan. 30, Double. The moft n. of two that are i degree
1782. afunder. Very unequal. L. w. ; S. dr. Diftance
with 278, 1/ 12'' 50^^^ Polition 41° o^ f preceding.

73. e Geminorum. Fl. 27. In boreall genu priEcedentis J^
Feb. 2, 1782. Double. L. w. Dlilance 1/ 50'^ 30'''..

74. Fl. 51 Geminorum.

Feb. 2, Has two very obfcure flrars in view. L. r. ; S. r, S. r,.
1782. The nearefl about li, the next 2 minutes. Pofition
of both about 4.0 or 50' n. following.

75. to Cancri. Fl. 4. Ad prlmum borealem forficem..

Feb. 2, Has a very obfcure ftar in view. L. pr. Diftance
1782.. about 1 1 minute. Pot'ition about 20*^ n. preceding. A
thlrd.about z', Pofition more north. *

76..

120 Mr. Hersckel's Qitafcgue

VI. y6, 0 Leonls. Fl. 14..

Feb. 2, Double. Extremely unequal. L. rw. ; S. r. DIC^

1782. tance i^ 3^^ 29^^^ Polition 49° 36' n. following^
yj. T Virgiiiis. Fl. 93.

Feb. 4, Double. Very unequal. L. w. ; S. dr. Diftancc

,782. I' 8'' 22^'^

78. f (Fl. 16=*'") Cancri fequitur.

Feb. 8, Double. About I degree following J Cancri, towards
1782. 17 Leonis. Extremely unequal. Diflaiice i' 3'''47^^^

79. (p Leonis. Fl. 74,

Feb. 9, Double. Very unequal. L. w. ; S. pr. Diftance
1782. i' 38'' 3S^^^' Poiition about 10 or 12'' n. preceding.

80. Fl. 93 Leonis,

Feb. 9, Double. Very unequal. L. w. ; S. 6h, Diftance
1782. 1' 10'' 13''.

81. Fl. 27 Virginis. In ala dextra.

F€b. 9, Double. Extremely unequal. L. w. Diftance
,782. 1^28'^ 48'^'.

82. Fl, 31 Monocerotis. In media cauda.

Feb. 9, Double. Very unequal. L. rw. ; S. db. Diftance
1782. 1' 10^' I3'^^« Polition 40*^ o' n. preceding.

83. Prope Fl. i^'^' Orionis.

Feb. 9, Double. A few minutes f. following the I ft, towards
1782. the belt of Orion. Confiderably unequal. L. pr. ; S.
r. Diftance 1' 20'' 58'^ Pofition 88^ 15^ n. fol-
lowing.
S4. Fl: 14 Canis minorls.

Feb ^, Treble. The neareft extremely unequal. L, rw. ;
1782. S. d. Diftance i' 5'' 28^^^. Pofition 26° 24' n. fol-
lowing.

cj Double Si ars, r.2i

"VI. lowing* The third forms an angle, a little larger than
a rectangle, with the other two. Pofition f. follcwing.

%^, Fl. 27 Hydrse. '

Feb. 9. Double. Very unequal. L. rw. ; S. pr. Diftance
1782. Vlth Clafs far. Pofition about 60° f. preceding.

86. Prima ad (T Cancri. Fl. 51.

March 5, Double. Extremely unequal. L. w. ; S. d. Pofi-
1782. tion n. following.

87. Tertia ad cr Cancri. Fl. 64.

March 5, Double. Very unequal. L. rw. ; S. dr. Diftance
1782. i^ 25^'' 45^^^ Pofition 25° 12^ n. preceding.

88. jG Aurigae. Fl. 34. In dextro humero.

March 5, Double. Extremely or exceffively unequal. L. fine
1782. bluifh w.; S. d. Diftance z' 49^" (y"'. Pofition 54"
I z' n. following. A third farther off. Very unequal.
About 40 or 50° n. following.

89. Fl. (y^ Bootis adjecta. ^

Mar. 12, Double. Juft following the 6th Bootis. A little
1782. unequal. L. r. ; S. deeper r. Diftance \' 19'^ 39^'^.
Pofition 58° 6' f. preceding.

90. Fl. 61 Virginis.

Apr. 3, Double. Very unequal. L. w. ; S. d, Diftance
1782. i' 13'' "i^s"'* Pofition about 75° n. preceding.

91. Prope y (Fl. 24^"") Geminorum.

Apr. 15, Double. Three or four minutes n. of y Geminorum.
1782. Confiderably unequal. Both fmall; too obfcure for

meafures with 7-feet; my 20-feet fhews a third ftar

between them with 1 2 inches aperture.

VoL.LXXV. R ^^*

1 22 Mr, Her$chel*s Catalogue

VI. 92. I (Fl. i^) Capricorni boreaiior.

June 34, Double. About | degree n. of | Capricorni. Very
1782. unequal. Both r. Diftance i' 2^'' \6'^\ Polition

2° 3' f. preceding.
92. fl Corona borealis. Fl. i^. Ad fummum.
July 18, Double. Very unequal. L. w. ; S. d. Diftance
1782. i^ 27'^ 44'^^ ; a little inaccurate. Pofition 54° 27^ C
following.
04. A Coronae borealis. Fl. 12.

July 18, Double. Extremely unequal. L. w. ; S. r. Dif-
1782. tancei'35^^ 14'^^ Pofition 33^ 12^ n. following,
^5. ij Bootis. Fl. 8. Triumin iiniftro crure borea.
Aug. 3, Double. Extremely unequal. L. w. inclining to
1782. orange; S. r. Diftance about li minute. Pofition
about 25 or 30° f. following.
06. Z, Perfei. Fl. 44. In pede finiflro.

Aug. 25, Treble. The neareft extremely unequal. I^. w. ;
1782. S. r. Diflance i' 11^^ 26'''. Pofition 66° 36' f. pre^ J
ceding. The fartheft very unequal. S. r. about i f
minute. 70 or 75° f. preceding.

97. Secunda ad t Aquarii. Fl. 71. In dextro crura.

Aug. 2S, Double. Very unequal. L. r. ; S. d. Diflance
1782. 2' 3'^ 3^^^\ mean meafure. Pofition 18° 30' n. pre-
ceding.

98. Fl. 46^"" Tauri fequens ad auflrum.

Sept. 7, Double. About i| degree f. following the 46th,

1782. nearly in a line parallel to the 38th Tauri and the 42d

Eridani. A little unequal. L. pr. ; S. r. Diftance

i' 2^^ 34^^^' Polition 43° 48^ n. preceding. A double

ftar of the Vth Clafs in view, following within 3^

Equal,

ef Double Stars, 1 23

VL Equal. Both fmall and r. Almoft fimilarly fituatcd
with the above, but pofition more n. preceding.

(^9. m Perfei. Fl. ^1- ^^^ ^^^^^'^ P^^^^ '^^^^•
Sept. 7, Double. Pretty unequal. L. r. ; S. rw. Diflance
1782. ' i' 36'' 27'"'. Pofition 71° 51' f. preceding.
100. / (Fl. 32^'-)Cephei fequens.

Sept. 30, Double. About t| degree n. follawing i, nearly
1782. towards y Cephei. A little unequal. Both pr. Dif-

tance \' 1'' $^'\ Pofition 8° 9' n. preceding,
loi. 5 Tauri. Fl. 68.

oa. 31, Has two ftars in view. The neareft exceffively une-

1782. qu^l. L. w. ; S. d. Diftance with 278, i' 3'^ i%"\

Pofition 35'' 24' f. preceding. The fartheil: extremely

unequal. S. r. About i \ minute. Pofition about 50"

n. preceding.

102. Fl* 5 Lyncis.

Nov. 13, Double. The largeft of a fmall triangle. Very
,782. unequal. L. r. ; S. garnet. Diftance \' zV zo"\
Pofition 2^ o' n. preceding.

103. ePegaii. Fl. 8.

Nov. 20, Double. Very unequal. L. pr. *, S. dr. Diftance
1782. \' 30'' 56^'^ Pofition 52° 45' n. preceding.

104. ^Bootis. Fl. 30. In dextro calcaneo.

Nov. 29, Has a very obfcure ftar in view. Extremely unequal.
' ,7^2. L. w. inclining to r.; S. d. Diftance about i| minute.
Pofition almcft diredly preceding.

105. Fl. 105 Tauri.

Dec. 7, Double. Very unequal. L. pr. ; S. r. Dift-ance
1782. \' 41" ^29'''. Pofition 1 8° o' f. preceding.

R2 . io6-

J 24 ^f^- Herschel's Catalogue

VI. 1 06. b Erldahi. "Fl. 62.
Dec. 7, Double. Confiderably unequal. L. w. ; S, pr.

1782. Diflance i' o'^ i(^"', Pofition 15* 9^ n. following.
107! Fl. 31^ Monocerotis auftralior et praecedens.

Dec. 21, Double. About i\ degree f. of, and a little pre-

1783. ceding the 31 iT Monocerotis, in a line parallel to f Hy-
drae and the 31 ft Monocerotis ; the moft fouth of two.

• Confiderably unequal. L. r. ; S. deeper r. Diftancc
about 1 1 minute. Pofition 50 or 60° f following.

108. 5 (Fl. 22^) Hydrae borealior etprcEcedens.

Dec. 28, Double. About | degree n. of, and a little pre-

1782. ceding ^, nearly in a line parallel to k and ^ Hydra;-
Very unequal. L. r. ; S. blackifh r. Vlth Clafs far.

c? . Pofition I or 2° n. preceding. A third ftar preceding.

109. Fl. 22 an 26 Cancri incertum.

Dec. 29, Double. One of the tw^o being loft *, it does not
\.^i7S2. -appear which is the remaining ftar. :, Very unequal.
L. n ; S. dr.

1 10. Telefcopica ad 0 Ceti. -

Jan. 2, Double. Looking for 0 Ceti, which was Invifible to
J 783. the naked eye, I miftook this for it. Pretty unequal,
L. rw. of about the eighth magnitude ; S. r. Diftance
i'2o''52'''. Pofition 33° 42'. ' ' .^

1 1 1. a Hydr^e. Fl. 30. Duarum contiguarum lucidior.

Jan. 8, Has two ftars within about 2 minutes ; the neareft

1783. exceflively unequal; the fartheft extremely unequal.
Both f. following.

112. Fl. 13 Bootis.

Jan. 8, Double. Extremely unequal. L. r. ; S. dr. Dif-
1783. tance \' \^/' S*^'"' Pofition 7^24^ n. preceding.

• See Phil, Tranf. vol. LXXHI. p. 252,

113.

bf Double. Stars, .. -, 125

VI. 113. Fl. 4 Virglnis.

Jan. 8. Double. Extremely unequal. L. wr. ; S. dr. Dif-
1783. tance 2^ 25^^ A^"^ '•> ^o^ obfcure for accuracy.

114. Fl. 69'"" Orionis prijecedens ad auftrum.

Jan. 9, Double. About I degree f. preceding the 69tli,
1783. nearly towards X Orionis. Confiderably unequal. L.

pr.; S. d. Diilance i' ^o" 38''^ Pofitioii 22^ 6' f,

following.

1 1 5. Fl. 2 1 ^"^ Crateris fequens ad auflrum.

Jan, 10, Double. About 2 1 degree f. following the 2ifi:, iii
1783. a line parallel to the 1 2th Crateris and 4th Corvi. Very
unequal. L. w. ; S. r. Polition 12^ i2^n. following.

116. Fl. 43 Herculis.

Jan. 10, Double. Very unequal. L. inclining to garnet ;
1783. S. r. Diftance i' i^' ^Y'\ Pofition 38^ 48^ f. pre^
ceding;.

117. Fl. 12^ Librae borealior et pr^ecedens.

Jan. 10, Double. About i| degree n. preceding the 12th
1783. Librae, towards Spica. Very unequal. L. rw. ; S. r.
Pofition about 40° f. preceduig.

118. Fl. 30 Monocerotis.

iFeb. 12, Double. Very or extremely unequal. Dlflance

1,783. 3' -as" 54"^-*: -■-:-:

iiiQ. 6 (Fl. 18*) Pifcis auftrlni auflralioret prsecedens.

}July28, Double. About i\ degree f. of, and a litfile pre*

i J783. ceding 6 Pifcis aufl:rini,in a line from (J Aquarii continued

* On account of the change in th^ magnitudes of the ill: and 2d- Hydrcc, this
fmall flar may be of ufe to afcertain whether the 30th Monocerotis, which is
fituated between them, has any confiderable proper motion. See Phil. Tranf. vol.

Lxxm. p. 255.

through

1 26 Mr. Herschel's Catalogue of Double Stars,

through e Pifcis. Pretty unequal. L. dpr. S. dr.

Diftaiice i' 2^' 58^"^ Pofitlon 6f 46^ f. following.
;20. Fl, 43*"" Saglttarli fequens ad auftrum.
Aug. 16, Double. Near i degree f. following the 43d, In a
1783. line parallel to J and 0 Sagittarii ; a confiderable ftar.

Very unequal. Both dr. Diftance with 2J78, i^ 14^'

9^^^ Pofition 37° o^ n. preceding.
121. Fl. 12 LacertaB.

Aug. 18, Double. Y^i'Y unequal. L. w. ; S. r. Diflance
1783. with 278, i' o'' 10^'^. Pofition 'j^'^ o' a. following.

Add the following errata of the Catalogue of Double Stars in
vol. LXXII. to thofe already noticed at the end of the
LXXIId and LXXIIId volumes.

Page.

Line.

For

Read 1

133

140

145
153
153
15^^

22

26

i 7
II

4

25-

19'' 14'"
35- 48-
V Capricorni, Fl.

33° 42'
Fl. 5.

I Oil

25*.

19" 26'"

36" 9'"

e Capricorni. Fl. 11.

61° 23'

Fl. 4.

lu-liU

P/„7ns.rr„m: /^./. Z A'A7 ' Tal, V „ ru

C 127 ]

VII. Obfervatlons of a new variable Star, In a Letter from
Edward Pigott, Efq. to Sir H. C. Englefield, Bart, F, jR. ^S".
and A, S,

Read December 23, 1784,

DEAR SIR,

FOR fome years pafl I have been employed in verifying
all the ftars fufpedled to be variable, in order that here«
after we may know with certainty what to depend upon. This
undertaking, which is nearly completed, has already proved
of ufe in deteding many miftakes, and producing fome difco-
veries ; among which, the following is one of the mofi: im-
portant. September 10, 1784, I firft perceived a change in
the brightnefs of the flar 17 Antinoi, and by a feries of obfer-
vations made ever iince, I find it fubje6: to a variation very
iimilar to that of Algol, though not exadly the fame in any
one particular.

7} Antinoi, when brlghteft, is of the thii'd or fourth magni-
tude, being between ^ and j9 Aquila^ ; and at its leaft bright-
nefs of the fourth or fifth magnitude, it then being between
that of i Antinoi and ^ Aquilae; therefore, its greatefl varia-
tion in brightnefs may be called about one magnitude ; and the
changes it undergoes, though probably not nicely afcertained
from fo few obfervations, are nearly thefe :

128 Mr.ViGorr^ChfervaUons

At its greateft brightnefs 44 ± hours.

In decreafing - - 62 zt hours.

At its leaft brightnefs 30 rt hours.

In increafing - - 3^ ± hours.

All thefe changes, which hitherto feem to be regular and con-
flant, are performed in 7 days 4 hours 38 — minutes; this Ifhall
ftlle its period, and hereafter will fhew how it is determined
with fuch exadlnefs.

The ftars to which t] Antinoi was compared are in order
thus : ^ Aquilae third magnitude, j6 Aquil^ and Q Serpentis
fourth magnitudes, i Antinoi fourth or fifth magnitude, and ^
Aquilse a bright fifth. I find, by feveral years obfervation,
that /3 AquiliE retains the fame brightnefs. ; Antinoi, which
has been examined with particular attention by Mr. Good-
RiCKE and myfelf, is fufpeded by us both to be fubjecl to a
fmall variation, but not fufficiently apparent, fo as to afFcd:
materially thefe comparifons, and poffibly it may be only the
effect of fome optical illufion ; for I have frequently remarked,
that both in the twilight and moon-light, or when the air is in
the leaft hazy, there is a greater difference between the bright-
nefs of many of the ilars, than in a dark night and clear Iky.
In the following journal of obfervations of ri Antinoi, the
Greek letters i3, (J, ^, belong to Aquila, and /, i/, to Antlnous ;
fecondly, the magnitudes marked in column the third are by
eflimation, and can be of no further ufe than merely to give,
at firft fight, an idea of the flares brightnefs ; and laftly, the
lines diftinguifhed by inverted commas, are extradls from Mr.
Goodricke's journal, whofe friendly afliftance I have often ex-
perienced, and was the more welcome on this occafion, becauie
repeated attention and great exadtnefs were requifite.

c Dates.

^J a nevu Varlahk S/.ir,

I2p

pates.

1783-

J«ly 17

27

1784
Sept. 10
12

13
19

20

23

28 1

2Q J

^9
30

oa. I

a

5

6

8

9
10

1 1
15

Hours.

Magni-
tude.

lOd:

IO±:
lOdz

io±

71

9

711

9§i
8

8

i'9i|
I II J

7f

I9 -1
8

Orh

9±
9±

8
8
8

9±
I 711
I9O

8±

8dr

8±
II

10

8±

8

3 -4

4
4

4
4

4
4
4

o
O
o
J

4
4
3
o

3

3

4
4
4

16

Vol. LXXV.

4
4

4

4

5

5

4
4

5
5
5

4
4

Journal of the comparative brightncfs of 5) Antinoi.

fLefs than $ Aquilac and brighter than 6 Scrpentis (/a
L Aquilce and S Serpentis are equal) weather hazy.
Rather brighter than (S Aquilie and S Serpentis.
If any difterence, lefs than /3 Aquilae.

N. B. Thefe times are from recoUedlion, arxd cannot
err more than i| hour.
Lefs than f? Aquijre and 6 Setpentis,
Much lefs than /2, equal to •.
' A little brighter than », air clear."

Lefs than J, brighter than /?, and much brighter than 1.

" Brighter than, and ^."

Rather brighter than /?, and much brighter than ^ -~

*' Lefs than <3 and«."

Much lefs than 0, and equal to »,

** Lefs than (3 and.."

/Brighter than /3 an-d «; at 1 1 h. it feemed to have
I increafed.

r Lefs than J, rather brighter than /3j thought it rather
I lefs at ii|h.; moon near.

Brighter than 0 ; moon-light.

If any difference^ rather brighter than /S.
" Rather brighter than ^."

Lefs than ^, brighter than.; air clear, moon-light.

Equal to ., much lefs than $,
*' Lefs than ,." "
Between the brightnefs of ^ and K
" Brighter than |S and .."

Rather brighter than g.

** Much the fame as yefterday."

f Brighter than 1 ; think it not lefs than $ -, this obfcr-
1 vation doubtful, occalioned by intervening clguds^
5 j*' Believe it lefs than .; weather bad."
5 ]" Certainly lefs than ;3; weather bad.*
5 ]*' Lefs than . ; iatlier r doubtful obfervation.'*

Rather lefs than |S, and bri"hter than ^,

iEqual to jS.

i" Rafher brighter than '^.^

jLefs than ^, brighter than ».

S ■ ' Dates.

130

Dates.

1784

Flours,

Migni
tilde.

Mr, Pigott's Obfervations

Journal continued.

31

Nov. 3

6
7

n

12

13
16

17

^9

20

21

Dec. 4

61-

8|
51

H

9
71

/

51

7

7

ff^}

51
8

6
8

6

7

6|
7
61

oa. i6

61

^7

^7 1
18 J

18

8

6i

19

7i

20,

Sit

22

Srt

^3

61

8

24

7

f 61 1

I7 J

25

61

26

6J-

9I

27

6

4

4

4
4

3

4
4

4
4

1

4
4
3
3
3

4
4

4
4

4

4

4
4
4

'* Lels than (3 nad »."
Undoubtedly lefs tlirm >.

Lefs than », brighter thaa/x,
"• Lefs than »."

4 jEvidently brighter than /?.

5i

4
4

5
5
4
4
4

5

5

" Much brighter tlianl3."

" Brighter than js,"

Lefs than |3.

" Not ib bright as |3, brighter than »."

Equal to •, much leis than ^ ; moon-light, air clear.

f " Lefa than « j rather, though very little, brighter
.1 than/.."

Much lefs than i3, equal to », brighter than f*.
Sometimes feemed rather lefs, but generally equal to^.
Equal, if not rather brighter than (3.

f " At 6| rather lefs, at 81 nearly equal, and at 9^

I " rather brighter than ^.".

r Remarkably bright, nearer ^ than ^; moon-light^.

1 air clear.

" Nearer to /S than to ^."

Seemed equal t© ;3 ; air not very clear.

" Rather brighter than (3."

Evidently lefs than ^. i

Much lefs than j3.

" Lefs than ^ and I,"

Brighter than ^, much lefs than J.

Rather brighter than ^, certainly equal,.

'^Rather brighter than^ and ».'*

Lefs than jS, equal to »,

'* Lefs than 0, and rather lefs than »."

r Evidently lefs than^, and rather brighter than»j at

1 8 it feemed increafed, and about
Between its leaft and full brightnefs.
'* Lefs than ^, and fomething lefs thant."

Brighter than/?.

If any difference, rather brigsuer than ^; clouds cov-
ered the moon: at 8h.if any difference rather lefs-
than &i moon-light, and air not fo clear as at 6.
Rather brighter than ^, brighter, than »."

Rather lefs than ^, brighter than ».

Lefs than ^, rather brighter than » j moon-light.

" Brighter than /S."

If any difference, lefs than |5.

In

of a new Variable Star, ■ i ^ i

In order to obtain a point of comparifon, for fettling the
jjeriodlcal changes of ^ Antinol, which I fuppofe to be con-
stant, it is natural to fix upon that phafis, which can be deter-
mined with the greateft preciiion ; and this feems to be at the
time when it is between its leaft and greateft brightnefs, as
clmoji the lohole increafe of brightnefs is completed in lefs than
24 hours, though the perfect completion is performed only in
36 ± hours ; thus having fettled this necelfary point, and found
roughly the length of a fingle period, the computations, in
order to dbtain greater exaftnefs, are as follows.

S 2 Time

np.

M/*.. Pigott's Ohjervatlons

Time when „ Ahtlnoi was
betueen its leaft and greateft
brightness.

Intervals between
the obfervations.

Number of pe-
riods in ditto.

4 each of

Let
flng

Days

7

igth of z
Ic period.-

Hours.

i7E4,Sept. 12. at, 20 ^
Ocl. 1 1, at 11 J

Days. Hours.
28 15

. Hours.
0*

Sept, i 2. at 2o v
Oct. 1 8. at 20 J

36 0

5-D^

r

41 +

Sept. 12. at sioi i<
Oct. 26. at 60 /

43 4

6 D°

r^^.

.4^ -

Sept. 12. at 20 -1
Nov. 16. at 8 J

64 12

9 D^

7

4

Sept. 19. at 20 T
Odt. 18. at 20 J

29 0

4 D°

7

6

Sept. 19. at 20 1
061. 26. at CO J

36 4

5 D^

7

5i +

Sept. 19. at 20 1
Nov. 16. at 8 J

SI 12

8 D^

7

41

Oifl. 1 1 . at II T
Nov. 1 6. at 8 J

35 21

5 D^

7

41-

Oa. 18. at 20 ")
Nov. 1 6. at 8 J

28 12

4 D^

>n a mean,

7 -

3

Length of a fingle period, c

7

4 30

Perhaps other aftronomers may not exadly agree with me,

in fixing the times as fet down in column the firft; for my

part, I determined them without paying any regard to the

refuits, by taking a mediuoi between the times when 53 Antinoi

4 had

cf a Jie-w V'ariable Star. ii^

had rather paffed its leaft brightnels, beuig nearly equal to ; An-
tinoi, and when it was a little, but undoubtedly, brjghtti-
than jQ Aquiliie. Though it does not appear, as I have already
laid, that any of the other phafes can be fettled with equal
precifion, different comparifons neverthelefs may prove fatii-
fa6lory towards corroborating the above ; I have therefore alfo
deduced its period from the befl and mofc diftant obfervations,
inade when at its leaft brightnefs ; they are thus : 7 days
o hours and 7 days 5 hours. Thefe refults I reject, and retain
the n:iean given by the hrfl fet, with w4:iich we may proceed on
to gain a much greater exa^tnefs ; let one period be fubtra^led
from the obfervation of July 27th, 1783, and it will appear,
that fi Antinoi had varied in brightnefs during the following
four days, though at that time it did not ftrike me.

July 17th, decidedly brighter than /3 Aquilae*

— I 8th, not obferved.

1783, "j — 19th, rather brighter than /3 Aquiiie^

— 20th (anfwering to the 27th) equal or rather
lefs than /3 Aquikt*

As it is therefore evident, that on July 19th and 27th, 1783,
'i] Antinoi was decreajing m brightnefs, 1 (hall compare thole
•days obfervations to correfpondlng ones- made in 1784.

Hours.

1784, Sept. 30. ^t 6]

Od. 7. at 16 1 ,

06k. ic at Aj Sinailar obfervations to that of 1783

Oa. 22. ati2r J"^^ ^9^1^' ^f loli- ±r i; Antinoi heing
Nov. 1 2. -at 2I ^■^'^^^^ brighter than /3 Aquilae/ .^V.

Nov. 19. at 00

17^4:5

1 ^ A Mr. Pi GOT T ■ s Ohfervatiom

•J •

Hours,

1784^ Sept. 30. at 1 81

Od". 1 5. at 14 /Similar Obfervntions to that of 178^

Od. 22* at 19 /■ July 27th, at 10 h. — > i? Antinol being

Nov. 12. at 1 4 1 equal to or rather lefs than /3 Aqullae* ,

Nov. 19. at 14 ) '

In eftimatlng the abov^ times, I paid much attention to the

obfervations of the preceding and following days ; however, a

few hours more or lefs do not make a material difference. Ti^

•refults of thefe comparifons are
D. H. Mi

"7

4

39*

7

4

44i

7

4

S^'^

7

4

541

7

4

3^

7

4

261

7

•4

32,.

7

4

4^1

7

4

43-*

7

4

26

7

4

211

oB^;

t)n a mean 7 4 38- length of a fingle perio^^

As this approaches the moft to the .preceding refult, it may be
aflumed as neareft the truth, provided the changes be uni-
'formly periodical.

Hitherto the opinion of aftronomers concerning the changes
of Algol's light fecm to be very unfettled ; at leafl none are
univerfally adopted, though various are the hypothefes to
account for it ; fuch, as fuppofing the ftar of fome other than

a fpherica!

of a new Variable Star, rq^

A fpherical form, or a large body revolving round it, or witii
feveral dark fpots or fmall bright ones on its furface, alib giv-
ing an inclination to its axis, &c. ; though moll: of thefe con-
je61:u res with regard to Algol be attended with difficulties^ fome
of them combined do, I think, account for the variation of
9; Antinoi-

Thofe perfons who are accuftomed to examine the fl:ars atten-
tively will not befuiprifed to find, that Mr. Goodricke and I
do not always perfe6tly agree in our obiervations ; thefe fmall
differences in the magnitudes of the flars are very difficult to be
afcertained with the naked eye, w^iich has often made me la-
ment,'^ we had not fome contrivance for determining their relative
brightnefs, and even I attempted feveral methods, but did not
purfue them with fufficient attention and diligence to obtain
any fatisfi6lory refults ; neverthelefs I (hall juft mention them^
as perhaps fomebody elfe may overcome thofe difficulties,
which to me appeared fo Ytxy confiderable. '

1. In 1778 I had fmall pieces of fine glafs ftained with dif-
ferent ffiades, which being applied to the eye end of a telefcope,
I could eafily find what degree of ihade was requifite to efface
ilars of different brightnefs ; and thu-s I obferved fome of the
ftars and planets*

2. Diaphragms were attempted ; but, befides other diffi-
culties, they did not efface ftars of the firfl magnitude.

3. A method which pleafed me much, and perhaps may not
prove unfuccefsful, is, by putting the ilars out of the focus of
ti telefcope till they become invifible ; this is performed by-
drawing the eye-tube of a refractor either in or out; the point
©f focal diftance being previoufly determined, the brighter tlie
itar the greater length of tube mufl be (lid either in or out to
efface it; thus I was in. hopes of determining their magni-

2-. tudes.

1^6 Mf.ViGoi:T''^Ohfcrvailons, &c.

tudes, and for that purpofe had in 1776 divifions engraved on
the eye- tube of a refractor; but faund that its high magnify-
ing powers prevented ftars of the firfl: and fecond magnitude
becoming invifible.

Laflly, I am inclined to think the following method practi-
cable, viz. to rcfle61: in a telefcope, by means of an illumina-
tor, different degrees of light in a known proportion, fo that
flars of all magnitudes may be obliterated.

The changeable flate of the weather will perhaps be thought
a confiderable obftacle to thefe contrivances, and to throw doubt
>Gn the obfervations ; but this may be fufficiently obviated by
attending to fmall tclefcopic ftars, which according to the
clearnefs of the atmolphere are more or lefs difl:in6tly feen«

I beg the favour of you, dear Sir, to prefent thefe obferva-
tions to the Royal Society ; and believe me, with the greateft
regard, &c.

York, Dec. 5, 178.1. EDWARD PIGOTT.

^^^*

[ ^11 ]

VI IT. Ajlronomical Obfervations* In two hellers from M.
Francis de Zach, Profeffbr of Mathcmalks^ and Member of
the Royal Academies of Sciences at Marfeilles, Dijon, and
Lyons, to Mr, Tiberius Cavallo, F. R, S,

Read December 23, 1784.

^ 1 R, Lyons, April 4, 1783.

1SEND you the account of the obfervations on the eclipfc
of the moon, which I have made together with the rev*
Father le Fevre, Aftronomer at Lyons, in the Obfervatory
called au grand College j to which I lliall add the obfervations of
the vernal equinox ; fome obfervations on Jupiter's fatellites,
made at Marfeilles by M. Saint Jacques de Svlvabelle ;
and, laflly, a new folution of a problem that occurs in com-
puting the orbits of comets. If you think that thefe obferva-
tions do in any way deferve the notice of the Royal Society, ][
fhall be very glad you would communicate them. In order to
afcertain the going of the pendulum clock, 1 took feveral cor-
refponding altitudes of the fun, which you will find in the fol-
lowing table* On the day of the ecliple the Iky was very
ferene, nothing could be finer, and it continued fo during the
obfervation. I determined to ufe an achromatic telefcope of
31 feet length, that fhews objedts in their natural pofition, be-
caufe the dihited and uncertain termination of the true fhadow
of the earth appears more perfectly defined by fmall than by
Vol. LXXV. T large

138 M. HE Zach's jyirotiomkal Obfervatkns.

large telefcopes, which magnify too much, and give too great a
tranfit between the penumbra and the true dark (hadow. On
that account fome celebrated aftronomers advife to ufe for the
echpfes of the moon no greater telefcopes than of four or five
feet length. It was remarked at Paris, that in an eclipfe of
tlie moon, obferved through a telefcope of DoLLOND,the focus
of its object lens being 30 inches, and likewife through a tele-
fcope of five feet length ; the eclipfe appeared to begin 4'' ^^
fooner, and to end 4^ 7^' later, through the fmall than
through the long telefcope ; the like has been remarked by
feveral others, and it has been alfo obferved by myfelf. As to
my obfervations I am tolerably fatisfied with them, as they do not
differ materially from thofe of Father le Fevre, though' it is
known that in eclipfes of the moon no greater exa61:nefs than
that of a minute can be obtained. The m^oon's fpots were
carefully obferved ; for it is known, that the mean of the ob-
fervations of the moon's fpots is fufficient to afcertain the
longitude of a place to 4^^ or 5'^ nearly. M. de la Lande
comparing the obfervations of the moon's fpots in an eclipfe,
made the 22d of November, 1760, in Vienna, by the Impe-
rial Aftronomer Abbe Hell, with thofe made at the fame
tim^e in Paris by M. Messier, finds the difference of meri-
dians to be 56^ 13^^, which agrees very exa(ftly with that afcer-
tain^d by other means.

Correfpondent

M. DE Zach*s JjiroHomical Obfervafions,

^39

'o

'■a

I

o

J-t 4-)

*i^

zi

rt

5_i

Oh

•n

Oh

rt

rt

p

O

o-

4->

rt

,i*l

o

13

'^

s

I-*

3

o

V— 1

*^

3

rt

•7J

4->

C

C

QJ

0-.

13

f/3

<u

r^

(U

4->

f-t

4-«

ct:

o

n«

rt

o

3

a

•T3

o

(

- CO

Ox

(>r

»H

vo

rt-

in

CJ

o»

'^

•-«

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■S c

-S 2

- O

vD

r^

oo

00

• O^

o .-

■^

w>

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>

-s oo

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o

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3 ^

CC 73

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•svO

O

sO

CO

1^

cs

J2 C

"^ W|

l-«

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t^

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o c

IVih
fervati

-.sO

*^

f^

oo

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A 00

en

CO

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^ o

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c«

c -n

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„ t>.

VI c«

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co

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w->

t~^

oo

oo

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en

CO

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T3 rt

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J3 oo

vn

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M

N

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)— (

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c»

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^ o

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*- 4-#

3 r::

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^ lO

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r^

oo

oo

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d

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j= oo

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t-«

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(S

u .

or

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^

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<^ c

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^ »n

fs

r^

00

00

r>

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cs

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^

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j= oo

^

CO

>^

w

O

►"

cs

t-^

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►" .

'^

c ti

.-• -t^

0**^

c// r«

° CJ

t — '^-^

,— A ,

f

^./X--^

, — ■ —

•

CO

CO
* —

re

s upper limb
; horizontal
caftern fide

m's upper limb at
the fame altitude,
weftern f.de

the fum by 2
nter on the

an as marked
clock

-a
o

flowtfr than
d folar time

ividing
m's ce

meridi
by the

<-•

«-«

2

lock
equate

H

•— •
40

ft C/D

W

U )

O

T 2

19th

I40

M. DE Zach's AJironomical Objervailons,

19th March, 1783.

SlHl's

Alcir.

ift obferva-
tion.

Sun's
Alt.

lid obler-
vation.

The fun's upper limb at the horizontal ->
wire of the firft telefcope on the eaftern >

fide ' ' :

Svin's upper limb at the fame altitude on 1
the weftera fide of the meridian - J

0 /
31 30

9 I 56

14 31 47

0
33

9 13 9

14 20 33.

Dividing the fum by 2

Sun's center on the meridian as marked by 1
the pendulum clock - • J
Equ itiou of the day

■

23 33 43

11 46 51I

12 7 57

23 33 42
II 46 51
«2 7 57

Clock flou'er than equated folar time

0 21 6

0 21 6

Clock flower than equated folar time 19th March 21 6
■ 1 8th March 19 32

Retarding of the clock upon 23 h. 58' 8" - i 34

I obferved too the mid-day at the great gnomon of the ob*
fervatory, and found at the fame time the meridian line erro-
iieous by 1 9'', as you will find in the following tables.

When the center of the fun's
image was on the meridian the
time pointed by the clock was

Equations of thofe days

}

the
17th
Mar.

11 50 50

12 8 33

17

Retarding on equated folar time
Retarding the 17 th

Retarding of the clock during thofe 2a. hours

^3

the
i8th

Mar.

11 48 56

12 8 15

the
19th
Mar.

the
i8th

19 19

17 43

I 36

11 47 a

12 7 57

19 19.

I 35,

] tixed therefore the retarding of the clock i' 2>S'^ •

True

M. DE Zach's j^Jir Gnomical Ohfervations.

J4I

True mid-day concluded by the fun's correfpon- 1
dent altitudes as the clock marked J

Equation of the mid-day

Retarding of the clock at the rate of i' 35" "1
per 24 hours - - J

True mid-day the peaduliim clock Ihould 1

have marked - - - J

Mid-day concluded at the gnomon of the 1

obfervatory . - - - J

Difference, the error of the meridian line
or gnomon . - _

the
18th

Mar.

II 48 42
- 18

+ 13

II 48 37
II 48 56

19

the
19th
Mar.

a

II 46 51
- 18
+ II

II 46 44

II 47 3

19

From thence I concluded,

Mid-day at true folar time 11 59 ^O
Mid-day the clock fliould "I ^

have marked on the 1 8th J ^ ^1

Retarding upon true folar
Jime

}

II 23

Mid-dayatequatedfolar time 12 8 15
Mid-day the clock ftiouldl „

have marked on the i8thj ^ ^'

Retarding upon equated 1
folar time - /

19 38-

Obfervation^

142

7W. DE Zach's AJlronomtcal bhfervations.

Obfervations of the moon's eclipfe the i8th March, 17S3.

My obfervations with an achrumaric telelcope of 3^

Time .-narked

True or

•ap.

feet length.

by the clock.

parent time.

IMMERSIONS.

Thebeginning of the eclipfc very doubtful.

h. . .

h. ,

It

shadow to\iches Grimaldi - ^ -

7 41 45

7 53

39

Grimaldi all in the fliadow

7 42 54

7 54

48

Shadow touches Maie Humorum

7 49 32

8 0 21

8 I
8 12

27
16

Copernicus all in the fliadow

8 2 29

8 14

24

Tycho touches the (hadow

8 6 18

8 18

13

8 12 19

8 24

15

8 13 43

8 25

39

Mare Serenitatis touches the fliadovv

8 lb 7

8 2b

3

8 21 31

8 ZZ

27

" luc uiaciuvv 111 me ruiuuie —

8 25 54

8 37

50

Proclus touches the fliadovv

8 32 21

8 44

18

Mare Crifium touches the fliadovv

8 33 29

8 45

26

8 35 36

8 47

33

8 36 56

8 48

53

Total immerlion . , ri.

8 3857

8 50 55

EMERSIONS.

Beginning of the emerfion

10 19 57

10 32

2

Grimaldi emeri{inor

10 23 ZZ

10 35

38

10 24 9

10 36

14

Mare Humorum emerging

10 29 34

10 41

39

I'otal emerfion of Mare Humorum

10 35 37

10 47

43

Copernicus all out of the fliadow

10 43 6

10 55

12

Mare Serenitatis all emerged

10 57 32

II 9

39

Mare Crifaun all emerged

II 15 44

II 27

51

End of the eclipfe

II 20 10

II 32

18

Total duration _ _ _

3 39

0

Fath

er

M, DE Zach*s AJlronomkd Ohjervatlons^

143

Father le FeVre's obfervations with a refle£lor 55 inches
focal length, magnifying 300 tinaes.

IMMERSIONS.

Grimaldi touches the Ihadow
Kepler touches the fliadow
all in the fliadow

Copernicus touches the fiiadow
all in the fliadow

Mare Serenitatis touches the fliadow

■ all in the fhadow

Mare Crifium touches the fliadow

all in the ftiadow

Total immerfion

E M E R S I O N S.
Beginning of the emerfion
Grimaldi emerged
Kepler all out of the fliadow
Copernicus all out
Mare Serenitatis all out
Crifium all out - -

End of the eclipfe
Total duration

Time by the
clock.

h.

7
7

41 43
52 2

7 53 24

8 o 22
8 2 26
8 16 7
8 26 2
8 z-?, 28

8 38 54

10 19 42

10 23 24

10 35 43

10 43 4

\o 57 19

11 ^5 50
II 20 22

Apparent

time.

h.

7
8

8

8

3

8

8

8

8

8

3

5

12

H
28

37

45
48

50

//

Zl

SI

19

17

21

3
58

25
SZ
52

10 31

47
10 35 29

10 47 49

io 55 10

11 9 26
II 27 57
II 32 30

3 39 20

The obfervation of the vernal equinox was made at tlie
gnomon. The height of thi« gnomon, taken from the center
of the hole by which the beams of the fun come in, is 1878
lines of a French inch ; the diftance from the bottom of the
gnomon to the equino£lial point is 1928 ; the dlftance from the
upper limb of the lun's image to the equlnodlial pol.'jt was
found 16,7 ; the diftance from the under Jimb 23,4 ; the dia-
meter of the hole = 6 ; therefore the diftance from the bottom
to the upper limb 1928-16,74-3=191 4,3 , to the under limb
1928 + 23,4 — 3=1948,4; which gives the time the equi^-
nox happened, the 20th of March, 5 h. 56' ^2!' P.M.

4 Obfervations

144 ^^' ^E Zach*s AJlronomJcal Ohfefvaiiom.

Obfervations of Jupiter's fatellites at Marfeilles*

ImmerCon of the Ift fatelHte at

Imm. Ift fat. - ■»

Imm. IVthJiat. was not total, but its I

ever difappearing ; the iky was ferene,

diftinftly.

Emerfion of the Ift fatellite

Em. lil fat. •

Em. lid fat, - - *

Em. Hid fat. . - ^

Em. lid fat. - *

Em. Ift fat.

Imm. Hid fat, * *

Em. Ift fat. - -

Em. Ift fat.

Em. lid fat,

Em. Hid fat. - -

Erti. Ift fat;

2 22 56 good
2 48 12 good
ight diminiflied fcnfibly without
and J-upiter had fix belts very

I 29 46

good

" 43 59

good

9 17 28

good

9 27 13

good

»i 51 59

good

10 I II

good

10 40 33

good

8 21 20

good

10 18 49

good

8 55 3'i

good

9 40 44

doubtful

8 6 48

good

H'

IT is k'nown^ that the indirect method to calculate the orbits
of comets in a conic fe(^ion, by means of three obfervations
given, is rendered more eafy and expeditious if there is a pofli-
bility of drawing a graphical figure thj^it reprefents nearly th^
orbit under conliideration, by means of which the calculation
is directed, and the requi;-ed elements of the comet's path may
be rigoroufly deterfnined* > To draw the orbit of a comet that
moves in a parabola or ellipfis^ the problem is reduced to find
the pofition of the axis and the perihelial diflance j this pofi-
tion of the axis will 'be' determined as foon as the angle is
known, that the axis forms with another line, whofe pofition
13 given ; this line may be an ordinate to a given point of the
curve, or a tangent, or a radius vedor, &c. The latter is to

y be

M. DE Zach's /^Jlronomical Obfervaiions, 14-^

be employed in preference, becaufe the perihellal diflance being
a conftant quantity, the angle of pofition then becomes the true
anomaly of the comet ; but as the data of this problem aie
only geocentric longitudes and latitudes of the comet, de-
duced from the immediate obfervations of right afcenhon and
declination, the heliocentric longitudes and latitudes mufl
firfl be calculated ; but as thofe data are not fiifficient, what is
not given mufl be arbitrarily fuppofed, 'viz. the fhortened dif-
t2incQ^(dlflantias curtatasyTKis fuppofition is changed and altered
until the calculation will agree with the three obfervations,
then the difference between two longitudes is the angle com-
prehended between the two fhortened diftances in the plane of the
ecliptic ; the whole reduced to the plane of the comet's orbit by
means of the heliocentric latitude, gives the difference between
the anomalies comprehended by two radius vectors, the problem
then is reduced : two radius vectors being given, with the angle
•comprehended, to find the two true anomalies, the perlhelial
diflance, and the time the comet puts in running its anomalies.
Let therefore T^^^ys reprcfent the ecliptic at an infinite dif-
tance ; QPR the apparent elliptical or parabolical path of a co-
met; S the fun's center; P the comet's perihelion ; T the place of
the earth when the comet was flrft obferved in C ; I the earth's
place when the comet was obferved in K ; ST = ^, SI = (?, the
dlflances from the earth to the fun at the firfl and fecond obfer-
vation known by aftronomical tables ; let Qm and K;z be two
perpendiculars to the plane of the ecliptic, it will be Sm=zUf
Sn = v the two fhortened diftances,

The obferved geocentric longitude of the comet in Tzzazzarc T Vj'G ;
the obferved geocentric longitude of the comet in I— azrarc TVfH;
the geocentric longitude of the fun by tables in Trz^~arc *Y*VS=s=A.;
the geocentric longitude of the fun by tables in I=^=:arc T ^^"B,

Vol. LXXV. U Now

14^ M. VE Zach's Jjtro?iG;nical Ohfervatlons.

. Islow fortlic hrfl: obfervation the-angle of elongatien \^b^n\.
for the nnglex^TG = arc AG =; T v^-^ A - T vjQ =: long, o - long*
cornet —d — a -^ -':

the angle ot tneaniuial parallax b/w i = — ^ — = e'}

the angle of commutation ;;?ST=r ^g^o - e -{- (^5 — a') =-f\

from whence the heliocentric longitude of the comet =3.

The fame at the fecond obfervartion in. L
Angle of elongation ~_/2 - ^ ;

Ancle CI anjiuai paraijaxe — — ;.-

Angle of commiiiation (^= , ^^-, — . £ + (/3 - a)- ;

t

heliocentric longitude of the comet in I = /3 - 180^ + $::= 9^;-.
putting novy the.beriocentrie latitude feen.from S'^^i;.
the geocentric latit-ude feen fro-m T = /;.;

Ill' • 1 • 1 'n 1 lin. r. tan?. / t

the heliocentric latitude w.nl.be - ' ■■ V ~ t^TJis;. k ;

-I. r -IT'- Ml 1 fi" <^ • tansr. ^ ^ 1 1-

the lame with \>^n it- will be ^ — ttt—^ =• tan8[. ;5 heliocentric

lip. (p ---■«_) ^

latitude in K'.

Having tfiiis oetermined th^ heliocentric latitudtes o^ twa
obfervations, the radius vectors will eafily be found in the fup»
pofiticn miade for the fhortened diflances, for they are in tha
famd'ratio to the i-adius ve6k)rs as th-e cofineof the heliocent
tric^ latitudes are to the radius = i ; therefore the radins ve6lo?

m of the firft obfervation will be =:—.-, and the radius vedor of
the fecond obfervation u = —r-- . .

'^ COi. X

Takinp- now the difference between the found' heliocentric
longitudes, we get the hejiocentric motion of the comet upon
tlie ecliptic betweeii two fhortened diflances,, which is to he
reduced upon the comet's orbit, tliis heliocentric niotiou is .
therefore y -^=.w. Now to reduce this motion we iiave, firfl:, .

fllUJS

M. DE Zaci^'s ^"yirofiomicjl Obfcr^jJlioni^' 14;;

'iinus totus =1 is to cofine m :: as cotangent /^ is to the tan-

.gent of an angle which I put = ?/, and ()o'^ - k '^^ n vviii

.give -an angle which I put = q. Laftly, the analog}'

cof. 71 : cof. q.y.fin.k'. will give the cofine of an angle ij/,

which is the" required motion upon the orbit, or the angle

'Conipreherided between the two radius veclors m and ^, Let

therefore ECPMND he the apparent parabolic path of a comet-;

S the fuK's center ; M and Ntwo places of the comet, the angle

INISN equal to its motion in longitude, ort'ie Comprehendeti

angle 4^; P the perihelion-; it is required to tind the two aiio*

malies ¥M, FN, that is, PSM and PSN, the perihelial dif-

tance SP, and the time the comet employed to come from its

.perihelion P to M andN. i

■n r ^ • - ' '

Keiolution>.

SM-m

NSB = .V

In the right-angled tri^ingleSMRand SNV\Ve hav€
MR = OS:=;;7fm. (4;:fi::.v) NV = QS = ^fin..r;
therefore OP^: |/) -m (fin. ij/ =t: x^ and PQ^
Ip^^tim. X ; but by the nature of the parabola
MSB= (i^^x)\ nvehaveSMrrAP-f POandSN=AP^-PQ;thatls
Parameter — /> | '/;/ ^ |/» — f't (fin. J^^t.v) ^u = -zp^^f^ fo. x

m + rn (fin-, i^rt -v) ~\p
/;/(!+ fin. ijy^tx) = {p

I and I 4- fin. (4'=fc'V)— -^—

iP

fATtzjx, im, X.

^ (l rp fill, x) =lf

2fn

1 =±: fin. X — ^; by

2> -

._i^

+ ■

_ P .

2>

reduc^

putting hito a fum i + fin. (t|^ — a) + irtrfin. x— ^ . ,
tion made 2 it fin. .v + fin-. (ij/dtA-) = /"'-^-^J/) ; but by trigono-
metrical fonnulae we have fm. (ij;=t:.v) = fin. ^ cof. A;=tfin. ^:
<:of. vj/. Subftituting this expreffion in its place we obtain^,

•2 =tfin. x+ fin.;!/ cof..v-j=fin. x cof.v!/ = (^^) p- By the fame

femulsci'we have cof." iv= i -fin.* ;t and cof. x~\/ 1 — fin.^^P

U 2 Sub'-

148

M. DE Zach's ^yii onomkal Obfervations,

13

0}

-t

i.

C

+

CO

s

•5

<;S

li

o
o

S3
»3

^1

J

c
• — «

o

O

\

+

3
o

a

o
o

bO

If

St

*

If

t

a.
4-

o

G

-f^

o "z

o

faX3 »<
a. C ji

+ !+

S

s

+
+

1+

•^ o

a.
+

1+
ii c

►=)-

i
5

3

o
IK

L§ if '^

5L

+

a.

o

I

-^

«■

O
u

H

««

*.

O

a

a.

^ *5

;-<
a

*^ C 5«

1

o

5<

) -

a

<u

r3
>

H
IT

^43

2 +.

+

o
u

a.

%

V5

O

o

a.

5

V
a.

5

* +

it

a.

s<

t^ . r-l

+ biD

•3" • ■-«

^ 2

o .tj

^ '^

II a

^ II

c
a.

CO

il

a

A.
+

3-

SO

11

c
a.

CO

a.

00

a
«s

1

•

c
va

•(
a.

1+

C

a.
5

CI

I

a.

S

II

a.

M.

00

■fl

i
II

c
a.

-^

II
a,
g

t4

1

•

0

c:

>-,

'J

<^

c:

S

«

1

■k>

s

1

»4

• t^

+

0

0

• —*

0

oj

u

c

^

ti:

0

•

S

•

c

+

<D

0

+

-^

J3

(U

v;

4>4

^a

§.

0

u

Vm
0

a

1— 1

Um

a

G

II

5*

0

4-1

C

s

0

c»

w

il

f

o.

Ci.

a

O
o

H

C

"a

II

o

U

g
I

o

•- n

a.
E

+ If

ID

««• O

B ^

2:> -G

s *-

2 bC

a
+
a
+

c

a.
5

= ^41

"^ Oh

bX)n3

£ S

G C

II 8

-^^

a <"

-. O

a
B

+
a

M

+

H
II

S^

M. t>t 'Zacm^s Jfronomical Dbferiiations,

x#

'x'5"o ^^' DE Zach's /ijlronomical Qhfervaiions^*

The angle x defines therefore the pofltlon of the axis and
the t\v6 anomalies required, the perihelial diftance being
ptB-z^i^x 2y. (in. .V, -it will be known alfo hy the angle x.

In order to find the time the comet employs in running its
anomalies, let the perihelial diftance jufl: now inveftigated^ be
equal to the radius of the earth's orbit, the parabolic area
fvvept hy the radius vector will be by the nature of the para-

bolatPOxOM + iSOxOM^iS^-^i^^t-^^^^-^^. Now

the ,per;phe.ry of the earth's orbit is j : zz v. 2p \~ p i

7

A A 0 2

therefore the whole rtrea -p. l/>— — p\ It is known that the
velocity of a heavenly body moved in a circular path, is to
the velocity in a parabolic path in the ratio s/i : i . If the pa-
rabolic area of the comet is divided by v/a it comes out

-^ -£3 —equal t-o an area that the earth'delcribes iii

6V/2 ^

the very fame time--; put therefore A equad to the time of a
lidereal year, we (hall recover the atialogy ; the whale area of
the earth's orbit is to the time in which it is defcribed as the
parabolic area h to the time confumed hi fweeping it ; therefore
^ P^ . A:-- (4PQ + 3SQ) ^IQ . 7A(4?Q + 3SO)MO.. ^^^ ^^^ _ '
T ^ ' '" 6v^2 '• ' 72/V2

SM . fm. anom. PSM and OS = SM . cof. anom. PSM ; let
the anomaly be=r^, we have OMrrw fin. (5*, and OS=zm cof. S;
therefore PO ~ p — m cof. I. Subllituting we obtain

7 A (4/)— 4w cof. ^-f 3w cof. i") m fin. ^ .... 7 A (4^ — m cof. a) m fin.
•]2p^^2 72/)^v^2

whereby the time is found in parts of a fidereal year.

1..^

I am, &C.

SIR,

M, DE Z.Aeifs AfronomkfJ, Ohfervrfilom, - 15^.

S' I R, ' Lyons-, May 4, 1783.

LATELY I received' f-rom-.the" Obfervfltory nt MarfejUes the
©blervatlon of the trnnfit of Mercury, which happened the 12th
Nov. I ; 82. The llcy not beings very favourable, only the two in-
ternal contadl's w^ere obierve'd';. the firft internal contail was ob-
ferved' byM. St. Jav-ques df. Sylvabellf.,' at 3 h. 18 '30^"''
apparent time j. the, lad internal conta6t by M. St. Jacques, at
4h.' 30^ \(^" \ by M. Bernard, his Adjunclus, at4h. 29^ 13^'.
The'nea'refl- diftances of Mercury's limb, to that of the fun- iiv
tHe f>Dr.tlieni parrdf its diik were at:

'if.

3-33^4

3 42 57 I 34 J> parts of the micrometer,

4 22 iy\ 19

The apparent dJa meter of the flrn was 2174 parts of this m:^
crometer : L fuppofe the- before-mentioned 2174 parts— 32^
'26^^,9-. T conclude farther- by the ebfervatibhs, the middle of
the'tranfit at 3h. 54' y\2^^; whe-peas I fix, by interpolation,
i:he diftances of the limbs at 3 h. 54^ 7''>25 = 35^^,6 i I have
therefore feml-diameXer of the fun — 16' 13^^,4-35-^,6 =
1 5^ 3-7'^8 -K^emi-diameter of Mercury — 6'^ = 15^ 43'^8 — totlie
leaft diftanoe of centers of the iun aiid Mercury. By M. de
LA Lande's tables it is 15^ 42'', only a difference of L^S.

M. Waulqt at. Earis has obferved this tranHt at the Royal'
Obfervatory,,

Firft external cmitaiSi* 2 56 28

Firft internal contact 3. 2. 3.

Second - - 4 i 7 i 8

Second external - 4 22 53
5. Vcml^-

;<j'^ M. DE Zach's JJlronomkal Obfervatlons,

I only add an important remark upon the diameter of Mer-
,'Cury, which the aftronomers fuppofed in this traafit=: 12'^.

Let ABC reprefent the fun's difk ; in P an external in Q^an
internal conta<£t ; ANC the apparent path of Mercury over tlic
fun.

The femi-diameter of the fun = 972^', this of Mercury in our
fuppofition = 6'% MN = 942'^ the leaft dlftances of the centers.
In the right-angled triangle MNP it is MP :=: 972'' + 6''rz 978'%
MQ=:972''-6''=966''; therefore NP will be foundr;26o'^
and NCi= 2 1 o"' : now NP — NQr: PQ^=: $0^', which converted
into time gives V i\" for the time the diameter of Mercury em-
ployed to run over the limb of the fun ; but by the obfervations
of M, Wallot I find this time conftantly in both contads
5' 35^^; therefore V 14'' : ii." :: 5' '3,^" : 8^137, whicU
(hould be the diameter of Mercury ; and indeed M. Wallot^
by an immediate meafure, taken with an excellent wire-micro-
meter, finds this apparent diameter not greater than 9"^ which
fufficiently (hews that this diameter fuppofed f wy the meg?^
diftance is alfo too great.

lam, &c..

/'////■..r./>.//,,i /;//..v.v;rnii>\'i./t

/""/r //.f

[ J 53 ]

^IX. Obfervatwns of a tie^v Variable Star, By John Goodrickb,
Efq. ; communicated by Sir II. C. Eoglehcld, Bart. F. R. Sc
^nJ A. S.

Rend January 2^, lyS^.

TO SIR H. C. ENGLEFIELD, BART.

DEAR SIR, York, Jan. lo, 1785,

if" B iHE account that lias been lately given of the regular
A varialion of AlgoFs light, and the notice aftronomers
have been pleafed'to take of it, are well known. It is natural
•tlierefore to fuppofe, that the relation of other fimilar phseno-
mena may alfo meet with the fame favourable reception. Of
this kind is the following, which! beg the favour of yon to
prefent to the Royal Society.

On the I oth of September, 1784, whilfl: my attention was
directed towards that part of the heavens where jG Lyrse was
iituated, I was furprifed to find this flar much lefs bright than
ufual, whereupon I fufpedled that it might be a variable ftar :
my fufpicions were afterwards confirmed by a feries of obfer-
vations, which have been regularly continued fince that time,
^nd which will pi'efently follow in their proper place. At firft
1 thought the light of this ftar fubjed to a periodical variation
t)f nearly yf.v days and nine hours^ though the degree of its di-
minution did not then appear to be conftant ; but now, upon a
more clofe examination of the obfervations themftives, I am

Vol. LXXV. X inclinea

I c4 Mr. Goodricke's Obfervations

inclined to think, that the extent of its variation is Hvelve days
and nineteen hours^ during which time it undergoes the fol-
lowing changes.

1. It is of the third magnitude for ahout two days.

2. It diminifhes in about one day and a quarter.

3. It is between the fifth and fourth magnitude for lefs thau
a day.

4. It increafes in about two days.

5. Itr is of the third magnitude for about three, days.

6. It dinnniflies in about one day.

7. It 's fomething larger than a ftar of the fourth magnitude
for little lefs than a day.

8. It increafes in about one day and three quarters to the firft
point, and fo completes a whole period.

Thefe eight points of the variation are perhaps Inaccurately
afcertained ; and indeed it cannot be expeded to be otherwife in
efiiimations of this nature, where it is very poffible to err even
feveral hours.

The relative brightnefs of /G Lyras, at its obfcuration in the
third and feventh points, is nearly as follows. When in that of
the third point, it is lefs than f and x, and nearly equal to
^ Lyras ; and when in that of the feventh point, it is rather
lefs than £ and ^ Herculis, and much brighter than f, y,^ and
I Lyras. At its greatefl brightnefs in the firft and fifth points,
it is fometimes brighter than y Lyras, but lefs than /G Cygni,
and fometimes only nearly equal to it ; but in thofe points it
feems to alter in its brightnefs feveral times in the fame night,
and that generally In a pretty confiderable degree. However,
this may perhaps be only owing to fome fallacy of obfervation ;
for I have often perceived, that the relative brightnefs of ftars
is affedled not only by the different flates of the air, but alfo by

their

of a new Variable Star» 15^

-their change of pofition occaiioned by the earth's diurnal
motion, and that particularly In ftars of a great altitude.

The magnitudes of the liars, to which /3 Lyrse was com-
pared during the progrefs of its variation, are as follows.
P Cygni and y LyriE of the third magnitude ; f and 5 Herculis
of between the fourth and third magnitude ; 0 Herculis is
fomething lefs than a ftar of the fourth magnitude; f, ;«, and
^ Lyr« are ftars of between the fourth and fifth magnitude, if
not nearer the fifth. The relative brightnefs of thefe ftars.
follows the order in which they are fet down.

OhfervaUons of the bright nefi aiid magnitude of jG Lyn*.

1784, Sept. 10. At 1 1 h. =^, much lefs than y Lyr:E ;
nearly equal to, if not rather brighter than ^, x, and ^ Lyrys,
and not fo bright as |, Q, and 0 Herculis ; between the fourth
and fifth magnitude.

Sept. II. At 8| h. nearly the fame as it was lafi: night, if
not brighter ; indifferent obfervation.

Sept. 12. At 8| h. and ph. between the third and fourth
magnitude ; lefs than y Lyras, brighter than Q, |, and 0 Her-
culis, and much brighter than f, x, and 2 Lyras. Mr. E.
Pi GOT T agrees with me nearly.

Sept. 13, 15, 18, 19, and 20. It was at or near its greateft
brightnefs,

Sept. 23. At 7 1 h. It was nearly equal to ^, x, and I Lyrae,
and much lefs than f, ^, and 0 Herculis.

At io| h. the air being extremely clear, I compared it more
attentively to the neighbouring ftars, and found it as follows :
rather a little brighter than ^, a little lefs than ^, and rather

X 2 lefs

2jK-&. Mr. Goodricke's Ohfervations

kis than k Lyi-a?. Mr. E. Pigott thought it had rather m».-
creafed from 8| to ii h.

Sept. 24. At 13! h. certaiiilv brighter than it wa<5 laft night,,
but intervening clouds prechaded rdl further obfervation.

Sept. 28. At I oh. not quite fo bright as y Lyrae, but rather-
brighter than 6, and J Heraulis. Mt, E. Pigott thought it;
nearly equal to y Lyras.

Sept. 29. At 7i h. not fo bright as 7 Lyrae; ,
At 84 h. to io| h. nearly equal to land; Q Plerculis ;^ but. if.
any thing it feemed rather lefs: than £,. and.rathej brighter thani
^; about the fourth magnitude.

At 1 1 ^ h. to 121 h. the fame, if not lefs ; I could not compare
it well to f aad^, beeaufe they were low ; ■ mcon-light, but- the
air was clear.

Sept; 30. At 7 h. rather lefs than G^ if not equal to It r a*
little lefs than J,, and brighter than d? Herculis ; about the-
fourth magnitude.

At II h. and i2|h. it feemed to be on its increafci being-'
for the moft part-larger than f and Q Herculis.

061. 1 and 2. About its greatefl: brigh'tnefs, but lefs than -
y Lyrie. Mr. E. Pigott' thought it brighter on the 2d
than on the ifl:, being on the 2d nearly equal to 7 Lyras.

Odi, 4. At \ol h. I thought it rather lefs, but the weather •
was hazv.

061:. 5. At 6| h. not fo bright as f and ^ HercuKs ; a little
brighter than (^, and brighter than ^ and x: Lyr^e; air clear.

At 9I hi n-eariy> equal to ^, and a little brighter than ^ and k,
Lyra^.

At i2-}h. a little lefs than ^, nearly equal to «;, and rather a
little brighter than 0 Lyra?-; between the foui-th and fifth mag- • ^
akude ; air very clear,

5. oa. „

of a 7iew Varlahk Star, j^y

Od:. 6. At 6| h. and 7$ h. lefs than f and k, and a little lefs
than d Lyrae ; between the fifth and fourth magnitude.

Oct. y. At 6^- h. between the fourth and third magnitude ^-
a little brighter than ^, and neai-lj equal to J Plerculis ;. much
brighter than ^,. «,. and 5 Lyr^ ;: I obferved It till t2.| h. when
it was certainly increafed..

At 7i.h. Mr. E^l^iGOTT. thought k brighter than J aiid 0
Herculis.

06^i 8;. At 8 h. nearly equal to y Lyrie ; on account of the
intervening clouds, I could not perceive which \vas largefl: ;..
third magnitude. .

Ocl, 9. At 7 h, rather lefs than y L.yrj£;

OS:. 10, At. 7 h. Ill h. and izh. nearly equal to y, i£.
not rather lefs.

0(£l. u.. At 8vh. loh. andiizh, rather lefs than y; . at
I2h. if any difference, lefs than it was laft night.

Otfl. 1-5^ At 8di.=t nearly- equal to^ though rather lefs
than, yLyrse.

O<0: 16. At 6| ,h. and pl.h. little lefs than 7, if not equal;.
to it.

At 1 1 h. rather larger than y, . but the v.'eather was fog.2:y,^
Mr. E. PiGOTT agrees with me in both obfervations.

O61:. 17. At 6| h. and 7 h. fomewhat lefs than y Lyra?,

0£li 1 8a At.6| h. between the fourth and fifth magnitude;:,
brighter than x. and ^, and rather brighter than .f Lyrae ; good,
obfervation.

At 9f h. I thought it was decreafed, being, equal to.^ and'.
rather brighter than y. Lyne. Mr. E. Pi got t alfo thought it-

was decreafinp;.

Od. 19. At 6|-h. it was rather lefs than .^ and »:, ami
brighter than ^ Lyr^-

Atx

158 Air. Goodricke's Ohfercat'wns

At 8| h. nearly the fame, If not increafed,

Oifl. 20. At 6| h, rather brighter than J and ^ Flercuiis^
and between the fourth and third magnitude.

At 8| h. and 1 1 h. I thought it was increafed, but it was
lefs than y LyriE ; between the third and fourth magnitude.

0£l. 22. At 6 h. 8 h. and 9 h. nearly equal to y Lyra^.

061. 23. At 6 h. 8 h. and 1 1 h. rather lefs than y, though
nearly equal to it.

Ocl. 24. At 6| h. and 1 1 h. lefs than y LyriE, and brighter
than J and (9 Herculis ; at 8 h. Mr. E. Pigott thought it
rather lefs than y Lyrae.

06r. 25. At 6 h. 8 h. and 1 1 h. nearly, though perhaps not
quite equal to 5 Herculis ; lefs than J Herculis, and brighter
than f and ^ Lyras; about the fourth magnitude. At 6i h»
Mr. E. Pigott thought it rather brighter than 5 and 0
Herculis.

Od. 26. At 6 h. and 1 1 h. brighter than 5 and | Herculis,
but lefs than y LyriE.

0£l. 27. At 6h. and 8| h. brighter than it was lafl: night,
but ftill lefs than y Lyras ; much brighter than | and ^ Her-
culis ; the moon was at its full.

0(£l. 28. At 8 h. dt rather lefs than y Lyrae.

Ocl. 29. At 9I h. nearly equal to, though rather brighter
than y Lyrae ; I faw them but for a Ihort time on account of
clouds coming on.

061. 31. At 8 h. between the fifth and fourth magnitude;
lefs than f and x, and brighter than I Lyrie. Mr. E. Pigott
thought it equal to f Lyrae at 85 h.

Nov. I. At 6| h. between the fourth and fifth magnitude;
rather brighter than ^, and brighter than -a and I Lyra;.

Nov. 3. At 5I h. little lefs than y Lyne.

Nov.

of a new Variable Star. i ^g

Nov. 6. At 8 h. rather lefs than y Lyrai^ and brighter
than d Herculis. Mr. E. Pigott thought it nearly equal to ^
Ly vse,

Nov. 7. At 7 h. and io| h. much lefs than y Lyra^ ;
nearly equal to, if not rather brighter than, d Herculis, and
rather lefs than | Herculis ; between the fourth and third magr
nitude.

Nov. 10. At io| h. nearly equal to y Lyri£. Mr. E.
PiGOTT thought it not quite fo blight as y at 1 1 h.

Nov. 11. At 5I h. and 7 h. a litule brighter than y Lyr;£ ;
afterwards I ratlier thought them equal, though 13 appeared
for the mod: part fomething brighter. At 1 1 h. and 12 h. they
appeared nearly equal. At 7 h. Mr. E. Pigott thought it was
lefs than y, if there was any difference.

Nov. 12. At 6| h. 8i h. and 10 h. much lefs than yhyrx^
but brighter than J and 9 Herculis ; between the fourth and
third magnitude.

Nov. 13. At 6| h. and 10 h. equal to, if not rather lefs
than J*, lefs than k, and brighter than ^ Lyrs ; between the
fifth and fourth magnitude. At 5I h. Mr. E. Pigott thought
it rather brighter than f Lyrae.

Nov. 16. At 7 1 h. little lefs thait y. At loh. certainly a
little brighter than it.

Nov. 17. At 6 h. rather brighter than y. At 84 h. 9I h.
and loi h. brighter than y, and lefs than (3 Cygni.

Nov. 18. At 9 h. 10 h. and 19 h. juft the fame.

Nov. 19. At 6f h. and 8 h. lefs than y Lyras, and brighter
than 9 and | Herculis ; between the third and fourth magnitude.
At 10 h. fomething brighter than d Herculis.

Nov. 20. At 7 h. 8 h. and io| h. rather lefs than |, and
rather brighter than & Herculis ; between the fourth and third

y ' magnitude.

i6o :Zt/>". Goodricke's Obfervations

magnitude. At i8| h. 1 thought it was increafed ; obferved iri

twilight.

Nov. 21. At 7 h. fomething blighter than 5 and J Hercuhs.

Nov. 2^. At 7 h. lefs than y Lyra?, and brigliter than 9
Tlerculis; between the fourth and third magnitude. At 9$h.
I thought it was decreafed, being now of the fourth mag-
nitude.

Nov. 26. At 9-h. rt: much lefs than y, and of between the
fourth and fifth magnitude ; but the w^eather was too hazy,
and the moon-light too ilrong, to obferve well.

Nov. 29.. At 7I h. and 8 h. rather brighter than y -Lyrae.
Mr* Edw. PiGOTT thought it nearly equal to y at 8 h.

Nov. 2,0- At 8 1 h. and io| h. brighter than y Lyra?, and
lefs than /3 Cygni ; air clear.

Dec. 4. At 5I h. 6t h. and lof h. lefs than y Lyrae, and
brighter than 6 Herculis ; between the third and fourth mag-
nitude. Mr. -E. PiGOTT thought it nearly equal to 7 at 6i h.

Dec. 9. At 8 h. much lefs than y Lyrae, and brighter
than ^ Lyras; about between the fourth and fifth magnitude.
At i8i h. it was increafed, and nearly equal to d? Herculis ; but
lefs than 5 and J ; not quite of the fourth magnitude.

Dec. II. At 6 h. and 8 h. lefs than 7 Lyr^e, and brighter
^than Q and f Herculis. At 8| h. 9!- h. and iSf h. nearly
equal to, though rather lefs than 7.

Dec. 12. At 5 h. and 6 h. nearly equal to y, though rather
lefs.

Dec. 13. At 5§ h. and 9I h. fomething brighter than y,

Dec. 14. At 7 h. and 8i h. rather brighter than y.

Dec. 17. At 5I h. lefs than y Lyrie, and brighter than
9 and J Herculis. At 7I h. nearly equal to 7, though rather
ikfs.

Dec*

of a new Variable Star, i6i

Dec. 19. At 9 h. I believe it was brighter than y, but the
weather was not very favourable.

At 19 h. little lefs than y.

Dec. 20. At 5|h. lefs than 7 I.yrs^, and brighter than
9 and P Herculls. At 6f h. nearly equal, thou?-h rather lefs
than y Lyric.

Dec. 21. At 8 h. much lefs than y, and confiderably
brighter than ^Lyras; not quite of tJic fourth magnitude.

At i8h. a little brighter than f and z, and brighter than 0
Lyras; between the fourth and fifth magnitude.

Dec. 28. At 6h. lefs than 7/ and brighter than 0 Herculls ;
between the third and fourth magnitude. At 8 h. nearly equai
to 9 Herculls ; between the fourth and third magnitude.

1785, Jan. 5. At 5^h. about equal to 0 Herculls; fourrh.
magnltudeo

Jan. 6. At 5 1 h. between y Lyrae and d Herculls, but rather
Bearer y. At 8| h. it feemed a little brighter than y.

From the above ferles of obfervations I have deduced all t'no
•conclufions relative to the eight points of the variation, as they
are ftated in the 'beginning of this paper. However, as at firfl ft
may not clearly appear, that the (hir has a more connderable
diminution in the third point than in the feventh, it will not
be improper to add a few words relating to that circumfrance :
for proof of it, therefore, I refer to an attentive compariion of
the obfervations of Sept.. 10. Sept. 23. 0£l. 5 and 6. 0£l',
18 and 19. &c. correfponding to the third point of the varia-
tion with thofe of Sept, 29 and 30. 0£l. 25, Nov. 7 and
19, &c. correfponding to the feventh point of -the varia-
tion. It may be objected, that in fome of the obfervations of
the feventh point, the ilar might have become ftili more di-
•mlnlfhed in the intermediate hours; but tiiis is, not probable.

Vol. LXXV. Y becaufe

1 62 Mr. GooDRicKE*s Obfervatiotis

becaufe in that point the ftar has been obferved of about the
fourth magnitude at intervals much fliorter than in the third
point, lb that, if it had continued to diminiih, its diminution
would have proceeded at a more rapid rate, which ftill {hews
that there is at leaft a difference between thefe two points.

With regard to the period of the variation, it is evident
from a collation of the preceding obfervations in a coarfe way,-
that it is nearly twelve days and three quarters. To determine it
with greater accuracy is a fubje<5l of confiderable difficulty, in
the prefent cafe ; for unlefs we can obtain very exacfl points of
comparlfon, the period would come out erroneous, efpecially
if deduced from intervals coniifting of only a very few periods,
as is the cafe here. However, as I have been able to obtain a
few obfervations of the middle of its obfcuration in the third
point accurate enough for our purpofe, I have formed the fol-
lowing calculation.

Times of the middle of its obfcuration
in the third point.

1784, Ocl. 6
— 18

oa. 18

— 3^
oa. 6

Hence the period on a mean is 1 2 1 9 r±=
In afcertaining the above times, I attended particularly to
the neareft obfervations both preceding and following. In the
manner above ftated the period may alfo lie deduced from the
middle of its obfcuration in the feventh point; but as thefe
obfervations are not fo exadt as the above, I fhall only, as a

further

h.

d.

h.

22;

only a fingle period of

12

21

221

D°

—

13

17

.;!

two periods,

each of

12

19

of a new Variable S/af\ i6a

further confirmation, compare two of the mofl: di^ant of
therrij viz, Sept. 29. 22 h. and Nov. 20. 6 h. which interval i
find contains fix periods, each of 12 d. 20 h. =i=:

I have it in my intention to purfiie the fubje6t further, and
when I have got a fufficient number of obfervations, it will
be eafy to determine the period with greater exadlnefs, and
alfo at the fame time to afcertain the other particulars of the
variation with more precifion. In the mean while I wifli that
this account may be confidered as being yet imperfe<£l ; but I
was induced to fend it -in its prefent ftate, in hopes that other
aflronomers may contribute by their obfervations to the eluci-^
Nation of this phiEnomenon.

As /3 Lyr^ is a quadruple ftar, N^ ^. of Mr. Herschel*s
Vth Clafs of Double Stars *, 1 was deiirous to fee if any of
the fmall ftars near it would be affe£led by its different changes ;
but they feemed not to fuffer any alteration, either when it
was at its greateft or at its leaft brightncfs. I attended to this
the more particularly becaufe the lots of the ftar's light was
very confiderable, and thephaenomenon feemed to be occafionefd
by a rotation on the ftar's axis, under a fuppodtion that ther&
are feveral large dark fpots upon its body, and that its axis is
inclined to the earth's orbit.

I muft not omit mentioning here that Mr. Herschel,
amongft thofe ftars which he fuppofes to have undergone an
alteration, reckons (3 or y Lyras ; becaufe he obferved that y was
much larger than (3, while Flamsteed marks both of the
fame magnitude -f*. It may alfo be added, as fhewing that /j
Lyrae varied in former times, that Hevelius, in his Catalogue,
differs from Flamsteed, and marks y^Q^ ^he third rnagnltucie,

* Phil. Tranf. for 1 782, p. 14?.
t Phil. Tranf. for 1783, p. 256.

Y % ■ aiid

1 64 Mr, Goodricke's Obfervations of a new Variable Star,

and iS of between the fourth and third. I have, however,
fome doubts whether the variation of this ftar does not entirely
ceafe or become lefs vifible in certain years. Thefe doubts arife
from fome obfervations of Cassini in Phil. Tranf. N° j^,
p. 2198. where I find that in obferving the new ftar, which
then appeared near the beak of the Swan, he compared it very
frequently for upwards of a month to /3 and y Lyrae, yet
without perceiving, or even fufpe6ling, that /3 was variable,,
though it was eafy for him to have perceived it, if th^ varia-^
tioa had then been even lefs than it is now.

lam, &c.

JOHN GOODRICKE*

[ »^5 ]

X. On the Motion of Bodies affedied by FnSlion. By the Rev,
Samuel Vince, A. M. of Cambridge ; CGinmunicated by
Anthony Shepherd, T). D. F» R. S. Plumian Profejfor cf
Afironomy and experimental Philofophy at Cambridge.

Read November 25, i78'4».

THE fubjed of the paper which I have now the honour
of prefenting to the Royal Society, feems to be of a
very conliderable importance both to the practical mechanic
and to the fpeculative philofopher ;. to the former, as a know-
ledge of the laws and quantity of the fri6tion of bodies in motion
upon each other will enable him at firft to render his machines
more perfect, and fave him in a great meafure the trouble of
correcting them by trials; and to the latter, as thofe laws
will fnrnifh him with principles for his theory, which when
eftablidied by experiments will render his conclufions appli-
cable to the real motion of bodies upon each other. But, how-
ever important a part of mechanics this fubjeCl may conftitute,
and however, from its obvious ufes,- it might have been ex-
pelled to have claimed a very conliderable attention both from
the mechanic and philofopher, yet it has, of ail the other parts
of this branch of natural philofophy, been the moft neglected.
The law by which the motions of bodies are retarded by fric-
tion has never, that I know of, been truly eftablifhed.
MusscHENBROEK fays, that in fmall velocities the friftion varies
very nearly as the velocity, but that in great velocities the fridioii
increafes ; he has alfo attempted to prove, that by increafing
2 the

1 66 Mr, VmcE on the Motion of

the weight of a body the fridioii does not always increafe exadl
in the fame ratio ; and that the fame body, if by changing its
pofition you change the magnitude of the furface on which it
moves, will have its quantity of fri6lion alfo changed. Hel-
SHAM and Ferguson, from the fame kind of experiments,
hav€ endeavoured to prove, that the friction does not vary by
changing the quantity of furface on which the body moves ;
and the latter of thefe afferts, that the fridlon increafes very
nearly as the velocity ; and that by inCrealing the weight,
the fritflion is increafed In they^;;?^' ratio. Thefe different con-
clufions induced me to repeat their experiments, in order to fee
how far they were concluiive in refpe^l: to the principles de-
duced from them : when it appeared, that there was another
caufe operating belides fri6lion, which they had not attended
to, and which rendered all their deductions totally inconclufive.
Of thofe who have written on the theory, no one has efta-
blifhed it altogether on true principles: Euler (whofe theory
is extremely elegant, and which, as he has fo fully confxdered
the fubje£l, would have precluded the neceHity of offering any
thing further,, had its principles been founded o\\ experiments)
fuppofes the fridion to vary in proportion to the velocity of the
body, and its preffure upon the plane, neither of which are
true : and others, who have imagined that friction is a uni-^
formly retarding force (and which conjecture will be confirmed
by our experiments), have ftill retained the other fuppofition,
and therefore rendered their folutions not at all applicable to
the cafes for which they were intended. I therefore endea-
voured by a fet of experiments to determine,

ift, Whether fridiion be a uniformly retarding force,

2dly, 'The quantity of fridiion, ^"^ ^' "^^

Bo^iei affeSied by FriSiion. 1 6*r

^dly, IV h ether the fridiion varies in proportion to the prejfure
ar izj eight.

4thly, Whether the friclion be the fame on 'whichever of its fur-
faces a body moves, , , ■

The experiments, in which 1 was alliited by my mgenious
friend the Rev. Mr. Jones, Fellow of Trinity College, were made
with the utmoft care and attention, and the feveral refults
agreed fovery exa6bly with each other, that I do not fcruple to
pronounce them to be concluiive.

. .SCI.;

2. A plane was adjufted parallel to the horizon^ at the extre-
mity of which w^as placed a pulley, which could be elevated or
dep relied in order to render the firing which connected the
body and the moving force parallel to the plane. . A fcale accu-
rately divided was placed by the fide of the pulley perpendi-
cular to the horizon, by the fide of which the moving force
defcendedi upon the fcale was placed a moveable ftage, which
could be adjufted to the fpace through which the moving force
defcended in any given time, which time was meafured by a
well regulated pendulum clock vibrating feconds. Every thing
being thus prepared, the following experiments were made to
afcertain the law of friction. But let me firfl obferve, that if
fridion be a uniform force, the difference between it and the
given force of the moving power mufl be alfo uniform, and
therefore the moving body mufl defcend with a uniformly ac-
celerated velocity, and confequently the fpaces defcribed from
the beginning of the motion mufl be as the fquares of the
times, jufl as when there was no fridion, only they will be
diminifhed on account of the fridllon.

3. Exp. I. A body was placed upon the horizontal plane,
and a moving force applied, which from repeated trials was found
to defcend 52I inches in 4'^ for by the beat of the clock and

7 ^^^

i6S Mr. ViNCE on the Motion of

the found of the moving force when it arrived at theflage, the
fpace could be very accurately adjufted to the time ; the ftage
was then removed to that point to which the moving force
would defcend in 3'^, upon uppofition that the fpaces defcribed
bythe moving power were as the fquares of the times ; and the
fpace was found to agree very accurately with the time ; the
ilage was then removed to that point to which the moving
force ought to defcend in 2''', upon the fame fuppofition, and
the defcent was found to agree exaclly with the time ; laflly,
the ft age was adjufted to that point to which the moving force
ought to delcend in i^\ upon the fame fuppofition, and the
fpace was obferved to agree with the time. Now, in order to
find whether a difference' in the time of defcent could be ob-
ferved, by removing the ftage a little above and below the pofl-
tions which correfponded to the above times, the experiment
was tried., and the delcent was always found too fbon in the
'former, and too late in the latter cafe ; by which I was aflured
that the fpaces firft m.entioned correfponded exadtly to the
times. And, for the greater certainty, each defcent was repeated
eight or ten times ; and every caution ufed in this experiment
was alfo made ufe of in all the following.

Exp. 2. A fecond body was laid upon the horizontal plane,
and a moving force applied which defcended 41 1 inches in 3^^;
the ftage was then adjufted to the fpace correfponding to 2'^,
■upon fuppoiition that the fpaces defcended through were as the
fquares of the times, and it was found to agree accurately with
the time ; the ftage was then adjufted to the fpace correfpond-
ing to i^\ upon the fame fuppofition, and it was found to agree
•with the tim.e.

Exp. 3. A third body was laid upon the horizontal plane, and
amoving force applied, which defcended 59I inches in 4'^ ; the

ftage

'Bodies nJfccieJ by Fyidtion, 169

^age was then ndjufted to the fpace correfpondlng to 3'^ upon
iuppofitioii that the fpaces defcended through were as the
fquares of the times, and it was found to agree with the time ;
the ftage was then adjufted to the fpace correfponding to 2'\
upon the fame fuppofition, and it was found to agree with the
time ; the ftage was then adjufted to the fpace correfponding
to i'\ and was found to agree with the time. .

Exp. 4. A fourth body was then taken and laid upon the
horizontal plane, and a moving force applied, which defcended
"55 inches in 4'^ ; the ftage was then adjufted to the fpace
through which it ought to defcend in 3'% upon fuppofition
that the fpaces defcended through were as the fquares of the
times, and it was found to agree with the time ; the ftage was
then adjufted to the fpace correfponding to z"^ upon the fame
fuppofition, and was found to agree with the time ; laftly, the
ftage was adjufted to the fpace correfponding to i''', and it wa^
found to agree exadly with the time.

Befides thefe experiments, a great number of others were
made with hard bodies, or thofe wbofe parts fo firmly cohered
as not to be moved inter fe by the friction ; and in each experi-
ment bodies of very different degrees of fri6lion were chofen,
and the refults all agreed with thofe related above ; we may
therefore conclude, that ihefriBion of loard bodies in motion is a
uniformly retarding force.

But to determine whether the fame was true for bodies when
covered with cloth, woollen, &c. experiments were made in
©rder to afcertain it ; when it was found in all cafes, that the
retarding force increafed with the velocity ; but, upon covering
bodies with paper, the confequences were found to agree with
thofe related above.

Vol. LXXV-. 7* 4. Having

i-o Mr. ViTsCE on the Motion of

4. Having proved that the retarding force of ali hard bodies
ariilng ITom fridion is uniform, the quantity of fridion, con-
iidered as equivalent to a weight without inertia drawing the
body on the horizontal plane backwards, or a<fling contrary to
the moving force, may be immediately deduced from the fore-
going experiments. For let M = the moving force exprefled by
its weight; F = the friction; W = the weight of the body
upon the horizontal plane ; S=rthe fpace through which the
moving force defcended in ti:ie tim.e / exprefled in feconds ;
rrs 1 6^^ feet ; then the whole acceierative force (the force of

\I — F

gravity being unity) will be ^j-t"^ ; hence, by the laws of uni-
formly accelerated motions, ^^ ^ x r/' _ S, confequently

F =:M ~ — 2^. To exemplify this, let us take the cafe of the

laft experiment, where M = 7, W=23i, 8—4/- feet, i — /i/'\

hence F= 7 - ^l\\^'u = ^A^1 » confequently the fri<i1ion was

to the weight of the rubbing body as 6.^i6y to 25.75. And
the great accuracy of determining the friction by this method is
manifeft from hence, that if an error of i inch had been made
in the defcent (and experiments carefully made may always de-
termine the fpace to a much greater exaflnefs) it would not
have affected the conclufion .^^.^dthpart of the whole.

5. We come in the next place to determine, whether fric-
tion, cateris paribus, varies in proportion to the weight or
preffure. Now if the whole quantity of the fridion of a body,
meafured by a weight without Inertia equivalent to the fri£lion
drawing the body backwards, increafes in proportion to its
weight, it is manifefl, that the retardation of the velocity of I
the body arifing from the fridion will not be altered; for the
7 retardation

Bodies affected by VrlcllofU \^\

dChiantity of friftion < • .■* « t «

ation vanes as ^ — 7-^—7 ; hence, it a bodv be put

Quantity or matter ' / r ^

in motion upon the horizontal plane by any moving force, if
both the weight of the body and the moving force be increafed
in the fame ratio, the acceleration arifing from that moving
force will remain the fame, becaufe the accelerative force varies
as the moving force divided by tlie whole quantity of matter,
and both are increafed in the fame ratio ; and if the quantity
of fri61:ion increafes alfo as the weight, then the retardation
arifmg from the fri£lion will, from what has been faid, remain
the iiime, and therefore the whole acceleration of the body will
not be altered ; confequently the body ought, upon this fuppo-
(itlon, ftill to defcribe the fame fpace in the fame time. Hence,
by obferving the fpaces defcribed in the fame time, when both
the body and the moving force are increafed in the fame ratio,
we may determine whether the fridlion increafes in proportion
to the weight. The following experiments were therefore
made in order to afcertain this matter.

Exp. I. A body weighing 10 oz. by a moving force of 4 oz.
defcribed in 2^^ a fpace of 5 i Inches ; by loading the body with
ID oz. and the moving force with 4 oz. it defcribed 56 inches
in z" \ and by loading the body again with 10 oz. and the
moving force with 4 oz. it defcribed 6 \ inches in z'\

Exp. 2. A bodv, whofe weight was 16 oz. by n moving
force of 5 oz. defcribed a fpace of 49 inches in 3'^ ; and by
loading tjie body with 64 oz. and the moving force with 20 oz.
the fpace deicribed in the fame time was 64 inches.

Exp. 3. A body weighing 6 oz. by a moving force of 2| oz,
defcribed 28 inches in z" ; and by Joading the body with 24
oz. and the moving force with 10 oz. tl;c fpace defcribed in the
fame time was 54 inches.

Zr, F Y O

7^2 , ^ Mr.Yi^cE, on the Motio7iof '

Exp. 4. A body weighing 8 oz. by a moving force of 4 oz»l
rIcTcribed 33! inches in 2'^; and by loading the body with 8
ozc and the moving force with 4 oz. the fpace deferibed in. the-
fame time was 47 inches,

Exp. 5. A body whofe weight was 9 oz. by a moving force of
4^ oz. deferibed 48 inches In i'^ ; and by loading the body with-
9 oz. and tiie moving force with 4I oz. the fpace deferibed iu:
the fame time was 60 inches.

Exp. 6, A body weighing 10 oz, by a moving force of 3 oz.
deferibed 20 inches in z'' \ by loading the body with 10 oz;
and the moving force with 3 oz. the fpace deferibed in the fame
time was 31 inches; and by loading the body again with 30^.
oz. and the moving force with 9 oz.the fpace deferibed was
34 inches in z'\

From thefe experiments, and" many others which it is notr
neceiTary here to relate, it appears, that the fpace deferibed is
aHvays increafed by increafmg the weight of the body and the
j^ccelerative force in the fame ratio ; and" as the acceleratloa
arifing from the moving force continued the fame, it is manifeft,
that the retardation arifing from the fridion muft have beea
diminiilied, for the whole acceleratlve force muft have been in-
creafed on account of the increafe of the fpace deferibed in the
fame time ; and hence (as the retardation from friftion varies as

Qiwntity of friftion \ 7 . ^,.^. . f. • in ^'

~ : — —. A the Quantity of friction increa es m a lefs ratio

Quantity ot matter J t^ y ^ <^ -J ./

t^m the quantity of matter or iveight of the body.

6. We came now to the laH: thing which it was propofed to
determine, that is, whether the fri£lion varies by varying the fur-
face on which the body moves. Let us call two of the furfaces
A and ^, the former being the greater, and the latter the lefs.
Now the weight on every given part of a is as much greater
2 than

Bodies affecied hy Fri^lion. ij^;

than the weight on an equal part of A, as A is greater, than a f
if therefore the friction was in proportion to the weiglit, c^^en's
paribus J it is manifefl, that the fridtlon on a would be equal to
the fri£lion on A, the whole friclion being, upon fuch a fuppo-
fitlon, as the weight on any given part of each furface multi-
plied into the number of fuch parts or into the whole area,
which products, from the proportion above, are equal. But
from, the laft experiments.it has been proved, that the fri6lioii
on any given furface increafcs in a lefs ratio than the weight;
confequently the. fridlion on any given, part of a has a lefs ratio
to the fridion on an equal part of A than A has to ^, and
hence the fridlion on^ is lefs than the friftion on A, tliat is,
the fmalleft furface has always the lead friction. But as this
conclufion. is contrary to the generally received opinion, I have
thought it proper to confirm the fame by a fet of experiments.
But before I proceed to relate them, I will beg leave to recom-
mend to thoie, who may afterwards be induced to repeat them9
the following cautions, which are extremely necefl'ary to be
attended to. Great care muft be taken that the two furfaces
have exactly the fame degree of roughnefs ; in order to be
certain of which, fuch bodies mirfl: be chofcn as have no knots
in them, and whofe grain is lb very regular that when the
two furfaces are planed with a fine rough plane, their rough-
nefs may be the fiime, which will not be the cafe if the body
be knotty, or. the grain irregular, or if it happens not to run
in the l^\me direction on both furfaces. When vou cannot de-
pend on the furfaces having the fame degree of roughnefs, the
beft way will be to pafl:e fome fine rough paper on each fur-
face, which perhaps will give a more equal degree of rough-
nefs than can be obtained by any other method. Now as the
proof which I have already given depends only on the motiori'

of.

I*'^ Mr. V'iNCE on the Motwn of

of the body upon the fame furface, it is not liable to any Inac-
curacy of the kind which the preceding cautions have been
given to avoid, nor indeed to any other, and therefore it mud .[
be perfectly conclufive. In the following experiments the
cautions mentioned above were carefully attended to.

Exp. I. A body was taken whofe flat furface was to its edge
as 22 : 9, and with the fame moving force the body defcribed
on its flat fide 33 1 inches in 2'\ and on its edge 47 inches in
the fame time.

Exp. 2. A fecond body was taken whofe flat furface was to
its edge as 32 : 3, and with the fame moving force it defcribed
on its flat fide ^z inches in 2'^, and on its edge it defcribed 35; -§
inches in the fame time.

Exp. 3. I took another body and covered one of its furfaceSj
whofe length was 9 inches, with a fine rough paper, and by
applying a moving force, it defcribed 25 inches in 2''' ; I then
took ofi^ fome paper from the middle, leaving only 4- of an inch
at the two ends, and with the fame moving force it defcribed
40 Inches in the fame time.

Exp. 4. Another body was taken which had one of* its fur-
faces, whofe length was 9 inches, covered with a fine rough
paper, and by applying a moving force it defcribed 42 inches
in 2^^ ; fome of the paper was then taken off from the mid-
dle, leaving only i| inches at the two ends, and with the fiime
moving force it defcribed 54 inches in 2''; 1 tlien took ofi
more paper, leaving only | of an inch at the two ends, and
the body then defcribed, by the fame moving force, 60 inches
in the fame time.

In the two lafl: experiments the paper which was taken off
the furface was laid on the body, that its weight might not be
altered.

Exp.

B'.dies affile d hy Fr'i£iion, i y^

Exp. 5. A bod}- was taken vvhofe flat furface was to its edge
as '^o : 17; the Jlui fide was laid upon the horizontal phme, a
moving force was applied, and the flage was fixed in order to
ftop the naovhig force, in confequence of which the body
would then go on with the velocity acquired until the fridion
had deftroved all its motion; when it appeared from a mean of
12 trials that the body moved, after its acceleration cealed,
5^ inches before it flopped. The edge was then applied, and the
moving force defcended through the fame ipace, and it was
found, from a mean of the fame number of trials, that the
fpace defcribed was jj inches before the body lofl all its motion,
after it ceafed to be accelerated.

Exp. 6. Another body was then taken whofe flat furface was
to its edge as 60 : 19, and, by proceeding as before, on the flat
furface it defcribed, at a mean of 1 2 trials, 5-J- inches, and on
the edge 6-ii inches, before it flopped, after the acceleration
ceafed.

Exp. 7. Another body was taken whofe flat furface was to
its edge as 26 : 3, and the fpaces defcribed on thefe two fur-
faces, after the acceleration ended, were, at a mean of 10
trials, 41 and 7-^^ inches refpedively.

From all thefe different experiments it appears, that the
fmallefl: furface had always the leafl fridion, which agrees
with the confequence deduced from the confideration that the
fridion does not increafe in fo great a ratio as the weight ; we
may therefore conclude, that the fritiion of a body does not con-
tinue the fame when it hjs different furfaces applied to the plane on
which it moves y but that the fmallefl furface will have the leafl
fri6iion,

7. Having thus eflabliflied, from the mofl declfive experi-
ments, all that I propofed relative to fridion, I think it proper,

before

1-6 'Mr. ViNCE on the 'Motion of

before I conclude, to give the refult of my examination mto
the nature of the experiments which have been made by-
others ; wliich were repeated, in order to fee how far they
were conclufive ill refpe6t to the principles which have been
.deduced fromthem. The experiments which have been made
by all the authors that I have (t^n^ have been thus inftituted.
To find what moving force would juft put a body at reft in
motion : and they concluded from thence, that the accelerative
force was then equal to the friction ; but it is manifeft, that
any force which will put a body in motion muft be greater
til an the force which oppofes its motion, otherwife it could not
overcome it ; and hence, if there were no other objeiStion than
this, it is evident, that the fridtion could not be very accurately
obtained ; but there is another objedion which totally deftroys
the experiment lb far as it tends to fhow the quantity of fric-
tion, which is the ftrong cohefion of the body to the plane
when it lies at reft; and this is confirmed by the following
experiments, ift', A body of 12| oz. was laid upon an hori-
zontal plane, and then loaded with a weight of 8 lb. and fuch
a moving force was applied as would, when the body was juft
put in motion, continue that motion without any acceleration,
in whi(^h cafe the fridlion muft be juft equal to the accelerative
force. The body was then ftopped, when it appeared, that the fame
moving force which had kept the body in motion before, would
not put "it in motion, and it was found neceflary to take off-
4I oz. from the body before the fame moving force wouU pxit^
it in motion "; it appears, therefore, that this body, when laid
"Upon the plane at reft, acquired a very ftrong cohefion to it,
~2dly, A body whofe weight was 1 6 oz. was laid at reft upon the
horizontal plane, and it was found that a moving force of 6 oz,
vB^ouldjuft put It in motion; but that a moving force of 4 oz,

would

Bodies affeSied by FrtSim* 177

"would^ when It was jufl put in motion, continue that motion
without any acceleration, and therefore the accelerative force
muil: then have been equal to the fridlion, and not when the
moving force of 6 oz. was applied.

From thefe experiments therefore it appears, how very
confiderable the cohelion was in proportion to the frI6i;ion when
the body was in motion ; it being, in the latter cafe, almoll:
I, and in the former it was found to be very nearly equal to
the whole fridlon. All the conclufions therefore deduced from
the experiments, which have been inditutcd to determine the
fridlion from the force neceflary to put a body in motion (and I
have never feen any defcribed but upon fuch a principle) have
manifeftly been totally falfe ; as fuch experiments only fhew
the refiftance which arifes from the cohefion and fri<Sion con-
jointly.

8. I fhall conclude this part of the fubje£l with a remark
upon Art, 5. It appears from all the experiments which I have
made, that the proportion of the increafe of the fri(flion to the
increafe of the weight was different in all the different bodies
which were made ufe of; no general rule therefore can be efia-
blilhed to determine this for all bodies, and the experiments
which I have hitherto made have not been fufficient to deter-
mine it for thofame body. At fome future opportunity, when
I have more leifure, I intend to repeat the experiments in order
to eftablifh, in fome particular cafes, the law by which the
quantity of fridion increafes by increafing the weight. Leaving
this fubjed therefore for the prefent, I (hall proceed to eftablilh
a theory upon the principles which we have already deduced
from our experiments.

V©L. LXXV. A a PRO-

J -5 ^Ir. ViNCE on I he Motion of

PROPOSITION!.

Let e, f, g, (fig. !•) reprefent either a cylinder^ or that circular*-
feB'ion of a body on which it rolls down the inclined plane CA in^
eonj'equencc cf its fricfion, to find the time of defcent and the*
number of revolutions.

As it has been proved in Art. 5. that the fridion of a ho^f^-
does not increase in proportion to its weight or preflure, we
cannot therefore, by knowing the fridion on any other plane,,
determine the fridion on CA ; the fri£lion therefore on CA can
only be determined by experiments made upon that plane, that
is, by letting the body defcend from reft, and obferving the
fpace defcribed in the firft fecond of time; call that fpace a^
and then, as by Art. 3. friction is a uniformly retarding force,
the body muft be uniformly accelerated, and confequently the

/AC

whole time of defcent in feconds will be = \/-j . Now to deter-
mine the number of revolutions, let j be the center of ofcillation
to the point of fufpenfion a * j then, becaufe no force adling at a
can afFed the motion of the point j, that point, notwithftanding
the a£lion of the fridion at ^, will always have a motion pa-
rallel to CA uniformly accelerated by a force equal to that
with which the body would be accelerated if it had no friftion ;
hence, if zm^'^i^ feet, the velocity acquired by the point j

ill the firfl fecond will be ~ ^ - ; now the excefs of the ve-

* a and s are not fixed points in the body, but the former always reprefents
that point of the tody in contaft with the plane, and the latter the correfponding
•;| center of ofcillation,

2 locity

I"

SoJies affecled by Fri^iGn. V^^

^locity of tlie point s above that of r (r being the center) is ma-
nifeftly the velocity with v^hich j is carried about r ; hence the

velocity of s about the center =' q^ ~^^ — c"-^: >

r ^1 . ^^ . 2mXCB-2rtxCA 2OTXrtfxCB — 2<7X''«xCA

confequentlv rs : r^ :: prr : — ttx-^- —

= the velocity with which a point of the circumference is car-
ried about the center, and which therefore expreffes the force
\vhich accelerates the rotation; now as 2a expreffes the accele'-
rative force of the body down the plane, and the fpaces dc-
fcribed In the fame time are in proportion to thofe forces, wo

have 2a : CA :: —prr — ' — ^- — ^-

th® fpace which any point of the circumference defcribes about
the center in the whole time of the body's defcent down CA ;
which being divided by the circumference p x ra (where

* = 6.282 fee.') will ffive^^ '^ '• for the whole numbcf

'of revolutions required. . ,

Cor, I. If ^ X QA^m ^ BC/ the number of revolutions = o,.
and therefore the body will then only flide ; confequently the
fridion Vanifhes,

Cor, 2, Let ^^rV (ng. 2.) be the next pofition of ars, and
draw / r'^ parallel to sa, then will s' i reprefetit the retardatioii
of the center r arifingfrom friction, and a^ ly v/ill reprefent the
acceleration of a point of the circumference about its center;
hence the retardation of the center : aceeleration of the cir-
cumference about the center :: s^f : a' b v. (by lim. A'f)
ir' : hr' :: rs : ra.

Cor. 3. If y coincides with /t, the body doQS not Jliik but
t>nly roi/; now in this cafe s s' : r/ :: as : ar; but as s s^ and
r/ reprefent the ratio of the velocities of the points s and r,

A a 2 they

i8o Mr. ViNCE on the Motion of

they will be to each other as "^^^ ■ : 2^ or asm x CB: a x CA;

hence, wheu the body rolls without JliJlngy a s : a r ;: m x

CB :ax CA.

/ac
Cor, 4. The time of defcent down CA ls= \l — ; but by

the laft Cor. when the body rolls without Jli Jin q- a = - — ^" ^,. • »

hence the time of defcent in that cafe = AC v/ ^^1; now

y mxraX BC

the time of defcent, if there were no fri6:ion, would be =1
, hence the time of defcent, when the body rolls with-

'^m X BC

out Jilting : time of free defcent :: \/sa : ^r a.

Cor, 5. By the laft Cor. it appears, that when the bodyjuft rc//f
without Jli cling, or w^hen the friftion is jufl equal to the accelera-

tive force, the time of defcent zzACd-

„„ , now It IS ma-

nifeft, that the time of defcent will continue the fame> if the
friction be increafed, for the body will ftill freely roll, as no
increafe of the fridlion afling at a can afFecl the motion of the
point s.

If the body be projected from C with a velocity, and at the
fame time have a rotatory motion, the time of defcent and
the number of revolutions may be determined from the com-
mon principles of uniformly accelerated motions, as we have
already invefligated the accelerative force of the body down
the plane and of its rotation about its axis ; it feems therefore
•unneceliary to lengthen out this paper with the iiiveftigations-.

PRO-

Bodies ajfecled by Friciion. \ % r

PROPOSITION II.

l^et the body be projedled on an horizontal plane LM (fig. 3.)
with a given velocity^ to deter^nine the fpctce through -which the
body zvill move before itjlops, or before its motion becomes uniform.

Case I. i. Suppofe the body to have no rotatory motion
when it begins to move; and let ^ = the velocity of proje6iion
per fecond meafured in feet, and let the retarding force of the
fridion of the body, meafured by the velocity of the body
which it can deftroy in one fecond of time, be determined by
experiment and called F, and let x be the fpace through which
the body would move by the time its motion was all deftroyed
when projedled with the velocity <?, and retarded by a force F ;
then, from the principles of uniformly retarded motion, x =

— , and if /=:time of defcribing that fpace, we have t~

2.

- , and hence the fpace defcribed m the firft fecond of time

2a— ¥

F

Now it is manifefb, that when the rotatory motion

of the body about its axis is equal to its progreflive motion, the
point a will be carried backwards by the former motion as much
as it is carried forwards by the latter ; confequently the point of
contaft of the body with the plane will then have no motion
in the direction of the plane, and hence the friction will at
that inftant ceafe, and the body will continue to ro/I on uni-
formly without Jliding with the velocity which it has at that
point. Put therefore z = the fpace defcribed from the com-
mencement of the motion till it becomes uniform, then the
body being uniformly retarded, the fpaces from the end of
7 the

'i^'t 'Mr. ViNCE on the Motion of

the motion vary as the fquares of the velocities, hencfe

2 2

~ : ^' (:: i^ 2F) :: — -z : a" ~ 2F% = fquare of the progref-

live velocity when the motion becomes uniform ; therefore the
velocity deflroyed by fri£tion =:^ — s/ a" — 2Fz ; hence, as the
velocitv generated or deftroyed in the fame time is iu'
proportion to the force, we have by Cor. 2= Prop. i.

r s : r a :'. a — \/a— zYz : - x a~\/a — 2 Fa the velocity o£
the circfimferenee ^/"^ generated about the center, confequently

s/ci — 2r zzz — x a - s/^ — 2rz, and hence 2 = ^ — =r- —

^ rs ' , «r X 2F -

the fpace which the body defcribes before the motion becomes^

uniform. il

2. If we fubftitute this value of % into the exprcffion for ther

velocity, we fliall have a x ~ for the velocity of the body when'

its motion becomes uniform ; hence therefore it appears, that-
the velocity of the body, when the fridion ceafes, will be the^^
iame whatever be the quantity of the fri6lion. If the body be^
the circumference of a circle, it will always iofe half the ve-^
locity before its motion becomes uniform.

Case II. i. Let the body, befides having a progreflive,
velocity in the direflion LM (fig. 3.) have alfo a rotatory mo-^
tion about its center in the diredlion gfe, and let 1; reprefeut^
the initial velocity of any point of the circumference about the
center, and fuppofe it firft to belefs than a ; then friction being,
a uniformly retarding force, no alteration of the velocity of-i
the point of contad of the body upon the plane can afFecl the .
'^quantity of friction ; hence the progrefTive velocity of the body
Hvill be the fame as before, and confequently the rotatory velo- ;

city

>

^Bodies affeSied by Fndlion. ig-^

city generated by fridioii will alfobe the fame, to which if wc
add the velocity about the center at the beginning of the mo-
tion, we (hall have the whole rotatory motion ; hence there-

fore, v-^-- X a~ s/a - 2F3 = s/c.i' — zFs, confequently % =z

a y.ai —V xrsA-ii'>^-ri

aF xas^

the fpace defcribed before the motion be-

comes uniform.

2. If this value of z be fubftituted into the expreflion for the

velocity, we ftiall have — ^ for the velocity when the

friction ceafes.

^. If T'=/7, then z—o, and hence the body will continue to
move uniformly with the firfl velocity.

4. If 'i; be greater than a, then the rotatory motion of the
point a on the plane being greater than its progreffive motion
and in a contrary diredion, the abfolute motion of the point
a upon the plane will be in the direction ML, and confequently
fridion will now ad in the diredion LM in which the body
moves, and therefore will accelerate t\\Q progrejjtve and retard
the ro/^/orj; motion ; hence it appears, that the pro grejjive mo-
tion of a body may be accelerated by ff-'iclion. Now to deter-
mine the fpace defcribed before the motion becomes uniform, we
may obferve, that as the progreffive motion of the body is now
accelerated, the velocity after it has defcribed any fpace % will-

be = v^^' -f 2F.S, hence the velocity acquired^: v^^' + 2Fz -^j,
and confequently the rotatory velocity deflroyed — x

^fl^+2Fz — ^, hence v — ~ x v/ir + 2Fz -^ = x/^' 4- 2F

z^

rsxvArray.a —a X as

thererore %=;- -^ . the Ipace required.

n. ir

184 ^^' ViNCE on the Motion of

5. If a — o, or the body be placed upon the plane without

any progreflive velocity, then z = ^ — ^,<.

Case III. i. Let the given rotatory motion be in the direc-
tion ^^y^; then as the frifbion mufl in this cafe always ad in
the dire£lion ML, it mufl continually tend to deftroy both the
progreflive and rotatory motion. Now as the velocity de-
ftroyed in the fame time is in proportion to the retarding force,
and the force which retards the rotatory is to the force which
retards the progrejive velocity by Cor. 2. Prop. 1. as r^ : r J,
therefore if 1; be to ^ as r^ is to r j, then the retarding forces
being in proportion to the velocities, both motions will be de-
ftroyed together, and confequently the body, after defcribing
a certain fpace, will reft ; which fpace, being that defcribed
by the body uniformly retarded by the force F, will, from

what was proved in Cafe I. be equal to — , .

2. If v bears a greater proportion to a than ra does to f s^
it is manifeft, that the rotatory motion will not be all deftroyed
when the progreflive is ; confequently the body, after it has"

defcribed the fpace — , will return back in the dIre£lIon ML;

for the progreflive motion being then defl:royed, and the rota-
tory motion fl:Ill continuing in the diredtion gef^ will caufe
the body to return with an accelerative velocity until the fric-
tion ceafes by the body's beginning to roll, after which it will
move on uniformly. Now to determine the fpace defcribed

before this happens, we have r s : r a :: a : — — - the rotatory

velocity defl:royed when the progreflive is all lofl: ; hence

rax a vxrs — axra ^i ^ ^ « • i ^ ^' U" U

-y = _ — the rotatory velocity at that tmie, whicn

/ being

Bodies affected by Friction* 1 85

being fubflituted for v in the lail article of Cafe II. gives

'V -f rs ~a x:a

for the fpace defcribed before the motion becomes

2F AUi^

uniform. '

3. If "0 has a iefs proportion to a than ?- a has to r s, it is
manlfefl:, that the rotatory motion will be deftroyed before the
progrejjive \ In which cafe a rotatory motion will be generated
in a contrary direction until the two motions become equal,
when the fridion will inftantly ceafe, and the body will then

move on uniformly. Now r a : r s :: v : '—^ the progreffivc

velocity deftroyed when the rotatory velocity ceafes, hence

a — — = =:progreiiive velocity when it begins its

rotatory motion in a contrary diredion ; fubflitute therefore
this quantity for a In the expreffion for % in Cafe L and we have

n -{■ 2>'! A 'a X a X ra — v X TS ^ t r ^ r •^ i r i

2 2 — -^ tor the Ipace deicribed after the rota-

cii X at X 2r ^

tory motion ceafes before the motion of the body becomes
unifjrm. Now to determine the fpace defcribed before the
rotatory motion was all deftroyed, we have (as the fpace from
the end of a uniformly retarded motion varies as the fquare of

^t 1 V \ a ^ aX^a — vXrs a Xra — v Xrs , -- ,

the velocity ) a : -^ : : ^ : v. z — the fpace that

•J y 2F ra 21" X ra ^

could have been defcribed from the time that the rotatory
velocity was deftroyed, until the progreffive motion would
have been deftroyed had the fri(Slon continued to a (ft ; hence

fi aX ra — v Xrs lav X ra X rs — 7;" X rs^

2F 2F X ra" ~ W777 == ^^^^ ^P^^^ defcribed when

the rotatory motion was all deftroyed, hence

♦ ,1

.1

fi +2rsxiaxaxa —vx 2avXraXrs — vxrs

as^xur^x2V + ^ ^F777 = whole fpace de-

fcribed by the body before its motion becomes uniform.

Vol. LXXV. B b d f.-

$6

Mr. ViNCE on the Motion of

DEFINITION.

The CENTER of FRICTION ts that point in the bafe of a body
on "which it revolves, into which if the ivhole fur face of the bafe^
and the mafs of the body were coUeSfed, and made to revolve about
the center of the bafe of the given body, the angular velocity de-
ftroyed by its fridiion would be equal to the angular velocity dsHroyed.
in the given body by itsfriciion in the fame tirne^

PROPOSITION III.

T^ofind the center of friction.

Let FGH (fig. 4.) be the bafe of a body revolving about Its
center C, and fuppofe about a, b, c, &c. to be indefinitely
fmall parts of the bafe, and let A, B, C, &c. be the correfpond-
ing parts of the folid, or theprlfmatic parts having a, b, c, &c.
for their bafes ; and P the center of fri6lion. Now it is ma-
nifeil:, that the decrement of the angular velocity muft vary
as the whole diminution of the momentum of rotation caufcd
by the friction diredily, and as the whole momentum of rota-
tion or efFe(fl of the inertia of all the particles of the folid //?-
verfely ; xht former being employed in diminifhing the angular
velocity, and the latter in oppofing that diminution by the en-
deavour of the particles to perfevere in their motion. Hence,
if the efFe6l of the friction varies as the effe£l of the inertia,
the decrements of the angular velocity in a given time will be
equal. Now as the quantity of fridlion (as has been proved
from experiments) does not depend on the velocity, the etFe(5t
of the fridlion of the elementary parts of the bafe a, b, c, &c.
2 will

Bodies affedled ly Priciirji. j S 7

will be as ^ X ^^C, b x i?C, c x cQ^ &c. alfo the ettccl of the iiiciti.i
of the correfpoadlng parts of the body will be as A x ^;C',
B X ^C", C X ^C% &c. Now when the whole furface of the
bafe and mafs of the body are concentrated in P, the effect of
the friction will be as ii + ^ + ^ + &c. x CP, and of the inertia as

A + B -}- C 4- &c. X CP" ; confequently a y. aO. -^ h a bO, ^ c x cQ
+ &c. : T+T+TT" &c, X CP :: Ax^C+B x hC^Q a cQ'
-j- &c. : A + B + C + &c. X CP' ; and hence

pp — -■- .^==: — = ( it S = the lu;il

^ aX<jC+^x^C + <:x^C + &c. xA + B + C-i-&c. ^

of the produ61:s of each particle into the fquare of its diilanco

from the axis of motion, T = the fum of the products of each

part of the bafe into its dilliance from the center, j == the are;i

of the bafe, / = the folid content of the bodv") '777—.

? it O P O S I T I O N IV.

Given tht velocity with which a body begins to revolve about the
center of its bafe^ to determine the number of revolutions which the
body will make before all its motion be dejiroyed.

Let the fridion, cxpreiTed by the velocity whicli it is able to

deftroy in the body if it were projecled in a right line horizon '

tally in one fecond, be determined by experiment, and called F;

.and fuppofe the initial velocity of the center of friclion P about

C to be a. Then conceivinsf the whole furface of tl^e bafe and

tnafsof the body to be colleOed into the point P, and (as has

.-■■'•. (P" ■

been proved In Prop. II.) —.will be the fpace which the body

fo concentrated' will defcribe before all its motion be deflroyed j

B b 2 hci\ce

•i88 'Mr. ViNCE on the Motion of

hence if we put a™ PC, j!? = the circumference of a circle
whofe radius is unity, then will /;s = circumference defcribed

by the point P ; confeqiiently "^= the number of revolutions

required.

Cor. Jf the folid be a cylinder and r be the radius of its bafe,

then z = ~ , and therefore the number of revolutions =

4' Ipr^'

PROPOSITION V.

To find the nature of the curve defcribed by mzy point of a body
Ctfecicd by fri5lion^ when it defends do'wn ary inclined plane.

Let efg (fig. 5 ) be the body, the points a, r, s, as in Prop. I,
and conceive st,r n, to be two indefinitely fmall fpaces defcribed
by the points s and r in the fame time, and which therefore
will reprefent the velocities of thole points ; but from Prop. I.
the ratio of thefe velocities U exprefled by m x CB : a x CA,
hence st^: rn :: m x CB : a x CA. With the center r let a
circle i; li' be defcribed touching the plane JLM which is parallel
to AC at the point b, and let the radius of this circle be fuch
that, conceiving it to defcend upon the plane LM along with
the body defcending on CA, the point b may be at reft, or the
circle may roll without Hiding. To determine which radius,
produce r s to .y, parallel to which draw n dy, and produce n t
to % ; now it is manifefl, that in order to anfwer the conditions
above-mentioned, the velocity of the point x muft be to the
velocity of the point r as 2:1, that is, %x ',yx\\ z\ i,
hence %yz=.yx = nr. Now zy : dt (:: ny \nd} \\ rxws'i

therefore dt=L- x%yzz— x^»r, hence ^i (^^td-^dszzid-^-nrzz
4 rs

r/dl,:i.T,ai,j.l''rl.L.\X\'/XAh?n\.p.l(li.

Bodies affcBed by Tridiion,

1 '^Q

rx

«r, confcqnently

r$ -f rx ^

IX

* •

t S

n r

r i
rx

(from what is proved above) 7;? x CB : /? x CA ; tberefor«
a X CA X r s ■]- a x CA x r x zz m x CB x r x^ hence rx^

— ~ — ^^^v the radius of the circle which rollinc^ down

the incHned plane LM, and carrying the body with it, will
give the true ratio of its progreffive to its rotatory motion,
and confequently that point of the circle which coincides with
any given point of the body will, as the circle revolves upon
the line LM, defcribe the fame curve as the correfponding
point of the body ; but as the nature of the curve defcribed by
any point of a circle revolving upon a ftraight line is already
very well known, it feems unnecedary to give the inveftigation.
By a method of reafoning, not very different, may the nature
of the curve, which is defcribed by any point of a body moving
^lpon an horizontal plane, and affe6led by fri6Hon, be determined.

[ 'p^ ]

XL Ohfeivatlons and Rxperhncnts on the Light of Bodies in a
State of Combujlion. By the Rev, Mr. Morgan ; communicated
By the Rev. Richard Price, LL.D. F,R.S.

Read January 27, 1 785.

rHE difcufTion which I now wifli to lay before the Roy^i
Society is nothing more than a feries of fadls, and of
conclufions which feem to flow from thofe facls, and from an
attention to the following data.

I. That light is a body, and like all other bodies fubjcvSt to
the laws of attraction.

II. That light is an heterogeneous body, and that the flime
attractive power operates with different degrees of force on its
different parts.

III. That the light which efcapes from combuftibles when
decompofed by heat, or by any other means, was, previous to I
its efcape, a component part of thofe fubftances.

It is an obvious conclufion from thefe data, that when
the attractive force, by which the feveral rays of light
are attached to a body, is weakened, fome of thofe rays will

efcape

Mr, Mo'RGAi^^s Ohfervatlous and Experiments^ &c. 191

efcdpefooner than others. Thofe which are united with theleaft
degree of power will efcape firft, and thofe which adhere to it
moft ftrongly will (if I may be allov/ed the expreflion) be the
lall; to quit their bafis. We may here have recourfe to a familiar
fa6l, which is analogous to this, and will illuflrate it.
If a mixture, confiding of equal parts of water, of fpirits
of wine, and of other more fixed bodies, be placed over
a fire ; the firfl influence of that heat, to which all the in-
gredients are alike expofed, will carry off the fpirits of
wine only. The next will carry off the fpirits of wine
blended with particles of water. A ftill greater degree of
heat will blend w4th the vapour which efcapes a part of
the more fixed bodies, til) at length what evaporates will be a
mixture of all the ingredients which were at fird expofed to
the fire. In like manner, when the furface of a combuilible is •
inaftate of decompofition, thofe parts which are the lead: fixed,
or which are united to it with the leaf!: force,, will be feparated
firft. Amongft thefe the indigo rays of light will make the-
earlieft appearance. By increafing the heat we fhall mix the'
violet with the indigo. By increafing it dill more we diall add
the blue and the green to the mixture, till at length we reach
that intenfity of heat which will caufe all the rays to efcape
at the fame indant, and make the flame of a combudible
perfectly white. It is not tny prefent deiign to fhew why
the mod: refrangible rays are the fird which efcape from a
burning body, but to enumerate the feveral hSis which feemtd^
fhew, that fuch a general law takes place in combudion ; and •
that the various colours of bodies in this date are uniforixily
regulated by that decreafe of attractive force now defcribed. "

i()Z Mr, Morgan's Oofcrvat'ions and E>:perifiieuts on

By examining the fliime of a common candle we may ob-<
ferve, that its iowefc extremities, or the part In which the black
colour of the wick terminates, dlf^jharges the lead heat; and
th;)t, as the vertex of the flame is approached, a fucceffive order
of jxirts is pafled through, in which the loweft is continually
addiiig to the heat of what is juH: above it, till wc come to
the top of the flame, near whicii all the heat is collected into a |
focus. At tile loweft extremity, however, where the heat is -
inconfiderable, a blue colour may be always obferved ; and
from this appearance, amongfl: others, it may, I think, be
fafely concluded, that the blue rays are fome of thofe which
efcape from combuftibles in an early period of their decompo-
fition ; and that if the decom^pofition could be examined in a
period ftill more early, the colour of their flame w^ould be
violet. By an a priori dedu6lion of this kind, I was led to
watch the appearances of a candle more attentively ; whence I
found that, to the external boundary of a common candle
is annexed a filament of light, which, if proper care be
taken to prevent the efcape of too much fmoke, will appear^
moll: beautifully coloured with the violet and indigo rays. To
the preceding inftance of a common candle many fa6ls may
be added, which fpeak a fimilar language. If fulphur or
gether is burned, or any of thofe combuftibles whofe .
vapour is kindled in a fmall degree of heat, a blue flame
will appear, which, if examined by the prifm, will be found
to confiil of the violet, the indigo, the blue, and fometlmes a ,
fmall quantity of the green rays. The beft mode, however,
of fhewing the efcape of fome rays l^y that degree of heat,
which will not feparate others till increafed, is the following*
Give a piece of brown paper a fpherical form, by prefling it

upon

the Li^ht of Bodies in a State of Combiijuon, 19^

tipon any hard globular fubftance. Gradually brnig the paper,
thus formed, to that diftance from the candle at which It will be-
gin to take fire. In this cafe a beautiful blue flame may be feen,
hanging as it were by the paper till a hole is made in it, when
the flame, owing to the increafed a6lion of the air upon all
parts of it, becomes white, though the edges ftill continue of
ii blue or violet colour. As a confirmation of what I have
concluded from the preceding facls, it may be obferved, that
the very flame which, when expofed to a certain degree of
heat, emitted the moll: refrangible rays only, will, if expofed
to a greater degree of heat, emit fuch as are lefs refrangible.
The flames of fulphur, fpirits of wine, &c. when fuddenly
expofed to the heat of a reverberatory, change their blue ap-
pearance for that which is perfectly white. But to gain a
more ftriking diverfity of this fact, I adopted Mr. Melvill's
mode of examining bodies whilft on fire. I darkened my
room, and placed between my eye and the combuftible a flieet
of pafteboard, in the center of which I made a fmall perfora-
tion. As the light of the burning body efcaped through this
perforation, I examined it with a prifm, and obferved the fol-
lowing appearances. When the fpirits of wine vv^ere fet on
fire, all the rays appeared in the perforation ; but the violet,
the blue, and the green, in the greateft abundance. When
the combuftion of the fpirits was checked by throwing fome
fal ammoniac into the mixture, the red rays difappeared ; but
when, by the long continuance of the flame, the fal ammoniac
was rendered fo hot as to increafe, rather than dlmlnlfh the
combuftion, the red rays again appeared at the perforation. If
the fcreen was managed lo that the different parts of the
flame might be examined feparately, I always obferved that
Vol. LXXV. C c the

194 ^^^^' Morgan's Obfervations and Experiments on
the colours varied according to the degree of heat. At
the bale of the flame, or where the heat was leafl:, the in-
digo, the violet, and a very fmall tinge of the blue and
green appeared. As I approached the vertex of the flame,
the rays which efcaped became more and more numerous
till 1 reached the top, when all the rays appeared in' the
prifm. It fhould be attended to^ that when the red rays firfl:
made their appearance, their quantity was fmall, and gradually
increafed as the eye in Its examination approached that part
v.liere the heat was greateih Mr. Melvill, when he made
fome of the preceding experiments, obferved, that the yellow
rays frequently efcaped in the greatefl: abundance j but this An-
gularity proceeded from feme circumftances which efcaped his
attention* In confequence of mixing acids or falts with the
burning fpirits, a very denfe fume of unignited particles arifes,
and before the rays of the burning body arrive at the perfora-
tion where the prifm catches them, they mufl pafs through a
medium which will abforb a great part of the indigo and the
violet. On the other hand, owing to the imperfedion of the
decompofltion, very few of the red rays are feparated from their
bails, and confequently the yellow and the orange rays are
thofe alone which pafs through the unburnt fmoke of the
flame.

I would now proceed with obferving, that, befides the in-
creafe or decreafe of heat, there are other modes of retarding
or accelerating the combuftion of bodies, by which alfo may
be examined fome of the preceding illuftrations,

I. A candle burns moft rapidly and brilliantly In dephlo-
gifticated air.

2. The

the Light of Bodies in a State of Combufion. \ ^ ;;

2. The blue colour of a fulphureous flame ia pure air is
•changed into a dazzling white.

a. The flame of inflammable air, when mixed with ni-
trous air, is green. It is white flrongly tinged w^iththe indigo
and violet when mixed with common air; but when mixed
with dephlogifticated air, or furrounded by it, the brilliancy
rof its flame is moll Angularly beautiful.

If the preceding fa6ts prove that light, as an heterogeneous
body, is gradually decompofed during combuftion ; if they
prove, likewife, that the indigo rays efcape with the leafl: heat^
and the red with the greateil: ; I think we may rationally ac-
count for feveral iingularities in the colours of different flames.
If a piece of paper, impregnated with a folution of copper in
the nitrous acid, be let on fire, the bottom and fides of the
flame are always tinged with green. Now this flame is evi-
dently in that weak ftate of decompofition, in which the mofi
refrangible rays efcape in the greateft abundance; but of thefe
rays the green efcape mofl: plentifully through the unignited
vapour and that portion of the atmofphere which feparates the
eye from the flame. The peculiarity which I have now endea-
voured to account for may be obferved in the greateft perfedion
in brafs founderies. The heat in this inftance, though very
ftrong, is fcarcely adequate to the decompofition of the metallic
vapour which efcapes from the melted brafs. A very Angular
flame therefore appears to the eye ; for while its edges are green,
its body is fuch as to give the objects around a very pallid or
ghaftly appearance, which is the confequence of its wanting
that portion of red rays which is neceflTary to make a perfed
white.

C c a The

io6 Mr. Morgan's Obfervations and Experiments on

The moil fingular phaenomenoii attending a burning body
is, perhaps, the red appearance it aflumes in its laft ftage o£
combuflion. The preceding facls and obfervations may, I
think, help ns to exphiin it..

1. After a body has continued to burn for forae time, its
external furface. is to. be regarded as having loH: a great portion.
if not the whole of thofe rays which the firft application of
iieat was able to feparate. But thefe rays were the indigo, the
violet, the blue, and perhaps the green. Nothing, therefore, will
remain to be feparated, but the yellow, the orange, and the red,
Confequently, the combuftion of the body,, in its laft ftate of de-
compofition, can affume no other than a reddifh appearance. But

2. Let us confider the external furface of the combuflible
as annexed to an inner furface, v/hich may be partly, but not fo
perfectly decompofed as itfelf : for the violence of the heat will
be found to leiien in its effeds the nearer it approaches to the
center of the fubftance which is expofed to it. Hence we are
to confider the parts v/hich are jufi: covered by the external fur-
face as having loft lefs of their component light than the exter-
nal furface itfelf. Or the former may retain the green rays
when the latter has loft both indigo, violet, blue, and green.

3. Thofe parts which are nearer the center of the body
than either of the preceding muft, as they are further from
the greateft violence of the heat, have lofl: proportionably
fewer of their rays. Or while the more external parts may
have lofl all but the red, thefe may have loft only the indigo
and violet.

4. The moft central parts may be unaftecled by the heat ;
and whenever the fire does reach thefe parts, they will imme-
diatsly difcharge their indigo rays, and be decompofed in the

gradual

the Light of Bodies ia a State of Comhuftion, i^y

gradual manner which I have ah'eady defcribed. A piece of
rotten wood, whilft burning, will exemplify and confirm the
preceding illuftration. When influenced by the external air
only, if examined through a prifm, no rays will be found to
efcape but the orange and the red. By blowing upon the
burning wood with a pair of bellows, the combuflion,
being increafed, will affect thofe internal parts of the body
which were not afted upon before. Thefe parts, therefore,
will begin to lofe their light, and a prifm wall fhew the
green, the blue, the violet, and indigo, all appearing in fuc-
cefiion. Appearances fimilar to the preceding may be ob-
ferved in a common kitchen fire. When it is falnteil, its
colour is mod: red, the other rays having been emitted, and
the combuftion at a {land ; but by blowing upon it in this
ftate, its brightnefs will be increafed, and more and more of
the rays which are yielded by the internal parts of the bgdy
will come to the eye, till at length, by continuing to blow, the
combufllon will be made fo complete as to yield all the rays,
or to make it appear perfectly white.

Many are the varieties difcoverable in the flames and in the
appearances of fixed burning bodies to which the preceding
obfervations may be applied ; but, to avoid unneceflary amplifi-
cation I will take notice only of what appears to me an imper-
fe£lion in Sir Isaac Newton's definition of flame. He conr
jedures, that it may be a vapour heated red-hot. I think I
Ihould rather fay, that flame is an inflance of combuflion
whofe colour will be determined by the degree of decompofi-
tion which takes place. If it be very imperfedl, the moft
refrangible rays only will appear. If it be very perfect, all
the rays will appear, and its flame will- be brilliant in

proportloii

jpS Mr. Morgan's Obfervations and Experiments on
proportion to this perfedlion. There are flames, however,
which coiifift of burning particles, whofe rays have partly
efcaped before they afcended in the form of vapour. Such
would be the flame of a red-hot coal, if expofed to luch a heat
as would gradually difperfe it into vapour. When the fire is.
very low under ihe furnace of an iron foundery, at the upper
orifice of the chimney a red flame of this kind may be feen, .
which is different from the flame that appears immediately after
frelli coals have been thrown upon the fire ; for, in confe-
quence of adding fuch a fupply to the burning fuel, a vaft
column of fmoke afcends, and forms a medium fo thick as t&
abforb mod: of the rays excepting the red.

E'^perimcfits on eleSirlc light*

If we w^ould wifli to procure any degree of certainty in any
hypothefis which we may form concerning electrical light,
perhaps the following general dedudlions may be of fome fer-
vice to us.

1. There is no fluid or folid body In its paiTagc through
which the eledric fluid may not be made luminous. In water,
fpirits, oil, animal fluids of all kinds, the difcharge of a Ley-
den phial of almofl any flze will appear very fplendid, pro-
vided we take care to place them in the circuit, fo that the
fluid may not pafs through too great a quantity of them. My
general method is to place the fluid, on which I mean to make
the experiment, in a tube three-quarters of an inch in diameter,
and four Inches long. I flop up the orifices of the tube with
two corks, through which I pufh two pointed wires, fo that the
points may approach within one-eighth of an inch to each
z ' other.

the Lighi of Bodies in a Slate of Comhujlion. ipp

other. The fluid in pafling through the interval which fepa-
rates the wires is always luminaus, if a force he uied fuffi-
ciently ftrong. I fhould obferve, that the ghifs tube, if not
very thick, always breaks when this experiment fucceeds. To
make the pafiage of the fluid luminous in the acids, they mufl
be placed in capillary tubes, and two wires introduced, as in
the preceding experiment, whofe points lliall be very near each
other. It is a well known fadl, that the difcharge of a fmall
Leyden phial in paffing over a flrip of gold, filver, or Dutch
metal leaf, will appear very luminous By conveying the con'
tents of ajar, measuring two gallons, over a ftrip of p-old leaf
one-eighth of an inch in diameter, and a yard long, I have
frequently given the whole a dazzling brightnefs. I cannot
fay, that a much greater length might not have been made
very fplendid, nor can I determine- to what length the
force of a battery might be made luminous in this manner.
We may give this experiment a curious diverlity, by laying
the gold or filver leaf on a piece of glafs, and then placing the
glafs in water; for the whole gold leaf will appear moft bril-
liantly luminous in the water by expofing, it, thus circum-
flanced, to the explofion of a battery.

2, The difficulty of making any quantity of the eleflrlcal
fluid luminous in any body increafes as the conducing power
of that body increafes.

EXP. I. In order to make the contents of a jar luminous
in boiling water, a much higher charge is neceflary than would
be fufficient to make it luminous in cold w^ater, which is uni-
verfally allowed to be the worft condudlor.

EXP. II, I have various reafons for believing the acids to
be very good condu£lors. If therefore into a tube, filled with
water, and circumflanced as I have already defcribed, a few

drops

zoo Mr. Morgan's Obfervations and Experiments on

drops of either of the mineral acids are poured, it will be
almoft impoffible to make the fluid luminous in its paflage
through the tube.

EXP. III. If a ftring*, whofe diameter is one-eighth of an
inch and whofe length is fix or eight inches, is moiftened with
water, th^e contents of a jar will pafs through it luminoufly,
but no fuch appearance can be produced by any charge of the
fame jar, provided the fame firing be moiftened with one of
the mineral acids. To the precedhig inftance we may add
the various inftances of metals which will conduct the eledlri-
cal fluid without any appearance of light, in circumftances
the fame with thofe in which the fame force would have ap-
peared luminous in paffing through other bodies whofe con-
dudling power is lefs. But I proceed to obfervT,

III. That the eafe with which the ele£lrical fluid is rendered
luminous in any particular body is increafed by increafing
the rarity of the body. The appearance of a fpark, or of
the difcharge of a Leyden phial, in rarefied air is well known.
But we need not reft the truth of the preceding obfervation on
the feveral varieties of this facSt ; (imilar phicnomena attend the
rarefaction of aether, of fpirits of wine, and of water. ^

EXP. IV. Into the orifice of a tube, 48 inches long, and two-
thirds of an inch in diameter, I cemented an iron ball, fo as to
bear the weight which prefled upon it when I filled the tube
with quickfilver, leaving only an interval at the open end,
which contained a few drops of water. Having inverted the
tube, and plunged the open end of it into a bafon of mercury,
the mercury in the tube flood nearly half an inch lower than it

'^J

* The thicknefs and diameter of the firing fliould be regulated by the force we
•employ.

did

m

^d m a barometer at th^ f^ma inftant, ©wing t-o the vapour
which was formed by the water* But thraugh this rai^eiSed wa«
ter the electrical fpark pafled m lurninouilj aa k daes through
air equally rareiied..

EXP. V. If, inflead of water, a few drops of fpirits of wrae aru
placed on the furface of the mercury, phaenomena fimilar to
thofe of the preceding experiment will be difcovered, with
this difference only, that as the vapour in this cafe is more
denfe, the electrical fpark in its paffage through it is not c^uita
fo luminous as it is- in the vapour of water,

EXP. VI, Good JEther fubftituted in the room of the fpirits
of wine will prefs the mercury down fo low as the height of
1 6 or ly inches. The eledlricai fluid in paffing through this
vapour (unlefs the force be very great indeed) is fcarcely lumi-
nous. But if the prefTure on the furface of the mercury in the
bafon be gradually leflened by the. aid of an air-pump, the va-
pour will become more and more rare, and the eleOric fpark in
paffing through it more and more luminous,

EXP. vji. I could not dlfcover that any vapour eicapedfrom
the mineral acids when expofed in vacuo. To give them,,
therefore, greater rarity or tenuity, I found different methods
neceflary. With a fme camel-hair pencil, dipped in the vi-
triolic, the nitrous, or the marine acid, I drew upon a piece of
glafs a line about one-eighth of an inch broad. In fome in-
ftances I extended this line to the length of 27 inches, and
found that the contents of an eledric battery, confiding of la
pint phials coated, would pafs over the whole length of this
line with the greateft brilliancy. If by widening the line, or
by laying on a drop of the acid, its quantity was increafed
in any particular part, the charge, in palling through that part,
never appeared luminous. Water, fpirits of wine, circum-
Vol. LXXY. D d ft^nced

202 Mr. Morgan's Ohfervatlons and Experltnenfs on

flaaced fimilarly to the acids in the preceding experiment^
were attended with fimilar, but not equal efFeds, becaufe, in
Gonfequence of the inferiority of their conducing power, it was
iieceflary to make the line through wiiich the charge pafled
confiderably (liorter.

4. The brilliancy or fplendor of the ele6lric fluid in its-
paflage through any body is always increafed by leflening the
dimendons of that body. I would explain my meaning by lay-
ing, thatafpark, or the difcharge of a battery which we might:
fuppofe equal to a fphere one quarter of an inch in diameter,
would appear much more brilliant if the fame quantity of fluid.
is comprefled into a fphere one-eighth of an inch in diameter..
This obfervation is the obvious confequenceof many known fa(fls.
If the machine be large enough to afford a fpark whofe length
is nine or ten inches, this fpark may be feen fometimes forming
itfelf into a brufh, in which ftate it occupies more room, but ap-
pears very faintly luminous. At other times the lame fpark may
be feen dividing itfelf into a variety of ramifications which (hoot
into the lurrounding air. In this cafe, likewife, the fluid is.
ditfufed over a large luiface, and in proportion to-the extent of^"
that furface, fo is the faintnefs of the appearance. A fpark,
which in the open air cannot exceed one quarter of an inch in
diameter, will appear to fill the whole of an exhaufted receiver
four inches v/ide and eight inches long. But in th.t former
cafe it is brilliant, and in the latter it grows fainter and fainter
asthefize of the receiver increafes. To prove the obfervation,
• which I think may be jufcified by the, preceding fa£ls, I made
t\\t follov*^ing experiments.

EXP. VIII. To an infulated ball, four inches in diameter, I

fixed a filver thread, about four yards long. This thread, at

the end which was remotefl; from the ball, was fixed to another

^ , infulated

i

the Light of Bodies in a State of Comhuflion, 203

infulated fubftance. I brought the ball within the ftriking
diftance of my conductor, and the fpark in pafling from the con-
ductor to the ball appeared very brilliant ; but the whole length
of the filver thread appeared faintly luminous at the fame in-
fant. In other words, when the fpark was confined within
the dimenlions of a fphere one-eighth of an inch in diameter,
it was bright, but, when dittufed over the furface of air which
received it from the thread, its light became fo faint as to be
it?:w only in a dark room. If I leflened the furface of air
which received the fpark by fhortening the thread, I never
failed to increafe the brightnefs of the appearance.

EXP. IX. To prove that the faintnefs of the electric light in
vacuo depends on the enlarged dimeniions of the fpace through
which it is diffufed, we have nothing more to do than to in-
troduce two pointed wires into the vacuum, fo that the fluid
may pafs from the point of the one to the point of the other,
when the diftance between them is not more than the one-tenth
of an inch. In this cafe we (hall find a brilliancy as great as
in the open air,

EXP. X. Into a Torricellian vacuum, 2,^ inches in length, I
conveyed as much air as would have filled two inches only of the
€xhaufl:ed tube, if it were inverted in water. This quantity of
air afforded refinance enough to condenfe the fluid as it pafled
through the tube into a fpark 38 inches in length. The bril-
liancy of the fpark in condenfed air, in water, and in all fub-
fiances through which it pafles with difficulty, depends oa
principles fimilar to thofe which account for the preceding fa<5tSo
I would now proceed to fhew,

5. That in the appearances of ele£i:rlclty, as well as in thofe
of burning bodies, there are cafes in which all the rays of light
do not efcape; and that the moft refrangible rays are thofe

D d 2 %vhick

a'04. Mr. Morgan's Obfervations and Experiments on
which efcape firft or moft eafily. The eleftrical brufh is
always of a purple or bluifh hue. If you convey a fpark
throuah a Torriceiriaii vacuum, made * without boilino- the
mercury in the tube, the brufh will difplay the indigo rays.
The fpark, however, may be divided and weakened even in
the open air, fo as to yield the mod: refrangible rays only.

EXP. XI. To an infulated metallic ball, four inches in dia-
meter, I fixed a wire a foot and a half long. This wire termi-
nated in four ramifications, each of which was fixed to a
metallic ball half an inch in diameter, and placed at an-
equal diftance from a metallic plate, which communicated by.
metallic conductors with the ground. A powerful fpark, after
falling on the large ball at one extremity of the wire, was-
divided in its paflage from the four fmall balls to the metallic
plate. When I examined this divifion of the fluid in a dark
room, I difcovered fome little ramifications wliich yielded the
indigo rays only: indeed, at the edges of all weak fparks the
fame purple appearance may be difcovered. We may likewife
obferve, that the nearer we approach the center of the fjpark,.'
the greater is the brilliancy of its colour. But I would now
"wifh tofhew |

6. That the influence of diflferent media on electrical light
is analogous to their influence on folar light, and will help us.
to account for fome very fingular appearances.

EXP.xii. Let a pointed wire, having a metallic ball fixed to one
of its extremities, be forced obliquely into a piece of wood, fo as
to make a fmall angle with the furface of the wood, and to make

* If the Torricellian vacuum is made with mercury perfeftly purged of air, it
becomes a perfeft non-conduftor. This, I believe, will be proved decifively by
X©me experiments which I hope will be foon communicated to the Royal Society.

Dr, Price,

I the

the Light of Bodies in a State of Combujlion. 295

tlie point He about one-eighth of an inch below the furface.
Let another pointed wire, which communicates with the ground,
be forced in the fame manner into the fame wood, fo that
its point likewife may lie about one-eighth of an inch below
the furface, and about two inches diftant from the point of
the firft wire. Let the wood be inlulated, and a flrong fpark
which ftrikes 011 the metallic ball will force its paflage through
the interval of wood which lies between the points, and appear
as red as blood. To prove that this appearance depends on the
wood's abforption of all the rays but the red, I would obferve,
that the greater the depth of the points is below the furface, the
lefs mixed are the red rays. I have been able fometimes, by in-
creafing or diminishing the depth of the points, to give the
fpark the following fuccellion of colours. When they w^re
deepeft below the furface, the red only came to the eye through
a prifm. When they were raifed a little nearer the furface,
the red and orange appeared. When nearer ftiil, the yellow ;
and fo on till, by making the fpark pafs through the wood very
near its furface, allthe rays were at length able to reach the
eye. If the points be only one-eighth of an inch below the
furface of foft deal wood, the red, the orange, and the yel-
low rays will appear as the fpark pafles through it. But when
the points are at an equal depth in a harder piece of wood (fuch
as box) the yellow, and perhaps the orange, will difappear. As
a farther proof that the phicnomena I am defcribing are owing to
the Interpofition of the wood, as a medium which abforbs fome
of the rays and fuffers others to efcape, it may be obferved, that
when the fpark ftrikes very brilliantly on one fide of the piece *
of deal, on the other fide it will appear very red. In like man-
ner a red appearance may be given to a fpark which ftrikes

brilliantlj

'266 Mr, MoRGAN*s Obfervations and Experiments on

brilliantly over the infide of a tube, merely by fp reading fome
pitch very thinly over the outfide of the fcime tube.

EXP. XIII. I would now give another fa6l, whofe fingulari-
ties depend v^ery much on the influence of the medium through
which the electrical light is made to pafs. If into a Torricel-
lian vacuum, of any length, a few drops of sther are conveyed,
and both ends of the vacuum are flopped up with metallic con-
dudors, fo that a fpark may pafs through it, the fpark in its
paflage will affume the following appearances- When the eye
is placed clofe to the tube, the fpark will appear perfectly
white. If the eye is removed to the diilance of two yards, it
will* appear green ; but at the diilance of fix or feven yards,
the colour of the fpark will be reddlfh. Thefe changes evi-
dently depend on the quantity of medium through which the
the light paffes ; and the red light more particularly, which
we fee at the greatell: diftance from the tube, is accounted for
on the fame principle as the red light of a diftant candle or a
beclouded fun.

EXP. XIV. Dr. Priestley long ago obferved the red ap-
pearance of the fpark when pafling through inflammable air.
But this appearance is very much diverfified by the quantity of
medium, through which you look at the fpark. When at a
very confiderable diftance, the red comes to the eye unmixed;
but, if the eye is placed clofe to the tube, the fpark appears
white and brilliant. In confirmation, however, of fome of
my conclufions, I would obferve, that by increafing the
quantity of fluid which is conveyed through any portion
ef inflammable air, or by condenfing that air, the fpark may
be entirely deprived of its red appearance, and made perfe6lly
brilliant. I have only to add, that all weak exploiions and

fpark s,

the Light of Bodies in a State of Comhujiion, 2o*t

fparks, when viewed at a dlftance, bear a reddifh hue. Such
are the explolioiis which have pafied through water, fpirits of
wine, or any bad condutflor, when confined in a tube whofe
diameter is not more than an inch. The reafon of thefe
appearances feems to be, that the weaker the fpark or explofon
IS, the lefs is the light which efcapes ; and the more vidble
the eife6l o^ any medium which has a power to abforb fome of
that light.

The preceding obfervations concerning elecrrical licht were
the refult of my attempts to arrange, under general heads,
the principal Angularities attending it. They may, perhaps,
affift others in determining how far they may have led my mind
aflray in giving birth to a theory which I would now briefly
defcribe in a few queries*

L If we confider all bodies as compounds, w^hofe conftltuent
parts are kept togeth-er by attracting one another with different
forces, can we avoid concluding, that the operations of that
attradive force are regulated, not only by the quality, but the
quantity likewile of thofe component parts ? If an union of a
certain number of one kind of particles, with a certain num-
ber of a fecond and third kind of particles, forms a particular
body, muft not the bond w^hich keeps that body together be
weakened or ftrengthened by increaiing or diminlfhing any one
of the different kinds of particles which enter into its confli-
tution •

II. When, to the natural fhare of the electric fiuid al-
ready exifling in the body, a frefh quantityr'of the fame
fluid is added, muft not fome of the component parts of that
body efcape ; or muft not that attractive force which kept all
together be fo far weakened as to let loofe fome conftituent

partSj.,

parts, and amoiigft thefe the particles of light in ^m*
cular ?

IIL JNIuft not this feparatron of pn;rts be great m propartloi^
to the cjuaatlty of extraneous particles which are added to the
body ? Or (agreeable to the 4th obfervation) mud not the
fpark be more fplendid and brilliant, the more the eledrical
fluid is concentered in any given fpace ^

IV. In the diminution or alteration of that attrai5live force od
which depends the conftitutio-n of bodies, may there not be a
gradation which, in the prefent cafe, as well as in that of
burning bodies, will caufe the efcape of fome rays fooncr thaa
others I

Otfervations on phojphork ligBL

It is obvious, from Mr. B. Wilson*s experiments, that
there are many curious diverfities in the appearances of phof-
phori. Some iliells, prepared agreeably to his diredions, after
expofure to the fun or to the flafh of a battery, emit a purple,
others a green, and others a reddifh light. If wdth Mr, Wil-
son we fuppofe, that thefe ihells are in a ftate of flow com-
budion., may we not conclude, that fome are jufl beginning to
burn, and therefore, agreeably to what I have obferved on com-
buflible bodies, emitting the maft refrangible rays; wbilft others ^
are in a more advanced flate of combuflion, and therefore
emitting the lead refrangiible. If this conclufion be right,
the ihells which are emitting the purple, or the green, muflr
Bill retain the yellow, the orange, and the red, which will
^Ifo make their appearance as foon as the combuftiou is fuffi*
cieutly increafed.

the Light of Bodies in a State 6f Comhujflon, 20^

EXP. XV. Place a fhell whilfl emitting its green rays on a
tvarm fhovel, and the appearance of the fhell will be foon
changed into that of a yellow mixed with red. To Mr. Wil-
son's theory, however, of (low combuftion the following ob-
-je£lions may be oppofed.

1°. If phofphoric fhells owe their light to this caufe, wc
muft confider the word combuftion when applied to them as
implying in its fignification all thofe circumftances which are
•the ufual attendants of a body whilfl on fire. Amongfl other
'iiecefTary confequences in fuch a cafe, the increafe of heat mufl
"increafe the decompofition of the combuflible ; whereas wc
difcover an effect the very oppolite to this in the appearance of
a phofphoric body, which never fails to lofe its light entirely
in a certain degree of heat, without lofing the power of be-
coming phofphoric again when it has been fufficiently cooled.
Beiides, when a phofphoric fhell has been made very hot, and
while it has continued lb, I have conveyed the moft brilliant
difcharge of a battery over it without efFe61:. In other words,
lieat, or the very caufe which promotes combuflion in all other
inflances, in this particular cafe puts an end to it. Mr. Wil-
son, in his Treatife on Phofphori, has defcribed an experiment
iimilar to the preceding. But the refult he mentions is diiferent
from that here mentioned. However, from a regard to his
authority^ I have fo frequently repeated my trials that I cannot
Juflly fufpe(5l myfelf of any inaccuracy, z'". When bodies
are wafted by combuftion, they can never be made to re-aflume
the appearances which they previoufly difplayed. No power
can give to afhes the phaenomena of a burning coal. But
phofphoric bodies are very different in this refpect ; for a fhell
may be made to lofe all its light by expofure to heat, and again
Vol. LXXV, E e mss

210 Mr. Morgan's Ohfervatlons and Expertmeni^ on

may be made as luminous as ever by expofure to the fun. Bat
3°. ft is obfervable, that fome bodies, which are moft beau-'
tl fully phofphorlc, or which, according to Mr. Wilson*s
theorv, are in the beft ftate of (low combuftion ; it is obfcrvable,
I fav, that the I'rme bodies are the moil obftinate in refifting the
/ire. The diamond, which to be decompoled requires the
force of a moll powerful furnace, is, according to this
theory, wafting away, owing to a reparation of parts which
is promoted by the weakeft influence of the fun's rays. — With-
out determining whether the preceding objedions be valid, let us
now fee the confequence of admitting the common hypothecs,
that the detention of thofe rays which fall upon phofphori is
owing to fome force which prevents their immediate refle(5lion,
but is not adequate to their entire abforption. This force,
whatever it be, cannot well be fuppofed to operate with equal
power on all the rays. And if this be not^the cafe, I think
we cannot avoid concluding, that phofphoric (hells will aflumc-
different colours, owing to the earlier and later efcape of the
different rays of light. This conclufion is juftified by an expe-
riment which I have already appealed to. When the force is
fach as to admit of the efcape of the purple, the blue, and the
green, we have only to leflbn that force by warming the body, ■
and the yellow, the orange, and red efcape. It is proved by-1
Bfccaria's extenfive experience on this fubjc61:, that there is'j
fcarcely any body which is not phofphoric, or which may not
be made fo by heat. But as the phofphoric force is moft
powerful when the purple rays only efcape, fo we are to con- jj
elude, that it is weakeft when it is able to retain the red rays only.
This conclufion is agreeable to fevtral fads. Chalk, oyfter-
ihells, together with thofe phofphoric bodies whofe goodnefs
7 has

the Lig/jf of BoMcs in a State of Combuflon, 2 1 1

has been very much impaired by long keeping; when
finely powdered and placed wltliln the circuit of an eledrical
battery, will exhibit by the^ir fcattered particles a fhower
of light; but thefe particles will appear reddi(h, or their
phofphoric power will be fufficient only to detain the
yellow, orange, and red rays. When fpirits of wine are in a
fimilar manner brought within the circuit of a battery, a
limilar effect may be difcovered ; its particles diverge in feveral
dire6lIons, difplaylng a mod beautiful golden appearance. The
metallic calces are, of all bodies, thbfe which are rendered
phofphoric with the grcateft difficulty. But even thefe may
be fcattered into a Ihower of red luminous particles by the
ele^lric flroke.

«♦ Norwich, Oct. 7, 1784.

POSTSCRIPT by the Rev. Dr. Price.

BY the phofphork force mentioned in the laft paragraph of
this paper, Mr. Morgan appears to mean, not the force with
which a phofphoric body emits^ but the force with which it
abforbs and reiams light. This laft force is proportioned
to the degree of attradion between the phofphoric body and
light; and therefore muft (as Mr. Morgan obferves) be
weakefl when it emits fo freely the light it has imbibed as not
to retain thofe rays which adhere to it moft ftrongly. Ac-
cording to Mr. Morgan's theory, thefe rays are thofe which

E e 2 ai^

2 1 2 Mr, MoR can's Ohftrtaiiom and Experiments^ &c .
jlre leafl refrangible. The obfervations and experiments hi
this paper feem to render this theory probable. It is, how-
ever, an obje<flion to it, that the lefs refrangibility of rays
feems to inaply a lefs force of attra£lion between them and the
fubftances which refract them ; but it fhould be confidered,.
that, poffibly, the force of cohefion, which unites the rays
of light to bodies j may be a different power from that which
re frails them.

[ 2^3 1

XII. On the ConJlruBion of the Heavens^
By William Herfchel, Efq, F. R. S.

Read February 3, 17B5.

THE fubje£t of the Conftrucllou of the Heavens, on
wh'ch I have fo lately ventured to deliver my thoughts
to this Society, is of fo extenfive and important a nature, that
we cannot exert too much attention in our endeavours to throw
all poffible light upon it ; I fhall, therefore, now attempt
to purfue the delineations of which a faint outline was begun
in my former paper.

By continuing to obferve the heavens with my lafl con-
ftruded, and fnice that tim.e much improved iuftrument, I am
now enabled to bring more confirmation to feveral parts that
were before but weakly fupported, and alfo to offer a few flill
further extended hints, fuch as they prefent themfelves to my
prefent view. But firfl let me mention that, if we w^ouid
hope to make any progrefs in an invelHgation of this delicate
nature, we ought to avoid two oppofite extremes, of which I
can hardly fay which is the moll: dangerous. If we indulge a
fanciful imagination and build worlds of our own, we muft:
not wonder at our going wide from the path of truth and
nature ; but thefe will vanifh like the Cartefian vortices, that
foon gave way when better theories were offered. On the other
hand, if we add obfervation to obfervation, without attempt-
ing to draw not only certain conclufions, but alfo conjectural

views

214' Mr, Herschel on the

views from them, we offend againft the verj end for wlVich
only obfervations ought to be made. I will endeavour to keep
a proper medium ; but if 1 fhould deviate from that, I could
wllh not to fall Into the latter error.

That the milky way is a moft extenfive ftratum of flars of
various fizes admits no longer of the leaft doubt ; and that our
fun is actually one of the heavenly bodies belonging to it is as
evident. I have now viewed and gaged this Ihlning zone in
almoft every dire£llon, and find it compofed of ftars whofc
number, by the account of thefe gages, conftantly increafes
and decreafes in proportion to its apparent brlghtnefs to the
naked eye. But in order to develop the ideas of the univerfe,
that have been fuggefted by my late obfervations, it will be heft
to take the fubjecl from a point of view at a confiderable
diflance both of fpace and of time.

'Theoretical ijiezv.

Let us then fuppofe numbcrlefs ftars of various fizes, fcat-
tered over an indefinite portion of fpace in fuch a manner as to
be almoft equally diftributed throughout the whole. The laws
of attradlon, which no doubt extend to the remotefl regions of
the fixed flars, will operate in fuch a manner as moft probably to
produce the following remarkable effeds. ^

Formation of nebulae.

/V.

Form I. In the firft place, fince we havefuppofed the flars i-
to be of various fizes, it will frequently happen that a ftar, ;
being confiderably larger than its neighbouring ones, will
attrad them more than they will be attraded by others that are

immediately

CotifiruclioTi of the HeaVtns. 2 1 5

immediately around them ; by which means they will be, hi
time, as it were, condenfed about a center ; or, in other words,
form themfelves into a clufter of flars of almoft a globular
figure, more or lefs regularly fo, according to the fize and
original diftance of the furroundiPig ftars. The perturbations
of thefe mutual attraflions mufl: undoubtedly be very intricate,
as we may eafily comprehend by conflderlng what Sir Isaac
Newton fays in the firfl: book of his Principla, in the 38th
and folio .vlng problems; but in order to apply this great
author's reafonlng of bodies moving in ellipfes to fuch as are
here, for a while, fuppofed to have no other motion than what
their mutual gravity has imparted to them, we muil: fuppofe
the conjugate axes of thefe ellipfes indefinitely diminilhed,
whereby the ellipfes will become flralght lines.

Form II. The next cafe, which will alfo happen almoft as
frequently as the former, is where a few ftars, though not
fuperlor in fize to the reft, may chance to be rather nearer each
other than the furrounding ones j for here alfo will be formed a
prevailing attraction in the combined center of gravity of them
all, which will occafion the neighbouring ftars to draw toge-
ther ; not indeed fo as to form a regular or globular figure, but
however in fuch a manner as to be condenfed towards the
common center of gravity of the whole irregular clufter. And
this conftruClion admits of the utmoft variety of fhapes, ac-
cording to the number and fituation of the ftars which firft
g-ave rife to the condenfation of the reft.

Form III. From the compofition and repeated conjun£tloit
of both the foregoing forms, a third may be derived, when many
large ftars, or combined fmall ones, are fituated in long ex-
tended, regular, or crooked rows, hooks, or branches ; for they
will alfo draw the furrounding ones, fo as to produce figures

of

2! 6 Mr, Herschel on the

of condenfed flars coarfely fimilar to tlie former which gav^c
rife to thefe condenfations.

Form IV. We may Hkewife admit of flill more extenfivc
combinations ; when, at the fame time that a clufter of flars
is forming in one part of fpace, there may be another colied-
. ing4n a different, but perhaps not far diftant quarter, which
may occafion a mutual approach towards ti^eir common center
of gravity .>

V. In the lafl: place, as- a natural confequence of the

former cafes, there will be formed great cavities or vacancies;
by the retreat of the ftars towards the various centers which
attra£l them ; fo that upon the whole there is evidently a field
of the greatefl variety for the mutual and combined attractions
of the heavenly bodies to exert themfelves in. I Ihali, there-
fore, without extending myfelf farther upon this fubjedl, pro-
ceed to a few confiderations, that will naturally occur to every
one who may view this fubje£l in the light I have here done,

Oh'je^wns conjldered^

Atfiril: fight then it will feem as if a fyftem, fuch as it has|
been difplayed in the foregoing paragraphs, would evidently
tend to a general deftrudion, by the fiiock of one flars
falling upon another. It would here be a fufficient anfwer to
fay, that if obfervation iliould prove this really to be the
fyftem of the univerfe, there is no doubt but that the great
Author of it has amply provided for the prefervation of the
whole, though it fhould not appear to us in what manner this
is effected. But I (hall moreover point out feveral circum-
ilances that do manifeflly tend to a general prefervation ; as, 'in *
i the firft place, the indefinite extent of the fidereal heavens,

.6 which

Conftruciion of the l-leavsm. , 21 y

which, mufl: produce a balance that will efietlually fecure all
the great parts of the whole from approaching to each other.
There remauis then only to fee how tlie particular ftars be-
longing to feparate clufters will be preferved from rufhing on
to their centers of attradlion. And here I muft obferve, that
thougli I have before, by way of rendering the cafe more fim-
ple, confidered the flails as being originally at reft, I intended
not to exclude projectile forces ; and the admiflion of them
will prove fuch a barrier againfl the feeming deftrutStive power
of attraction as to fecure from it all the flars belonging to a
clufter, if not for ever, at leaft for millions of ages. Befides,
we ought perhaps to look upon fuch cluflers, and the deftruc-
tion of now and then a ftar, in fome thoufands of ages, as
perhaps the very means by which the whole is preferved and
renewed. Thefe clufters may be the L^/^orj/(?r/Vjof theuniverfe,
if I may fo exprefs myfelf, wherein the mofl falutary remedies
for the decay of the whole are prepared.

Optica/ appearances.

From this theoretical view of the heavens, which has been
taken, as we obferved, from a point not lefs difliant in time

. than in fpace, we will now retreat to our own retired fliation,
in one of the planets, attending a ftar in its great combination

; with numberlefs others ; and in order to invefligate what will
be the appearances from this contracted fituation, let us begin
with" the naked eye. The ftars of the firft magnitude being
in all probability the neareft, will furnifli us with a ftep to
begin our fcale ; fetting off, therefore, with the diftance of
Sirius or ArCturus, for inftance, as unity, we will at pre fen t
fuppofe, that thofe of the fecond magnitude are at double, and
Vol. LXXV. F f thofe

2.B . Mr, Herschel on the

thofe of the third at treble the diftance, and fo forth. It is liot
necelTary critically to examiue what quantity of light or mag^
nitude of a ftar ititltles it to be eftimated of fuch or fuch a pro-
portional diftance, as the common coarfe eftimation will anfwer
our prefent purpofe as well ; taking it then for granted, that a
]ftar of the feventh magnitude is about feven times as far as
one of the firfl, it follows, that an obferver, who is inclofed
in a globular clufler of flars, and not far from the center, will
never be able, with the naked eye, to fee to the end of it : fof",
fince, according to the above efliimations, he can only extend his
view to about feven times the diflance of Sirius, it cannot be
expe6ted that his eyes fhould r^ach the borders of a clufter
which has perhaps not lefs than fifty ftars in depth every whefe
around him. The whole univerfe, therefore, to him will be
comprifed in a fet of conflellations, richly ornamented with
fcattered flars of ail fizes. Or if the united brightnefs of a
neighbouring clufler of ftars (hould, in a remarkable clear
night, reach his fight, it will put on the appearance of a finall,
faint, whitifli, nebulous cloud, not to be perceived without
the greatefl attention. To pafs by other fituations, let him
be placed in a much extended ftratum, or branching cluflrer of
millions of flars, fuch as may fall under the III"^ form of ne-
bulae confidered in a foregoing paragraph. Here alfo the hea-
vens will not only be richly fcattered over with brilliant con-
flellations, but a fhining zone or milky way will be perceived
to furround the whole fphere of the heavens, owing to the
combined light of thofe ftars which are too fmall, that is, t<Jo
remote to be feen. Our obferver's fight will be fo Confined,
that he will imagine this fingle colledlon of ftars, of which be
does not even perceive the thoufandth part, to be the whde
contents of the heavens. Allowing hini now the ufe of a
4 common

Conjlruciton of the Heavens, 2 1 9

common telefcope, he begins to fufped that all the milkinefs
of the bright path which furrounds the fphere may be owing
to ftars. He perceives a few clufters of them in various parts
of the heavens, and finds alfo that there are a kind of nebu-
lous patches ; but ftill his views are not extended fo far as to
reach to the end of the ftratum in which he is fituated, fo that
he looks upon thefe patches as belonging to that fyflem which
to him feems to comprehend every celeftial obje£l. He now
mcreafes his power of vifion, and, applying himfelf to a clofe
obfervatlon, finds that the milky way is indeed no other than a
qolle5:ion of very fmall flars. He perceives that thofe objects
which had been called nebulae are evidently nothing but clufters
of ftars. He finds their number increafe upon him, and when
he refolves one iiebula into ftars he difcovers ten new ones
which he cannot refolve, He then forms the idea of immenfe
ftrata of fixed flars, of clufters of ftars and of nebula (^) ; till^
going on with fuch interefting obfervations, he now perceives
that all thefe appearances muft naturally arife from the con-
fined fituation in which we are placed* Confined it mayjuftly
be called J though in no lefs a fpace than what before appeared
to be the whole region of the fixed ftars ; but which now has
affumed the fhape of a crookedly branching nebula ; not, in-
deed, one of the leaft, but perhaps very far from being the
moft confiderable of thofe numberlefs clufters that enter into
the conftrudiou of the heaven s*

"Result of Obfervaiionsk

1 (hall now endeavour to fhew, that the theoretical view of
the fyftem of the nniverfe, which has been expofed in the
(tf) See a former paper 00 the Conftrudion of the Heavens.

F f 2 fore*

I

zio A/r. Kersckel ofi the ■

ibregoiiig part of -this paper, is perfe6lly confident with fads,
and feems to be confiimed and eflabliflied by a feries of obfer-
vations. It Vv'ill appear, that many hundreds of nebulae of the
firft and fecond forms are adually to be (e.Qii in the heavens,'
and their phices will hereafter be pointed out. Many of the
third form will be defcribed, and inftances of the fourth re-
lated. A few of the cavities mentioned in the fifth will be
particularifed, though many more have already been obferved ;'
lb that, upon the whole, I believe, it will be found, that the
foregoing theoretical view, with all its confequentlal appear-'
ances, as leen by an eye inclofed in one of the nebulae, is no
other than a drawing from nature, wherein the features of the'
original have been clofely copied ; and 1 hope the refemblance'
will not be called a bad one, when it fhall be confidcred how-
very limited muft be the pencil of an inhabitant of fo fmalF
and retired a portion of an indefinite fyftem in attempting the
picture of fo unbounded an extent.

But to proceed to particulars : I fhall begin by giving the
following table of gages that have been taken. In the firft
column is the right afcenfion, and in the fecond the north ■
polar diftance, both reduced to the time of Flamsteed's
Catalogue. In the third are the contents of the heavens, being
the refult of the gages. The fourth fhews from how many'
fields of view the gages were deduced, which have been ten or
more where the number of the flars was not very confiderable ;'
but, as it would have taken too much time, in high numbers,
to count fo many fields, the gages are generally fingle. Where
the ftars happened to be uncommonly crouded, no more than
half a field was counted, and even fometimes only a quadrant ;
but then it was always done with the precaution of fixing 01:1 '■
fome row of ftars that would point out the divifioa of the field,

fo

ConJiriiBion of the He\i'^ens, iii

fo as to prevent any confiderabie miftake. When five, ten, or
more fields are gaged, the polar diftance in the fecond column
of the table is that of the middle of the fweep, which was
generally from 2 to 2f degrees in breadth; and, in gaging, a
regular diftribution of the fields, from the bottom of the fweep
to the top, was always ftridlly attended to. The fifth column,
contains occafional remarks relating to the gages.

I. Table of Star-Gages.

R.A.

P.D.

Stars.

Fields.

Memorandums.

.

H. M. S

D. M.

0 I 41

78 47

9.9

10

0 4 55

65 36

20,0

10

0 7 54

74 13

"'3

10

Meft of the ftars extremely fraall.

0 8 24

49 7

60

I

0 9 52

113 17

4>i

10

% The gages marked with an afterlfk

0 12 52

113 17

3>2

10

^ are thofe by which, fig. 4.

tab.

0 16 48

67 44

11,9

10

VIII. has been delineated

0 21 52

113 17

3.9

10

^

0 22 21

87 10

5,9

10

0 28 26

46 54

60

I

0 31 38

46 54

40

I

0 33 33

65 32

20,4

10

0 34 22

56 38

20

I

, 0 35 22

55 38

24

I

_

' 0 36 39

76 32

11,3

10

0 39 56

78 43

8,1

10

0 40 29

48 43

60

2

0 44 21

87 10

7»^

10

0 46 22

69 51

II

10

, 0 46 33

65 32

13

10

'

• 0 48 42

5847

40

I

^ 0 48 50

58 13

17

I

. 0 53 18

67 41

9,8

10

A little hazy.

0 53 40

45 37

73

I

Q, 54r 10

75 16

13

I

IvoA.

222

Mr* Hehschel on the

R.A.

P.D.

Stars.

Fields.

Memorandums.

H. M. S.

D. M.

o 55 lo

73 16

14

I

o 56 4

74 0

15

I

0 57 52

113 17

3»8

10

ii-

0 59 10

74 25

14

I

I 0 16

74 16

II, I

10

I I 10

74 5

11,2

10

- r ■ 1 1- II

I I 18

III 0

5»2

10

Very clear for this altitude.

I 2 52

52 0

28,1

10

Moll of the ftars very fmall*

I 3 52

113 17

2,8

10

^

I 4 15

94 52

7»5

10

I 4 33

65 32

11,0

10

I 5 55

78 3t

9,2

10

I 7 27

45 23

58

I

'

I 12 0

58 37

20

I

1 12 48

to 19

»i

I

I 13 4

94 50

6,3

10

I 15 51

48 40

30

I

I 18 21

48 40

58

I

I 23 21

48 40

44

I

I 27 JO

65 42

12,9

10

<

I 31 21

87 7

5,8

10

•I 32 4

94 50

Z'^

10

1 33 i^

100 8

6,4

10

i

I 33 32

92 35

7,1

10

ir

I 34 52

60 8

17

I

I 43 30

65 42

14,4

10

I 45 24

69 43

7,1

10

I 48 4

100 12

4,9

10

I 54 24

76 28

12,1

10

i ^

I 58 55

61 55

15,0

10

2 4 28

87 5

6,4

10

J

2 4 36

78 38

9'3

10

2 7 12

94 56

7.8

10

'

i

280
2 10 4

83 3

7.3

10

\

100 12

4.3

10

iviA*

ConJiruBton of the Heavens*

223

R.A.

P.D.

Stars.

Fields.

Memorandums.

H. M. S.

D. M.

2 II 30

65 45

14,8

10

2 16 27

no 54

4.2

10

"^

2 19 27

76 24

o9'9

10

2 22 17

45 31

82

I

2 23 6

60 i6

14

I

2 23 19

113 8

4»2

10

^

2 24 6

58 30

15

I

2 27 40

115 21

3>o

10

% The fituationtoo low for great accu-

2 30 0

94 56

6

10

racy.

2 31 23

76 22

i3>8

10

2 35 14

87 2

5,6

10

2 38 0

94 56

6,6

10

2 42 7

61 50

14,8

10

2 47 32

74 3

II, I

10

Moft of the ftars exceedingly fmall.

2 49 22

92 55

9»o

10

2 49 30

no 55

6,1

10

%

2 50 0

94 56

6,8

lO

2 54 53

76 22

9.2

10

2 59 56

81 10

6,1

10

3 I 53

78 37

4»i

10

3 I 56

81 10

5,1

10

3 4 53

78 37

3»5

10

3 10 20

100 2

6,8

10

3 II 6

59 29

7»o

5

■J In a part of the heavens which looks

3 13 6

59 29

6,1

10

pretty full of flars to the naked

3 15 6

59 29

9'4

10

eye.

3 22 57

83 I

10,3

10

3 23 21

92 49

10,1

10

3 29 41

46 35

55

I

3 35 0

62 I

15

I

About I5:fi:ars generally in the field.

3 35 12

100 3

7,4

10

3 3^ I

"3 3

4,9

10

•^

3 42 49

46 10

54

I

3 48 16

99 59

8,1

10

^i^, "

74 2

11,0

\

R.A.

.224

Mr. Hbrschel on the

R.A.

F.D.

Stars.

Fitlds.

Memorandu»r-s.

"■~H. M' S.

D. M.

,

4 I 24

92 48

13,8

10

4 6 18

82 57

13,4

10

4 « 3^

iH 55

4,2

10

■H-

4 ^2 41

69 33

J5'3

10

And many more, extremely fniall,

4 i(^ 34

112 45

6,2

10

# fufpefted.

4 26 34

112 45

8,8"

10

%

4 27 11

70 41

25

I

4 28 41

7a I

17

.T

4 29 5

69 24

30

I

4 30 14

99 50

9'7

10

4 31 ^9

67 33

15.6

10

4 32 29

69 2

3^

I

4 33 31

114 55

8,1

10

■if-

4 42-14

86 ^7

i9>9

10

4 53 22

72 59

5t)

I

4 57 45

.83 22

38 ■

I

4 58 45

84 36

35

I

5 I 16

69 23

34

I

5 3 45

83 29

17,7

6

5 10 52

69 22

74

I

5 II 22

96 37

24

I

5 17 22

96 15

8,9

8

5 18 0

80 46

30

I

About 30 ftars in the field, not very

:5 21. 7 ;

92 52

19,1

10

exadly gaged.

5 24 1 2

66 5

36

I

5 27 3

68 52

58

I

5 27 48

1 10 40

17.7

10

^

5 33 4

76 10

65

I

5 33 12

66 26

86

I

5 3'3^7,;

iH 59

i3'5

10

^

5 34 45

70 33

50

I

5 36 30

62 I

20—30

From |20 to 3D flars in the fields, not

5 37 4

74 26

140

\

very exadly gaged.

5 38 45

70 8

73

1

5 41 12

66 43

60

I

R.A.

ConJlruHion of the Heavens.

225

R.A.

?.D.

Stars.

Fields.

Memorandums.

H. M. S.

D. M.

5 44 0

116 43

11:5

10

^

5 45 3^^

83 30

50

5 47 34

112 34

i9'3

10

^

5 4B 30

62 I

30

About 30 ftars in the field; not very

' 5 48 44

92 51

22,4

exactly gaged.

5 49 0

80 5

50

1

5 52 H

Q3 14

44

i

5 52 30

83 30

60

1

5 53 0

80 5

no

5 55 4

92 56

57

5 56 40

70 27

73

I

5 57 0

80 5

60

5 57 37

1 10 33

19,6

10

^

5 58 51

88 36

90

5 59 30

83 30

80

6 0 23

86 38

24,1

10

6 I 0

80 5

70

640

80 5

90

654

67 17

120

Very unequally fcattered.

6 6 14

96 16

52

6 6 30

83 30

80

6 6 30

80 5

70

6 6 38

91 4i

54

Like the reft, or many fuch fields.

6 6 40

68 24

56

690

80 5

74

6 9 34

"3 35

26

%

6 II 0

62 I

30—40

Between.

6 II 0

80 5

63

The leaft number of ftars in the field I

6 II 34

112 5

32>

■^ could find in this neighbourhood.

6 II 37

90 15

About 60 or 70 generally.

6 14 4

68 II

178

6 14 38

90 15

77

6 17 45

62 I

50

6 18 14

96 12

38

Very unequally fcattered.

6 ig 14

9^ 59 72

VcL. LXXV.

g

R.A.

*♦ 26

«M <>rf *»^

Mr, Herschfl on the

K.A.

!M).

Stars.

Fields.

McmoraiicluiTis.

H. l\\, b.

D. M.

6 26 17

iH 59

15.9

10

6 27 14

c4 3^

132

I

7.

^

6 27 3^

70 23

53

I

6 31 48

ii5 40

40

I

6 34. 44

92 25

94

I

- t

6 34 5 5

79 5

50

I

Genernlly about 50 ftars.

6 36 0

94 5^

02

I

Twilight.

6 37 15

75 5

70

I

Generally about 70 ftars-.

6 39 8

99 7

50

I

%

6 40 0

116 43

3^3

10

■

1 "

6 43 25

79 5

67

I

6 44 28

ICO 30

^^7

I

^

^ 49 5

87 21

120

I

^

6 49 30

77 3^

50

I

Many fields like this, ■ !

6 49 44
6 51 8

92 Z'l

120

98 33

/B

1

■)(•

6 52 0

116 2J

48

I

:

6 52 25

79 5

Go

I

About 60 ftars,.

6 52 44

92 59

u8

J"

I

6 54 9

III II

45

I

^

6 57 8

100 I

34

I

-;f

6 57 38

98 50

83

I

% \

6 5S 39

112 48

81

I

% !

7 0 25

79 5

70

1

-■

7 4 0

92 3

102

1

I

■ii-

7 4 38

98 59

70

1

%

7 5 9

III 11

70

I

^

7 8 9

112 15

(?2

I

#

7 12 8

100 5

118

I
2

^ 1

7 15 38

98 12

I 12

I
2

■ 7 19 0

91 5^

58

I

^

7 20 0

/S 59

48

I

•

7 25 9

III 21

168

I

A-

^ One of the richeft fields.. J

7 28 9

112 34

2C4

I

% A field like the reft. 1

1 7 3^ 3

1 15 28

86

I

T

R.A.

Conjlrudfhn of the Heavens,

227

R.A-.

P.D.

Stars.

Fields.

Memorandums.

H. M. S.

D. M.

7 41 9

1 13 26

108

1

2

^

7 53 4

86 39

28,3

10

%

8 I 4

III 15

b'o

^

8 3 4

113 31

66

8 6 38

100 5

40

8 7 3S

99 3

45

^

-

b II 8

99 25

2A,2

10

^

8 12 34

112 I <;

52

^

8 22 4

III 30

35

^

8 31 4

112 I

33

8 32 24

112 7

30

8 35 4

112 17

24

8 35 14

III 19

20

8 40 4

III II

22

^

8 45 4

113 22

13

8 46 39

91 26

20,3

10

^

8 48 4

112 23

16,2

10

8 57 25

66 20

8,3

10

^

9 5 38

91 22

13,8

10

i(-

9 10 4

115 17

14,0

10

9 20 4

112 23

15.8

10

9 20 40

99 12

II, I

10

9 20 58

88 7

11,5

10

#

9 35 4

112 23

13,0

10

9 38 4

115 17

10,1

10

9 38 8

90 23

7'9

10

^

9 42 16

86 16

7,7

10

^

9 45 49

112 21

1?.2

10

Strong twilight.

10 0 4

115 17

9'i

10

10 16 8 ■

88 8

7.2

10

■X-

10 19 32

91 14

6,5

10

lO 25 8

88 8

4,9

10

^

10 26 0

81 41

5,6

7

^

.

.11 4 4

81 38

5,3

6

^

II 7 36

91 14

5,6

10

G g

l>-o/l«

Mr* Herschel on the

RA.

P.P.

Srars.

Fields.

Memorandums.

H. M. S.

D. M.

1 1 1 o 6

1^5 23

6,S

10

Twilight,

II i6 s^

Si 38

0 1

8

^

11 ;.c 37

91 17

4,9

10

11 53 43

81 39

6,0

5

'X-

12 c 6

78 57

2,2

^3

-^

12 30 40

79 3

3-4

1 1

if-

' ii 4'J S^

81 40

4,6

13

■X-

12 48 19

79 4

3'9

13

i^

12 53 45

loi 45

9'3

10

T'.vilight.

12 57 B

99 5^

8,1

10
12

Pretty itrong day-light.

13 I 19

79 4

3^8

Twilight.

i ^3 17 27

101 45

8,6

JO

! 13 22 4)

ICO I

8,4

10

Some day-light.

i 13 27 57

loi 45

Ho

10

13 31 )0

75 55

5-6

I

A~ Generally about 5or 6ftars in the field. 1

13 38 53

104 27

8,5

10

' 13 48 49

100 1

9,2

10

Strong twilight.

13 51 27

iOl 45

10,0

10

13 55 44

58 II

7.4

10

^ Twilight.

13 57 53

104 27

12,3

10

JMoft very fmall.

14 9 49

100 I

11,2

10

Twilight.

J4 13 52

113 4

9'7

10

14 14 57

101 45

8,8

10

14 24 49

81 5^>

2,7

6

14 29 45

100 5

^3^3

10

14 30 7

66 3

8,8

10

■X- All lizes. -

14 30 8

So 38

3-5

13

14 33 22

58 7

^,9

10

:)f Chiefly fmall.

H 33 52

H3 4

10,3

10

1

H 39 57

lOi 45

14,0

10

All fizes. '

14 40 36

64 47

6,4

10

14 44 II

114 54

10,3

10

14 49 52

113 4

12,8

10

I

14 51 14

58 10

9,2

10

Jf Twilight. 1
■X- Strong Avirora'borealis.

14 52 58

60 41

4,4-

10

R.A.

-$'\

ConJlruBion of the Heavens,

R.A.

P.D.

Stars.

Fields.

>]cmoranduins.

H. M. S.

D. M.

1

H 53 7

65 15

9,0

10

Chiefly large.

H 55 30

64 47

0,6

10

Moil very iraalL

M- S'-> II

114 5^

8,8

10

15 2 42

62 a8

8^^

10

15 3 7

66 15

9>5

JO

15 4 i''

64 47

5^0

10

15 ^ 37

113 0

14,1

10

K

!:» 8 45

9^ 5

9'4

1 2

Very feali.

5 13 4^

02 48

8,9

10

ij 15 44

S8 17

10,0

10

^ Twilight.

15 19 n^3

60 40

4>9

10

■^ Strong Aurora borealis, fo as

toaflVfr

13 20 0

75 52

9,5

4

the gages.

15 2 1 0

93 5

10,9

12

15 26 7

^i 53

1 1,0

5

15 0.3 48

99 51

i3'i

10

15 29 7

66 15

10,6

10

A!l fizes.

13 29 44

58 17

8,9

10

^ Twilight.

■5 32 0

75 51

6

6

■

15 33 52

HI 32

12,8

10

15 35 0

75 51

fc,5

6

15 42 2

58 14

13,1

10

% Twilight.

15 42 3

116 56

18,6

10

15 42 53

113 47

32,5

2

The ftars too fmall for the gage,

15 46 30

93 5

10,8

J2

15 48 37

113 0

i7>i

10

15 48 46

63 4

12,4

io

15 49 52

III 32

18,1

10

The fit nation 10 low that it

requires

i 15 50 20

iM 55

9,2

20

attention to fee the llara.

15 57 3

116 56

7'2

10

i5 0 2

58 14

12,2

10

^ Twilight.

16 0 3

116 56

6,1

10

16 0 12

"4 5.7

1,6

10

16 3 12

iH 57

2,0

10

16 4 0

75 43

^3

6

All fizes.

16 4 IQ

113 6

'5

10

Perfeaiy clear. See p, 256.

K.A-

230

Mr. Herschel on the

R.A.

P.D.

Stars.

Fields.

iMeinorandums.

H. Ai. S.

D. M.

it> 4 46

63 4

12,0

10

Moil frnall.

16 4 52

99 SI

14,6

10

Moon and twilight.

16 6 28

113 4

.7

10

Perfect!)- clear.

16 7 12

bb IS

130

10

16 rf 6

. ■ ■ Ml'

US 1

3>^

6

16 8 II

93 9

12,2

12

16 8 16

1 16 48

11,6

10

16 9 28

113 4

1,1

10

Perfectly clear. See p. 256.

16 u 28

113 4

1.4

10

The fame.

16 13 28

113 4

1,8

10

g Serpen tarii and 19 Scorpii

vifible to

16 13 52

58 24

14,2

10

-X- Moil fmall. [the

naked eye.

16 14 42

^3 7

15,1

10

Moll verv fmall.

16 15 37

80 40

9.7

12

All fizes.

16 17 28

"3 4

4,7

10

16 20 51

81 57

13,8

6

I

16 23 0

73 '43

24

I

16 23 28

"3 4

13,6

10

16 24 II

93 9

13,6

12

Require attention to he feen.

16 25 7

80 40

14,6

n

16 27 32

68 23

21,6

10

Twilight.

16 29 16

116 48

5o»4

10

16 30 37

80 40

34

I

16 31 12

66 15

18,4

10

Strong twilight.

16 32 28

"3 4

20,3

iO

Moftextrem-ely fmall.

16 32 52

58 24

15,^

10

•^ Moll fmall.

16 35 42

63 7

16,5

10

-^

16 35 48

93 15

18,6 .

12

All fizes.

16 38 12

6b 15

20,1

10

Strong twilight.

16 38 45

107 57

i9'9

10

Strong twilight.

16 40 51

113 14

41,1

8

16 45 32

68 23

19,0

4

Hazy.

16 51 45

107 57

29,8

10

16 52 22

66 26

16,6

10

Day-light pretty flrong.

16 55 42

63 7

26,6

10

^ Strong tv.'ilight.

17 I 34

58 II

18,8

10

^ Strong day light.

1*.

R.A»

ConJlru5llon of the Heavens.

R.A.

P.D.

^tars.

Fields 1

IMcniorandums,

H. M. S.

D. M.

1

17 3 22

66 26

35

1

Jf Lav-ligl-.t too flrcng for gaging.

17 6 36

98 38

13.7

10

iVIoft I'mall, aad more iujpected.

17 9 30

"^ 55

7,(>

10

17 9 32

68 23

32-3

10

17 11 10

66 2&

38

1

^ Dny-Iight pretty ftrong.

17 13 24

63 21

32,8

10

■^ otrong day-light.

17 17 36

III 47

i5v3

10

ivlcon and day-light.

17 25 7

108 5

23.

10

17 27 29

116 48

25

i

17 28 32

68 23

42,2

5

# Twilight.

17 30 29

116 48

42

I

17 33 29

116 48

52

I

Day-light very ftrong.

17 34 3^

98 38

18,5

10

Very ftrong twilight.

17 39 34

120 0

84

I

MoIT: large.

17 40 41

114 52

77

I

Day-light very ftrong.

17 41 29

116 48

82

I

Day- light very ftrong.

17 43 45

105 S

80

I

Flying clouds.

17 48 0

61 18

25,6

5

Mcft large.

17 50 4

56 16

27,2

10

Twilight.

17 50 7

108 5

59

I

Like the reft in this part of the heaven.

' 17 52 7

• 108 5

118

I

Many fuch fields juft by.

17 52 17

98 43

7,6

10

17 52 30

62 12

40

I

Mo ft large.

17 52 32

68 19

54

I

■^ Strong day-light.

17 55 7

108 5

2?2
*" »j "^

I

z

17 55 15

106 6

112

I

Many fuch fields.

17 55 3«

112 54

112

I

2

17 57 30

60 28

38

I

Moft large.

17 58 37

103 24

35

I

17 58 41

ii8 57

64

I

17 58 49

122 17

17

I

17 59 I

108 8

320

I
2

^ 59 19

104 24

68

I

18 0 13

122 II

27

I

18 3 49

120 42

19

I
g ■

K.» A«

•5^

Mr. Herschel on the

R.A. .

P.D.

Stars.

Fields.

Memorandums.

H. M. S

D. M.

iS 5 17

98 47

65

I

18 0 37

90 35

9>4

10

Too foon for gaging, not having been

i3 7 4

62 14

40

I

Moll: large. J long enough out '

Lin the dark.

18 7 4

56 16

38,2

5

18 7 37

103 25

88,0

0

18 10 7

120 58

20

I

iB 10 52

61 8 78

J

Chiefly large.

18 II 49

104 6 170

I
2

'8 13 37

104 16

238

i.
2

"

i^ 13 52

93 i^

2,0

7

1 8 14 46

56 20

48

I

18 J5 28

92 42

3.4

7

18 16 52

92 42

8,9

7

18 18 40

92 42

13,8

7

18 19 37

102 34

9.5

2

18 20 7

103 18

19

18 20 46

92 42

25,8

b

18 21 I

103 55

22

18 21 12

90 41

8,6

10

rS 21 31

103 36

24

18 22 4

62 7

48

Large and fmall.

18 22 4

56 16

39.6

18 22 19

104 6

H

18 22 37

103 45

30

18 24 3

115 10

35

18 24 4

109 35

Twilight, L

18 24 7

102 31

30

18 24 iO

92 59

88

18 24 43

103 39

25

18 25 37

102 34

39

18 26 17

9S 3

1 1 1

18 26 25

103 57

60

18 26 47

97 43

250

18 27 I

120 58

30

'8 27 55

120 44

32

R.A.

ConJlru6lion of the Heavens,

23

R.A.

P.D,

Stars.

Fields.

Memorandums,

H. M. S
18 28 7
18 28 8
18 28 25
18 28 37
18 29 25

D. M-

102 51
91 44

103 9
122 25
103 24

»3

39

20

12

20

I
I

I
I
I

Extremely fmall,
Moft fmall.
Extremely fmall.

Extremely fmall.

18 29 47
18 29 49
18 30 34
18 31 10
18 31 10

97 50
121 39

57 18

92 42
108 53

»5o

24

62

13.7

74

I
I
I

7

I

Twilight,

18 31 13
18 31 17
18 31 34
18 31 49

18 33 4

103 19

97 53

62 34

121 39

108 43

112

188
76

i9»3

88

I

I
2

I

10

I

All fizes.

Many more fufpecled,
•*. Large and fmall.

Twilight,

18 33 7
18 34 5
18 34 47
18 34 58
18 36 34

103 53

98 34

71 53
60 41

no 12

146

130

78

80

83

I
2

I

I
I
I

Large and fmall.
Twilight.

1

18 36 34
18 36 47
18 37 34
18 38 I

18 39 40

91 37

72 28

93 29

104 14

93 52

176
224

5
118

116

I

r
2

I

X
2

I

4-

^

18 40 28
18 40 47
18 41 22
18 42 49
18 43 17

92 47

71 48

91 37
121 39

72 8

10
236
156

I5»2

368

I

1

I
4

10

I
4

-
Very clear for this altitude.

18 43 33
18 44 34
18 44 34
18 47 32
18 48 4

1 19 21

112 43

60 34

91 14

1 10 12

21

53

84

328

83

I
I

I

5

>

All fizes,

.• i ■> ' »■ -

VcL. LXXV.

Hh

R.A.

23-

Mr, Herschel on the

R.A.

P.D.

Stars. !

Fields.

rvleinorandums.

H. M. S.

D. M.

ri

i8 50 16

60 55

136

T
1

Many of them fmall.

J

18 51 4

57 '^^

84

I

r 1

18 51 32

108 26

36,8

5

Strong twilight.

18 52 49

115 30

26,2

18 54 4

57 18

93

I

I

4

-

18 54 8

91 14

328

i8 54 55

104 23

180

I
2

-

18 55 4

108 41

80

I

18 55 16

62 31

206

I
2

18 59 8

91 14

328

X

4

18 59 26

72 37

40

I

Too foon for gaging.

1

1912

71 40

75

1

«

19 I 34

5^ 47

127

I

Moonlight.

nk

19 2 29

74 Sl>

204

I

4-

^ Twilight.

.1

19 2 37

103 i5

160

I
2

1

19 2 49

121 39

' 14.1

10

■

19 3 34

55 56

146

I
2

D

■

19 6 34

61 8

196

1
2

And many fmall befides.

1

19 7 34

56 56

130

I

2

D

i

19 7 52

57 59

116

I

2

^

19 8 38

92 8

120

I
2

19 9 37

109 I

60

I

"i

19 9 40

5^ 51

130

I

B' '^ ~

19 12 59

75 21

58

I

^

19 13 50

59 59

256

I
4

19 13 52

59 29

158

I
2

19 14 2

72 15

60

I

^

19 14 4

61 21

279

I
3

Too crowded for accuracy.

^ '^j

19 H 55

103 36

64

I

Changeable focus.

t

19 15 40

55 26

160

I

D bright.

19 16 50

60 43

296

I
4-

b

19 16 59

7^ 23

5^

I

#

n

19 17 44

108 12

50

I

r|

19 18 23

78 9

196

1
4-

:f

19 18 28

61 21

279

I
3

' 1

R,A<

ConJlruBlon of the Hea^dens^

n '^ •'

R.A.

P.D.

Stars.

Fields.

Memorandums.

H. M. S.
19 19 52

^ 19 19 56
19 20 51

19 21 I

19 21 34

D. M.

57 H
108 12

60 55

78 47

55 17

180

55

384

472

208

r
2

I

I

A-

I

I

2

•3f
D bright.

19 22 27
19 24 36

19 24 49
19 24 50

19 24 53

62 29

56 49

104 24
60 43

"3 SI

320

224

36
296
18,3

I
I
4-

I
I
4-

10

Changeable focus.

1

19 25 4
19 25 16
19 25 22
19 25 37
19 27 36

57 9
64 18

59 3^
103 50

72 34

190

280

340

55
424

I
1

I

I
4-

]) bright.

Changeable focus.
■^ Too fmall and tod crowded to be cer-

19 27 44
19 28 I
19 28 6
19 28 52
19 28 52

61 8

103 30
56 49
59 26
5^ 47

240

45
288

344
186

r
3

I
I

t

[tain of the nuaiber.
Changeable focus. ^

J very bright.

19 29 46
19 30 36
19 30 36

19 31 33
19 32 9

65 10

74 Z^

54 53

92 34
109 44

34
588

312

62,2
23,8

I

I

I

5

10

19 32 15

^9 Z3 4

19 33 7

19 33 14
19 33 20

62 35

55 34

103 12

61 8
S8 59

296
212

50
240

232

I

4-

r
2

I
I
3

I

A-

1

Changeable focus.

19 34 51

19 35 34
19 36 6

19 36 37
19 36 50

"5 44
63 19

54 57
102 31

60 35

14,1
256

384

68

296

10

I

4.
I
-J-

I

I

4-

■
Ciiangeable focus.

Hh

JVtile

2j6

Mr. Herschel on the

R.A.

P.D.

Stars.

Fields.

Memorandums.

H. M. S.

D. M.

iQ 40 33

63 0

296

I

4

19 40 46

59 12

192

4-

19 40 48

74 '33

588

I

A-

:¥•

19 42 ?>2>

73 ^4

'' C ")

'•i

:)f

19 43 30
59 43 56

57 23

130

I
2

D

64 27

124

I
2

i\Ioli large.

19 45 3^

77 5«

140

1
2

:;f i'aint D .

19 45 37

103 3

50

1

:■

19 46 21

73 H

-.52

I

4

^

19 46 51

115 44

12,8

10

Strong twilight.

19 47 8

60 35

312

I

19 47 18

109 46

20,9

10

19 47 22

57 38

312

I
4-

Very unequally fcattered.

19 49 6

57 13

268

I

4

19 49 48

56 s^

120

I
2

D

19 50 5

V- 39

39'2

5

% Moll fmall.

19 51 37

62 37

51

1

4

19 52 0

57 15

220

1

1

D

%

19 53 I

60 36

80

1

19 53 28

63 40

52

2

' i

19 53 40

54 59

306

I

4

I

19 S3 49

121 39

7,7

10

1

19 54 0

55 12

i6o

r
2

D

^

19 54 12

7« 3

120

I
2

% Faint D .

19 54 22

59 5«

136

I

4

19 55 7

62 41

48

1

^

19 56 19

60 44

112

r
•7

19 56 22

57 17

192

i

4

k

19 57 19

62 34

45

1

f:

19 57 40

58 29

104

I
2

itj

19 59 49

62 37

41

I

20 0 21

79 3

56

I

•Jf Strong D .

20 0 24

55 12

184

I
2

»

20 0 25

60 33

80

I

Moft of the ftars extremely fmall.

20 0 51

liq 44

12,2

10

Twilight.

K..A>»

Conjlru^lhn of the Heavens,

•37

R.A-.

P.D.

Stars.

Fields.

Memorandums.

H. M. S.

D. M.

20 I 39

79 34

68

I

•^ Strong ]) .

20 5 26

5^ 34

46

I

D

20 5 27

72 56

280

I

4

1

20 6 23

107 27

22,6

10

20 6 43

62 32

75

I

Many fmall.

20 8 26

56 27

^7.4

5

D

20 8 27

72 56

2S0

I

4

20 8 58

103 37

3«

I

20 9 6

log 40

24,2

5

20 9 52

102 48

3^

I

20 12 22

58 14

76

I

-7

20 17 20

76 12

184

I

4

Some twilight.

20 18 51

1^5 44

10,6

10

Twilight.

20 20 58

61 27

88

I

20 21 36

71 28

104

1
2

Hazy.

20 22 56

56 27

66

I

J

20 22 58

103 26

20

I

20 24 51

115 44

9'3

10

Twilight.

20 25 58

103 26

22,8

10

Changeable focus.

20 25 59

67 27

248

I
5

20 26 I

92 44

30,8

^

20 26 46

109 37

16,7

10

Not clear.

20 26 49

121 39

7,7

10

A little hazy.

20 27 2>?>

96 7

39

I

Moft fmall.

20 34 51

115 44

9'5

10

D

20 35 5?>

61 20

142

I
2

20 37 18

58 28

108

I
2

20 37 34

97 6

26,6

10

"^

20 38 I

92 44

28,2

5

1^

20 39 42

66 37

78

I

2

20 40 22

56 21

192

I
4

20 41 II

67 54

108

I
Z

20 41 56

74 r:>

116

I
2

20 42 59

62 14

112

1

20 43 I

70 29

76

I

lv.A.

x^t

Mr, Herschel on the

R.A.

P.D.

Stars.

Fields.

Memorandums.

H. M. S.

D. M.

20 43 30

54 47

260

I

5

Moll of the ftars of the fame fizc*

20 44 59

70 6

80

I

20 4| 13
20 49 I

60 46

120

I
2

92 44

27,0

5

^

20 49 10

57 "

248

I

Mofl of a fize.

26 50 59

103 26

17,2

3

20 51 23

68 30

70

I

20 53 29

103 26

17,4

5

(

20 54 1

107 47

10,3

10

20 56 59

103 26

14,9

10

Mort extremely fmall.

20 57 55

61 25

64

I

Twilight.

20 59 I

92 44

21,4

5

if-

21 I 6

96 43

40

I

% Mofl fmall.

21 3 29

66 39

80

I
2

21 3 53

73 9

55

1

21 6 13

69 23

40

1

A little hazv.

•

21 6 55

103 32

11,1

10

21 7 49

109 45

12,8

10

2r 7 59

64 58

no

i

21 9 25

61 36

75

i

Strong twilight*

21 10 13

60 39

70

I

Strong twilight.

21 II 17

73 »8

50

I

•

1

21 II 42

96 13

25

I

i(-

21 12 I

92 44

16,4

5

21 15 3

109 56

15,3

10

21 16 43

59 7

76

1

-

21 18 54

57 20

50

I

21 20 18

9^ 43

24

I

*

21 21 0

107 49

8,1

10

21 22 14

76 33

30.0

5

21 25 31

92 44

8,0

5

21 29 12

83 11

21,6

5

21 30 58

78 57

i8,9

10

,:

21 32 10

57 14

25

I

21 33 I

92 44

15.4

,5,

Strong twilight.

fT

R.A,

ConJlruBion of the Heavens,

'■i<)

R.A.

P.D.

Stars.

Fields.

IMemorandums.

H. M. S.

D.-M.

21 34 55

97 »7

i3»6

10

:^

21 36 38

65 55

42

1

1

21 38 20

65 38

60

I

21 39 55

96 17

18

I

#

21 41 52

58 42

44

I

21 43 22

109 55

11,5

10

^

. 2 1 45 4

59 39

52

I

21 48 22

59 30

29

I

21 51 52

58 56

61

I

21 51 55

97 17

11,5

10

^

21 54 22

109 55

12,8

10

^

21 57 49

59 37

60

I

2

21 58 4

75 7

33

I

\

21 58 19

59 6

40

I

1

21 58 43

58 34

32,6

5

D

.21 58 49

58 20

34

I

, 22 2 25

60 9

42,6

5

22 2 52

109 55

7,4

10

#

' 22 3 56

71 48

25,1

10

1 22 7 22

1

109 55

8,9
26

10

9f

22 10 28

75 2

I

22 II 32

97 H

10,7

10

^ Twilight.

22 i-.i 35

65 48

26,6

5

22 1.8 32

97 H

9,1

10

■)(. Twilight.

'1 22 20 35

109 58

8,3

10

:^

22 20 55

78 54

11,7

10

Bright 1) ,

22 27 41

95 4

8,1

10

: 22 30 35

109 58

5,0

10

■)^

22 31 28

73 59

17,3

10

22 33 6

76 52

- 16,5

10

22 34 40

61 56

20,1

10

. 22 35 35

109 58

7,1:

10

#

22 36 49

71 57

18,5^

10

22 39 41

82 5

19

I

22 40 5

65 48

21,3

10

K-j/io

240

Mr. Herschel on the

R.A.

P.D.

H. M. S.
22 43 55
22 45 3
22 45 30
22 48 49
22 52 9

22 52 41

22 55 40
22 56 55

22 58 19

23 o 27

23 03^
23 2 59
23 5 35
23 8 52

23 to 4

23 II 40

23 12 40

23 17 50

23 23 58

23 25 32

23 32 2
,23 33 20

23 43 2
23 44 47
23 46 52

23 46 55
23 59 21
23 59 56

D. M.

60 9
80 47
58 38
71 57
78 43

95

71

67
78

"3

4
54

53
42
12

58 38

65 50
109 58

95 I
H 55

61 48

71 54
81 o

69 48
113 12

69

79
69

45
"3

51
45
51
24
17

65 36
87 10

95 4

Stars.

Fields.

26,7

10

13,2

10

17,2

10

i3'4
8,2

10
10

8,9
11,6

10
10

12,1

10

9,2

10

4,4

10

18,7

10

21,3

10

7,3

7,5
26

10

10

I

21,1

10

11,9

9,7
12,1

10

10

10

3,1

10

9,5
10

10

I

10,9

10

50

4,2

I

10

15,3
5,6

7,8

10
lO
10

Memorandums.

Faint >
I)

Mofl extremely fmall.

■N

PRO-

Corjlruclion of the Heavens. .241

PROBLEM.

Thejlars heirig fuppofed to he nearly equally fcaltcredy ana thai*
number, in a fclci of view of a knoivn angular diameter , being
given, to determine the length of the vifiial ra\\

Here, the arrangement of the ftars not being hxed upon, wc
mufl endeavour to find which way they niay be placed lo as to
fill a given fpace moft equally. Suppofe a rectangular cone
cut into fruftula by many equidiftant planes perpendicular to
the axis ; then, if oneitar be placed at the vertex, and another
in the axis at the firfl: interfc6lion, fix ftars may be fet around it:
fo as to be equally diftant from one another and from the cen-
tral liar. Thefe pofitions being carried on in the fame manner,
we fliall have every ftar within the cone furrounded by eight
others, at an equal diflance from that ftar taken as a center.
Fig. I. (tab. VIII.) contains four fedions of fuch a cone diilin-
guiihed by alternate Ihades, which will be fufficlent to explain
what fort of arrangement I would point out.

The feries of the number of flars contained in the fe-
veral fedions will be 1.7. 19. 37. 61. 91. &c. which
continued to n terms, the fum of it, by the differential method,

will be n a-\-n , "—— d' -{-n , ^— • - — d^\ &c. ; where a is

2*23'

the firfl term d\ d^\ d''\ &c. the ifl, 2d, and 3d differences.
Then, fince tf = i, d' — 6^ d"—(i, d'^' — o, the fum of the
feries will be n^. Let S be the given number of ftars; i, the
diameter of the bafe of the field of view ; and B, the
diameter of the bafe of the great re(5langular cone ; and, by

trigonometry, we fhall have Br:: ^ Tfigid' Now, fince the
Vol. LXXV. I i ' field

24.2 M^^' Herschel 071 the

field of view of a telefcope is a cone, we fliall have its (o-
lidity to that of the great cone of flars, formed by the above
conftrufllon as the fquare of the diameter of the bafe of the
fic-d of view, to the fquare of the diameter of the bafe of the
great cone, the height of both being the fame ; and the flars iii
each cone being in the ratio of the foUdity, as being equally fcat-
tered (^), we have 72= v^B'S. And the length of the vilual
ray = « - i, which was to be determined.

(/) We o\ight to remark, that the periphery and bafe of the cone of the field
of vicv, in g'Tgint,', would ir» all probability feldom fall exaftly on fuch ftars as
would produce a perfecl e(pi:'.lity of fituation between the ilars contained in the
fmall and the great cone; and that, confequer.tly, the folution of this problem,,
where we fu-ppoie the flars of one cone to be to thofe of the other in the ratio'
of the folidity on account of their being equally fcattered, will not be flriAly
true. But it fliould be remembered, that in fmall numbers, where the different
terminations of the fields would moll affev^ this folution, the ftars in view havci
always been afcertained from gages that were often repeated, and each of vvhich^
confiilcd of no lefs than ten fields fucceffively taken, fo that the different deviations
at the periphery and bafe of the cone would certainly compenfate- each other
fufficienrly for the purpofe of this calculation. And that, on the other hand, in-
higli gages, which could not have the advantage of being fo often repeated, thefc
deviations would bear a much fmaller proportion to the great number of liars ia
a field of view j and therefore, on this account, fuch gages may very juflly be
admitted in a folution where praftical truth rather than mathematical precifion
is the end we have in vicvv. It is moreover not to be fuppofed that we imagine
the flars to be actually arranged in this regular manner, and, returning therefor©
to our general hypothefis of their being equally fcattered, any one field of view
pfomifcuoufly taken may, in this general fenfe, be fuppofed to contain a due
proportion of them ; fo that the principle on which this folution is founded may
therefore be faid to be even more rigoroufly true than we have occafion to mfift
upon in an argument of this kind, ^

the

ConJlrudiloJi of the Heavens, 242

Thefatne other wife.

If a different arrangement of the flars fhould be felecled,
fuch as that hi fig. 2. where one ftar Is at the vertex of a cone ;
three in the circumference of the firO: fe6lIon, at an equal dif-
tance from the vertex and from each other -, fix in the circum-
ference of the next fedlion, with one in the axis or center;
and fo on, always placing three ftars in a lower fedlon in fuch a
manner as to form an equilateral pyramid with one above them:
then we fliall have every ftar, which is fufficiently within
the cone, furrounded by twelve others at an equal diflance from
the central fl:ar and from each other. And by the differential
method, the fum of the two feries equally continued, into
which this cone may be refolved, will be 2?7^+ 1 1 ^^'^ + li''";
where n ftands for the number of terms in each feries. To
find the angle which a line v:c^ paffing from the vertex v over
the flars 'U, n^ -6, /, &Co to x, at the outfide of the cone, makes
with the axis ; we have, by conflrucSlion, v i in fig. 3.
reprefenting the planes of the firfl and fecond fe6lions =
2 X cof.30° := cp, to the radius p j, of the firfl fe6lion =: i . Hence

it will be v^(p' — i—v p = \vm\ or vm = 2 s/ (f — i : and, by
trigonometry, ?-^=:T. Where T is the tangent of the

required angle to the radius R (c) j and putting / = tangent of

(c) In finding this angle we have fuppofed the cone to be generated by a
revolving reftangular triangle of which the line vx, fig. 2. is the hypotenufe ;
but the ftars in the fecond feries will occafion the cone to be contained under a
waving lurface, wherefore the above fuppofition of the generation of the cone is
not ftridly true ; but then thefe waves are fo inconfiderable, that, for the pre-
fent purpofe, they may fafely be neglected in this calculation,

I i 2 half

2-44- ■^'^' Herschel on the

T
half the given field of view, it will be - B, the bafe of the

cone. And — - — rrj, will be an expreffion iov vp, in terms

of V5^ which is the mutual ditlance of tlie fcattered ilaps.

Then having — rr ;2' -f | «*+ I ;z, we may find ?} ; whence

zdn - d, the vifual ray, will be obtained.

The refult of this arrangement gives a fiiorter ray than that
of the former ; but fince the dlfixrence is not fb confiderable as
very materially to afFc£l the conclaiions, I fliall, on account of
the greater convenience, make uie of the hrft»

We inh^ihit the planet of a Jlar hAonging to a Compvund Nebula

of the third form.

I fhall now proceed to fliew that the ftupendous fidereal fyiLem
we inhabit, this extenfive flratum and its fecondary branch,
confifting of many millions of ftars, is, in all probability, a
detached Nebula. In order to go upon grounds that feem to me
to be capable of great certainty, they being no lefs than an
actual furvey of the boundaries of our fidereal fy ftem, which
J have plainly perceived, as far as I have yet gone round it,
every where terminated, and in mofl places very narrowly too,
it will be proper to (hew the length of my founding line, if I
may fo call it, that it may appear whether it was fufficiently
long for the purpofe.

In the moft crowded part of the milky way I have had fields
of view that contained no lefs than 588 ftars (^), and thefe were
continued for many minutes, fo that in one quarter of an hour's
time there palled no lefs than 1 16000 ftars thiough the field of

{'i) Sec the table of Gages, p. 235.

view

ConJlriLBion of the Heavens. 242;

view of my telefcope (£-). Now, if we compute the length of
the viilial rny by putting 8 = 588, and the diameter of the

field of view fifteen minutes, we fhall find « = \/B S = 498 ; lo
that it appears the length of what 1 have called my founding Une,
or n- I, was probably not lefs than 497 times the diilance of
Sirius from the fun. The fame gage calculated by the fecond

arran

gem.ent of ftars gives v/(p^"— i = 1.41421 ;

R(p

o

^/<p2_l

T „ ^ . -^V-i

tangent of 31° 28' 55'^77 ; "^ =B= 280,69 ' ~~^ — ~ d ~

,81649; — =z2^i6^^o^,y=:n- -{- ^ n^ + I n ; where «= 284,8

nearly; and idn- 1 =464, the vifual ray.

It may feem inaccurate that we (liould found an argument on
the ftars being equally fcattered, when in all probability there
mav not be two of them in the heavens, whofe mutual didance
Ihall be equal to thatof any other two given ftars ; but it fhould
be confidered, that when we take ail the ftars colle6lively there
will be a mean diftance which may be aflbmed as the general
one; and an argument founded on fuch a fuppolition will liave-
in its favour the greateft })robabiiity of not being far fliort of
truth. What will render the fuppofition of an equal diftribu-
tion of the ftars, with regard to the gages, ftill lefs expoled lo
obje6tions is, that whenever the ftars happened either to be
uncommonly crowded or deficient in number, fo as very fud-

i^e) The breadth of my fweep was 2° 26', to which muft be added 15' for two
-femi-diameters of the field. Then, putting i6intf, the number of fields In
15 minutes of time ; ,7854 = ^, the proportion of a circle to i, its circumfcribed
fquare; (jzrfine of 74^^22', the polar diftance of the middle of the fwtep reduced'^
to the prefent time ; and 588 = 8, the number of ftars in a field of view, we have

— 1 16076 ftars.

d^nlj

^46 ^^' Herschel on the

denly to pafs ov^r from one extreme to the other, the gages
were reduced to other forms, fuch as the border-gage, the
diilance-gage, &c. which terms, and the ufe of fuch gages,
I (hall hereafter find an opportunity of explaniing. And none
of thofe kinds of gages have been admitted in this table, which
eonfiils only of fuch as have been taken in places where the
irars apparently feemed to be, in general, pretty evenly fcat-
tered ; and to increafe and decreafe in number by a certain gra-
dual progrefiion. Nor has any part of the heavens containing
a clufler of Ifars been put in the gages ; and here I mull: ob-
ferve, that the difference between a crowded place and a clufter
may eafily be perceived by the arrangement as well as the fize
and mutual diilance of the ilars : for in a clufter they are
generally not only refembling each other pretty nearly in fize,
but a certain uniformity of diilance alfo takes place ; they are
more and more accumulated towards the center, and put on all
the appearances which we fhould naturally expecl from a num-
ber of them colle£ltd into a group at a certain diflance from
lis. On the other hand, the rich parts of the milky way, as
well as thofe in the diftant broad part of the ftratumx, confid:
of a mixture of flars of all poffible fizes, that are feemingly
placed without any particular apparent order. Perhaps we might
recoliecl, that a greater condenlation tow^ards the center of our
fyllcm than towards the borders of it fhould be taken into con-
fideration ; but, w- itli a nebula of the third form, containing
fuch various and extenfive combinations, as I have found to
take place in ours, this circumftance, which in one of the firfl"
form v/ould be of confid^rable moment, may, I think, be
lafely neglected. However, I would not be undei flood to lay
a greater ftrefs on thcfe and the following calculations than the
principles on which they are founded will periiiit ; and if here-
after

^

Corjlrucllon of the Hecvens. 'i\^

after Vv'e fhall find reafoii, from experience and obiervatlon, to-.
believe that there are parts of our fyflem where the flars are
not fcattered in the manner here fupportd, we ought then to
make proper exceptions.

But to return : if fome other high gage be fele6l"ed from the
table, luch as 472 or 344, the length of the vifual ray will be
found 461 and 415. iind although, in confequence of what
has been faid, a certain degree of doubt may be left about the
arrangement and fcattering of the ftars, yet when I recollecSl:,
that in thofe parts of the milky v/ay where thefe high gages
were taken, the fiars were neither fo fmall, nor fo crowded,
as they muft have been on a luppofition of a m.uch far-
ther continuance of them, when certainly a milky or ne-
bulous appearance mAifl: have come on, I need not fear to have
over-rated the extent of my vifual ray. And indeed every
thing that can be faid to fhorten it will only contracl the lim/its
of our nebula, as it has in moft places been of fufficient length
to go far beyond the bounds of it. Thus, in the lides of the-
flratum oppof te to our fituation in it, where the gages often
run below 5, our nebula cannot extend to 100 times the dif-
tance of Sirius ; and the fime telefcope, which could Ihew 58 8
flars in a field of view of 15 minutes, mufi: certainly have pre-
fen ted me alfo with the ftars in thefe fit nations as w~ell as the
former, had they been there. If we (hould anlwer this by ob-
lerving that they might be at too great a diftance to be per-
ceived, it will be allowing that there mufl: at leaf! be a vacancy
amounting to the length of a vifual ray not (hort of 400 times
the diftance of Sirius ; and this is amply fufficient to make our
nebula a detached one. It is true, that it would not be con-
fiftent confidently to affirm that we were on an ifland unlefs
we had adually found ourfelves every where bounded by the

oceaiij

248 Mr, Herschel on the

ocean, and therefore I fliall go no farther than the gages will
authorifs ; but confidering the httle depth of the ftratum in
all thofe places which have been actually gaged, to which muft
be added all the intermediate parts that have been viewed and
found to be much like the reft, there is but little room toexpe6i:
a conneclion between ournebuhi and any of the neighbouring
ones. I ought alio to add, that a telefcope with a much larger
aperture than my prelent one, gralping together a greater quan-
tity oi light, and thereby enabling us to fee farther into fpace,
will be the f-arefl: means of compleating and eflablifliing the
arofuments that have been ufed : for if our nebula is not abfo-
lutely a detached one, I am firmly perl-Jaded, that an inftru-
ment may be made large enough to diicover the places where
the ftars continue onwards. A \evj bright milky nebuloficy
muft there undoubtedly come on, fmce the flars in a Held of view
will increafe in the ratio of fi\ greater than that of the cube
of the vifual ray. Thus, if 588 flars in a given field of view
are to be fcen by a ray of 497 times the diftance of Sirius ;
when this is lengthened to 1000, which is but little more
than double the former, the number of ftars in the fame field
of view will be no lefs than 4774 : for when the vifual i^ay r

is giv^n, the number S of fl:ars will be = ^; where «=:r4-i;

and a telefcope with a three-fold power of extending into fpace,
or with a ray of 1500, which, I think, may eafily be con-
flru6:ed, will give us 16096 flars. Now, thefe would not be
fo clofe but that a good power applied to luch an inflrument
might eafily diflinguifh them ; for they need not, if arranged
in regular Iquares, approach nearer to each other than 6^^,27;
but what would produce the milky nebulofity wiiich I have
mentioned is the numberlefs flars beyond them, which in one

refpcdl

Confii'ucilon of the Heavens. 249

refpe^t the vlfual ra}^ might alfo be faid to reach. *Vq make
this appear we mufl return to the naked eye, which, as we
have before eilimated, can only fee the ilars of the fevcnth
magnitude fo as to diftinguifh them ; but it is neverthelcfs very
-evident that the united lurtre of millions of ilars, fuch as I
fuppofe the nebula in Andromeda to be, will reach our fight in
the Ihape of a very fmall, faint nebulofity ; fmce the nebula of
which I fpeak may eafdy be feen in a fine evening. In the
fame manner my prefent telefcope, as I have argued, has not
only a vifual ray that will reach the flars at 497 times the dif-
tance of Sirius io as to diftinguifli them (and probably mucii
farther), but alfo a power of ihewing the united luftre of the
accumulated ftars that compofe a milky nebuiofity, at a diifance
far exceeding the former limits ; 10 that from thefe conlidera-
tions it appears again highly probable, that my preient teleicopey
not fhewing fuch a nebulofity in the milky way,. goes already far
beyond its extent : and confequently, much more would an
inftrument, fuch as I have mentioned, remove all doubt on:
the fubjeft, both by (hewing the ftars in the continuation of
the flratum, and by expofing a very flrong milky nebulontv
i)eyond them, that could no longer be miftaken for the dark
ground of the heavens.

To thefe arguments, which reft on the firm bafis of a feries
-of obfervation, we may add the following confiderations drawn
from analogy. Among the great number of nebulcC which 1
have now already feen, amounting to more than 900, there
are many which in all probability are equally extenfive with
that which we inhabit ; And yet they are all feparated from each
other by very confiderable intervals. Some indeed there are
that feem to be double and treble; and though Vv^ith mou of
thefe it may be, that they are at a very great diftance from each

Vol. LXXV\ K k ' ' other,

2;;o Mr, Herschel on the

other, yet we allow that fome fuch conjun£lions really are to
be found ; nor is this what we mean to exclude. But then
thefe compound or double nebul'je, which are thofe of the third
raid fourth forms, ftill make a detached link in the great chain.
It is alio to be luppolcd, that there may ll:iil be fome thinly
fcattered folitary ftars between the large interfaces of nebulae,
which, being iituated fo as to be nearly equally attrad^ed by the
feveral clufters when they were forming, remain unaffociated.
And though we cannot expe£l to fee thefe ftars, on account of
their vafl diftance, yet we may well prefume, that their num-
ber cannot be very conliderable in comparifon to thofe that are
already drawn into fyftems ; which conje6lure is alio abun-
dantly confirmed in fituations where the nebulae are near enough
to have their ftars vlfible ; for they are all inlulated, and gene-
rally to be feen upon a very clear and pure ground, without
any flar near them that might be fuppofed to belong to them.
And though I have often feen them in beds of ffcars, yet from
the fize of thefe latter we may be certain, that they were
much nearer to us than thofe nebulas, and belonged undoubtedly
to our own fyflem^

Ufe of the gages,

A delineation of our nebula, by an application of the gages
in the manner which has been propofed to be done in my for-
mer paper, may now be attempted, and the following table is
calculated for this purpofe. It gives us the length of the vifual
ray for any number of flars in the field of view contained In
the third column of the foregoing table of gages from ^^ to
looooo. If the number required is not to be found in the firft
4 , column

ConJlruSilon of the Heavens, 251

column of this table, a proportional mean may be taken be-
tween the two neareft rays in the fecond column, without any
material error, except in the few lail; numbers. The calcula-
tions of refolvable and milky nebulofity, at the end of the .
table, are founded, the firfl, on a fuppoiition of the flars '•
being fo crowded as to have only a fquare fecond of fpace
allowed them; the next affigning them only lialf a fecond
fquare. However, we (hould coniider that in all probability a
very different accumulation of ftars may take place in different
nebulas ; by which means fome of them may ail^ume the milky
appearance, though not near fo far removed from us ; w^hile
clufters of ftars alfo may become refolvable nebulae from the
fame caufe. The dlftindnefs of the inftrument is here alfo
concerned ; and as telefcopes with large apertures are not eafily
brought to a good figure, nebulous appearances of both forts
may probably come on much before the diflance annexed to
them in the table. '

Kk2 TABLE

252

Mr. Hersciiel on the

T A ]

3 L E

II.

Stars in

Vifual

Stars

Ray.

St.^rs.

Ray.

Stars,

Ray.

Stars.

Ray.

cne nf 10

ray.

Q I

186

7 I

245
246

•' 10

QC2

700
800

527
551

o,i

27

0^

32

188

/ '

- ■•>

1 —

220

358

0,2

34

33

190

73

247

230

3^3

900

573

0,3

39

3+

192

'^ 1

249

240

3b8

1000

593

0,4

43

35

193

75

250

250

374

1 0000

1280

0.5

4b

3'^

195

70

251

260

378

I 00000

2758

0,6

49

37

197

77

252

270

383

0,7

52

38

199

7^

253

280

388

0,8

54

39

201

79

254

290

393

0,9

5^

40

2C2

80

255

300

397

I

,ss

41

204

81

256

310

401

2

74

42

206

82

257

320

406

636175

1

3

^S

43

207

«3

258

330

410

or

.5112

4

93

44

209

^4

259

340

414

refolvable

5

101

45

210

85

260

350

418

nebulofity

«

6

107

46

212

86

261

360

422

7

113

47

214

87

262

370

426

8

118

48

215

88

263

380

430

9

123

49

217

89

264

390

433

10

127

50
51

218

90

265

400

437

II

131

219

91

266

410

441

12

135

52

221

92

267

420

444

2544700

^

13

139

53

222

93

268

430

448

or

I8115

14

142

54

224

94

269

440

451

milky

IS

146

55

225

95

270

450

455

nebulofity

J

16

149

S^

226

96

271

460

458

17

15^

57

223

97

272

47^.

461

18

155

5S

229

98

273

480

464

19

15^

59

230

99

274

490

468

20

160

60

232

100

275

500

471

21

163

61

233

no

284

510

474

22

166

62

234

120

291

520

477

23

168

63

236

130

300

530

^80

24

170

64

237

140

308

540

483

.

25

173

65

238

150

315

550

486

2.6

17s

66

239

160

0 T O

560

489

27

177

67

240

170

328

570

492

28

180

68

242

180

335

580

495

29

182

69

243

190

341

590

498

1

30

184

70

244 1

200

347

6co

500

Sediion

Conjlruction of the Heavens, 25

^

Sedi'ion of our fidereal fjlem.

By taking out of this table the vifual rays which anfwer to
the gages, and applying lines proportional to them around a
point, according to their refpedlive right afcenfions and north
polar diflances, we may delineate a folid by means of the end';
of thefe lines, which will give us fo many points in its fur-
face ; I fliall, however, content myfelf at prefent with a fec-
tion only* I have taken one which paffcs through the poles of
our fyftem, and is at re£langies to the conjunction of the
branches which I have called its length. The name of poles
feemed to me not improperly applied to thofe points which are
90 degrees diftant from a circle paffing along the milky way,
and the north pole is here aifumed to be fituated in R.A. 186"
and P.D. 58°. The fe£lion reprefented in fig. 4. is one which
makes an angle of 35 degrees with our equator, eroding it in
124I and 3041 degrees. A celeflial globe, adjufted to the lati-
tude of ^^"i .north, and having 0- Ceti near the meridian, will
have the plane of this fe£lion pointed out by the horizon, and
the gages which have been ufed in this delineation are thofe
which in table I. are marked by afterifks* When the vifual
rays arifwering to them are taken out of the fecond table, they
muft be projected on the plane of the horizon of the latitude
which has been pointed out ; and this may be done accurately
enough for the prefent purpofe hy a globe adjufted as above di-
tecled ; for as gages, exadly in the plane of the fedion, were
often wanting, I have ufed many at fome fmall diftance above
and below the fame, for the fake of obtaining more delineating
points ; and in the figure the ftars at the borders which are
larger than the reft are thofe pointed out by the gages. The
3 inter-

2 54 ^^^* Herschel o?t the

intermediate parts are filled up by fmaller ftars arranged in
flraight lines between the gaged ones. The delineating points,
though pretty numerous, are not fo clofe as we might wifh ;
« it is however to be hoped that in fome future time this
branch of aftronomy will become more cultivated, fo that we
may have gages for every quarter of a degree of the heavens at
leaft, and thefe often repeated in the mofl: favourable circum-
ftances. And whenever that fliall be the cafe, the delineations
may then be repeated vv^ithall the accuracy that long experience
may enable us to introduce ; for, this fubje6t being fo new, I
look upon what is here given partly as only an example to
illuflrate the fpirit of the method. From this figure how*
ever, which :1 hope is not a very inaccurate one, we may fee
that our nebula, as we obferved before, is of the third form ;
that is: A very extenjlve, branching, compound Congeries of
many millions of Jlars\ which mofi: probably owes its origin to
many remarkably large as well as pretty clofely fcattered fmall
ftars, that may have drawn together the reft. Now, to have
fome idea of the wonderful extent of this fyftem, I muft ob-
ferve that this fec^ion of it is drawn upon a fcale where the
diftance of Sirius is no more than the 8oth part of an inch ; fb
that probably all the ftars, which in the fineft nights we are
able to diftinguifh with the naked eye, may be comprehended
within a fphere, drawn round the large ftar near the middle,
reprefenting our fituation in the nebula, of lefs than half a
quarter of an inch radius. *

^he Origin of nebulous Strata.

If it were poflible to dlftinguifti between the parts of an
indefinitely extended whole, the nebula we inhabit might be

faid

Conjlruciion of the Heavens. 255

faid to be one that has fewer marks of profound antiquity upon
it than the reft. To explain this idea perhaps more clearly, we
fhouid recoiled that the condenfation of clufters of (lars has
been afcribed to a gradual approach ; and whoever refiecrs on
the numbers of ages that muft have paft before fome of the
clufters, that will be found in my intended catalogue of them,
could be fo far condenfed as we find them at prefent, will not
wonder if I afcribe a certain air of youth and vigour to many
very regularly fcattered regions of our fidereal ftratum. There
are moreover many places in it where there is the greateft
reafon to believe that the ftars, if we may judge from ap-
pearances, are now drawing towards various fecondary centers,
and will in time feparate into different clufters, fo as to occa-
fion many fub-divifions. Hence we may furmife that when a
nebulous ftratum coniifts chiefly of nebulie of the firft and fe- -
cond form, it probably owes its originate what may be called '
the decay of a great compound nebula of the third form ; and
that the fub-diviiions, which happened to it in length of time,
occafioned all the fmall nebulae which fprung from it to lie in a
certain range, according as they were detached from the pri-
mary one. In like manner our fyftem, after numbers of ages,
may very poftibly become divided fo as to give rife to a ftratum '
of two or three hundred nebulas; for it would not be difficult
to point out fo many beginning or gathering clufters in it ( / ).
This view of the prelent fuLije£l throws a contiderable light '
\3p0n the appearance of that- remarkable coUedion of many ■

{/) Mr. MiciiELL has alfo conGdered the ftars as gathered tcgerher into '
groups (Phil. Tranf. vol. LVII. p. 249.) ; which idea agrees with the fish divilicn ■
of our great fyftem here pointed out. He founds an elegant proof of this on •
the computation of probabilities, and mentions the Pleiades, the Piafepe Cancri,
and the nebula (or duller of liars) in the hilt of Perfcus's fword, as infrance'^.

hu-iidreds

aj5 Mr, Herschel on the

hundreds of nebula which are to be feeii In what I have called
the nebulous flratum of Coma Berenices. It appears from the
extended and branching figure of our nebuLi, that there is room
for the decompofed fmall nebula of a large, reduced, former
great one to approach nearer to us in the fides than in other
parts. Nay, pofllbly, there might originally be another very
large joining branch, which in time became feparated by the
condenfation of the ftars ; and this may be the reafon of the
little remaining breadth of cur fyRem in that very place : for
the nebulae of the ftratum of the Coma are brighteft and mofl".
crowded jufl: oppofite our fituationj or in the pole of our fyftem/ ,
As foon as this idea was fjggefted, I tried alfo the oppofite pole,
where accordingly I have met with a great number of nebula,;
•though under a much mors fcattered form. '

An Opening in the heavens.

Some parts of our lyflem indeed feem already to have fuf-
tained greater ravages of time than others j if this way of ex--
prefiing myfelf may be allowed ; for inflance, in the body of
the Scorpion is^yan opening, or hole, w^hich is probably owing to
this caufe. 1 found it while I was gaging in the parallel fronii
112 to 1 14 degrees of north poiar diflance. As I approached >
the milky way, the.gageshad been gradually running up from
9,7 to I 7,1 ; when, all of a fudden, they fell down to nothing,
a very few pretty large flars excepted, which made them fheW'
0,5, 0,7, I5I, 1,4, 1,8; after which they again rofe to 4,7,
13, 5j 2C)j3, and foon after to 41,1. This opening is at leaft
4 degrees broad, but its height I have not yet afcertained. It^
■is remarkable, that the 80 Nebuleufe fans etoiles of the G?«*
''mijfance des Temps, which is one of the richeft and mofl com-

prefl'ed

ConJlruSlkn of the Heavens, z^y

prefied cluiler^ of fmall fl:ars I remember to have feen, is
iituated juft on the weftern border of it, and would almoft au-
thorife a fufplclon that the ftars, of wliich it is compofed, were
collected from that place, and had left the vacancy. What adds
not a little to this furmife is, that the fame pha^nomenon is
once more repeated with the fourth clufler of ilars of the
Cojitioijfance des Temps ; which is alfo on the weftern border of
another vacancy, and has moreover a fmall, miniature clufter,
or eafily refolvabie nebula of about 2| minutes in diameter,
north following it, at no very great diilance.

Phi^nomcna at the Poles of our Nebula,

I ought to obferve, that there is a remarkable purity or clear-v
nefs in the heavens when we look out of our ftratum at the
fides; that is, towards Leo, Virgo, and Coma Berenices, on one
hand, and towards : Cetus on the other; whereas the ground
of the heavens becomes troubled as we approach towards the
length or height of it. ■ It was a good while before I could
trace the caufc of thefe phasnomena ; bat fince I have been
acquainted with the fliape of our fyftem, it is plain that thefe
troubled appearances, when we approach to the fides, are eafily
to be explained by afcribing them to fome of ihe diflant, flrag-
gling ftars, that yield hardly light enough to be diftinguiOiecL
And 1 have, indeed, often experienced this to be actually the
caufe, by examining thefe troubled fpots for a k >^; while toge-
ther, when, at lafl:, 1 generally perceived the ftai t v/hich occa-
fioned them. But when we look towards the ^ poles of our
fyflem, where the vifual ray does not graze along .tl;s fide, the ^

Vol. LXXV. L 1 ftraggling'

jtjS Mr. Herschel on the

ftragglmg ftars of courle will be very few in number ; and
therefore the ground of the heavens will afllime that purity
"which 1 have always oblerved to take place in thofe regions.

Knvmeration of *very compcund Nebulise or Milky'Ways,

As we are ufed to call the appearance of the heavens, wherd
it is furrounded with a bright zone, the Milky-Way, it may
not be amifs to point out fome other very remarkable Nebnlae
which cannot well be lefs, but are probably much larger than,
•our own fyflem ; and, being alfo extended, the inhabitants of
the planets that attend the fears which compofe them muft
likewife perceive the fame phaenomena. For which reafon they
may alfo be called milky-ways by way of diflindiion.

My opinion of their fize is grounded on the following ob-
fervations. There are'^many round nebula, of the firft form,
of about five or fix minutes in diameter, the ftars of which t
can iee vej;y difl;infl:ly ; and on comparing them with the vifual
ray calculated from fome of my long gages, I fuppofe,by the ap-
pearance of the fmall ftars in thofe gages, that the centers of thefej
round nebulae m.ay be 600 times the diftance of Sirius from us.

In eflimating the diftance of fuch cluflers I confulted-
rather the comparatively apparent fize of the ftars than'
their mutual diflance; for the condenfation in thelb cluflers.'
being probably much greater than in our own fyilem, if we
were to overlook this circumllance and calculate by their appa-
rent comprefiicn, where, in about fix minutes diamefef, there
are perhaps ten or more f^ars in the line of irieafures, we fhould
find, that on the fuppofition of an equal fcattering of the flars.'
throughout all nebula, the difi:ance of the center of fuch a
clufler from us could not be lefs than 6000 times the dillance^

ConftruSlkn of ihe Heavem* 25 c/

of Slrius. And, perhaps, in putting it, by the apparent fize
of the ilars, at. 600 only, I may have coniiderably under-rated
it; but my argument, if that fliouid be the cafe, will be fo
much the ftronger. Now to proceed,

Some of theie round nebulae have others near them, perfectly
fimilar in form, colour, and the didribution of flars, but of only
half the diameter: aiidtheftarsintiiemfeem to be doubly crowded,
and only at about half the diliance from each other : they arc
indeed \o fmail as not to be vlfible without the utmoft attention,
I fuppofe theie miniature nebulae to be at double the dllfance of
the firft. An inifance, equally remarkable and infl:ru6tive, is
a cafe where, in the neighbourhood of two fuch nebulae as
have been mentioned, I met with a third, fimilar, refolvable,
but much fmaller and flfmter nebula. The frars of it are no
longer to be perceived ; but a refemblance of colour witli the
former two, and its dimlnhhed fize and light, may well per-
mit us to place it at full twice the diftance of the fecond, or^
about four or five times that of the firft. And yet the nebu-
lofity is not of the milky kind ; nor is it fo much as difficultly
refolvable, or colourlefs. Now, in a few of the extended ne-
bulcc, the light changes gradually fo as from the refolvable to
approach to the milky kind; which appears to me an indica-
tion that the milky light of nebula? is owing to their much
greater diftance. A nebula, therefore, whofe light is perfedly
milky, cannot well be fuppofed to be at lefs than fix or eight
thoufand times the diftance of Slrius ; and though the numbers
here ailumed are not to be taken otherwife than as very coarfc
eftimates, yet an extended nebula, which in an oblique fitua-
tion, where it is pofiibly fore-fhortened by one-half, two-thirds,
or three- fourths of its length, fubtends a degree or more in

L 1 -i diameter,

260 Mr. Herschel on the

diameter, cannot be otherwife than of a wonderful magnitude^
and may well outvie our milky-way in grandeur.

The iirfi: I iliall mention is a milky Ray of more than a de-|
gree in lei]gth. It takes k (Fl. 52.)Cygni into its extent, to
the north of which it is crookedly bent {o as to be convex
towards the following (ide ; and the light of it is pretty intenfe,;/
To the fouth of k it is more difFufed, lefs bright, and lofes
itfelf with fome extenfiou in two branches, I believe ; but for
want of light I could not determine this circumflance. The
northern half is near two minutes broad, but the fouthern is
not fufficiently defined to afcertain its breadth.

The next is an extremely faint milky Ray, above | degree
long, and 8 or 10^ broad; extended from north preceding to
fouth following. It makes an angle of about 30 or 40 degrees
with the meridian, and contains three or four places that are
brighter than the reft. The ftars of the Galaxy are fcattered
over it in the fame manner as over the reft of the heavens. It
follows 6 Cygni 1 1,5 minutes in time, and is 2° 19^ more fouth.

The third is a branching Nebulofity of about a degree and a
half in right afcenfion, and about 48^ extent in polar diftance.
The following part of it is divided into feveral ftreams and
windings, which, after feparating, meet each other again
towards the fouth. It precedes f Cygni 16' in time, and is
1° 16^ more north. I fuppofe this to be joined to the preceding
one ; but having obferved them in different fweeps, there was
no opportunity of tracing their connexion.

The fourth is a faint, extended milky Ray of about 17' in
length, and 12^ in breadth. It is brighteft and broadeft in the
middle, and the ends lofe themfelves. It has a fmall, round,
very faint nebula juft north of it ; and alfo, in another place,
a fpot, brighter than the reft, almoft detached enough to form

a different

Conjlruciion of the Heavens, 261

a ditferent nebula, but probably belonging to the great one.
The Ray precedes « Trianguli 18^,8 in time, and is 55' more
north. Another obfervatlon of the fame, in a finer evening,
mentions its extending much farther towards the fouth, and
that the breadth of it probably is not lefs than half a degree ;
but being fhaded away by imperceptible gradations, it is diffi«
cult exactly to affign its limits.

The fifth is a Streak of light about 27^ long, and in the
brlghteft part 3 or 4^ broad. The extent is nearly in the meri-
dian, or a little from fouth preceding to north following. It
follows /3 Cetl 5^,9 in time, and is 2° 43^ more fouth. The
fituation is fo low, that it would probably appear of a much
greater extent in a higher altitude.

The fixth is an extenfive milky Nebuloflty divided into two
parts ; the mofl north being the ftrongefl:. Its extent exceeds
15'; the fbuthern part is followed by a parcel of flars whicli
I fuppofe to be the 8th of the Cumioijfance des Temps ^

The feventh is a wonderful, extenlive Nebulofity of the milky
kind. There are feveral flars viiible in it, but thev can have
no connection with that nebulofity, and are, doubtlefs, belong-
ing to our own fyflem fcattered before it. It is the 17th of
the Connoiffance des Temps,

In the lifl of thefe muft alfo be reckoned the beautiful Ne-
bula of Orion. Its extent is much above one degree ; the
eaflern branch paffes between two very fmall flars, and runs on'
till it meets a very bright one. Clofe to the four fmall ftars,
which can have no connection with the nebula, is a total black-
nefs ; and within the open part, towards the north-eafl, is a
diftinCt, fmall, faint nebula, of an extended fhape, at a diftance
from the border of the great one, to which it runs in a parallel-
4 diredlion.

^^2 Mr. Herschel on ihe

dire^liori, refembllng the Ihoals that are feea near the coafls of

Ibme iilaiids.

The nhith is that hi the girdle of Andromeda, which is un-
doubtedly the neareil: of ail the great nebulae ; its extent is
above a degree and a half in length, and, in even one of the
narrowed places, not lefs than 16^ in breadth. The brighteft
par!" of it approaches to the refolvable nebulofity, and begins
to fhew a fahit red colour ; which, from many obfervations on
the colour and magnitude of nebulae, I believe to be an indica-
tion that its diflance in this coloured part does not exceed 2000
times the diftance of Sirius. There is a very confiderable,
broad, pretty faint, fmall nebula near it ; my Sifter difcovered
it Augufl: 27, 1783, with a Newtonian 2-feet fweeper. It fliew5f
the fame faint colour with the great one, and is, no doubt, in
the neighbourhood of it. It is not the 3 2d of the Connoiffance
des 'Temps ; which is a pretty large round nebula, much con-
den fed in the middle, and fouth following the great one ; but
this is about two-thirds of a degree north preceding it, in a
line parallel to jG and y Andromedae.

To thefe may be added the nebula in Vulpecula : for, thougk
its appearance is not large, it is probably a double ifratum of
flars of a very great extent, one end whereof is turned towards
us. That it is thus lituated may be furmifed from its contain-
ing, in different parts, nearly all the three nebuloiities ; viz,
the refolvable, the coloured but irrefolvable, and a tincture of
the milky kind. Now, what great length muft be required to
produce thefe effects may eafily be conceived when, in all pro-r
hability, our whole {y^kQin, of about 8co ilars in diameter, if
it were {qqu. at fuch a diftance that one end of it might aflbme
the refolvable nebulofity, would not, at the other end, prefent

us

Conjiru5lhn of the Heavtns, a^-*

us with the Irrefolvable, much lefs with the colourlefs and
milky fort of nebuloiities.

A F erf orated 'Nebula^ or Ring of Stars,
Among the curiofities of the heavens fhoLild be placed a
nebula, that has a regular, concentric, dark fpot in the middle,
and is probably a Ring of ftars. It is of an oval Jfhape, the
fliorter axis being to the longer as about 83 to 100 ; fo that, if
the flars form a circle, its inclination to a line drawn from the
fun to the center of this nebula mufl be about ^6 degrees. The
light is of the refolvable kind, and in the northern fide three
very fbiint (lars may be feen, as alfo one or two in the foutherii
part. The vertices of the longer axis feem lefs bright and not
fo well defined as the reft. There are feveral fmall flars very
near, but none that feem to belong to it. It is the c-^th of
the ConnoiJJance des Temps, Fig. 5. is a reprefentation of it.

Planetary Ntbul^e.

I ihall conclude this paper with an account of a few hea-
venly bodies, that from their lingular appearance leave me almofl
ill doubt where to clafs them.

The firft precedes v Aquarli 5^,4 in time, and is i^ more
north, its place, with regard to a fmall ftar Sept. 7, 1782,
was, Diflance 8' j ^" 5 1^^^ ; but on account of the low fituation,
and other unfavourable circumftances, the meafure cannot be
very exa£l. Auguft 25, T783, Diflance 7^ 5^^ 11^^', veryexa<5t,
and to my fatisfa^lion ; the light being thrown in by an opaque-
microfcopic-iUumination (£•). Sept. 20, 1783, Pofition 41° 24.'

fouth

{g) It mny be of ufe to explain thrs kind of illumination for which the New-
tonian refleftoF is admirably confifufted. On the fide oppofite the eye-piece an
opening is to be made in the tube, through which the^light may be thrown in, {o
as to tall oa fome refleding body, or concave perforated mirror^, witliin the eye-

piece^

264. Mr. Herschel on the

fouth preceding the fame ftar ; very exa£l, and by the fame
kind of illumination. Od. 17, 1783, Diilance 6' 55^'' 7'^' ;
a fecond meafure 6'' 56^^ ii^^^ as exacl: as pofTible. Od. 23,
1783, l^olition 42^ 57^ ; a fecond meafure 42° 45' ; fingle lens ;
power '^'i; opaque-microfcopic-illumination. Nov. 14, 1783,
Diftance 7' 4^' 35^'^ Nov. 12, 1784, DilTiance 7' 22'' 35^''" ;
Pofition 38^ 39^ Its diameter is about loor 15^''. I haveexa-
mined it with the powers of 71, 227, 278, 460, and 932 ;
and it follows the lav\^s of magnifying, fo that its hody is no
illuiion of light. It is a little oval, and in the 7-feet refle6lor
pretty well defined, but not fl'iarp on the edges. In the 20 -feet,
of 18,7 Inch, aperture, it is much better defined, and has much
of a planetary appearance, being all over of an uniform bright-
nefs, in which it differs from nebulae : its light fecms however
to be of tiie ftarry nature, which fuffers not nearly fo much as
the planetary difks are known to do, when much magnified.

T'he fecond of thefe bodies precedes the 13th of Flam-
steed's Andromeda about 1^6 in time, and is 22^ more fouth.
It has a round, bright, pretty well defined planetary difk of
about \2^^ diameter, and is a little elliptical. When it is viewed
with a 7-feet refle6i:or, or other inferior inftruments, it is not
nearly fo well defined as with the 20-feet. Its fituation with
regard to a pretty confiderable ftar is, Diflance (with a com-
pound glafs of a low power) f 51'^ 34^^^ Pofition i2°o^ f.
preceding. Diameter taken with 278, 14^^ 42''''''.

The third follows B (Fl. 44.) Ophiuchi 4^,1 in time, and
is 23^ more north. It is round, tolerably well defined, and
pretty bright ; its diameter is about 30^^

piece, that may throw it back upon the wires. By this means none of the direft
rays can reach the eye, and thofe iew which are refleded again from the wires do
not interfere fenfibly with the fainteft objects, which may thus be fecn undif-
turbed.

The

Cofijlruclion of the Heavens. 26 c

The fourth follows y\ Sagitt^e 1 7^ i in time, and is 2' more

north. It is perfeclly round, pretty bright, and pretty well

defined ; about % min. in diameter.

The fifth follows the 21II: Vulpecul^ 2^i in time, and is

1° 46^ more north. It is exatlly round, of an equal light

throughout, but pretty fiint, and about 1' in diameter.

The fixth precedes h (Fl. 39.) Cygni 8^,1 in time, and is

1° 26^ more fouth. It is perfe6lly round, and of an equal

light, but pretty faint; its diameter is near i\ and the edges

are pretty well defined.

The planetary appearance of the two firft is fo remarkable,
that we can hardly fuppofe them to be nebulise ; their light is
fo uniform, as well as vivid, the diameters fo fmall and well
defined, as to make it almoll improbable they fhould belong to
that fpecies of bodies. On the other hand, the effed: of dif-
ferent powers feems to be much againft their light's being of a
planetary nature, fince it preferves its brightnels nearly in the
fame manner as the ftars do in fimilar trials. If we would fup^
pofe them to befingle ftars with large diameters we (hall find it
difficult to account for their not being brighter ; unlefs we
Ihould admit that the intrinfic light of fome flars may be very
much Inferior to that of the generality, which however can
hardly be imagined to extend to fuch a degree. We might
fufpe£l them to be comets about their aphelion, if the bright-
nefs as well as magnitude of the diameters did not oppofe this
idea; fo that after all, we can hardly find any hypothefis fo
probable as that of their being Nebulic ; but then they muff
confift of flars that are comprefled and accumulated in the
higheft degree. If it were not perhaps too hazardous to puriue
a former furmife of a renewal in what I figuratively called the
Laboratories of the univerfe, the ftars forming thefe extraordi-
nary nebula, by fome decay or wafte of nature, being no longer
Vol. LXXV. iM m ht

266 Mr. Herschel on the ConJlruSiion of the Heavens,

fit for their former purpofes, and having their projedile forces,
if any fuch they had, retarded in each others atmcfphere, may
rufh at lait together, and either in fuccefilon, or by one general
tremendous fhock, unite into a new body. Perhaps the ex-
traordinary and fuddcn blaze of a new ftar in Cafliopea's chair,
in 1572, might pofiibly be of fuch a nature. But left I fhould
he led too fc\r from the path of obfervation, to which I am
rcfolved to limit myfelf, 1 (liall only point o\it a confiderable
ufe that may be made of the^e curious bodies. If a little atten-
tion to them iliould prove that, iiaving no annual parallax, they
belong moll probably to the clais of nebulae, they may then
be expected to keep their fituation better than any one of the
(lars belonging to our lyflrem, on account of their being pro-
bably at a very great diftanee. Now to liave a fixed point
fomevvhere in the heavens, to which the motions of the reft
may be referred, is certainl}^ of confiderable conlequence in
Aftronomy ; and both thefe bodies are bright and fmall enough,
to anfwer that end (/6).

Datchet near Windfor, W. HERSCHEL.

January i, 1 785.

{h) Having found two more of tliefe curioTis objefls, I add the place of them
here, in hopes that thoie who have fixed inllruments may be induced to take an
early opportunity of obferviug them carefully.

Feb. I, 1785. A very bright, planetary nebula, about half a minute in diarae*
ter, but the edges are not very well defined. It is perfedly round, or perhaps a
very little elliptical, and all over of an uniform brightntis : with higher powers
it becomes proportionally magnified. It follows y Eridani 16' 16" in time, and
is 49' more north than that ftar.

Feb. 7, 1785. A beautiful, very brilliant globe of light ; a little hazy on the
edges, but the hazinefs goes ofi" very fuddenly, fo as not to exceed the 20th part
of the diameter, which I fuppofe to be from 30 to 40''. It is round, or perhaps
a very little elliptical, and all over of an imiform brightnefs : I fuppofe the intenfity
of its light to be equal to that of a flar of the ninth magnitude. It precedes the
third b (Fjl. 6.) Crateris 28' 36" in time, and is 1° 25' more north than that flar.

/■h'/.-j. r,M,>^ n//..v-Yr r.-.h-Mii./. 2f.6.

[ ^67 ]

XIII. Remarks on fpecijic Cravitws taken at different Degrees of
Heat, and an eajy Method of reducing them to a common Stan-
dard. By Richard Kirwan, Efq. F. R. S\

Read February 17, 1785.

THAT a comparative view of the weiohts of equal vohimes
of water and ail other fubftanccs is highly ufefnl 011
many occations, Is too well known to require any proof; but
that a principal ufe refulting from this comparifon, when pro-
perly made, is unattainable by a perufalof the common tables*
I fliall here endeavour to (hew, and at the fame time point
out a remedy for this defe(5l.

One capital advantage derivable from a table of fpecific gra-
vities, is the knowledge of the abfolute weight of any fohd
meafure of the fubftances therein contained, or that of the folid
meafure of a given weight of thofe fubftances, a cubic foot of
water being fuppofed to weigh 1000 ounces avoirdupois, and
confequently a cubic inch of water weighing 253,182 grains.
But the authors who havedifcovered this equation of weight and
meafure, and all thofe who have fince treated this fubje£t, have
negle<5ted to inform us of the temperature at which this agree-
ment takes place ; yet that it cannot take place in all tempera-
tures is evident from the experiments of Dr. Halley and
others, who have found, that from a few degrees above the
freezing to the boiling point, water is dilated about ^'^ of its
bulk; and, confequently, if 1000 ounces at the freezing point
be equal to one cubic foot, they mufl: be equal at the boili'r;'

M m 2 point.

268 M?\ Kir WAN's Remarks onfpecific Gravities

point to one cubic foot and 66,46 cubic inches. And if the-
dilatations are proportional to the degrees of heat throughout
the fcale, there mufl' be an augmentation of 3,136 cubic inches
j^tT cubic foot, produced by every 10 degrees of heat. Both'
thefe points remain, therefore, to be determined ; firil, at what
temperature a cubic foot of water weighs, exaflly 1000 ounces
avoirdupois ; and,2dly, whether the dilatations produced by fuc-
cefiive degrees of heat are proportional to the degrees that pro-
duce them. This laft point has indeed been handled by others,
but with different views j and their determinations are not eafily
appHcable to the prefent queftion.

To examine this matter experirnentally, I ordered a hollow
tinned iron cone to .be made, of four inches diameter in the
bale, one-tenth of an inch diameter in the fummit infide, and
10 inches perpendicular height, whofe folid contents fliould be
42,961 cubic inches, but by a flight diminution of the dia-
meter, and a protuberance arifuig from the foldering, I found
it to contain, in the temperature of 62°, but 42,731 cubic
inches, according to the eftimation of 1000 ounces to the
cubic foot ; and having filled it by immerfion in boiling w^ater,
and taken it up at different degrees of heat, and weighed it
when cold, I found its contents as exprefled in the following
table ; the firft column of which fhews the degrees of heat at
which it was taken up ; the fecond, the weight of the water
contained in it ; the third, the diminution of weight occafioned
by thole degrees of heatj the fourth, the fum of the diminu-
tions of weight in the cubic foot, by the preceding degrees of
heat ; the fifth fhews tlie weight of a cubic inch of water in-
each of thofe degrees of heat ; and the fixth,^the augmentation
of bulk in the cubic foot by every 20'' of heat. The horizontal
lines, marked thus *, 1 have added from the experiments of Mr*

2 Bladh,

at different Degrees of Heat, 26^

Bladh, in the Memoirs of the Academy of Stockhohii for the
year 1776, vvhofe determinations, as far as they reached, agreed
very nearly with mine. The water I ufed was common water
well boiled and filtered. The experiments were for the moil
part three times repeated, and the difference in each trial
amounted to a very few grains.

I.

11.

III.

IV.

V.

VI.

- -

Contents of

Dimin.

Sum of

Weight of

Increafe

Degrees

the eone in

in

dim. in a

a cubic

in cubic

trains.

0

grains.

cubic foot.

inch.

inches.

212

10418,75

29^5

Grs.
16589

243.8

4,892

202

10448,25

77,5

15354

244,51

12,818

182

10525.75

71,75

12133

246,33

",533

162

10596,00

62,60

917I

247,97

10,209

142

10658,60

56,15

6602

249'43

9»i03

122

10714,75

49,00

4310

250,75

7,920

102

10763,75

35,5

2226

25^89

5,7

82

10799,25^

19,5

788

252,72

3,120

^70

252,8
252,97

— — —

,

■^

*"~ ~ '

*66

253,06

_ _ -

•*«

62

10818,75

0

0

253,182

0

Total increafe of

^Vr^,

253,3
253^46

bulk from 62° to
2l2°zr65,327cu.
bic inches.

5^

»5o

Increafe

Increafe

^

"" *"

"^

•

Decreafe

Total from 36'^ to

42

10830,75

12

485,3

253,463

1,936

212=67,327 cu-

^36,5

253,5

0,064

bic inches.

Hence we fee, that a cubic foot of water weighs 4^5,3 grains
more at 42° than at 62°, and confequently is equal to 1001,109
avoirdupois ounces, and in the temperature of 82^ it weighs lels
than at 62° by 788,5 grains, and therefore is equal to 998,198
ounces. At the boiHng point it wants 16589 grains, or 37,915
ounces of the weight it poffefles at 62°, and confequently
weighs but 962,085 ounces, &c^

la

,^70 i\/r. Kirwan's Remarks onfpecifc Gravities

In this calculation I take no account of the difference arlfing
from the expanfion of the veffel, it being only 0,067 of an
iuch at the boiling point; for, according to Bouguer, iron is
dilated 0,00055 of Its bulk from the freezing to the boiling
point; confequently 42,961 cubic inches gain only 0,067 °^ ^^^
inch, augmenting the diameter and perpendicular height of
this fruftum of a cone at the boiling point in that proportion.

-Hence alfo we fee, that the expanfions of water are not pro-
portional to the degrees of heat ; for by 20 degrees of heat from
62° to 82 a cubic foot of water is dilated onlyj,! 2 inches, but by
the next 20 degrees of heat, that is, from 82° to 102°, it is
expanded 5,7 inches, &;c.

Mr. Bladh found the volume of wat?er at 32° to be equal
to that at 53°,6 ; but that this irregular expanfion ceafed at 36"6,
and, according to Mr. De Luc (who firfl dlfcovered it) at 43''.

As the expaiilion of liquids by equal degrees of heat is much
greater than that of folids, it happens, that the fpecific gravi-
ties of the fame folid taken at different temperatures will be
ditferent ; and, what appears more extraordinary, the fame folid
will appear fpecifically heavier in higher than in lower tempera-
tures ; for the fame volume of water being lighter in higher
than in lower temperatures, the folid will lofe lei's of Its weight
in it in the former than in the latter cafe : this miftake we
may remedy by Infpe^ting the fifth column of the foregoing
table and the following analogy : as the weight of a cubic inch
of water at the temperature of 62° is to the weight of a cubic
inch of water at n degrees of temperature, fo is the fpeciiic
gravity found at n degrees of temperature to that which will
'be found at 62^.

Thus., if 1000 grains of iron be weighed in water of the
temperature of 62% and it iofcs therein 1 3,^^33 grains, if the

* fame

at djfereni Decrees of Heat, i^r

fame piece of iron be weighed in water of the temperature of
73®, it will lofe but 13,313 grains; for the loflcs of weight
will be as the weights of equal volumes of water at thofe tem-
peratures, which, as we have feen, are as 253, 1 8 to 252,8 ; there-
fare, its fpecific gravity in water of the temperature of 62*
will' be 7,49; and in water of the temperature of 75°. 'jr^ii ;
but we may corre£l this by the above analogy,, for
— 253,8 . 252,18 :: 7,511 . 7,49.

By this means we obtain the advantage of difcovering the
true weight of a cubic foot of any fubflance whofe fpecific gra-
vity is known, which it is now plain cannot be known when
bodies are hydroffcatically weighed at any temperature a fev/
degrees above or below 62'', without fuch redudion, or fub-
tracting the quantities in the fourth column,.

This method is equally applicable, and with equal neceffity,
to other means of finding fpecific gravities, as areometers, the
comparlfon of the weights of equal meafures of liquids, the
different lofles of weight of the fame folid, when weighed in
difi^erent liquids, &c. In all which cafes the weight of water
at 62°, or the lofs of weight of a Iblid in water at 62°, (hould
be found by the above analogy.

Dr. Hales and fome others have eflimated the weight of a
cubic inch of water at 254 grains, which is an evident miflake,
as it is true in no degree of temperature, and produces an error'
of more than three ounces in the cubic foot.

[ 272 ]

XIV. Electrical Experiments made In order to af cert am the non-
cotiducti?ig Power of a perfeSl Vacuum^ &c. By Mr, 'Wil-
liam Morgan ; communicated by the Rev. Richard Price,
LL.D, F.R.S,

Read February 24, i"]^S*

THE non-condu£ling power of a perfect vacuum is a fa£t
in electricity which has been much controverted among
philofophers. The experiments made by Mr. Walsh, F.R.S. in'
the double barometer tube clearly demonftrated the impermeabi-
lity of the eledtric light through a vacuum ; nor was it, 1 think,
precipitate to conclude from them the impermeability of the
c\cd:nc Jluid itfelf. But this conclufion has not been univerfally
admitted, and the following experiments were made with the
view of determining its truth or fallacy. When I firft attended
to the fubje6l, I was not aware that any other attempts had
been made befides thofe of Mr. Walsh; and though I have
iince found myfelf to have been in part anticipated in one of
my experiments, it may not perhaps be improper to give fome
account of them, not only as they are an additional teftimony
in fupport of this fa6l, but as they led to the obfervation of
fome phaenomena which appear to be new and interefting.

A mercurial gage B (fee tab. IX. fig. 1.) about 15 inches l_
long, carefully and accurately boiled till every particle of air
was expelled from the infide, was coated with tin-foil five
inches down from its fealed end (A), and being inverted into

mercury

Mr. Morgan's Experiments, ScCs 273

-mercury through a perforation (D) in the brafs cap (E) which
covered the mouth of the ciftern (H), the whole was cemented
together, and the air was exhaufted from the iniide of tlie
ciftern through a valve (C) in the brafs cap (E) jufl: mentioned,
■which producing a perfect vacuum in the gage (B) afforded an
inftrument peculiarly well adapted for experiments of this
kind. Things being thus adjufled (a fmall wire (F) having
been prevloully fixed on the infide of the ciflern to form a com-
munication between the brafs cap (E) and the mercury (G)
into which the gage was inverted) the coated end (A) was ap-
plied to the conductor of an electrical machine, and notwith-
ftanding every effort, neither the fmalleft ray of light, nor the
ilighteft charge, could ever be procured in this exhaufted gage,
I need not obferve, that if the vacuum on its infide had been a
conductor of eleCtricity, the latter at leaft muft have taken
place , for it is well known (and I have myfelf often made the
experiment) that if a glafs tube be exhaufted by an air-pump,
and coated on the outfide, both light and a charge may very
readily be procured. If the mercury in the gage be imperfectly
boiled, the experiment will not fucceed ; but the colour of thc-
eleCtric light, which, in air rarefied by an exhaufter, is always
violet or purple, appears in this cafe of a beautiful green, and,
what is very curious, the degree of the air's rarefaction may be
nearly determined by this means ; for I have known inftances,
during the courfe of thefe experiments, where a fmall particle
of air having found its way into the tube (B), the eleCtrlc
light became vifible, and as ufual of a green colour ; but the
charge being often repeated, the gage has at length cracked at
its fealed end, and in confequence the external air, by being
admitted into the infide, has gradually produced a change in
the eleCtrIc light from green to blue, from blue to indigo, and
Vol. LXXV. N n io

2r4 Mr. Morgan's Experiments toafcertain the

' fo on to violet and purple, till the medium has at lall: become fo
Azw^t as no longer to be a conductor of ele6lricity. I think
there can be little doubt from the above experiments of the
non-condu6ling power of a perfe(5l vacuum ; and this fa6l is
flill more flrongly confirmed by the phaenomena which appear
upon the admiflion of a very minute particle of air into the
iniide of the gage. In this cafe the whole becomes imme-
diately luminous upon the flightefl application of electricity,
and a charge takes place, which continues to grow more and
more powerful in proportion as frefh air is admitted, till the
denfity of the conducting medium arrives at its maximum,
which it always does when the colour of the ele(ftric light is
indigo or violet. Under thefe circumftances the charge may
be fo far increafed as frequently to break the glafs. In fome
tubes, which have not been completely boiled, 1 have obferved,
that they will not condud the eledlric fluid when the mercury is
fallen very low in them, yet upon letting in air into the ciftern
(H), fo that the mercury fhall rife in the gage (B), the elec-
tric fluid, which was before latent in the iniide, (hall now be-
come vifible, and as the mercury continues to rife, and of con-
fequence the medium is rendered lefs rare, the light fhall grow
more and more vifible, and the gage fhall at lafl be charged,
notwithflanding it has not been near an eledlrical machine for
two or three days. This feems to prove, that there Is a limit
even in the rarefa£llon of air, which fets bounds to its con-
dudling power ; or, in other words, that the particles of air may
be fo far feparated from each other as no longer to be able to
tranfmit the ele£lric fluid ; that if they are brought within a
certain diflance of each other,their conducing power begins, and
continually increafes till their approach alfo arrives at its limit,
when the particles again become fo near as to refiil the paflage
4 of

noyi'CondudVing Powe^ of a perfedl Vacuum, 2*^5

of the fluid entirely, without employing violence, v/hich is
the cafe in common and condenfed air, but more particularly
in the latter. Thele experiments, however, belong to another
fubje6t, and may poffibly be communicated at Ibrae future
time.

It is furprifing to obferv^e, how readily an exhaufted tube is
charged with eledricity. By placing it at ten or' twelve inches
from the conductor the light may be feen pervading its in{ide,and
as ftrong a charge may fometimes be procured as if it were in
contact with the condudlor: nor does it fignify how narrow the
bore of the glafs may be ; for even a thermometer tube, having
the minuteil: perforation poffible, will charge with the utmoft
facility ; and in this experiment the ph'jenomena are peculiarly
beautiful.

Let one end of a thermometer tube be fealed hennetically.
Let the other end be cemented into a brafs cap with a valve,
or into a brafs cock, fo that it may be fitted to the plate of an
air-pump. When it is exhaufted, let the fealed end be applied
to the conductor of an electrical machine, while the other end
is either held in the hand or conne£ted to the floor. Upon the
flighteft excitation the eleCtric fluid will accumulate at the fealed
end, and be difcharged through the infide in the form of a
fpark, and this accumulation and difcharge may be inceffantly
repeated till the tube is broken. By this means I have had a
fpark 42 inches long, and, had I been provided with a proper tube,
I do not doubt but that I might have had a fpark of four times
thatlengtli. If, inftead of the fealed end, a bulb be blown at that
extremity of the tube, the eleftric light will fill the whole of
that bulb, and then pafs through the tube in the form of a
brilliant fpark, as in the foregoing experiment j but in this cafe
1 have feldom been able to repeat the trials above three or four

N n 5 times

276 Mr. Morgan's Experiments to a/certain the

times before the charge has made a fmall perforation in- the.
bulb. If again a thermometer filled with mercury be inverted
into a ciftern, and the air exhaufted in the manner I have de-
scribed for making the experiment with the gage, a Torricellian!
vacuum will be produced ; and now the elettric light in the
bulb, as well as the fpark in the tube, will be of a vivid green;
but the bulb will not bear a frequent repetition of charges be-
fore it is perforated in like manner as when it has been ex-
haufted by an air-pump. It can hardly be neceflary to obferve,.
that in thefe cafes the ele£tric fluid affumes the appearance of a.
fpark *, from the narrownefs- of the pafiage through which it
forces its way» If a tube, 40 inches long, be fixed into a globe:
8 or 9 inches in diameter, and the whole be ex-haufted,. the eledtric
fluid, after pafling in the form of a brilliant fpark throughout
the length of the tube, will, when it gets into the infide of the
globe, expand itfelf in all diredlions, entirely filling it with a;
violet and purple light, and exhibiting a ftriking inftance of the.
vail elafticity of the eledric fluid.

I cannot conclude this paper without acknowledging my obli^-
gations to the ingenious Mr. Brook, of Norwich, who, by com-
municating to me his method of boih.ng mercury, has been the
chief caufe of my fuccefs in thefe experiments t. I have lately

learned'

* By cementing the firing of a giiittar into, one end of a thermometer tube,, a
fpark may be obtained as well as if the tube had been fealed hermetically.

t Mr. Brook's method of making mercurial gages is nearly as follows. Let a-
glafs tube L (fee fig. 2.), fealed hermetically at one end, be bent into a right-
angle within two orthree inches cf theother end. At the diflance of about an inch.
or lefs from the angle let a bulb (K), of about | of an inch in diameter, be blown
m the curved end, and let the reniaiadcr of this part of the tube be drawn out (I)

non-conch^iing Power of a per feSi Vacuum, z'-j

kanied from him, that he has alfo afcertained the non-cone ucliiig,
power of a perfe<£l vacuum ', but what f!:eps he took for that pur-
pofe I know not. Of his accuracy, however, I am fo well con-
vinced, that hadlnever made an experiment myfelf,! (hould,upoii
his teftimony alone, have been equally afllired of the fad. To
mod: of the preceding experiments Dr. Price, Mr. Lane, and
fome others of my triends, have been eye-witnelles, and I be-
lieve that they were as thoroughly fatisfied as myfelf with the
refults of them. I mufr beg leave to obferve to thofe who wiih
to repeat them,, that the firft experiment requires fome nicety,,
and no inconfiderable degree of labour and patience. I have
boiled many gages for feveral hours together without fuccefs,,

fo as to be fufficiently long to take hold of, when the mercury is boiling. The'
bulb (K) is defigned as a receptacle for the mercury^, to prevent its boiling over,
and the bent figure of the tube is adapted for its inverfion into the ciftern ; for by
breaking off the tube at (M) within | or | of an inch of the angle, the open
end of the gage may be held perpendicular to the horizon when if is dipped into
the mercury in the ciftern, without obliging us to bring our finger, or any other
fubftance, into contaft with the mercury in the gage, which never fails to render the
inftrument imperfeft. It is neceflary to obferve, that if the tube be fourteen-
or fifteen inches long, I have never been able to boil it effe£lually for theexperi-^
ments mentioned in this paper in Icfs than three or four hours, although Mr,
Brook feems to prefcribe a much fliorter time for the purpofe ; nor will it even
then fucceed, unlefs the greateft attention be paid that no bubbles of air lurk
behind, which to my own mortification I have frequently found to have been the
cafe ; but experience has at length taught me to guard pretty well againfl this
difappointment, particularly by taking care that the tube be completely dry before
the mercury is put into it ; for if this caution be not obferved, the inftrument can
never be made perfedl. There is, however, one evil which I have not yet been able to
remedy; and that is, the introduction of air into the gage, owing to the unboiled
mercury in the ciftern ; for when the gage has been a few times exhaufted, the mer-
cury which originally filled it becomes mixedv/ith that into which it is inverted, and
in confequence the vacuum is rendered iefs and lefs perfeft, till at laft the inftru-
ment is entirely fpoiled. I have juft conftrufted a gage fo as to be able to boil the
mercury in the ciikrn, but have not yet afcertained its fuccefs,

and!

27'8 Mr. M^noA^^h Experiments, &c.

and was for fome time difpofed to believe the contrary of what
1 am now convinced to be the^^^truth. Indeed, if we reafon
a priori, I think we cannot luppofe a perfect vacuum to be a
perfect condudor Vv^ithout fuppofing an abfurdity: for if this
were the cale, eitlier our atmofphere muft have long ago been
deprived of all its eledlric fluid by being every where fur-
rounded by a boundlels condu6lor, or this fluid muft pervade
every part of infinite fpace, and confequently there can be no
fuch thing as a perfeft vacuum in the univerfe. If, on the
contrary, the truth of the preceding experiments be admitted,
it will follow, that the conducing power of our atmofphere in-
creafes only to a certain height, beyond which this power be-
gins to diminifh, till at laft it entirely vanlflies ; but in what
part of the upper regions of the air thefe limits are place i, I
will not prefume to determine. It would not, perhaps, have
been difficult -to have applied the refults of fome of thefe ex-
periments to the explanation of meteors, which are probably
owing to an accumulation of eledtricity. It is not, however,
my prefent deflgn to give loofe to my imagination. I am {qi\^
iible, that by indulging it too freely, much harm is done to,
real knowledge ; and therefore, that one fa6t in philofophy well
afcertained is more to be valued than whole volumes of ipecu-
latlve hypothefes.

dhatham-Place, Feb. 12, 1785.

J'/„fr,Tmm i:./ /. XXJ ■ Till, IXy,

ms.

y

'•:^y<f. 2.

[ ^19 3

XV. Experiments and Obfervations relating to Air and Water »
By the Rev. Jofeph Prieflley, LL,D. F.R.S,

Read February 24, 1785.

EVER fince the difcovery of the diminution of refpirabic
air in thofe proceffes which are generally called phlogijiicy
it lias been a great objed with philofophers to find what be-
comes of the air which difappears in them. Among others, I
have made and publifhed a variety of experiments with that
view; but though by this means fome farther progrefs was
made in the philofophy of air, and confequently our know-
ledge of the principles, or conflituent parts, of natural fub-
fiances was extended, I did not by any means fucceed to my
fatisfadion with refpedt to the immediate obje6l of my re-
fearches. Others, however, were more fuccefsful, and their
fuccefs has at length enabled me to refume my experiments
with more advantage ; by which means I have been led both to
confirm their conclufions, and, by diverfifying the experi-
ments, to throw confiderable light upon various other chemical
procefies. The refult of thefe obfervations I fhall lay before
the Society, with as much brevity and diftindnefs as I can.

In the experiments of which I fhall now give an account,
I was principally guided by a view to the opinions which have
lately been advanced by Mr. Cavendish, Mr. Watt, and
M. Lavoisier. Mr. Cavendish was of opinion, that when
^/r is decompofed, water only is produced; and Mr. Watt

concluded ■

2'8o Dr. Priestley's Experiments and Obfervatwns

concluded from fome experiments, of which I gave an account ^
to the Society, and alfo from fome obfervations of his own, I
that water confifts of dephlogifticated and inflammable air,
in which Mr. Cavendish and M. Lavoisier concur with i
him; but Mr. Lavoisier is well known to maintain, that j
there is no fuch thing as what has been called phlogijlon, affirm-
ing inflammable air to be nothing elfe but one of the elements
or conftituent parts of water. In the following experiments I
alfo had a particular viev/ to a concluiion which I had drawn
from thofe experiments, of which an account is given in my
laft communications to the Royal Society ; ^'/z. that inflam-
mable air is pure phlogifton in the form of air, at lead with
the element of heat ; and that fixed air confifls of dephloglfti-
Gated and inflammable air ; both which do£lrines had been firfl;
advanced by Mr. Kirwan, before I had made the experiments
which I tlien thought clearly proved them.

Such were the hypothefes to which I had a view when I
began the following courfe of experiments, which I hope will
be an a(Jmonition to myfelf, as well as to others, to adhere as
rigoroufly as poffible to actual obfervations, and to be extremely
careful not to overlook any circumftance that may poffibly con-
tribute to any particular refult. I (hall have occafion to notice
my own miilakes with refped to conchifions, though all the
faBs were (Iridly as I have reprefented them. But whllft phi-
lofophers are faithful narrators of what they obferve, no perfoii
can juftly complain of being milled by them ; for to reajon
from the fads with which they are fupplied is no more the
province of the perfon who difcovers them, than of him to^
whom they are difcovered.

One of the mod fimple of all phlogiftic proceiTes is that \\\

which metals are ignited in dephlogifticated air. I therefore

3 began

relating io Air and Water, 28 1

began with this, with a view to afcertaiii whether any Wiitcr
is produced when the air is made to dlf:ippear in it. i\ccord-
ingly, into a glafs veflel containing 7 ounce meafares of pretty
pure dephlogifticated air, I introduced a quantity of iron turn-
ings (which is iron in fmall thin pieces, exceedingly conve-
nient for thefe and many other experiments) having previoufly
made them, together with the veiTcl, the air, and the mercury
by which it was confined, as dry as I poffibly could AHo, to
prevent the air from, imbibing any moifture, I received it imme-
diately in the veffel in which the experiment was made, from
the procefs of procurhig it from red precipitate ; fo that it had
never been in contact with any water.

I then fired the iron, by means of a burning lens, and pre-
fently reduced the 7 ounce meafures of air to .65 ; but I found no
more water after this procefs than I imagined it had not been
poffibie for me to exclude, as it bore no proportion to the air
which had difappeared. Examining the refiduum of the air, I
found one-fifth of it to be fixed air, and when I tried the purity
of that which remained by the tefi- of nitrous air, it did not
appear that any phlogifticated air had been produced in the pro-
cefs : for though it was more impure than I fuppofc the air
with which I began the experiment muft have been, it was not
more fo than the phlogifticated air of the 7 ounce meafures,
which had not been affe£led by the procefs, and which muft
have been contained in tne refiduum, would neceilarily make
it. In this cafe one meafure of this refiduum and two of ni-
trous air occupied the fpace of .32.

In another experiment of this kind, ten ounce meafures of
dephlogifticated air were reduced to .8, and by wafliing in lime
water to . :8. In another experiment, in which 7! ounce mea-
fures of dephlogifi:icated air were reduced to half an ounce
Vol, LXXV. O o meafure,

282 Dr. Piii&sTr,EY*s Uxperlmenh and Ohfervatiom

meaflire, of which one-fifth was fixed air, the refiduum wag
quite as pure as tiie air with which I began the experiment, the
teft with nitrous air, in the proportions above-mentioned,,
giving .4 in both cafes.. To what circumftance the. difterence;
mipht be owina: I c.annot tell.

In thefe experiments the fixed.air mufi, I prefume, have been-
formed by the union of the phlogiflion from the iron and the,
dephlcgiilicated air in which it was ignited ; but the quantity)
of it was very fmall in proportion to the air which had difap^-
peared, and at. that time I, had no fufpicion that the iron, which.
liad been melted, and gathered into round balls, could have,
imbibed it; a melting heat having been fufficient, as I had.
imagined, to expel, every thing that was capable of afluming
the form of air from any fubflance whatever. I was therefore;
Intirely at a iofs about what muil: have become of the. air.

Senfible, however,, that fuch a quantity of air muft have,
been imbibed hy fo met hing to w^^iich it mu ft have given a, very
perceivable addition of weight, and feeing . nothing elfe that
could have imbibed it,, it occurred to ma to weigh the calx, into,
which the iron had been reduced ; and I prefently, found, that
the dephlpgifticated air had adually been' imbibed by the melted
iron, in the fcjme manner as inflammable air, ia my former,
experiments, had been imbibed by the melted calces of metals,
however impoffible fuch an abforption might have appeared to
vat a priori. In the firfl: inftance, about twelve ounce mea--
fures af dephlogiliicated air had difappeared, and the iron had
gained fix grains in weight. Repeating the experiment very,
frequently, I always found, that other quantities of iron,
treated in the fame manner, gained fimilar additions of weight,,
which was always very nearly that of the air which haddif-^
appeared, .

This

relating to Air and Water. .283

This calx of iron, I then concluded, was by no means what
1 had before taken it to be, viz, 2. pure calx o'C f.ag^ but either
the calx, or the iron itfelf, faturated with pure air. This cal-
ciform fubflance I found, by various experiments, to be the
fame thing with the fca/es that fly from iron wh-en it is made
red-hot, or the fubflance into which it runs in a verv intenfe
heat, in an open fire.

Concluding from the preceding experiment, that iron, fufli-
ciently heated, was capable of faturating itfelf with pure air,
extracted from the mefs of the atmofphere, I then. proceeded to
melt it with the beat of a burning lens in the open air; and I
prefently found, that perfect iron was eafily fufed in this way,
and continued in this fufion a certain time, exhibiting the ap-
pearance of boiling or throwing out air, whereas it was on the
contrary imbibing air; and when it was faturated the fufion
ceafed, and the heat of my lens could not make any farther
imprefiion upon it. When this was the cafe, I always found
that it had gained weight in the proportion of yl to 24, which
is very nearly one-third of its original weight. The fame was
the effe(5l when .1 meltedy?i'^/in^the fame circumflances, and
alfo every kind of iron on which the experiment could be tried.
But I havefome reafon to tliink, that with a greater degree of
heat than I could apply, the iron might have been kept in a
fiate of fuiion fomewhat longer, and by that means have im-
bibed more air, even more than one-third of its original
weight.

There was a peculiar circumflance attending the melting of

caji iron with a burning lens, w^hich made it impoflible to afcer-

tain the addition that was made to its weight, and at the fame

time afforded an amazing fpeclacle ; for the moment that any

quantity of it was melted, and gathered into^i. round ball, It began

O 0 2 t.Q

284 D^'- Priestley's Experiments andOhfervations
to difperfe in a thoufand dire£tlons, exhibiting the appearance of
a mofl beautiful fire- work, fome of the particles flying to the
diflance of half a yard from the place of fufion ; and the whole
was attended with a confiderable hifiins: nolle. Some of the
targcft pieces which had been dlfperfed in this manner 1 was
able to collect, and having fiibje6led them to the heat of the
lens, they exliiblted the fame appearance as the larger mafs from
which they had beeii fcattered.

When I melted this caft iron in the bottom of a deep glafs
receiver, in order to colle£t all the particles that were dlfperfed,
they firmly adhered to the glafs, melting it fuperhclally,
though without making it crack, fo that it w^as fllli Impoflible
to colle6l and weigh the particles. However, I generally
found that, notwithflanding the copious difperiion, what re-
mained after the experiment rather exceeded than fell fliort of
the original weight of the iron. Sometimes a piece of com-
mon iron, and efpecially fleel, would make a little hiffing in
the fufion, and a particle or two w^ould fly off; but this was
liever confiderable *.

Having now procured what I thought to be a new calx of
iron, or a calx faturated with pure air, 1 endeavoured to revive
it bv maklnp- it imbibe inflammable air, in the fame manner
that I had before made iron, and various other metals, by melt-
ing them in a veilel containing inflammable air. In this I fuc-
qeeded ; but in the courfe of the experiment a new and very
nnexpecSled appearance occurred. I took a piece of iron which
I had faturated with pure air, and putting it into a glafs vefTel

* On being informed of the above-mentioned phenomena, Mr. Watt con-
cluded, that the bafis of the dephlogillicatcd air united to the phlogifton of the iron,,
and formed luaUr, which was attraded by, and remained fo firmly united to the
culx of iron, as to refill the effefts of heat to feparate them,

containing

relating to u4Ir and JVater, 2S5

containing inflammable air, confined by water, threw upon it
the focus of the lens, and prefently perceived the inflammable
air to difappear, and without thinking of any thing efcaping
from the calx of iron (which had been fubjeded to a greater
heat before) I imagined that I fhould have found the addition of
the weight of air in the iron, and the refult might be an iron
different from the common fort. But 1 found, to my furprife,
that the iron, which had exhibited no new appearance in tliis
mode of treatment, had loft weight, inftead of gaining any.
The piece of iron on which I made this firft experiment weighed
III grains, and 7! ounce meafures of inflammable air had dif-
appeared while the iron had loft i\ grains.

Confidering the quantity of Inflammable air that had dlfap-
peared, vh. yi ounce meafures, and the dephloglfticated air
which had been expelled from the Iron, vk. 2| grains, which
is equal to about 4.1 ounce meafures, I found that they were
very nearly in the proper proportion to faturate each other,
when decompofed by the eledrical fpark, viz. two meafures of
inflammable air to one of dephloglfticated air. I therefore had
now no doubt but that the two kinds of air had united, and
had formed either Jixed air or water ; but which it was I could
not tell, having had water on the receiver in which the experi-
ment was made, and having neglected to examine the ftate of
the air that remained, except in a general way, by which I
found, that it was ftill, to appearance, as inflamm.able as ever.

With a view to determine whether y£iW^/r, or ivater, would
be the produce of this mode of combining inflammable and
dephloglfticated air, I repeated the experim.ent in a veflel in
which the inflammable air was confined by mercury, and both
the veflel and the mercury had been previoufly made as dry as
poflible. I had no fooner begun to heat the iron, or rather/^^.

in

2*56 Dr. Priestlev's Experiments mid Obfervations
in thefe circumftances, than I perceived the air to diminifh, and
at the fame time the infide of the veflel to grow very cloudy,
with particles of dew, that covered almofl: the whole of it.
Thefe particles by degrees gathered into drops, and ran down the
fides of the veflel in all places, except where it was heated by
the fun-beams ; fo that it then appeared to me very evident,
that water, with or without fixed air, was the produce of the
inflammable aii*, and the pure air let loofe from the iron in this
aiode of operation-; though afterwards I was taught by Mr.
Watt to correct. thiG hypothefis, and to account for this refult
in a different ^rn.anner. When I had examined the remaining
air, it was as inflammable as ever, without containing any
mixture of -fixed air at all.

When I collected the water which was produced in this ex-
periment by means of a piece of filtering paper, carefully in-
troduced to abforb it, I found it to be, as nearly as poflible, of
the fame weight with that which had been loft by the iron :
and alfo, in every experiment of this kind, in which I attended
to this circumftance^ I found that the quantity of inflammable
air which had dlfappeared was about double to <that of the de-
phlogiftlcated air fet loofe from the iron, fuppofing that weight
to have been reduced into air. Thys at one time I made a piece
of this flag imbibe 5 1. ounce meafures of inflammable air, while
it loft as much as the weight of about 3. ounce ^^eafures of de- |
phlogiftlcated air, and the water colleded weighed 2 grains.
Another time a piece of flag loft 1.5 grains^ and the water
produceil was 1.7 grains; but perfect, accuracy is not to be ex-
pe(5ted. I fliall only mention one more experiment of this
kind, in which ~6| ounce meafures of inflammable air were
reduced to .92 ounce meafare, and the iron had loft 2 grains,
^q(jual in weight to 3.3 ounce meafures of dephloglfticated air.

In

relating to Air and Water, 2 S 7

Jn all the above-mentioned experiments, the inflammable air
was that which is produced by the lolution of iron In acid-.

As before I had finifhed this courfe of experiments I had-
fatisfied mvfeif that inflammable air always contains a portioii-
of water, and alfo, that: when it has been lome time confined
by water, it imbibes more, foas to-be increaied in its fpecinc.
gravity by that means, L repeated the experiment w^ith inflam-
mable air which had not been confined by water j. but which was-
received in a veflel of- dry mercury from tha veflel in which it
was -generated ; but I prefently perceived that wrater was oro-
duced in this cate alfo, and to appearance as copioufly as in the
former experiment, hideed, the quantity of WT.ter produced,
which fo greatly exceeded the w^eight of all the inflammable
air,^ is fufficient to prove that it muil: have had fom.e other-
fource tiian any conflituent part of:that air, or the whole of it.^..
together with the water, conttained in it, without taking into^
confideratlon the correfpondinglofs of weight in the iron.-

I mufi: here obfervc, tliat the iron flag which I had treated ill-
this manner, and which had thereby loft the weight which -
it had acquired by melting in dephlogifticated air, became per-
feoi iron as at flrft, and was then capable of being melted^ by
the burning lens again; fo that the fame piece of iron would"
ferve for thefe experiments as long as the operator fhould chufe.
It was evident, therefore, that if the iron had loft its phlo-
gifton in the preceding fufion, it had acquired it again from the^
inflammable air which it had abforbed ; and I do not fee. how the
experiment can be accounted for in any other way,, which ne- •
ceflarily implies the reality of phlogifton as a conftituent prin-
ciple in bodies. This, at leaft, is the moft natural way of.
accouiitiDg for the appearances. -

5 , Having"

2'8S Dr. Priestley's Experiments and Obfervations

Having had this fuccefs with the calx, or icales of iron, I
tried the calx of copper^ or thofe fcales which fly from it when
it is made red-hot ; and I found water produced in the inflam-
mable air in the fame manner as when I ufed the fcales of iron
in the fame circumflances. I alfo had the fame refult when I
Yewived. precipitate per fe m inflammable air; but having at that
time a very weak winter's fun, I could not make the experi-
ment with fo much advantage as I could have wiflied.

Iron, I found, acquired this additional weight by melting
in an earthen retort, as well as in the open air by the fun-
beams, if it were pofTible for it to attract air, or whatever elfe"
it is that is the immediate caufe of its additional weight.
Three ounces of common iron filings, expofed to a flrong heat
in an earthen retort, gained 1 1 dwts, or 264 grains, and yet
was very far from having been completely fufed. Having a
glafs tube communicating with the retort, in order to collect
any air that the iron filings might give out, I found that when
they were very hot, the water alcended within the tube ; which
fhews that the iron was then in a ftate of abforbing, and not'
of giving out any air.

Seeing (o much water produced in thefe experiments with
inflammable air, I was particularly led to reflect on the relation
which they bore to each other, and efpecially to Mr. Cav^.n-
dish's ideas on the fubje6l. He had told me that, notwith-
ftanding the experiments of which I had given an account to^
the Royal Society, and from which I had concluded that in-
flammable air was pure phlogifton, he was perluaded that wafer-
was eliential to the produclion of it, and even entered into if
as a conftltuent principle, x^t that time I did not perceive the'
force of the arguments which he flated to me, efpscially as, iit'
the experiments with charcoal, I totally difperfed any quantity

of

relating to Air and IVater, 28^

of it with a burning lens In vacm, and thereby filled my,
receiver with nothing but inflammable air. I kad no fufpicion
that the wet leather on which my receiver flood could have
any influence in the cafe, while the piece of charcoal was fub-
je6l to the intenfe heat of the lens, and placed feveral inches
above the leather. I had alfo procured inflammable air from
charcoal in a glazed earthen retort two whole days fucceflively,
in which it had given inflammable air without intermifliou.
Alfo iron filings in a gun-barrel, and a gun- barrel itfelf, had
always given inflammable air whenever I tried the experiment.

Thefe circumflances, however, deceived me, and perhaps
would have deceived any other perfon ; for I did not know,
and could not have believed, the powerful attraiflion that chm--
coal, or iron, appear to have for water when they are intenfely
hot. They will find, and attra£l it, in the midfl of the hottefl
fire, and through any pores that may be left open in a retort;
and iron filings are feldom fb dry as not to have moiflure
enough adhering to them, capable of enabling them to give a.
conliderable quantity of inflammable air. But my attention
benig now fully awake to the fubjeifl, I prefently found that
the circumflances above-mentioned had adlually mifled me; I
mean with refpe£l to the conclitjion which T drew from the expe-
riments, and not with refpedt to the experiments themfelves,
every one of which, I doubt not, will be found to anfwer,
whenever they are tried by perfons of fuf^cient fkill and pro-
perly attentive to all the circumflances.

Being thus apprifed of the influence of unperceived moiflure
in the production of inflammable air, and wiUing toafcertain it
to my perfect fatisfadion, I began with filling a gun-barrel with
iron fihngs in their common flate, without taking any parti-
cular precaution to dry them, and I found that they gave air as

Vol. LXXV. P p they

/

290 T)r, FRiEsrLEY''s: Expen'me?2l5 and Objervailons
they had been ufed to do, and conthined to do fo many hours ■;-.
1 even got ten ounce meafures of intlammable air from two^
ounces of iron filings in a coated glafs rttort. At length, how-
ever, the produ6tion of inflammable air from the gun-barrel'
ceafed ; but on putting water into i'c, the air was produced^
again, and a few repetitions of the experiment fully fatisfied'
3ie that r had been too precipitate in concluding th-at inflam-
mable air is pure phlogiilon.

I then repeated the experiment with the charcoal, making-
the receiver, the fland on w^iich I placed the charcoal^ and the-
charcoal itfelf,, as dry and as hot as poffible, and ufing cement
inftead of a wet leather to exclude the air. In thefe circum-
ifances I was not able, with the advantage of a good fun, and-
an excellent burning lens, to decompofe quite fo much as two^"
grains of the piece of charcoal, which gave me ten ounce mea-
fures of inflammable air; and this, I imagine, was effected by
means of fo much moifture as was depofited from the air in its
fl:ate of rarefaction, and before it could be drawn from the
receiver. To the production of this kind of inflammable air I
was therefore now convincedj that? water is as necellkry as to
that' from iron.

It was in this frate of my experiments that I received an au-
thentic account of thofe of M. Lavojsier, on tranfmitting water
through an hot iron tube and alfo through a hot copper tube-
containing charcoalj and thereby procuring large quantities of
inflammable air, M. Lavoisier himfelf having been fo obliging^
as to fend me a copy of his Memoir on that fubjeft. I had
heard an account of the experiments Ibme months before; but*
it was fo imperfeCl a one, that I own I paid little attention to
them. At this time, however, I was prepared to be fufficiently
fenfible of their value.

In

relailng to Air and 'IVu kr. £ 9 1

In my laft communications to the Royal Society, it will be
ieen that I had tranfmitted the vapour of feveral fluid lub-
ftances through red-hot earthen tubes, and thereby procured
different kinds of air. M. Lavoisier adopted the fame pro-
cefs, but ufed an iron tube ; and by means of that circumliancc
made a very valuable difcovery which had efcaped me. I had
indeed on one occafion madeuie of an iron tube, and tranfmit-
ted fteam through it ; but not having at that time any view to
the production of alr^ I did net collect it at all, contenting
myfelf with obferving that ivater^ after being made -red-hot
was flill water, there being no change in Its fenfible properties.
Being now fartlier infl:ru6i:ed by the experiment of M. La-
voisier, I was determined to repeat the procefs with all the
attention I could give to it ; but I fliould not have done this
with fo much advantage, if I had not had the afliflance of Mr^
Watt, who alway-s thought that M, Lavoisier's experi-
ments by no means favoured the conclufion that he drew fi'om
them. As to myfelf, I was a long time of opinion that his
conclufion was juft, and that the inflammable air w^is really
furnlfhed by the water being deconipofed in the procefs. But
though I continued to be of this opinion for fome time, the
frequent repetition of the experiments, with the lig;ht which
Mr. Watt's obfervations threw upon them, fatlstied me at
length that the inflammable air came principally from the cliar*
coal, or the iron.

I fhall firfl: relate the refult of the experiment that was made
with charcoal^ and then thofe with iron and other fubftances, in
contad with which (when they were in a ftate of fufion, or at
leafl: red-hot) I made fleam, or the vapour of other liquid fub-
fiances, to pafs. I fhall only obferve that, previous, to this, I
began to make the experiments with coated glafs tubes, which

P p 3 I found

2^1 Dr. Priestley's Experiments and Objcrvatlons
I found to anfwer very well during the procefs, though they
never failed to break in cooling. At length I procured a tube
of copper^ on which, as M. Lavoisier difcovered, fleam had
no effect ; and at iafl: I made ufe of earthen tubes, with which
Mr. Wedgewood, that mod generous promoter of fcience,
liberally fupplied me for the purpofe ; and thefe glazed on the
outfide only I find far preferable to copper. They are, indeed,
every thing that I could wifli for in experiments of this kind;
the reafcn of which will appear in my account of another courfe
of experiments, which I hope to lay before the Society in due
time.

The difpofition of the apparatus, with which thefe experi-
ments were made, was as follows. The water was m.adeto boil
in a giafs retort, which communicated with the copper or
earthen tube which contained the charcoal or iron, &c. and
which, being placed in an horizontal pofition, was furrounded
with hot coals. The end of this tube oppofite to the retort
communicated with the pipe of a common worm tub, fuch as
is generally ufed in diflillations, by means of which all the
fuperfluous fleam was condenfed, and colle(5led in a proper re-
ceptacle, while the air which had been produced, and had
come along with it through the worm tub, was tranfmitted
into a trough of water, where proper veflels were placed to-
receive it, and afcertain the quantity of it ; after which I
could examine the quality of it at leifure.

In the experiment with charcoal^ I found unexpe6led diffi-
culties, and confiderable variations in the refult ; the proportion
between the charcoal and water expended, and alfo between each
ofthemani the ^/r produced, not being fo nearly the fame
as I imagined they would have been. Alfo the quantity of
fixed air that was mixed with the inflammable air varied very
4 much.

relating to Air and Water, 293

much* This lafl circumftance, however, fome of my experi-
ments may ferve to explain. Whenever I had no more water
than was fufficient for the produ(5lion of the air, there was
never any fenfible quantity of uncombined fixed air mixed with
the inflammable air from charcoal. This was particularly the
cafe when I produced the air by means of a burning lens in an
exhaufted receiver, and alfo in an earthen retort with the appli-
cation of an intenfe heat. I therefore prefume, that when the
fleam tranfmitted through the hot tube containing the charcoal
was very copious, the fixed air in the produce was greater than.
it would otherwife have been. The extremes that I have ob-
ferved in the proportion of the fixed to the inflammable air have
been from one-twelfth to one-fifth of the whole. As I gene-
rally produced this air, the latter was the ufual proportion ; and
this was exclufive of the fixed air that was intimately combined
with the inflammable air, and which could not be feparated
from it except by decompofition with dephlogiflicated air ; and
this combined fixed air I fometimes found to be one-third of the
whole mafs, though at other times not quite fo much.

To afcertain this, I mixed one meafure of this inflammable
air from charcoal (after the uncombined fixed air had been fepa-
rated from it by lime-water) with one meafure of dephlogifli-
cated air, and then fired them by the ele(^ric fpark. After this
I always found that tlie air which remained made lime-water
very turbid, and the proportion in which it was now dimi-
nifhed, by wafliing in lime-water, fhewed the quantity of
fixed air that had been combined with the inflammable. That
the fixed air is not generated in this pr.ocefs, is evident from
there being no fixed air found after the explofion of dephlogifti-
cated ail* aud inflammable air from iron.

Not with-

2r)4- ^^' Priestley's Experiments and Ohfervathns

Notvvith (landing the above-mentioned variations, the lofs of
weight in the charcoal was always much exceeded by the weight
©f the water expended, which was generally more than double
of tl)e charcoal ; and this water was intimately combined with
the air ; for when I received a portion of it in mercury, no
water was ever depofited from it.

Tlie experiment which, upon the whole, gave me the mod
{iitisfacllon, and the particulars of which 1 fhall therefore re-
cite, was the following. Expending 94 grains of perfect
charcoal (by which I mean charcoal made with a very ftrong
heat, {o as to expel all fixed air from it) and 240 grains of
water, I procured 840 ounce meafures of air, one-fifth of
which was fixed air, and of the inflammable part nearly one-
third more appeared to be fixed air by decompofition.

Receiving this kind of air in a variety of experiments, but
not in the preceding ones in particular (for then I could not
have afcertained the quantity of it) confifting of fixed and in-
flammable air together, I found fome variations in its fpecific
gravity, owing, I imagine, to the ditterent proportions of
fixed air contained in it ; but upon the whole, I think, that the
proportion of 14 grains to 40 ounce meafures is pretty near the
truth, when the proportion of fixed air is about one-fifth of the
whole. With refpe6t to the weight of the inflammable air after
the fixed air was feparated from it, I found no great difierence,
and think it may be eftimated at 8 grains to 30 ounce meafures.

Upon thefe principles, the whole weight of the 840 ounce-
meafures of air will be - 294 grains

that of the charcoal will be 94 '

that of the water - 240

334 which, confidering tihe na-

7 ture

relating^ to Air and Water, 295

tnre of the experinienr, will perhaps be thought to be tolerably
i)£ar that of the air.

If the air be analyzed, the 840 ounce meafures will be
found to contain - 168 of uncombined fixed air =: 151 grains.

and 672 impure imflammable =1:179

fo that the whole 840 will weigh - - 330

Laflly, if the 672 ounce meafures of impure inflammable
air be decompolsd, it will be found to contain

164 ounce meafures of fixed air= 147.6 gT3.
and 508 inflammable - - = 30.7

fo that the whole 672 will weigh - - '^1^-2,

which is very near toi79, the weight of the whole together.

It may, however, be fafely concluded from this experiment,
and indeed from every other that I made with cliarcoal, rhar
there was no more pure inflammable air produced than the
charcoal itfelf may be very well fiippofed to have fupplied.

There is, therefore, no reafon for deferting the old eflablilhed
hypothelis of phhgijlofi on account of thefe experiments, fmce-
the faft is by no means inconliftent with it. The pure inflam-
mable air with the water neceflarily contained in it would
weigh no more than about 30 grains, while the lofs of weight
in the charcoal was 94 grains. But to this muft be added the-
phlogiflon contained in 392 ounce meafures of fixed air,
which, according to Mr. Kirwan's proportion, will be nearly
65 grains, and this and the 30 grains will be 95 grains.

The bafis to this fixed air, as well as to the inflammable,
muft have been furnlfhed by the wafer ; and from this it may
be concluded, that the water mufl have been fo far altered as
to be changed into fixed air, which will be thought not to be-
any great paradox, if it be confidered thc»t3. according to the

latefl:..

2 9'6 ^^- Pr r E ST L E Y*s Experlmenls and Obfervations
latefl: difcovenes, fixed air and water appear to confift of the
fame ingredients, namely dephlogiflicated and inflammable air.
However, in this change of the water we cannot be abfolutelv
lb re that the fame proportion of the ingredients is contained, and
therefore it cannot be abfolutelv determined whether the inflam-
mable air w^hich it contains enters wholly into the fixed air, or
not. Farther experiments, or a careful comparifon of thefe ex-
periments wath thofe made by Mr. Kirwan and others, may
perhaps throw fome light upon this fubjecl. Whether the com-'
bined fixed air comes wholly from the charcoal, or whether the
charcoal only fupplies the phlogifton, and the water its bafis,
that is, the dephlogifticated air, deferves to be inveftigated.

Before I conclude my account of the experiments with char-
coal, I would obferve, that there is another in which I place
fome dependance, in wd:>ich, with the lofs of 178 grains of
charcoal, and 528 grains of w^ater, I procured 1410 ounce
meafures of air, of which the laft portion (for I did not exa-
mine the reft) contained one-fixth part of uncombined fixed
air. This was made in an earthen tube glazed on the outfide.

The experiments with iron were more fatisfa£lory than thof*^;
with charcoal, being fubje6l to lefs variation; and it is ftill
more evident from them, that the inflammable air does not
come from the ivater^ but only from the iron^ as the quantity
of water expended, added to the weight of the air produced,-
was as nearly as could be expected in experiments of this kind,
found in the addition of weight gained by the iron. And-
though the inflammable air procured in this procefs is between
one-third and one-half more than can be procured from iron by^
a folution in acids, the reafon may be, that much phlogifton,
is retained in the folutions, and therefore much more may be.
expelled from iron, when pure water, without any acid, takes ;i
the place of it. I would further obferve, that the produce of

air,

relating to Aif and Water, 2:9 7

air, and alfo the addition of weight gained by the iron, are
much more eafily afcertained in thefe experiments than the
quantity of water expended in them, on account of the great
length of the veffels ufed in the procefs, and the different quan-
tities that may perhaps be retained in the worm of the tub,
though I did not fail to ufe all the precautions that I could think
of to guard againft any variation on thefe accounts.

Of the many experiments which I made with iron^ I {hall
content myfelf with reciting the following refults. With the
addition of 267 grains to a quantity of iron, and the lofs of
336 grains of water, I procured 840 ounce meafures of in-
flammable air ; and with the addition of 140 grains to another
quantity of iron, and the confumption of 253 grains of water,
I got 420 ounce m^eafures of air*.

The inflammable air produced in this manner is of the
lighteft kind, and free from that very qff'enjive fmell which is
generally occafioned by the rapid folution of metals in oil of
vitriol, and it is extricated in as little time in this way as it is
poffible to do it by any mode of folution. On this account it
occurred to me, that it mufl be by much the cheapefl method
that has yet been ufed of filling balloo?7S with the lighted: inflam-
mable air. For this purpofe it will be proper to make ufe of
cafl-iron cylinders of a confiderable length, and about three or
four inches, or perhaps more, in diameter. Though the iron
tube itfelf will contribute to the production of air, ^nd there-
fore may become unfit for the purpofe in time ; yet, for any

* If the perfeft accuracy of the former of thefe experiments may be depended
on (and it may always be prefumed, that thofe in which little water is expended
are preferable to thofe in which more is confumed) the ^vater that neceflarily enters
into this kind of inflammable air is about equal in weight to t\\Q phlogijion that is
in it. But I propofe to give more particular attention to this fubje^l.

Vol, LXXV. Q^q thing

2^2 Dr. Priestley's Experiments and Obfcrvatlojir

thing that I know to the contrary, the fame tnhe may ferve-.
for a very great number of proccffes, and perhaps the c'.ang^-
made in the in fide furface may protect it from any farther adion.
of the water, if the tube be of fufticient thicLnefs ; but thii
can only be determxined by experiment.

Some eftimate of what may be expeded fi'om this method ofi
procuring inflammable air may be formed from the following*
ebfervations. About twelve inches in length of a copper tube,
three-fourths of an inch in diameter, filled with iron turning:^
(which are more convenient for this purpofethan ironjilings, aa
they do not lie fo clofe, but admit the fteam to pafs through
their interftice>). when it was heated, and a fufficient quantity of
fteam pafl'ed through it, yielded thirty ounce meafures of air in
fifty feconds ; and eighteen inches of another copper tube, an
inch and a quarter in diameter, filled and treated in. the fame
manner, gave two hundred ounce meafures in one minute and
twenty-five feconds ; fo that this larger tube gave air in pro-
portion to its folid contents compared with the Imaller ; but to
what extent this might be depended upon I cannot tell. How-
ever, as the heat penetrates fo readily to fome diftance, the rate
of giving air will always be in a greater proportion than that cf
the fimple diameter of the tube.

The following experiment was made with a view to afcertaia
the quantity of inflammable air that may be procured in this
way from any given quantity of iron. Two ounces of iron^
or 960 grains, when diflblved in acids, will yield about 8o.<2>
ounce meafures of air ; but treated in this manner it yieldedi
1054 ounce meafures, and then the iron had gained ^zpgrainS'
in weight, which is little fhort of one-third of the weight of
the iron^

Confidering

'

relating to JAr and Water, 299

■Goiifrdermg how little this inflammable air weighs, vh, the
Avhole 1054 ounce meafures not more than 63 grains, and the
difficulty of afcertaining the lofs of water to {o fmali a ciuan-
tity as this, it is not poffible to determine, from a procefs of
this kind, how much water enters into the compoiition of the
inflammable air of metals. It would be more eafy to deter-
mine this circumflance with refpe6l to the inflammable air of
charcoal, efpecially by means of the experiment made with a
burning lens in vacuo. In this method two grains of charcoal
gave at a medium thirteen ounce meafures of inflammable air,
which, in the proportion of 30 ounce meafures to 8 grains,
will weigh 3.3 grains; fo that water in the compofition of this
kind of inflammable air is in the proportion of 1.3 to 2, though
there will be fome difficulty with refpe6l to the fixed air inti-
mately combined with this kind of inflammable air.

Since iron gains the fame addition of weight by melting in
dephlogijllcated air, and alfo by the addition of water when
red-hot, and becomes, as I have alread)/ obferved, in all re-
Ipedlsthe fame fubftance, it is evident, that this air or water, as
exifting in the iron, is the very iame thing ; and this can
hardly be explained but upon the fuppofition that water confiils
of two kinds of air ; viz. inflammable and dephlogifticatedL
I (hall endeavour to explain thefe procefles in the following

manner.

■■♦■

When iron is melted in dephlogiflicated air, we may fuppofe
that, though part of its phlogifton efcapes, to enter into the
compoiition of the fmall quantity of fixed air which is then
procured, yet enough remains to form water with the addition
of dephlogiilicated air which it has imbibed, fo that this calx
of iron confiils of the intimate union of the pure earth of iron
aad of water ; and therefore when the fame calx, thus fatu-

Q q a rated

300 Dr. Priestley's Experiments and Ohfei'vations

rated with water, is expofed to heat m inflammable air, this
air enters into it, deftroys the attraction between the water and
the earth, and revives the iron, while the v>^ater is expelled in
its proper form.

Confequentiy, in the procefs \mt\\Jieam, nothing is neceffary
to be fuppofed but the entrance of the water, and the expul-*
fion of the phlogiflon belonging to the iron, no more phlo-
gifton remaining in it than what the water brought along with
it, and which is retained as a confiituent part of the water,
or of the new compound.

Having procured water from the fcales of iron (which I muft
again obferve is, in all refpe6ls, the fame fubftance with iron
melted in dephloglfticated air, or fatu rated with fteam by means
of heat) and having thereby converted it into perfe6l iron again,
I did not entertain a doubt but that I (hould be able to produce
the fame effe6l by heating it with charcoal in a retort; and I
had iikewife no doubt but I fhould be able to extract the addi-
tional weight which the iron had gained (viz, one-third of the
whole) in water. In the former of thefe conjectures I was
right ; but with refpe6: to the latter, I was totally miftaken.

Having made the fcales of iron, and alfo the powder of
charcoal very hot, previous to the experiment, fo that I was
fatisfied that no air could be extrafted from either of them fe-
parately by any degree of heat, and having mixed them toge-
ther while they were hot, I put them into an earthen retort,
glazed within and without, which was quite impervious to air.
This I placed in a furnace, in which I could give it a very
ftrongheat; and connected with it proper veffels to condenfe
and collect the water which I expelled to receive in the courfe
of the procefs. But, to my great furprife, not one particle

of

relating to Air and Water, 301

of moijlure came over, but a prodigious quantity of air^ and
the rapidity of its produdlion aftonifhed me ; fo that I had no
doubt but that the weight of the air would have been equal to
the lofs of weight both in the fcales and in the charcoal ; and
when I examined the air, which I repeatedly did, I found it to
contain one-tenth of fixed air, and the inflammable air, which
remained when the fixed air was feparated from it, was of a
very remarkable kind, being quite as heavy as common air.
The reafon of this was fufficiently apparent when it was de~
compofed by means of dephlogiflicated air ; for the greateil:
part of it was fixed air.

The theory of this procefs I imagine to be, that the phlo-
gifton from the charcoal reviving the iron, the water with
which it had been faturated, being now fet loole, affe^^led the
hot charcoal as it would have done if it had been applied to it
in the ionno^Jieam as in the preceding experiments; and there-
fore the air produced in thefe two difi^erent modes have a near
refemblance to each other, each containing fixed air, both com-
bined and uncombined, though in different proportions ; and
in both the cafes I found thefe proportions fubjeO: to variations.
In one procefs with charcoal and fcales of iron, the firfi: pro-
duce contained one-fifth of uncombined fixed air, the middle
par) one-tenth, and the laft none at all. But in ail thefe cafes
the proportion of combined fixed air varied very little.

Why air and not water fhould be produced in this cafe, as
well as in the preceding, when the iron is equally revived in
both, I do not pretend perfectly to underftand. There is, in-
deed, an obvious difiierence in the circumftances of the tvvo
experiments ; as in that with charcoal the phlogiflon is found
in a combined flate ; whereas in that of inflammable air, it is

ioofcj

302 Dr, Priestley's Experiments and Ohfej vations

ioofe, or only niiited to water ; and perhaps future experi-
jtiients may difcovcr the operation of this circumflance.

There is foaie analogy between the experiment of the calx
of iron imbibing inflammable air, and the iron itielf imbibing
dephiogidicated air. In the former cafe water is produced, and
in the latter Jixed air. However, this cafe of iron imbibing
dephlogifticated air more nearly relembles the cafe of the blood
in the lungs imbibing tlie fame kind of air, and in both the
cafes as dephlogifticated air is imbibed, fixed air is formed.
This, therefore, feems to be a confirmation of the conclufioii
which I drew from my former experiments on blood, viz. that
it parts with phlogifton in re fpi ration. Only I would now
add, that at the fame time that it parts with phlogifton it takes
in dephlogifticated air, which makes the cafe perfectly fimilar
to that of the experiment with iron, which likewife parts with
phlogifton to form fixed air, at the fame time that it imbibes
dephlogifticated air in conta6l with which it is fufed.

I propofe to referve for a future communication the conti-
nuation of thefe experiments, containing an account of the ap-
plication of the fame procefs to other fubftances ; but it may
not be amifs juft to mention a few of the general refults, and
thofe which have the neareft connexion with the experiments
recited above.

After having tranfmitted fteam in contact with charcoal and I
iron in a copper tube, I propofed to do the fame with other fub- ■
ftances containing phlogifton, and J began with bones^ which
were burnt black, and had been fubje^led to an intenfe heat,
covered with fand, in an earthen retort. From three ounces of
bone thus prepared, and treated as I had done the charcoal, I
got 840 ounce meafures of air, with the lofs of 288 grains of
water. The bones were by this means made perfedly white,
3 and

relating to Air and Water. ^503

and had loft 3 10 grains of their weight. As the air ceafed to
come a coniiderable time before all the water had been tranf-
mitted through the tube containing them, I concluded that the
air was formed from the phlogifton contained in the bones, and
fo much water as was necefiary to give it the form of air.

This air differs confiderably from any other kind of inflam-
mable air,, being in feveral refpecls a medium between that
from charcoal. and that from iron. It contains about one- fourth
of its bulk of uncombined fixed air, but not quite one-tenth
intimately combined with the remainder. The water that
came over was blue, and pretty fti'ongly alkaline, which muft
have been occafioned by the volatile alkali not having been in-
tirely expelled from the bones in the former procefs, and its
having in part diflblved the copper of the tube in which the
experiment was made.

I fubjeded to the fame procefs a variety of fubflances that
are faid not to contain phlogifion, but I was never able to pro-
cure inflammable air by means, of them ; which ftrengthens
the hypothefls of the principal element in the conftitution of
this hir having been derived from the fubftance fuppofed to con-
tain phlogifton, and therefore that phlogifl:on is a real fub-
fiance, capable of aflTuming the form of air by means of water
and heat.

The experiments above-mentioned relating to iron were made
with that kind which is malleable ; but 1 had the fame refult
when I made ufe of fmall nails of cajj, iron^ except that thefe
were firmly faftened together after the experiment, the furfaces
of them being cryflallized, and the cryfl'als mixing with each
other, fo that it was with great difficulty that they could be
got out of the tube after the experiment, and in general the
Iblid parts of the nails were broken before they were feparated

from-

3^4 D^.VKViz'tLv.Y^^ Experiments and Obfervailons

from each other. Indeed the pieces of malleable iron adhered
together after the experiment, but by no means fo firmly.

Cafl: iron anncLiIed (by being kept red-hot in charcoal) is
remarkably different from the caft iron which has not under-
gone tliat operation, efpeciallj in its being, to an extraordinary
degree, more loluble in acids. With the turnings of annealed
caft iron I made the following experiment. From 960 grains of
this iron, and with the lofs of 480 grains of water, I got 870
ounce meafures of inflammable air, and tranfmitting fteam
through them a fecond time, I got 150 ounce meafures more.
The iron had then gained 246 grains in weight, and the pieces
adhered firmly together ; but being thin they were eafily broken
and got out of the tube, whereas it had required a long time,
and a Iharp fteel inftrument, to clear the tube of the caft-iroii
nails.

Having got water from tlie fcales of iron and of copper fatu-
rated with dephlogifticated air, by heating them in inflammable
air, it occurred to me to make the fame experiment with preci-
pitate per fe^ and I found, that the moment that the focus of
the lens fell upon this fubftance the mercury began to revive,
the inflammable air rapidly difappeared, and water was formed
on the fides of the vefl'el in which the experiment was made. For
want of a better fun, I could not afcertain every circumftance
relating to this procefs ; but what I did feemed to afford a
fufficient proof that mercury contains phlogiflon, and that it is
not revived by the mere expulfion of dephlogifticated air, as
M. Lavoisier fuppofes ; efpecially as no fixed air was found in
what remained of the inflammable air. In one of thefe expe-
riments 4.5 ounce meafures of inflammable air had difappeared,
and 1.6 ounce meafure remained ; and this appeared to contain
fome dephlogifticated air mixed with the inflammable. *

4 Willing

relating to Air and Water* 3 ©5

Willing to try the effed of heating iron, and other fub-
flances, in all the different kinds of air, without any particular
expectation, I found that iron melted more readily in vitriolic
acid air than in dephlogifticated air, the air was diminifhed as
rapidly, and the inlide of the veffel was covered with a black
footy matter^ which, when expofed to heat, readily fublimed in
the form of a white vapour, and left the glafs quite clean.
The iron, after the experiment, was quite brittle, and
muft, I prefume, be the fame thing with iron that is ful-
phurated\ but I did not particularly examine it. Of feven
ounce meafures of vitriolic acid air, in one of thefe experi-
ments, not more than three-tenths of an ounce meafure re-
mained ; of this two-thirds was fixed air, and the refiduum
of this was inflammable. I had put three of fuch refiduums
together, in order to m.ake the experiment with the greater
certainty.

Having tranfmitted Jleam, or the vapour of water, through
a copper tube, I was willing to try the efteds oi fpirit of wifie
through the fame tube when red-hot, having before procured
inflammable air by fending the fame vapour through a. red- hot-
tobacco-pipe. In this cafe, the vapour of the fpirit cf wine
had no fooner entered the hot copper tube, than I was perfedly
aftonirtied at the rapid produ6tion of air. It refembled the
blowing of a pair of bellows. But I had not ufed four ounces,
of the fpirit of wine before I very unexpectedly found, that
the tube was perforated in feveral places ; and prefently after-
wards it was fo far deftroyed, that in attempting to remove it
from the nre it adually fell in pieces. The infide waS' full of a
black footy matter refembling lamp-black.

Upon this I had recourfe to earthen tubes, and found, that by
melting copper and other metals in them, and tranfmitting the

Vol. LXXV. R r vapour

306 Dr4 PiiiEstLEY'a Experiments and Obfervattons

vapour of fpint of wine in contact with them, different fiib-
''ilances were formed according to the metals employed. The
new fubdances hereby formed may be faid to be the feveral
metals fu per- fatu rated with phlogifton, and may. perhaps not
be improperly called the charcoal of metals.

That this appellation is not very im.proper, may appear from
thefe fubflances yielding inflammable air very copioufly when
they are made red-hot, and the fteam of tvater is tranfmitted
in contacl with them, juft as when the charcoal of wood is
treated in the fame manner. The detail of thefe experiments
1 referve for another communication, as alfo thofe of the con-
verfion of fplrit of wine, ather, and oil, into different kinds of
inflammable air, by tranfmitting them, in vapour, through
hot earthen tubes. In the mean time, I fhall think myfelf
happy if the communication of the preceding experiments (hall
give any fatisfadlon to the Members of the Society.

P O S T S C R I P T,

BEFORE I clofe this paper, 1 wifh to make a iow general
inferences from the principal of the experiments above-men-
tioned, efpecially relating to the proportional quantity of phlo«
gifton contained' in /row and water.

When any quantity of iron is melted in dephlogiftlcated air,
it imbibes the greatefl part of it, and gains an addition of
weight very nearly equal to that of the air imbibed. Thus the
abforption of twelve ounce meafures of dephlogifticated air

2 gave

relattng to Air and IVaier. -^oy

gave an addition of fix grains to the piece of iron which had
been melted in it. But there was always a quantity oi fixed
air produced in this procefs ; and on the fuppofition that this
air confifts of the union of dephlogifticated and inflammable
air, it proves that the dephlogifticated air which enters the
iron expels more phlogifton than is neceffary to conftitute an
equal weight of water, fo that water does not contnin fo much
phlogifton as iron ; but the difference is not very confiderable.

Admitting Mr. Kirwan's conciufion, viz. that loo cubic
inches of fixed air contain 8,357 grains of phlogifton, the . 1 3 ounce
meafure of fixed aiif, which (in an experiment recited in thefe
papers) was found in the refiduum of feven ounce meafures of
dephlogifticated air abforbed by iron, would not have contained
more than .01 grain of phlogifton, or about .16 ounce mea-
fure of inflammable air. Then, as the abforption of 22
ounce meafures of dephlogifticated air occafioned an addition of
6'grains to the weight of the iron which had abforbed it, the
abforption of feven ounce meafures muft have occafioned the
addition of 3.5 grains to the iron which had im.bibed it. But
the fame addition of weight to iron given hyjlemn (which car-
ries its own inflammable air along with it) would have expelled
near 12 ounce meafures of inflammable air: confequenth .,
about ten ounce meafures of inflammable air (or the phlogifioii
requifite to form it) mufi-, in the former experiment, have been
retained in the iron, in order to compofe the water which was
now made by the union of the dephlogifiicated air imbibed by
the iron and the phlogifi:on contained in it: and therefore the
proportion between the quantity of phlogifton in iroji to that
which is contained in an equal weight of water, may be about •
12 to 10, or more accurately to 10.4.

Had no fixed air at all been found in the refiduum above-
mentioned,, it might have been concluded, that water had con-

R r 2 tained

3o8 Dr.VKiE^rL'E.Y's Experiments and Ohfervations
tained the^very fame proportion of phlogiftoii with iron. Since
when iron that has been faturated with dephlogiflicated air is
heated in inflammable air (in which procefs an equal weight of
water is produced, and the lols of weight in the iron is equal to
that of fuch a quantity of dephlogiflicated air as would have
been one-half of the bulk of the inflammable air which difap-
pears in that procefs) it might have been concluded, thiit one*
fifth of any quantity in water had been inflammable air.

For, negleding the difference between the weight of dephlo-
gifticated and common air, which is not confiderable, and eili-
mating the latter -^-g-5-th part of water, and inflammable air at
one-tenth of the weight of common air, an ounce meafure of
dephlogiflicated air will weigh .6 grain, and two ounce mea-
fures of inflammable air will weigh .12 grain, which num-
bers are to each other as 5 to i *.

Though, in confequence of the fmall quantity of fixed air
which is found in the procefs of melting iron in dephlogifli-
cated air, this coiicluflon is not accurate, it is pretty nearly
fo ; and it is remarkable that, upon this fuppofition, about as
much inflammable air is expelled from iron when water is com- :

■^' It appears from the profeCution of thefe experiments, that the water whicfe
is found on heating the fcales of iron in inflammable air, is not formed by the
dephlogiflicated air CKpelled from them uniting with the inflammable air in the
veflel, but was the water previoufly contained in the fcales, v.hich is made to quit ,
its place 'by the introduclion of the phlogifton from the inflammable air ; yet that
water carries out with it not much lefs phlogifton than was taken in by the iron,
and a little more muft be allowed for that water which was neceflary to make
inflammable air, and which could not enter the iron when it was revived ; fo that^
on the whole, the phlogifton in the water that is found after the procefs muft be
•very nearly the fame quantity that is imbibed by the iron, and the water is nearly
the fame that would have been produced, on the fuppofltion of its being made
from dephlogifticated air expelled from the fcales uniting with the inflammable
air in the veflel.

5 ■" bined

relating to Air and Wafer, J09

bined ^vlth it, ns the water itfelf brings along with it, as an
effential ingredient in its compofition. For in one experiment
296 grains added to the weight of a quantity of iron by fleam,
made it to yield about 1000 ounce meafures of inflammable air.
This would weigh 60 grauis, and one-fifth of the 296 grains
of water will be 59.2 grains. Again, 267 grains added to iron
by fleam made it to yield 840 ounce meaiures of inflammable
air, which would weigh 50,4 grains, and one-fifth of the 267
would be 53.4 grains.

When the experiments on the melting of iron in dephlo-
gifticated air fliall be repeated on a larger fcale, which it will
not be difficult to do by the help of a larger burning lens than
I am at prefent poflefTed of, it will be eafy to reduce thefe cal-
culations to a greater certainty. All that I can do at prefent is
to approximate to fuch general conclufions as I have mentioned ;
but they are of fo much confequence in philofophy, that it
will certainly be well worth while to afcertain them with as
much accuracy as poffible. Nice calculations would be ill be-
llowed on the imperfeft data which I am as yet able to furnifh.
Attention muft alfo be given to the quantity of water -contained
In inflammable air from iron ; which not being yet afcertained
is not confldered in thefe inferences. I wi(h only to hint iii
this Poftfcript, that fome important conclufions feems to he
aiearly within our reach.

2ND OF I* ART I. G^ VOL, LXiCV*

K R R A

Page, Line. ''

VOL. LXVIL

he"-

289. 17. dele the tvhole line except —^ xp. Whence

e
a

VOL. LXXIV.

32. 20. for 2 'OOOOOOOOO I, J'^C J 2 — '0000000001.
34. 8. for to tangent, read to cotangent.

VOL. LXXV,

78. 2o for unequal, read unequal ;

94. 25. for 20' 39'" r^tf^ 20" 39"'

120. 10. for Fl. 74, r^fl^ Fl. 74.

1 70. 1 0. for 1 6-j.^ r^«^ 1 6-,V

aoo. 15. yir IIL read 3.

270. 14. for 36^6 r^^i/ 36'',5

PHILOSOPHICA L

TRANSACTIONS,

OF THE

ROYAL SOCIETY

O F

O N D O N

VOL. LXXV. For the Year 1785,
PART IL

3a^BT^/e,

LONDON,

/

SOLD BY LOCKYER DAVIS, AND PETER ELMSLY,
PRINTERS TO THE ROYAL SOCIETY.

MDCCLXXXV.

■■— ^>a-*»i'-wn' ■W^M^BB— i^i^W^— — ^^1— ^wi— ^^^■^wN^W^IIBiHW^^
■ I n I I I, !■ iM tJ^ ■JJ«i W ' w II ■ I 1 W— WW— ^WWtgjy

CONTENTS

O F

VOL. LXXV. Part II.

XVI. r\ F the Rotatory Motion of a Body of any Fohn what-'

ever, revolving, without Rejlraint, about any Axis
fajjtng through its center of Gravity, By Mr. John Landeii,
F.RS. page 3 ; I

XVII. Defcription of a new Marine Animal, In a Letter frum
Mr, Everard Home, Surgeon, to John Hunter, Efq. F.R.S^
With a Poffcript by Mr, Hunter, containing anatomical Re^
marks upon the fame, p. 333

XVIII. A Defcription of a new Syfem of IFires in the Focus of a
Telefcope^ for obferving the comparative Right Afcenfions and
Declinations of ccelefial Objedis ; together with a Method of in»
vefigating the fame when obferved by the Rhombus, though it
happen 7iot to be truly in an equatorial Fofition^ By the ReVi
Francis Wollafton, LL,B, F,R,S, pi 346

XIX. An Account of a Stag's Head and Horns, found at Alport^
in the Parif of Youlgreave, in the County of Derby. In ct

S f 2 hetter

h CONTENTS.

Letter from the Rev. Robert Barker, B. D. to John Jebb, AI.D,
F.R,S. p. 353

XX. y^n j^ccount of the fenfittve ^laliiy of the Tree Averrhoa
Carambola. In a Letter from Robert Bruce, MX>, to Sir
Jofeph Banlis, Bart, P.R.S, p. 356

XXI. j^n Account of fame Kxperments on the Lofs of JVeight in
Bodies on being ?nelted or heated. In a Letter from George
Fordyce, M.D. F.R,S. to Sir Jofeph Banks, Bart. P,R,S.

p. 361

XXI L Sketches and Dcfcriptions of three fimple Lijlruments for

drawing Architecture and Machinery in PerfpeBive, By Mr.

James Peacock ; communicated by Robert Myhie, Lfq, F.R.S,

p«366

XXIII. Experiments on j^ir. By Henry Cavendifh, Efq,
F.R.S. and A.S. p. 372

XXIV. An Account of the Meafurement of aBafeon Hounflow-
Heath. By Major-General William Roy, F.R.S. and A.S,

XXV. Abjlraci of a Regifer of the Barometer, 'Thermometer^ and
Rain, tf/ Lyndon, in Rutland, 1784. j5y Thomas Barker,
Efq, Afo of the Rain at South Lambeth, Surrey; and at
Selbourn and Fyfield, Hampfhire. Communicated by Thomas
White, Y.^Q^,F.R.S. p. 481

PHILOSOPHICAL

TRANSACTIONS.

XVI. Of the Rotatory Motion of a Body of any Form whatever,
r^ revolving, without Reflraint, about any Axis pajjing through
its center of Gravity, By Mr, John Landen, F.RS.

\

Rpad March 17, 1785.

A SPHERICAL body, uniformly denfe, it is obvious,
will, if made to revolve freely about any axis paffing
through its center, continue to revolve about the fame axis;
and, by what I have fhewn in the PhiJofophical TranfaBions
for the year 1777, it appears, that a cylinder of uniform den-

fity, whofe length is to its radius as v/3 to i, will do the

fame. It likewife appears, by my Mathematical Memoirs,

Vol. LXXV. T t that

^ii Mr-. l^Ai^DZi^'s Invefrig.'?rf'on of

that a cone, a conoid, a prifm^ or a pyramid, &c. of certain
tiimeiifions, will have the like property of continuhig, with-
out any refb-aint, t6 revolve about any axis paffing through its
center of gravity.

When the axis, about wliich a body may be made to
r-evolve, is not a permanent one, the centrifugal force of its
particles will difturb its rotatory motion, fo as to caufe it to
change its axis of rotation (and confequently its poles) every
inflant, and endeavour to revolve about a new one : and I can-
not think it will be deemed an uninterefting proportion to de-
termine in what track, and at wliat rate, the poles of fuch
momentary , axis will be varied in any body whatever; as,
without the knowledge to be obtained from the folution of
fuch problemx, we cannot be certain whether the earth, or any
other planet, may not, from the inertia of its own par-
ticles, fo change its m.omentary axis, that the poles thereof
fliall approach nearer ancl nearer to the prefent equator, or
whether the evngation of the momentary poles, arifing from
that caufe, will not be limited by fome known lefler circle.
Which certainly is an important confideratioii in aftronomy ;
efpecially now that branch of fcience is carried to great per-
fection, and the acute aftronomer endeavours to determine the
motions of the heav-enly bodies with the greateft exadnefs
poffjble.

I do not know that the problem has before been folved by
any mathematician in thefe kingdoms; but I am aware that it
has been coniidered by fome gentlemen, very eminent for their
mathematical knowledge, in other nations. The folutions of
it, given by the celebrated M. LeoiNhard Euler and M»
D'Alembert, 1 have feen : and we learn from what the laft
mentioned gentleman has faid, in his Opujcules Mathematiques^

that

the Rotatory Motio?j of Bodies, : 3 ij

that a folution of it, inveftlgatcd by M. John Albert
EuLER (after a method fiinilar to his father's) obtained the
prize given by the Academy of Sciences in the year 1761. The
conclufions deduced by thofe very Jearned gentlemen diiFcriiig
greatly from mine made me fufpeci, for fome time, that I had
fomewhere erred in my inveftigation, and induced me ^o revile
my procefs again and again with the grcateft circumipeclion.
At length my fcrutiny has fo removed my doubts, that, being-
well aflured of the truth of my theory, I now beg leav^e to
present it to the Royal Society ; prefuming that it will be found
not unworthy of the notice of fuch readers, as are curious in
contemplating the various motions which bodies ma)^ naturally
have, in confequence of Inftantaneous or continued impulfe.

In the Philofophical T^ranfacimis referred to above, I gave a

fpecimen of this theory, as far as it relates to the motion of a

Jpheroid and a cylinder. The improvements I have fmce made

in it, enable me now to extend it to the motion of any body

whatever^ how irregular foever its form may be.

What I here infer therefrom will be found to differ very ma-
terially from the deductions in the folutions given by the gen-
tlemen above-mentioned. They reprefent the angular velocity,
and the momentum of rotation of the revolving body, as ahvays
variable^ when the axis about which it has a tendency to re-
volve is a momentary one, except in a particular caie. By my
inveftigation it appears, that the angular velocity and the mo-
mentum of rotation will always be invariable in any revolving
body, though the axis about which it endeavours to revolve be
continually varied ; and the tracks of the varying poles upon
the furface of tlxe body are thereby determined with great
facility.

T t 2 I-t

^14 Mr, Landen's Invejiigaiion of

It is not only obfervable, that the tracks which the varying-^
poles take, in the furface of any revoking body, are fiich that
its momentum of rotation may continue the lame whilft its
angular velocity continues the fame ; but it may be obferved,
that, in any given body, there is only one fuch track which a
momentary pole can purfue from any given point.

If the angular velocity and the momentum of rotation of a
revolving body were to vary according to the computations ad-
verted to above, it would follow, that a body might acquire an
increafe of force from its own motion, without being any way
afFc(fled by any other body whatever, as the fame percuffive
force, applied at the fame diftance from the momentary axis,
would not always deftroy the rotatory motion of the body,
which furely cannot poffibly be true. From the principles or
laws of motion, which I coniider as undoubtedly true (and
which indeed are no other than the common principles of me-
chanics), I conclude that a revolving body, not afFe6led by any
external impulfe, can no more acquire an increafe in its mo-
mentum of rotation, than any other body, moving freely, can
acquire an increafe in its momentum, or quantity of motion, in
any given direction, without being impelled'by gravity or fome
other force. And the truth of this conclufion (which is here-
inafter proved by other reafoning) may be eafily inferred from
the property of the lever; feeing that the joint centrifugal
force of the particles of the revolving body (which is the only
difturbing force) has no tendency to accelerate or retard their
motion about the momentary axis, but only to alter the por-
tion of fuch axis, the direction in which that force a£i:s beiqg
always in a plane wherein that axis will be found.

By the theory explained in this paper, it appears that a pa*

raUelopjpedon may always be conceived of fuch dimenfions,

4 that

the Rotatory Motion oj Bodies^

o

I

6':>

that being, by feme force or forces, made to revolve about an
axis, paffing through its center of gravity, with a certain an-
gular velocity, it fhall move exadly in the fame manner as any
other given body will move, if made to revolve, by the fume
force or forces, about an axispading through its center of gra-
vity; the quantity of matter (as well as the initial angular
velocity) being fuppofed the fame in both bodies ; and due re-
gard being had, in the application of the moving force or
forces, to the correfponding planes in the bodies. Therefore,
as we may from thence always affign the dimenlions of a pa-
rallelopipedon that fhall be affected exadly in the fame manner
as any other given body will be affeded, as well with regard to
the centrifugal force of the refpeftive particles of the bodies, as to
the adlion of equal percuffive forces, or ofcillation ; it will,
after (hewing how the dimenfions of fuch parallelopipedon may
be computed, be only neceffary, in inveftigating the proportion
under confideration, to determine the tracks and velocities of
the poles of the momentary axis, about which any parallelopi"
pedon may be made to revolve.

Firft then to find fuch parallelopipedon (P), that, with re-
fpe£l: to the a6lion of fuch forces as are mentioned above, it
may be affefted exa£lly in the fame manner as any other given,
body (Q). Let it be confidered that G(tab.X.fig.i.) being the
centerof gravity, N a point of fufpenfion, and O the correfpond-
ing center of ofcillation or percuffion, the redangle GN x GO
will be an invariable quantity, the diredlion NGO continuing
the fame ; and that a cylindric furface being defcribed, fuch
that the center of the middle circular fe6lion thereof fliall be
G, and radius —s/Q^ x GO, and whofe axis (hall be perpen-
dicular to the plane wherein the line NGO is fuppofed to be
impelled to move ; if all the matter in the body were placed

any

4 15 Mr, Landen^s LroeJligaUon of

any where in that furface, fo that G fhould be the center of
gravity of the matter fo placed, any given force or forces, acting
on the body in the plane juft now mentioned, would caufc the
line NGO in the body to move exaclly in the fame manner as it
would move, if it were carried with the matter placed in the
faid furface (as berore-mentioned) after having been put in
motion by the aclion of the fame force or forces. Moreover,
let it be confidered, that there will at leail: be three permanent
axes of rotation in the body Q, at right angles to each other
(as I have proved in my Mathematical Memoirs^ ; and that,
fuppofmg NGO to coincide with thofe three axes in three fuc-
cefhve cafes wherein the matter in Q^(hall, in each cale, be con-
ceived to be placed in a cylindric furface as delciibed above, we
may conceive it poffible fo to place the matter of the body,
that all of it (hall be in each of thofe three furfaccs, and G
ftill continue its center of gravity. And, a computation being
iTiade accordingly, it appears, that the matter of the body Q
mufl: be placed^ in equal quantities, at each of the eight an-
gular points of a parallelopipedon (R) whole dlmenfions
(length, breadth, and thicknels) fliall ho, s/ zd' -\- ^f~ — ie~ ^
v/2^^ -f 2/ - - 2^% and s/ ^d ^ -{■ ze^ - 2f ^ ; d, e^ and /", being

the three values of \/GN x GO, when NGO is fucceffively a
permanent axis of rotation, with refpe6t to the body Q, in
three dlre(ftions at right angles to each other.

If Q^were a parallelopipedon, it may be eafily prov^ed,
that its dlmenfions muil: be \/bd'^ + 6/ ^ — 6f% \/be' + 6/ ' — 6^\
and v/6i/'4- te^ — 6/", that the correfpondlng parallelopipedon,
at the angular points whereof the matter of Q is conceived to
he placed as above, may have the fame dlmenfions as thofe
which we have found our parallelopipedon R mufl have.

2 Whence

iJye Rotatory Motion of Bodies, ^ i y

Whence we may infer, that tl\e parallcloplpedon {P\ which
we propoi'ed to find, muft have the dimenficns laft written ;
namely, length, breadth, and thicknefs, refpedively equal to
^6d^- + 0/ ' - 6r, s/"6? -{-bj^ -(yd , and v/6i/- + 0f -6/':
which may be connrmed by a iTiore ftri<£t dcmonftration founded
on the principles made ufe of in my fourth Memoir, Yov it
appears by what is there proved, that the centrifugal forces of
fhe particles of any revolving body, in two diredions at right
fingles to each other, may be exprefled in terms of A, B, K,
and variable quantities fhewing the politlon of the momentary
axis ; and tliat, in a parallcloplpedon whofe dimenlions (length,
breadth, and thicknefs) are a^ b^ k\ and whofe mafs, or con-

tent, is — M; A will be~ — , Bn — , andK=— . If there-
fore a be — s/bd"- + 6/' - te\ b — \/t)e"^bJ~'-()d'^ and k-=z
i/bd' + ti' -bf ; in fuch body,

A will be = ^ x ^M7^^%

M

!■ K =--xd~-\-e'-t\

Bat, in any body whatever,

M >^ .^'is =: the fum of all the IF+z^ xp,
Mx e^ = the funi of all they + 2' x p,
JV^ xf^ :. •=- the fum of all the x^+y x /,

and ^— X d' +e"^f" = the fum of all the x'-\-y- + z" xp : x, y,

2

and % carrefpondlng to the place of the particle p in the body ;
.T being meafured from the center of gravity upon a permanent
axis of rotatipn, y at right angles to .v, and z at right angles

to

51 8 Mr,LA}^DE\*s Inv^JigaiiGH of

to y In a plane to which the fald axis is perpendicular.

Therefore,

A, which 15 := the Turn of all the .v* x /», will be = — x ^- +y " - e\

M

B, =:thefumofallthe>'' x^, =:— x e'-" +/ ^ - J\

M

K, =thefumof allthez' X j5, —— x d^ + e' ~J^^

Hence it is evident, that cl, e, and^ being determined from
any body whatever, the values of A, B, and K will be the
fame in that body as in our parallelopipedon P ; and that the
centrifugal forces of the particles will be the fame in both bo-
dies. Confequently, their motions about fucceflive momentary
axes (whofe poles are varied by the perturbation arifmg froni
thofe forces), will be the fame in both bodies ; their initial an-
gular velocities being the fame ; as well as the pofition of their
initial momentary axes, with refpe£l to the correlpondent per^
manent axes of rotation in each body.

Let us now proceed to find how any parallelopipedon will
revolve about fucceflive momentary axes pafling through its
center of gravity : by which means, with the help of tb&
theorem juft now inveftigated, we fhali be enabled to define
how any body whatever will revolve about fuch axes ; which is
the chief purpofe of this difqulfition.

Fig. 2. and 3. The length, breadth, and thicknefs of the
revolving parallelopipedon (P) being id, 2c, and 2^, conceive a
fpherical furface without matter, whofe center is the center of
gravity of the body P, to be carried about with that body'
during its motion ; and let the faid furface be orthographlcally
projedled, fo that the radius upon which 5 is meafured may be

rep re fen ted

the 'Rotatory Motion of Bodies. ^ ^ 0

reprefented by AB; the radius upon which ^ is meafured may
•be reprefented by AD ; and the radius AC, upon which c is
meafured, may be projected into the central point A. Let P
be the momentary pole, and PQjthe continuation of the great
circle CP. Let a denote the radius AB (=r AD) ; g and y the
fine and cofine of the arc CP ; s and / the fine and cofme of
the arc BQ, to the fame radius a ; e the angular velocity of the
body and fpherical fur face, meafured at the diftance a froni
the momentary axis ; and M the mafs or content of the paral-
lelopipedon (j=z^bcdj.

Then the motive force E, urging the pole P towards Q.,
will (by what I have proved in my Mathematical Memoirs) be

7 ^ Di" - Qa'' ; and the motive force E, uip-ins: the fame

pole in a dire<ftion Po, at right angles to that in which E afts,

= 6 X T)st ; C and D being equal to c^ - if" and d"" - F re-

II

fpeclively. Let P^ be to Po as E to E ; complete the paral-
lelogram oV qr^ and draw the diagonal Pr. This laO: men-
tioned line will (by what I have fliewn in the FIdilofophical
Tranfa5lions for the year 1777) be perpendicular to tlie tan-

I! Ill

gent to the polar track at P. Therefore P/>/>/> being the pro-
je<Slion of that track, and P^ an indefinitely fmall particle
thereof; \i fu be perpendicular to P«A, and the quantities

d~ — c~, c^ — b'^ be not negative; - x Dj-" — C^' will be to T>st

(as Vq to Po) as/« toP//, the triangles Vor and Vtip being
fimilarv, andcr^Pj-. But with refpeft to our fpherical fur-

face, i>u will be to P^^ as — to - — ; therefore, CV/ - Ds~ x f^
^ t 7

will be = D^?- J J, aiid^ == — r-^^— T. Whence, by taking the

Vol. LXXV. U u fluents,

210 Mr. LAND^.^''s In'vcjl'igailon.of

ucnts, we have s — cv y, — -— z — , and t ^^a" K -=-^-;

^g ^g

m and « denoting the values of s and /, when g ls = jand
y — O', and B being put to denote the difference D - C = ^^ - c".
If now /S and (5* be put to denote the cofmes of EP and DP
to the radius ^, we fhall, fronn what is done above, have

, d_ — =: —J — ;

P =r _ = ^'' ~oy y--t_.

^' + y- + r = a% (3f^+yy + ^l=.Q;
^'/3' + cy -l-^Trr^V-f ^W, and 3^/3/3 + c>^ + J^^irro.

Drawing AR fo that D^ x fine of BR (hall be = C^^, it is
"jery remarkable, that the momentary pole (P) will run round
about the point B, or about the point D, in the fpherical furface,
according as the initial pole fliall be in the part BCR or DCR.
of the faid furface ; that is, according as D/«^ Is jefs or greater
than Qa^ : and that, if the. initial pole {^P) be any where in
the great circle CR, the momentary pole, keeping in the arc
of that circle, will continually approach nearer and nearer to
the point C in the furface of the fphere ; but, by what fol-
lows, we fhall find that it never can arrive at that point in any
finite time !

The equation of the track of the pole In the projedion to
which we have hitherto referred will, it is nov/ obvious, be

B , . C^r-D

z

y"^ ~— X x~ ■] ~-^ ; X, meafured from the center A upoii

AD, bein.g=^; andjy, at right angles thereto, =z/G.

If C be=:o (that is, if c ht — b'), x will be equal to the In*
variable quantity m ; the projecled track, a right Vme parallel to
AB ; and the track upon the furface of the fpherej a lejer
ehcie in a plane parallel to the plane of the great circle BC,

5 If

the Uofato^y Motion of BoJieS,

J"

I

It CberrD, y will be equal to the invariable quantity « J'
the projected track, a right line parallel to AD ; and the track
on the furface of the fphere, a lejjer circle in a plane parallel to
the plane of the great circle CD.

If D/«" be::=C^?" the projeded track will be the right line AR,

r

andj/zr-^^ xa;; the track upon the furface of the fphere be-
ing the great circle CR.
" In all other cafes in this projection, the track will be an by'

Co^c^TL)^

^erboU vAio^Q center is A, femi-axis Aa— — —z , and the

; the right line AR being always an

Other lemi-axis r: ;:

ajypmtote.

Fig. 4. When the track is projected on a plane ACD, to
which the radius AB Is perpendicular (the point D being the

vertex as before) the equation thereof will hty~ — .— x ;;r - x~ ;

a;^ meafjred from the center A upon AD, being ~ ^ (as before) ;
andjv, at right angles thereto = 7. This projection of the track
of the pole will therefore always be an elUpjis a b (or a circle }
whofe center is A ; femi-axis A a = ;« ; and the other femi-axis

r=— ] yim: except ^ be = 3; in which cafe the proje£led track

^ill be a right line a b parallel to AC.

Fig. 5. Moreover, the equation of the track projeCled on the
plane ABC, to which the radius AD is perpendicular, will be

y''— — y,n'' — x^\ x^ meafured from the center A upon AB,

being =z)S; andjy, at right angles thereto, =y. The track of
the pole in this projedtion will therefore always be aii eUipfis

U u 2 ab

32 2 Mr. Landen*s Invejllgation of

ab (or a circle) whofe center is A ; femi-axis A a=;z ; and the

other femi- axis = — i x 7z ; excepts be = ^; in which cafe the

proje6lecl track will be a right line a b parallel to AC.

With regard to the permanent axes of rotation of our paral-
lel opipedon, it appears, by my Mathematical Memoirs^ that if
two of its dimeniio-ns be equal (that is, when the body is a
fquare prifmj^ any line paffing through the center of gravity of
the body, in a plane to which the other dimenlion is perpendi-
cular, will be a permanent axis of rotation ; as will the line
paffing through that center, at right angles to that plane. If
all the three dimenlions be equal (that is, when the body is a
cube), zny line whatever paffing through the center af gravity
of the body will be a permanent axis of rotation.

It is obfervabLe, that the momentum of rotation of the
body, about the momentary axis, is found by computatiork-

always = -V X b'm~ -f ca' + d^^n\ e denoting the angular velocity,-
But 4- X ^'^^"^ +c'a~ -{-d^n'' is the initial momentum of rotation.

a^

Therefore, confidering the momentum of rotation as invariable,
the angular velocity will be invariable, e being always =yi
which here denotes the initial angular velocity.

Our next bufinefs is to find the length of the track defcribed
by the momentary pole (P), upon the fpherical furface; and_
the velocity of the pole in that track.

Fig. 2, 3. It appearing, that the motive force E is =

-4" X D//r - Ca~ X - , and the motive force E - -4- ^ y^^^'^~ - ^y

X v/0//-B7' ; we fnd F = V E^ + E' (the force compounded

of thofe two forces) = -r ^ v/D'w V - BC^^y ; and, F being

1 to

the Rotatory Motion of Bodies. 323

to E as a to the fine of the angle />P«, it follows, that the

fine of pVu will be =: ■ — ^— ^ ~ / "^ ,, and its co{ine =

— — ■ ^ , / ^ . Therefore, that cofine being to radius as

( — J the fluxion of the arc PQ to (z) the fluxion of the polar

o

track on the Iphericai iurfaee, J2 will be = — == ■

-/D?/?- - C/ X V Dn^~ B/
Now,, P/jIvN being a quadrant of a great circle (touching the
faid polar track at P), and NAN a diameter of that circle ; if
we put w to. denote the diflance of any particle ^^^ of the?
parallelopipedon from that diameter, and G to denote the ac-
celerative force of any fuch particle when iv is-ia ; the motive

force F {='- — -J X v/D';?2'«^ - BCa'y^), computed above,will be = '
-^ y^the fum of all the w'-xp-, which fum, by computation, is
found =: - X D-;;.V-BC.V • Confequentiy,

G will be ^^3 X^^^, _ DW-.y ^.'.'+.V ■ BC/- But, by
what. I have done in the' Fhilofophical . Tranfa^ions for the
year i jyy, — will be =: 1; •= the velocity wherewith the

momentary pole; changies its place in the fpherical furface ta
which it is referred. Therefore,

V will be = -^ X ^^^,^„,,._^^j^^_^c^ ; =!nd - =^ 1 ,,

2

the fluxion of the time = — x

ny d^ + b"- . Wtrrn'--b^nr + cV + d';.'' . BC>'

^ V-D^VC-ZX ^^D«^-B/x D^wSjVBCA'

^21^ Mr, L A N DE IN'* s Jnvefij^aiwn of

[ .^ „. +

X D 7rtny

, Z ,,Z , .2 2,, /2 2 '

when D;»" is ~ Ca", becoities s: r

^"-'-•''=

V .ay

e ^'BC . 7^

It is evident,, that ;S^ X,"^ xbyp.log. of~~, the vakie of

T in that particular cafe, will be infinite when -^ is = ^ ; and this
conciuiion agrees with what is faid above refpe6ting the motion
of the momentary pole along the great circle CR (fig. 2*
and 3.).

I have not found, that the value of T will, in general, be?
afligned by the arcs of the canic Jeciions ; but my Tables * fliew^
that It will be fo affigned when Diir- is=:B^% and in fome
other particular cafes*

We have ftill to inveiligate the track of the momentary
pole in the immoveable concave Ipherical' furface, which we
muft conceive to furround our moveable convex fpherical fur-
face, fuppofing the center of both thofe furfaces to coincide
with the centers of gravity of our parallelopipedon : which
central point is always in this difquifition fuppofed at reft.

Let AL be the projedlon of part of a great circle CL,
at" right angles to the great circle P/»LN; then will the

fine of the arc CL be ^ "' ~ ''_^iZ^ ; its cofine —

, I

D^v/D«^/zVr - Urn^- Ca'-m^ + Ca^n

VDW«^-BCflV

; and, the fluxion of that fine

being = ^' " ^ ^^^ 5 the fluxion of that arc CCL") will be

* Mathematical Memoirs, publiflied in ijSc)*

tin' Rciatoiy Motion of B^lcs,- ^^r

^ ^S?3bc7?">;Vd?S^ Confequently,

the line of the arc PL being = -^ — zzz ~~ -^ -^ ;

and this fine being to radius as the flvixion of the arc CL to tlie
meafure of the angle of contacl of the polar track on the 7?jovea-
ble fpherical furface with a great circle, we find that meafure

The meafure of the angle of con tad of the track of the
momentary pole, in the immoveable fpherical furface, with a
great circle, will accordingly be

^T- ^, =';7h^^^ JKC--~'' ^y"^^''^^^S of which-

meafure we may defcribe, by points, the track of the momeiir
tary pole in the fpherical furface lafl mentioned.

There are other methods of finding that track ; but I know
none that is lefs difficult than this method, or in any refped
more fatisfa6lory.

The radius of the leffer circle, which is the circle of curva-
ture of the polar track in our immoveable fpherical furface,
will be =

'V'i^o-iq.of tliemeaf.of theang.ofcont. '^ ff^l^"^ . ■^^-^jT^^jT^^ .n—'&Qy' '

When B is=:o, or very fmall in comparifon with D, and
D/»" is lefs than C^% the lafl: mentioned radius will be equal, or

nearly equal, to the invariable quantitv -. ;

the track of the pole in the immoveable fpherical furface being
then exadly, or very nearly, alefler circle. At the fame time,

the

'j2''6 -^^' Landen's Invejltgatlon of

the polar track upon the moveable fpherical fur face will be

■exactly, or very nearly, a lelTer circle whofe radius is m.

When Cis=:o, or very fmall in comparifon vv^ith D, and
D/»^ is greater than Qdr^ the track of the pole in the immovea-
ble fpherical furface will be exadly, or very nearly, a lefler

circle whofe radius is = , zzzzz-^, ■ ; and then the polar

track upon the moveable fpherical fiirface will be exa£lly, or
very nearly, a lefler circle whofe radius is n.

Whatever the curves may be which the momentary
pole fhall defcribe in thofe two fpherical furfaces, the track-
upon the moveable furface will always touch and roll along
the track in the immoveable furface (whilH: the common cen-
ter of both furfaces remains at reft), in the manner defcribed
in my Paper in the Philofophical 'Tranfadiions for the year
17^7 ; the velocity of the point of conta6l being equal to tlie
value of i; computed above, which velocity when B is — o, or very
fiiiall dn comparifon with D, and Dm" is lei's than Qa^, will be

exactly, or very nearly, =-t-— tzX-^-; and when C is — o, or
very fmall in comparifon with D, and Dw^ is greater than C^',

di' '111 ni 1 ^ — c~ mne

lat velocity will be exactly, or very nearly, = 753—5 X -^'

The polar track upon the moveable fpherical furface.
will always roll along the convexity of the track iii
the iiTimoveable fpherical furface ; the convexity or con-
cavity of the former being turned towards the convexity
of the latter, according as Dm" is greater or lefs than C^%
Which track in the immoveable Ipherical furface, when it
is not circular, will touch a certain circle as often as y^ during
the motion, fhair become = 0 ; and likewife another parallel

circle

the Rotatory Motion of Bodies, 327

circle as often as y fliall become equal to ^ X w, or ^j x «;

the parts of the track between the points of contad being per-
fedly fimilar. If Dw' be = Crf^ (D«^ being- then = B^z% and

-confequently ^ X^«= -j- y.n — a), the faid track will make

an infinite number of revolutions about a certain point, con-
tinually approaching nearer and nearer thereto, without arriv-
ing thereat in any finite time, though the length of the fpiral
fo defcribed cannot exceed a certain finite quantity.

M. EuLER has computed, that if the motive forces to turn
the revolving body about AB, AC, AD, be relpe<5lively de-
noted by H, I, K ;

xflux. of ^/3 -— 5 . B/7^,

H will be

~ 3

I

" 3

K

M

C23T

X flux, of el-—-. . Ce-(3y;

-X flux, of ^>' + :;-5 . De^f^Q,

y being fuppofed to decreafe as T increafes : and he has put the
value of each of thofe forces (H, I, K) = o. In doing fo, it
feems to me, that he has erroneoufly affumed equations as
generally true, which are only fo in a particular cafe. For

—5 • B^V^is the motive force to turn the body about AB, ariling

from the centrifugal force of its particles revolving ?!>out the
momentary axis AP, fuppofing the pole to keep its place;

and — • — A X flux, of eQ h the value of the motive force

requlfite to caufe the ivhole variation of the velocity (y j about

AB. But the firfl mentioned force dlojie does not, in general,
Vol. LXXV. Xx caufe

^2^ Mr. Landen's hivejiigatton of

c^ufe all the variation of the velocity about AE ; that velocity
varies in confequence of the evagation of the pole P; and that
evagation is caufed by the motive forces urging the body to
turn about AB, AC, AD, conjunBly. Therefore the motive force

— ^ • Bd'^'^J about AB only will not, in general, be equal to

— • — :-xflux. of ^jG, the value of the whole motive force
3 «3T

requiiite to caufe the variation of the velocity — , as M. Euler

reckoned.

The like objeclion may, I conceive, be juftly made to his
other two equations fuTiilar to that which is here particularly
adverted to.

M. D'Alembert's radical errors, in treating this fubjedl,
aj)pear to me nearly fimilar to M. Euler's.

Other arguments may be adduced to prove, that the equa-
tions affumed by thofe gentlemen are not well founded. If the
forces to turn the body about the lines AB, AC, AD were
each = o, the velocities about thofe lines mud each remain inva-
riable; but it feems abfolutely impoffible that they can ever
remain fo, whilft the angles which thofe lines make with the
momentary axis are each continually varying. Moreover, ac-
cording to their conclufions, the tangent at P to the track of
polar evagation, upon tlie moveable fpherical furface, will not
always be perpendicular to the dire£lion in which the pole P
will be urged to turn by the joint centrifugal force of the par-
ticles of the revolving body; whereas it is proved, Iprefume,
beyond a doubt, in my Paper above-mentioned, that the faid
track will always be interfefled at right angles by the direction
in which the momentary pole fhall, at any inftant of time, be
urged to turn by the force caufing its evagation.

4 If

the Rotatory Motion of Bodies, ^ip

If we refolve each of the three forces H, I, K, into two
^hers ; the one to turn the body about the diameter NAN, and
tlie other to turn it about the momentary axis PAP, at right
angles to that diameter ; the forces to turn it in the laft men-
tioned diredlion, arifiiig from the faid forces H, I, K, will be

— t= _ . — __ X ^ flux, of ^/S - — 0 . Be-M,

— = _ . — T—yiy flux, of ey + -—^ ' T)e~^y^,

_ = r-x^flux. of e^ -, 'Ce'fiyl

The fum of thefe forces, it is obvious, muflberro; the di-
reȣlion wherein they are fuppofed to a6l being at right angles
to that in which the body will be actually urged to turn by the
joint centrifugal force of its particles, and that being the only
force whereby the motion of the body is fuppofed to be affedted :

which fum (B + C - D being s=o) is, when divided by — :-,

d- +c' . 13^' e '\- d' -{• b' . y- e ^ c' + b~ . ^'e

= 0.

J- + c^ . e(3(3-i-d~-{-b~ . eyy-\-c'+b- . ed^
But 13^-hyy + f^ being before found = 0, we have

^' + r + i^'XiSiQ 4- 7/7 + ^^=0; and F~(l(3'\-c'yy'\-d'U being
alfo found = 0 ; it evidently follows, that

d'^c"-. /G/3 + ^N^. y'y\- c' •{■ b"- . ol wilIbe = o.
Therefore F+? . /GV + F+¥ . y'e + c' + b"- . Ve will be = o :
confequently e will be = o, and e invariable; which agrees with
what is faid above refpeding the momentum of rotation.

The other forces arifmg by refolution from the forces H, I, ,
K, to turn the body about the diameter NAN, will be

XX2

-30 Mr, Land en's Invcjligatio?! of

S 3^^ st ' 3^-^^

. C^/3>'.^+:f^.e/3y;

S being — v/D'/zT/z' — BC^/^.
And, no external force being luppofed to a<5l on the body, it fol-
lows, that the fum of thefe three forces mufl be = o: there-
fore we may infer, that

T will ber= - X n23^i-^^r--fi2 2 ; wnich agree*

ing with the value of T found above,, the truth of our pre-
ceding procefs is. thus confirmed.

M

The force ~^- X By r 4- D /3T + e/3y , arifing, from thofe.

three forces, is the whok ^owVi centrifugal force of the particles,
of the revolving body, to turn it about the diameter NAN the
way it. will adually be urged to turn by fuch force; the value

whereof fo computed will be {^~-^%s/Wnfn'--'SiQa'y —

-—y) ^qual to the value of the force F computed above, both

being confidered as urging the body to turn m the fame
diredion. And the quantity

Ue

q«3sT

-x^' + r . y^(^-d' -\-b'- . D/55>. + r + ^^ . C(^y^

( = -^ Xthe fum of all the w'YifJis the value of the motive

force which, ading in that very direction , is requifite to caufe
the momentary pole to change its place as abov^e defcribed.
Thus we fee diftindly how the equation arifes, by which the

value of T is jufl now determined. I do

the Rotatf/ry Motion of Bodies, 33!

I do not find that the refolving the forces H, I, K, in any other
manner will conduce to the attainment of any uieful conclufion.
It appears, by what is done above, that the force

His = -^^xCDW/3^/3',

3<23RT

I is = — "-^ X BC . Cfir - Bm~ . -y^,
3«niT

K = "-^ X BD V^^i ;
3^'RT

R being = B>^o"^+D^iGT+e/3y.
And it is obvious, that each of the three lafl: mentioned forces
will be = o, if any two of the quantities b, c, d, be equal ;
two of the values of thofe forces then vanifhing, by reafon of
that equality; and the third value alfo vanifhing by either

/3, y, or (5", being at the fame timerro. Therefore, in that"
cafe it happens, that M. Euler's computation agrees with
mine: in every other cafe, I am clearly of opinion, his con-
clufions are, not true. The fame may be faid of M. D'Alem-
bert's conclufions refpe£ling the fame propofition.

The evagation of the pole, of a revolving, body confidered
above, does not arife from gravity, the attra6lion of any other
body, or any external impulfe whatever ; but is only the con-
fequence of the inertia of matter^ and muft neceflarily enfue, .
according to the theory here explained, in every body in the
"univerfe, after having been made to revolve, without reftraint,'
about any line pafling through its center of gravity, that is not^.
permanent axis of rotation.

The Earth being neither uniformly denfe nor a perfect
fpheroid mufl, in ftridnefs, be confidered as having only three'
permanent axes of rotation, agreeably to what I have proved
in my" Mathematical Memoirs ; and, as it is difturbed in its
rotatory motion by the attrad:ion of the fun and moon (and

other

23 1 M)\ Landen's tnveftigation^ Sac,

other bodies in our fyflem) ; It follows ; that it will not conti-
luially revolve about either of thofe axes, but will revolve, or
endeavour to revolve, about fucceffive momentary axes, as fliewn
above. If then its three permanent axes of rotation be called
itsfirji-, ft'cond, and third axes ; and the poles of its Jir/i axis be
thofe about which its momentary poles are carried according to
our theory ; the fecond and ibird axes will be in the plane of its
equator, the three being at right angles to each other. There-
fore, with refpecl to the above theory, this terreftrial mafs muft
be confidered of fuch a form, that its equator, and any fedlion
parallel thereto, fliall rather be elliptical than circular. And,
denoting its firft, fecond, and third axes by ^, c, d, refpectively,.
obfervations evince, that the difference c -^ If will be much
greater than the difference J -c. Whence it follows, that (fup-
pofing the earth's rotatory motion to be difturbed only by the
centrifugal force arihng from the inertia of its own particles) the
track of polar evagation with us will be nearly circular, and the
radius of the limiting circle very fmall, whether we have regard
to the moveable or immoveable fpherical furface referred to
above ; but that, in the latter furface, fuch circle will be much
lefs than in the former : and it moreover follows, that the con-
cavity of the track upon the moveable furface will continually
touch and roll along the convexity of the track in the immove-
able furface.

In other planets, the tracks of polar evagation may, from a
fimilar caufe, be very different. The theory above explained
evidently proves, that their axes of rotation may poflibly vary
greatly in portion, merely through the inertia of matter i whilfl
Providence has fo ordered it, that the pofition of the axes of
rotation of this planet fhall, by that caufe, be but very little
altered.

'^!B

Pl„l,., r,.,,,.,. Vcl Z.VAT I ab. xp AM.

[ 335 J

XVII. Defer 7 pt ton of a new Marine Animal. In a Letter from
Mr, Everard Home, Surgeon, to John Hunter, Efq. F.R.S,
With a P offer ipt by Mr, Hunter^ containing anatomical Re-
marks upon the fame.

Read March 7, 1785.

TO JOHN HUNTER, ESQ. F.R.S.
DEAR SIR, Sept. 20, 1784.

I SENT you, about three years ago, a fea animal from Bar-
badoes, which was unlike any one I had ever feen. From
the want of books and other information in that illand, I was
unable at the time to find out, whether it was a new acquifi-
tion, or had been defcribed by any authors in natural hiftory.

Since my arrival in England, I have examined the libraries
of fome men of fcience for an account of this animal, and
have made other enquiries among the naturalifts, without fuc-
cefs. The fpecimen I fent you was found on a pai*t of the
coaft which had undergone very remarkable changes, in confe-
quence of a violent hurricane. Thefe changes were indeed the
means of its being difcovered, and prefent a probable reafon why
it was not difcovered before. The extraordinary circumfiance:^
which brought it within our reach, and the filence of all the
authors on natural hiftory which I have been able to confult,
incline me to believe it to be a non-defcript. As the peculiar!-*
ties of its flrudure may add to the knowledge of the natural

hi (lory.

334 ^'^' Home's Difcriptlon of

hiftory of other animals of this genus, at prefent fo little un-
derflood, I have drawn out a more particular account of it;
which, if you think it deferves attention, you may prefent to
th.e Royal Society.

This animal was found on the fouth-eaft coafl: of Barbadoes,
dole to Charles Fort, about a mile from Bridge Town, in fome
fhoal water, feparated from the fea by the Itones and fand
thrown up by the dreadful hurricane, which happened in the
year 1780, and did fo much mifchief to the ifland.

The wind, in the beg-inninp* of the Iform, which w^as in the
afternoon, blew very furioufly from the north-wefl:, making a
prodigious ifweil in the fea ; and in the middle of the night
changing fuddenly to the fouth-eaft, it blew from that quartef
upon the fea, already agitated, forcing it upon the fhore with
•fo much violence, that it threw down the rampart of Fort
.Charles, which was oppofed to it, although thirty feet broad,
bv the buriling of one lea. It forced up, at the fame time, im-
menfe quantities of large coral rocks from the bottom of the
bay, making a reef along this part of the coafl for the extent
of feveral miles, at only a few yards diflance from the fhore.

The foundings of the harbour were found afterwards to be
ir.tirely changed, by the quantity of materials removed from
the bottom in different places. In the reef of coral was found
an infinite number of large pieces of brain-ftone, containing
the (hell of this animal; but the animals had either been
long dead, or more probably deftroyed by the motion of th^i
rocks in the ftorm : fome few of the brain- ftones, however,
that had been thrown beyond the reef, and lodged in the fhoal
water, receiving lefs injury, the animals were preferved unhurt.

The animal, with the fhell, is almofl intirely inclofed in the
brain -flone, fo that at the depth in which they generally lie,

2 thejr

a ncju Marine AnimaL ^^5

they are hardly fllfcernible, through the water, from the com-
mon furface of the braln-ftone ; but when in fearch of food
they throw out two cones, with membranes twifled round
them in a fpiral manner, which have a loole fringed tdge,
looking at the bottom of the fea like two flowers ; and in this
Hate they were dlfcovered.

The fpecies of Acllnia called in Barbadoes the Animal
Flower, and common to many parts of that ifland, altliough
rarely before {esn on this part of the coaft, was now found in
confiderable numbers in this {hoal water.

The animal was firfl: obferved by Captain Hendie, the officer
commanding Fort Charles, in looking for (liells which were
thrown up in great num^bers from the bottom of the harbour.
He found a piece of brain-flone containing three of them in
different parts of it. Some little time after, I was lucky enough
to find another brain-flone with two in it ; one of them is the
fpecimen in your poffeffion ; the other was deflined for exami-
nation, of which the following is the account.

The animal, when taken out of the fhell, including the two
cones and their membranes, is five inches in length ; of which
the body is three inches and three-quarters, and the apparatus for
catching its prey, which may be confidered as its tentacula,
about an inch and a quarter.

The body of the animal is attached to its fhell, for about
three-quarters of an inch in length, at the anterior part where
the two cones arife, by means of two cartilaginous fubftances*
with one fide adapted to the body of the animal, the other to
the internal furface of the (hell : the refl of the body is unat-
tached, of a darkifh white colour, about half an inch broad, a
little flattened, and rather narrower towards the tail. The
mufcular fibres upon its back are tranfverfe ; thofe on the belly
Vol. LXXV. Y y longi-

^^(j Mr. Home's Defcription of

longitudinal, making a band the whole length of the body, on;
the edge of which the tranfverfe fibres running acrofs the back

terminate.

The two cartilaginous fubftances by which the animal ad-
heres to its fbell, are placed one on each fide of the body, and are
joined together upon the back of the animal at their pofterior
edges : they are about three-quarters of an inch long, are very
narrow at their anterior end, becoming broader as they go
backwards ; and at their pofiierior end they are the whole
breadth of the body of the animal. Upon their external fur-
face there are fix tranfverfe ridges, or narrow folds ; and along
their external edges, at the end or termination of each ridge,
is a little eminence refembling the point of a hair pencil, fo
that on each fide of the animal there arc fix of thefe little pro-
je6llng fiiuds, for the purpofe of adhering to the fides of the fhell
in Vv'hich the animal is inclofed. The internal i'urfiices of
t\\t{Q cartilages are firmly attached to the body of the animal, in-
their middle part, by a kind of band or ligament ; but the upper
and lower ends are lying looie.

From the end of the body, between the two upper ends of
thefe cartilages, arifewhatl fuppofe to be the tentacula, confift-
inp- of two cones, each having a fpiral membrane twining round
it : they are clofe to each other at their bafes, and diverge as-
they rife up, being about an inch and a quarter in length, and
nearly one-fixth of an inch in thicknefs at their bafe, and gra-
dually diminifhing till they terminate in points. The mem-
branes w^iich twine round theie cones alfo take their origin
from the body of the animal, and make five fpiral turns and a
half round each, being loft in the points of the cones ; they
are loofe from the cone at the lowefi: fpiral turn which they
make, and are nearly half an inch in breadth; they are exceed-

ingly

a new Mail fie AnimaL 337

liio-ly delicate, and have at fmall diftances fibres running acrofs
them from then* attachment at the fi:em to the loofe edge,
which gives them a ribbed appearance. Thefe fibres are conti-
nued about one-tenth of an inch beyond the membrane, having
their edges finely ferrated, like the tentacula of the Adinise
found in Barbadoes : thefe tentacula (liorten as the fpiral turns
become fmaller, and are entirely loft in that part of the mem-
■brane which terminates in the point of the cone.

Behind the origin of thefe cones arifes a fmall fhell, which,
for one-fixth of an inch from its attachment to the animal, is
very (lender: it is about three quarters of an inch in length,
becoming confiderably broader at the other end, which is flat,
and about one-third of an inch broad; the flattened extremity
is covered with a kind of hair, and has rifmg out of it two
fmall claws, about one-fixth of an inch in length. If the hair,
•and mucus entangled in it, be taken away, this extremity of the
fhell becomes concave, is of a pink colour, and the two
claws rifing out from its middle part have each three fliort
-branches, not unlike the horns of a deer. The body of this
■fhell has a foft cartilaginous covering, with an irregular but
poliflied furfacet on this the cones red in their collapfed ftate,
in which ftate the whole of the fhell is drawn into the cavity of
the brain-ftone, excepting the flattened end with the two

-claws.

Before the c6nes there is a thin membrane, which appears to
be of the fame length vv'ith the fliell juft defcribed. In the col-
lapfed ftate it lies between the cones and the fliell in which trie
animal is inclofed ; but, when the tentacula are thrown out, it
•is alfo protruded.

The fhell of this animal is a tube, which is very thin, and
adapted to its body: the internal furface is fraooth, and of a

Y y 2 pink-

^^8 Mr, Home's Defcription of

pln.kifh white colour : its outer fnrface is covered by the brain-
ilone in which it is inclofed, and the turnings and windings
which it makes are very numerous, The end of the (hell,
which opens externally, riles above the furface of the flone on
one fide half an inch in height, for about half the circum-
ference of the aperture, bending a little forw^ards over it, and
becoming narrower and narrov/er as it goes up, terminating at
laft in a point jufl: over the center of the opening of the fhell ;
on the other fide it forms a round margin to the furface of the
brain-ftone. This part of the fhell is much thicker and
Ibonger than that part which is incloied in the brain-ftone : its
outer furface is of a darkifh brown colour; its inner of a
plnkifh white.

The animal, when at reft,, is wholly concealed in its fhell ;.
but when it feeks for food, the moveable fhell is puihed flowly
out with the cones and their membranes in a coUapfed ftate ;.
and when the whole is expofed, the moveable (hell falls a little
back, and the membrane round each of the cones is expanded,,
the tentacula at the hafes of the cones having jufl room enough
to move without touching one another. The thin membrane
which lay between the cones and the inclofmg (hell is pro^
truded in the form of a fold, and lies over the external (hell
which projedls from the brain-ftone.

The membranes have a flow fpiral motion, which continues
during the whole time of their being expanded ;. and the ten-
tacula upon their edges are in conftant acflion. The motion of
the membrane of the one cone feeras to be a little different
from that of the other, and they change from the one kind of
motion to the other alternately, a variation in the colour of
the membrane at the fame time taking place, either becoming
a (hade lighter or darker ; and this change in the colour, while

the

a new Marine AnhnaL n^Q>

the whole is in motion, produces a pleafing'efFecl:, and is moft
ftriking when the fun is very bright. The membranes, how-
ever, at fome particular times appear to be of the feme colour.

While the membranes are in motion, a httle mucus is ofteiii
feparated from the tentacula at the point of the conie. Upon
the leaft motion being given to the water, the cones are imme-
diately, and very fuddenly, drawn in. /

This apparatus for catching food is the moft dehcate and
complicated that I have feen ; but I (hall not trouble you with
any conjectures upon what that food may be, as I have not
attained fufficlent knowledge of the animal to fpeak with the
fm.alleil certainty,

I have endeavoured to defcrlbe the external, appearances as I
ilnv them ; and have annexed two drawings of the animal
iii its two different flates, one In fearch of food, and one while
lying at reil: ; thefe are a little magnified, to fhow the parts
more diflinclly.

p I fhali not fay any thing of the internal parts, or their ufeSj-
as the animal is in your pofleffion, whoare fo much better able
to explain its internal oeconomy..

r am, &c.

EVERARD HOiME,.

F O S T-

2|o Mr. Hunter's Anatomical Remarks

POSTSCRIPT,

BY JOHN HUNTER, E 3 Q^ F. R. S*

ANlMxA-LS which come from foreign countries, and can*
not be brouglit to England alive, mud be kept in fpirits to
preferve them from putrefaclibn, which makes them lefs fitted
for anatomical examination ; for the fpirits, which preferve
them, produce a change in many of their properties, and altec
the natural colours, and texture of the parts, fo that often
the ftrudure alone of the animal can be afcertained ; and where
this is not naturally diftinft, it becomes frequently intirely ob*
fcured, and the texture of the finer parts is wholly dethoyed,
requiring a very extenfive knowledge of fuch parts in animals
at large, to affifr us in bringing them to light : this happens to
be the cafe with the animal whofe diileflion is tlie fubjecl of
this Poftfcrlpti

The animal may be faid to confifc of a flefliy covering, a
ftomach and inteftinal canal, and the two cones with their ten-
tacula and moveable fliell, which lafl may be confidered as ap-
pendages.

The, body of the animal is flattened, and terminates in t\v6
edees, which are interfcfted bv rug.^. the fafciculi of tranfverfe
mufcular fibres which run acrois the back being continued
over them. Upon each of theie edges is placed a row of fine
hairs, which project to lome diifance from the Ikin.

The flefhy covering confifts principally of mufcular fibres:

thofe upon the back are placed tranlverfely, to contract the body

5 laterally i

x)n a new Marine AnimaL 241

laterally; thofe on the belly longitudinally, to fhorten theani-
inal when llretched out, and to draw it into thefiiell.

The flomach and inteftine make one ftraight canal : the ante-
rior end of this forms the mouth, which opens into the grooves
made by the fpiral turns of the tentacula round the llem of
each of the cones ; and the inteftine at tlie poflerior end opens
externally, forming the anus. From the contraded fbte of
the animal, the inteftine is thrown into a number of folds.

On examining the cones and the tentacula, I at firil: believed
that the fpiral form arofe from their being in a contraded ftate ;
and that, w'hen the tentacula wereereded, the cone untwifled,.
forming a longer cone with the tentacula ariiing from its fides,
like the plume from the ilem of a feather; and that this flem
was drawn in or fhortened by means of a mufcle pafling along
the center, which threw the tentacula into a fpiral line, iimilar
to the penis's of many birds ; but \\o\w far this is really the
caie, I have not been able to afcertain.

The internal (Irudure of this animal, like moil of thofe
which have tentacula, is very fmiple ; it differs, however, ma-
terially from many, in having an anus, mofl: animals of this
tribe, as the Polypi, having only one opening, by which the
food is received, and the excrementitious part of it alfo after-
wards thrown out ; this we muil have fuppofed, from analogy,
to take place in the animal which is here defcribed, more parti-
cularly fince it is inclofed in a hard (liell, at the bottom of
which there appears to be no outlet ; but as there is an anus
this cannot be the cafe.

It is very fingular, that in the Leach, Polypi, &c. where no
apparent inconvenience can arile from having an anus, there
is not one, while in this animal, v/here it would feem to
be attended with many, we find one ; but there being no anus

iix

^42 Mr, HuNTER*s Anatomical Remarks

ill the Leach, Polypi, &c. may depend upon fome circumf^ance iii
the animal oeconomy which we are at prefent not fully ac-
quainted with.

The univalves, whofe bodies are under (imilar circumftances
refpefting the (hell with this animal, have the intefllne refledled
back, and the anus, by that means, brought near to the exter-
nal opening of the fliell, the more readily to difcharge the ex-
crement; and although this {IrutSture, in thefe animals, appears
to be folely intended to anlwer that purpofe, yet when we find
the fiuTie ftrufture in the black Snail, which has no fhell, this
reafoning will not wholly apply, and we mufl: refer it to fome
other intention in the animal oeconomy. «

In this animal we mufl: therefore reft fatisfied that the difad-
vantagebus fituation of the anus, with refpe£l to the excrement's
being difcharged from the fhell, anfwers fome purpofe in the
oeconomy of the animal, which more than counter-balances the
inconveniences produced by it.

It would appear, from coniidering all the circumftances,
that the excrement thrown out at the anus muft pafs from the
tail along the infide of the tube, between it and the body of
the animal, till it comes to the external opening of the fhell, as
there is no other evident mode of difcharging it.

How the tube or fhell is formed in flone or coral is not eafily
afcertained. It may be afked, whether this animal has the
power of boring backwards as the Teredo Navalis probably
does, or whether the ftone or coral is formed at the fame time
with the animal, and grows and increafes with it : and if we
confider all the circumftances, this laft would appear to be moft
probable, and agree beft with the different pha^nomena ; for the
coral is lined with a fhell, which could not be the cafe if the
animal was continually increaiing this hole, both in length and

I breadth.

on a new Marine AnhnaL ^4j

breadth, in proportion to its growth ; but if the coral and the
animal increafe together, it is then fimilar to the growth of all
fhells, whether bivalve or univalve.

The animal does not appear to have the power of increaiing
its canal, being only compofed of foft parts. This, however,
is no argument againfl: its doing it, for every fhell fifh has the
power of removing a part of its fliell, fo as to adapt the new
and the old together ; which is not done by any mechanical
power, but by abforptlon.

The tribe of animals which have tentacula confids of an
almoll: infinite variety, and many of the fpecies have been de-
fcribed. Of that kind, however, which has the double cones, I
believe hitherto no account has been given. It is moil pro-
bably to be found in the feas furrounding the different Iflands
in the Weft Indies ; for I received an animal, fome years ago,
from Mr. Oliver, furgeon, at Tenby in Pembrokeihlre,
which he had procured from a gentleman at St. Vincent's ;
which, upon examination, proves to be the fame animal with
that above defcribed, only that the moveable (hell is wanting.

Since I began this Poftfcript, I find there is a defcrlption of
a double-coned Terebella, publiflied by the rev. Mr. Cor di-
ner, at Bamf in Scotland, which was found upon that coaft ;
in which the cones have their tentacula palling out from the
end, and when ere£led they fpread from the cone as from a
center. This proves that the double-coned tentacula alfo have
different fpecies.

Vol. LXXV. Z z s x p l a-

/ >

-44 Mr, Hx7KTEr's Anatomical Remarks

EXPLANATION OF THE FIGURES, TAB. XI.

FIG. I.

A drawing of the animal after death, as it appeared ia fp-
rits, a httle magnified.

A. The under fide of the body.

BB. The cartilages which attach the animal to the fides oF
the cavity in which it lies.

C. One of the cones covered by its membrane in a collapfed

flate.

D. The lowefl fpiral turn of the membrane and its ten-
tacula fpread out.

EE. The cut edges of the divided membrane, which are
turned on each lide to (hev/ the cone.

F. The cone as it appears in the intervals between the fpiral
turns of the membrane.

G. The moveable fhell, with the fmooth cartilaginous cover-
ing, in an outfide view.

H. The flattened end of the moveable fhell, with hair upon
it.

11. The two claws that arife from the furface of the flattened
end of the moveable fhell.

K. The anus, into which a hog's briflle is introduced.

FIG. II.

A drawing of the animal, with its tentacula expanded in

fearch of food, as it appears in the fea ; taken from a fketch

made in Barbadoes, where no draughtfman could be procured

4 while

r/u7.;Jn,m. /!/, /„V.W'.T«1>, Xl.y.. ,j/;.

Fi<r-II-

on a new Marine Animal, 345

while the Bnhn^al was alive. This alfo is larger than the

animal.

a. The fort of brain-flone in which the animal was dif-
covered.

b. The external prominent (liell.

cc. The membrane which is protruded with the cones and
moveable (hell, and makes a fold over the edges of the promi-
nent {hell.

dd. The membranes and tentacula in a ftate of expanfion.

e. The inner fic!e of the moveable fliell, as it appears when
protruded.

f. The hole in the brain-ftone as it appears when the promi-
nent fhell is brok^en oft, and which may be feen in many fpeci'
mens of brain-ftone.

Zz 2

[ 346 ]

XVIII. ^ Defcription of a new Syjlem of Wires in the "Focus of a
Tekfcnpe, for objerving the comparative Right Jfcenfions and
Declinations of ccekfial Objedls ; together with a Method oj In^
vejil gating the fame when obferved by the Rhombus^ though it
happen 72ot to be truly in an equatorial Pofition, By the Rev*
Francis Wollaftoo, LL,B. F.R.S.

Read April 7, 1785.

IN confequence of a paper communicated the laft year ta
this Society, and honoured with a place in our Tranfa£lions,
it may be expedled of me, that I fliould now deliver in an ac-
count of what farther obfervations I have made on that con-
flellation of which I then gave a rough map. This I readily
would do, if they were in any degree worthy of the Society's
notice. But as yet they are far from perfedt : how much better
they may fucceed hereafter, time muft fhew.

Yet has this year perhaps not quite been loft ; the difficulties
which difappointed my hopes, having led to what appears to me
an improvement in the Inflrument with which to purfue fuch
obfervations.

My defign, as was hinted in that Paper, was to afcertain, as
well as I was able, the right afcenfions and declinations of the
ftars I had laid down ; by obferving their meridian pajfages and
meridian altitudes^ where that could be done with fuch fmall
inflruments as mine ; as alfo by their comparative pajfages
through the field of an equatorial telefcope furnifhed with a
7 iyflem

Mr. Wollaston's Befcnption of, &c. 347

iyflem of wires invented by Dr. Bradley, and called by the
French Reticule Rhomboide, whence it has comnaonly obtained
in Englifh the name of the Rhomboid.

In the former I was difappointed by the weather ; which from
the time I went into the country, in the middle of May, till
the end of June, when that conftellation came to the meridian
in the day-light, afforded me very few evenings fit for obfer-
vatlon.

In the latter I failed, through the imperfecllon of my Inftru-
ment, or my own want of Ikill in the ufe of it ; for though
a fingle fet of obfervatlons in any one evening would appear
very good, yet when reduced by calculation, and confronted
with other repeated trials, they never gave me the fatisfadioa
I wiflied.

The jrhombus (for a rhombus, and not a rhomboid, it ought
moft properly to be called) is very good in theory ; but very
difficult to get executed with preclfion, and liable to fome inac-
curacy in the obfervatlon. The truth of it depends upon the
longer diagonal being exactly twice the length of the fhorter
one ; which requires an aukward angle (^^'^° Y 48^^) at the ver-
tex, not eafily to be hit by the workmen, and therefore feldom
fufficiently true. Befide this, as the fides of the rhombus, on
which depends the calculation for differences of declination, are
but 26° 2>3^ 54^'' declining from the perpendicular or horary
wire, a very fmall error in obferving the pafl'age of a flar
makes a very material difference in the refult.

This determined me upon making trial of a fquare placed
angularly (an addition to M. Cassini's wires at 45°, as may be
feen in tab. XII. fig. i.) which feems to anfwcr better. I
rnufl: confefs I have not yet had opportunity for trying it fo
completely as I could wifli : but I was. unwilling to let this

year

^4-3 ■ Mr. Wor.LASTON*s Defcription of a

year (lip by, vvithout making it known ; fmce, I think, from'
wh:it I have done with it, I may be confident of its utihty *. '
The properties and advaniuges of Inch a fyftem of wires '
fcarcely need to be pointed out to afironomers. The whole ex« '
terit of the field is employed as it is in the rhombus (the want
of which was faid to be Dr. Bradley's objedion to M. Cas- ■
siNi's wires) ; but being formed of right angles or half- right
angles, to which workmen are moft accuflomed, they will
always be apt to execute their part better; and the obliques;
from the dltferences being juif double to what they are in the'
rhombus, give the comparative declinations with twice the^
certainty. To this the number of correfponding obfervations
in the paflage of every flar add confiderably ; fuice you may
calculate its dllfance from the center C, from the angle D or E •
or from one of the intermediate angles K, as you fhall fee occa-
fion. The fame indeed you may do in the rhombus from D or
from E; or, if the rhombus be formed of wires, from the'
angle at L, fig. 2. ; but only with half the precifion. The'
refult of a (ingle pafTage of any one ftar (excepting towards the*'
extremities of the field) gives the extent of the field equally ia^
each, provided the declination of the flar be known, by de-i
ducing its diftance from thofe feveral angles ; and fuch deduc-
tions ferve as a ilill farther check upon every obfervation ; be-' I

1

* What is here offered is by no means to be underftood as recommending any "
fyftem of wires in preference to aftual meafurement with a micrometer, but to
render the ufe of them as convenient as may be to fuch gentlemen as are not 1
provided with better inftruments. The equatorial micrometer with a large field
(fuch as I have feen at Mr. Aubert's, of Mr. Smeaton's conftruftion) I take to
be the beft inftrument for taking differences of right afcenfion and declination
out of the meridian ; and far fuperior to any fyflem of fixed wires, or indeed to
any equatorial feitor whatever.

caufe,

new Syjlem of Wires in a T^elefcope, 34c>

caufe, if any part of it be thought doubtful, its tallying or not
tallying with the known extent of the field will fhew whe-
ther there be any error, or where it lies. i\nd, in each of
them, the parallel wires will tell you whether the placing of
your inftrument be true or faulty ; becaufe, if truly made and
truly fet, the fame ftar mufl: take the fame time in paffing from
one wire to its correfponding parallel ; which will differ confi-
derably, and in every ftar the fame way, if the poiition be
faulty.

Some of thefe latter remarks might have been fpared, but
that they may ferve as hints to fuch gentlemen as may be in-
clined to lend their affiftance to what was propofed the lafl
year, and who may not have confidered the many helps to be
derived from a crofs examination of theobfervations they make.
For their ufe alfo it may be proper to add, what indeed is no-
thing new, that if the pofition of the infh'ument be found
erroneous, the formula given by M. de la Lande in his
Aflronomy will ferve to redify the obfervation. Calling the
larger interval between the paflage of any oblique and the ho-
rary wire w, and the fmalleronew, — , ^ will give the dif-
ference of declination (in time, to be converted into degrees,
and multiplied by the cofine of declination) from the angle

where that oblique meets the horary; and — i — r- the dif-

ference in right afcenfion from the fame angle. It mufl: furely
be almoft needlefs to mention, that where the pofition is true,
half the interval of time betwesn a ftar's paffing any two cor-
refponding obliques, converted into degrees, and multiplied by
the cofine of declination, will give the difference in declination
of that ftar from the angle where thofe obliques meet, as the

'whole interval does in the rhombus.

But

2$o Mr. Wollaston's Defcrtption of a

But it may, perhaps, be of fervice to aflronomy, or at leaft
not unacceptable to thofe gentlemen who ufe the Rhombus,
that I Ihould fubjoin another formula (contrived for me the laft
llimmer by my Son, now Mathematical Le6lurer at Sidney
College, Cambridge) for investigating the comparative right
afcenfions and declinations of ftars obferved by it, when the
inftrument is not placed truly in the plane of the equator. I
was led into wifhing for fome fuch formula, in confequence of
an ingenious Paper, kindly communicated to me by Sir H. C.
Englefield, Bart. F. R. S. giving an account of his method
of doing it by a fcale and figure ; which, though very eafy
when one is provided with fuch a fcale, appeared to me to be of
lefs general ufe than by calculation ; and I do not know that
any thing of the kind is to be met with in any publication.

Let the angle DLL, fig. 2. (which, by conftrudlion, is
6f 26' 6'') be called . - - . ^

The diagonal LL (whofe extent, that is, what portion of
a great circle it comprehends, muil be known to theobferver)
be called - - - - _ j

The larger interval obferved between the paffage of a flar
by an oblique and the horary wire (as b c^ - - m

The fmaller ditto of the fame flar (as c d) - n

The larger ditto of another flar (as jQ y) • - jt*

The fmaller ditto (as y J) - - - v

Then — ^ — = tangent of the angle which LL makes

with a parallel of declination : call this (^
The angle q being thus found, then

^. «c^>x in. g — £ ^^^^ _ (jjffgj-gj^j^g \^ declination between the

two points on the vertical wire where

thofe

fiew Syjlem of JVtres in a Tele/cope, 351

thofe ftars pafs it. N. B, This be-
ing in tune muft be converted into
degrees^ and multiplied by cofine of
declination as ufual, to give the true
dIfFerencc in declination between the
ftars.
And the fame expreffion, viz,
^ . w^yx irutf — q_ ^ ^^^^ _ ^j_^^ difference in J^ between thofe two

•JR. X lin. a 2

points ; to be applied as a correction
to the obferved times.
The fame may be done by the larger intervals tn and ^, only

by fubftituting ^ ~ ^ in the place of ^ 4-^, thus :

1 . TTi '^ U.X fin. a— a r t/t* 'ii** i

~-^ X col. q — ditterence ui dechnation as above ;

R X fill, a 2

or . . . . . X fin. ^ = afcenfional difference.

If the ftars differ too much in declination to come within

the expreflion above (as N° 2. and 3.) then the differences of

the angles D and E in declination and right afcenfion may be

fmind thus:

— ^" ' ^ = difference in declination between D and E j,

— ^"' ^ — their afcenfional difference ;

K.

and the difference of each ftar from its refpeflively neareft
angle of the rhombus, may be deduced by the former expref-
fion, leaving out the confideration of the other ftar, thus :

2 . »x in.g + y ^ ^^|- _ difference of the ftar in declinatioa

R X fin. a -*

from its neareft angle,
and . . . X fin. ^=s its difference in right afcenfion.

The application of thefe formulie is very eafy: for having
ound qy if you fet down its cofine in one column for declina-

VoL. LXXV. A a a tion,

352 Mr, WoLt A STOMAS Dejcription, &c.

tion, aiid its fine in another calumii for right afcenllon, and
under each the conftant fm. a-\-q^ and the arithmetical compl.
of fin. ii ; thefe heing added together will make two fums,
for the comparative obfervations of every ftar which may pafs
your field ; and, iinlefs your field be very large, and the decli-
xiation of the flars very great, if to the column for declination
you add the cofine of declination of the center of your field, it
will adapt itfelf to all the. produds.

FRANCIS WOLLASTON.

Charter-hoiife-Square,
March 15, 1785.

POSTSCRIPT.

SINCE the delivery of this Paper, it has occurred to me,
t,hat it may fometimes be convenient to know the angle of^
deviation from the true equatorial pofition in the new fyftem of
wires. This is to be deduced nearly in the fame manner as in

the rhombus ; for — — = tang, q. By this angle any obferved

differences in right afcenfion may be corredled : for the dif-
ference in declination between any two ftars (or their dif-
ference from the angle) multiplied by fin. q, will give the cor-
redion required. I

r/ii/,:, T,a„.. i;>/./,.VA-|-T.-.l..Sll /. JJ2 .

i 353 3

XIX. An Account of a ^tag^i Head and Horns, found at Alport,
in the Parijh of Youlgreave, /;/ the County of Derby. In a
Letter from the Rev. Robert Barker, B.p, to John Jebb, M.D,
F.R.S,

Read April 14, 1785.

ABOUT five years ago, fome men working in a quarry of
that kind of ftone which in this part of the country we call
tuft ■*, at about five or fix feet below the furfiice,, in a very
Iblid part of the rock, met with feveral fragments of the horns
and bones of one or different animals. Amongft the reft, out
of a large piece of the rock, which they got entire, ^lere ap-
peared the tips of three or four horns, projecting a few inches
from it, and the fcapula of fome animal adhering to theoutfide
of it. A friend of mine, to whom the quarry belongs, fent
the piece of the rock to me in the ftate they got it, in which I leC
it remain for fome time. But fufpedting that they might be tips
of the horns of fome head enclofed in the lump, I determined
to gratify my curlofi.ty by clearing away the ftone from the
horns. On doing which I found that the lump contained
a very large ftag's head, with two antlers upon each horn, ii^
very perfect prefervatlon, inclofed in it.

* Tuft is a ftone formed by the depofit left by water paffing through beds
of fticks, roots, vegetables, &c. of which there is a large ilraturu at Matlock
Bath, in this county,

A a a 2 Thougla

354 ^^* Barker's jtlccount of a

Though the horns are fo much larger than thofe of any ftag
I have ever feen, yet, from the futures in the ikull appearmg
very dlftni(5l In it, one would fuppofe that it was not the head
of a very old animal. 1 have one of the horns nearly entire,
and the greatefl: part of the other, but fo broken in the getting
out of the rock, that one part will not join to the other, as the
parts of the other horn do. The horns are of that fpecies
which park-keepers in this part of the country call throftie-neft
horns, from the peculiar formation of the upper part of them,
which is branched out into a number of fhort antlers which form
an hollow about large enough to contain a thrufli's neft. I fend
you the dimenfions of the different parts of them, compared
with the horns of the fame fpecies of a large ftag, which have
probably hung in the place from whence 1 procured them two
or three or perhaps more centuries ; and with another pair of horns .
of a ditFerent kind, which are terminated by one fingle pointed
antler, and which were the honis of a feven-year-old ftag.

The river Larkell runs down the valley, and part of it falls
into the quarry where thefe horns were found, the water of
which has not the property of incrufting any bodies it paffes
through. It is therefore probable, that the animal to which
thefe horns belonged was wafhed into the place where they
were found, at the time of fome of thofe convulfions which
contributed to raife this part of the iftand out of the fea. Be-
fides this complete head;, I have feveral pieces of horns, bones
(particularly the fcapula I mentioned above), and feveral ver-
tebrae of the back, found in the fame quarry ; fome, if not all;
©f them probably belonging to the animal whofe head is in my
poiTeffion-.

Stag's Head and Horn»

355

Dimenjions of the horns found at Alport.

Circumference at their infertiori into the corona.

Length of the lowefl: antler.

Length of fecond ditto, . ,

Length of third ditto, , ,

Length of the horn, , . ,

Dimenfons of a large pair of throflk'nef horns.

Circumference at their infertioa Into thq corona.
Length of the lowefl antler, . . ,

Length of fecond ditto, ...

Length of third ditto, . ♦ ,

Length of the horn, . . ,

Dimenfions of the horns of a flag feven years old.

Circumference at their infertion into the corona.
Length of the loweft antler, . , ,

Length of fecond ditto, .

Length of third ditto, ...

Length of the horn, . * i ;

Youlgreave, Jan, 23, 1785.

Ft.

In.

0

9^

I

2

0

iif

I

i§

3

3i

o
I

o
o

o
o

2

7
o

o 104.

o Ilf

n

si

9
10

10

8^

[ 356 ]

2a.1L Afi Jlccount of the fenfiiive S^mlity of the Tree Averrlioa
Carambpla. In a Letter frmi Robert Bruce, Af.D. to Sir
Jolcph Banks, Bart. P.R.S.

Read April 14, 1785.

"^HE Averrlioa Carambola of Linn^us, a tree called in
Bengal the Camruc or Camrunga, is poffeffed of a power
fomewhat fimilar to thofe Ipecics of Mimofa which are termed
fenfitive plants ; its leaves, on being touched, move very per-
ceptibly.

In the Mimofa the moving faculty extends to the branches ;
but, from the hardnefs of the wood, this cannot be expelled iii
the Camrunga. The leaves are alternately pinnated, with an
odd one ; and in their moft common pofition in the day-time
iire horizontal, or on the fame plane with the branch from
which they come out. On being touched, they move them-
felves downwards, frequently in {o great a degree that the two
oppofite almoft touch one another by their under fides, and the
young ones fometimes either come into contact or even pafs
^ach other.

The whole of the leaves of one pinna move by ftriking the ;
branch with the nail of the finger, or other hard fubftance ;
or each leaf can be moved fingly, by making an impreflion that
ihall not extend beyond that leaf. In this way, the leaves of
one fide of the pinna may be made to move, one after another,
whilfl the oppofite continue as they were ; or you may make

them

i)r. Bruce's Account of, &t, 3^57

them move alternately, or, in fhort, m any ordef yoir pleafe './
touching hi a proper manner the leaf you. wifh to put in mo-
tion. Bat if the impreilion, although made on a fnigle leaf,,
be flrong, all the leaves on that pinna, and femetimes on tlie
neighbouring ones, will be affected by it.

What at firfl feemed furprifing was, that notwithftanding
this apparent feniibility of the leaf, I could with a pair of
fharp fciffars make large incifions in it, without occafioning the
fmaliefl motion ; nay, even cut it almoft entirely off, and the
remaining part flill continue unmoved;, and that then, by
touching the. wounded leaf with the finger or point of tlie
fciffars, motion would take place as if no injury had been
offered. But, on further examination, I found', that although
the leaf was the oftenfible part v/hich moved, it was in hCt
entirely paffive, and that the petiolus was the feat both of fcnfe
and adion : for although the leaf might be cut in pieces, or
fqueezed with great force, provided its diredion was not"
changed,, without any motion being occafioned; yet, if theim-
preflion on the leaf was made in fuch a way as to affcdl the
petiolus, the motion took place. When, therefore, I wanted;
to confine the motion to a fingle leaf, I either touched it fo as
only to affed its own petiolus, or, without meddling with the
leaf, touched the petiolus with any fmall-pointed body, as a p.ia
or knife.

By comprefling the univerfal petiolus near fhe place where
a partial one comes out, the leaf moves in a few feconds, in the-
fame manner as if you had touched the partial petiolus.

Whether the impreffion be made bypundure, percuflion, or •
compreffion, the motion does not inftantly follow ; generally
feveral feconds intervene, and then it is not by a jirk, but

regular

358 Dr. Bruce's Account of a

regular and gradual. Afterwards, when the leaves return to
their former lituation, which is commonly in a quarter of an
hour or lefs, it is in fo flow a manner as to be almofl imper-
ceptible.

On flicking a pin into the univerfal petiolus at its origin,
the leaf next it, which is always on the outer iide, moves firft ;
then the firfl: leaf on the oppofite fide, next the fecond leaf on
the outer, and fo on. But this regular progreffion feldom con-
tinues throughout ; for the leaves on the outer fide of the pinna -
leem to be affected both more quickly, and with more energy,
than thofe of the inner, fo that the fourth leaf on the outer
fide frequently moves as foon as the third on the inner ; and
fometimes a leaf, efpecially on the mner fide, does not move
at all, whilft thofe above and below it are afFe£ted in their pro-
per time. Sometimes the leaves at the extremity of the petio-
lus move fooner than feveral others which were nearer the
place where the pin was put in.

On making a compreflion with a pair of pincers on the uni-
verfal petiolus, between any two pair of leaves, thofe above
the compreflcd part, or nearer the extremity of the petiolus,
move fooner than thofe under it, or nearer the origin ; and fre-
quently the motion will extend upwards to the extreme leaf,
whilft below it perhaps does not go farther than the neareft
pair.

If the leaves happen to be blown by the wind againft one
another, or againft the branches, they are frequently put iii'-
motion ; but when a branch is moved gently, either by the
hand or the wind, without ftriking againft any thing, no
motion of the leaves takes place.

When left to themfelves in the day-time, (haded from the
fun, wind, rain, or any difturbing caufe, the appearance of

7 ' the

Jenjitive ^al'ity of the Averrhoa Carambola. ^rp

the leaves is diiferent from that of other pinnated plants. In
the lafl: a great uniformity iubfifls in the reiped:iv^e polition of
the leaves on the pinna ; but here fome will be {zzvi on the
horizontal plane, ^fome raifed above it, and others fallen under
it ; and in an hour or io, without any order or re2;ularity, whicii
I could obferve, all thefe vv'ill have changed tlieir relpedive
pofitions. I have feen a leaf, which was high up, fall down ;
this it did as quickly as if a ftrong impreflion had been made
en it, but there was no cauie to be perceived.

Cutting the bark of the branch down to the wood, and even
feparating it about the fpace of half an inch all round, fo as to
flop all communication by the veffels of the bark, does not for
the firll: day affe6l the leaves, either in their polition or their
aptitude for motion.

In a branch, which T cut through in fuch a manner as to
leave it fufpended only by a little of the bark no thicker than a
thread, the leaves next day did not rife fo high as the others ;
but they were green and frefh, and, on being touched, moved,
but in a much lefs degree than formerly.

After fun-fet the leaves go to lleep, tirfl moving down {o as
to touch one another by their under iides ; tliey therefore per-
form rather more extenfive motion at night of themfelves than
they can be made to do in the day-time by external imprehions.
With -a eonvex lens I have collected the rays oi the fun on a
leaf, fo as to burn a hole in it, without occalioning any motion-
But when the experiment is tried on the petiolus, the motion is
as quick as if from flrong percuflion, although tlie rays were
not fo much concentrated as to caufe pain when applied hi the
fame degree on the back of the hand j. nor had the texture .of
the petiolus been any ways changed by this ; for next Hay it

Vol. LXXV. B b b / could

.^^o Dr. Brvce's Account, Sec.

could not be diftinguifhed, either by its appearance or moving
povver^ £roni>thofe on which no experiment had been made.

The kaves mpve very faft from the ele6trical (hock, even
although a very gentle one ; but the flate of the atmolphere
was fo unfavourable for experiments of this kind, that I could
not purfue them fo far as 1 wifhed.

There are two other plants mentioned as fpecies of this
genus by LiNMiEUS. The firft, the Averrhoa Bilimbi, I have
not had an opportunity of feeing. The other, or Averrhoa
Acida, does not feem to belong to the fame clafs ; nor do its
leaves poflefs any of the moving properties of the Carambola.,,
Lin Nous's generic defcription of the Averrhoa, as of many
other phuits in this country which he had not an opportunity ot
feeing frefh, is not altogether accurate. The petals are con-
iie(fl:cd by the lower part of the lamina, and in this way they
^all off whilft the ungues are quite diflindl:. The ftamina are-
In five pairs, phKcd in the angles of the germen. Of each
pair only one ftamen is fertile, or furnished with an tinthera..
The filaments are curved, adapted to the fliape of the germeru
They may be preffed do-wn gently, fo as to remain ; and then,
when moved a little upwards, rife with a fpring. The fertile-
are twice the length of thafe deftitiyte of anthers.

Cakxitta, Nov. 23, 1783^

^^:^.

C 361 3

XXI. jin Account of fome 'Experiments on the Lofs of Weight in
Bodies on being melted or heated. In a 'Letter from George
Fordyce, ^f.D. F.R.S. to ^/r Jofeph Banks, Bart. P.R.S.

Read April 28, 17S5.

SIR,

ALTHOUGH I have made many experiments on the
fubje(£l of the lofs of weight in bodies on being melted,
or heated, I do not think it worth while to lay them all before
the Society, as there has not appeared any circumftance of
contradidion in them. I fhall content myfelf with relating the
following one, which appears to me couclufive in determining
the lofs of weight in ice when thawed into water, and fubje6t
to the leaft fallacy of any I have hitherto made, in fhewing the
lofs of weight in ice on being heated.

The beam I made ufe of was fo adjufted as that, with a
weight between four and five ounces in each fcale, _^*-^-^part
of a grain made a difference of one divifion on the index. It
was placed in a room, the heat of which was ^y degrees of
Fahrenheit's thermometer, between one and two in the after-
noon, and left till the whole apparatus and the brafs weights
acquired the fame temperature.

A glafs globe, of three inches diameter nearly, with an
indentation at the bottom, and a tube at the top, weigh-
ing about 45 1 grains, had about 1 700 grains of New- River
water poured into it, and was hermetically fealed, fo that the

B b b 2 whole,

6

362 Dr. Fordyce's Experiments on the Lofs of

whole, when perfedlly clean, weighed 2150^4. of a grain
exa6lly ; the heat being brought to 32 degrees, by placing it In
a cooling mixture of lalt and ice till it jufl: began to freeze, and
fhaking the whole together.

After it was weighed it was again put into the freezing mix-
ture, and let ftand for about twenty minutes; it was then
taken out of the mixture ; part of tlic w^ater was found to be
frozen ; and it was carefaily \\iped, tirO; with a dry linen cloth,
and afterwards with dry wafiied leather ; and on putting it into
the Icale it was found to have gained about the ^l^ part of a grain.
This was repeated {i\'Q times : at each time more of the water
was frozen, and more weight gained. In the mean time the
heat of trie room and apparatus had funk to the freezing
point.

When the whole was frozen, it was carefully wiped and
weighed, and found to have gained J-^ of a grain and four di-
vifions of the index. Upon ilanding in the fcale for about a
minute, 1 found it began' to lofe weight, on which 1 imme-
diately took it out, and placed it at a diftance from the beam.
I alio immediately plunged a thermometer in the freezing
mixture, and found the temperature 10 degrees; and on put-
ting the ball of the thermometer in the hollow at the bottom
of the glafs Yt&\, it fhewed 1 2 degrees. 1 left the whole for
h^lf an hour, and found the therm.ometer, applied to the hol-
low of the glafs, at 32°. Every thing now being at the fame
temperature, 1 w eighed the glafs containing the ice, after wiping
it carefully, and found it had loll: 4 and five divifions ; fo that
It weighed _'-y, all but one divifion, more than when the water
was fluid.

I now melted the ice, excepting a very fmall quantity, and
left the glafs vcflel expofed to the air in the temperature of 32

degrees

Weight in Bodies on being melted or heated, ^63

degrees for a quarter of an hour ; the little bit of ice continued
nearly the iame. I now weighed it, after carefully wiping the
glafs, and found it heavier than the water was at firft one divi-
fion of the beam. Lailly, I took out the weights, and found
the beam exactly balanced as before the experiment.

The acquifition of weight found on water's being converted
into ice, may arife from ?.n increafe of the attraction of gravi-
tation of the matter of the water ; or from fome fubflance im^
bibed through the glafs, which is necefiary to render the water

folid.

Which of thefe pofitions is true may be determined, by
forming a pendulum of water, and another of ice, of the fame
length, and in every other refpe6t fimilar, and making them
fwing equal arcs. If they mark equal times, then certainly
there is fome matter added to the water. If the pendulum of
ice is quicker in its vibrations, then the attraction of gravita-
tion is increafed. For there is no pofition more certain, than
that a fmgle particle of inanimate- matter is perfedly incapable
of putting itfelf in motion, or bringing itfelf to reft ; and
therefore, that a certain force applied to any mafs of matter, .
fo as to give it a certain velocity, will give half the quantity of
matter double the velocity, and twice the quantity, half the
velocity ; and, generally, a velocity exa*£lly in the inverfe pro^
portion to the quantity of matter. Now, if there be the fame
quantity of matter in water as there is in ice, and if the force
of gravity in water be ^-^-^-^-o- part lefs than in ice, and the
pendulum of ice fwing feconds, the pendulum of water will
lofe -1 of a fecond in each vibration, or one fecond in

2. s o o o

28000, which is almoft three feconds a day, a quantity eaiily

meafured.

2 lAall

364 -Dr. Fouuyce's Experiments on the Lofs of

I (hall juft take notice of an opinion which has been adopted
by Tome, that there is matter abfolutely light, or which repels
inflead of attracting other matter. I confels this appears ab-
furd to me ; but the following experiment would prove or dif-
prove it. Suppofing, for inftance, that heat was a body, and
abfolutely light, and that ice gained weight by lofing heat;
then a pendulum of ice would fwing through the fame arc in
^^.^-.-^--g. lefs time than a fmiilar pendulum of water ; for the
fame power would not only a6t upon a lefs quantity of matter,
but a counter-a6l:ing force would alfo be taken away.

Till the experiment of the pendulum can be made, or fome
other equally certain be fuggefted and made, it would be waft,
ing time to enter into conjecture about thecaufe of the gain of
weight in the converfion of water into ice in a glafs veflel her-
metically fealed.

I fhall only obferve, that heat certainly dimlniflies the at-
tradlions of cohefion, chemiftry, magnetifm, and electricity;
and if it fhould alfo turn out, that it diminifhes the attradioa
of gravitation, I fhould not helitate to coniider heat as the
quality of diminution of attra^Slion, which would in that cafe
account for all its efFe6ls.

We come,, in the next place, to take notice of the fecond
part of the experiment, viz. that the ice gained an eighth part
of a grain on being cooled to 12 degrees of Fahrenheit's
thermometer. In this cafe, a variation may arife from the con-
tradlion of the glafs veflel, and confequent increafe of fpeclfic
gravity in proportion to the air. But it is unneceflary to ob-
ferve, that this would be fo very fmall a quantity as not to be
obfervable upon a beam adjufted only to the degree of fenfibility
with which this experiment was tried. In the fecond place,
the air cooled by the ice above the fcale becoming heavier than
3 the

iVe'ight in Bodies on being melted or he ate J. ^6^

the furrounding atmofphere, would prefs upon the fcale down-
ward with the whole force of the difference. If a little more
than half a pint of air was cooled over the fcale to ths heat of
the ice and glafs containing it, that is, twenty degrees below
the freezing point, the difference, according to General Roy's
table, would have been the eighth part of a grain, which
was the weight acquired ; but the air within half an inch of
the glafs veffel being only one degree below the freezing pointy
I cannot conceive, that even an eighth part of a pint of air
could be cooled over the fcale to twenty degrees below the
freezing point; nor that the whole difference of the weight of
the air over the fcale could ever amount to the ^zd of a grain,
I have, however, contrived an apparatus which is executing, in
which this caufe of fallacy will be totally removed. I (hall,
therefore, reft at prefent the ftate of this part of the fubject ;
and leave it only proved, that water gains weight on being
fi'ozen.

I am. Sec

G. FORDYCE,

[ 366 ]

XX 11. Sketches and Defcriptlons of three Jlmple Injlruments for
drawhig Arch'itediure and Mcichinery hi PeffpeSiive. By Mr*
James Peacock ; cotmrnmicated by Robert Myltie, Efq» F.R.S,

Read March 17, 1785.

i-

OME of the following machines muft be placed upon the
front edge of tlie table upon which they are to ftand.
The fights may befupported by a three-legged ftafF.
The ftocks of the fquares or indexes may have fteel fprings
upon their edges, in order to keep them in any affigned part of
the grooves in which they are to Aide.

F I G. I. (t AEi XIII.)

ABCD a drawing board, to be fixed on a table or ftand, &c,
in a vertical pofition. AB a fliding-piece for the top of the T
fquare, having a rebate therein to form a groove, as expreffed
by the dotted line. CD, fliding-piece for the bottom of the fquare,
having a rebate therein to form a groove for the reception of
the ftock as defcribed by the dotted line ; this fliding-piece to
be of fufficient length to receive and fupport the faid ftock
when the blade of the fquare is coincident v/ith the lines
KNFH or LNGI. E a hole to receive the arm or Aider of the
fight-piece, to be ccnftrucled in the ufual manner. FGHI an
opening forming the field of view for the prototype. KLMNT a
iheet of paper fixed on the upper part of the board for the
•^copy, the four inner lines whereof form and inclofe a fpace of

the;

Mr. Peacock's Defcnptions, Sec, ^6y

the fame dlmenfions as the field of view refpe6liv^ely. OP a
fleel fliding-piece, equal in length to the diflance KF Or IN ;
at the lower end P is a ileel arm terminating in a point; and at
the upper end, at O, is a fimilar arm, terminating with a brafs
button, in the center of which is a fharp fteel pricker ; the faid
pricker and the point P are to be equi-diftant from the edge of
the blade of the fquare : this arm O is to have the faculty of a
fpring, in order that the pricker may clear itfelf of the furface of
the paper as foon as the finger quits the button, in the fame man-
ner as is ufual in the apparatus of large protradors. This flidinp-
fteel-piece may be drawn out of the dove-tailed or rebated
groove at pleafure, and the T fquare will then be fit for ordi-
nary ufes.

To ufe the Injlrument,

Having fixed the board truly level and perpendicular, and /
placed the point of fight, or hole for vifion, at fuch a height and
diftance as fliall be produ6live of the befl: effe£l, move the
fquare with one hand, and the fleel Aider with the other, until
the point P coincides with the eye and any point or angle in
the original obje£t. Prefs the pricker at O, and the puntcure
will be the true place, or copy, of fuch original point or angle, &c.

N. B. All perpendicular lines may be drawn at once (in
pencil), by bringing the left-hand edge of the fquare to coin-
cide with the original line and the eye ; and their lengths may
be very nearly determined by the graduated edge of the fquare,
fo as to prevent confufion from unneceflary lengths of lines.
The faid graduated edge will alfo give the points in all curved
or irregular objedts.

Vol. LXXV. C c c f i g.»

368; Mr. pE A c ock's Defiriptions of b:firumenis

T I G. II. (t a B. XIV.)

As the inftrnment, fig, i. proceeds chiefly by finding the po-
fitions of PointSj this is contrived to find the pofitions of Lines,
and to determine their limits by their reciprocal interfe6lions.

ABOCDE is a compound board, to be placed in a vertical
pofition. FGHI is the opening, or field of view. KLMN is a
loofe board, upon which paper is to be fixed ; and the edges of
the faid board are to be rebated, as defcribed in the plan at zz,
XYMN and OPQR are grooved receiles, to receive the faid"
loofe board, as occafion may require. STUW is a moveable
parallelogram, compofed of a rebated flock SU, two like gra-
duated rulers ST and UW, and the regulating piece TW ;
the whole connected with fcrews, fo as to move freely with a
fmall force ; and the diflances between the centers of motion
SU or TW to be equal to KF or HQ^. AE and ED are rebated
grooves, in which the flock of the parallelogram is to move.

To life the Injlrument,

Having fixed the compound board ABOCDE truly vertical,
flip the papered board KLMN into the recefs XYMN, or
OPQR, as the fubjed to be drawn may render firft neceflary,
and Aide the flock SU of the parallelogram into the groove AE,
or ED, to correfpond therewith ; then, by moving the fl:ock in
the groove with one hand, and at the fame time regulating the
parallelogram with the other, the top edge of the ruler UW
may be brought to coincide with any line in the original obje^l,
and the figured divifions on the edge of the ruler will at the
fame time determine the limits thereof, near enough to avoid a
confufion of unneceifary lengths of line, &c. The true repre-
4 V fentatioii

for di'Q'iving in PerJpeSfive, 569

feiitatioii of the place and pofitloii of the line may be then
drawn upon the paper, by the top edge of the ruler ST, a trifle
longer at each extremity than it appears to be. This operatioii
may be repeated for as many lines as can be obtained in the
iirfl pofition of the papered board and parallelogram ; when they
nuifl: be fliifted into the other recefs and groove, to find the reft,
which may be now done without taking any further notice of
the divifions on the rulers.

N. B. A common T fquare, applied to a board of this kind,
will anfwer mofl purpofes. For example : place the flock of
fuch a fquare in one of the grooves, having a blade not lefs
than the length PIK or HR ; mark the fpaces HI and QR
upon the upper edge thereof, and divide each of them into any
convenient number of equal parts, and figure the faid parts in
the ufual manner, to correfpond with each other, as may be
feen in fg. i . Now, fuppofe the flock of the fquare to be in
ED, it is plain, that all perpendicular lines may be drawn
upon the paper KLMN in their proper places, 'and (by means
of the divilions on the edge of the fquare) neaily of (though
properly a trifle more than) their true length. All the lines of
this defcription being obtained, the fhifting board mufl be
placed in its other recefs, and the ftock of the fquare into the
other groove ; then, beginning with the £rfl line, ^briiig the
edge of the fquare to agree with its limits, and mark them oft"
upon the line on the paper, and fo of all the refl in fucceflion 5
and join the points,- where necefTary, with a common ruler.

FIG. III. (t a B. XIV.)

.. This apparatus Ts contrived to avoid the trouble qf conti-
nually working againfl a board in a vertical pofition. Jij grd^r

C c c 2 to

5^(3? Mr. Peacock's Defer ipt ions of Injlruments

to this, two fquare boards are to be provided, equal in fize, and
cf fimllar conil:ru6lIon ; one is to be fixed in a vertical poiition,
for viewing the original object through a proper aperture ; and
the oiher is to be laid flat upon a deik or table, for the greater
cafe and conveniency of drawing the copy upon paper to be
fixed thereon for that purpofe.

ABCD is the vertical board ; EFGH the opening therein,
forming the held of view ; IKL the T fquare, the blade
thereof PL being moveable about the center P, wltii a mode-
rate degree of ftiffnefs ; the flock K is to (lide in a rebated or
dove-tail groove AD, and be fixable to any part thereof by th^
fcrew O ; the fteel points MN are to move with moderate eafe
in a rebated or dove-tail brafs groove in the middle of the
blade of the fquare ; upon the back of the groove AD are to be
fixed two brafs pins QQ, to refh in proper holes, funilar to-
the holes marked RR; and the fame kind of holes are to be made
in the corner of the board whereon the copy is to be made.

To ufe the Machine.

Having placed the board ABCD in a truly vertical poiition',
fix the fhifting groove AD in the rebate, on the moft conve-
nient j(ide of the board, by means of entering the pins Q^into
the holes R ; then loofen the fcrew O, and move the flock
IK, and at the fame time turn the blade PL upon its center P,
until one of its edges fhall be coincident with fome original
line ; then fix the ftock by turning the fcrew O ; move the
points M and N, till they exa£lly include the apparent length of
the faid line ; then take off the fhifting groove AD, together
with the T fquare or bevll fixed thereto, and apply the fame to

the

fZ/rf.... r,,,,-: r,'/ /.xxv.'inh xiii/. 370

/'//(/, J- rr.i,i.f.V,.t LXXV. T;il>.XIVy,,5^j.

Jor drawing In PerfpeSihe. 371

the correfponding {ide of the board on your defk or table, and
draw the line of its precife length and pofition.

N. B. If this is thought too operofe, the brafs groove and
Aiding pieces M, N, may be rejedled, and the blade of the
fquare may be graduated on one or both of its edges at pleafure ;
and all lines in the fame diredion may be drawn thereby exa6tly
as to their pofitions, and nearly, though fomewhat exceeding,
their lengths * ; and their precife lengths may be determined at
the fame time the lines in the contrary pofitions are drawn,
whofe lengths will be given at the fame time by the lines firft
drawn.

Ht

This will be efFe«5led, by noticing the numbers upon the blade, and taking
thofe next beyond the apparent limits of the line j and by this means the drawing
will advance without theleaft confufion.

'wmm.

f 37' 3

XXIII. Experime?2ts on Air,
By Henry Cavendifn, EJq. F,R.S. and A.S,

Read June 2, 17S5.

IN a Paper, printed in the laft volume of" the Philofophical
Tranfaclions, in which I gave my reafons for thinking that
the diminution produced in atmoipheric air hy phlogifticatioii
is not owing to the generation of fixed air, I laid it feemed mofl
likely, that the phlogiftication of air by the elei^rlc fpark was
owing to the burning of fome inflammable matter in the appa-
ratus ; and that the fixed air, fuppofed to be produced in that
procefs, was only feparated from that inflammable matter by
the burning. At that time, having made no experiments 011
the fubje£t myfelf, I was obliged to form my opinion from
■thofe already publifhed ; but I now find, that though I was
right in fuppoling the phlogiflication of the air does not pro-
ceed from phlogilion communicated to it by the electric fpark,
and that no part of the air is converted into fixed air ; yet that
the real caufe of the diminution is very different from what I
fufpe6led, and depends upon the converfioii of phlogifticated
air into nitrous acid.

The apparatus ufed in making the experiments was as follows.
The air through which the fpark was intended to be palled, was
confined in a glafs tube M, bent to an angle, as in fig. i. (tab.
XV.) which, after being filled with quickfilver, was inverted
into two glaffes of the fame fluid, as in the figure. The air to

be

Mr. Cavendish's Experiments on Air^ 370

be tried was then Introduced by i"fteans of afmali tube, fuch as
is ufed for thermometer?, ber.t in the manner reprefented by
ABC (fig. 2.) the bent end of which, after being previoufly
filled with quickfilver, was introduced, as in the figure, under
the glafs D£F, inverted into water, and filled with the proper
kind of air, the end C of the tube being kept flopped by the
finger ; then, on removing the finger from C, the quickfilver
in the tube defcended in the leg BC, and its place was iupplied
with air from the glafs DEF. Having thus got the proper
quantity of air into the tube ABC, it was held with the end C
uppermofl:, and flopped with the finger; and the end A, made
fmaller for that purpoie, being introduced into one end of the
bent tube M, (fig, i .) the air, on removing the finger fi'om C,
was forced into that tube by the prefilire of the quickfilver in
the leg BC. By thefe means I was enabled to introduce the
exa£t quantity I pleafed of any kind of air into the tube M ;
and, by the fame means, I could let up any quantity of loap-
lees,or any other liquor which I wanted to^be in contadl with
the air.

In one cafe, however, in which I wanted to introduce air
into the tube many times in the fame experiment, I ufed the
apparatus reprefented in fig. 3. confifting of a tube AB of a
fmall bore, a ball C, and a tube DE of a larger bore. This
apparatus was firfl filled with quickfilver; and then the ball
C, and the tube AB, were filled with air, by introducing the
end A under a glafs inverted into w^ater, which contained the
proper kind of air, and drawing out the quickfilver from the
leg ED by a fyphon. After being thus furniflied with air, the
apparatus was weighed, and the end A introduced into one end
of the tube M, and kept there during the experiment ; the
way of forcing air out of this apparatus into the tube being by

thrufting

374 -^^^ Cavendish's 'Experiments on Air,

thruftiijg down the tube ED a wooden cylinder of fuch a lize
as almoil; to fill up the whole bore, and by occailonally pouring
quickfilv-cr into the lame tube, to fupply the place of that
'puthed into the ball C. After the experiment was finiflied, the
apparatus was weighed again, wliich Ihewed exadly how much
air had been forced into the tube M during the whole experi-
ment ; it being equal in bulk to a quantity of quicklilver, whofe
weight was equal to the increafe of weight of the apparatus.

The bore of the tube M ufed in molt of the following ex-
periments, was about one-tenth of an inch ; and the length of
the column of air, occupying the upper part of the tube, w^as
in general from 1 1 to | of an inch.

It is fcarcely ncceliary to inform any one ufed to e'le6lrlcal
experiments, that in order to force an electrical fpark through
the tube, it was neceilary, not to make a communication be-
tw^een the tube and the conductor, but to place an infulated ball
at fuch a diftance from the condudor as to receive a fpark from
it, and to make a communication between that ball and the
quickfilver in one of the glafles, while the quicklilver in the
other glafs communicated with the ground,

I now proceed to the experiments.

When the ele£tric fpark was made to pafs through common
air, included between fliort columns of a folution of litmus,
the folution acquired a red colour, and the air was diminifhed,
conformably to what was obferved by Dr. Priestley.

When lime-water was ufed inftead of the folution of litmus,
and the fpark was continued till the air could be no further di-
minifhed, not the leafh cloud could be perceived in the lime-
water ; but the air was reduced to two-thirds of its original
bulk ; which is a greater diminution than it could have fuffered
by mere phlogiftication, as that is very little more than one-
fifth of the whole. The

Mr. Cavendish's Experiments on Air, 375

The experiment was next repeated with fome impure de-
plilogiilicated air. The air was very much diminifhed, but
without the leall: cloud beiwg produced in the lime-water. Nei-
ther was any cloud produced when fixed air was let up to it ;
but on the further addition of a little cauflic volatile alkali, a
brown fediment >vas immediately perceived.

Hence we may conclude, that the lime-water was faturated
by fome acid formed during the operation ; as in this cafe it is
evident, that no earth could be precipitated by the fixed air
alone, but that cauftic volatile alkali, on being added, wpuld
abforb the fixed air, and thus becoming miild, would imme-
diately precipitate the earth ; whereas, if the earth in the lime-
water had not been faturated with an acid, it would have been
precipitated by the fixed air. As to the brown colour of the
fediment, it mofl likely proceeded from fome of the quickfilver
having been diflblved.

It muff: be obferved, that if any fixed air, as well as acid, had
been generated in thefe two experiments with the lime-water,
■a cloud mull: have been at firft perceived in it, though that
cloud would afterwards difappear by the earth being re-diilolved
by the acid ; for till the acid produced was fufTicient to dilTolve
the whole of the earth, fome of the remainder would be pre-
cipitated by the fixed air ; fo that we may fafcly conclude, that ,
no fixed air was generated in the operation.

When the air is confined by foap-lees,. the diminution pro-
ceeds rather fifler than when it is confined by lime-v*-ater ; for
which realbuj as well as on account of their containing fo
much more alkaline matter in propmtion to their bulk, foap-
lees feemed better adapted for experiments defigned to invefti-
gate the nature of this acid, than lime-water. I accordingly
made fome experiments to determine what degree of purity the
Vol. LXXV. D d d ' air

■■qyi^ Mr. Cavendishes Experiwenis on Au\

air {hould be of, in order to be dlminifhed moft readily, and to-
t-he greatefl: degree; and 1 found, that, when good dephlogiOi*-
cated air was iiltd, the diminution waj but fmall ; when per-
fedly phlogifticated air was, ufed, no fenfible diminution took-
place; but when iivc parts of pure dephlogirticated air were
mixed wirli^ three parts of common- air, almoft the wJiole of
the air was made to di (appear.

It muft be confidered, that common air confifFs of one part^
of dephlogiflicated air, mixed with four of phlogifticated ; To-
that a trixture of (ive parts of pure dephlogifticated air, and-
three of common air, is the fame tiling as- a- mixture ©f feven-
parts of dephlogifticated air with threeof phlogifticated.

Having made thefe previous trials, I introduced in&o the tube^;
a~ little foap-lees,. and- then let- up fome dephlogifticated and
common air, mixed in the above-mentioned^proportions, which
rikng to the top of the tube M, divided the -loap-lees into its-
two legs. As fafi-^ as the air was dimini(hed by the electric
fpark, I contihued adding mors of the fame k-ind, till no fur-
ther diminution took place: aftervvhich a little pure dephlo-
gifticnted air, and afrer that^ a little cammon air, were added^
in m-der to fee whether the ceiiation of diminution was not
owing to ion^ imperfe(2:i(5n in the proportion of the two kinds -
of air to each other^; but without effe6l % The f»ap-iees being -
then poured out of the tube, and feparated from the quick—

■i-,

* Frogi whnt follaws it appears,,, that thft reafonvvh'y the air ceafed to diminish. .
vns, that as the foap-Iee<S' were then l/ecomc neutmlized, noalkaiiTemainedto ab*
foFb the acid fsrm«i i>y the ope<ration^ and in coHlcquence fcaree any aii-vvns turned •
into acid. The fpjirk, however, was not continued long enough after the appa-.
rspt cefiation .of diminution, to determine with certainty, whether it was only,
that the diminution went on remarkably flower than before, or that it was ahuoft
cuiTie to a fland, and could not have been .carried 'nyjch' further, though I lad
y«;riiiled"«in pr.HJng the fparks,

fiJvsr, ,

Mr, Cavendish's Experiments on ^ir^ ^.yy-

filver, fecmed to be pcrftCdy neutralized, as they did not at all
dlfcolour paper tinged with the juice of blue flowers. Being
evaporated to dryneis, they left a fmall quantity of fait, which
was evidently nitre, as appeared by the manner in which paper,
impregnated with a folution of it, burned.

, For more fatisfa-^ipn, I tried this experiment over again on a
larger fcale. About five times the former quantity of foap-lees
were now let up into a tube of a larger bore ; and a mixture of
dephlogifticated and common air, in the fame proportions as
before, being introduced by the apparatus reprefented in ng. 3.
the fpark was continued till nq more air could be made to difap-
pear. The liquor, when poured out of the tube, fmelled evidently
of phlogifticated .nitrous acid, and being evaporated to dryne<^,
yielded i .V gr. of fait, which is pretty exactly equal in weight to
the nitre which that quantity of foap-lees would have afforded if
faturated with nitrous acid. This fait was found, by the man-
ner in which paper dipped into a folution of it burned, to b?
true nitre. It appeared, by the teft of terra potiderofa falitit^ to
contain not more vitriolic acid than the foap-lees themfelves
contained, which was exceffively little ; and there is no reafon
to think that any other acid entered into it, except the nitrpus.
. A circumftance, however, occurred, which at firft feeme4
to fliew, that this fait contained fome marine acid ; namely^
an evident precipitation took place, when a folution of lilver
was added to fome of it diflblved in \yater| though the foap-
lees u fed in its formation were perfetflly free from marine. acid,
and though, to prevent all danger of any precipitate being
formed by an excefs of alkali tn^it, 'fome purified nitrouS' acid -
had been added to it, previous to the addition of the folutioii
of filver. On confideration, however, 1 fufpe£led,, that this
precipitation might arife from the nitrous acid in it being phlo-

D d d 2 gidicated ;

0-8 Mr. Cavkndi^h''s Experiments on Air.

pifticated ; and therefore I tried whether nitre, much phlogiflr-
cated, would precipitate lilver from its folution. For this pur-
pofe I expofed feme nitre to the fire, in an earthen retort, till it
had yielded a gocd deal of dephlogiilicated air; and then,hav-
ins: diflblved it in water, and added to it fome well purified
fpirit of nitre till it was fenfibly acid, in order to be certain

4. "

that the alkali did not predominate, I dropped into it fom©
folution of filver, which immediately made a very copious pre-
cinitate. This folution, however, being deprived of fome of
its phlogifl:on by evaporation to drynefs, and expofure for a feW
weeks to the air, lofl: the property of precipitating lilver from
its folution ; a proof that this property depeiided only on its-
phlogiftication, and not on its having abforbed fea-falt from
the retort, or by any other means.

Hence it is certain, that nitre, when m-uch phlogiflicated, is-:
capable of making a precipitate with a folution of filver; and
therefore there is no reafon to think, that the precipitate^
which our fait occafioned with a folution of filver, proceeded
from any other caufe than that of its being phlogifticated j.
efpecially as it appeared by the fmell, both on firil: taking it
out of the tube, and on the addition of the fpirit of nirre,'
previous to dropping in the folution of filver, that the acid in
it was much phlogifticated. This property of phlogiflicated
nitre is w^orth the attention of chemifts ; as otherwife they may
fometimes be led into^ miffakes, in iuvefligating the prefence of
marine acid by a folution of filver.

In the above-mentioned Paper I faid, that when nitre is deto-
nated with charcoal, the acid is converted into phlogifticated
air ; that is, into a fubffan<:e which^ as far as I could perceive^ -
pofTefTes all the properties of the phlogiffcicated air of our at-
mofphere ; from which I concluded; that phlogifficated air i&
5 , jiothing.

f

Mr. C avendish's Experiments on Air, ^79

nothing elfc than nitrous ac'd united to phlogidon. According
to this conclufion, phlogiftlcaced air' onglit to he reduced to
nitrous acid hy being deprived ot its piiloglfton. But as de^
phlogifticatcd air is only water deprived of phlogifton, it is
plain, that adding dcphJooKVicatcd air to a body, is equivalent
to depriving it of phloglllon, and adding water to it; and
tlierefore, phlogidicated air ought alfo to be reduced to nitrous
acid, by being made to unite to, or form a chemical combina-'
tion with, dephlogifticated air ; only the acid formed this \ta^
will be more dilute, than if the phlogifticated air was Tmiply
deprived of phlogifton.

This being premifed, we may fafely conclude, th:it in the
prefent experiments the phlogifticated air was enabled, bj
means of the electrical fpark, to unite ta, or form a chemical
combiDation with, the dephlogifticated air, and was thereby
reduced to nitrous acid, which united to. the foap-iees, and
formed a folution of nitre; for in thefe experiments thofe two
airs afluallj difappeared, and nitrous acid was actually formed
in their room; and as, moreover, it has juft been fhewn, from
C)ther circumftances, that phlogifticated air muft form nitrous acid^
when eom.bined with dephlogifticated air, the above-mentioned
opinion feems to be fufficiently eftabliftied. A further confirma-
tion of it is, that, as- far as I can perceive, no diminution- of air is
produced when the eleflric fpark is pafted either through pure
dephlogifticated air, or through perfectly phlogifttcated air;,
which indicates the necefftty of a combination of thefe two
airs to produce the acid. Moreover, it was found in the lafl
experiment, that the quantity of nitre procured was the.-> fame
that the foap-lees would have produced if faturated witb ni-
trous acid ; which (hews, that the production of the: nicre'^^va^
not owing to any decompofitlon of the foap-lees,

Jt

i8o Mr. Cavf-Kdish*s E^iperiments oh Air.

It may be worth remarking, that whereas hi the detonation
of nitre with inflammable fubrtances, the acid unites to plUo-
gidon, and forms phlogifticated air, in thefe experiments the
reverfe of this procefs was carried on ; namely, the phlogiftl-
cated air united to the dephlogiilicatt- d air, wliich is equivalent
to being deprived of its phlogiflon, and was reduced to nitrous

acid.

In the above-mentioned Paper I alfo gave my reafons for
thinking, that the fmall quantity of nitrous acid, produced bjr
the explofion of dephlogifticated and inflammable air, pro-
ceedcd from a portion of phlogifticated air mixed with the de-
phlogifticated, which I fuppofed was deprived of its phlogifton,
and turned into nitrous acid, by the adlion of the dtplilogifti-
cated air on it, airilled by the heat of the explofion. Thii
opinion, as mufl: appear to every one, is confirmed in a re-
markable, manner by the foregoing experiments ; as from thera
it is evident, that dephlogifticated air is able to deprive phlo-
gifticated air of its phlogiflon, and reduce it into acid, when
affirted by the electric fpark ; and therefore it is not extraordi-
nary that it fhould do fo, when aflifted by the heat of the
explofion.

The foap-lees ufed in the foregoing experiments were made
from lalt of tartar, prepared without nitre ; and were of fuch
a firength as to yield one-tenth of their weight of nitre when
faturated with nitrous acid. The dephloglfticated air alfo was
prepared without nitre, that ufed in t'le firfl experiment with
the foap-lees being procured from the black powder formed by
the agitstion-:of-quickfilver mixed with Iead% and that ufed

^* This aif vvjtsf as pure as any that can be procured by moil proceiTes. 1 pro*
pofe giving an accouctt of the experiment, in which it was prepared, in a future
Paiper^ij-;:.^-- , .

it)

Mr . C A V r, N D I sn' s Experments on Atr, 38 1

in the latter from turbith mineral. In the firft experiment, the
quantity of foap-lees iifed was 3 ; meafures, each of which was
equal in bulk to one grain of quickfilver ; and that of the air
abforbed was 416 fuch meafures- of phlogifiicated air, and 914
of dephlogifticatedi.. }n the fccond experiment, 778 meafures
of fonp-leea were nfed, nnd they abforbed 1920 of phlogifti-
cated air, and 48^0 of dephlogilricated. It mulf be obferved,
however, that m b<^th experiments fome air remained in the
tube uucondcnfed,- whafe degree of purity I had no way of
trying; fo that the pTop&rtion.of" each fpecies of air abforbed is
not known with mucli exaclneisi

As far a.s the experiments- hitherto publiflled extend, we
fcarcely know more of the nature of the phlogifticated part of
our atm.ofphere, than that it is not diminilh^d by lime-water,
caultic alkalies, or nitrons air; that it i3 unfit to fupport fire^
or maintain lit© in animals ;- and that its fpecific gravity is'
not much lefs than that of common air : fo that, though the
nitrous- ncid, by being united to phlogilfon, is converted into
air policlicd of thefe properties, and confequently, though it
was reafonable to fuppofe, that part at leaft ot the phlogiill-
cated air of the atmofphcre confifts-of this acid united 'to phiO-
gilfon, yet it miglit fairly be doubted .whether the whok is of
this kind, or whether there are not in reality many ditfeTent
fubftances confounded together by. us under the name of phlo-
gifticated air. h therefore made an experiment to determiney
whether the whole of a. given iportion of tlie pklogifticatcd air
cf the atmofphere could be reduced to nitrous acid, or whether
there was not a part of a different nature from the reft, which
v^ould refufe to undergo that change. The foregoing experi-
ments indeed in fome meafure decided this point, as much the
greatefl: part of the air let up into the tube loft its elaftlcity;.

yet.

j82 Mr. CAVE-smsfCs Experiments on Air,

yet, :^,o iome remained unablorbed, it di^^ not appear for certain
whether that, <was at the fame nature as the reft or not. For this
purpofe I dlminiihed a iimiiar mixtu:e of dephlagifticated and
common air, in the lame manner as before, till it was reduced to a
fmall part of its original bulk. I then, in order todecompor.nd
as much asIcould.ot" the phlogiilicated air which remained in-j
the tube, added i^niQ dcpiilogiilicated air to ir, and continued the
ipark till no furtht;r diminution took phice. Having by thefe"
means condenfed as much as I could of the phlogldicated air, I-
iet up ibme folution of liver of fulphur to abforb the deplilo-;
gilficated air ; after which only a fmall bubble of air remained
unabforbcd, wliich certainly was rjot more than ^L.^ of the
bulk of the phlogifticated air let up into the tube; fo that if
there is any part of the phlogiilicated air of our atmofpher©.
which ditters from the rell, and cannot be reduced to nitrous '
acid, we may fafely conclude^ that it is not more than t-t^-
part of the whole.

The foregoing experiments fhew, that the chief caufe of.
the diminution which common air, or a mixture of common^,
and dephlogiilicated air, fuffers by the ele€lrlc fpark, is the
converfion of the air into nitrous acid; but yet it feemed not:
unlikely, that when any liquor, containing inflammable mat-
ter, was in contacl with the air ia the tube, fome of this :
matter might be burnt by the fpark, and thereby diminifh the •
air, as I fuppofed in the above-mentioned Paper to be the cafe.
The bed way which occurred to me of difcovering whether
this happened or not, was to pafs the fpark through dephlogiifi- •■
cated airj included between different liquors: for then, it the
diminution proceeded folely from the converlion of air into
nitrous acid, it is plain that, when the dephloglfticated air was i
perfedlly pure, no diminution would take place ; but when it »

contained

Mr. Cavendish's Experiments on Air. ^ 383
contained any phlogiilicated air, all this phlogiflicated air,
joined to as much of the dephlogifticated air as miift unite to it
in order to reduce it into acid, that is, two or three times its
bulk, would difappear, and no more; fo that the whole dimi-
nution could not exceed three or four times the hulk of the
phlogiftlcated air : whereas, if the diminution proceeded from
the burning of the inflammable matter, the purer the dephlo-
giilicated air was, the greater and quicker would be the dimi-
nution.

The refult of the experiments was, that when dephlo-
gifticated air, containing only -^.^ of its bulk of phlo*
giflicated air (that being the pureft air I then had), was con-
fined between (hort columns of foap lees, and the fpark pafled
through it till no further diminution could be perceived, the
air loft _±^v ^^ i^^ \^\!X^ ; which is not a greater diminution than
might very likely proceed from the firft-mentioned caufe ; as
the dephlogifticated air might eafily be mixed with a little
common air while introducing into the tube.

When the fame dephlogifticated air was confined between
columns of diftilled water, the diminution was rather greater
than before, and a white powder was formed on the lurface of
the quickiilver beneath ; the reafon of which, in all probabi-
lity, was, that the acid produced in the operation corroded
the quickfilver, and formed the white powder ; and that the
nitrous air, produced by that corroiion, united to the dephlo-
gifticated air, and caufed a greater diminution than would
otherwife have taken place.

When a folution of litmus was ufed, inftead of diftilled
water, the folution foon acquired a red colour, which grew
paler and paler as the fpark was continued, till at laft it be-
came quite colourlefs and tranfparent. The air was diminiflied

Vol. LXXV. E e e by

3S4 Mr. Cavendish's Experiments on Air,

by almoft half, nnd I believe might have been ftill further di-
niinifhed, had the fpark been continued. When lime-water
was let np into the tube, a cloud was formed, and the air was
further dlminiOied by about one-fifth. The remaining air was
good dephlogifticated air. In this experiment, therefore, the
litmus was, if not burnt,, at leaft decompounded, fo as to lofe
entirely its purple colour, and to yield fixed air ; fo that, though
foap'lees cannot be decompounded by this procefs, yet the folu-
tion of litmus can, and fo very likely might the folutions of
many other com.buflible fubflances. But there is nothing, in. ^ny
of thefe experiments, which favours the opinion of the air being
at all diminifhed by means of phlogifton comno^unicated to it
by the ele6lric fpark.

/■/,//,,. ],.,„. I'.i /■ \.V|- n.li j;\-./...!>i.

>JiU

ill 1r;n ■:^-'J<^

[ 385 J

XXIV. An Account of the Meafurement of a Bcifeon Honnflow-
Heath. By Major 'GejieralWilYi'um'Koy, F.R.S, and AS.

Read from April 21 to June 16, 1785.

INTRODUCTION.

CCURATE furveys of a country are univerfally ad-
mitted to be works of great public utility, as affording
the fureft foundation for almoil: every kind of internal improve-
ment in time of peace, and the beft means of forming judi-
cious plans of defence againil: the invaiions of an enemy in
time of war, in which laft circumftances their importance
ufually becomes the mod apparent. Hence it happens, that if
a country has not a(Slually been furveyed, or is but little known,
aftate-of warfare generally produces the firft improvements in
its geography : for in the various movements of armies in the
field, efpecially if the theatre of war be extenlive, each indi-
vidual officer has repeated opportunities of contributing,
according to his fituation, more or lefs towards its per-
fedlion ; and thefe obfervations being ultimately collected, a
map is fent forth into the world, confiderably improved indeed,
but which, being ftill defective, points out the necefTity of
ibmething more accurate being undertaken, when times and
circumftances may favour the delign. f^^

The rife and progrefs of the rebellion which broke out iii
the Highlands of Scotland in 1 745, and which was finally fup-

E e e 2 preiTed,

^86 MiiJor-Gener/iI RoY^s Account of the

prefied, by his Royal Highnefs the late Di>ke of Cumberland, at
the battle of Cullodeii in the following year, convinced Go-
vernment of what infinite importance it would be to the State,
that a country, fo very inacceilible by nature, fhould be tho-
roughly explored and laid open, by eftabhfhing military pofts
in its inmoft receffes, and carrying roads of communication to
its remotefl: parts. With a view to the commencement of
arrangements of this fort, a body of infantry was encamped at
Fort Auguftus in 1747, under the command of the late Lord
Blake NEY, at that time a Major*General ; at which camp my
much refpe6led friend, the late Lieutenant-General Watson,
then Deputy Quarter-Mafler-General in North Britain, was
officially employed. This officer, being himfelf an engi-
neer, aiflive and indefatigable, a zealous promoter of every
ufeful undertaking, and the warm and fteady friend of the in-
duftrious, firft conceived the idea of making a map of the High-
lands. As affiftant Quarter-Mafter, it fell to my lot to begin, and
afterwards to have a confiderable fhare in, the execution of tbat
map; which being undertaken under the aufpices of the Duke
of Cumberland, and meant at firft to be confined to the
Highlands only, was neverthelefs at lafl: extended to the Low-
lands ; and thus made general in what related to the mainland
of Scotland, the iflands (excepting fome lefler ones near the
coaft) not having been furveyed.

Although this work, which is ftill in manufcript, and in an
unfinlfhed flate, pofl'effes confiderable merit, and perfedlly an-
fwered the purpofe for which it was originally intended ; yet,
having been carried on with inflruments of the common, or
even inferior kind, and the fum annually allowed for it being
inadequate to the execution of fo great a defign in the heft
manner, it is rather to be confidered as a magnificent military
4 jketch,

Mecjfurenient of a Bafe on Hounflow-Heath. 38^

/ketch, than a very accurate map of a country. It would,
however, have heen completed, and many of its imperfedlions
no doubt remedied ; but the breaking out of the war of 1755
prevented both, by furnifhing fcrvice oi other kinds for tiiofe
who had been employed upon it.

On the conclufion of the peace of 1763, it came for tlie
firft time under the confideration of Government, to make a
general furvey of the whole ifland at the public cofL To-
wards the execution of this work, whereof the direc^lion w^as
to have been committed to my charge, tbe map of Scotland
was to have been made fublervient, by extending the great tri-
angles quite to the northern extremity of the ifland, and filling
them in from the original map. Thus that imperfect work
would have been effe<fLualIy completed, 'and the nation would
have reaped the benefit of what had been already donty at a
very moderate extra-expence.

It will not be expelled, that I fliould here attempt to affign
caufes for the long delay tbat lias taken place in carrying a
work of fo laudable a nature into execution : fuffice it to fay,
that a period of twelve years having elapfed, lince the fcheme
had been firft propofed, as a v/ork that could be beft executed
in time of profound peace, without any tiling being done in ity*
previous to the nation's being unfortunately involved in the
American war ; it was fufficiently obvious, that peace muft be
once more reftored, before any new effort could be made for
that purpofe. In the mean while, as I ftill entertained hopes
that a work which feemed to merit the attention of the public^-
would, at fome future period, be begun, and, by gradual per-^
feverance, ultimately brought to pertection ; therefbre, ■ ill
the courfe of my ordinary military employments,- wher-eirf!
the very beft opportunities have offered of acquiring a

thorough

3B8 Major 'General ^o^^s Account cf the

thorough knowledge of the country, 1 have not failed to ob-
ferve, at lead in a general way, fuch fituatlons as feemed to
be the \:>t{l adapted for the meafurement of the bafes that
would he necefiary for the formation of the great triangles,
.and connecfling the different feriefes of them together.

The peace of 1783 being concluded, and official bufinefs
having detained me In or near town during the whole of that
fummer, I embraced the opportunity, for my own private
amufement, to meafure a bafe of 7744.3 feet, acrofs the fields
between the Jews-Harp, near Marybone, and Black-Lane,
Rear Pancras ; as a foundation for a ferie? of triangles, carried
on at the fame time, for determining the relative lituatlons of
the mod: remarkable fteeples, and other places, in and about
the Capital, with regard to each other, and the Royal Obfer-
vatory at Greenwich. The principal obje<£l: I had here in view
(befides that it might poffibly ferve as a hint to the public, for
t'he revival of the now almoft forgotten fcheme of 1763)
was, to facilitate the comparifon of the oblervations, made by
the lovers of aflronomy, within the limits of the projected
furvey ; namely, Richmond and Harrow, on the weft; and
Shooter's-Hlll and Wanfted, on the eaft : and thinking, that a
Paper, containing the refult of thefe trigonometrical operations,
might not prove unacceptable to the Royal Society, I was en-
gaged in making the computations for that purpofe, when,
very unexpeftedly, I found, that an operation of the fame
Rature, but much more important in its obje£t, was really in
agitation. This I faw would fuperfede, at lead for the prefent,
iny ov/n private obfervations, and perhaps render them wholly
iifelefs, unlefs it were as a matter of mere curiofity hereafter,
to fee how far fuch as depended on a fhort bafe, and a fmall
.ip^flrument (a Cj^uadrant of a foot radius) would agree with
I thofe

Meafurement of a Bnfe on Hounflow-Hcath. 389

tliofe founded on a much longer bafe, and angles determined
by a large circular inf>rument, being that propofed, as the
beft that could be made ufe of in the operation now to be
mentioned.

In the beginning of CXftober, 1783-, Comte d'Adkemar,..
the French Ambaiiador, tranfmitted to Mr. Fox, then one of
his Majefty's principal Secretaries of State, a Memoir of M.
CAssirii DE Thury, m which he fets forth the great advan-
tage that would accrue to aftronomy, by carrying a feries of
triangles from, the neighbourhood of London to Dover, there
to be Gonnedled w^ith thofe already executed in France, by
which combined operations the relative fituations of the two
mcft famous obfervatories in Europe, Greenwich and Paris^
would be more accurately afcertained than they are at prefent *».

This Memoir the Secretary of State, by his Majefly's com-
mand, tranfmitted to Sir Joseph Banks, the very refpedable
and worthy Prefident of the Royal Society -, who, about the
middle xDf November, was pleafed to communicate it to me,
propofing at the fame time, that I fhould, on the part of the
Society, charge myfelf with the execution of the operation..
To this proportion I readily aflented, on being foon afterwards
aflured, through the proper official channels, that my under-
taking it met with his Majefty's moil: gracious approbation.

A generous and beneficent Monarch, whofe knowledge and
love of the fciences are fufficiently evinced by the prote£lioa
which HE conftantly affords them, and under whofe aufpices
they are feen daily to flourifh, foon fupplied the funds that
were judged neceflary. What his Majefty has been pleafed to^

P* M. Cassini's Memoir, with the Aftronomer Royal's remarks on what is
therein alledged, concerning the uncertainty of the relative fitua-tions of the two
Obfervatories, will be given in the feqiiel.

give

3^0 Major -General Roy's Account of the

give fo Hbcrally, it is our duty to manage with proper and be-
coming frugality, confiftent with the befl: poflible execution of
the bulinefs to be done, fo as to make it redound to the credit:
of the Nation in general, and of this Society in particular.

The operation, whereof we are now to give fome account,
being the firfl of the kind, on any exteniive fcale, ever under-
taken in this country, naturally enough fub-dlvides itfelf into
two parts. Firft, the choice and meafurement of the baf^, with'
every poflible care and attention, as the foundation of th'd
work ; fecondly, the dlfpofition of the triangles, whereby ^d
bafe is to be connected with fuch parts of the coafl of this
iflandas are nearefl: to the coafl of France, and the determlna^
tlon of their ang'les, by means of the befl inftrument that can be
obtained for the purpofe, from which the reiult or concluiioit
will be drawn. It is the firft part only, as a fubjeft of itfelf
fufficlently diflinil, that we are now to lay before the Society ;
it having been judged more advllable, to fhew that no time
has been loft in making reafonable progrefs, than to defer the
account till the whole operation fhould be ultimately com-
pleted.

Choke of the Bafe. Tab. XVI.

Hounfiow-Heath having always appeared to be one of the
moft eligible fituations, for any general purpofe of the fort
now under confideration, becaufe of its vicinity to the Capital
and Royal Obfervatory at Greenwich, its great extent, and the
extraordinary levelnefs of its furface, without any local ob-
ftrudions whatever to render the meafurement difficult ; be-
ing likewife commodioufly fituated for any future operations of
a fimilar nature, which his Majefty may pleafe to order to be

extended

Meajiirement of a Bafe on HounflovvJieath, 391

extended from thence, in different diredions, to the more re-
mote parts of the ifland, it was propofed to Sir Joseph Banks,
that the local circumftances iliould be adually examined ; fo
far, at leaft, as to enable us to form fome judgement, of the
, beft pofition of the line to be meafured.

The i6th day of April, 1784, being accordingly fixed on
for the piirpofe, and Mr. Cavendish and Dr. Blagden
accompanying the Prefident on this occafion, we began our
obfervations at a place called King's Arbour, at the north-wefh
extremity of the Heath, between Cranford -Bridge and Long-
ford ; and having proceeded from thence through the narrow
gorge, formed by Hanworth-Park and Hanworth-Farm, we
finifhed at Hampton Poor-houfe, near the fide of Bufhy-Park,
at the foutheaft extremity ; the total diftance, from the furvey
of Middlefex, leing upwards of five miles.
- On this infpeftion it was immediately perceived, that the
firfl part of the operation, in order to facilitate the meafure-
ment, would be, the clearing from furze-buflies and ant-hills,
a narrow tra£l along the heath, as foon as the ground fl^-ould
be fufiiciently dry to permit the bale to be accurately traced out
thereon.

VirJ} tracing of the Bafe, and clearing of the Ground, Tab. XVI.

Chiefly with a view to the more effectual execution of the
work, it was judged to be a right meafure to obtain and em-
ploy foldiers, inltead of country labourers, in tracing the bafe,
clearing the ground, and affifliing in the fubfequent operations.
For, at the fame time that this was obviouOy the moil: frugal
method, it was evident, that foldiers would be more attentive
to orders than country labourers ; and by encamping on the

Vcj.. LXXV. F f f fpot

3Q2 Major-General Roy's Account of the '

foot would furnifh the neceflary centinels, particularly during
the njo-ht, for guarding fuch parts of tlie apparatus, as it was
fbrefeen muft remain carefully untouched, in the frequent in-
terims of difcontinuing and refuming the work. Accordingly,
a party of the 12th regiment of foot, confifting of a ferjeant,
corporal, and 10 men, were ordered to march from Windfor
to Houuflovv- Heath, where they encamped on the 26th of
May, ciofe by Hanworth Summer-houfe, to which fpot the
neceflary tents, camp equipage, and entrenching tools, &c»
had been previoufly fent.

Whatever might have been the particular dire^Slion given to
the bafe confidered by its extremities, from confulting the plan
it will eafily appear, that it muft always neceflarily lead
through the narrow gorge of the Heath formed by Hanworth-
Park and Hanworth-Farm. The firft point therefore to be
attended to, in tracing it out, was, that it might lead through
this pafs, without interfering with certain ponds, or gravel-pits
full of water, which are in it. Thefe were eafily avoided by
carrying the line pretty near to Hanworth Summer-houfe ; and
in direding the telefcope from thence towards the fouth-eaft,
it was accidentally found, that by leaving Hampton Poor-
houfe a very little to the weftvvard, or right, the line would
coincide with a remarkable high fplre, feen at the diflance of
eleven or twelve miles, and known afterwards to be Banfled-
Church. As there could i^ot be a better fituated^ or more
conspicuous objed than this, therefore the firfl: or fouth-eafl
iedlion of the bafe, comprehended between the Summer-houfe
and the angle of the fmall fie-ld adjoining to Hampton Poor-
houie, was immediately direfted upon it ; and the foldiers were
the fame day fet to work to clear the trad, which, at a me-
dium, was made from two to three yards in breadth. This

ojperation

/

Menfuremeni of a Bafe on Hounflow-Heath. ^^3

operation continued eight or ten clays, owing to the lower part
of the heath, between Wolfey-River and the Poor-houle,
being encumbered with brufh-wood.

When the clearing of the firfl: fe<3:ion was completed, the
fecond, comprehended between the Summer-houfe and the great
road leading from Staines to London, was traced out in the
following manner. One of the pyramidal bell-tents (whereoF
two had been provided, one of twenty-five, and the other of
fifteen feet in height) being placed at the ftation near the
Summer-houfe, camp colours were then arranged from diflance
to diftance, fo as to be in a line with the bell-tent and Banfted
fpire. In like manner, the third fecflion, comprehended be-
tween the Staines Road and King's Arbour, was traced out.

This firfl tracing of the bafe was done by means of a com-
mon telefcope held in the hand only, that no time might be
loft in employing the foldiers to fmooth the tra6l which was to
be meafured ; becaufe the tranlit inftrument (my own pro-
perty, for which a portable fland had been for fome time pre^
paring) was not yet ready to be applied, as it afterwards was^
in tracing out the bafe more accurately.

The camp ftill remained, where it was originally pitched,
at the angle of Hanworth-Park, this being a very convenient
pofition, with regard to the firfc and fecond le(5lions ; but being
too remote from the third, that time might not be loft, and
the men unneceflarily fatigued in marching backwards ai:Md for-
wards ; therefore, one half of the party, under the comrpand
of the corporal, was detached to the northward, and quartered
in the neighbouring villages, to dear the third feflion, while
the ferjeant, with the remainder, were occupied in fmoothing
the fecond. Owing to the extraordinary wetnefs of the fea-
fon, this operation required more time than had been at firfl

F f f 2 imaginod^

394 Major-General Roy's Account of the

imagined, not having been entirely finillied before the firft.
week of July. VVe fhall therefore leave it going mi, and in
the mean time proceed to defcrlbe the inftruments that were
fubfequently made ufe of in the firfl and fecond meafare-
nients.

Steel Chain. Tab. XVII.

One of the firfl: inftruments, which that able artift Mr^
Ramsden had orders to prepare, was a fteel chain, one hun-
dred feet in length, the befl: that he could make. Not that it
was intended, nor could it be fuppofed, that we fhould abfo-
lutely abide by the refult that this chain fhould furniili us^
with, for the length of the bafe ; but it was hoped, that an
inftrument of tliis fort might be made, which would meafure
diftances much more accurately than any thing of that kind
had ever done before: and it was confidered as an object of
fome canfequence, to endeavour to iimplify, and render aseafy
as poffible, the meafurement of bafes in future ; an operation
which, hitherto, has always been found to be tedious and
troublefome, to which we may now further add, uncertain
iikewife, when done with rods of deal, as will appear from the
account hereafter to be given.

The conftru£lion of the chain, which is on the principles of
that of a watch, will be underftood from the reprefentation of
fome of its chief parts, to the full fize, in tab. XVII. where
the firfl:, or zero-end link, is fliewn both in plan and elevation,
in the ftate in which it was originally applied to meafurement
on the fur face oi the ground. Each link coniifts of three
principal parts-; namely, a long plate ; two fliort ones, half
the thicknefs of the former, with circular holes near the
5 extremities

Meafurement of a Bufe on Hon n flow- Heath.- ^9 5

extremities of each ; and two caft-fleel pins, or axes, fuited to
the diameters of the holes, which ferve to conned the adjoin-
ing hnks together. The holes in the fhort plates are made
rough or jagged with a file; fo that when they have embraced
the ends of two adjoining long ones, and tlie pins have palled
th rough all the holes, in rivetting their extremities, they are
made perfectly fart, and as it were united to the fhort plates;
while the embraced ends of the long ones turn freely round
on the middle part of the pins.

At every tenth link the joint, juft now defcribed, has a
pofition at right-angles to the former ; that is to fay, the Ihort
plates lie here horizontally, and the pins paffing through
them fland vertically. Thus, there being in the whole chain
two hundred caft-fteel pins, one hundred and eigiity lie hori-
zontally ; and twenty, including the tw^o by which the han-
dles are attached, ftand vertically. Thefe crofs-joints, which
were chiefly intended that the chain might fold up in a fmaller
compais, by returning upon itfelf at every tenth link, are
likewife ufeful in prefenting a horizontal furface, to which
fmall circular pieces of brafs are fcrewed, with figures i, 2, 3,
&c. to 9, engraved on them, denoting the decimal parts of the
length. Thus the middle crols-joint, or that which feparates
the 50th from the 51 ft link, is fhewn in the Plate with the
figure 5 upon it.

The chain, in its firfl confl:ru6!:ion (for we are now to point
out fon:ie alterations that were afterwards made in it), was one
hundred feet in length, including the two brals handles ; in
"the extremity of each of which there Wxas a femi -circular hole,
of the fame diameter with the fleel arrow^s fucceffively fixed
in the ground, and ferving to keep the account of the number
of chains, when applied to common meafurement. In this its

firft

2q6 M^jor-General Roy*s Account of the

firfl: mode of application it was fooii difcovered, as we fliall
have occalioQ to mention hereafter, how admirably the chain
performed ; and that, with fome farther precautions, a ftill'
greater degree of exactnefs might be attained, by fupporting it
on ftands, or even on planks, laid on, or but little removed
from, the common furface of the earth. For this purpofe,
the two end-links were altered, each being now miade equal to
one foot, exclufive of the handles. By referring to tab,
XVII. the nature of this alteration will be eafily conceived. It
confifted in fcrewing to the under fide of the handles, very
near the joints, two feather- edged pieces of brafs * ; the one
denoting zero, and the other loo feet. Over the dart at the
iirft, a plummet with a fine lilver wire being fufpended, that
wire, by a very fimple apparatus, hereafter to be defcribed,
may be brought accurately to coincide with any point whatever
of commencement: and at the fe.:ond, a fine line with a
knife, or other fliarp inftrument, being drawn on a piece of
card placed there for the purpofe, and changed as often as
needful ; or, as was likewife pradifed, and found to anfwer
better, a line on a moveable (lide of brafs, attached to the top
of the fland or plank, being brought to coincide with the fea-
ther-edge, and then faftened underneath ; the extremity of the
100 feet is readily afcertained : and thus the meafurement
may be continued on with great accuracy to any diftance at
pleafure.

That the chain, in this its altered ftate, may flill be advan-
tageoufly applied to ordinary meafurSment on the furface of.
the earth, the pieces above defcribed, having fteady pins, and
being faftened with fcrews, can be eaiily removed, and others,

* They w^jre originaUy of, hrafs, but are now of fteel, that tlve edges by being
harder, might run lefs rifk of being damaged.

7 cxadly

Meafurement of a Baje on Houiiflow-Heatli. ^^r^

ex3(£lly of the fame length, fubflituted in then- fl:ead, with
iemi-circular holes (as reprefented in the Plate by dotted lines
near the joint of the handle) to receive the fteel arrows, then
to be made ufe of in the manner already mentioned.

This moft excellent chain feems not to have fuftcred any
perceptible extenlion from the ule that has hitherto been made
of it. It is fo accurately conftrucled, that when ftretched out
on the ground, as in common ufe, all the long plates lying
vertically or edge-wife, if a perfon, laying hold of either end
with both hai]ds, gives it a flip or jerk, the motion is, in a
few feconds, communicated to the other end, in a beautiful
vertical Terpentine line ; when the perfon, holding that handle,
receives a fudden (hock, by the weight of the cbain pulling
him forcibly. The chain weighs about eighteen pounds, and
when folded up is eafily contained in a deal box, about four-
teen inches long, eight inches broad, and the fame in depth.

Deal Rods, Tab. XVIII.

k. The bafes which have hitherto been meafured in different
countries, with the greateft appearance of care and exaftnefs,
have all, or for the moft part, been done with deal rods of one
kind or other, whofe lengths being originally afcertained by
means of fome metal ftandard, were, in the fubfequent appli-
cations of them, corrected by the fame ftandard. Having thus
had fo many precedents, ferving as examples to guide us in our
choice, it w^as natural enough that we fhould purine the fame
method in the meafurement to be executed on Hovmfiow-
Heath ; taking, however, all imaginable care, that our rods
ihould be made of the very befl materiafls that could be pro-
cured;

298 Major-General Roy's Account of the

cured; with this farther precaution, that by trufTIiig them,
they Ihould be rendered perfectly inflexible, a clrcumilance not
before attended to.

As fome difficulty had been found in procuring well-feafoncd
Pine -wood of fufficient length, and perfectly free from knots,
for the intended purpole; therefore Sir Joseph Banks had
early applied to the Admiralty for affiilnnce in this refped: ;
and forthwith obtained an order to be furniflied with what we
might have occafion for, fronn his Majefty's yard at Deptford,
where an old New-England maft, and aUo one of Riga wood,
were fpeedily cut up for our ufe.

New-England white Pine is lighter, lefs liable to warp, and
lefs affected by moifture, than Riga red wood. But the New-,
England maft, when it came to be very minutely examined, was
found to be too much wounded by lliot-holes in fome parts,
or too much decayed or knotty in others, to afford us a fuffi-
ciency. This being the calc we had recourfe to the Riga
wood, wbich was indeed extremely fmooth and beautiful; and
fo perfectly ftraight-gralned, that a fibre of it, when lifted up,
might be drawn, like a thread, almofl from one end to the
other.

It had been in contemplation, to make the rods of twenty-

iive or thirty i&tl in length ; and one of the former dimenfions

;Was aicually conllructed : but tliis being found to be rather too

'Unwieldy, it was judged bell: to content ourfelves with thofe of

about twenty feet.

Different opinions have been entertained with regard to the bed
mode of applying rods in meaiuremen.t ; fome contending tijat
contads, or that of butting the end of one rod againft the end of
the other, is the befl ; while others (with more probability of

being

Meofurement of a Bafe on Hounflow-Heath. 399

being right) are of opinion, that the adjuftment hy the coin-
cidences of lines fliould have the preference. The firll is un-
doubtedly the mod expeditious method ; but feems at the fame
time to be liable to this very objection able circumftance, that
the probable errors fall all one way : whereas, in the fecond me-
thod, although by far the moil tedious, the errors of coinci-
dence falling fometimcs on one fide, and fometimes on the
othej', they compenfate for, or deftroy, each other; and tliere-
fore no error is committed.

With the view of fatisfylng both parties, and in order to put
the matter, if poffible, out of doubt, it was judged proper to
conftrucl the rods in fuch a manner as to admit of both me-
thods being tried, that w^e might adhere to that which fhould
be found by experience to be the befl:.

Three meafuring ro^ls were accordingly ordered to be
made, and alfo a ftandard rod, With which the former
were from time to time to be compared. Their general
conflruiflion will be better conceived from the plan and
elevation, and other reprefentations of their principal parts,
in tab. XVIII. than by any defcription, however parti-
cular, conveyed in words. It will be fufficient to fay, that
the ftems of the three meafuring rods are each twenty feet
three inches in length, reckoning from the extremities of the
bell-metal tippings ; very near two inches deep ; and about i J
inch broad. Being truffed laterally and vertically, they are thereby
rendered perfe£lly, or at leaft as to {qi\{q, inflexible. The ftan-
dard rod could only be truffed laterally ; and it is juftly repre-
fented by the plan of the other rods, excepting that its ftem
is fomething ftronger, and that it has two or three inches at
each end of extra-length, the reafons for which differences
will appear hereafter.

Vol. LXXV. G g g By

ij 00 M jor- Gcmral R o v * s /iLCcunt of the

By referring to the Piatt it will be obferved, that two nar-
row pieces of ivory, eacli faftencd with two faiall fcrews, are
inlaid into the iipper furtace of the rods, within one inch and
a half of the extremities of the tipplngs. Iliefe ivory pieces
received the fine black lines cut into them when the lengths of
the rods were laid oil', in the manner hereafter to be mentioned,
and accurately determined the intermediate dlftance of 20 feet,
or 240 inches, the mcalure to be ufed in the application by
coincidences : whereas, in that by contacts, the fpace com-
prehended between the extremities of the projeding lips of
the tlppings, is 243 inches.

Immediately behind each ivory piece, a cavity is formed un-
derneath, in the middle of the flem. This receives a brafs
wheel, about eight-tenths of an inch in diameter, whofe axis
turns in the fork of a brafs fpriiig, five inches long, faftened
by a fcrew to the under fiirface juft before the crofs feet*
Thefe fprings are only of fuch fl:rength as to permit the wheels
to be forced up into the cavities by the wreight of the rod,
which, in its adjufted flate, always refts entirely on the fur-
faces of the two ftands that fupport its extremities. But
when the rod is to be raifed from the ftands, then, the miiled-
hcaded fcrews, proje cling above the upper furfiKe, and ftanding
over the middle of the fprings, being brought to a61:, the
wheels are thereby prelled downwards, and receive the full
weight of the rod, which is then eafily moved backwards or
forwards to its true poiition, either of contact or coincidence.

The crofs-feet, placed about 5§ inches from the ends of the
rods, and il inch from the infcrtion of the truflings, are each,
about nine inches long, if broad, and nearly an inch in depths
having their lower furfaces level with that of the flcm. By

2 means

Meofurement of a Bafe on Hounuo^v-Heath- 401

means of thefe, the rods are not only kept more ftcady on the
{lands, againfi: the common asflion of the wind upon the truf-
iings ; hut they Hkewiie ferve as holds for the vertical and hori«
zontal hiafs clamps, wherehy the rods are made fafl to the
Hands on one Tide or other, and in both modes cf application,
contacts and coincidences ; as will be more hilly explained
hereafter, in defcribing the tops of the lT:ands.

Brajs Standard Scale, and method cf laying off the knglhs cf the

Deal Rods.

At the fale of the lnil:rnment3 of the late ingenious optician
Mr. James Short, I purchaled a hnely divided hrafs Icale, of
the length of 42 inches, with a Vernier's divifion of iod at
one end, and one of c^o at the other, whereby the loocth part
of an inch is very perceptible. It was originally the property
of the late Mr. Graham, the celebrated Watch-maker; has
the name of Jonathan Sisson engraved npon it ; but is
known to have been divided by the late Mr. Bird, who then
worked with SissoN.

It is fufficiently well known to this Society, that their brafs
ftandard fcale, about 42 inches long, which contains on it
the length of the flandard yard from the Tower, that from
the Exchequer, and alfo the French half-toile, together witli
the duplicate of the faid fcale, fent to Paris for the ufe of the
Royal Academy of Sciences, were both made by Mr. Jona-
than Sisson, under Mr. Graham's immediate direction.
Now, although there fcemcd to be every reafon to fuppofe,
that the fcale at prefent in my poffefiion, originally Mr. Gra-'

G g g 2 ham's

402 Major-General Roy's Account of the

ham's property, would correfpond with thofe above-mentioned,
which he had been dire(5led by the Pvoyal Sociey, with fo much
care and pains, to provide; yet, that nothing of this fort
mipht remain doubtful, it w^as judged right, in fetthng the
abfoUite length of the bafe, which I meafured near London
in 1 785, as has been mentioned in the introduction to this
Paper, that the two fcales fl"iould be actually compared. Hav-
ing accordingly obtained an order from the Frefident, for ad'
miffion into the Society's Apartments, I went there in the
afternoon of the 13th of Augufc, and laid both fcales takers
out of their cafes on the table of the meeting- room, with
thermometers along-fide of them, that they might acquire
the fame temperature. On the forenoon of the 1 5th of Au-
gufl the comparifon was made, with the afli fiance of Mr.
Ramsden, who for that purpofe carried along with him hisi
curious beam-compaffes, whofe micromcter-fcrew fhews very
perceptibly a motion of ^^V-^th part of an inch. Thus the
extent of three feet, being carefully taken from the Society's
ftandard, and applied to my fcale, it was found to reach exadtly
to 0^6 inches, the temperature being 65°. In like manner, the
beam-compafles being applied to the length of the Exchequer
yard, the extent was now found by the micrometer to over-
reach that yard by -roV-c-o-^^^j or nearly -,J-^-^th. parts of an
inch.

Having thus fhewn that my fcale is accurately of the fame
length with the Society's ftandard, it remains to point out the
ufe that was made of it, for afcertaining the lengths of the
deal rods, intended for the operation on Hounflow- Heath, In
the firfl place, Mr. Ramsden prepared a beam-compafs, fuf-
ficient to take in twenty feet, trufled in all refpeds like the

mea^

Meafuremcnt of a Bafe on Hounllow-Heath. 403

jneafuiing rodi;, but fomethiog deeper, and fitted as ufual with
proper points and micrometer. The ftandard rod being now
confl:ru6led was laid on the fliop board, ftrongly framed for
the purpofe, and nearly level. To one fide of it, at the diftance
of about twenty feet two inches from center to center, two
ftronp' bell-metal cocks were firmlv fcrewed. Thefe cocks
were about 2| inches in length, three-eighths in thicknefs,
and rofe above the ftem nearly two inches, fo as to be on the
fame plane with the furface of the meafuring rods, when
placed upon it.

A large plank, cut from the New-England m.afl:, upwards of
thirty feet long, nine or ten inches broad, and about three
inches thick, being fet edge-wife in the fame room, on part of
*the ftands now ready for the operation, was, in that poiition,
planed perfediy fmooth and ftraight. A filver wire being then
flretched very tight, along the middle of the plank, from one
end to the other, fix fpaces of forty inches each w^ere marked
off by the fide of the wire, at which points feven brafs pins,
about one-tenth of an inch in diameter, were driven into the
wood, and their tops polifhed with the ftone. During the whole
of this operation, and that which followed, the thermometer,
lying by the iide of the brafs fcale, continued fleadily at or very
near 63".

A fine dot being now made on one of the extreme pins, and
the filver wire being ftretched over the dot, and as near as pof-
fible over the middle of the other pins, in which pofition it
was made faft ; the extent of forty inches, taken with the
utmoft care from the brafs fcale, was then marked off, by
placing one point of the beam-compafles in the dot, and with
the other defcribing a fliort faint arc on the furface of the fe-

cond

404 M^jor-General 'R.oy's Account of the

cond pin. The beam being then removed, and one point
placed in the interfection of the arc and wire, with the other
point a dot was made on the third pin, under the middle of
the wire. Upon this dot, as a center, a faint arc was next
defcribed on the fame pin where tiie firft had been traced. In.
this manner the fix times forty inches were marked off, alter-
nately with dots and arcs ; a method found by Mr. Ramsden,
in' his practice, to be more accurate, than when dots only are
made ufe of.

The exa6l length of twenty feet, thus obtained, was next
' taken between the points of the long beam-compaffes, and
transferred to thetops of the bell-metal cocks, pilaced, as has
been already mentioned, on the fide of the frandard rod, in
fucli m^anner as to leave more than one inch and a half of the
faid cocks beyond or without the luies denoting the extent of
the twenty feet. This being done, the meafuring rods were
fuccefiively placed on the ftandard, and their fides applying
clofe to the cocks, the diftance of twenty feet was readily
transferred from them to the inlaid ivory pieces, on which fine
lines were afterwards cut, by marks accurately made for that
purpofe.

With regard to the adjuflmcnt of the lips of the 'bell-metal"
tippings, which extend exadly one inch and a half beyond the
ivory lines, fo as to make the total length of the rod 243
inches, it is to be obferved, tliat they terminate in flat curves
of 3^ inches radius, pafling through the inch and half points,
to which they were cautioufly ground down, that at firfl they
migl:it rather exceed than be defective in length. Any two
of the rods, lying in the fiune plane, and alio in the fame
ilraigljt line, being brought into contad with each other ; if

of

Meafuremeni of a Bafe on Hounflow- Heath. 405

of. the true length, the fpace in that pofition, comprehended
between the two lines on the inlaid ivory pieces, muft be
exadly three inches. For the pnrpofe of this adjuftment, the
extent o.f three inches was therefore taken from the brais fcale
and cut upon the fide of a detached piece of ivory ; which
being readily applied to the aforefaid intermediite fpace, the
fame was. gradually reduced, by grinding the lips equally, till
it exactly correfponded with that taken from the fcale.

The three rods are numbered, by a cypher on the furface of
the metal at each end,. 1.2 ; 3.4; 5.6 ; and that being the order .
in which they were to be applied in aclual meafurement, fo it .
was likewife the order in which they w^ere adjufted ; that is to
fay, the. rod r.z was adjufted with ^^.4, and with 5.6; and
the rod 3.4 was, in like manner, adjufted witli 1.2 and 5.6.

One of thefe deal rods, when finiflied, was found to weigh
twenty-four pounds. They were intended to be contained in
two chefts, one large and the other fmaller.. The large cheft,
which is about 2i feet deep, may be called a double one, becaufe
it has two lids that lift quite off, which, in turning upfide
down, become alternately top and bottom, having between
them, but much: nearer to the one than the other,, a bottom
that is common to both. The fhallow fide holds the ftandard
rod; and the other, two of the meafuring rods; which lail: is
rendered pra6licable by^ having one of the fide braces of each
fixed only with fcrews, fo as to be removed and replaced at
pleafure. Thus one of the rods rbeing laid in its place, the
other is put over it in an inverted pofition; and both having the
proper faftenings to keep them in their pofitions, the lid is"'-
then put on, and fixed by fcrews. The chelt being now turned
upfide down, and the other lid removed, the ftandard i.>

thereby

4 o 6 Major- General R o y *s Account of the

thereby difcovered refling on the common bottom, which has
bands laid acrofs it for the purpofe, a few inches below what
has now become the'furface of the cheft. It was necef-
fiary that the ftandard fhould reft thus high, both that the
light might come freely upon it, and that, being fupported by
the deep fides of the cheft, it might be prevented from twift-
ing, for it will be remembered that it is only trufled laterally.
By means of a fmall brafs fpring fixed to each end of the
ftandard, a fine filk thread, as being lefs liable to accident than
filver wire, is ftretched along its ftem, which by fmall wedges
prepared for the purpofe, and flipped in between it and the
bands on which it refts, is always brought into the fame poii-
tion. This being done, the filk thread is turned off, fo as to
permit the meafuring rods to be laid on the ftandard for com-
parifon. With regard to the fmaller cheft, fuch a one was
aftually made, and lent down to the heath, towards the clofe
of the operation with the deal rods ; but from fome miftake in
its dimenfions, it would not admit the third rod.

Stands for the Meafuring Rods. Tab. XVIII. and XIX.

From the extraordinary levelnefs of Hounflow-Heath, the
afcent from the fouth-eaft towards the north-weft being little
more than one foot in a thoufand in the diftance of five miles,
it was eafiiy (Qtn, that the computed bafe-line, or that actually
forming a curve parallel to the furface of the fea, at that height
above it, would fall fo little fhort of the hypothenufal diftance,
meafured on, or parallel to, the furface of the Heath, as
Icarcely to deferve notice, had it not been thought neceflliry to
3 fliew

Meafzirement of a Bafe on Hounflow-Heath, 407

^ew, how much one end of the bafe was really higher than
the other; and to convince the world, that in an operation of
this fort, where fo rtinch accuracy was expelled, no pains
were fpared, nor the moll: trivial circumflances neglected.

From the trouble and uncertainty attending the frequent ufc
of plummets, efpecially in windy weather, inftead of mea-
furing level or bafe lines, as has hitherto been cuftomary (in
which cafe it would have been neceflary to make ufe of the
plummet, or fome fuch contrivance, at every f^ep of afcent or
defcent) it was judged to be a bettf^r method to meafure hy-
pothenufes, and, having obtained the relative heights of the
ftations by the accurate application of the telefcopic fpirit-
level, to compute the bafe lines. Thus it was propofed, that
'the length of the bafe on Hounflow-Heath fhoald be obtained
by meafuring a line through the air, drawn parallel to
.. ,the common furface from ftation to ftatlon, in equal diftances
of 200 yards or 600 feet each, as repreiented in the figure at
the top of tab. XVill.

For this purpofe, two kinds of ftands were ufed ; one whofe
height was fixed, to be placed at the beginning and end of
each 200 yards ; and the others, whofe heights were movea-
ble, that their furfaces might be brought more eafily to coinr
clde with the line paffing through the air from one fixed
Hand to the other. The fixed ftands in their firft flate, repre-
fented by that towards the left-hand in the plate for the deal
rods, were only two feet {^w&w inches in height ; but when the
glafs rods were afterwards ufed, they had an additional pl^ce
of ten inches faftened to the top (as in the left-hand ftand of
tab. XIX.) which made their total height above the Heath,
including the platform on which they flood, three feet and a
half. They are tripods of white deal, whofe legs extend about
Vol. LXXV. H h h three

^c8 Major-General Roy's Account of the

three feet froai each other ; and being braced diagonally, arc
mortolfed at top into circles of the iame fort of wood. Over
this circle, a fqiiarc table of about \\\ inches is fixed, com-
pofed of oak, and mahogany at top ; but both taken together
do not exceed i| inch in thlcknefs.

The nature of the moveable ftands, whereof there were at
lafl: no fewer than feventeen provided, will be comprehended
from the reprefentations of them towards the right-hand in
tab. XVIII. and XIX. Their general con{lru<5lion, in what
regards the part of them which is fixed, dlffc:rs not from that
of the others, excepting that they were of different heights,
from two iztt to about two feet eight inches, fo as better to
fuit the irregularities of the ground v^^here it mjght be necef-
fary to place them In the middle of each of thefe, an hexa-
gonal wooden pipe defcends, from the top to within two or
three inches of the bottom, where it is joined by a brace
reaching from each leg. This pipe receives the common
cheefe prefs wooden fcrew (having three fides fcrewed and
three plane], to the top of which the fqiiare table is attached.
It is embraced by the circular nut, or winch with four handles,
whereby the table is elevated or deprelTed at pleafure ; and being
brought to its proper height, is there made perfedly faft by
means of the flat-headed iron fcrew, which pafling through
one of the legs, prefles an iron plate, fixed in the infide of the
pipe, againft one of the plane fides of the fcrew.

In defcrlbing the deal rods, there has already been occafion to
make mention of the vertical and horizontal clamps, whereby the
crofs-feet are faftened to the table on the top of the fland. The na-
ture of thefe tables will be beft underftood by confulting the two
plans of them towards the right hand in tab. XVIII. ; whereof .
one reprefents the two grooves fitted for the alternate reception
2 of

Meafuremeni of a Bafe on Ho.unflow-Heath. 409

of the horizoatai clamp, according to the fide on which the
rod lies that is to be moved on into coincidence ; and the other

■: ihews it actually in its place, with the clamp itielf detached in
elevation along-lidc of it. Thus from the plan it may be
perceived, that the firfl, or adjufled rod, lies towards the far-
ther fide of the table, and is there fecured by the vertical
clamp. The fecond, or moveable rod, lies on the hither fide,
and therefore the horizontal clamp is placed in the farther
groove, where it is firmly pinched by the nut underneath. The
rod has been brought to coincidence by working with the tv/o
milled-headed fcrews agalnft the oppofite fides of the crofs foot.
This apparatus, although perfectly good in theory, was found
to be much too confined in its nature to anfvver well in prac-

'tice, requiring the flands to be placed with a degree of preci-
fion, which could not be efFe6led in the field without great lofs
of time ; and this was the real caufe, as will be feen hereafter,
that the meafurement by coincidences with the deal rods was
given up, and that by conta6ls adhered to.

Towards the left-hand of tab. XVIII. the plan of one of
the fquare tables is reprefented with the ends of the f:cond and
third rods upon it in conta£t. In this operation it will h^
perceived, that only one crofs-fcot.of each rod could no^v. rcfl
on and be clamped to the ftand, the tables having beeiilnad-
vertently cut too fmall to admit of both ; and although tliis
has the appearance of iraperfeclion, yet no incoaveniency
whatever waj. found to refult from it in pradice^ experience
having (hewn, that the clamping of either end fufiiceci to keep
the„rod fleady. i\long-fide of the table, the vertical clamp,
being that now folely made ufe of, is likewife reprefented in

elevation.

Hhh2 On

4 1 o Major- General R o y ' s Account of the

On the face or exterior fide of each leg of all the f^ands,
fixed as well as moveable, a plate of brafs is fcrewed near tl^er
bottom, with two holes in each, over a groove purpofely made
in the wood underneath. By means of thefe plates^ parallelopici
leaden weights, about fourteen pounds each, having brafs pins
with heads fuited to enter the holes, and fail down in the
grooves, into a narrow-pointed part of them,, are readily
flipped on or off each leg. Thus every ftand, excluiive of its
own weight, which is about thirty-one pounds, being loaded:
with forty-two pounds of lead, is thereby rendered perfedlly
firm and fteady.

A number of wedges were alfo prepared, and always ready
to be placed under the legs ; by means of which, and a fpirit
level laid on the table, its plane is brought to the proper -
pofition.

Notwithdanding all thefe precautions, it having been found,.
in the meafurement with the deal rods, that time was loft ia>
levelling the ftands, particularly in fituations where the ifurface
happened to be more than ufually uneven, or where it was gf
a loofe or fpungy nature; therefore Mr, Smeaton advifed;
(and no man's advice is more deferving of attention), that deal
platforms, ftanding on pickets driven into the ground, and
properly levelled, fhould be ufed to receive the legs of the
ftands. Accordingly, for the operation with the glafs rods
(table XIX.) twenty fuch triangular platforms made of inch
deal, whofe fides were each three feet two inches in length,
and void in the middle, were provided ; as alfo a number of
beech-pickets, about an inch and a half fquare, and of dif-
ferent lengths, from feven to twelve or fourteen inches. Three
of thefe pickets, ftiort or long as the fituation required, being
driveo into the ground, till their heads (by the carpenter's .
I level)

Meafuremint of a Bafe on Hounflow-Heath. 41- k

level) were brought to the proper height, the platform was
laid upon them ; and on that the ftand itfelf being placed, its
pofition was ultimately correded by the fpirit level laid on
the top of the table. Each of the beech pickets had a hole
bored through its top, fit to receive a piece of flrong tent-
line, by which, and the help of one of the camp mallets, the
pickets were eafily pulled up again, when the platform w^s to.
be removed to a new fituation.

Boning Tetejhope and Rods, Tab. XVIIL

In order to trace the line of 200 yards or 6co feet through
the air, fmm one fixed ftand to the other, it was ufual, in the
iirft place, to flretch a cord extremely tight along the ground,
and to divide the fpace into rod lengths, by fmall wooden pii>s
placed clofe by the cord, which remained there, and accordingly
marked, very nearly, the points over which the centers of the
intermediate flands were to come. A piece of wood, abouf
fourteen inches in length, and one and a half in breadth,,
painted white, with a narrow black line along the middle of
it, being prepared for the purpofe, was laid on the furface of
^e farther ftand. The boning telefcope, fourteen. inches long,
and one and a half in diameter, with, a fmall magnifying,
■power, and moveable obje6l-glafs,' fo as to fit it for very fhort
diftances, was th6n laid on the furface of the nearefl: ftand ;.
which, by means of wedges placed under the legs, had that
■'fide towards the farther ftand fo elevated or deprefiedy. as to ■
bring the crofs v/ires to- coincide- with the black line on the
painted board. Twenty- four boning rods had been originally
provided ; but it rarely happened, that more than eight or tern

• of

4T 3 Major-General Roy's Account of the

of that number were ufed in any one ftatlon. They are of
clean deal, iipwarid's "^'^ five feet in length, one inch fquare,
and pointed with plate iron at the botton:, fo as to be eafily fixed
into the ground. Each rod carries a crofs vane, fix or fevea
inches in length, and three-quarters of an inch in breadth.
This crofs vane, being moved upwards or downwards along
the rod, till its upper furface coincided with the crofs wires of
the telefcope and black line on the painted board, its under fur-
face then marked the height to which the furface of the ftand
was to be brought at that particular place. In this manner, a
certain number of points, in the line paffing through the air
from one fixed ftand to the other, being accurately obtained,
it was very eafy, at all the intermediate places, by the appli-
cation of the eye alone to the furface of any one fland or rod,
to bring the furfaces of the other, flands near it into the fame
. plane.

'Clip and T'ripod for preferring the 'point upon the ground, where
the meafurement was difcont'mued at nighty and refumed next
morning. Tab. XVIII.

It has been already mentioned, and, in giving the account
of the rough meafurement with the chain, there will be far-
ther occafion to remark, that the bafe was divided into hypo-
thenufes of 200 yards or 600 feet each, where fquare pickets
were driven into the ground, and regularly numbered, fo as to
be eafily referred to on any occafion. In the meafurement
with the rods, it was cuftomary to finifh the day's work at or
near one of thefe ftations. When the rods of twenty feet
iwere ufed, the termination of a rod was, of courfe, always

found

Meofurement of a Bofe on HounPiOw Heath. 41 j

found to be within a few inches of the picket correfponding
with the hypothenufe, ns determined by the chain. But with
the rods of twenty feet three inches, the day's work was al-
ways ended with a fractional rod, by fufpending a plummet
from fome convenient part of the ftem, marked for the pur-
pofe, and which confequently became the point of commence-

ment next mornmg.

The brafs cup, made ufe of on thefe occafions, is of the
figure of an inverted truncated cone, whofe mean diameter is
four Inches, and Its depth about five, with a very fm all incli-
nation in the fides. It was placed in a hole dug for it in the
earth, immediately under the point of fufpenfion of the plum-
met, ferving only to hold the water in which it vibrated.

The nature of the tripod will be heft conceived from the
plan and elevation of It in tab. XVllI. It confifls of two
flrong pieces of beech wood, mortoifed into each other, fo as
to lefemble a half crofs, or the letter T inverted, having three
ftrong iron prongs, about twelve" inches in length, which pafs
through the ends of the wood, and are faftened to it by fquare
nuts at top. On the furface of the tripod lies a fimilar half
crofs of mahogany, moveable by means of grooves in the di-
redion of the longefl fide, and fixable by its proper fcrevvs,
when brought to the defired pofition. This mahogany half-
crofs carries on its furface a brafs ruler, moveable at right-angle?
to the former dire6lion, fixable alfo by means of its own
fcrev^'S, and on whofe end is cut a very fine interfe<flion."
Thus any day's operation having been finilhed, the tripod was
placed near the cup, with it longed fide parallel to the line of
meafurement, and its prongs driven into the ground, fo as to
be rendered perfeClly immoveable without great violence. The
plummet being then fjfpended by a fine gilt wire, at any part

of

4'is}. Mcijor-Gcneral Roy's Account of tloe

of the ftem of the deal rods indifferently, but always at the fixed *
-or hindermoft end of the glafs rods, the brafs ruler was advanced
fo near as almofl to touch the wire, and there made faft. This
being done, the mahogany half-crofs was laftly moved back-
wards or forwards, in the diredion of the line of meafurement,
■■until the interfe£lion, as feen by a perfon lying down on the
aground forthe purpofe, accurately coincided with the gilt wire,
where it was likewife faftened by its proper fcrews. A tent
was then pitched very near the apparatus, for the foldiers who
furniflied the centinel for its fecurity, till the meafurement
was refumed ; and particularly to guard it from being
•^iilurbed by cattle during the night.

Wheels for ienn'matlng^ In a permanent manner^ the extremities of

It he Bafe. Tab. XVIII.

Before any accurate meafurement could ultimately be made
of the bafe by means of rods, in order that we might with
certainty refer to the fame poir^t, on any occafion that might
arife of correction or repetition of the work, it had all along
been forefeen, that it would be abfolutely neceffary to fink deep
into the ground wooden pipes, or fuch like things, at the ex-
tremities of the bafe, which could not be removed, or even
difturbed, by idle or ignorant people, without very confiderable
labour. Mr. Mylne, F.R.S. was accordingly requefted to

* That this might be conveniently done, a moveable ftand was placed, under

the glafs rod, about four feet from the fixed end, and its table elevated till, by

bearing againft the lower part of the cafe, it received its weight. This permitted

the ftand undei the fixed cad to be lowered and removed, to make room for the

♦ apparatus.

order

Meajurement of a Bcife on. Hounriow-Heath. 415

order; two fuch pipes to be provided, about fix feet in length
each, and one foot in diameter, with a bore of four inches in
the uppermofl: end, for the depth .of two feet, and crofs-arms
near the lowermofl: end, in the ftile of the' common warping
polls. As an improvement on this idea, Mr. MyLne vexy
judicioufly propofed that, inftead of. the crofs-arms, the lower
ends' of the pipes (liould pafs through the nave of an old
coach-wheel, and then be fecured by a bolt underneath. This
alteration was approved of ; and the n,iachines, thus executed'^'
wereifent foon- after by water to Flampton.

The plan and fedion of ' one of thefe w^heeis, with' thb
difhed fide downwards, are reprefented tovvards the left-hand':
in tab. XVIII. where it will be perceived, that by means of
four knee-pieces, made of crooked oak, the pipe is firmly
bolted to the wheel, and thereby kept at right-angles to its
plane/ The top. of. the pipe is .alfo fecured exteriorly by an
iron hoop, and has a caft-iron box "driven into it, whofe inner
diameter is four inches, anfwering to .that of the bore. . Four
oak' piles for eacl;i, .wheel were preparec( to be driven into the
bottoms of the pits dug for their reception, wlncjx ^^^ei^e fix feet"
in diameter, and the fame in depth. The foil n'e^r Hamptoii''
Poor-houfe being of a loofe fandy nature,, there" the'pile^ were
eafily driven jnto the bottom, until- their top3,were on the fame
level. The flat of the fellies. of the wheel beincr then'laid bii'"
the piles, the earth was filled in and wejl. rammed around the^
pipe, quite up to the furface, with wdilch its mouth is even*
Butthe foil at King's Arbour, being a hardr bound gravel,, the
piles could not be driven into the bottom of that pit ; where-
fore, the flat of the wheel refls there on the, gravel only. '

The brafs cup, formerly defcribed, was ffoni fh.e 'firfl: in-
tended to be placed in the pipes, for which purpole it h^s two

Vol, LXXV. lii ' lids;

41 6 Mdjor-Genera! V^oy'^s Account of the

lids ; one a femi-circle, with the central point marked by a.
line cut on its diameter, brougl:it into the dire(5lion of the bafe;
with which line the gilt wire, fufpended at the extremity of
the firft rod, was made to coincide on the commencement of
the meafurement. The other lid has a very fmall hole made
in its center, through which the plummet wire is to pafs,
when fufpended from the center of theinftrument, hereafter ta^
be made ufe of for the determination of the angles at the bafe,
or in any other flation whatever, where it may be neceffary ta
bring it very accurately over a point on the furface of the
ground underneath.

'Rough meafurement of the Bfe with the Chain ^ anddetennma^
tion of the relative heights of the Stations by means of the:
Telefcopic Spirit Level Tab. XVI. and XVIL

Having in the preceding defcription of the '^jlhbus inft'ru-
ments, originally provided for the meafurement of the bafe^.
fully explained their conftrudlions, ufes, and modes of appli-
cation ; and having thereby anticipated, in a great degree
what muft otherwife have been faid to make them underllood
m any account, blended with that of the execution ; little
more now remains to be given than the journal of our pro-
ceedings from day to day, and the ultimate refult of the ope-
ration-
After a vejy tedious delay, Mr. Ramsden having at lait
produced his hundred- feet chain, with the portable tranfit inftru-
ment ; and having lent us an excellent teiefcopic fpirit levels
for determining the relative heights; two fedions of the bafe
being likewife cleared by the foldiers, and Ibme progrefs made in
5 the

f

Meafiirement of a Bafe on Hounflow-Heath. 417

the third, we found ourfelves, on the i6th of June, in readi-
nefs to begin the rough meafurement.

Lieut. Colonel Calderwood, of his Majefty's Horfe-
■Guards, F.R.S. had, from the beginning, been fo good as
to promife his affiftance in the operation. Lieut. Colonel Pr in-
gle too, of the Corps of Engineers, obligingly became a
volunteer on the occafion ; as did alfo Mr. Lloyd, F.R.S. a
few days afterwards; while Enfign Reynolds, of the 34th
regiment, who had for fome time pafl been employed in fur-
veying the environs of the Heath, continued that work with
fuch fpare hands as could be afforded him for that purpofe ;
and it is to the plan (tab. XVI.) done by that officer, that it will
be necefTary to refer in any thing regarding locality, in what
has hitherto been faid, as well as in the fubfcquent relation.

The lower end of the bafe had for fome time paft been dif-
tinguiflied by a St. George's flag fixed to the top of a fir fpar,
thirty-five feet in height; and one of the fignal bell-tents flili
remained at the flation near the fummer-houfe. A rope of
200 yards being made very faft by a flrong iron picket, driven
into the ground at the bottom of the flag-ftaff, the other end
was carried on along the bafe, and placed at the bottom of a
camp-colour, in a line with the bell-tent. The rope beuig
wound around a flrong iron reel, prepared for the purpofe, was
thereby ft retched extremely tight, a perfon occafionally lifting it
up in the middle, or at other places, and letting it drop again, fo
as to bring the whole into the fame ftraight line. Five perfbns
were neceffary for the proper management of the chain ; two
at each end for its adjuftment there, and one towards the mid-
dle, to lay it clofe to the rope, or to bear it up in any particu-
lar place, where the circumftances of the ground rendered
fuch precautions ufefuL The zero or rear end of the chain

I i i 2 being

41 8 MiJor-GenerdI "RoY^i Account of the

being ftrained back fo as to coincide with the point of com-
mencement, a ileel arrow was placed as ere6l as poffible in the
fenn-circular cavity of the brafs handle at the other end. The
chain being then drawn on, till the cavity in the rear handle
could be apphed to the firft arrow, a fecond was then placed in
that of the front handle, and fo on until lix chain lengths were
thus meaiuredoff; which terminating the firft hypotheniife, a
beech picket, fomething more than an inch fquare, and about
feven in length, with N^ I. cut upon it, was driven into the
ground, till its head was nearly level with the furface. It is
however to be remarked, that the fixth arrow of each hvpo-
thenufe was conftantly left in the ground till the firft of the
fucceeding one was placed, to avoid the error that would have
otherwife arifen in applying the rear end of the chain to the
picket inftead of the arrow.

In this manner we proceeded on the i6th of June, and in
the fpace of about three hours and a half, completed the f ril
meafurement of the fouth-eafl: fedion of the bafe, comprehend-
ing the thirteen hypothenufes between the flag ftaff and ftation
nearHanworth Summer-houfe, the diftance being 78 chains or
78.00 feet, making 2600 yards ; and the mean temperature of
the air being 6'^''»

On the fubfequent day this fefllon was re-meafured with..
equal care, when the total extent fell ihort of the thirteenth
picket only five inches. And here it is to be obferved, that a
confiderable part of this difference prcbably arofe from the
ftretching of the chain acrofs Wolfey River, at the fame time
that the irregularities of the ground are greater in this thaa
in either of the other two fedions. The mean heat of this
day was 65°.

The

Menfuremcnt of a Bafe on Honnflow-Her.th. 41 «

The operation with the chain was fulpended during the i8th
and 19th of June, thole days having been employed in lettllrjg
certain matters with Mr. Ramsden relative to the deal rods,
as well as to give time for the m.aking of a holdfait for the
rear end of th.e chain, invented by i^ieut. Colonel Pringls.
This machine, whereof the plan at large is reprefented by
dotted lines at the handle of the chain, as it is in fmall
by the two elev.itions adjoining in tab. XVII. confifts of a
femi-circular iron plate, from the bottom of which projc6ls
two double and one lingle prong. In the middle, between the
two double prongs, a femi-circular cavity is formed, fitted to
receive the fteel arrow on one fide, while that in the brafs re-
ceives it on the other. In a focket in the middle, a ftrong
wooden handle, refembling that of a fpade, is placed. Thus
the rear handle of the chain being applied to the arrow, the
hoidfaft embraces with its double prongs the ftraight part of
the brafs, and in that pofition, being forced into the ground by
the a6llon of a man at the handle, the rear end of the chain is
thereby kept fo firm as to be immoveable by the efforts of the
two men at the other end, in ftretching it to its true pofition^
for the front arrow.

On Monday, the 2iil: of June, the operations were refumed,
by meafuring twice with the chain (forwards and again back-
wards) the thirteen hypothenufes comprehended in the fecond
fection of the bafe, between Hanworth Summer- houfe and
the north-weft bank of the great road (an old Roman way)
leading from Staines to London. This being the fmootheft
part of the Heath, and the hoidfaft being now applied, the
two meafurements differed only one inch and a half in the
diftance of 7800 feet. This inftauce of accuracy is alone fuf-

ficient

420 Major 'General Roy's Account ^f the

flcient to prove the great excellence ot the chain, althougli
another will be given hereafter ft ill mce furpriliiig.

On the fame day that the fecond fedlion of the bafe was
meafured, the levels of that and the firft were taken. The
operation of levelling is fo univerfally known, as to render any
detail of it nnneceilary. It will be fufticient to fay, that the
fpirit level made ufe of on this occafion was a very good one,
about eighteen inches in length, and could at all times be very
readily and accurately adjufted by inverfion in its Y's. The tops
of the pickets, marking the hypothenufal diftances, were the
points on which the levelling rods were placed on each iide of
the level ; which being inverted at the intermediate picket,
points equi-diflant from the center of the earth w^ere thereby
obtained, at the crofs vanes of the levelling rods, and no cor-
reftion for curvature or refra6lion neceflary. It will be readily
underftood, that the relative heights of the pickets were found
by meafuring their diflances from the centers of the crofs
vanes and axis of the telefcope refpeitively.

The fix firft columns towards the left-hand of the
firfl: or general table fubjolned to this Paper, fhew dlf^
tlndly every thing relating to the levels of the whole
bafe, thofe of the third fedion having been determined
on the 2 2d of June. By examining the table it will be
feen, that the alcent on the firfl: fecllon is 10.555 ^^^^>

on the fecond , 8.380

and on the third . 12.130

Total . . 31.265 feet, be-

tween the lower extremity at Hamptoi\ Poor-houfe, and the
higher near King's- Arbour.

The

1

M'lfiretnert of a Bop on Hounflow- Heath. 42;^'

The computed numbers in the leventh column are the
redudioiis * depending on the aforefaid heights, or the dif-
ferences between the hypothenufal diftances of 6co feet each
and the reduced bafe difbances. With regard to the remaining
cohimns of the table, or thofe towards the right hand, they
win be feverally fpoken to hereafter, in taking into considera-
tion the expanfion of metals, as determined witk great accu-
racy by the experiments with the pyrometer.

Hitherto no ufe had been made of the tranfit inftrument :
for, in order that it might be applied to advantage, there was
a neceflity for laying the wheel into tiie ground at the lower
end of the bafe, and fo to modify the St. George's flag-ftaff
that, being placed in the pipe, it might be fteadily fupported
By braces in a true vertical pofition ; which we found, from'
experience, could not be effetted by ropes only.

The wheel being accordingly laid in its place, and the other
precautions taken for fecuring the flag-ll:aff, which was like-
wife painted white, that it might be more diftindiy feen from-

* The redudtion- in the feventh column, I have computed by the difference
between the fquare of the hypothenufe,. aftually imeafured, and the fqiiare of
the height found by the level ; and Lieut. Colonel Calderwood has done the fame
thing by a much fliorter method. Thus, in the annexed

figure, CE being the hypothenufe of 6oo feet, DE the / \E

perpendicular height obtained by levelling, DB the re-
dudtion required, or the difference between the hypothe-
nufe and true bafe j then, fubftituting the chord BE in-A
fteadofDE, the following analogy is obtainedj AB : BE ::

BE*
BE :DB; confequently, iz DB : th'at is, the fquarc of the perpendicular

height being divided by double the diflance, or i200 feet, the quotient is equal to
DB the redMftion, without fenfible error. For if DE were four feet, the greateft
perpendicular height in the bafe, BE the chord would only exceed it -734ot(3» which
would not be more than -^i-^ part of an inch. The difference between the refults,
by the two modes of computation, is fo trifling as not to deferve notice.

the

^22 Mjj 0 r-Gt'?ieraI Roy\ Account of the

the farther extremity ; on the 22d of June, the tranfit inflrn-
raeiit was adjuiled over the thirteenth picket at Han worth
Summer-houfe, while direcled upon the flag-ftaff". But it being
now found, that the vertical plane pafiing through the flag-ftaff"
fell to the eaftward of the center of Banded ^pire, therefore
the tranfit was gradually moved to the eaftward, until by
repeated trials the three points were perceived to 'be in the fame
vertical plane, when the picket was moved, and re-placed
exactly under the axis of the telefcope, a few inches from its
lirft poiition. The fame operation w^^s repeated at the twenty-
iixth ftation, on the. farther hank of the Staines Road ; and,,
laftly, at the forty- fixth, forming the north- weft extremity, of
the bafe ; where a pit was immediately dug for the wheel,
whicii was placed therein, without however tilling in the earth
for the prefent,, that being deferred till near the completion
of the meafurement with the deal rods. Thus the two extre-
mities, and two intermediate points of the bafe, being accu-
iMtely placed, by the help of the tranfit inftrument, in the
lame vertical plane with Banfted Spire, it was eafily feen, that
by arranging camp colours in the intervals at any time, all the.
other points might be brought fo nearly to coincide with thele,
firft, as not to occafion, by deviation, any fenfible error in the.
meafurement afterwards to=bemade. This .application of tlie
tranfit fttewed us, however, that fome labour had been loft by
not ufing it fooner : for at the Staines Road, the tra61: cleared'
by the foldiers deviated about two feet and a half too much to
the weftward for the true line; and at King's Arbour it was.
twice as much ; fo that we were now obliged to widen the
cleared tra8:, by adding to the eaftern fide of It.

On the fame day that the chief points in the bafe were jfixed^
by means of the tranfit, aud the levels of the third fe£lion,

taken

Meajiirement of a Bafe on Houn (low-Heath. 423

taken as before-mentioned, the rough meafurement of that
ietSlioii with the chain was completed, and found to contain
nineteen hypothenufal diftances of 600 feet each, and one of
404.55, making in the whole 11804,55 feet, between the
twenty-lixth fration at the Staines Road and the center of the
pipe near King's Arbour, the mean temperature being 62"|,
Here it is to be obferved, that this laft feftion was only mea-
fured once with the chain, the tracl not being yet fafficiently
cleared to admit of its being done to the beft advantage ; and.,
when completed, it was judged to be better to proceed diredWy
in the operation with the rods, than to lofe time in the ufual
repetition, (ince the merits of the chain, in this way of ap-
plying it, were already fufficiently well eftabiiihed ; and any
future tefts to which it was to be put were propofed to be of
a more rigid nature.

When the length of the chain, in its original ftate-, was
tifcertained by the dots on the brafs pins in the New-England
plank, it was found, in the then temperature of 74°, to ex-
ceed the 100 feet by near one quarter of an inch, or 0.245 hich.
Therefore, in the temperature of 63°, being that in which
the lengths of the deal rods were laid off, and differing very
little from what was iikewife the mean heat e^ the air, whea
applied upon the Heath, the chaiii> according to the experi-
ments on the expanfion of the very fame freel, would exceed
the lod feet by 0.161 inch, or 0.0134 foot. Hence the
fum of the three fedions of the bafe, 274 chains, being mul-
tiplied by 0.0134 foot, wefliall have 3.67 feet forthe equation
of the chain 4-4.55 ^^^^' ^^ be added to its length, which will
then become 27408.22 feet from the center of one pipe to the
center of the other : and this would have been the true length
HJf the bafe, as given by the rough meafurement with the

Vol. LXXV, K k k chain.

42 4 M^'jor -General Roy's Account of the

chain, if the furface had been one uniform incrined plane
throughout its whole extent. But, although the alcent of
Hounflovv-Heath is fo fmall, and fo gradual, as to occaiioii
little more than half an inch of redudl:ion, from the 46 hypo-
thenufal to the 46 bafe diftanccs, into which it is divided, as
maj be feen by referring to the table; yet each of thefe hy-
pothenufes containing again many other Imall irregularities, all
of which affe6l the meafurement by the chain, in proportion to-
their number and height, in every fpace of 600 teet, their'
united effe£ls, including the lateral deviations from the true
line in meafurlng, do fomewhat more than compenfate for the
extra-length of the chain, as will be feen hereafter in com-
paring the length of the bafe juft now obtained with that:
given by the rods.

The weather, which during the greater part of June had-"
been wet, became ftiil worfe towards the end of the month
and firft week of July % fo much fo, that even if the deal rods-
had been ready they could not have been ufed with 'advantage..
The foldiers, neverthelefs, were not idle, being, when the-
weather would permit, partly employed in clearing; the Heath,,
and partly in affifling Mr» Reynolds in the furvey, towards-,
the perfecting of which many chief points were fixed by
means of my aftronomical quadrant, placed for that ptrrpofe at*
feveral different ftations of the bafe. At this time too (July-
8th) I levelled from the lower end of the bafe to the furface of
the Thanaes at Hampton, and found the defcent to be 36.11
feet.

Meafurement-

Meafiiremenl of a Bafe on Hounflow^Heatli, 4-^5

Meafurcment of the Bafe with the Deal Rods,
Tab. XVI. and XVIII.

Such extraordinary care and pains had been befrowed in the
cbnftrudion of the deal rods, in order to render them the beil:
which had ever been made, that, although begun early in
June, they were liot completely jfinifhed before the 1 «jth of
July. They were brought that afternoon by Mr. Ramsden,
together with the various parts of the apparattis neceffary for
their application in the field, to the camp now moved from
Hanworth Summer-houfe to the interfedion of the bafe with
Wolfey River ; whence they were tranfported, early next
morning, to the pipe near Hampton Poor-houfe, where we
were met by Sir Joseph Banks, accompanied by Meff. Blag-
den, Cavendish, Lloyd, and Smeaton, all ready to lend
their affiflance in the fubfequent menfuration.

Before I proceed farther, 1 think it here incumbent upon
me very gratefully to remark, that the refpe£lable and very
worthy Prefident of the Royal Society, ever zealous in the
caufe of fcience, and who had repeatedly viiited the heath, to
offer aid, if fuch had been neceffary, while the firft and
rougher part of the operations were going on ; now, that others
of a more delicate nature were to commence, and where it was
of importance, that thofe entrufled with the execution fliould
meet with as few, and as fliort, interruptions as poffible, not
only gave his attendance from morning to night in the field,
during the whole progrefs of the work ; but alfo, with that
liberality of mind which diftinguifhes all his a-flions, ordered his
^nts to be continually pitched near at hand, where his immediate

K k k 2 g^ei^S

426 Miijor-General Roy's Account of the

guefts, and the numerous vifitors whom curiofity drew to the
fpot, met with the moft hofpitable fupply of every necefl'ary
and even elegant refrefhment. It will eafily be imagined, how
greatly this tended to expedite the work, and how much more
comfortable and pleafant it rendered the labour to all who
obligingly took part in it ; but more efpecially to him, who,
being a volunteer in it at firft, confidered himfelf as bound to
perfevere in his beft endeavours to bring it to a fuccelsful con-
clufion.

From the defcription that has been given of the deal rods, it
will be remembered, that they are fitted to be applied in mea-
furing, either by the coincidences of lines, inlaid one inch and
a half from each extremity, or by the conra<51:s of the fphcrical
lips of the bell-metal with which they are tipped^ The firfl",
feeming to be th^ mod accurate, although the mofl tedious
method, was that by which we propofed to fet out.

The flag-ftafF having been previoufly removed from the^
pipe, and the brafs cup filled with water put in its flead, all
the necelTary precautions being likewife taken for preferving
the line of dire£lion, horizontally, by the rope ftretched along
the firft hypothenufe, and vertically, by means of the bonuig
rods ; the firft ivory line on the firft rod was brought by the
plummet to coincide with the center of the cup,- in which,
pofition, being clamped, it accurately marked the commence-
ment of the bafe. The fecond rod being now applied to the
firft, and moved up by the apparatus formerly defcribed (tab*
XVIII.) till its line coincided with that on the firft; and, in
like manner, the third rod being applied on the alternate fide
of the fecond, moved up and clamped as the reft; thus the
exaft.diftance of fixty feet was afcertained, care being always
taken, that the firft adjuftments were not difturbed, while the

iiibfecj^uent

Mcafurement of a Bcife on Houn flow- Heaths 4-2;^

iubfequent ones were forming. The clamps faftening the firil:
rod to its {lands being then detached, it was carried by tvvo
men and laid on the alternate fide of the third ; and fo on in
fucceffion, until fifteen rod lengths were meafured off, being
the half of the firft hjpothenufe.

The time confumed in meafuring this (hort diftance of 300
feet was not lefs than five hours ; owing, as has been formerly
mentioned, to the confined nature of the apparatus for moving
therodson intocoincidence, which requiredfuch nicety in placing
the ftands, as could not be efieded until after feveral repeated
unfuccefsful trials. All the executive people were therefore of
opinion, that it would be proper to difcontinue this miode of
meafurement, at lead: until a more convenient apparatus could
be thought of for the purpofe ; and that, in the mean time,
we iliould proceed by the method of contacts, as the only al-
ternative we could for the prefent adopt*.

The rods being accordingly placed in conta6l with each
other, we foon made greater progrefs, finifhing the operations
©f the day at the middle of the fourth hypothenufe, where
the tripod, with its guard, was placed, to preferve the point of
commencement for theenfuing morning,.

* Although I acquiefced in the change thiis become necefTary, yet it was with
much reluclance, becaufe it left undecided the contefled point, with regard to
coincidences and contafts. If we could have proceeded with the coincident rods
till eighty one lengths were meafured off, and then meafured back the fjme fpace
by placing eighty rods in contaft, the point would have been clearly fettled. For
if the termination of the eightieth rod agreed exaftly with the point of departure,
contafts being the moft expeditious would have been judged the beft method. On
the contrary, if the eightieth rod fell fhort of reaching the point of departure,-
there could have been no doubt, that the difference muft have aril'en from
butting one rod agalnft the other, whereby a certain fmall proportion of each
rod came to be loft in the aceount^ by being meafured twice overt

Tha

42 B MajonOenerd'^oYS Account of the

The meafuring rods, when put into the chefl: in London^,
had been compared and found to agree with the ftandard. The
comparifon was not repeated on the i6th; but this being done
on the I 7th, at 7 h. A.M. under the oil-cloth canopy at the
camp, they vvere found at a medium to exceed the ftandard by
one-iiftieth of an inch, the temperature then being 62°. After
the comparifon they were carried to the place of the fppod,
when the operation was refumed by bringing, with the helppfthe
plummet, the fame point of the rod v^ith which w^e had left off
work, to coincide wdth the interfeCtion on the brals ruler. The
meafurement of this day w^as clofed at the end of the tenth hypo-
thenufe, when the rods being carried back to camp, were com^
pared, and found accurately to agree with the ftandard.

A confide rable fall in the barometer, between the evening of'
the 17th and the morning of the 19th, portended rain. Ne-
verthelefs, all parties repaired to the place of rendezvous,
which was appointed at the lower end of the bafe, in order to
r£-meafure the two firft hypothenufes, by placing all the rods
in contact, which on the 16th had been done partly one way
and partly the otlier. The operation being according repeated
w4th great care, the point of the fixtieth rod, which formerly
correfponded to the center of the fecond picket, was now found
to be pufhed forward exaftly forty-five inches, anfwerable to
the deficiency on the fifteefi coincident rods, with which the
menfuration was begun, 'it now began to rain, therefore the
rods were carried back to camp, and being feverally compared,
they were found to exceed the ftandard each by one-thirtieth af
an inch, occafioned by the extraordinary humidity of the air.
A heavy rain enfued ; and vvhat made this much more regretted
by all was, that in the forenoon their Majefties gracioufly con-
defcended to honour the camp with their prefence,, and con-
tinued

\

■

Meofurement of a Bafe on Houn (low- Heath. 42(7-

tinned there lome time ; but the weather becpralng rather
worie, it was utterly impolhble to Hiew their Majeflies tlie
nature of the operation,, by any progrefs that could at that
time be made in the work.

After a continuance of unfavourable weather forfeveral days,
the operations were relumed at 9 h. A.M. of the 23d, when the
rods being compared were found flill to exceed the fl:andard by
one-thirtieth of an inch, and the tempereture now w^as 61°..
Here it is to beobferved, that in our progrefs forward, an accu-
rate regifler had been all along kept of that point of each rod
correfponding to the center of the hypothenufal pickets, by
noting its diftance from either end, whereby the error of the
chain at each ftation was readily difcovered, at the fame time
that the revolutions of the three rods ferved to keep the account
of the toi:al meafurement. In order, therefore, that this me-
thod might be diftindly adhered to, it was judged proper to
pufh on the rod that lay over the tripod at N? 10. exactly forty-
five inches, to make good the deficiency of the firfl fifteeu.
coincident rods, and that the account might be kept from the
lower end of the bafe in entire rods of 243, and complete
revolutions of 729 inches each. This being done, the reft
were placed in the ordinary fucceffion ; and we finifhed the
buiinefs of the day at the eighteenth flatlon, where the rods
being compared at 6 h. P.M. their mean length was found to
exceed that of the flandard ^'.^th part of an inch,- the tempera--
ture then being 54".

On Saturday the 24th of July, 'the rods were three times
compared; at 7 h. 30^ A.M., 11 h. 15^ A.M., and 5h. 45' P.M.
Th^ir mean excefs above the ftandard was found to be one-
thirtieth of an inch, and the mean heat 64°, In the courfe of
the. day, the jneafuremeut was continued irona the eighteenth to

the.

43^ Major-General Roy's Accowit of the

the twenty- feventh ftation, or firil: of the third fedlon of the
bafe, where the tripod was placed as ulual ; and there it re-
iTiained untouched, on account of bad weather, till Monday-
the 2d of Auguft. '

Confidering how much time and labour had been beftowed in
obtaining what we certainly had twQvy reafon to conclude were
the befl deal rods that ever were made, it was no fmall difap-
pointment now to find, that they were fo liable to lengthen
and fhorten by the humid and dry ftates of the atmofphere, as
to leave us no hopes of being able, by their means, to deter-
mine the length of the bafe to that degree of precifion we had
all along aimed at. But fince more than one-half of it was
already meafured, it was judged proper to proceed with them in
their prefent flate, and then to have them carefully painted or
varniflied, before they fliould be farther ufed.

The unfavourablenefs of the feafon, and delays in obtaining
the inflruments, had already been the caufes of protrafting the
operations on Hounflow-Heath greatly beyond what was at
firft expe£led ; and the failure of the deal rods gave no imme-
diate profped: of their being fpeedily brought to a conclufion.
On revolving in my own mind the different alternatives w&
might ultimately be obliged to have recourfe to, metal rods of
fome kind or other, whofe expanfion could always be deter-
mined by experiment, feemed to promife a refult that might '
be fafely relied on. Caft iron was what I had thoughts of
propofing, knowing from an experiment which I had made
myfelf, that it expanded lefs than fteel. The cumberfomenefs
of its weight appeared indeed obje(9:'ionable ; but that incon-
venience was either to be fubmitt-ed to, or one of another kind,
namely, the reduction of the length, which was always, if
poffible, to be avoided.

S At

Meafurement of a Bafe on Honnflow-Heath. 401

Kt this time Llent. Colonel Calderwood ccjld not conve-
niently lend us bis afiiftance in the field ; but he viiited us
occaiional]y, and on one of thefe vitits propoled to me, that
glafs rods (hould be made uie of inftead of deal ; pvitting n'le in
mind of another experiment * that I had made, which feemed to
fhew that folid giafs rods expanded lels than tubes. This pro-
pontion the Lieutenant Colonel, betore he came to the heath,
had made to Mr. Ramsden, who appeared averfe from making
the trial, becaufe of the great length of the rods, and the
brittlenefs of the material. Neverthelefs, it being fufliciently
obvious, that glafs rods or tubes of the full length, or fome-
thing approaching towards it, would be much fooner provided
than any metal rods whatever, and the faving of time being
a point of confequence ; Lieut. Colonel Calderwood was ac-
cordingly requeued to make the trial at the glafs-houfe, as foon
as poffible after his return to town. Next day he fucceeded in
getting a iine tube drawn, eighteen feet long^ and about one
inch in diameter; and there leemed to be no longer any
doubt, that thofe of the proper length might be obtained. It
was found, that folid glafs rods of fuch extraordinary dimeniions
could not be had, it being impoffible to take at once a fufficient

* The experiment here aIIu<Jed to was made with Mr. Cumming's pyrometer,,
"which from its conftru6tion did not admit of a very accurate eftimation of the
heat communicated to the ilandard bar, the rod, and tube refpeftively. Either,
thereforti, the natures of the glafs rod and tube, made life of at that time, muft.
h'ave been ret)' diflferenr,, to caiile the d-ifferenee of expanfion ; or fomc circum.
ftance- in the inftrument uaattended to had occafioned the fallacious appearance ;■
i&c it will be found, froHH the experiments hereafter to be given in detail, that a
folid glafs pendulum rod expands fully as much as, nay in this particular inftance
even more than a tube ; but different glafs, having different fpecific gravities,
will no doubt be fufceptible of different degrees of expanfibility,.

VoL, LXXV, L 1 I quantity

-4-3^ 'Major-General Roy*s Account of the t

<quanhty of the melted metal on the irons, made ufc of for
xlrawing them at the glafs-houfe.

The week of rainy weather, which ended the month of
•July, occafionlng, as has been faid, a total fufpenfion of the-
opeiations on the heath, was employed in procuring a fuffi-
cient number of glafs tubes (one whereof was not lefs than
twenty-fix feet long) and regulating with Mr. Ramsden
every thing concerning their conftrudion into meafuring rods.
The defcription of them we (hall however defer until the time
of their application in the field, after having finifhed the opera-
tion with thofe of deal.

On Monday the 2d of Augufl, the operations on the heath
were refumed at 8 h. 30^ A.M. Ly comparing the rods with
the ftandard, which they were found to exceed by one-fortieth
of an inch, the temperature then being 66°. The forward
end of the rod now placed over the tripod at N' 27, com-
pleting the Sooth length, reckoned from the lower end of
the bafe by rods of 24:; inches each ; and theie being equal
to 810 rods of 240 inches; it was judged proper to mark a
p(^ii;i,tiiipon the ground correfponding to this forward end, that |
it might , be referred to in returning back with the mealurement
by the glafs rod§. - This was done by fuiking two fmall pickets
iiito the ground, about a foot afunder, one on each fide of the
bafe, and at right angles to it. A filk thread being then |
flretched over the tops of the pickets, and gently moved on
till it touched the filver .wire fufpended from the end of the |
rod, fine notches were then made with a pen-knife in the tops
of the pickets, whereby the thread could be replaced in the
iame fituation ; which being dope, the pic}cets were covered over
•with earth. In the courfe of this day nine hypothenufes were
measured ; and at 7 h. P.M. the tripod was placed at the thirty-

fixth

Meafurement of a Bafe on Hounilow- Heath.. 4jjf

fixth ftatlbn. The rods, being now compared, were found to
agree with the flandard ; and the temperature was 67^1.

On Tuefday the 3d of Aiigiift", the rod's were coinpared
at 7 h. A.M. and found only to exceed the ftandard by one-
fixtieth of an' inch. Being arrived at the middle of the forty-
lirft hypothenufe, a point correipondrng to the forward end of
the 1215th rod was transferred to the ground by the double
pickets and- filk-thread, as had been done at the twenty- feventh
ftation. The meafurement was then continued to the nortli-
weft extremity of the bafe, which was found in the whole to
contain 1353 complete long rods of 243 inches each +21
inches, where the tripod was placed, in the point which of
courfe correfponded to the 13 70th (hort rod of 240 inches
each, equal to 328800 inches, or 27400 ittX. To which
diflance we have yet to add 4.31 feet, being tiie fpace inter-
cepted between the interfedion on the tripod and the center of
the pipe marking the north-weft extremity of the bafe ; whofe
total length, as given by the deal rods, without regard to ex-
panhon, or redudion of the hypothenufal- line, becomes
27404.31 feet. And here it is to be obferved, that the inter-
fe£lion on the tripod terminating the 27400 feet only over- fhot
the picket anfwering to the 274th chain by two inches and
nine- tenths. But this nice agreement between the refult by
the deal rods, and that furnifhed by the rough meafurement
with the chain, arifes from the extra-length of this laft, which
fo nearly compenfated for all the irregularities of the furface.

The meafurement with the deal rods being finifhed, they
were compared at 5 h. PM. and found to agree with the
ftandard, the temperature then being 75°.

L 1 1 z Expnnjton.

^-»^ • M^ij&f 'General RoY*3 Account of the

'Expanjion of the Deal Rods,

It has been an opinion generally enough, although, i^ we
have feen, erroneoufly received, that very ftraight-fibred 4eal
vz-as not at all, or but little, affe6led longitudinally by the; hu-
midity of the air. That we might not be led aftray by truft-
ing to fallacies of this fort, the flandard rod had been. provided;
which benig always clofely fhut up in its cheit, except during
the fliort interim of comparifon, could feel but a fmall propor-.
tion of the effeds which the meafuring rods fuffered, thejfe:
being conftantly expofed to the open air throughout the day, as,
well as to the moifture of the night, when lying under the.
oil-cloth canopy-. The ftandard rod, it is true, coi^Id not be-
accurately compared wdth the brafs fcale : for although when
conftru6led, . brafs pins, forty inches afunder,^ had been driven:
into its ftem, forthe purpofe of fuch comparifon, yet thefe
had afterwards been difplaced, or at leaft the points upon thetn
dejfaped, by the planing over of t;he, upper furface. This cir-.
cumflance, which was unattended to when the operations!
cpmmenced, isino^;of no -cqnfequeiice ; becaufe> from an ex-
periment hereafter to be mentioned;, the length e;uilg of the flan-:
di^rd may be pretty nearly afcertairied. But UnzQ there are fome
contradictory circumftances, foon to be mentioned, in the ope-
ration with the deal rods, which would have^ made a repetition,
•of it abfolutely neceffary, if^ we had not now obtained thofe of
a different kind, fo very ynexc-eptionable in thbir nature and
mode of application, as, in tj^e^ |)v.e.(eul;;. cafe, to admit of no
competition between the two refults, and to render it improper
on our part ever to have farther recourfe to the firfl; fo there

: . can

Mea/urement of a Bafion Hounflow-Heath. 43 ^

'Can be little doubt, that de^il rods will be unlverfally reje8:ed by-
other countries, in any meafurements they may have occafioii-
to make ia future.

About the loth of July, two rods, one of Nevv-Ei>gknd
and the other of Riga deal, being meafured by the fixed points
in the great plank in Mr. Ramsden's fhop, and having each
two brafs pins driven into them at the diilance of twenty feefj'
were laid on the top of the houfe, w^iere they remained until
the 26th, the weather, for the greater part of the time, having
been very wet. They were then taken down, and being, by
means of the long beam compares, compared with the mea-
fures on'the plank, the New-England rod was found to have
lengthened 0,03 1 inch, and the Riga rod 0.041 inch. By which
experiment tl^e ■fa<^ feems to be eftabliflied, that Riga red-
wood, notwithftanding the quantity of turpentine which it
contains, is' m-ore fufceptible of the effedls of moifture than
New-England, white wowl. Mr. Ramsden likewife finds,
that the great plank fo often mentioned, fuffers, in ordinarry
fummer weather, an alternate expanfion and contraction,
amounting at a medium to 0.0041 of an inch every day : that
is to fay, if the diftance between the twrenty-feet brafs points
be meafured from the fcale, by means of the beam compafles,
in the evening, it is found to have lengthened next morning
0.0041 of an inch, by the humidity of the intervening night.
In the courfe of the following day it contrads again to its for-
mer length, and fo on. Mr. Ramsden has often obfervcd
this alternate change in the deal plank ; but it was particularly
on the I ith and 1 2th of Auguft, that the quantity was a(3:ually
meafured. It will readily be underftood, that any difference of
temperature which might have happened in the brafs fcale, at

the

4^6 Major-General Roy's Acccunt of the

the times of comparlfon, was always carefully taken into the
account.

Now, from this laft experiment, it feems probable, that we-
Hiall not be very wide of the truth in fuppofing, that the
ftandard deal rod, which lay clofed up in its cheft, inider the
canopy on Hounflow- Heath, would fuffer the fame ibrt of
alternate expanfion and contratlion with the above-mentioned
plank ; that is to fay, being of Riga wood, its mean expan-
lion about the middle of the day would be ^-j^VW ^^ ^^^ inch..
By this quantity then we mufl augment the a€lual obferved'
expanfion of the meafuring rods, in order to obtain within
certain probable limits (lince we cannot determine it accurately);
the equation for the expanfion ; or that fpace by which thei'
apparent meafurement, given by the 1370 deal rods, (hould be.
augmented in order to obtain the true length of the bafe ; or.
that which would have been given by unalterable rods, of the
fame original length with thofe of deal, as expreffed in tha
following table.

-

Table

Meafurement of a Bafe en Hounflow-IIeatli.

437

T;2ble of the Expanfioii of th(

2 Deal Rods.

M of

Hour of

Temp. Obferv-

Deci-

Equation

Eqi^ation

Total

Days.

rods

comparilon.

of the

ed ex-

mal

for the

for the

expan-

meaf.

air.

panfion.

mean.

meaf. rods.

{landard.

' fion.

h. ,

0

In.

In.

In.

In.

July 1 6

1^5]

4 OA.INI.
6 OP.M.

48 1
62 J

TVth \
0 /

o.oio

1.050

0.2625

i.3ri5

17

195 1

7 OA.M.
6 OP.M.

62 "I

Tsth 1
0 J

0.0 10

1.950

0.4875

2-4375

23

240

9 oA.M.
6 oP.M.

61 1

54 ;

0.021

5.040

0.6000

5.6400

(

7 30A.M.

61

24

27oi

II 15A.M.

66

I

0.033

8.910

0.6650

9-5750

1

5 45 P.M.

64

71 J

Aug. 2

270 1
290 1

8 30A.M.
7 OP.M.

66
67I

'0 ]

0.0125

3-375

0.6650

4.0400

3

7 oA.M,
5 oP.xM.

56 1
75 J

1 -.
oS 1

0 /

0.017

0.493

0.7250

1. 2180

Total

1370

20.818

3-405

24.223

N. B. Although the rods \

vere not compax-ed wit!

1 the flandard on the 16th

of July, yet the expanlior

1 probably was, and therefore has been eftimated, at

the fame rate as it was fou

nd on the following day.

By examining the preceding table, it will appear, that the
total expanfion on the 1370 deal rods, including the fmall
equation for the lengthening of the ftandard, amounts to
24.223 inches, or 2.02 feet; which being added to the appa-
rent length of the bafe 27404.31 feet formerly obtained, we
fhall have, for the hypothenufal length, 27406.33 feet: and
from this deducing 0.07 foot, the excefs of the hypothenufal
above the bafe line, or the redu6lion contained in the feventh
column of the general table of the bafe, there will remain
27406,26 for thediftance given, by the deal rods, between the
I centers

438 Major^Gmeral Roy's Account of the

centers of the pipes terminating the hafe, reduced to the level,
of the lowefl-, or tl^iat at Hampton Poor-houfe, in the tempe-
rature of 63% being that of the brafs fcale when the lengths
of the deal rods were laid off. All this, however, fuppofes
three things to be abfohitely certain : tirrt", that tlie expaniioix
of the rods has been accurately eftimated; fecondly, that no.
enor has arifen fron?i the butting of the rods againfl each-
other, in order to bring them into contafL ; and, thirdly, that
no miftake of any kind has been committed 'in the execution^
When we come to give the true length of the bafe, as ulti*
mately afcertained by means of the glafs rods, it will appear^
that one or more of thefe three have actually taken place;:
although it is moil probable, that only the two firfl: fources o£"
error have contributed their fhare of the total difference be-
tween the two refults. But the difcuffion of this point muHr
be deferred for the prefent ; and I Ihall now finifh the fubjett
of the expanfion of the deal rods, by raentioni-ng two other
comparifons of them, w'hich lerve to (hew ffcill more obvioufly,,
how improper they are for very accurate meafurement!.

It has already been remarked, th-nt the lail.week of July
was fo wet as to occalion a total HUpenfion of the operations on-
Hounflow-Heath. On the 26th of that month, at 8 h. A.M.
the temperature being then 63''', the rods were compared with;
the ftandard, and found to exceed it, at a, medium, one-fifteentH
part of an inch. Now, if we fuppofe die whole bafe to have-
been meafured with the rods in that ffate, the difference would;
have amounted to more than 7I feet, exclufive of what thft-
ftandard itlelf might have altered from its original length.

The other comparifon was made at Spring-Grove, in the
beginning of September, after our operations on the heath had
been iiuilhed, and the deal rods with their apparatus depofited

under

*7
J

Meafurement of a B^tfe on Hounflow-Heath. 4^^

tinder the roof of Sir Joseph Banks's Barn. The obje£l here
in view was the meafurement of fuch a fpace as the garden
would conveniently admit of, when the rods were in their dry
or contracted ftate ; and to re-meafure the fame fpace next
morning, when the rods, being left out for the purpofe, had
imbibed all the humidity they could from the moifture of the
intervening night. Accordingly, the fourth being a fine dry
day, the fun fliining bright, and the thermometer about 68°,
feventeen ftands were arranged in the long walk, with fo much
nicety in the fame inclined plane as to appear but like one.
The firft or lowermofl {land had a brafs cock fcrewed to its
top. The two uppermoft, that is to fay, the fixteenth and
feventeenth, were of the fixed kind, each with a brafs flide,
and placed only forty-five inches afunder. The firft deal rod
was made to butt againfl: the brafs cock, and the.^ft fuccef^
fively againft each other, until fifteen rod lengths were mea-
fured off, and a fine line drawn on the Aide marking the extre-
mity of the fifteenth. That rod being removed, forty-five
inches, taken from the brafs fcale, were then laid off back-
wards from the line on the flide of the feventeenth to the flide
of the fixteenth ll"and, where another fine line was drawn.
Thus the fpace comprehended between this laft line and the cock
on the firft ftand, wasjuft 300 feet, or fifteen coincident rods.
During the night of the 4th, which was very fine, the rods
lay on the fmooth grafs. About fun-rlfing of the 5th there
came on a thick fog, which entirely difpelled about 8 o'clock.
At 7 h. A.M. the rods being lifted from the grafs, it was per-
ceived, that the under fides were perfectly dry, while all the
Teft was quite wet with the dew that had fallen. The four-
teen ftands, comprehended between the firft and fixteenth,
Jiaving their diftances gradually reduced from twenty feet three
VcL. LXXV, M m ra inches

^fO Mcijor-Gencrnl Roy's Account of the

inches to twenty feet, the operation of re-meafurement was
then begun, by placing the rods in coincidence with each
other (which was now found <:o be eafily and -.tccurately effeifted
by a few repeated ilrokes with a wooden wedge only) until the
fifteen rod lengths were meafured off, and a fine line, cor-
refpondiiig with the ivory on the fifteenth, was drawn on the
brafs Aide. This line was found to be o.-^*/_^^\., or near half an
inch beyond that which terminated the 300 feet the preceding
evening. Hence it is evident, that the dew imbibed only in
one night, or a fpace of time not exceeding fourteen hours,
occafioned fuch an expanfion in the deal rods, as in the whole
bafe would have amounted to 45.484 inches.

It is fufficiently obvious, that this laft mentioned experi-
ment was more accurate, in the proportion of about fifteen to
one, than a.:^y comparifon we could at that time have made with 3
the ftandard. But fince immediately after it was finifhed, the-^
fun fhone out very bright, it is by no means certain, how foon
the rods would again have contra6led to their former length, or
near it, had they been expofed to his rays. Repeated compa-
rifons for afcertaining fa6ls of this fort, at very ihort interims,
are abfolutely incompatible with the nature of fuch tedious and
troublefome operations as the meafurement of long bafes : and
here, indeed, lies the great objedion to the ufe of deal rods,
that at no time can we be certain how foon, after a comparifon
has been made, they may alter their length in a proportion, and
fometlmes too even ia a fenfe, different from what was ex-
peded.

Defcription

Meafurcment of a Bafe on HounOow-Hcath. 441

DefcnptJon of the Ghfs Rods, ultimately made ufe of to deter-
7nine the length of the Bafe. Tab. XIX.

It has been already mentioned, that the week of rainy wea-
ther in the end of July was employed in providing the glafs
tubes, and in concerting matters with Mr. Ramsden, relative to
their conftrudion as meafuring rods. Notwithfknding their
great length, they were found to be fo flraight that, when laid
on a table, the eye, placed at one end looking through them^
could fee any fmall obje6i: in the axis of the bore at the other
end.

The nature and conftruiflion of the glafs rods, whereof
three were finifhed for the operation, will be befl conceived by
confidering, with care and attention, the plans and elevations
of them, in whole or in part, to different fcales in tab. XIX. ;
where likewlfe may be feen, plans and feclions of the ends of
the tubes, in their real dimenfions, for the better nnderflanding
the ieveral parts of the apparatus placed therein*

The cafe containing the tube, and w^hich ferves to keep it
from bending in its original flraight pofition, is every whereof
the depth of eight inches, of the fame width in the middle,
and tapers from thence, in a curvilinear manner, towards
each end, where it is only two inches and a quarter broad. It is
made of clean white deal, the two fides being half an inch,
and the top and bottom three-eighths in thicknefs. Thefe
laft are placed in grooves fitted to receive them, about half an
inch from the upper and lower edges of the fides, which bend-
ing eafily, and applying clofely, are then firmly faftened by
two rows of wood fcrews on each fide, to the top and bottom

M m m 2 J refpec*

^^2 Mcijor-Generd Roy's Account of the

rerpe6llvely. Thus, the depth of the fides in one fenfe, and
the fpring which they have by bending in the other, a6b as
trufles, prevent the cafe from warping, and render it fuifv
ciently fhrong, although at the lame time, conlidering its great
length, very light.

The plan of the middle rod reprefents the cafe with the top
off, that the tube may be feen placed therein : the right and
left-hand rods have the tops on, whereby may be ittw the
oval opening in the middle of each, fliut by a mahogany lid ;
and alfo the pofitions of the two therm.ometers, with tubes
bent at right-angles, fo as to place the ball about two inches
downwards within the cafe, for the better afcertaining the
temperature of the glafs, as will eafily be conceived, by confi-
dering the reprefentation of the tube and ball in the fedlioii
acrofs the middle of the rod.

It is to be obferved, that the middle of the tube Is m.ade fad
to the middle of the cafe in the following manner. Firft,
around the middle of the tube, a quantity of pack-thread, im-
merfed in liquid glue, was wound by feveral returns on itfelf,
for the fpace of about two inches in length ; and upon this
mafs of pack-thread, while the glue was warm, a flrong ma-
hogany collar was forced ; whereby the three fubftances became
fo perfectly united to each other, that they might be confidered
as one only. Acrofs the bottom of the cafe in the infide,
three mahogany braces or girders, one in the middle, and one
half-way between it and each end, are faflened, by means of
fcrews, to the bottom and fides. Thefe rife about if inch,
above the bottom, fo as to place the axis of the tube, when in
life, about 2§ inches above the furface of the flands on which
it refts. The end-pieces of the cafe are likewife of mahogany,
about 1 1 inch thick. Each confiUs of two parts, alowerandaii

upper.-

Mccifurement of a Bafe on Hounflow-Heath. 44^

upper. In the lower parts, as well as in the crofs braces, there
are femi-circular cavities lined with broad-cloth, fitted to re~
ceive the diameter of the tube, which refts in them, and is
confequently fupported at five different points. The nppcr
end-pieces, having likewife femi-circular cavities fitted to em-
brace the upper part of the tube, flip down upon it, when it
has been, by repeated trials, brought to its true pofition ; that
is to fay, the axis of the bore into the fame ftraight line, the
cafe being all the while fupported by its extremities on two
{lands only, in the manner in which the rods are applied iii
adual meafurement. The braces within the cafe have alfo
their upper pieces, which, in like manner, apply clofely to
the tube, and are fixed to the lower ones by means of fcrews.
The whole together ferve only as flays to keep the tube in its
true place from fliaking ; but without binding it however too
clofely. Laftly, the mahogany collar glued to the pack-thread
on the middle of the tube, being ftrongly fixed by four fcrews
to the middle brace, as may be feen in the fedion, is that by
'which the tube is kept perfectly immoveable with refpe£l: to
the middle of the cafe ; while it is un confined Ibngitudinaily ia
the cavities lined with broad-cloth every where eife.

Both ends of the tube are ground perfe6tly fmooth, and
truly at right-angles to the axis of the bore. That end, which
in meafuring ufually lies towards the left-hand (fince mofl
people will work the fcrew with the right) projedls about;
leven-tenths of an inch without the cafe, and is called the
fixed end, becaufe the apparatus belonging to it is fixed. The
other end towards the right-hand projeds about nine-tenths
of an inch, and, having a moveable apparatus, is called the
moveable end.

Th&

^44 Major-General Roy's Account oj the

The fixed apparatus confifts of a cork about three inches ia
length, made of the very bell: material, and fo nicely fitted to
the bore as juft to admit of being forced into without burfting
it. In the middle of the cork a cylindrical brafs tube is placed,,
whofc fides are thin> the inward end thick, .and the outward
end open. It receives a fteel pin, whole inward end being
formed into a fcrew, is thereby fixed into the thick metal of
the tube. The fteel pin carries outwardly a button and neck
of bell-metal. The neck fits lb very clolely the open end of
the brafs tube as to prevent any Ihake there ; at the fame time
that the infide of the button applies very juftly to the ground
end of the glafs tube, to which the outward furface (being
a true plane) is exadly parallel.

The moveable apparatus confifts, like the other, of a cork
and brafs tube of the fame length. Before the infertion of this
cork, an oblong piece feven-tenths of an inch long, and two-
tenths broad, was cut from it, in that part of its cylinder an-
fwering to the upper part of the outward end of the glafs tube,
on the inward furface of which, about half an inch from the
end, a fine line had been previoully cut by a diamond point.
The brafs tube in this cork contains within it a loofe fleel
worm, or helical fpring, lomething lefs than the interior dia-
meter of the tube. Along the cavity formed by the fpiral,
there paffes a fteel pin, like that in the fixed end ; but it i-s
longer, and has no fcrew at the inward end, that being nicely
ground, fo as to fit a circular hole in the inward end of the
brafs tube, while a triangular bell-metal neck fits one ot that
figure in the outward end. Thus the pin moves freely back-
wards or forwards without any fhake, and prefles upon the
fleel fpring, by means of a circular brafs collar, placed for the
purpofe, at the inward end of the neck ; while the outward
c end

Meafurcmeni of a Bcif en Hon nilow- Heath. 44 j

end 15 Jittached to a bell -metal bntton. The outward furface ot
this moveable button Is fpherical, defcribed 011 a radius oF
about two inches ; while the inward furface^^like that at the
fixed end, would apply clolely to the ground end of the glais
tube, but Ihould not be pulhed io far forward as to touch it.
A circle and narrow Aide, cut from, a folid cylinder of ivory,
fitted originally to enter eafily the glafs tube, is attached to the
in fide of the button by fmall fcrews, and permits the neck to
pafs through a hole made on purpofe in the circle. The Aide
is about eight -tenths of an inch long, and has a fine interfec-
tion cut upon it near the inward end, made black to render it
inore confpicuous. Thus, two rods being brought into conta6:,
and the fixed button of one being prefled again ff the moveable
button of the other, the interiedrion is thereby pufhed for-
wards until it coincides with the diamond line on the interior
furface of the tube ; whofe length is fo adjufted, as that, when
the coincidence is perfect, the diftance betw^een the plane fur-
face of one button, and the fpherical furface of the other, i»
exactly twenty feet. The left-hand fide of the plate repre-
fents the relative pofitions of the extremities of the firfl: and
fecond rods, when the ivory is in coincidence with the dia-
mond line. And the right-hand fide fhews the relative fitua-
tions of the extremities of the fecond and third rods, before
the ivory is brought to coincidence with the diamond line, the
flide being then pufhed out by the action of the fpiral fpring
within the cork.

Every rod has four wheels, two at each end. They are two
inches in diameter, and conneded by a common fteel axis,
which rifes and falls in a vacuity prepared for its admiflion in
the mahogany end-pieces, the under part of which vacuity is
afterwards filled up.

A brafs

446 Major-General ^^q>y\ Account of the

A brafs ftrap or bridle, about eight-tenths of an inch broad,
paffes over the top of the cafe, and defcending down each fide,
bends outwards, fo as to form a projection for the reception of
the wheels, whofe pivots turn in, but near to the lower end
of the bridle, which is kept in its place by means of the two
fide fcrew^s working in grooves, and the milled-headed fcrew at
top. This laft ferves likewife to raife or deprefs the wheels at
plea fu re.

Each rod has two crofs feet, placed immediately behind
their refpedtlve pair of wheels, extending outwards about 4I
inches from the center on each fide. Under their outward ex-
treniities, fmall pieces of hardened fteel, formed into the teeth
of a file, are fixed by means of fcrews. When the firft rod
has been laid in its true place, by unfcrewing the milled heads,
the wheels are fuffered to rife; whereby the whole weight is
removed from them, and thrown upon the teeth of the files,
which then indent themfelves into the furface of the ftand,
mid become as it were united to it. But when the fixed button
of the fecond rod is brought to prefs againfl the moveable but-
ton of the firfl, the weight being then thrown upon the
wheels by fcrewing the milled heads at top, the rod is eafily
moved on by the following apparatus.

The three rods are numbered, as were thofe of deal, 1.2; 3.4 ;
£.6. On the firft or odd end of each rod i. 3. and 5. there ftands
a brafs fork, about two inches high, fixed by four fcrews and aii
oblong plate to the top of the cafe. On the fecond, or even
end of each, 2. 4. and 6. there ftands a brafs pillar of the fame
height with the fork, likewife fixed to tlie top of the cafe by
foiir fcrews and a circular plate. Two fteels rods or hooks
were indifferently ufed for bringing up the moveable rod (the
weight then lying ou the wheels) into its true place. They

are

I

Menfurement of a "Bafe on Hon n (low- Heath. 4.^.-^

are both reprefented lii the plate, and only differ from
each other in the fliape of the brafs milled-headed nuts
that work upon the fcrew, of about 2| inches in length,
■ into which the right-hand end of each hook is formed,
•Thus, while the nut enters very freely into, and reil:s upon,
the fork, the left-hand end of the hook has a circular hole in
it, whereby it flips eafdy off and on of the brafs pillar. Bvr
referring to the plate, it will appear fufficiently obvious, from
the nature of the nut on the left-hand Ir-^ok, that it could onlv
move the rod on to coincidence, and could not bring it back
again, if the bufniefs happened at any time to be overdone ;
in which cafe it was neceffary to move the rod ^ little back-
wards by the hand, and then to work anew with the iiXit,
until the coincidence was accurate : whereas the nut on the
right-hand hook, having two fhoulders, could either pufli or
pull the rod forwards or backwards : and although this ap-
peared to be an advantage, yet it was found from experience,
that it rather bound the hook too much, and occafioned a kind
-of fpring in the parts, which fometimes difhurbed the coin-
■cldence on the removal of the hook ; wherefore it was often ap-
plied, like the other, by placing the fcrew itfelf in the fork^
and v/orking with both fhoulders of the nut behind it.

The pofitions of the thermometers, and mahogany oval lid
on the top of the cafe, have already been mentionedo This
laft, being unlocked and removed, permits the cafe to be looked
into, or the hand to be admitted, in order to be certain that
the faftenings remain fafe and entire in the infide. Brafs caps,
with the refpe£live number of the rods engraved on them, are
likewife fcrewed on the maie-fcrews in the ends of the cafe,
through which the extremities of the tubes projed, to pre-
serve them from accidents when not in ufe. And, laflly, to

Vol. LXXV. N n n flrengthen

44^ Mo.j or 'General Roy's Account of the

ftrengthen the cafes, but more particularly to prevent tliemi
from being rent when long expofed to the fun's rays in the*
£eld, the fuies are covered with brown linen laid on ver\r
fiiioothly, and carefully glued with thin glue, ufed as a Wronger
Icind of pafte, to which it may yet be neceilkry to add a coat
of oil paint.

Each of the glafs rods, completed in the mariner above-
mentioned, weighs about fixty-one pounds. Their lengths
were afcertained by means of new brafs points placed in th©
great plank, the fpaces of forty inches being laid off, with the
iitmofl care, from the brafs fcale, when the temperature of all
had remained for the greater part of two days (Aiigufl 15th;
and 1 6th) at or very near 68°. For- this purpofe two brafs
reiSlangular cocks, whofe alternate furfaces had been previoufly
ground together, were placed upon the plank, fo as to bifecl:
the extreme dots ; in which fituation they prefented to each
other furfaces that were truly parallel. The rods being then feve-
rally placed between the cocks * (or, as was found to be a better

methodj

•■^ The firft of thefe.cacks, .or that to v\4iich the fixed button was applied, had
a hole in it exaftly of the height of the center of the button, and large enough
to permit the point of the micrometer fcrew to pafs through it, the faid fcrew
being fixed on the farther fide, or beyond the cock. Thus, while the tempera-
iure continued accurately at 68°, the fixed button^ or any other plane furface,
being brought up to the hole in the cock, and the micrometer point fcrewed {0
far as juft to touch it, the coincidence continuing in. the interim perfed, the exav^
diilance of twenty feet was obtained between the point of the fcrew and the
fecondcock ; at which time the divifion anfwering to the index on the head of tire
micrometer was carefully noted. This being done, the cock with the hole was
removed from the plank, and the rods were feverally adjufled by being placed
between the point of the fcrew and the fecond cock. This fubftitution of the
micrometer point, inftead of the firllcock, was found neceflaryj becaufe, during
, the operation of adjullment, the temperature would fometimcs change a degree,

generally

•J

Meafuremeni of a Bafe on Hon nilow- Heath, 44Q

raethod, between the pohit of a micrometer fcrew, fupplylng
the place of the firft cock, and the fecond) the ivory mterfecuou
was at firft neceffarlly carried beyond the diamond line, foas to
make the intermediate fpace lefs than it (liould be, until by the
gradual grinding down of the moveable bell-metal button, it
was enlarged to twenty feet, as then fnewn by the accurate
coincidence of the interfection with the diamond line.

It was by thefe diflances In tlie great plank, prolonged to
twenty- five feet, that the new length of the fteel chain was
•now fettled, fo as to obtain the full one hundred feet at four
meafurements. At this time too, brafs points were introduced
into the chain at every twenty-five feet, whereby its extent may
be compared on any future occafion; but the temperature had
now fallen to 66°i.

Dljpojition of the Stands for the double 7neafurement with the
Chain and Glafs Rods ; defcription of the apparatus then applied
to the ends of the Chain ; and ultimate continuation of the
meafurement with the Glafs Rods alone. Tab. XVH. and
XIX.

From the various circumftances already mentioned, in the
courfe of this tedious, yet neceffary recital, it had been for a
confiderable fpace of time forefeen, that the refult given by
the meafurement with the deal rods muil be entirely rejeded,

generally in excefs, from handling the inftruments. One degree of alteration,
producing a difference of about TsV^th part of aa inch in the twenty feet, ^vas
very eafily and accurately allowed for by fiich a tnicrometer as this, which fliewed
the coincidence of the ivory interfeftion with the diamond line to be more or lefs
perfeft, when the head of the fcrew was moved two djvifiQns, that is to fay,
i-sf&gths or T^Wth part of an ijich.

N n n 2 snd

4' CO Major-General Roy's jIc count of the

and that by the glafs rods adhered to, ns every way defervlng-
of the preference ; becaufe of the obvious impropriety there
would be, in taking a mean between one indifputably good
and another lefs perfeft, however fmall or trifling in reality
the difference of the two might ultimately be found, on a
minute and fcrupulous comparifon.

Ill order, therefore, to avoid any repetition of the operatioa
with the glafs rods, and at the fame time to give fomethlng
like a fair trial to the chain, it was propofed, that a double
ineafurement fhould be carried on with both at once ; that is
to fay, that the number of ftands, and feveral other parts of
the apparatus, fhould be fo far augmented, as to admit the
chain to be placed twice in advance, and then the rods to fol-
low in fucceffion on the fame ftands. Accordingly, the various-
articles having been fent to the north-weft end of the bafe on.
,the evening of the 1 7th of Auguft, the operation of the dou*
ble meafurement commenced next morning the iSth.

By referring to tab. XVII. it will be feen, that feventeen-.
ilands were neceffary for fupporting the chain, the apparatus-
attached to each end of it, and ten coffers, whereof tVQry five
made about ninety-eight feet, in oi-der that one length of the
chain being meafured off in the firft five, it might be drawn
jjfqrward into the laft five, and fo on. Theie feventeen ftands -
were difpofed of in three groups of three each, and four inter-
mediate, between the central and extreme groups. The mid--
die or Aide ftand of each group (fo diftinguiflied becaufe fome
of them had brafs flides on their tops) fupported the handle of"
the chain, and of courfe received the traces made at the feather- -
edged pieces of brafs, terminating the beginning and ending of
the hundred feet. Thus, there were in all fix ftands, inter--
mediate to thofe iu the center of each group that fupported
5 ' the

Meafuremcnt of a llafe on FIoutiilow-He?ithi 4 -71

"the ninety-eight feet of coffering, \vhich was kept fo mucli
:lhort of the hundred feet, that its extreme parts might not reft
upon, or even touch, the central ftands. To that on the left of
the center was attached the apparatus for the firft or zeroend of the
chain ; and to that on the right of the center was attached the
apparatus for the lafl; end oi the chain. When the fecond
chain length had heen meafured off, the firll: and fixth of the
coffer ftands of the firft chain were moved forward to prepare
for the third chain ; and the four remaining coffer ftands w^ere
raifed, until their furfaces came into the fame plane with the
flide flands, for the reception of the glafs rods,- The fpace by
which thefe ftands were raifed was about three inches; for fb'
much higher was the furface of the Interfole or flooring of tho
coffers than the ftands which fupported them.

The apparatus attached to the firft end of the chain, or that
which ferved to pull it back to the point of commencement,
while a weight continued fufpended at the farther end, con-
fifts of two parts, as may be feen by referring to the left-hand
f'fide of tab, XVII. Firft, a fmall wooden frame, fitted to flip
on to the top of any one of the ordinary ftands, placed imme-
diately to the left of that which fupports the handle. Secondly,
' a flat fteel rod, about two feet in length, wherein a number of
rholes are pierced, about an inch afunder, for the reception of
a fteel pin placed in one of the holes, as beft fuits the diftance
of the ftand from the handle. That end of the fteel rod
neareft to the end of the chain is formed into a fcrew about
four inches in length, 'and it receives upon it a forked hook
fitted to lay hold of the ftraight part of the handle of the chain.
Within the forked hook there works a ftrong milled-headed
brafs nut, which ailing upon the bottom of the fork, the chain
is thereby pulled back, until the wire fufpeading the plummet

from-

jj.r2 Mtijor-G eneral '^.oy''s Account cf the

from the dart on the feather-edge coincides with the point df
commencement on the ground underneath ; for which purpofe
there is a hole in the top of the ftand through which the wire
palles. The apparatus iland, thus ferving to pull back the
chain, was commonly loaded with double weights, placed on
the two hindermofl: legs. ^

The apparatus for the laft end of the chain confifts, like tlie
■former, of a fmall wooden frame that can be readily flipped
upon any of the common ftands, as may be iQ&n by referrinp*
to the right-hand lide of tab. XVII. This frame carries a
pulley, over which a rope pafl'es having fourteen pounds weight
fufpended at one end of it, while a forked iron hook at the
other end lays hold of the ftraight part of the brafs handle. By
means of thefe two apparatufes the chain is always kept to the
fame degree of tenfion in its coffers, in each of which a ther-
mometer was placed to indicate the temperature ; the whole
being covered up from the direft rays of the fun by a narrow
piece of linen cloth, ftretched along it from one end to the other.

Each coffer confifted of three boards about half an inch
thick. The fides were about five inches deep, nailed at the
middle to an interfole bottom of four inches, in fuch manner
as to be reprefented in feftion by the letter H. They were ill
made, being by their parallelogram fliape apt to warp, which
might have been prevented by giving them the:figure of the
cafes of the glafs rods, that is to i^^y^ making thena wide in the \
middle and narrow at each end.

We are now to proceed to give fome account of the double
mealuremcnt with the chain and glafs rods ; wherein it muflbe
remembered, as alfo in continuing the operation with the glafs
rods alone, that in referring to the map for the daily progrefs
in the v/ork, .we are going from the forty-fixth towards the firft

jdation ;

Meafurement of a Bnfe on Hounflow-Heath. 45^

i^-^tion ; and in having recourfe to the general table of the bafe,
f©r altitude, temperature, or corredlion for expanfion, we are
afcendi tig from the bottom towards the top, contrarily to the
order in which the operation with the deal rods was conducfled.

On the morning of the 18th of Auguft, the (lands with the
various parts of the a.pparatus being placed in the manner juft
now defcribed, the operation was begun by bringing the firfl;
end of the chain to coincide with the interfedion on the tripod,
anfvvering to the end of the i3^oth deal rod,, and 4.^1 feet
diftant from the center of the pipe terminating the north-weft
extremity of the bafe. The chain being ftretched along its
five cotters by the, fourteen pounds weight fufpended over the
pulley at the farther end, and the temperatures of the five ther-
mometers being regiftered in a book kept for that purpofe,' a
fine trace was made on a piece of card faftened under the fea-
ther-edge at the farther handle, denoting the end of the firil:'
hundred feet. The chain being then moved on into the next
five Coffers, thofe that had been thus vacated were carried for-
ward to prepare for the third chain length, and thereby permit
the firfl: fet of ftands to be elevated for the reception of the-
glafs rods ; and fo in fucceflion with the others.

In this manner we proceeded, and in the courfe of the day
were only able to meafurt the length of ten chains, or loco
feet, being the forty-fixth and forty-fifth hypothenufes of the
bafe, the firft of 400 and the laft of 600 feet* Being arrived
at this point it was found, that the fine line on the brafs flide,
marking the extremity of the tenth chain, fell fliort of ano-
ther fine line on the fame flide, denoting the end of the fiftieth
glafs rod, juft two-tenths of an inch. Now it will appear
hereafter, when we come to fhew, by the experiments with
the pyrometer, what the real contradions of the chain and

glafs

'4'^'4 Mdjor-Getjet'dl V^oy' ?, Account of the

glafs rods were, for the degrees of difference of temperature^
below that in which their refpedive lengths were laid otf, that
this fmall apparent difference of two- tenths of an inch, be-
tween the two modes of meafuring the thoufand feet, fhould
jiave been 0.17938 in. to have made the two refults exa^lly
-agree, which is a real difference of only 0.02062 of an inch.
Suppofing then every thoufand feet of the bafe to have been
meafiired by the chain with the fame attention, and confe-
quentiy with the fame, or nearly the fame fuccefs (and there
furely cannot be any reafon to doubt of the praclicability) we
Ihall have 27.404x0.02062 in. = o.565in. or a defeat of fome-
thing more than half an inch on the whole length of the
bafe.

* When the length of the chain was laid off, the heat was 66''|, and that of the
glafs rods 68\ They will, therefore, only agree with each other accurately in
thefe refpeftive temperatures. The mean of twenty thermometers for the four
chain lengths of the forty-fixth hypothenufe gave a heat of 6i'^.6; and for the
fix chain lengths of the forty-fifth, the mean of thirty thermometers gave 59°.75.
The temperature of the 400 feet of glafs by the mean of forty thermometers
was 65°.3; and of the 60O feet, by the mean of fixty thermometers, it was
6o°.8. Now, from thefe data, and the expanfions of fleel and glafs, as deter-
mined by the pyrometer, the computation will Hand as follows :

In. In. In.

Steel / 4°^ 66.5-61.6=4.9 xo.03052=o.i4955'l_Q^^g^gr contract.

l6oo 66.5-59.75=6.75x0.04578=030901/ '^ |ofiooo

leet.

]6oo 68.0—60.8 =27.2 X 0.03102=0.22334] " J "^^ ^°^^

"^ feet.

Glafs/^OO 68.0-65.3=2.7 X0.O2o6Szro.05584') _Q^^^^3j-contraa.
(_6oo 68.0—60.8 =27.2 X 0.03102=0.22334]

The 1000 feet of fteel fhould have contrafted more than! __

the 1000 feet of glafs, - -

But the difference was found to be - - =0.20000

H =0.17938

Therefore the error of- the chain in tlefe<^ was - 0.02062X27.404=2

0.565 in, or little more than half an inch on the whole bafet

So

Meafurement of a Bafe on Hounflow-Heath. 455

So nice an agreement between two refults, with iiiflruments
fo very different, could not fail to be confidered as aftonidiiiig ;
and as it rarely happens, that the graduation of thermometers
will fo nearly correfpond with each other, as not to occafion a
much greater error, all were very defirous that it could have
been farther confirmed by continuing the operation in the fame
way through a more confiderable proportion of the whole
length. But befides the tedious nature of the double mea-
furement, owing to the multiplicity of {lands, platform3|
coffers, and other articles, that were now fucceflively to be
moved forward, and for which purpofe it had been found ne-
cellary to re-inforce the party of foldiers with fix additional
men ; the operation had already trained out to a much more
confiderable length than had been expefted ; the fummer was
now far advanced, and the continuance of good weather un-
certain ; the coffers likewife for the chain, having been con-
flru(£led in a hurry, were found to be defe6live : in (liort, all
thefe reafons contributed to induce us to give up, for the pre-
fent, any farther experiment with the chain, and to proceed
with the glafs rods alone in the completion of the meafurement.

Accordingly, on Thurfday the 19th of Auguff, the opera-
tion with the glafs rods was continued for the five hypothe-
nufes, from the forty-fourth to the fortieth inclufive. It will
be remembered, that in proceeding with the deal rods, double
pickets had been placed in the ground, at the middle of the
forty-firft hypothenufe, or that point which terminated the
1315th rod, reckoning from the fouth-eaft, or the 155th from
the north-weft end of the bafe. Now, in returning to this point
with the glafs rods, the extremity of the 155th fell ihort of
the filk thread ftretched from picket to picket, juft one-tenth
of an inch. The expanfion of the brafs flandard fcale, and

Vol. LXXV. O o o that

456 Mnjor-General Roy's Account of the

tliat of glafs being taken into the account, it appears, that the-
fmall expanfion * of the deal rods from the humidity of the
iair, muil, at this point, have exceeded what it was eftimated
at in the general table by 0.931 of an inch, fuppoiing no error
of any kind whatever to have arifen in the execution, froni
bringing the rods into contaft, or otherwife.

On Saturday the 21 ft of Auguft, the meafurement was^
refumed at the thirty-ninth ftation, and continued for five hypo*
thenufes to the thirty-fifth inclufive.

This day, about noon, hi^ majesty deigned to honour tha-
operation by His prelence, for the Ipace of two hours, enter-
ing very minutely into the mode af condu<5fing it, which met
with HIS gracious approbation.

On Monday the 23d, the menfuration was farther continued
for five hypothenufes, that is, to the thirtieth inclufive.

On Tuefday the 24th, we proceeded with the meafurement
for the fpace of feven hypothenufes, finifhing the bulinefs o£
the day at the twenty- fecond ftation,.

* 155 deal rods
=33100 feet

In.

r -f 0.383 for I® excefs of ternperatiSre of the brafs fcale froiij,
62'' to 63°.
-J- 0.651 proportionable part of th& eftimated expanfion froiri'

h>umidity..

1.034 equation of the deal rods on 3100 feet,.

I' +2.3UI lor o excels or tne near or -tae crais icaie iroiB'
62" to 68^ ^i|

,- s, —0.4.56 obferved contraction of the dafs from the nth an^
•-3i00teet J ^^ . , r -.u . ui

*'• j 1 2ih columns ct the table.

I +0.100 by which tbe 155th rod fell fliort of the thread.

4- 1.965 equation of the glafs rods on 3100 feet.

f Difference of the two equations, undfer-rated in thfe
•yS I I exnanfion of the deal rods-.

It

Meafurement of a Baje c?i MounlloW- Heath. ^i^^"^^

■ \t will be remembered, that in carrying on the operation
with the deal rods, double pickets were left in the ground at
the twenty-feventh ftation, anlwering to the extremity of the
Sioth rod fi-om the firff, or the 560th from the laft end oi"
the bafe. Now, on arrival at this point, the 560th glafs rod
overfliot the filk thread, ftretched from one picket to the other,
2.525 inches. Here again we find, that the lengthening * of
the deal rods from the moifliure of the atmolphere differs but
little from what it has been eftimated at by comparifon with
the ftandard, being over- rated only two-tenths of an inch on
the 560 rods. In this day's operation, in paffing the bridge laid
over the old river, the meafurement, inftead of being made in
the hypothenufal, w'as carried on in the level line, for the
;lpace of twenty rods, namely, fifteen rods of the twenty-
feventh, and five of the twenty-fixth hypothenufe ; which
occalions the alteration in the reduction of thefe two fpaces,
ITiarked with afteriiks in the general table.

As fome trouble had been found to attend the eroding of
■the great road, in the firft meafurement, owing to the num-
ber of carriages that were continually pafiing, the depth of

In.

* 560 deai;.( -f 1.39^0 for i° excefs of heat of the brafs fcale from 62"

50.0 aeaa; r
rods'Zr J
1 1 209 ft. I

to 6:5

+ 5.258 eftimated expanfion from moifturcj

+ 6^648 equation of the 560 deal rods

\ c +^-343 for 6" excefs of heat of the brafs fcale from 62° io 68''.
j^,^° ?1^ \ + 1.821 obferved expanfion-^f glafs \ from columns . I nh

— 1. 1 91 obferved contraftion of ditto J and 12th.

— 2.525 over-fli,Qt the fil)c-thread.

+ 6.448 equation of the 560 glafs rods.

i'ods =:
i 1 200 ft.

..f-rr?rt-

f Difference .over-rated irt the exnaufipn of the 560

O o o 2 the

458 Major-Gcneral Roy*s Account of the

the ditches, and height of the banks of the old Roman way ;
therefore trellels, fuited for the purpofe, had been now pre-
pared-: and left any accident might have happened in conduct*
ing this part of the operation, lo as to oblige us to a repetition^
double pickets were placed in the nfual manner in the ground
two rod lengths from the twenty-fixth flation, to which we
could have referred, witliout going back as fir as the tripod
left at the twenty- ninth ftation, the point from which we ha4
departed in the morning.

Bad weather prevented any progrefs being made on the 25th;
and, on the 26th, all that could be done was to meafurc the
tvventy-fecond and twenty-firfl: hypothenufes.

On Friday the 27th, the work w^ent on more expeditioufly,
having in the courfe of that day meafured lix hypothenufes,
and placed the tripod at the fourteenth ftation.

On Saturday the 28th, eight hypothenufes were meafiired,
and the tripod was placed at the fixth ftation. In this" day's
operation, being arrived near the bridge laid over Wolfey River,
double pickets "\vere placed in the ground in the point anfwer-
ing to the extremity of the ii72d rod, reckoning from the
north-wefl, or the 198th rod from the fouth-eafl: end of the
bafe, that we might recur to them in cafe of accident ; and
the eighteen rod lengths, between this point and the fixth
ftation, were meafured on the level, inftead of the hypothe-
nuial line, which required the alteration of the reduction as
diftlngulfhed by the afterifk In the general table.
.,.On Monday the 30th of Augufl, the meafurementwith the
glafs rods was completed* ; when the extremity of the i37cth

rod

* The gentlemen who were prefent at, and affifling in, the laft day's operation
were jj^^s^tain, BissET,vMr, Grevule, Sir William Hamilton, ]\lr, Lloyd,

and

Meafurement of a B'afe on Hounflow-Hfeath. 4-5^.

rod ovei'-fhot the center of the pipe termlnatnig the bafe
towards the foiith-eall: by iJ^^JS inches, or 1.49 foot. Hence,,
when the feveral equations for expanfions are refpe£lively taken
into the account, we find, that the alteration of the deal rods
from the humidity of the air, which, by comparifon with the
flandard, was apparently moft confiderable in the firft and
fecond fe6lions of the bafe, has now wholly vanifhed ; that is
to fay, the total amount of it has been over- rated by 20.964.
inches*; and this is the contradictory circumflance that has.
been formerly alluded to.

I have already fuggefted what appear to me to have been
the only three pofTible caufes of this difference,, found between
the eflimated and. real expaiifion of the deal rods ; and as we
are to. abandon that meafurement entirely, it is of little or no.
importance now to endeavour to difcover, were it poffible,.
whence it may have arifen. If any, error was actually com-

and Dr. Usher, Profeflbr of Aftronomy in the College of D,ublin. This laft

gentleman was fo obliging as to obferve, with the mofl fcrupulous attention,

throughout the whole operation with the glafs rods, that the coincidence of the

fecond with the firft remained undillurbed, while that of the third with the fecond>

was completing.

In.,
* 1^70 deal") r, . r.

rods rr I + 3-389 ^or 1 of. the brafs fcale from 62° to 63°.
27400 ft. J "^ 24.223 eftimatedexpanfion from humidity.

+ 27.612 equation of the 1 370 deal rods.

r + 20.336 for 6° of the brafs fcale from 62° to 68°.
1370 glafs I -f 5.989 obferved expanlion of glafs "| from columns iith.
rods— — 1.802 obferved contraftion of ditto J and 12th.

27400 ft. V. — 17.875 fpace by which the 1370th rod over-fliot the pipe.

+ 6.648 equation of the I370.glafs rods.

ao.964 over-rated in the total expanfion of the deal rods.

mitted, .

460 Major-General Roy*s Account of the

mitted, whicli is the leaft of all probable, it could only ha\^
happened at the place of the tripod, by bringing a wrong"
point of the fceiTi over it when the operation was refumed.
But it i^ well known, how much care and pains were taken to
prevent any thing of that fort. Indeed the hypothenufal dif*
tances, as given by the chain, agreed fo nearly among them-
j elves, that even a foot or ten inches would have made fo re-
markable a difference in the fituation of the next picket as
could not have paffed unobferved. Befides, in returning with
the glafs rods, after paffing the Staines Road, the meafure-
ment was gradually found (without any leap whatever) to
over-fhoot the pickets, and at laft over-reached the fouth-eafl
pipe by 17.875 inches. I am therefore inclined to believe/
that the difference arifes partly from what may have been loft"
by conftantly butting one rod againfl the other, whereby the
end of the 1370th did not reach fo near to the north- weft pipe
as it ought to, and would have done, if the rods had been
applied to each other by coincident lines. It muft, however,
be confefted, that the near agreement between the glafs and
deal rods in the upper part of the heath feems not perfectly
reconcileable to this fuppolition. Neverthelefs, the defcent
being quickeft, and the irregularities of the furface much
more confiderable in the lower than the upper part, might
produce fome effe6l in one which did not take place in the
other. But the chief part of the difference I take to have pro-
ceeded from over-rated expanfion ; that is to fay, the rods,
when brought into ufe, contracfled fooner than ave imagined,
and thereby gave a fhorier meafure than what was affignabk
to them from the mean of any two or moreromparifons.

The.

Meafurement of a Bafe on Hounflow-Heath. 461.

The laft day of Augnft was employed in dlfcharghig the
party, and removing the various parts of the apparatus to
Spring-Grove Houfe.

"Dejcrtption of the Microfcopic Pyrometer, made tife of for deter-
mining by experiment the expanfion of the metals concerned in
the meafurement of the Bafe, Tab. XX.

Having, in the preceding part of this Paper, given a very mi-
nute account of the adual operations in the field, that the
Public, being thus informed of every circumftance, might be
the better enabled to judge of the accuracy of the reiult, it
remains yet to paint out, in what manner the equations for
the expanlions of the flandard fcale, fteel chain, and glafs rods,
■applied to the apparent meafurement of the bafe, in feveral of
the preceding notes, have been obtained by means of experi-
.ments with the pyrometer.

It is fufiiciently well known, that many years ago, a very

ingenious and valuable Member of this Society did publiih in

,the Phiiofbphical Tranfaaions (vo-l. XLVIII. 1754, N^ 79.)

.an account of experiments nciade with a pyrometer of his in-

-vention. No doubt was entertained of the accuracy of the

experiments here alluded to; on the contrary, they will be

confirmed by the account now to be given of thefe recently

•made, with which they very nearly agree. But as .different

pieces of metal of the fame kiad are certainly fufceptible of

different degrees of expanfion, it was judged heft, on the pre-

fent occafion, to put rods to the tell: of thofe very ipetals that

had been made ufe of in the adual meafurement of the bafe.

7 For,

46.2 Major-General Roy^s Account of 'the

For, fuppofmg both fets of experiments to have been made with
iuflruments equally perfe<£l, and to have been in other refpe^s
equally well conducted, this muft always be coniidered as the
mod: unexceptionable method. Bciides, the expaniion of rods
of the length of five feet being nfcertained, the unavoidable
error of obfervations of this delicate nature, becomes leffened
In proportion to the excels of their length above (liorter rods.
'In thefe new experiments too, another fort of pyrometer, in-
vented by Mr. Ramsden, has been applied, of fuch accurate
conftruclion that it feems not eafy to improve it.

The microfcopic pyrometer, lo named becaufe, by means
^of two microfcopes attached to it, the expanfion is meafured,
confifts of a ftrong deal frame five feet in length, nearly
twenty-eight inches broad, and about forty- two inches in
height. The elevation of the eye-piece fide, or that which
prefents itfelf to the obferver, and alfo of the micrometer end,
-or that which is towards his right-hand, as well as the general
.plan of the top, are reprefented by a fcale of one inch to a
foot, or one-twelfth part of the real dimenlions, in tab. XX.
•^vhere likewife may be {t^w the angular view of the fixed end,
together with plans, fedlions, and elevations, of feveral of the
principal parts, done to larger fcales. From thefe, it is hoped,
^he conftrudion of the machine will be eafily underftood,
without entering into a minute defcription of the almofl num-
•^berlefs fmaller parts whereof it is compofed.

On the top of the frame, two deal troughs, upwards of five
■feet in length, are firmly fcrewed. That towards the obferver
overhangs the frame fomething more than an inch : that on
■the farther fide is even with the back part. Each of thefe
^troughs, which, are about three inches fquare in the infide,
icontains a caft-iron llandard prifm, whofe fides are i \ inch.

The

Meafurement of a B'afe o« Hounllow-Heath. 46^

The manner in which the prifms are fastened to the bottoms of
their refpe6live troughs, and the nature of the apparatufes they
carry on their extremities, will be readily conceived, by refer- .
ring to the particular plans and elevations of them, compre-
hended in the group of eight fmaU figures towards the right-
hand of the general plan. Four of thefe appertain to the left-
hand or fixed microfcope; and the other four to the right-hand
or micrometer microfcope, fo diftinguiflied becaufe it has a
micrometer attached to it. By means of the brafs collars
which embrace the prifms, their left-hand or fixed ends are
fcrewed down extremely fafl to the brafs pieces whereon they
reft, fo as to be perfe6lly immoveable there with regard to
their troughs ; whereas their right-hand ends are kept ealy,
yet without fhake, in their collars, that they may contract or
lengthen freely as the temperature may require, without occa-
fioning any ftrain upon the parts. The prifm in the neareft
trough may be called the eye-piece prifm, becaufe it carries the
eye-pieces of the microfcopes ; and that in the farther trough,
the mark prifm, becaufe it carries the marks or crofs wires at
which the microfcopes refpedlively points The troughs are
covered with pitch in the infide, to make them hold water ;
and each has a cock in the left-hand end for difcharging it.

Between the two deal troughs, one of copper, as a boiler,
is placed, fomewhat fhorter than the former, but flill upwards
of five feet in length. It is about 2| inches broad, and 3I in
depth. The center of the boiler, or rather the center of the
objeft lens which ftands ia it, as we fhall have occaiion fbon to
point out, is diftant from the crofs wires of the mark 5.81
inches ; and from the wires of the micrometer attached to the
correfponding eye-piece 20.33 inches. The boiler refls on five
fmall rollers, one being fixed to each end of the frame, and

Vol. LXXV. P p p the

4^4 Major- General Roy's Account oj the

the other three to the braces which run acrofs it. This cop-
per trough has llkewife a cock in the left-hand end ; and m
the general plan a caft iron prifni is reprefented in it ; but this
lafl: carries no apparatus, as thofe in the wooden troughs do,
being exa6lly of the length of five feet, and only placed there
as one of the rods whofe expanfion was tried, and to fliew that
the machine v/as capable of receiving a rod of that weight
and magnitude.

By referring to the general plan It will be feen, that twelve-
lamps are made ufe of to bring the water in t^ii^ copper to boiL
They ftand on four fhelves, three in each compartment formed
by th^e crofs braces of the frame. They can readily be pufhed
forwards or drawn backwards, and when a6lually in ufe, their
handles are only feen, projedling from under the copper. It
was found, by burning oil in the lamps, the heat of the water
could not be raifed above 209"" or 210"^? but with fpirits of
wine it was brought into violent ebullition. The plan of the
frame llkewife fhews, that the tubes of the microfcopes are
fub-divided into feveral diflincfl parts ; and that one of thefe
parts is attached by a collar to a mahogany prifm, which reaches
from one end to the other. But the ufe of thefe contrivances
it will be beft to defer fpeaklng of, till after having defcribed.;
the apparatufes that are placed within the copper boiler.

At the bottom of the plate the boiler is reprefented, both in
plan and longitudinal fe£lion, to a fcale of one-fourth part of
its real dim.enfions. It contains within it two brafs Aides, the
one long and the other fhort ; which, from the braces that
bind the cheeks together, very much refemble the form of a
ladder. The long Aide, whofe cheeks are i| inch deep,
reaches almoft the whole length of the copper, although every
where unconneded with it except at the points A and B. At
I the

Meafuremeni of a 'Bafe on Hounflo^v-Heath. 46?

the firil: of tliefe, two (Irong pieces of brafs, fixed to the cheeks,
and notched underneath, embrace the ends of a brafs cylin-
drical bar faftened to the bottom. At the laft, the cheeks of
the Aide reft on a roller. Whence it follows, that the copper and
Hide remain immov^eable with regard to each other at A ; but
ll from thenJe, towards either end, they have fall liberty to
•change place ; that is to fay, to expand by heat, or contrail by
cold, in any proportion their different natures may require.
The left-hand end of the Aide is (hut up by a ftrong perpen-
dicular piece of brafs, conne6led with the two fide rings which
fupport the object lens of the fixed microfcope, whofe center
correfponds accurately with its inward face. This piece being
firmly fcrew^ed to the checks of the Aide, and counter-arched
outwardly, forms a flrong butt for the fixed end of the ex-
panding rod (fuppofed here to be the fleel bar) to acl againil.
Within the right-hand end of the long Aide, reAs a Ihort one
-of about 14I inches in length, whofe cheeks are i 5 inch deep.
Its outward end, at C, reAs on the cylindrical furface of the laA:
brace of the long Aide, fitted purpofely to receive it ; while a
narrow longitudinal bar fixed in its inward end, at DE in the
fedlion, moves freely in the notch of a bridge F, framed for it
^in the long Aide. The outward end of this Aiort Aide is Aiut
up in a fimilar manner with the oppofite end of the long one.
This end-piece is al'fo conneded with the two fide rings
which fupport the tube containing the object lens of the mi-
crometer microfcope, whofe center is perpendicularly over its
inward face, and being fortified outwardly by an edge bar, it
forms a butt for the expanding end of the rod that is in experi-
ment to puAi agaiiift. ^y attending to the plate it will be
perceived, that to this end of the boiler a brafs tube (R) is
fixed, which contains within it a brafs rbd, furrounded by a

V p p 2 helical

466 Major-Genera/ Roy'!? Account of the

helical fleel fpring ; which a(fling upon abroad fhoulder of thsr:
rod prepared for the purpofe, thereby prelies its inward end,
which enters- the boiler^ againft the perpendicular furface of
the end-piece of the. fhort flide. Thus, the farther endof the
rod in experiment, lupppfed now to be in its contra6led ftate, ,
is conftautly made to bear againft the furface that \s under the
fixed microfcope. But on the application of heat, the irre-
liftible force of expanfion in the rod obliges, the fpring to give-
way ; the fhort. flide changes its place, and with it the object
lens of the micrometer microfcope moves on a fpace . propor^ -
tionable to the degree of heat that. is applied ; and it is this ^
diftance, meafured by means of the micrometer, as hereafter
will be fhewn, that determines, the quantity of expanfion, or
the fpace by which the rod has lengthened. From . the plate
it will be further obferved, that the rod in experiment refls on
the furfaces of three rollers, about an inch in diameter; and
by means of- three pair of milled-headed nuts i| inch in dia-
3Tieter, which move on axes that are formed into fcrews,. until
they almoft touch the fides of the rod, this is kept in its true
€entrical pofition, whatever may be its form or lateral
dimenfions.-

The microfcope towards the left-hand has been denominated
£xed, becaufe it correfponds with the firfl or fixed end of the
rod in experiment, and never changes its place while thefe are
of the length of five feet. But it appearing to be of confe-
quence, that the expanfion of the ftandard brafs fcale, which
is not quite forty- three inches long, fliould be determined, the
pyrometer has therefore been adapted for the reception of any
rods lefs than five feet, whereby it is made more univerfally ufeful.
For this purpofe it becomes necefi[ary to move the marks and
(E?ye-pieces of the fixed microfcope, along their refpedive prifms,

to

Meafurement of a Eafe on Hounflow-Heath. 467-

tb the proper pofition for the rod that is to be tried. Neverthelefs
the object lens remains in its original place; and in its flead
another lens^- of the fame focal diftance,. is fixed on a fimilar
end- piece,, that can be firmly clamped to any correfponding
place whatever of the cheeks of the long Aide. Hence will
appear the reafon for breaking the fcreening tubes of the mi-
crofcopes into feveral parts, and the ufe of the mahogany prifm,
along which the thick part of the tube moves from one end to
the other.

The. pyrometer, fince it was firfl made and tried, has under-
gone feveral fmall alterations, by way of improvements, which
it is now unneceflary to defcribe particularly. One of thefe
was the application of crofs levels to the parts of the tube (SS
In the general plan) conne6led wdth the object glafles. The
manner in which they are fixed on will appear from the re-
prefentations of them in the lowermoft left-hand angle of. the
plate. And the fedion at the right-hand angle fhews the ap-
pearance .of the double brafs hook, univerfal joint, and milled-
headed nut, applied . acrofs the middle of the boiler (at TU) ?
whereby the levels are brought' to be confiflent, when the water
is boiling, with the polition they had been adjufted to when •
the temperature w^as at freezing; that is to fay, they are kept -
parallel to themfelves in both ftates. This was thought necef*-
fary, becaufe the application of the boiling water funk the
middle of the ilide a fmall'matter, and "thereby made the levels
run outwards.

The micrometer fo often mentioned, being a very eiTential
part of the machine, is reprefented both in elevation and horir
zontal fedlion to the full fize. Its chief parts confifl: of a ^mi-
crometer fteelfcrew, which works in the fqu are nut of a brafs
Hide, while the plane part of it enters into/ a long brafs focket,

nicely

4SS Major-Qeneral Roy's Account of tls

nicely ground to receive it, and thereby preventing all fhake*
To the fquare nut, one end of a watch chain is attached ; the
other end having palTed around is fixed to a barrel, ^which con-
tains a watch fpring colled up in the ufual manner. By this
contrivance, any lofs of time in the motion of the moveable
wire, fixed to the iquare flide, is effediually prevented, whe-
ther the fcrew be turned backwards or forwards. The fixed
wire, fo called becaufe it is only m^ade ufe of occafionaily, ap«
pears in the elevation to the left-hand of the former, and is
farther removed from the obferver, being attached to the oval
flide which bounds the field of the micrometer. This wire
is moved by theinfertion of a milled-headed key (although not
reprefented in the plate) fitted to flip upon the fquare end of
its proper fcrew, which may be feen, in the elevation, projecting
above the micrometer head. It has but little motion, being
only intended for the micafurement of fmall differences of ex-
panfion, or any fmall fpace, by leaving it there, 'while the
other wire is repeatedly brought to coincide with, and again
depart from it. For particular purpofes this wire may be ufe-
ful ; neverthelefs, the inflirument would have performed very
well without it.

The confl:ru6lion of the microfcopes will be readily un*
derftood, by referring to the figures under that head on
the right-hand lide of the plate ; where the relative fitua-
tions of the different eye-glafles, with regard to the wires
or place of the magnified image, as well as to the eye, are
truly reprefented in their real dim^enfions; but the diftances
from thefe to the objedl lenfes and marks refpedively, are con*
tracled or broken off, from want of fufficient room to delineate
them Gtherwife. To increafe the angle of vifion in microfcopes,
it is always nec^ffary that they fliould have at leafl two eye-
glafles, and the fixed microfcope in the plate (hews them in

their

Meafuremeni of a Bafe on Hoiin flow- Heath. 4^0

their ufual pofitlon, the image from the objed: lens there beincr
formed between the two,, that the difperfioii of rays in the firft
may be correcled by that of the fecond. But although this con-
fl;ruclion ferves perfectly well every purpofe of the fixed micro- ^
fcope, yet it eould not anfwerin the moveable one, to which the
micrometer is attached, where equal parts of an image, or their
motion, are to be meafured by the equable motion of the ob--
ieil lens, as fhewn by the micrometer : for in that cafe, the-
interpofition of an eye-glafs before the image was formed,-
would not only have diminiilied its lize, and thereby rendered
the meafure lefs accurate ; but likewife, by refrading the
oblique pencils more than thofe nearer the center, it would
have defiToyed the equality of the fcale, and made equal parts
of the objecb itfelf to have been reprefented unequally in the
magnified image, and confequently erroneoufly meafured by
unequal parts of the micrometer. It was to remedy a defeft
of this fort that Mr. Ramsden propofed his new fy ftem of
eye-glafles, defcribed in the Philofophical Tranfa(£lions, vol.
LXXIII. 1783, N° 5. And he has here applied that fyflem
in the conflru<flion of the micrometer microfcope ; where it?
will be perceived, that both glaffes ftand between the eye and
the image, whereby the greater magnitude of this lafl is ob*
vioufiy preferved, as well as the juft iixjiilarity of all its parts
to thofe of the objed itfelf.

With regard to the fcale of the pyrometer, it is, in the firfl
place, to be obferved, that the head of the micrometer fcrew,
which is nine-tenths of an inch in diameter, is divided into-
fifty equal parts, each of which being reckoned two, it is
therefore numbered to 100. Fifty-five revolutions of the
head, being equal to 0.77175 of an inch, as meafured with-
great accuracy by Mr. Ramsden's itraig.ht-line engine, it

follows y

470 Major-General Roy's Account of the

follows, that thereare 7i.:?7 threiids of the fere w in an mch-;
that feven revolutions and nearly -j-V^th parts move the wire of
the micrometer one- tenth of an inch ; and that ^-^^th part of
a revolution, or half a divifion, anfwers to a motion of fome-
thlng more than 0.00014 of an inch.

Having thus obtained the number of revolutions and parts of
the micrometer (7* 13) correfponding to one- tenth of an inch at
the wires, it is fufEciently obvious, that the number anfwering
to one-tenth LM at the mark being likewife obtained, and
added to the former, their fum will give the meafure of one-
tenth at the obje(Sl lens, or the fpace by which the expanding
rod has lengthened, as {hewn by the motion of the lens from
0 to p. This meafure of one-tenth of an inch at the mark
was afcertained in two different ways, and the refults exa6lly
agreed with each other. In the firft place, a very thin ivory
Aide, whereon feveral twentieths of an inch were nicely divided
by exceeding fine lines, was prepared, and made to move in the
mark where the brafs fiide now exifls. A candle being then
placed behind it at night, while the pyrometer flood within
doors, and the micrometer wire being repeatedly moved by the
fcrew, its coincidence with the lines was diftindtly ieen through
the ivory ; whereby two of the fpaces were found to be mea-
sured by 24.93 revolutions of the head. The fecond method
'was, by means of two exceeding fine wires placed parallel to
each other on the brafs ilide, where they now remain, at the
diftance of one-twentieth of an inch on each fide of the inter-
feiStion wires, as may be feen by obferving the real mark, or
rather its magnified image, as fliewn in the oval field of the
micrometer, in the centralfigure of conftru6lion. The revo-
lutions of the micrometer anfwering to the diftance between
ithefe parallel wires was, as before, found to be 24.93 » which

being

Meajiirement of a Bdfe en Hounilow-Heath. 471

being added to 7.13, we have 32.06 for the number of revolu-
tions meafuring a motion of one-tenth at the objed lens, or
the expanfion of one-tenth. In this manner Mr. Ramsden ob-
tains the fcale of his pyrometer in the eafieft and moil fimplc
way im.aginable, without any neceflity for knowing the abfo-
iute diftances of the objea; lens from the wires of the mark on
one hand, and thofe of the micrometer on the other ; diftances
not eafily afcertained by a6lual meafurement, on account of
the pofition of that giafs in its cell, which cannot conveniently
be come at. Thus, in tab. XX. as well as in the annexed
figure, LM being the object at the diftance of
the mark, equal to one-tenth of an inch; 3
then ml vf'iW be its magnified image, in pro-
portion to the former as mo is to oM, And,
if through the point p, the place to which
the object lens 0 has been carried by the mo-
tion of the expanding rod, a line M^ be drawn
parallel to L/, we fliall have ml= 24.93 -f- Z^-
*j,i^ — mq— '^2.o6y the number of revolutions
of the micrometer meafuring op the expanfion.
Having thus obtained the total number of
revolutions correfponding to mq-, and having
iikewnfe meafured the total diftance mM —
26.144 inches, a fpace eafily afcertained be-
tween the wires of the micrometer and thofe
of the mark, the partial diftances mo and oM may t%e!l
be readily found by computation : for mq : ml :'. wM : moz:z
20.33 i^^^^hes; and mq : wM :: op : oM— 5.814 inches.

In order to finifli the defcription of the pyrometer, it is

only neceftary to obferve farther, that the circular ' fcale,

- feen in the elevation of the micrometer, whofe zero ap-

VoL. Lxxv. Q q q r^^^s

47 z Major 'General Roy's Account of the

pears to coincide with the dart on the plane part of the brafi^.
is that which ferves by its motion to regifter the turns of the
head, h forked key, fitted to enter the holes near the circuiTi-
ference of the circle, is- made ufe of for the adjuflment of this,
zero* The circle (honld never be turned backwards or towards
the left, left the watch chain fliould thereby be thrown off tiie
barrel, but always forwards or towards the right, even if it
iliould be neceflkry to move it almoft an entire revolution. The
zero of the head is that which fliould be fii-fl: brought to cor--
jefpond with its proper dart. They may be feen to coincidje
in the horizontal fedion of the micrometer; and the departure
of zero from this dart, indicates, by the number of divifions
that are intercepted, the value of any fradional part of a:
revolution.

Account of the experiments with the Pyrometer^.

Although the inftrument which I have here endeavoured to
defcribe was begun early in the winter of 1784, yet it was not
iiniflied till the beginning- of laft April ; at which time it was
brought to Argyll-Street, and being placed truly level on the
ftone pavement of the yard, was covered with an oil-cloth
canopy, that the experiments might not be interrupted by
rainy weather.

To fill the three troughs completely it required from twenty-
five to thirty pounds of pounded ice, which was always put in with
great care, fo as to apply as compact ly as poffible to the ftan-
dard prifms and rod refpedively, with but little common water *

* When common water was ufed, although not in any very confiderable pro-
portion, the therrhoa>eter kept always half, and fometimes three quarters of a
ilegree above 3a",

at

Meafwement of a Bcife on Houiiflow-Heath. 6^*^^'^

at fii'fl added ; it having been found in thefe experiments, that
ice water only, fuch as drains from the ice itfelf, is that which
ihonld properly be made ufe of to mix with the pounded ice,
,in order to bring the whole mafs to the true freezing tempera-
ture. Being at the commencement uncertain what time might
'be neceffary for the rods, efpecially when of fo large a fize as
the ft^ndard prifms, to acquire the jufl temperature of freezing,
at firft the ice w^as put into the troughs over night, to prepare
for the continuation of the experiment next morning. But
after many repeated trials, this precaution was found to be
iieedlefs ; a quarter of an hour being more than fufficient to
give to all the freezing temperature, as well as to render the
lens on the expanding rod ftationary, after the water fupplying
the place of the ice had been brought fairly to boil.

The inftrument, in its firft ftate, having in fome cafes made
the expanfion appear to be progreffive, and not equable ; there-
fore its rate was attempted to be afcertained by noting the pro-
greflion anfwering to 60°, 120°, and 180'' above freezing. But
when the inftrument was rendered perfe(fl, and that no fenfiblc
difFeren-ce was found between the expanfion at the lower and
that at the upper part of the fcale, a fair mean being taken be-
tween its afcending and defcending rates, and allowing for the
difficulty of keeping the water, for any length of time, pre-
cifely to the fame intermediate heat ; then this tedious mode of
conducing the experiments was given up, and the expanfion
for 1 80° was at once determined by bringing the water to boil
around that rod, which but a little before had been lying in
melting ice, and which the ftandard prifms flill continued to
do throughout each experiment, care being taken to have a
fupply of pounded ice always ready to keep thefe two troughs
iquite full.

Q q q 2 Two

474 Major-General Roy's Account of the

Two obfervers are neceflary for the effeilual application of the*
pyrometer. He whooblerves with the fixed mlcrofcope, takes
care that its object lens is kept in its true place,, that is to fay,.
that the wire in the eje-piece accurately biiedts the interfetliou. '
wires of the mark. This he is enabled to do by means of the-
apparatus attached to the fixed end of the boiler, as will be bed
conceived hj obferving the plan (at WX) along with the ele-
vation of that end placed near it. The apparatus confifts of
two milled- headed fcrcws, working in bralB plates faftened to
the end of the frame, and acliijg againil; a fmall cock whicb
projedls from the lower part of the boiler, whereby this lafl
receives fuch longitudinal motion to and fro on its rollers, as^
Is fufficient for the adjuftment of the lens. He who obferves^
with the micrometer microfcope, having brought the zero of
the micrometer head to its dart, as fliewn in the horizontal^ '
fedion, and alfo the revolution zero to its dart, as reprefented^
in the elevation, takes care, when the rod has acquired the-
freezing temperature, that the micrometer wire bife£ls the in-
terfe£lion wires of its proper mark. This he effeds by work-
ing with the milled-headed fcrew, reprefented in the plan and- i
elevation of that mark, whereby the mark itfelf is moved
until the bifedlion is accurate ; and during the vi^hole of this
time, the firft obferver muft be extremely attentive to k^ep his
lens adjufted.

One affiftant at leafl is neceffary, who takes his ilation on
the oppofite fide of the pyrometer, to obferve the levels, and
keep them adjufted, by means of the double hook applied^ near
the middle of the boiler, and reprefented in the fedion on the
line TU, at the lowermoft right-hand angle of the plate.

The pyrometer having been adjufted in the manner here de-

fcribed, by giving fufficient time for the flandard prlfms and

I ' rod

Mecifurement of a Bafe on Hounflow-ITeatli. 47- jt

roJ to contract to the true freezing temperature, as- Was eafily
known by the wires becoming perfedly fixed and flationary
with regard to the marks ; the ice was then removed from the
copper trough ; and tlie fame being filled with water nearly on
the boil, the ebullition was completed, and kept up, by means
of the lamps now lighted for the purpole, and flipped in
underneath.

The expanfion, anAvering to the 180^ between freezing and
boiling, was now meafured by working with the micrometer
fcrew until the bifedion * of its wire with thofe of the mark
was again complete ; the obferver at the fixed microfcope taking
alfo efpecial care all the while to keep his bifedion perfectly
accurate. The number of revolutions, regiflered by the num-
ber of entire divifions that the zero of the circular fcale had
departed from its dart or index, and alfo the value of any frac-
tional revolution, regiftered by the divifions on the head in-
tercepted between zero and its proper dart, were then noted, as
exprefTed in the firft column of the fubjolned table of experi-
ments ; which requires no other explanation than what is
therein inferted, and which has been extended purpofely to
fhew at one view, from infpedion only, how much the length
of our bafe would have been afIe(Sted, if meafured by thefe
metals refpe£tively, in temperatures between 32' and 61°,

All the experiments were repeated at leaft twice, and fome
©f them three times, except the ftandard fcale and glafs pen-

* This bifei^ion of the wires may always be made to a great degree of preci-
fion, by one with a tolerably good eye, and accullomed to obfervations cf this fort.-
I have myfelf repeatedly adjufted the wires eight or ten times running, allowing
another perfon to read off and unadjuft each time, without the mean difference
exceeding one-fourth of a divifion of the head, which is only ^4^o^th part of an-
inch.

duluiia?

47^ Major-General Roy's Account of the

dulum rod, whofe expanfions were only tried once. The dif-
ference of a few divifions between the mean and extremes oti
the heat of i8o° being, in things of this fort, of no importance,
it was judged wholly unneceiTary to aim at a greater degree of
precifion in repeating them oftener. By referring to the table^
particularly that cdlumn containing the expanfions on one foot
by 1 80°, it will be perceived, that they are uniformly a fmall
iKatter lefs than what has been affigned to the fame metals
refpeflively, in the experiments formerly alluded to,

Ullhnale deferm'mation of the length of the Bafe on Hounflow-

Heath.

'In the former part of this paper, we have had occafioii
to fpeak of the feven firft columns of the general table
of the bafe; and the titles at the lops of the others re*
fpedtively ferve fufficiently to explain thofe towards the right-
hand ; the expanfion of glafs above,' and its contraction below
62°, contained in the eleventh Jind twelfth columns, being

• deduced from the recent experiments with the pyrometer.

Feet,

The hypothenufal length of the bafe, as mea-
fured by 1369.925521 glafs rods of twenty feet
each +4.31 feet, being the -diftance between the ^
lafl: rod and th-e center of the north- weft pipe, has
-been lliewn to be - - - 2"^4b2.S2b4

The reduction ^contained in the feventh column
of the general table to be dedu<5led is ; . 0*0714

Hence the apparent length of the bafe, reduced

toL-the level of the foiith-ea ft extremity, becomes 274-02^7490

Me(jfurement of a Bafe on Hounflow-Heath. 477

Feet,.
The apparent length is to he augmented hy the

excefs of the expanfion ahove the contradion of
the glafs rods, contauied hi the thirteenth column
of the general tahle — 4.1867 inches, reduced to
the heat of 62°, as has heen.ufually done in former
operationsof this nature . .. .. o.^^g.i

The apparent length is farther to he augmented.
hy the equation for 6° difference of temperature of.
the {landard brafs fcale between 62"^ and 68*, this
laft being the heat in which the. lengths of the
glafs rods were laid off — 20.3352 inches, as de-
duced from, the experiments with the pyrometer i . 6946

Hence we have the correal length of the bafe in
the temperature of 62° reduced to the level of the
lowermofl extremity^ near Hampton Poor-houfe, 27404.7925

This laft length requires yet a fmall reduction
for the height of this lowermoft end above the
mean level of the fea, fuppofed to be fifty-four
feet, or nine fathomSj . .. , •- 0.0706

Hence the true or ultimate length of the bafe, .
reduced to the level of the fea, and making a por-
tion of the mean circumference of the earth, .
becomes •. • • • 2.7404.7219 .■

As fome fmall degree of uncertainty remains with regard to
this lafl redu^ion, it may not be improper to fay yet a few
words on the principles that have been adhered to in making
the computation. It will be remembered, that the meafure-
ment was made'. 3I feet above the furfiice of the heath, that
being the height of the ftands whereon the rods were placed ;.

and

47'8 'Major-General Roy's Account of the

and that the telefcoplc fpirit level gave a defcent of 36.1 feet
from the lowerrnoft pipe to the furface of fummer water in the
Thames at Hampton. The accurate fe6lion of the river lately
publiihed, gives a fall of 3 3._^3 feet from Hampton to the level
of low water fpring tides at Ifle worth. Now thefe thr^e being
added together, we have nearly fifty-three feet for the height
of the bafe above Ifleworth. Having had no immediate means
of determining what real difference there may be between Ifle-
worth and low water fpritig tides at the mouth of the Thames
(for infrance at the Hope or the Nore), I have fuppofed that
fall to be about feven feet, fo as to make the total defcent fixty
feet. Now, fuppofing the fpring tides at the Nore to rife eigh^
teen feet, if, according to M. de la Lande's method, we de-
du£l one-third of eighteen, viz. fix feet from fixty, w^e fliall have
fifty- four feet, or nine fathoms, that the mean furface of the fea is
below the meafured bafe. Whether this conclufion be perfedly
accurate or not is of no moment, fince a whole fathom of
difference (and I apprehend we are not farther from the truth)
does not vary the reduclion quite one-teuth of an inch. The
reduced bafe has therefore been found by the following ana-
logy : as the mean femi-diameter of the earth (fuppofed here
to be 3492915 fathoms) augmented by nine fathoms, is to the
mean femi-diameter, fo is the meafured bafe 27404.7925 to the
reduced bafe 27404.7219 at the level of the fea. It will
doubtlefs be allowed, that infinite pains have been taken in the
field and otherwife, throughout the whole of this operation, to
obtain a juft conclufion ; but as the mofi: accurate meafurement
imaginable is flill more liable to err in excefs than in defeat, we
will throw away fome ufelefs decimals, and effablifh the ulti-
Miate length of the bafe at 27404 feet and feven-tenths.

General

M.ijw-Gcneral Roy's Account of the Menftircmenl of a Btfe on IIounflow-Heath.

uuiif-ral T.iMc of tlic Bad-, (heuijig the relntive lieights of the

Stations

above the fouth-eaft extremity near Hampt
1 for tlie Temperature of the Glafs Rod

I'oor-houfe, tlie Keduflion of ihc Hypotljcnufcf, ni

d the Corrcflioi

whence tlic true length is obtained in the heat of 62

1

2

3 4 1 S 1 6

7

8

9

10

11 12 '3

14

SciliolK-

— "5 ^

Relative lui^hts.

Kcdu£tion
of tlic hypo-

Number
of rods,

Temp

laturc.

Corrrflion for temperature.

1

Total afcciit.

Oblcrved

Excels

Expanl'ion IContraft.

Correfl Jcng

"fil

Arccnt.'Dcfcent

thenufes'.

feet each.

mean of

or defeft

above 62"

hcloH- 62°

Difference.

oi the bsG

2--g

Hypoth.

Sections.

60 therm.

from 62'.

+ apitt. lei-s

— .n-i ■'"="£■

Ti l-"«'-

l-cct.

1-ect.

Feet.

Feet.

Feet.

J,

Inches.

Inches.

inches.

Feet.

5

I

0.07

- -

0.07

0.000012

294-
.925521

?■ 4

+ 9-4

+ 0.2909

1

2

1.85s

- -

■•925

O.QO2875

30

80 7

-H8.7

+ 0.5801

c "

3

i.SiS

0.07

0.002875

30

S0.6

-H8.6

+ 0.5770

4

2-74S

- -

2.S15

0.006288

30

74.0

+ 12.0

+ 0.3722

s

2.92

- -

5-735

0 Q07114

50

62 6

-1- 0.6

+ 0.0186

i "4

b

0.76

- -

6.49s

0.000489

3°

5S.7

- 3-3

— 0.1024

V 0 y

7

■57

_ _

8.0O5

"0.000825

30

60.5

- '-5

— 0.0465

^- 5

8

2.91

0.6S

10.975

0.007065

30

63.3

+ '-3

+ 0.0403

3 S

9

- -

10.295

0.00039J

3°

64.1

-I- 2,1

+ 0.0651

1 ^ 5 to

1 '°

0.65

- -

10.945

0.000360

3°

66.6

+ 4.6

+ 0.1427

5|-5 1 M

- -

o.a).

10.905

o.ooooog

30

70.4

+ 8.4

+ 0.2606

?|2

12

- -

i.iS

9-725

0.001168

30

699

-f 7.9

+ 0.2451

■3

0.83

~ '

10-555

'0-555

0.000581

30

62.7

-1- 0.7

+ 0.0217

»3-

■4

- -

0.94

9.61s

0.000745

30

60 7

- ■-S

-0.0403

1-5

IS

0.42

- -

10.03s

0.000191

30

63.2

-f 1.2

+ 0.0372

c'i^

16

- -

r.63

8.405

0.002222

30

69.0

-1- 7.0

+ 0.2171

ivo

17

□.28

- -

8.685

0 000073

30

71.1

+ 9.1

+ 0.2823

u C."

18

416

- -

12.845

0.014439

30

686

+ 6.6

+ 0.2047

"30

'9

- -

0.44

12.405

0.000169

30

63-S

■1- 1.5

+ 0.0465

I'A

20

0.19

_ _

12.595

0 000036

30

59-2

- 2.8

— 0.0S69

''%-

21

..87

- -

14465

0.002922

30

56.2

- J-8

-0.1799

t ^

22

0.73

- -

15.195

0.000452

30

57-°

- S"

-0.1551

=j!

n

0'39

_ -

15585

0.000135

3°

64.1

4- 2.1

+ 0,0651

24

09s

_ _

■6-535

0.000760

30

64-3

4- 23

+ 0.0713

s^l

25

0.49

- -

17.025

0-000208

30

62.S

+ 0.5

+ 0,0155

I'M)

26

2.11

- -

.9.135

8.58

^0.000063

30

71. 1

+ 9.1

+ 0.2823

'ts 1

27

- -

0.71

18.425

0.0002 14

3°

70 5

+ 8.5

+ 0.2637

? =

2S

0.24s

- -

18.67

0.000057

30

63-3

+ '-3

+ 0.0403

' .=

29

1.21

- -

19.88

0.001228

30

59.2

- 2.8

-O.o86g

fi

3°

- -

0.165

19.715

0.000028

30

66.2

4- 4-2

+ 0.1303

h=^

31

0.14

- _

■9-855

0.000024

30

73-8

4-11.8

+ 0.3660

?..

32

- -

0.12

■9 735

0000019

30

77.6

4-15.6

+ 0.4839

£»

33

- -

0.14

■9-595

0.Q00024

3°

73 7

-HI. 7

+ 0 3629

Ui

34

1. 21

- -

20.B05
2221

0.001228
0.001653

30
30

68 8
65.8
6SS

+ 6.8
+ 3.8

■^ 3-s

+ 0.2:09

'll

%

2-34

_ _

24-SS

0.004571

+ 0.1179
+ 0.1086

!-- (■ 37 1

- -

1.085

23.465

0.000985

3°

61s

- °s

— 0.0155

38

0.47

- -

23-935

0.000192

.so

59.4

- 2.6

-.O.0S07

c^-i

39

0.525

- -

24.46

0 000238

3°

55 6

- 6.4

-0 1985

\ \^

40

1.265

- -

25-725

0.001341

3°

S5^

- 6.9

-0.2140

41

1.18

_ _

26.905

0,001168

30

56.1

- 5-9

— 0.1830

I'-J^l

42

- -

0,19

26.715

0.000036

30

58.4

- 3-6

-0.1117

= 9.2.

43

■•365

- -

28.28

0 002049

3°

58.2

- 3-8

-0.1179

- " ^

44

,.485

- -

29-76.S

0.001845

3°

F-§

- 47

-0.1458

T3 OCJ

♦S

0.24

30.005

0 000055

3°

60.8

— 1.2

— 0^372

•=-3 a

4(>

1.26

- -

31.265

12.130

0.001973

20

6s-3

■^ 3-3

+ 0.0682

!=«•= J

400 ft.

+4.1867

40.44

9..7S

31.265

31.265

0,071401

1369-1-
.925521

+ 5.9890

- 1.8023

Hvpothcmifal length of tli: bale containing 1369.925521 glafs rods

of twenty

feet each

+ 4.3'f«t, - - =

27402.820.

RcJuflion contained in the fevcntli column to be lubtraitcd,

-

-

- - -

0.0714

Total apparent length of the bafe reduced to the level of the fouth

eaft extrCE

nity.

•

27402.749c

AdJ to the appaiciit length the difTcrcnce between the expanlio
contain:d ill the tliirtvviitli cohinnl =4. 1867 inches =

1 of glafs

above, ar

d the contraftion of it below 62", 1,

0.348c

-

-

Add further to the ai.pa.ein length the equation for 6 difference of

tenipcratL

le of the

fiandard brafs fcale between 62" and I

i.694f

68 , the heat in which the glafs rods were laidoff=20.33S2 inch

Correft length of the bafe in the tcrapiraturc of 6a', reduced to th
Rcduaion for llK height of the lower end of the bafe above the m

es,=:

e level of

the lowenl

J ^
loft cxfrcmiry, - - =

274°4-792.

ean level c

f the fca.

fuppolcd to be 54 feet 01 9 fatlioms — —

o.o;oe

True length of the bafe reduced to the mean level of the Tea,

-

-

z=

2;404-72l<

Vol. LXXV.

Table

480

Major-Gfrifral RoY*s Jccount of the Meafurmmt of a Safe on Houiiflow-Heath.

Table of the Expantions of Metals, deduced from experiments made with the Microfcoplc Pyrometer In April 1785.

DLrcriptioii of tlie Metal Rods put to experimciiL

Revoluiionsand
partj of the
micromi;Cerfor
the expanfion
on five tcct.

Standard brafs
Icale.

Englifh phte
brafs, inform
of a rod.

EnglKh plate
brafs, in form
of a trough,

Steel rod.

Caft iron
prifm.

Glafs tube.

Solid glafs rod,

r Suppofcd to be Hamburgii pJatc brafs ; length "

I 4'. 187 inches, or 3.568 ftet; breadth 0.55

J inc!i ; thicknefs 0.25 inch; and wcii;Iit i lb.

ir ! 07.. Its expanfion was mcafured by :;5.+7

revolutions of the micromttcr, wherefore that

on five tcct would have been mcafured by -

Length five feet, breadth 0.9 inch; thick-'
nefs 015 inch i and weight 2 lbs. 5I oz.
Difficult troni its thinnefs to be kept free from
warpmg, - . _

Length five feet; breadJi 1.4 inch; depth I -

inch , weight 8 lbs. 3 oz. Perfcdly ftrongand I

•ftraight, - _ _ J

{Length five feet; breadth 0.5 inch ; thicknefs ^
0.3 inch ; weight 2 lbs. ■]{ 02. Made from the '
very fame bar wiih the chain, ~ - J

{Length five feet , eath of its fides il inch ; -^
and weight 11 lbs. 9 oz Cut from the fame
rod with the ftandard prifms of the pyrometer, J
{Length five feet. yV^ths inch diameter i^
weight I lb. 13I 07,. Drawn from the fame '
p6t of metal with the mcafuringrods, - J
ILcngth40.44incK£S,or3.37feet; mean dia-*)
merer fix-tenths of an inch ; and weight i ]b. '
2 07,. Jl had been applied for fcvcral years to a [
clock. Its expanfion was mcafured by 10.46 [
revolutions of th-* micrometer ; wherefore that i
ton five feet would have been meafured by - J

Hyi8o°|By i'

lUv.Pts. Parts.

35-69

36.41

36.45
22.02
21.34
^•93

'554

I2.AV

Aftual expanfion in parts of an
inch by i8o% the rcvoiutions
being divided by 32.06.

On 5 feet

On r foot,

In.

0,111323

0.11356S

0.1 1 3693

0.068684
0.066563
0.046569

0.048472

0.0222646

0.0227136

0.0227386
0.0137368
0.0133126
0.0093138

0.0096944

On 100 ft.

2.22646

2.27136

2.27386
1.37368
1.33126
0.93138

0^6944

i" of Fahrenheit the expanfion is

On I foot.

0.0001237

0.0001262

0.0001263
0.0000763
0.0000740
00000517

0.0000539

10 feet.

0.001237

0.001262

0.001263
0.000763
0.000740
0.000517

0.000539

xoo feet. 400 feet. 600 feet-

In.

In.

In.

0,01237 0.04948 0.07422

0.01262

0.01263
0.00763
0.00740

0.Q05 1 7

0,00530

0.05048

0.05052
0.03052

0.02960
0.02068

0.02156

0.07572

0.07578
0.04578
0.04440
003102

0.03234

lOOO ft

In.
0.1237

0.1262

0.1263
0.0763
0.0740

0.0517

0.0539

Bafcs of

17400 feet of tUefe mcta
would expand.

By I ,

3'38938

3.45788

3,46062
2.09062
2.02760
1.41658

1.47686

By lo'".

In.

33-8938

34.5788

34.6062
20.9062
20.2760
14.1658

14.7686

67.7876

69.1576

69,2124
41.8124
40.5520
2?.33i6

29.5372

In. "~

101,6814

103.816S

60.828c
42-49;4

44-30j! f

i

PLAN (liewing the I«iiniion ol' the BASE luearuivd on HOUNSLOW HEATH in bummer 1784.^

n.>.~,T^j^ r-v /xn"[>t> xm/ ,■

r/<ff. -Tr/K, y / t.XJiv T»t.x\n// ,fy

HoldTall for Or /End
of the ChBin,

i

\.

-4..

»-«.iJiii^|»ii i.«iui'iiiiii»

Apporaltij for the
i'!Eiul ofthcCliRMi
6 of ibe rwal dimtmlioii* .

— — — ^tn

for //if De.vchij't/on a/If/ AppL/cAriox of i/u- Steel Chain.

Plan of Ihr ifLink of the Chnin in il» orijinol State.

:L3a

EnJ pircr i,r tlir ."LitiL i.. ll, ,.lUrcd aui

Film or the Oof* joint at everv io*Link.

d pifTP or ihc UA Link in >U altnrd Slate. f^U

Elpi-ntion t.r (lif i''Liiik In ill 0r^(r^nal Stale.

OiTpoQtion of Srvcntecn Stnndi Tor (he d><ii1>1r Mf aruremcul »-itIi the Chain mid GUri Rodi .

» =3 ms — a

Top of the Card Stand,

Side ElevBtion ot Itae C&rd Stand.

V

For thr DESCRIi'TION r/>/,/ .-i/'r/.K.lJ'/OA' of f/jf /}E.IL RODS kc

/•/••/■J r:i»i i:/ /JfATVIalOOlll/- 4f>-

il'ioii of ihc Ground of one H.-potlieimfc of iioo Fee

ud niethod of irnciug ihc Luc itiroug^i the Air byrncin. of ihc BoniiicRo'li

mi^ Tr."» ''"' ''^*' ^•*' "'" /' '•*^'

/;./ Mt DEscmi'Titi.v ,111,/ Arri.ii-.iTitix ,'/■ i/,r c'l.iss Kuds

2? or midd\c Rud

-?P^

nTP'i

-:^^!: r

"+■ ! .'•--''■

. ' 1

I

■">f

t 481 3

XXV. AhflraB of a ReglJIer of the Barometer, Thermometer^ and
Rain, ^^ Lyndon, w Rutland, 1784. B_y Thomas Barker,
Efq, Alfo of the Rain at South Lambeth, Surrey ; and at
Selboura and Fyfield, Hampiiiire. Communicated by Thoiiias
White, EJ\, F,R,S.

Read June 16, 1785.

Jan.

Feb..

Mar.

Apr.

May

J line

July

Barometer.

Morn.

A.ftern,

Morn

Aftern

Morn.

nftcrn.

Morn.

Aftern.

Morn.

Aftern.

Morn.
, r 2Q,Q2

Thermometer.

Rain.

Hisihefl Loweft. Mean.

Inches. Jnches.
29,96 28,49

30,00

29><^3
29,74

28,50

28,59
28,44

Aug.

Sept.

oa.

Nov,

Dec] ^,5

29,92] 29,17
28,98

9,92 i 29,04

Morn. 1 o - ' o
Aftern. ^^'^5, 28,74

Morn.

Aftern.

Morn. •

Aftern.

Morn.

Aftern.

piorn.

JAftern.

Morn,
j Aftern.

29,90
30,00

29,8.5

29,75

29,01
28,98
28,75
28,15

Inches.
29,34

29>23

29^23

29,26

29,62

29,43
29,48
29,56
29,55

29,62

29,3s

29,26

In the Houi'e.

High.jLow.

!

40 T
42 i

47

471

471

4.84

501

53

661

*^3i
09

72
65

60I

sn

S3i

51

51

435.

43

28
29

30

31

36

36

351

3^

47

56

57

54

Si

53

54
42
43

39i

41
3^i

321

Mean

Abroad.

34
36

37

40 j

43 i

45

57i

59i

,.1.'

-.-.^

5^A

61

63

59
60

61
63 1

49 i
45 I

4s||

01 zl

iigh.

Low.

0

0

40

154

484

244

45

9

5H

23

4-S

21

52

3ii

51

29

604

35

^3

41

/B

48!

6ii

48

71

53

66

51

791

571

bo^

42i

/ '2

51

57

39

73j

5ii

45

27I

55i

40

SH

23!

53

.-, 0 I

002

41

i3i

4b 4

'9

Mean

Lyndon

S.Lam-
beth,
Surrey,

Inch.

324] ' '^

15225
1,096

1,741
2,890

3,810
5,080
2,814
1,740
0,223

29
36
32!

40 i

48
■ -,

65
54

^3i;

^6 •
67 I
52 1

63
52

64

39 i

49

■^ I 2,276
44 3 '-5^

29

3^:

2,335

Inches 27,207

Inch.
2,54

1,49
2,63

2,5t'

1,36

3'45
2,26

2,84

1,65
0,83

5,60

Sel-
bourn,
Hants.

Inch.
3,18

0,77
3,82

3'92
1,52

3,65

2,40

3,83

2,51

0'39
4,70
3.06

F)

27,21 133,80

2.

Vol. LXXV.

S f f

The

I

482 ^f' Barker's Regifter of

The froil, which began at Chriflmas laft year, continued,
except a few thawing days, till February 21, and was very
fevere, and with frequent fnow. Some thought it the hardeft
winter fuice 1740; but that may be hard to determine, Ja-
nuary 1776 feems to have been rather colder than this; but
the froft lafted only a month. In 1780 the froft was not out
of the ground for nine or ten weeks ; but it was not fo fteady
as this. It was certainly one of the mildeft winters before
Chriftmas, and one of the fevereft after it ; yet the corn and
other plants did not fuffer fo much as might be feared. After
the froft there was fome warm, windy, (howery weather ; but
moft part of March was frofty mornings, and was often fo in-
the fhade all day ; and at the latter end ftrong cold winds,
with fnow and perfe6l winter ; and it did not much mend till
near the middle of April. '

While in January and February moft parts of Europe had
fevere froft, the fouthern parts of it feem to have had great
ftorms and floods ; and, at the breaking of the froft, the flat
countries by the fides of the great rivers of Europe fuffered
much by floods and ice.

The latter half of April the weather mended, and things>
came on gradually, yet with frequent frofty mornings till the
firft week in May ; then, for three weeks, one of the fineft
and hotteft Mays ever known ; every thing before was exceed-
ing backward, but now came on at a vaft rate ; the grafs and
leaves were remarkably green, a great bloftbm year, and plenty
of fruit. This hot weather brought up thunder, which turned
the weather wet near the end of May, and it was wet Or
ihowery and cool all June; this brought on the corn again,
which was made rather thin by fo much heat too early. Near
the firft two thirds of July was agnin fine and hot, and being

the Weather at Lyndon In Rutland, &:c. 483

in the height o£ hay time, a good deal of it was well made ;
but fome of the firil: cut, and the latter was caught in the wet ;
for after the 1 9th it was ihowery or wet, and the 30th and
31ft were, all over Leicefterfhire, Rutland, and part of Lin-
colnfhire, the greateft flood fince July 1736 ; and it continued
wet and cool all AugufI:, fo that the fummer was in general
cold, wet, and backward, yet with fome very fine fits in it.
The harveft began but indifferently ; but being late this year,
and the weather wet, not much was carried before September,
when, in about three weeks calm, hot, and dry weather, yet
with vaft dews, moft of the white corn was well got in this
country ; but fome of the peafe, and, where it was earlier and
later, fome of the white corn was carried damp, for the end
of September was again wet.

The autumn was various ; a dry and fine 06lober, toward the
end of it iharp frofty mornings ; a {howery November, with a
fharp froft in the middle, yet often pleafant ; and after Decem-
ber 5th, a confiderable fnow (in fome countries it was very
great) and a feverer frofl than is ufual before Chriftmas lafted
tijll into January,

%ii%

■:uni:

t 4«S 1

PRESENTS

MADE TO THE

ROYAL SOCIETY

From Anguft 1784 to June 1785;

WITH

The NAMES of the DONOR S.

Prefents.

Donorsi

1784.
Aug.

12. Oenvres de Charles Bonnet. Tom. VI, VIT.
VUI. Neufchatd. 1782, 1783. 4^

— - — Effay II. on the Nature and Principles of

Public Credit. St. Auguftine, Eall

Florida. 1784. fol.

Nov. 4. Deftriprion geometrique de la France. Par

M. Cainni'de Thury. Paris. 1783. 4°

— — . Rapport des Commiflaires charges par le
Roi de 1' examen du . Magnetifme Ani-
mal. Paris. 1784. 4°

r . . Tableau methodique des Mineraux. Par
M. Dauben.ton. Paris. 1784. 8'^

m. Lettre fur les Experiences des Friftions

glaciales pour la guerifoh de la Pefte.
Par M. D..5arao"ilovvitz. Paris^ 1781.

8»

m... Lettre a I'Academie de Dijon avec reponfe

h ce qui a paru douteux dans le Me-
moire fur I'Inoculation dela'Pefte. Par
M. D. Samoilowitz. Paris, 1783, 8*

The Author.
S. Gale, Efcj,

The Author.
The Authors..

The Author.
The Author.

The Author.

Prefents

[ 486 ]

PrtTcnts,

Ko/. 4.

lU'j"">n^c a M. Gormand, fur b queAion :
" Si Irs CauUreSy pciz'VCRt crrc qtidquc pre^
•' fcrvaftf centre J a Pcfte pendant fes
'^ ravages." Par M. D. Samoilowitz.

12°

. Die beftiir.mung der Geftalt \ind Grbfle der

Eide: voa F. W. Gerlach. Wicn. 1782.

— — The original Aftronoinical Obfervations
made in the courle uf" a Vwage to the
Northern Pacific Ocean, by Cap:. James
Cook, Lieut. James King, and Mr.
William Bayly. London. 1782. 4"

Annals of Agriculture. By Arthur Young,

Efq. London. 1784. 8^

— A Treatife on the Difeafes of Children.

By Michael Underwood, M. D. Lon-
don. 1784. 12°
Nov. It. Deir Architettura Dialogl : di Ermene-
giido Pini. Milano. 1770. 4"
_ — Offervazioni mineralogiche fu la Miniera di
Ferro dell' Ifola d'Eiba : di E. Pini.
Milano. 1 777. 8°
_— Memoire fur des nouvelles Criftallifations
deFeldfpath. Par E. Pini. Milan. 1779.

8"

-.1 ■ I . Hfermenegildi Pini de Venarum metallica-

rum excodione Vol. L et IL Mediolani.

1779, 1780. 4"^

■■« r.Temoria mineralogica fuUa Montagna e fiii

contorni di S. Gottardo : di E. Pini.

Milano. 1783. 8°

■ Defcrizione di un Pantaulo : di E. Pini.

Milano. 1783. 8*

Delia maniera di ofTervare nei Monti la dif-

pofizione degli Strati : di E. Pini. 4°

Dell' Elevazione dei principali Monti della

Lombardia Auftriaca : di E. Pini. 4"

OfTervazioni mineralogiche fuUa Montagna

di S. Gottardo : di E. Pini. 4°

Mcmoires et Obfervations de Chimie, Par

M. deFourcroy. Paris. 1784. 8°

Obfervations fur la Cure de la Gonorrhee.

Trad, de I'Anglois de M« S.F. Simmons;

Donors,
The Author,

dO .F

The Author,

; , ,2

The Comiiii^oners of Lcn-

gitude.

The Author.
The Author,

The Author.
The Author.

The Author.

The Author.

The Author.

The Author.

{►The Author.

The Author,

The Tianflator.

Frcfent9\

■h

I 40V

*i

1784.

Prefents.
par Gabriel

Mafayer. Montpellier,

1783- . . 2°

Nov, II. Medicai Communicationsc Vol. I, London.

1784. _ S'*

18. Obfervations on the !ate Contefts in the
Royal Society. By Andrew Kippis,
D. D. London. 1784. 8^

pec. 9. An ElTay on the Ufe of the Red Peruvian
Bark. By Edward Rig'oy. London.

178

:>•

1785.
Jan

— Ah Efl'ay on the uterine Haemorrhage

which precedes the Delivery of the full-
grown Foetus. By E. Rigl'y. Lond.
1784. 8*

— An Aftronomicat MS. in the Perfic Lan-

guage. 8"

16. Defcription des Projets et de la Conftruc-

tion des Poats, &c. Par M. Perronet.

Tom. L n. Paris. 1782, 1783. fol.

— Defcription of a Method of taking the

Differences of Right Afcenlion and De-
clination with the Reticule Rhomboide
of Dr. Bradley. By H. E. Bath. 4=*

— An Enquiry into the various Theories and

Methods of Cure in Apoplexies and Pal-
fies. By B. Chandler, M. D. Canter-
bury. 1785. 8"
A meteorological Journal kept at Fort
William, Calcutta. MS. fol.

23

13

A Treatife on Time. By W. Watfon, jun.

M. D. London. 1785. 8^

20. The London Medical Journal. Vol. V.

London. 1 785. 8"

■ An Effay on Comets. By Andrew Oliver,

jun. Salem, New-England. 1 772. 8°

Tcb, 3. Meteorological Journals kept at Nain,

Okkak, and Hoffenthal, in Labrador,

MS. 4"

10. An Account .of the Mufical Performances

in Commemoration of Handel. By C.

Burney, Muf. D. London. 1785. 4*

17. Obfervations fur la Phyfique, fur I'Hiftoire

jiaturelle, et fur les Arts. Par M, I'Abbe

Donors,

The Society for promoting

Medical Kiio.vledgeo
The Authoro

The Authoro

The Author o

Major Pierfon;
The Author.

Sir Henry C. Englefield,
Bart,

The Author.

Major Pearce,

The Author.

8. F. Simmons, M. D.

The Rev, Profeflbr Wil-

Hams.
The Rev. Mr. La Trobe.

The Author and the IMufi'
cal Society,

The Editors,

prefents*

£ 488 ]

tj^'

Prcfents.

J^onori^

The Author.

The Author,

Rozier, et par M. J. A. Mongez le jeune.

Tom. XXV. Paris. 1784. 4"

iFcb, 24. An Inquiry how to prevent the Small-Pox,

&:c. By John Haygarth, M. B. Chef-

ter. 1784. 8"*

Mar. 10. Remarks on morbid Retentions of Urine.

By C. Brandon Trye. Glocefter.

1774. ^^

37. A Portrait of the Eleftor Palatine Duke of

Bavaria.
» Quatrieme Lettre du Chev. Rofa fur fes

Decouvertes Phyiiologiques (tranflated

from the Italian) MS. fol.

■■ ■■' Commentarii de Rebus in Scientia naturali Mr. Philip Hurlock,

et Medicina geftis. Vol. XXV. Lipfiat.

1782. S'*

— — ConnoilTance des Temps, pour I'Annee

1787. Par M. Jeaurat. Paris. 1784.

His moft ferene Highnefe

the Eledtor Palatine.
The Marquis de Hautefort.

The Author.

12

*•- — i- Memoire fur une Machine propre a creufer
et curer les Canaux, Rivieres ou Ports,
Par les Freres F. et A. Eckhardt. 4*^

■ <' Succin£t Account of the Advantages of

Mills with inclined float-board Wheels.

By Mr. A. G. Eckhardt. fo}.

April 7. The Theory and Praftice of Aeroftation.

By Tiberius Cavallo. London. 1785.

8^

II Obfervations on the Ufe of Opium in re-

moving fymptoms fuppofed to be ov.ing
to morbid irritability. By Alexander
Grant. London. 1785. 4*^

■ '"■I" Opufcules de Pierre Richer de Belleval.
Nouvelle Edition ; par M. Brouffonet.
Paris. 1785. S'*

— •■'»■ Lettre fur I'Antimcphitique. ParM. Janin
dc Combe-Blanche. Vienne. 1783. 8°

■^ "■" Seconde, troifieme, et quatrieme Lettres a

♦ M. Cadet. Par M. Janin de Combe-

Blanche. Vienne. 1 783, 1 784. 8°

■ >■ .L*Homme noye dans une Fofl'e, a-t-il peri

par le Mephitifme ? Lettre par M, Ja-
nin de Combe-Blanch«, IJ'
6

M, A. Eckhardt.
The Author.
The Author.
The Author.

The Editor,

The Author,
The Author.

The Author,

^Vidtntfp

[ 4^9 J

14.

Prefents

April 7, Preuves que rHomme s'ed: noye dans la
foffe; et que le Mephitifme n'a pas
canie fa mori. Lettre par M. Jatiin de
Conabe-Blanche. 8°

"—r— Nouvellcs Experiences qui confirment celles
qui ont ete annoncccs dans rAntimcplii-
tiquc. Par M. Janin de Combe-Blanche.,

8°
—— Reponfe au Difcours de M. O-Rian fur le
Magnetifme Animal. Par M. Janin de
Combe-Blanche. Geneve. 1784. 8*
Relief from accidental Death. By Alexan-
der Johnfon, M. D. London. 1785.

12"

28. Three Regiflers of a Pocket Chronometer.

By Count De Bruhl. 4=*

m — A Memoir on fome Improvements in Book-

bindmg. By M. Aniffon le fils (in
French) MS. fol.

May 5. An Eflay on the Nature and Cure of the
Phthifis pulmonalis, fecond edit. By
Thomas Reid, M. D. London. 1785.

8'
m Reports of the Humane Society for the

years 1783 and 1784. 8°

■ Account of a Machine conflrufted for the

purpofe of deepening and fcouring Ca-
nals, Rivers, and Ports. By the Bro-
thers F. and A. Eckhardt. fol,
12. Lettres 1. IL IIL IV. V. VL fur
l'Archite6^ure. Par M. Viel de Saint-
Maux. Bruxellcs. 1779, 1780. Pa-
ris. 1784. 8^
26. Differtatio Botanica de Sida. Au£l. A. J.
Cavanilles. Pariliis. 1785. 4*^
.. Obfervations de M. PAbbe Cavanilles fur
PArticle Efpagne de la Nouvelle Ency-
clopedie. Paris. 1784. 8*
— — . Parallele entre le Magnetifme Animal,
I'Eleftricite, et les Bains medicinaux.
ParM. L***. Paris, 1785. 8^
. Memoire fur la Decompcntion de I' Air at-
mofpherique par le Plomb. Par M.

Donors.
The Author.

The Author.

The Author.

'The .\uthor.

The Author.
The Author.

The Author.

The Humane Society,
Mr. A. Eckhardt,

The Author.

The Author.
The Author.

M, Laugier.

The Author,

Vol. LXXV.

Luzuriaga,

Paris, 1784.

8*

Ttt

Prefents,

[ 490 ]

Presents.

1785.

May 26. Eflays of Reform on the Syflem of the
Finances of Great-Britain. By J. Van
Per Hey. Vol.1, London. 1785. 4"
« — — Reports of the CommifTioners appointed to
exaniine, take, and ftate the Public Ac-
counts of the Kingdom. By John Lane.
Vol. IL London. 1785. 4°

June 2. Ionian Antiquities. London. 1769. foL

H. M. Marcard Befchreibung vonPyrmont.

I. Band. Leipzig. 1784. 8°

g. Mathematical Tables. By Charles Hut-
ton, LL.D. London. 1785. 8°

•^ Jacobi Dickfon Fafciculus Plantarum cryp-

togamicarum Britannia. Londini. 1785.

4^
j6. Reflexions on the Study of Nature : tran-

flated from the Latin of Linnaeus, Lon-
don. 1785. . r

Donors,
The Author.

The Conamiilioners*

Society of Dilettante
The Author.

The Author,

The Author,

J. E. Smith, Efqj

L" 492 ]

AN

INDEX

TO THE

SEVENTY-FIFTH VOLUME

OF THE

PHILOSOPHICAL TRANSACTIONS.

A.

yfCT'jNiA. See BarlaJoes.

^ Air, Experiments on, by Henry Cavendifh, Bfq. p. 372. The diminution of the
ail by the ekiStric fpark depends upon the converfion of phlogiftlcated air into nitrous
acid, ibid. Defcription of the apparatus made ufe of (tab. XV.). ibid. Fig. 1,2,
and 3. explained, p. 373. Method of forcing the ele(flric fpark through the tube,
p. 374. Experiments, when the cle61ric fpark was paffed through common air,
included between fliort columns of a folution of litmus, ibid. When lime-water was
ufed inftead of the folution of litmus, ibid. With impure dephlogillicated air, p.
375. Obfervations on the refults of thofe experiments, ibid. When air was confined
by foap-lees, 375 — 377. Experiments to determine what degree of purity the air fhould
be of, in order to be dimlnifhed the moll; readily, and to the gveateft degree, p. 376,
Precipitation of a folution of filver by phlogifticaied nitre, p. 377. General reafoning
upon all the experiments, p. 378 — 380. Method of preparing the foap-lees, and
dephlogifticated air, ufed in tbefe experiments, p. 380. Quantities of each ufed therein,
p. 381. Experiment to determine whether all the phlogiftlcated air of the atmofphere
is of the fame nature, p. 381 — 3S2. See Phlogijikated Air. Another caufe of the

T t t 2 dimi-

[ 49^ 3

diminution of air by the electric fpark, p. 3S2 — 384. No ph'ogiflon communicated
by the eleftric fpark, p. 384.

Air eindWatcr^ Experiments and obfervstions relating to, by the rev. JoJeph Prieflley,
LL.D. p. 279. Opinions of Mr. Cavendilh, Mr. Watt, and M. Lavoifier, con-
cerning decompofed air, p. 2S0. The author's opinion of inflammable air, and
fixed air, both which had been firft advanced by Mr. Kirwan, ibid. Experiment to
afcertain whether any water is produced when the air is made to difappear, p. 281.
Other experiments of the fame kind, p. 28 i. A peculiar circumilance attending the
inelting of call iron with a burning lens, p. 283. Refult of mel-ing caft iron in the
bottom of a deep glafs receiver, p. 284. Mr. Watt's conclufion thereon, ibid. A
new and unexpected appearance which occurred in endeavouring to revive the calx of
iron, or a calx faturaced with pure air, ibid. Experiments to determine whether
fixed air or water would be the produce of combining inflammable and dephlogifti-
cated air, p. 2S5 — 287. Obfervation thereon, p. 287. Refults of other experi-
ments with the calx of copper, and precipirate, perfe, in infi:rmmab!e air, p. 288.
Refledion on the relation of water to inflammable air, and efpecially Mr. Cavendifh's
ideas on the fubied, ibid. The powerful attraction that charcoal or iron appear to
have for vvater, when thty are intenfely hot, p. 289. Experiment to afcertain the
influence of unperctived molfl:ure in the produdlion of infla<rimable air, ibid. M.
Lavoificr's method of obtaining inflammable air with an hot iron tube and an hot
copper tube, p. 290. Refult of experiments made with charcoal, p, 291 — 296.
And of others made with iron, p. 297. Obfervations thereon, p. 298. See Bal-
loons> Experiment to afcertain the quantity of inflammable air which may be
obtained from any given quantity of iron, p. 298. The fuppofition that vvater confifts
of two kinds of air endeavoured to be explained, p. 299. Procefs of that invefliga-
lion, p. 300. Theory -of that p.rocef?, p. 301. Analogy betvveen the experiment
of the calx of iron imbibing inflammable air, and the iron itfelf imbibing dephlo-
gifticated air, p. 302. Experiments to prove that phlogifton is a real fubftance capable
of afiuming the form of air by means of water and hear, p. 303. Call iron
annealed remarkably different from that which has not undeigone that operation, p.
304. Experiment wi(h precipitate per Je^ ibid. EiFefts of heating iron in all the
different kinds of air, p. 305. And of tranfmitting fleam through a copper tube,
to try the effeAs of fpiiit of wine, ibid. Charcoal of metals explained, p. 306.
General inferences from the principal experiments, ibid.

Algd, ^^t Variable Star, Opinion of aftronomers very unfettled concerning the change
of its light, p. 134.

Anderfon^ Mr, James. ^tQ MorneGarou.

Animal Floiver. See Barbadoes,

Animals, preferved in fplrits, not fo fit for anatomical examination, p. 340.

ArchiteSlurt, (kc. Sketches and defcriptions of three fimple inftruments for drawing

architeAure and machinery in perfpe6^ive, by Mr. James Peacock, p. 366. Direc-

7 tions

[ 493 1

tions for placing the macKInes, &cc. ibid. Defci/ption of the drawing-board (fig. i.
tab. XilL). ibid. Ufe of ditto, p. 367. Ho'.v to draw all perpendicular lines at
once, ibid. Defcription of the compound-boa'd (fig. 2. tab. XIV.), p. 368. Ufe
of ditto, ibid. The T fcjuare, its ulcfulnefs, p. 369. Defcription of tlie vertical-
board (fig. V tab. XIV.), p. 368. Ufe of ditto, p. 370.

A'tifcial Springy account of one, by Erafnuis Darwin, M. D. p. 1, Old difufed well
near the doflor's houfe in Derbyftiire defcrlbed, p. 2. St. A'kmund's well, its
fituation, ibid. A new fpring difcovered, itiJ. Method of preventing the
mixture of the old water with the new, p. 3. And of trying the height of the
new fpring, ibid. New water nearly of the fame properties with St. Alkmuad's
well, p. 4. See Mounta'ms. Increafe in quantity and quality, ibid. And why,
p. 6.

Aja Fceuda^ defcription of a plant yielding it, in a letter from John Hope, M. D. p.
36. General defcription, ibid — 38. The afa fcetida plant not fatisfad'torily known
till Ksempfer defcribed it, p. 36. Letter from Dr. Pallas to Dr. Guthrie, with two
of the plants, ibid. One of which planted in the Botanic Garden at Edinburgh, p,
iq. The juice feems to be of the fame nature with the officinal afa foetida, ibid.

Aftronomical Obfervatiom, in two letters from M. Francis de Zach, Proieflbr of Mathe-
matics, and Member of the Royal Academies at Marfeilles, Dijon, and Lyons, p.
137. Account of his obfervations of an eciipfe of the moon, made with Father le
Fevre, Aftronomer at Lyons, in the Ohkxvsi'ioxy c?\\GdL au gra?ici College, ibid. State
of the fky at the time of making the obfervation, ibid. Short telefcopcs preferable
to long ones in obferving eclipfes of the moon, p. 13S. In eclipfes of the moon no
greater exadnefs than that of a minute can be obtained, ibid. Agreement between
the Imperial Aftronomer, I'Abbe Hell's obfervations of the moon's fpots made at
Vienna, with thofe made by M. Meffier at Parif, ibid. Correfpondent altitudes of
the fun taken with a quadrant of three-foot radius, in order to adjufl the pendulum-
clock to apparent time, p. 139. Obfervations of the moon's eciipfe the iSth of
March, 1783, p. 142. Father le Fevre's obfervations with a rcfleftor fifty-five inches
focal length, p. 143. Obfervations of Jupiter's fatellites at Marfeilles, by M. Saint
JaC']ues de Svlvabella, p. 144. Obfervation of the tranfit of Mercury, Nov. iz,
1782, at Marfeilles, by the fame, p. 151. and by M. Wallot, at the Royal Obferva-
torv at Paris, ibid. Important remark upon the diameter of Mercury, p. 152.

Averrhca Cara/nbola, an account of the fenfitive quality, in a letter from Robert Bruce,
M. D. p. 356. Is a fpecies of fenfitive plant, ibid. Is differently affected by being
touched in different manners, p. 356, 357. Method of confining the motion to a
fingle leaf, p. 357. Effeft of impreffing it by pundlurc, percuffion, or compreffion,
ibid. Ditto on flicking a pin into the univerfal petlolus, p. 358. On making a
compreffion with a pair of pincers on ditto, ibid. On the leaves being blown again it
each other, or the branches, ibid. Appearance of the leaves when fhaded from any
dillarbing caufe in the day-time, p. 359. The leaves naturally perform a more

extenfivitr

[ 494 3

e;:tei:nve motion when going to fleep than by external imprefllons In the day-time,
ibid. Efiedls produced on a leaf by the burning lens, ibid. And the eleftricai
ftack, p. 360. Two other fpecies of this genus mentioned by Linnaeus, ibid.

B

Sal'oor.s, the cheapeft method of filliiig them with the Hghteft inflammable air, p. 297.

Barhadocs^ eife«Ss of the dreadful hurricane there in 1780, p. 334. The aftinia, or a
fpecies of animal flower, then Found m confiderable numbers on that coaft, p. 355.

Barker y rev, Pvobert, B. D. See Stag's Head and Hornt-.

— Thomas, Efq. See Barometer^ &c»

Ritromcler, Thermometer, and Rain^ Abftradl: of a Regifter of, at Lyndon, In Rutland, In
1784. By Thomas Barker, Efq. Alfo of the Rain at South Lambeth, Surrey j and
at Selbourn and Fyfield, Hampfhire, p. 481,

:Bnfe, account of the Meafurement of a bafe on Hounflow- Heath, by Major-general
William Roy, p. 385. Introdudion, ibid. — 390. The author's acknowledgements of the
affiftance of feveral fcientific gentlemen, p. 389. 391. 417. 425. Particularly of the
worthy Prefident of the Royal Society, p. 425. 458. Choice of the bafe, tab. XVI.
p. 390. Firll: tracing of the bafe, and clearing of the ground, tab. XVI. p. 391. Sol-
diers preferred to country labourers, and why, ibid. A detachment encamped near
Hanworth Sumraer-houfe, ibid. Clearing of the firft feftion of the bafe, p. 392.
Tracing of the fecond and third fedions, p. 393, Half the foldiers quartered in the
neighbouring villages to clear the third feftion, while the remainder fmoothed the
fecond, ibid. Inftrumenrs made ufe of in the firft and fecond meafurements, p. 394.
Steel chain, tab. XVII. ibid. Conltruclion of the chain, ibid. Alteration of the
chain, p. 39^. Deal rods, tab. XVIII. p. 397, Different opinions concerning the
beft method of applying rods in meafurement, p. 398. Meafuring rods and ftandard rod
defcribed, p. 399. Brafs flandard fcale, and method of laying off the lengths of the deal
rods, p. 401. Major-General Roy's fcale compared with the Society's flandard, p. 402.
Manner of afcertaining the length ot the deal rods with it, p. 403 — 405. Chells for
holding the deal rods and ftandards, p. 405. Stands for the meafuring rods, tab.
XVIII. and XIX. p. 406. Method of drawing a line through the air, parallel to the
common fuiface from flation to ftation, in equal dillances of 200 yards or 600 feet,
as in the figure at the top of tab. XVIII. p. 407. Nature of the moveable (lands
(towards the right-hand in tab. XVIII. and XIX.) explained, p. 408. Plans of the
two tables (towards the right-hand in tab. XVIJI.) explained, ibid. Plan of one of
the fquare tables (towards the left-hand of tab. XVIII.) with the ends upon the fecond
■and third rods upon it in contadt explained, p. 409. Mr. Smeaton's deal platforms,
Handing on pickets drlvtn into the ground, and properly levelled ('tab, XIX.)
-<lefcribed, p. 410. Boning telefcope and rods, tab. XVIII. p. 411. IMethod of
tracing the line of 200 yards, &c. from one fixed hand to the other, ibid. Boning

telefcope

C 495 ]

telefcope defciibed, ibid. Boning rods, and their ufe, dcfcribcd, p. 412. Cup and
tripod for prefer ving the point upon the ground, where the meafurement was difcon-
tinued at nighr, and refumed next morning, p. 412. Difference between meafuring
with a rod of twenty feet, and with rods of twenty feet three inches, p. 412. Brafs
Clip iifed on thefe occalions defcnbed, p. 41^. ^i^. Nature of the tripod (tab.
XVIII.) exphiined, p. 413. Method of fufpending the plummet from any part of
the deal rods indifferently, p. 414. Wheels for terminating, in a permanent manner,
the extremities of the bafe, tab. XVIII. ibid. Mr. Mylne's improved machines for
certainly referring to the fame point on any occafion of correAing or repeating the
work (reprefented in tab. XVIII.), p. 415. Rough meafurement of the bafe with
the chain, and determination of the relative heights of the ftations by means of the
telefcopic fpirit level (tab. XVI. and XVII.), p. 416. The firft meafurement of the
fouth-eaft fedion of the bafe completed in three hours and a half, p. 417, 418.
The fame feftion re-meafured, wish the probable caufe of the variation, p. 418.
The operation with the chain fufpended, and why, p. 419. Defcription of a hold-
faft for the rear-end of the chain, invented by Col. Pringle (reprefented by two ele-
vations adjoining in tab. XVII.), ibid. The operations refumed by meafuring twice
with the chain forwards and back again the fecond fe£tion of the bafe, ibid. The
level of the iiril and fecond feftion of the bafe taken, with an account of the fpiiit-
level made ufe of, p. 420. The firft general table relating to the levels of the
bafe explained, ibid, p, 421. Col. Calderwood's method of computing the difference
between the hypothenufal diftances of 600 feet each, and the reduced bafe diflances,
p. 420. Tracing of the bafe with the tranfit inftrument, p. 421, 422. Confecjuenceof
delaying the ufe of that inftrument, p. 422. Levels of the third feftion taken, and
the rough meafurement thereof with the chain completed, p. 422, 423. Refult of the
examination of the length of the chain in different temperatures, p. 42:;. Defcenc
from the lower end of the bafe to the furface of the Thames at Hampton, p. 424.
Meafurement of the bafe with the deal rods, p. 425. Method of performing that
operation, p. 426. Difference of meafuring by coincidences and contacts accounted
for, p. 427. The two firft hypothenufes re-meafured, with the refult, p. 428.
Their Maiellies prevented by the weather from feeirg the nature of the operations,
p. 429. Method of difcovering the error of the chain at each ibtion, p. 429. In-
conveniences occurring from the humid and dry flate of the atmofphere, &c. p. 430.
See Expanjibiliiy. Different comparifons of the rods with the ftandard, and the
refult, p. 432, 433. Near agreement between the refult by the deal rods, and that
furnifhed by the rough meafurement with the chain, accounted for, p. 433. Mea*
furement with the deal rods finifhed, ibid. Expanfion of the deal rods, p.
434 — 436. See Riga Red-iuoodt Deal Rods. Mr. Ramfden's obfervations o£
the ditierent expanfions, p. 435. Operations on Hounflow-Heath totally fuf-
pended, p. 438. Comparilon made in the beginning of September at Spring
Grove, when the rods were in their dry or contraiTied (late, and the remeafure-

jnent

[ 496 ]

. meat of the faire fpzce the next morning, when, being left out on purpofe, they
had contraftcd all the humidity they could, p. 439, 440. Defcription of the
fi'hifs rod?, ultimately ufed to determine the length of the bafe, tab. XIX. p. 441 —
449. The cafe containing the tube defcribed, p. 441. Manner in which the middle
or the tube is made fall to the middle of the cafe, p. 442. Fixed and moveable ends
of the tube aefcribed, p. 443. Fixed and moveable apparatus defcribed, p. 444 — 447.
IVIahogany lid on the top of the cafe defcribed, p. 447. Method of afcertaining the
length of the glafs rods, p. 440. Difpofuion ot the Hands for the double meafurement
with the chain and glafs rods; defcrijnionof the apparatus then applied to the ends of the
chain ; and ulcimate continuation of the medfurement witb the glafs rods alone, tab.
XVil. and XIX. p. -449- Reafons for rejedling the deal rods, ibid. Commencement
of the operation for the double meafarement, p. 450. 455. Apparatus attached to the
Hrll end of the chain, p. 451. Ditto for the lall end (to the right-hand fide of tab.
XVII.), p. 452. Comparifon of thecontraflionof fteel and glafs, with the error of the
chain in defe6t, p. 454. Farther experiments with the chain given up, and why, p.45^.
His Majefty honours the operation with his prefence, p. 456. Equation of the deal rods
and of the glafs rods, on 3 1 00 feet, ibid. Difference over-rated in the expanfion of the
^60 deal rods, p. 457. Meafurement with the glafs rods completed, p. 458. Equa-
lionof the 1370 deal rods and of the 1370 glafs rods, with the difference over-rated in
the total expanfion of the deal rods, p. 459. Conjecture concerning the caufe of the
eftimated and real expanfion of the deal rods, ibid. p. 460. Defcription of the mi-
crofcopic pyrometer, ufed for determining by experiment the expanfion of the metals
concerned in the meafurement of the bafe, tab. XX. p. 461 — 472. The microfcopic
pyrometer (tab. XX.) defcribed, p. 462 — 472. Ufe and defcription of the fixed
microfcope, p. 466. Ditto of the micrometer, p. 467. Ufe of two eye glaiTes ia
microfcopes, p, 468. Scale of the pyrometer explained, p. 469. Account of the
experiments with the pyrometer, p. 472 — 476. Ultimate determination of the bafe
on HounUow-Heath, p. 476 — 478. General table of the bafe, fhewing the relative
heights of the llations above the fouth-eall extremity near Hampton Poor-houfe, the
leduftion of the hypothcnufes, and the correilion for the temperature of the glafs
rods, whereby the true length is obtained in the heat of 62 degrees, p. 479. Table
of the expanfion of metals, deduced from experiments made with the microfcopic
pyrometer in 1785, p. 480.

BlaS, Mr. See Specific Gravities,

Bnuguer. See Specijic Graviiies.

Breedo7i, Leicefteriliire, obfervations on the lime-mountain there, p. 4.

Brook.^ Mr. See Vacuum.

Bruce, Robert, M. D. See Avtrrhoa Caramhla,

Burning Mountains. See Morne Garou^ Caribbce IJIands*

C. Cahknvoodj

[ 497 ]
c.

CaUcriuootl^ Col, Sec Bafc.

Ca'ibhee Ijlandi^ realbns for fjppofing a commuuicat'icn bctvyeen the burning mount;iln«
in them and the volcanos on the high mountains in An-iCrica, p. 30. bhotks of
earthquakes tiequent near them, ibid.
Cavend:Jh^ Henry, Efq. See jiir.

Cowhujlion^ Obfervations and Experiments on the Liglit of Bodies In a State of, by the
Rev. Mr. Morgan, p. 190. Dara to be attended to, iuid. Concluiion drawn from
them, ibid. Manner in which the rays of light efcape, when decompofed by heat,
p. 191. Observations on the flame of a candle, p. ig». The beft mode of fhewing the
efcape of fome rays by that degree q\ heat which will not fcparate others till incfeafed
p. 193. Mr. Melvill's mode of examitiing bodies whilll on Hre, ibid. Befides the
incrcafe or decreafe of heat, there are other modes ot retarding or accelerating the
combuftion of bodies, p% 194. Singularities in the colours of different flames ac-
counted for, p. 19;. Singular pha;nomenon attending a burning body explained,
p. 196. Imperfedtion in Sir Ifaac Newton's definition of flame, p. 197. Exoeri-
ments on ele6tric li^ht, p. 198 — 206. General deductions ufeful in procuring any
degree of cer rain ty in any hypothefis, p. 198. Obfervations on phofphoric light, p.
208. Mr. Wilfon's theory of the flow combuftion of fliells, ibid. Objedions to
that theory, p. 209 — 211. Poflfcript by Dr. Price, p. 21/.
'ConJlru£lion of the Heavens , on the, by William Herfchel, Efq. p. 213. Two oppofite
extremes to be avoided, 5^ we hope to make any progrefs in an inveftigation of this
delicate nature, ibid. Ti.eoretical view of the univerfe, p. 214. Formation of
nebulae, ibid. Objeftlons confidered, p. 216. Optical appearances confidered, p.
ai7 — 219. Refult of obfervations, p. 219. The theoretical viexv of the univerfe,
p. 214. Shewn to be perfeftly confident with facts, p. 220. I. Table of ftar-gages,
p. 221-^240. Problem, the ftars being fuppofed to be nearly fcattered, and their
number, in a field of view of a known angular diameter bfcing given, to determine
the length of the vifual ray, p. 241-. The fame otherwife, p. 243. We inhabit the
planet of a ftar belonging to a compound nebula of the third form, p. 244. DiiFerence
between a crowd and a duller of ftars, ^p. 246. Ufe of the gage*, p. 250. Table
II. p. 252. Seftion of our fidereal fyftem, p. 253. The origin of nebulous ftrata*
p. 254. An opening in the heavens defcribed, p. 256. Phenomena at the poles of
our nebula, p. 257. Enumeration of very compound nebulae or milky ways, p. 2580
Some very remarkable nebulas pointed out, ibid. Several extended nebulae defcribed,
p. 260 — 262. A perforated nebula or ring of »ftar9, p, 263, Planetary nebulae, p°
363 — 266.

Vol. LXXV. U u tt D, D'AUmbm^

[ 498 ]

D' Ahmlert. See Rotatory Motion.

Darivm^ Dr. Eral'mus. See Artificial Spring,

Deal Rods, table of the expanfion of, with obfervations, p. 437. Are improper for
very accurate meafurement, p. 438.

De la Lamh. See JVires.

De l.ucy Mr. See Specific Gravities,

Double Stars. Catalogue of, by William Herfchel, Efq. p. 40. Method of pointing
out thofe ftars in this colleftion which are not in Mr. Flamftead's Catalogue, p. 41.
and of applying it, ibid. Precaution to be obferved where other ftars are very near
rhofe to be pointed out, p. 42. The obferver (hould be furnifhed with Flamftead's
Coeleltia! Atlas, which muft have the ftars marked from the author's Catalogue, p. 45.
Precaution in relation to examining the clofeft of the double ftars, ibid. All the
obfervations in this Catalogue are fuppofed to be made with a power of 460, unlefs
marked otherwifc, p. 45. Method of taking the meafures of the diftances, ibid.
S^c Micrometer. Catalogue of double ftars, p. 47. Firft clafs, ibid. — p. 65. Second
clafs, p. 65 — 78. Third clafs, p. 78 — 90. Fourth clafs, p. 91 — 105. Fifth clafs,
p. 105 — 118. Sixth clafs, p. 118 — 126. Additional errata to the Catalogue of
Double Stars in vol. LXXII. p. 126. See Variable Star.

JR-agUfione, See Router.

Earthquakes. See Caribbee I/lands.

Eclipfies. See Afironomical Qb/er^uaiions,

Equatorial Micrometer, Mr. Smeaton's recomnacnded, p. 34S.

Euler^ M. Leonhard. See Rotatory Motion,

M. John Albert. See Ditto,

Xxpajfibility, obfervation on that of glafs, with Mr. Cumming's pyrometer, p. 431;
See Dtai Rods,

F

Tergufon. See FriHion.

Fixed Air and F'^r/sr appear to confift of the fame ingredients, p. 296. Set Air,
Fordyce^ George, M. D. See iVeight.

Fridlion^ on the Motion of Bodies afFefted by, by the Rev. Samuel Vince, A. M. of
Cambridge, p. j6_j. This Ijranch of natural philofophy, nothwithftanding its im-
portance

C 499 ]

portance to the practical mechanic, has been, of all others, the mod neglct'Ved, ibicJ,
Muflchenbroeck's, Helfham's, and Fergufon's opinions of the law by which the
motions of bodies are retarded by fridtion, p. i66. Euler's theory not true, ibid.
Experiments to determine different properties of friftion, ibid. p. 167. The fridioa
of hard bodies in motion is a uniformly retarding force, p. i6g. Experiments to deter-
mine whether fridion, ca^teris paribus^ varies in proportion to the weight or preflure,
p. 170 — 172. Obfeivations thereon, ibid. Experiments proving that the fridion
of a body does net continue the fame when it has different furtaces applied to the plane
on which it moves, but that the fniallefi fiirface will have "the leatt friftion, p. 170 —
175. Refult of the author's examination into the nature of the experiments whicb
have been made by others, p. 176. Theory eflabiifhea upon the principles already
deduced, p. 178. Prop. I. to find the time of defcent and the number of revolutions
of a cylinder, or that circular feftion of a body on which it rolls down an inclined
• plane in confequence of its fridion, ibid. Cor. i. p. 179. Cor. 2. ibid. Cor. 3.
ibid. Cor. 4. p. 180. Cor. 5. ibid. Prop. II. the body being projefted on an hori-
zontal plane, with a given velocity, to determine the fpace through which the bodj'
will move before it flops, or before its motion becomes uniform, p. i8r. Cafe I.
ibid. Cafe II. p. 182. Cafe HI. p. 184. Definition of the centre of fridion, p.
186. Prop. III. to find the centre of fridion, ibid. Prop. IV. given the velocity
with which a body begins to revolve about the centre of its bafe, to determine the
number of revolutions which the body will make before all its motion be dcftroyed,
p. 187. Prop. V. to find the nature of a curve defcribed by any point of a b«d/
afFeded by fridion, when it defcends down any declined plane, p. 188.

G.

Goodrich, John, Efq. See VarlaUe Star,

H.

HaleSy Dr. miflake of his, p. 271.

Hea/, diminiflies the attradions of cohefion, chemiflry, ttiagnetifm, and elcdricity,

p. 364.
Hell, Abbe. See AJlronotnical OL/ervatiofi^,
Hclfoam. Sec FriSlion.

Hcr/chel, William, Efq. See Douhle Sfa' s, ConJlruSlion 0/ the HeaveftJ,
Home, Mr. Kverard. See Marine AniraaL
Hrpe, John, M. D. See A/a Fa-tida.
Hunter, John, Efq. See Marine AnimaU

J u 2

\^ hJlM^,

[ 5^0 3

I.

Jiilh':^, in Lancaihirf, maancr of digging for water there, p. 6..

K.

Kiriuany Richard, Eft]. ^&z Specific Gravitiei*

L.

Latx^efiy Mr. John. See Rotatory Motion.

Larkell river, has not the property of incrurtation, p. 354.

Lavotfigr, M. See Air and Water,

Leach, has no anus, p. 341.

X« luvre. See Afirenomical Ohfervations,

Lightfcotf Rev. John. See MotaciUa,^

M..

I^achinety in Pe'ffe^i've, See ArchiieHure,

Marine Ammai, Dcfcription of a new one, in a Letter from Mr. Everard Home, Sur»>
geon, to John Hunger, Efq. ; with a Poftfcript by Mr. Hunfer, containing anatomi-v.
cal Remarks upon ihe fame, p. 333, Reafons for believing this animal to be a non--
ceicripr, ihid. Where and when found, p. 334. See Barbadoes. By whom firft-
obfervcd, p. 335. Defcription of, ibid.-^33g. Poftfciipc, by John Hunter, Efq,
p. 340 — ^343. See Animals. Anatomical divlfioa of the animal, p. 340. Its
Ilomach and inteftipe dekribed, p. 341. Differs materially from moft animals with
tentacula, ibid. See Leach, Polypi, Univahe Fijh, Manner of voiding its cx-
creaients, p. 342. Enquiry into the manner of incrcafi,ng its (hell, ibid. Where
snofl^ probable to be found, p. 343, Explanation of the figures, tab. XI. fig. i. p»,
344. Fig. 2. ibid.

Melvill, Mr. St&Comhuftjon,

MiJJier, M. See Ajlreno7nkal Ohfervations.

Meteors, arc probably owing to an accumulation of elecTtricity, p» 278,

Micrometer, improvement in Mcff. Nairne and Blum's, p. 46. See Baje,

Microfcipe. Sec BaJe.

Morgan, Rev. Mr. See Comhuftion,.

«— — — Mr. William. See Vacuum,

Morne Garou, a Mountain in the Ifland of St. Vincent, Account of, with a DcrcriptloB
of the Volcano on its fummit, in a Letter from Mr. James Anderfon, Surgeon, p»,
lit. Difficulties in exploring the interior parts of the. mountain, ibid. Wkich has
i- alf«.

[ 5<^J ]

alfo been mentlonecl to have had volcanic eruptions from it, ibid. Of wHicH, o»
examination, fevcral iiidicarions appeared, p. 17. The authoi's friendly reception
at Mr. Maloune's (where he lay) about a mile from the mountain, ibid. Arrives at
the bottom of the mountain, aitecded by two negroes of Mr. Maloune's and a boy,
p. 18. After climbing a rock, forty feet high, they come to fome clear ground,
belonging to a Mr. Gafco, ibid. Who receivss them kindly,, p. 19. Sec W(/i Indies.
Return to Mi Gafco's, being unable to get forward, p. 20. Defcripiion and fituatioa
of his hut, ibid. DifHcuhies Mr. Andcrfon encountered in his feco«d attempt, p. 21.
Arrives at the bottom of a very high precipice, ibid. His dangerous fituation on
gaining the top, p. 22. Meets four negroes from Mr. Maloune's, with provifions,
p. 23. Difcovers a ravin by which he might have gained the fummit of the moun-
tain with httle difHcuIty, ibid. After a moft difagreeable night on the mountain, gets a
fight of the fummit, p. 25, With a defcription of ir, ibid. Two negroes leaving
hira, and the reft le fifing to proceed, he is forced to rsturn, p. 25, 26. Sets out
again, accompanied by Mr. Frafer, and attended by two negroes, p. 26. Finds
fome beautiful plants and mofs (of which he faw none elf« in the Weft Indies) ia
great abund;mce, ibid. Gains the fummit, with a defcription of the awful ap-
pearance of the ex.:avation there, p. 27. 29. Burning mountain at the bottom
thereof defcrlbed, p. 27. Various minerals found on all parts of the mountain, p.
28 Author's realbns for fuppofing it has but lately begun to burn, ibid. Two
cha'ybcaie lakes on the fides of the crater, and a conje£^ure on the manner of their
being fupplied, ibid. Singular- motioB- of the clouds on the mountain, p, 29. Sec
Caribbee IJlands, Reftfcnces to the figure, p 31.

Moiacilla, Account of an Engtilh Bird of that Genus, fuppofed to be hitherto unnoticed
b) Britifl-. Ornithologills, obfervtd by the Rev. John Lightfoot, p. 8. Generic cha-
raders, ibid, Marks evincing it to be of the fprcics of Vjotacilla, p. 10, ii.
Named aher the Linnsan manner, p. 11. Sepp the only author who can be fuf-
pe^ed of noticing this bird, p. 12.. Which may not i npioperly be denominatr^ rhe
Reed IVren, ibid.. Ls haunts, ibui. Its toO' I and note, p. 13. Iti neft. i\M, Ma-
terials and fitu'tion of its neit, ibid. Number ana defcuption- oi its eggs,, p. 14,
Conjeftured to be a migrating biid, ibid.

Mountains^ theory of the formation of, p. 4—7... -

li/ljine^ Mr. See Bafe.

N-

Ulevj.England twhite-ivood, S'^e Riga red-iuood,
Nenvton^ Sir Ifaac. See ComhuPAon,

Nitre, when much phlogifticated, ia capable of mitkijig a preclpiute with a' foliuioa-
©f filvcr, p. 37^,

Fo Peacack^

p.

Teacock^ Mr. James. ?)Ct,/4rchite^ure, &c.

Phlogifiicatcd Air^ whether many different fubflancci are not in rctlity confounded toge-
ther under this name, p. 381.
PhlogiJIon. See Ah:
Phofphoric Light, See CombuJlloH,
Pigott, Edward, Efq. See Fariahle Starsr
Polypus^ has no anus, p. 341.
Price, Dr. See Comhufiion,
Priejlley, Rev. Jofeph. See Air, and Water*
Pringle^ Col. See Bafe,
Pyrometer, See Bafe,

R.

B.ain* See Barometer, &c.

Ramfderty Mr. his curious beam compafles, p. 402. See Bafe, His ca(y and fimple
way •£ obtaining the fcale of his pyrometer, p. 471.

Reed'-xvren, See Motacilla.

Richmond, in Surrey, method of boring for water there, p. 6.

Riga Red-vjotd, more fufceptlble of the eftefts of moillure than New-England white-'
wood, p. 435.

Rotatory Motion. Of the Rotatory Motion of a Body of any Form whatever, revolving,
without Rellraint, about any Axis palfing through its Center of Gravity, by Mr.
John Landen, p. 311. When the axis, about which a body is made to revolve, is not
a permanent one, the centrifugal force of its particles will didurb its rotatory motion,
&c. p. 312. To determine in what track, and at what rate, the poles of fuch mo-
mentary axis will be varied, not an uninterefting proportion, ibid. The folutions
of that problem by M. Leonhard Euler, M. D'Alembert, and M. John Albert Euler,
reftified by the author, ibid. Difference between him and the above gentlemen con-
cerning the angular velocity and the momentum of rotation, p. 313. How to find a
parallelopipedon that being by fome force or forces made to revolve about an axis,
with a certain angular velocity, fhall move exadly in the fame manner as any other
given body, if made to revolve with the fame force, about an axis paffing through
its centre of gravity, p. 315. Tab. X. fig. i. explained, ibid. Method of finding
how a parallelopipedon will revolve about fuccefTive momentary axes pafTing through
its center of gravity, p. 318. Fig. 2. and 3. explained, p. 318. 322. Fig. 4. ditto,
p. 321. Fig. 5. ditto, ibid. Errors of M. Euler pjiuted our, p. 327, 328. To
which M. D'Alembert's feem nearly fimilar, p. 328.

6 Rtuitr^

[ 5^3 ]

Itouiert or Eagle-flone mountain in the Peak, its volcanic origin, p. ^.
Jioj/f Major General William. See Ba/e,

S.

Schoems Lhbofpermos, a fpecies of grafs In the Weft Indies, p. 19.

Senjiti've Plant. See Averrhoa Carambola.

Sepp, See Motacilla.

Shells. See Comhujlion.

Smeaton, Mr. See Equatorial Micrometer^ Bafe.

Specific Gravities, Remarks on, taken at different Degrees ©f Heat, and an ea/y Method
of reducing them to a common Standard, by Richard Kirwan, Efq. p. 267. Ufcful-
jiefs of a comparative view oi the weights of equal volumes of water, &c. ibid. A
capital advantage derivable from a table of fpecific graviiies, ibid. Inilrument for
making experiments defcribed, p. 268. Table of fpecific gravities, p. 269. Re-
marks and obfervations by Bouguer, Mr. Bladh, Mr. De Luc, &c. p. 270. Advan-
tages of this method pointed out, p. 271.

Sui£i Head and Horns, Account of, found at Alport, in the Parifh of Youlgreave, ia
the County of Derby. In a Letter from the Rev, Robert Barker, B. D. p. 353.
Place and manner of difcovering them, ibid. Not fuppofed to belong to a very old
animal, p. J54. Are of the throftel-neft fpecies, ibid. SctThroJicl-jteJi Herns. Con-
jedure how they were depofited where found, ibid. See Larkell. Dimenfions of the
horns found at Alport, p. 355. Ditto of a large pair of throftel-nefts horns, ibid.
Ditto of the horns of a feven-years old flag, ibid.

Summation of hfinite Series, Supplement to the Third Part of the Paper on, in 1782, by
the Rev. S, Vince, M. A, p. 32.

Sylvabelkt M. Saint Jacques. See AJironomical Oh/ervations.

T.

Telejcopes. See AJironomical Obfervations ^ Wires*

Tentacula, animals with tentacula confift of an almofl infinite variety, p. 343.

Terehella, a double-coned one, found by Mr. Cordiiier, at Bamff, in Scotland, p. 343.

thermometer. See Barometer, &c,

^hrojlle-nejl Horns, defcribed, p. 354.

Tvfty a kind of ilone, defcribed, p. 353;

U.

Vacuum, Ele»arical Experiments made In order to afcertain the non-condu£Kng Power of
a perfca one, &c, by Mr, William Morgan, p. ^-jz^ Conclufion drawn from Mr.

Wallh's

[ 5^4 ]

\Varfii''s experiments in the d«uble barometer tube, not unlverfally ailmltfed, ibid-.
Account of the author's experiments to determine its truth or fallacy, ibid. Tab. IXi
fig, I. explained, ibid. Account of various eledrical experiments, p. 274. 276,
Mr. Brook's method of making mercurial gages, p. 276, 277. Sec Meteors.

Variable Star, Obfcrvations on a new one, in a Letter from Edward Pigott, El'q. p. 127.
Ufe of verifying (lars fuppofed to be variable, ibid. Variation ot the liar u Antiiioi
very fimilar to that of Algol, though not exaiStly the fame in any particular, ibid.
Changes undergone by n Antinoi, p. 128. Order ot the liars to which it was com-
pared, ibid. Greater difference between the biightnefs of many liars in t.silight and
moon-light, or the lealt hazy air, than in a dark and clear fky, ibid. Journal of ob-
fervationi of n Antinoi, p. 129. Natural method ot obtaining a point of compa-
rifon fur fettling irs penodical changes, p. 131. Com^.utations (the rough length of
a fingle period being found;) to obtain greater exaclnels, p. 132. iMethod of deter-
mining the time whenn Antinoi was between its lead and greatelt brightnefs, ibid.
Obfert'ations on its decreafing brightnefs in 1,783 compared with correfpondino- ones
ma«Jc in 17S4, p. 134.. Refults of thofe comparifons, ibid. Account of feveral
attempts to determine the relative brightnefs of ftars, p. 135, 136.

«— — Obfervations oti a new one, byJoh-H Goodricke, Efq. p. 153, The ftar )S Lyras
difcovered to be variable, ibid. Eight points of its variation in twelve days and
nineteen hours, p. Ijf4, Its relative brightnefs at its obfcuration in the third and
feventh points, ibid. p. 161. Magnitudes of the ftars to which it was compared
during the progrefs of its variation, p. 15^. Series of obfervations of its brightnefs
and magnitude, ibid. Obfervations thereon, p. 161. Calculation of the times of the
middle of its obfcuration in the third point, p. 162. Remarks thereon, ibid. Mr,
Herfchel reckons $ or y Lyrae amongft thofe liars which he fuppofes to have under*
gone an alteration, p. 163.

VincBy Rev, Samuel, M. A. See Summation of hifimte Series^ FriBl0n„

t/»/Ww Fi/^, their internal formation, p. 342. ^

J^alloty M. See Afironomkal OlftTi'aiiom,

ITalfhy Mr, Sec Vacuum.

Watty Mr. See Air and fFater.

Weighty An Account of fome Experiments on the Lofs of, in Bodies on being melted or
heated. By George Fordyce, M. D. p. 361. Several experiments made by the
Dodtor, which not being contradiftory, are not worth laying before the Society, ibid*
Account of a conclufive one in determining the lofs of weight in ice when thawed,
and on being heated, ibid. p. 363. Conjedures of the caufe of the acquifition of
weight on water's being converted into ice, p. 363. Method to determine which w
true, ibid. Experiment to afcenain whether there is matter abfolutely light, or which

repeli

[ s^s 1

?fpe!$ inllcad of attra»5lmg other matter, p. 364. See Heat. Conje(5lure on the
increafe of the weight of ice on being cooled, ibid.

TFe^ hiXeSf difficulty of going through the woods there, p. 19,

Wil/oTtj Mr. See Combujiion.

IVireSf A Defcripiion of a new Syflem of, in the Focus of a Telefcope, for obferving
the comparative Right Afcenfions and Declinations of coeleflial ObjciSts j together
with a Method of i«veftigating the fame, when obferved by the Rhombus, thojgh it
happen not to be in an equatorial Pofuion, by the Rev. Francis WoUifton, LL.B»
p. 346. The author twice difappoimed in attempting ro afcertain the right afcenfions
and declinations of the ftars he had laid down, p. 346, 347. The rhombus is very good
in theory, but feldom true enough to be depended on, p^ 347. A very fmall error in
©bferving the paffage of a flar naakes a very material -difference in the refult, ibid.
Trial with a fquare placed angularly, which feems to anfwer better, ibid. See,£,jua-
ierial Micromeitr, Tab. XII. fig. i. explained, p. 347. Properties and advantages of
the fquare preferably to the rhombus, p. 348. Method of redlifying the erroneous
pofition of the inftrument by the formula given by M. De la Lande in his Aflro-
aomy, p. 349, Formula conftruded by the author's fon, for inveftigating the com-
parative right afcenfions and declinations of ftars, ibid. Application of the formulae,
p. 551. How to deduce the angle of deviation from the true equatorial pofition ia
the new fyflem of wires, p. 352.

WoUaften, Rev. Francis, LL.B. Se© Wires,

Z.

^ii', Francis de. See Aflronomkal Oh/ervationu

FROM THE PRESS OF J. NICHOLS,

Vol. LXXV, X x »

jR jR. 3X A X Aa

VOL. LXXIE, PART I.

Wage, Line*
18, 19. far lOat as I to 4 read was as i to ^„

VOL. LXXV, PART L

•83. 50. for amazing read amufing

a8^, 22. ^r on rf#^ in

396. 1 4» j^r in rW on

301. 17. j^r air r^aiair* '

309, 3^. ftr feems »*«</ fecm

VOL. LXXV. PART Ih
^iQ» 4. ^parailel<>pIdrM^paraIIeIopip(cl9

-vV^f

i

( >