343 
HOROLOGY. 
which we hardly know which mod: to admire, the fimpli- 
city of the conftruflion, or the complexity of the various 
offices conltantly and mod: correctly performed. 
II. Of WATCHES. 
Watches, flridtly taken, are all fuch movements as 
fhow the parts of time; as clocks are fuch as publiffi it, 
by firiking on a bell, Sec. But commonly the name watch 
is appropriated to fuch as are carried in the pocket ; and 
clock to the large movements, whether they Itrike the hour 
or not. 
The invention of fpring or pocket watches belongs to 
the 18th century. It is true, we find mention made of a 
watch prefented to Charles V. in the hiftory of that prince; 
but this, in all probability, was no more than a kind of 
clock to be fet on a table, feme refemblance whereof we 
have kill remaining in the ancient pieces made before the 
year 1670. There was alio a ltory of a watch having been 
difeovered in Scotland belonging to king Robert Bruce : 
but this has turned out altogether falie. The glory of 
this very ufeful invention lies between Dr. Hooke and 
M. Huygens ; but to which of them it properly belongs, 
has been greatly diiputed; the Engliih ai'eribing it to the 
former, and the French, Dutch, See. to the latter. Mr. 
Derhani; in his Artificial Clock-maker, fays roundly, that 
Dr. Hooke was the inventor ; and adds, that he contrived 
various ways of regulation. One way was with a load- 
Itone. Another with a tender flraight fpring, one end 
whereof played backwards and forwards with the balance; 
fo that the balance was to the fpring as the bob to a pen¬ 
dulum, and the fpring as the rod thereof. A third me¬ 
thod was with two balances, of which there were divers 
forts; fome having a fpiral fpring to the balance for a re¬ 
gulator, and others without. But the way that prevailed, 
and which continues in mode, was with one balance, and 
one fpring running round the upper part of the verge 
thereof; though this lias a difadvantage, which thole with 
two fprings, See. were frge from; in that a fudden jerk, 
or confided ffiake, will alter its vibrations, and put it in 
an unufual hurry. 
The time of thefe inventions was about the year 1658 ; 
as appears, among other evidences, from an infeription 
on one of the double-balance watches prefented to king 
Charles II. viz. “Rob. Hooke inveri. 1658. T. Tompion 
fecit, 1675.” The invention prefently got into reputation, 
both at home and abroad ; and two of them were fent for 
by the dauphin of France. Soor* after this, M. Huygen’s 
watch with a lpiral fpring got abroad, and made a great 
noile in England, as if the longitude could be found by 
it. It is- certain, however, that his invention was later 
than the year 1673, when his book De Horol. Ofcillat. was 
publiffied ; wherein he has not one word of this, though 
he has of feveral other contrivances in the fame way. 
One of thefe the lord Brouncker fent for out of France, 
where Huygens had got a patent for them. This watch 
agreed with Dr. Hooke’s in the application of the fpring 
to the balance; only M. Huygens’s had a longer fpiral- 
fpring, and the pulfes and beats were much flower. The 
balance, inftead of turning quite round, as Dr. Hooke’s, 
turns feveral rounds every vibration. 
Mr. Derham fuggefts, that he has reafon to doubt M.- 
Huygen’s fancy fir-t was fet to work by fome intelligence 
he might have of Dr. Hooke’s invention from Mr. Olden¬ 
burg, or fome other of his correfpondents in England; 
and this, notwithstanding Mr. Oldenburg’s attempt to 
vindicate himfelf in the Philofophical Tran fa <51 ions, ap-. 
pears to be the truth. Huygens invented divers other 
kinds of watches, fome of them without any firing or 
chain at all ; which he called, particularly, pendulum- 
watches. 
Watches, as well as clocks, are compofed of wheels and 
pinions, and a regulator to direct the quicknefs or flovv- 
nefs of the wheels, and of a fpring which Communicates 
motion to the whole machine. But the regulator and 
fpring of a watch are vaflly inferior to the weight and 
pendulum of a clock, neither cf which can be employed 
in watches. In place of a pendulum, therefore, w6 are 
obliged to ufe a balance to regulate the motion of a watch, 
as delineated in the Horology Plate XII. fig;. 76; and a 
fpring, fig. 77, which ferves in place of a weight, to give 
motion to the wheels and balance. 
The wheels of a watch, like thofe of a clock, are placed 
in a frame formed of two plates .and four pillars. In the 
fame Engraving, fig. 78, reprefents the infide of a watch, 
after the plate, fig. 79, is taken off. A is the barrel which 
contains the fpring, fig. 77; the chain is rolled about the 
barrel', with one end of it fixed to the barrel A, fig. 8c, 
and t!ie other to the fufee B. In figures 78 and 80, the 
fame letters denote the fame parts. Now, when the watch 
is wound up, the chain which was upon the barrel winds 
about the fufee, and by this means the fpring is flretched; 
for the interior end of the fpring is fixed by a hook to the 
immoveable axis about which the barrel revolves; the 
exterior end of the fpring is fixed to the infide of the bar¬ 
rel, which turns upon an axis. It is therefore eafy to 
perceive how the fpring extends itfeif, and how its elafti- 
city forces the barrel to turn round, and confequently 
obliges the chain, which is upon the fufee, to unfold and 
turn the fufee ; the motion of the fufee is communicated 
to the wheel C, fig. 80 ; then, by means of the teeth, to 
the pinion c, which carries the wheel D ; then to the pi¬ 
nion d, which carries the wheel E; then to the pinion e, 
which carries the wheel F; then to the pinion f, upon 
which is the balance-wheel G, whofe pivot runs in the 
pieces A, called the potence, and B called a follower, which 
are fixed on the plate, at fig. 79. This plate, of which 
only a part is reprefented, is applied to that of fig. 78, in 
fuch a manner that the pivots of the wheels enter into 
holes made in the plate, at fig. 79. Thefe holes are not 
vifible in the figure, but they have larger orifices fcooped 
out on the back of the plate, in which oil is put to help 
the motion of the wheels. Thus the impreffed force of 
the fpring is communicated to the wheels; and the pinion 
f, being then connefted to the wheel F, obliges it to turn, 
as ffiown in fig. 80. This wheel acts upon the pallets of 
the verge 1, 2, in fig. 76, the axis of which carries the 
balance HH. The pivot I, in the end of the verge, en¬ 
ters into the hole e, in the potence A, fig. 79. In this 
figure the pallets are reprefented ; but the balance is on 
the other fide of the plate, as may be feen in fig. 81. 
The pivot 3 of the balance enters into a hole in the cen¬ 
tre of the cock, B C, fig 82, in which figure alio the dial 
of the regulator is ffiown. The balance turns between 
the cock and the potence e, fig. 79, as in a kind of cage. 
The aftion of the balance-wheel upon the pallets 1, 2, 
fig. 76, is the fame as with regard to the fame wheel in 
the clock; i. e. in a watch, the balance-wheel'obliges the 
balance to vibrate backwards and forwards like a pendu¬ 
lum. At each vibration of the balance a pallet allows a 
tooth of the balance-wheel to efcape; fo that the quicknefs 
of the motion of the wheels is entirely determined by.the 
quicknefs of the vibrations of the balance; and thefe vi¬ 
brations of the balance and motion of the wheels are pro¬ 
duced by the afticn of the fpring. But the quicknefs or 
flownefs of the vibrations of the balance, depend not folely 
upon theaflion of the main fpring, but chiefly upon the ac¬ 
tion of the fpring-a, l>, c, called the balance-fpring, fig. 83, 
fituated under the balance H, and reprefented in ■ perfpe'c- 
tive at fig. 81. The exterior end of the fpiral is fixed by 
the pin a, fig. 83, by means of a flud foldered on the up¬ 
per plate in a, as feen in fig. 8r. The interior end of the 
fpiral is fixed by a pin to the centre of the balance at-if; 
Hence if the balance is turned upon itfeif, the plates re¬ 
maining immoveable, the fpring will extend itlelf, and 
make the balance perform one 'revolution. Now, after 
the fpiral is thus extended, if the balance be left to itfeif, 
the eiafticity of the fpiral will bring back the balanee,. 
and in this manner the alternate vibrations of the balance 
are produced. 
In fig. So, the whole feries of wheels above deferibedj 
1- are 
