ORRERY. 
tables themfelves for finding the places, as given i 
Nautical Almanac, and White’s Ephemeris, without the 
affiftance of thofe helps. The end of the annual arm is pro- 
longed acrofs this circular plate, and receives an index piece, 
, in the form of a cock, that carries a filken thread ftretched 
long enough to reach over all the divided circles, as well as =m 
e 
the fpiral, which thread at once indicates the day of the month 
in leap year, or any of the three following years, the fun’s mean 
place in the ecliptic, and the correfponding equation, additive 
or fubftraGtive, as the cafe may require. 
this plate the contrate wheel of 62 for the earih’s parallelifm 
is {crewed faft, and is thus attached to the fixed tube. 
i found convenient to make the earth’s diftanc 
d 
e to be afcertain far as Mars, inclufive, the pro- 
portional diftances are preferved ; but beyond Mars certain 
proportional parts were neceffarily adopted, inftead of t 
whole diftan ic turn would have been 73 inches, 
and in Georgian 1 e following table contains the 
in : 
{cale of diftances which appeared to be, on the whole, moft 
defirable to fix upon for the refpeétive lengths of the arms, 
that revolve with the planetary balls in this machine ; and 
thofe of Saturn and Georgian are made of tubes that flide 
within one another for the fake of lightnefs, as well as o 
cking. 
Table of Diftances from the Sun. 
Mercury 2.89 inches, 
Venus 5°45 
Earth 
Mars 11.45 
Vetta 13-4 viz. % Of 15.3 
Juno 4 of 19.9 
Ceres and 
Pallas each 16.6 4 of 20.7 
19.6 E of 39.2 
aturn 21.9 vs OF 73 
Georgian 24.0 2 of 1 
In order that an exact idea may be formed of the real pro- 
To the under face of 
3 
connected with tht 
geocentric appearances, as well as if the arms had been all 
lengthened into due pro ortion ; for when 
places are afcertained, the upright wires, b 
their centres of motion, will bring the planets into the afcer- 
ton 
tubes afford the means of doing this by turning one within 
another 
We come now to explain the mechanifm conne&ed with, 
and carried by, Jupiter’s arm, which we have feen is 19.6 
inches long: it will be recolleGted that we have traced the 
tran{miffion of motion from the feven days’ arbor to a tube 
of si days, revolving next within Jupiter’s tube: upon the 
upper end of this tube of 54 days, a contrate wheel of 60 
is clamped with the teeth pointing down towards Jupiter’s 
arm, with which it comes in conta is arm is a long 
tube, and admits an arbor of the fame length within it, which, 
confequently, is not feen, except where the arm is difunite 
this long horizontal arbor has a pinion of 8 at each end of it, 
one of which is impelled by the faid wheel of 60, which de- 
fcends through a notch made in the upper fide of the arm or 
tube, till it catches the pinion ; and the other drives a fimi- 
lar wheel of 60 at the remote end of the tube, where a notch is 
Jupiter’s period, it is made to revolve 2, or 7 times in this 
period oftener than it would have done in a fixed pofition. 
Again, the fecond inion of 8, which may be confidered 
5-95 + 5-9493014 $ 
period diminifhed by 5.5 d is the w eC 
wheels’ calculated revolution, to its diminifhed period of a 
revolution: and as a proof of the correcinefs of this ftate- 
ments 
