ORRERY. 
36524, or rather 365% 5" 48" 48°, the effec of its error is, 
that the diurnal motion, compared with the annual motion, 
in every year, fo that the 
with the tubed 
along with the 
the calculation, one being a multiplier, and the other a di- 
vifor, and then there would have been one arbor fewer; 
but then the axis of the earth was to have an inclination, 
which it could not have if placed on the tube of the laft 
10, it being of no confequence what they are, provided 
they fimilar; but hence arifes a new motion, which the 
in 
n 
h it, whilft 
its teeth are connected with the teeth of the central pinion 
on the tube, this pision makes one retrograde revolution 
in a year from this caufe, and brings the earth back again 
one entire revolution in that time, fo that, in fad, the 
earth, by this mechanifm, makes only 364 complete revo- 
lutions on its axis in each year, inftead of 365, for which 
hence, an horary index is alto- 
ao} 
? 
fu 
s 
al 
ct 
a 
ad 
Co 
o 
oO 
i) 
“~ 
cr 
os 
~ 
i?s) 
ro) 
* 
pete 
we 
o 
rx) 
QO 
= 
z 
eS) 
a 
Qa 
@ 
ry) 
a 
(o) 
=] 
fre} 
= 
| ol 
ct 
ed 
Vv 
refpond with the earth’s rotations by one day in a year 
and this defeé&t being found out, was probably the reafon 
why no horary index is defcribed as belonging to this in- 
itrument. 
But there remains yet a further deduétion of a day in the 
year, in this inftrument, to be explained, which reduces the 
but which is not conneéted with, nor 
kers, that p 
vided the earth had no diurnal motion at ail during its annual 
have added another day to the days in a year if the earth’s ro- 
tation had been from -eaft to weft, and what is now the num- 
ber of fidereal days, would then have been folar, without 
eft, by means 
d once more me way about, in this cafe, 
by means of the fecond pinion, on the bar of parallelifm as it 
of the fame number fixed 
ft) tube, which would make 366 rotations; add now a 
third pinion to the earth’s axis, and it will revolve 366 
ti rom to eaft, and the annual gyration will make 
the neceflary deduGtion, but ftill there would be a defeé&t of 
5" 48™ 485 in each year. 
necting the nodes, w meets the moon in 
Thefe three periods have each a feparate train of wheels, in 
each of which the common pair ne , ufed in the tellurian, 
3 
forms the firft portion ; the three trains, with their values in 
time, are thefe, viz. 
Moon’s fynodic? 59 20 10 » 
revolution te a a ee 29 12 0 
59 124. 18 
Moon’s apogee 365 ee Res 3221 9g 36 
, pee erase 
Moon’s nodes 6% &*% 6% G 7080 0 oO 
The large wheel of 365 is here again a fixed wheel, round 
which 
