ORRERY. 
like that of the common planetarium, and partly of trains 
i m fraGtions ; and retains much of the 
Venus under the bridge, the value of which train is - x 
t of a folar year, or 2249 16% 41™ 535; again to this laft 
wheel on Venus’ tube is made faft the wheel 78 of Mercury’s 
train, which impels its fellow 97 round the annual bar, below 
the loofe pair of Venus, and has 2a wheel of 108 faft to it, 
which again drives the wheel 34 on Mercury’s tube in a x 
34 of Venus’s period, or in 874 23" 14™ 37%. It is of 
10 
importance that the periods of thefe two planets be correct, 
becaufe an error in either of them would accumulate in the 
way that will be explained by and by: it is thus communi- 
o is made faft to the vertical diurnal 
arbor, that impels another of 1oo fixed on the tube that 
volution of Mars, viz. fee the 42 faft on the annual 
‘arbor, and the 79 attached to the tube, the value of which 
fimple fraGtion.of a year is 687° 0° 4™ oF. 
Next to the tube of Mars comes that of Vefta, with 29 
faft on the arbor driving 106 on the tube in 1335% 0" 33™ 3255 
-after that 31 on the arbor drives 135 with the tube of Juno 
round in 15907 13 25; and over thefe wheels a 
common pair, ze carry both Pallas and Ceres round in 
16804 25 44™ 278, by means of the 30, attached to the re- 
volving arbor, impelling the 138 attached to their common 
tube. The pair af wheels which fucceed the new planets 
before Jupiter’s wheels come, are 2s the 70 fixed on the 
; ng motion 
to Jupiter’s moons, in the manner we fhall prefently defcribe. 
Above this tube of 5% days revolves Jupiter’s in “ of a 
year, or in 43307 17" 30™ 18, the 14 on the annual arbor 
giving motion to 166 with the tube upon it, and this is the 
airs. 
The motion of Saturn is derived from Jupiter’s period in 
this manner, like that of Venus from the Earth; the wheel 
of 53 isattached to Jupiter's 166, and revolves with it, driv- 
ing so round the annual arbor loofely, w ile-46 is pinned to 
it, which in its turn drives the wheel 121 made faft to 
Saturn’s tube in the period of 107464 21" 18™ 25%, or 7 x 
3 
ie and laftly, the train of Georgian takes its 
a of Jupiter’s ; 
motion from the tube of Saturn in a fimilar manner; the 
wheel 86 is fixed on the tubed wheel 121 of Saturn, and 
a@tuates the wheels 46 and 28 pinned together round the 
arbor, ufed asa ftem, and the latter of them again urges 
46 149 
86 * 28 
the wheel 149 on Georgian’s tube in of Saturn’s 
period, or in 305898 8" 32” 25°. . 
Thus twenty-eight wheels and pinions are employed to 
give the revolutions of the eleven primary planets, as taken 
from the annual arbor, which wheelwork alone would fuffice 
to make an accurate planetarium by a fimilar application, 
without the other mechanifm. 
fun’s motion on hi 
which: form very interefting portions of the fyftem. We 
have already traced the communication of motion from the 
the other inftrument. 
the letters a 4, is a flat bar of brafs, made firm by an 
i rofs-piece, ¢ d, at 
its remote end, (feen in fig. 4. and partially in Plate VIII.) 
: : 
it is fecured to the upper en 
wheel 85, by which it is carried round in a folar year; but 
, 
the end of the tube of two days’ period, to which it is 
clamped 
