113 
II O R O 
dulum-rods. The wood called fapadillo is faid to be Hill 
better. There is good reafon to believe, that the previous 
baking, varnifhing, gilding, or foaking of thefe woods in 
any melted matter, only tends to impair the property that 
renders them valuable. They fliould be limply rubbed on 
the outfide with wax and a cloth. In pendulums of this 
conftruflion the error is greatly diminilhed, but not taken 
away. 
Rater's Pendulum. This is a compenfation-pendulum 
defcribed by lieutenant Kater in Nicholfon’s Philofophical 
Journal, vol. xx. p. 214.—The principal novelty in this 
pendulum is, that, inftead of the various expanlions ot 
different metals being made to compenfate each other, as 
in other pendulums of this defcription, in it the expanlson 
of a deal rod is compenfated by that of a zink tube or 
frame, about ten inches long. 
Two methods of applying the zink are defcribed : In 
the firft it is call into the form of a frame, ten inches high, 
two inches broad at the bottom, and one inch at the top, 
which is fcrewed to the cock of the time-piece in a ver¬ 
tical pofition. In the top of this frame, to regulate its 
length, a thick fcrew of zink, with a fine fpiral, is inferted 
vertically, through a brafs plate half an inch thick, loi¬ 
tered to the frame and tapped to receive it, which has 
about a quarter of an inch of its top filed fquare, to admit 
an inftrument being applied to turn it; this zink lcrew 
has a hole drilled through it lengthways, through which 
a fteel wire-fcrew pafl'es freely from the fufpending fpring 
of the pendulum, and is fecured by a moveable nut rett¬ 
ing on the top of the zink fcrew. The fufpending fpring 
palfes through a flit in a brafs plate on which the zink 
frame refts, and through a hole in the bottom of this 
frame, and is faftened to a flit in the lower end of the 
ffeel wire by a trani'verfe pin. The fteel-wire lcrew regu¬ 
lates the length of the pendulum, as the zink fcrew does 
that of the zink compenfation : a thin nut of brafs is added 
to this latter fcrew above the zink frame, to fix it more 
fteadily at the defired height. 
In the fecond method of applying the zink compenfa- 
tion, a fquare tube of zink, feven inches long, three quar¬ 
ters of an inch in diameter outfide, and four-tenths of an 
inch infide, fnrrounds the lower end of the deal rod of the 
pendulum, to the extremity of which it is connected by 
a zink fcrew and fteel fcrew, for the fame purpofes of re¬ 
gulation as in the firft method, but in a reverfed pofition. 
The zink fcrew has a fmall oftagonal plate of brafs lol- 
dered at its lower end to prevent injury from the nut of 
the fteel lcrew on which it refts, and to form a.fort of in¬ 
dex for dividing each revolution of the fcrew, and of the 
nut, into eight parts. The zink tube, which riies tip- 
wards from the nut, pafl'es freely into the centre of the 
weight or bob of the pendulum, through a hole made fo 
as to let it Hide as it expands, but clofe enough to pre¬ 
vent a {hake ; at its upper end it is faftened to the centre 
of the bob by means of two grooves cut in its fides; cor- 
refponding to which two fimilar grooves are made in the 
fides of the perforation of the bob, into the cavity formed 
by which melted lead is poured, after which the external 
plates of the bob are faftened together. 
The pendulum-rod, for both methods, is made of white 
deal, three quarters of an inch broad, and four-tenths of 
an inch tfiick, well-feafoned, ftraight-grained, and per¬ 
fectly free from knots, baked in an oven till its outward 
furface became a little charred, then cleaned and coated 
leveral times with copal varnifh, and having its ends 
dipped in melted fealing-wax, to exclude all moilture, 
which it is of the greateft importance to the perfection of 
the rod to repel perfectly. A cut is made at the top of 
the rod by a fine faw, to receive the end of the fufpending 
fpring, where it is fecured by two or three fmall pins 
palling through both. When the fecond mode of apply¬ 
ing the zink is ufed, the lower end of the deal rod is cut 
at the fides fo as to Aide freely in the zink tube, and at 
its extremity a brafs cap is faftened, from the bottom of 
which proceeds the deal fcrew, before defcribed, by which 
the zink tube and the bob are fuftained. 
Wol.X. No. 663. 
L 0 G Y. 
The deal rod was found by experiments with a pyro¬ 
meter to expand in one foot o'oo+g pafts of an inch with 
180 0 difference of temperature ; theexpanlion of zink Mr. 
Kater computes to be to that of deal as 353 to 49, and to 
that of fteel as 353 to 147. And reckoning the fteel fcrew 
to be 12-5 inches long, the fteel fulpending-fpring 3 
inches, and the deal rod 37 inches long, in the firft me¬ 
thod, he calculates that the proper length of the zink to 
compenfate the expanfions of thele leveral parts fliould be 
10-3 inches: and in the fecond method, reckoning the 
part of the fteel fcrew included between the nut and the 
end of the rod to be two inches long, the fufpending fteel 
fpring to be one inch long, and the deal rod to be 44'5 
inches long, lie computes that the zink compenfation 
fliould be 7’42 inches long. 
Mr. Kater attaches a fmall weight below the bob, 
when he willies to regulate the pendulum to the greateft 
nicety in the fecond method ; which he thinks would be 
fuperior to the firft, in being more Ample and having the 
compenfation fhorter, if the zink tube in it was not ex¬ 
cluded from the free contafl of the atmolphere, by being 
included in the bob of the pendulum. But the objection 
to this fecond method might perhaps be obviated by leav¬ 
ing an open paflage for the air in the lead of the bob 
round the zink tube, and preferving the fteadinefs of its 
motion by blunt points, or other fmall fniooth furfaces, 
or by fmall friftion-vvheels, projefting from the fides of 
the aperture. 
It would moreover tend much to complete information 
on this fubjefl, if the eartheiiware rods for pendulums, 
propofed by Mr. Troughton, were tried in the fame ac¬ 
curate manner in which the deal rods have been by lieut. 
Kater. The principle on which Mr. Troughton recom¬ 
mended rods of pottery was, the permanent contraction 
obferved in this Jubilance by Mr. Wedgewood at a given 
temperature. Rods of pottery would have the advantage 
of rods of deal in not being liable to be attested by damp. 
Of the BALANCE. 
The balance is the regulator of portable time-pieces, or 
watches, as the pendulum is of fixed machines, or clocks. 
The balance is a circular body, concentric with its axis, 
and perfectly in equilibrium in every pofition. The ex¬ 
tremities of the axis terminate in pivots, which, by mov¬ 
ing in holes of a convenient fize, facilitate the motion of 
the balance. The pendulum vibrates by means of a 
weight; the balance by the effeCt of a very elaltic fpiral 
fpring, the inner coil of which is pinned to a collar juft 
beneath the balance itfelf; and the outer coil of the fpi¬ 
ral is pinned to a perforated piece, or ftud, fixed on the 
upper plate. 
It appears from the teftimony of hiftorical accounts, as 
well as ether evidences, that the balance was univerfally 
adopted in the confirmation of the firft clocks and watches; 
nor was it till the year 1657, that Mr. Huygens united 
pendulums with clock-work. In watches of early con- 
ftru&ion, the balance vibrated merely by the impulfes of 
the wheels, without any other control or regulation; the 
motion communicated to the balance by one impulfe con¬ 
tinued till it was deftroyed, partly by friftion, and partly 
by a fucceeding impulfe in the oppofite direction; and 
therefore the vibrations mull, of courfe, have been very 
unfteady and irregular. Thefe imperfections were in a 
great meafure remedied by Dr. Hooke’s ingenious inven¬ 
tion of applying a fpiral fpring to the balance, the action 
of which on the balance of a watch is fimilar to that of 
gravity on a pendulum ; each kind of force having the 
effeft of correcting the irregularities of impulfe and refin¬ 
ance which otherwife difturb the ifochronifm of the vibra¬ 
tions. In clocks and watches, the real meafure of time is 
the balance, and all the other work ferves merely to con¬ 
tinue the motion of the balance, and to indicate the time 
as meafured by its vibrations. 
The balance, being once fet in motion, would continue 
to ol'cillate for ever, if the refilla'nce- of the air, and the 
friCtion of the pivots in their holes, were not by little and 
ft L little 
