ORRERY. 
by intermediate wheels to anfwer this purpofe in the beft 
way that could be devifed, than that {uch complex data, as 
ain y an 
cefs, other than a affumption o 
make them an{wer by fubfidiary additions ; 
which Brean" ace accounts pretty well for the great 
number of aie uence which form no part of - 
calculation, and a 
ftrength, 
the fun’s rotation to be performed in exatly 25 Poe a 
73 
12 
mechanifm for carrying round the lamp, viz. ees of 
25 would in that cafe give a revolution in exaCtly 365 days ; 
which, therefore, moft likely, was the period intended ; in- 
deed fuch a concurrence of four whole periods without a 
fraGtion, under fucha sioael of circumftances, puts the 
matter mot beyond a 
erb orrery at Ric 
Wright, mathematical in ftrument-maker 
ma George II. in the year 1733; it was our 
intention to have analyfed the wheelwork, fo as to have 
ae a particular account of each train, but when 
verin were taken off, we fo a that the time 
pieces for — 
nus, appeared to be 
undon 
diurnal and annual wheels of the earth as accurately as we 
could, fince the other periods take the earth’s motion as the 
flandard of hase time. At the firft peep into the interior 
ut man 
Beyend the 
orbit of Venus there are nine large concentric rings indented, 
revolving round rollers placed on ftuds on the bottom of the 
machine, and regularly increafing in diameter till the ninth, 
or laft, which is a fixed one, nearly filling ae idea within 
the furrounding ecliptic, which within is 42 es in oi 
andle enters the fide of the ornamented c 
rings, but b aving three different contrate 
wheels faft to it in fight, and being conneGted with feveral 
Pinions, in a way not feen; fome of which are fupported under 
the bottom plate by a fliding ba bar, that brings them into or 
a pinion of 9, appearing to revolve, by means of the con- 
cealed mechanif{m, in 172 days, or turns of the handle, ace 
tuated, when forced boned into ation, the third ring of 560 
teeth; the period correfponding to which numbers is = 
of 172 days = 10702.2. This Il by we can hardly fup- 
pofe to be the exact one intended by the maker of the 
tified will be 10746.8 days, nearly as in nature: this rin 
carries the ball of Saturn, ona ftem conne ith i 
diftance of 17.5 inches from the fun. ain, a pinion of 
, on the concealed fliding bar, drives the fifth ring of 480 
teeth in apparently 72 days; but the correfponding period 
ae of 72 = 4320, is too little = 10.6 days: we mutt, 
10 in a5 of 19 ae apparently, or in 693.5 days, the planet 
being at 104 inches from the fun ; but this is too inaccurate 
alfo, therefore fubftitute 18.82 days for the period of the 
pinion, and the retified period will be 395 of 18.82, or 
686.93 days, pretty nearly the truth. Thus have we been 
able to afcertain the values of the concealed wheels, which may 
be reprefented very eafily by wheels of common numbers, 
deriving their motions firft from the horizontal diurnal arbor, 
and then from one another, from the quickeft to the floweft 
movers in fucceffion. 
ich - pinion revolves was afcertain to be 20 
ays, fo that e f wheel eat a an 
revolution of the “handle, = nee as we fha ll foon fee, a ‘folar 
day: on this wheel the annual arm is fu append. and. like. 
wife the mechanifm for the feeelaous of the Sun, Mercury, 
and Venus, as before defcribed, but their periods will not 
6 exactly the fame, becaufe — the year confifts of only 
365 days; whereas in the {maller inftrument it had 3654 as 
the ftandard peried. We will return to the diurnal motion, 
when we fave defcribed the remaining indented rings: the 
which we have faid is _ fix ed faft, is ufed for preferving 
which feveral 
horizontal diurnal arbor, which has thirty teeth; but a 
wheels for producing the periods of the five fatellites of 
aturn (the a 
arab te 
importance in 
ions, 
