ORRERY. 
nual pag as is ufually done, eee the fame wheel from 
which the earth derives ich firft mo ae wheel 
ought to be nearly equally diftant f from all the laft mo ving 
wheels in the inftrument, in order that the eolnne incipient 
motions may be contemporary ; to effect this defirable pur- 
pofe, the wheel of 94, belonging to the earth’s train, is 
cut both at the edge, and alfo as a contrate wheel, to be 
driven by the unfeen el of 18, placed on the arbor of 
the handle T, and revolving in 24 hours, for the fame rea- 
fon that the other wheel of 18 on the long tube revolves in 
this time ; by this fituation of the handle, all the different 
trains are coupled together, and begin to move at the fame 
inftant ; o be moreover an advantage, the 
le@urer cash “7 conveniently turn the handle for Spier 
eae mpanie arth in its ag circuit, 
eads ie divifions on = different faces. orary face 
U; contains alfo the feven days of the week, indicat ed by a 
18 7 
= 3g 2. 
73 of a — which is an ex- 
fecond hand revolving in 
act week. 
The train of wheels for ae moon’s fynodic 
aia or month 
nthly motion, being conneéted alike with the 
acne and diurnal ends of te ear hs train, on account of 
having its motion communicated from the middle of the 
earth’s train, may be differently denominated, and may have 
its value afcertained, either as the improper fraction of a 
ftituent portion of its own, whereb — becomes a Cone 
in the number cf wheels, without a diminution of accuracy 
in the value of the train : for if we begin to calculate from the 
large wheel of 269, and eoufides it as conftituting the . 
wheel of the lunar train, we fhall have ae x a2 43 x 
269 13 
of 365.4242 = 297 12" 44™ 3.28765; but if we begin at 
a lunation is to an anomaliftic revolution of the 
777 are to 716, very nearly, which numbers are ek of 
forming the train it x 2 
of a lunation, which will be 
a period of 27% m 367 in which the error : + 1.13 
only. The To of this train is thus; the wheel 74 is 
fixed faft on the tube of bridge H, and has ieceh no mo- 
tion, while the monthly arm, X X, is carried round it; the 
pinion 16 lies on the upper face of this arm, inferted faft on 
the upper pivot of a vertical arbor, the lower end of which 
refts on the two-fold cock, feen above U, but which, together 
with the faid pinion, is nearly concealed by plate N lying 
over them ; on the under fide of the month y arm, and on the 
fame vertical arbor, completely concealed, 1s the {mall wheel 
42 driving the contrate wheel 179, on ADS horizontal arbor, 
that lies parallel to, and under the arm: the rim of this con- 
trate wheel is wide enough to admit of fe divifions for — 
ing the moon’s latitude, by the edge of the arm ufed a 
index, and its poftericr face has an excentric plate, een 
a circle suaae i on ore fide, and furrounded by an edze-bar 
of the fame fhape, which edge-bar taking the fork of the 
fteel ieee Y, gives it the alternate motion which raifes and 
lowers the moon’s ftem. A {crew in the cock Z, under the 
arm, preffes againft the horizontal arbor of wheel 17g, and 
allows its teeth to come out of ation when {crewed back, fo 
that the graduated rim may be brought to adjuftment for 
latitude, in any fituation of the arm, and {crewing in puts 
the teeth again into a€tion, ‘The moon’s ok Soe of Jati- 
pa or a from the node, is alfo ed on the rim 
1793 and the fulcrum of the lever is = edna of its 
ee from the forked end, in i aso 
» the mechanifm ort 
; 
) 
epends, remains yet to be explained. By a peculiarity in 
the conftruction of this inftrument, there is not an anoma- 
the earth’s axis with the wheel of 18, we fhall have 24 indicating when the moon ought to approach to and recede 
: 18 * rom the earth, as is ufual in inftrumen anoma. 
26 x 43 ~ liftic mechanifm is introduced ; but the moon herfelf aGtually 
Io 13 * 33 of a day = 29° 125 44™ 35.28765, as be- oves in an excentric orbit, in t e proper anomaliitic period 
at the fame time preferves the due inclination of her 
fore, four extra wheels being all that we have occafion to in- | _ 
ition 
to ed earth’s train, to effe€t a degree 
the whi 
thing that has been done i ny other country, 
with the fame number of whe Divas error pane little more 
than a quarter of a fecond in an entire m 
fat the wheel u the cock W, of 73, which wheel 
drives the tubed wheel of 48 round in the time already 
fpecified ; the of the wheel of revolves round 
8 
earth, and fupports the mechanifm belongin 
monthly bar may be adjufted to any fituation by the clamping 
piece feen near the handle T. The moon’s latitude is not re- 
gulated by an inclined plate, commonly called the nodes’ 
piste. which, for a globe of nine inches diameter, would 
been too ao and heavy for the wheelwork ; but by a 
ae ever of fteel, on which the moon’s ftem relts, that is 
d and ines alternately during the period with refpeét 
to ‘the nodes ; this motion is derived from the lunation thus ; 
aie node revolution thus 5 
xed faft onthe top of the tube of bridge 
H, round Bre ic moon’s arm revolves, whilft the wheel 
of 67 has a connection with a baa of 643 the con- 
made to re volve, and 
8, which conftruétion requires 
, the wheels 46 ard 41 to be both of them contrate ; the ef- 
: ; . 6 rf 2747 
feétive train, therefore, is 7 x ae — st 4 of 29.5306 
days, or the lunation of the wheelwork = 27° mn 32%, 
during which alee the deviation from the as oni to 
only 1. "9499 of t 
The item, a, of an crank, abcd, is fquare, and paffes 
through the ‘focket of wheel 41, which is round without and 
{quare within, and pivoted into the cock e, and lunar arm 
2 x. Thi 
