ORRERY. 
‘clamped faft, while . teeth are in Li ea wae a 
of a pinion of 8 under the faid 3; but great 
neceflary, before the "anal clampings, es the pinion’s ayer 
be put at a proper ating depth into thofe of the wheel 
this pinion has an arbor extending the whole length nearly 
of the arm, and parallel to it, but is carried by two cocks 
beneath it, in a way fimilar to the horizontal arbor feen 
above the arm: the remote end of this lower horizontal 
‘arbor has a fimilar pinion attached to it, which drives 
another wheel of 48 teeth, alfo contrate, but with its 
teeth pointing upwards to alter the direction of motion ; the 
time of a oo of this latter wheel i is, therefore, one 
96 that revolves 
a 
it penetrates at § of an inch above: 
a gene perpendicular to i arm, 
about 2, in diameter. On the upper end of this 
mply by frigtion, a {mall wheel of 36, im- 
be r i 
is ¢ 
ad of 3654 revolutions in the 
ee of a nature would pronounce ‘this to be an error 
two da t s thefe two days’ motion are 
aciieed cae alteration to the ear aie axis; but the 
truth is, the effe& of this combination was not only fore- 
feen, but taken into the calculation of the annual train as a 
compenfation for a deduction of two days’ motion, which 
the earth experiences from a combination, in eT A aaa 
of ano ene i ae but to the fame amou 
sent a ees duGion of a day in the year: thefe 
wo days fubtrated from the 3672, produced in the way 
in a year 3 a> 
want of a compenfation of this fo 
that the old orreries and tellurians are moft of them of little 
P 
value in the folution roblems where time is concerned, 
as we have already had occafion to notic t doing 
juftice to the ingenuity of Janvier, the Fre chanic, to 
afcribe to him the contrivance of this ingenious mode of 
compenfatio hich is very convenient when the diurna 
handle 
a fimilar era at 
remote end gives ao to snare contrate whee 
with its teeth turned up, on account of the ieee di. 
rection of its motion. The tube of this laft gee feen de- 
tached in fig. 4, furrounds _ diurnal iain arbor, and 
fupports the bearing piece P, in fg. 1, on which the earth’s 
axis refts, which axis will come out ‘of the bearing piece 
when the pin with a circular head is drawn out of the fide 
of the focket carried by this bearing piece ; for a circular 
groove turned on the earth’s axis, within the focket, allows 
the pin to pafs at one fide of it along the groove, by which 
pin it is kept in its place, and is yet at liberty to revolve. 
The {mall Sainte circle O, for eftimating the geocentric 
— of the mo on and Tee, refts alfo on this ann ual 
of ig fnerouadin the fun. 
parallelifm, aa is alfo the period of - 
ae, s, thus; an annual wheel of 107, beft feen in fig. 4, i 
made faft to.the 62, and, partaking of its motion, dtives 
a pinion of 12, through the medium of a pinion of 15, 
which only changes the direCtion of motion, and the arbor 
of the pinion 15, which is a tube revolving on a ftud at the 
end of the crofs-piece ¢ d, carries on its upper end the 
wheel 86, which makes another wheel of 62 realy with 
its tube, in a proper dire€tion, in a period of X 36 ? of a 
train the error is 
n like 
year, or in 29% 128 44™ 1.82, in which t 
little more than one fecond ger month in defe&: 
manner, the train for the period of the nodes is in ee 76 
62 
~ ofa 
wa hare as it moves forward in oe orbit. 
revolution of the moon is taken from the lunation, and the 
train, eoueed in ie monthly frnall frame, for giving the 
67 _ 46 
— a 
64 41 
13" 18™ 325, as in the larger machine be- 
Before we take leave of the earth’s arm, 
principal equation and variation of diftance, is of a. 
lunation, or aoe 
fore defcribed. 
n 
of the monthly frame; and alfo that the fixed rim Q, that 
s the moon’s age m. it, a crofled out 
s the plac 
poftione c fie glo 
fee eafy mea 
the of p 
een an oe earth’s arm a circular plate, N, is 
4H 2 clamped 
