ORRERY. 
ment, if we multiply the _— dates of : pied by .006986, 
the difference between the t term r the — ion 
5-5 days, we muft ord §-493014 as 
la tion of the ese wheel of 60, the arbor 
i commen arbor of four other wheels. 
which drive each oulbe wheel, foldered to as many tubes 
refpectively, to carry the arms of the four fatellites, as feen 
in the drawings. The wheels, with their refpective periods a 
correfponding, are contained in the fubjoined table, where 
it is to be underftood that the denominators of each fraétion 
are the drivers made faft to the arbor of 5.493014 days, and 
the numerators are the wheels faft to the tubes refpectively. 
Tas ce of Jupiter’s Satellites. 
Satel. | Wheels ufed as Fra&t. | Periods correfponding. | Prrose in each 
D. DH. M.S. i 4 
1 so of 5-493014 | 1 18 28 45.49 | + © 9.40 
2 = of ditto 3.13 18 11.78 |+ 0 17.78 
3 : of ditto 7 357 188 |— 2 17.2 
4 o of ditto 1618 5 19.05 | + © 12.05 
The common arbor is held in a vertical pofition by two 
cke, one above the e:.d of the tube, and one below, which 
alfo holds the ftem of Jupiter, round which ‘he tubes revolve, 
and likewife the ian i feen in Plate V hich fup- 
en for receiving the hadows of the fatel- 
lites when a ap: uf-d ; but when a lamp 1s not ufed, a 
conical piece of brafs fits on the ftem bebind J- ipiter, to 
per: nt the fhadow of his body, and to explain the immer- 
fions or emerfions of the fecondaries as they revolve. ‘T'he 
diftances of the fatellites are taken in diameters of the fmall 
ball that reprefents Jupiter. For a defcription of other inftru- 
ments, that have been conftructed to anfwer this purpofe fepa- 
rately, we o to refer to our ae peer aiie a 
e have now arrived at the 8 of bie 
box, and “rhe wheels a guide Ac indication which will 
aan our wines of this machine. e vertical 
diurnal arbor that carries one of ie bevel aie at fir 
oe is inferted an adjuttable hand that indicates mean 
folar time, ona rim of 24 hours fixed to the cover of the box: 
this rim is 34 inches in diameter, and § broad; within this 
nd in the fame plane revolves a circular dial of 24 hours 
in a retrograde dire€tion, juft once in a folar year ; and the 
fame hand that indicates mean folar time on the fed rim, 
indicates alfo fidereal time on the revolving dial with equa 
ccuracy 5 . as the revolving dial meets the hand th 
r Reve of a circle fooner in each fucceflive revo- 
lution, one more in a year is indicated on this revolving 
dial than on the fixed plate, in the way that 1s done in Mar- 
gett’s chronometer, but with much more accuracy, as the 
train here between a day and a year is p order to 
‘produce this retrograde motion ‘af the title dial of 24 fidereal 
‘hours, one pinion only was neceflary, which is fixed at the 
poe of a tube that revolves round the diurnal arbor as 
{pace of 
be eecalleae d that a pinion of 14, 
drives a large wheel of 166 for the motion of Jupiter: nowa 
fimilar pinion of 14, reer over the bevel wheels, round the 
diurnal arbor, which is at the fame diftance as the annual 
arbor from the edge of 166, willa& with it in “thie fituation 
alfo, and will revolve in a fame time that the firft 14 does, 
which has been fhewn to be a folar year. The intern.ediate 
wheel of 166 only aie ie motion ot pe except as 
to its dire&tiou, which otherwife would not have bean retro- 
grade: thus from means the moft fimp' 4 ttle ies the ut- 
moft importance are derived, beth as to utility an curacy ; 
and, what is not to be relate the ragnation falls i imme- 
d: rately under the eye o turer, who muft neceffarily 
oe at the handle of the eae, while he is giving his lec- 
ure. The weekly vertical arbor, feen detached in fig. 2, 
ftands at the fame dittance from the fun, or centre of the 
box, as the other two arbors rs, and, as has been faid, forms 
Another rim, fimilar t to 
ec one we 
for the { ven days: this motion is produced iy means aie 
imple; the firft whee’ of the train that cones Saturn with 
Jupiter is 53, revolving faft to a refore in 
arbor, and therefore admits another wheel of 53 to a& with 
it from this arbor, and this 53 revolving in the fame direc- 
tion as the 14 under it, and, in the period of Jupiter euisk 
on its tube an joer dial, over which the annual hand 
in the fynodic revolution of the earth, as c~*mpare oil Ju- 
piter. This little dial, if divided into 360°, would have 
fhewn the diftance of Jupiter to ie we at any time, as feen 
from the earth, but it was thought t to 
fhew this diftance in time, which pee reprefents Ju- 
piter’s meridian paflages when the index is put to XXIV on 
the day of Jupiter’s conjunétion with the fun. 
e of culmmating of any other planet might 
inte eed, if an horary circle could conveniently 
be attached to the earth's arm, round the centre of its mo- 
tion, under the large graduated circle of days, &c. the 
planetary arms would be fo many indexes, though at t fome 
diftance above and below it, to point out thereon the refpective 
times of culmination of all the primary Sant agreeably to 
their mean motions. Jupiter’s time of fou is, however, 
a matter of daily importance, as it 18 a wide to his vifibility 
or invifibility at any given hour, eas the eclipfes of = fas 
teliites occur, and alfo fhews whether the immer r 
hef 
Jupiter is a or sheges nind the fun, or, in other 
or lefs than 12 s from the fun, as feen from > earth. 
x, round 
faces require no additional ie ar but are pointed to by 
one hand adjufted to the top of the annual arbor, a Ne 
