ORRERY. 
In this analyfis of the wheelwork and their powers, it is 
to be underftood that the 83 is the fame wheel in each train, 
through the other fockets, and 85 mea 
of three {mall equal wheels, a proper motion to the aus 
axis. 
he inventor fays that the diurnal motion of the earth, 
and the motions of Jupiter’s fatellites, were not originally 
ies ed to make a par this machinery is, it was 
intended to i“ fimply a planetarium, but it was afterwards 
verted 1 an orr ertained our doubts 
Y: 
whether in this conftruction of the train, that regulates the 
da Ny motion, the earth’s motion on its axis would be uni- 
formly fteady, but in a fecond communication from the au- 
thor we learnt, that ** by accurately proportioning the fizes of 
the wheels and pinions, and ufing high numbers in this train, 
the {mall globe is made to revolve with regularity, and with- 
out any inconvenient friction or vali on the teeth.” For 
the moon’s phafes there is, moreov a fucceffion of three 
ae wheels, the firft made faft toa cera focket in the ufual 
or the motions of Jupiter and his moons the following 
fancinee is ufed. n the lower end of the {quare - 
andle. By thefe means the faid {quare axis will move round 
by the train 95 72 210, 29 ae = x = = x 
g 10 72° 183 * 783 ay 
= 7 22.» or 7.21918 days coming dire&tly from a handle , 
183 
but the pinion of 10 teeth is carried by Jupiter’s arm 
or 18.3 revolutions pegeblodey in each period of J yaa each 
of whic o 7.21918 days; therefore, the whole 
14 
fatellites. ‘The motion of the arbor of the pinion 10 is tranf- 
mitted to the common arbor of the drivers by the train 2 
66 * 
cl = 79? or unity ; therefore the common vertical arbor 
12 792 
turns in the fame time as the one at the interior end, an 
ated, 
he wheelwork of the four fatellites of Jupiter, as well 
as of his diurnal motion, are thefe, with their annexed values, 
Die 
D H M. Sz. 
Jupiter’s wheels of 6.99892 @ 9 57 52 
ea 21 , 
I. Satellite 9 of ditto 1 16 32 43 
33 
2. Ditto & of 6.99892 3 13 16 44 
3. Ditto z of ditto 7 4 a1 1 
4. Ditto 19 of ditto 16 18 7 411 
Of thefe numbers it may be obferved that they are not 
fo accurate as Roemer’s, which take their motions from a 
period of feven days, which is very nearly alfo the period 
of the common arbor in this inftrument that contains the 
drivers. 
The new Orrery fer equated Motions in three Parts, ty fe 
Rev. W. Pearfon.—After the planetarium, conftruéted at 
Royal Inititution, had been finithed under Mr. Pearfon’ 8 fu 
ry 
ae, i ae aur 
? 
tanh 5 Es As 
a 
IT. 
companiment, with a view to have it conftruéted for the ufe of 
the inftitution; but circumftances prevented fuch meafure be- 
e ma- 
in any pee 
TE portions of this fu- 
chines that have hitherto been inve 
ortion may, 
cording to our definition, be confidered in itelf as the moft 
sential a of the orrery : but i may 
be proper to mention, that the aa oO coe 
planets, in fale planetarium « or fecond portion, move in ee 
tric orbs with thei d velocities, making 
equal areas in equal times in aa exact tem of times ; 
three portions are applied, or may be applied, in fucceffion, 
to the fame ornamental ftand, as oa fubje& may demand, 
er they may have each a feparate fta 
An inftrument capable of reprefenting with extreme ae- 
curacy, and on a large fcale, all the motions of the earth 
and the moon at the fame time, had long been a defideratum 
in the philofophical world. For while the attention of the 
mathematical inftrument-maker was occupied by 
on, taken co pears are inexplicable by it. It muft be 
allowed, hag that from obferving the modern tellurian 
in motion, a {pectator fai 
likewife, by attending to the lunar 
caufe of eclipfes and lunar afpeéts explained ; ih, as to 
4Gz the 
