ORRERY. 
tic, oa : circle of declination, but no months, or day of 
It would 
ner in which thofe moft effential parts are placed to perform 
their refpetive offices, has enabled us to make fuch a corre& 
report, as we truft will be intelligible to fuch of our readers 
as have perufed with attention our article NumBers Pla- 
netary, where the different modes of appreciating the value 
of whe celwork, aGting under different circumitances, are 
fuch — as feem neceffary to explain tie conftruction o 
each portio 
raham’s Perino examining Rpegee we be 
our operations out what of conneétion ie 
handle has bie the aaa motion of ie earth, which mo- 
tion, in all machines of this nature, is made the ‘Randard by 
which all the ethics cena: are examined and eftimated. We 
found fifteen wheels and pinions employed in communicating 
the motion of the handle to the earth’s axis: but as none of 
thefe were found to be concerned in the train conftituted of 
the ratio pet weet a day anda year mek are no otherwife 
e intervention of the wheel 
tion, with the ¢ earth’s axis, as borne by the annual bar, and 
placed therefore ina variable slp as it regards the fun, 
the centre of its motion ; ; from w 
be thus explained : 
one of the wheels, which takes Ge een of the handle, 
and conveys it to the earth’s annual arm, is neceffarily con- 
centric with the fun’s item, and has the faid arm revolving 
round it in a year ; its number of teeth is 96, and the pinion 
which it a€tuates has 24 teeth: this pinion has its teeth in ac- 
tion with thofe of wheel 96, while 1t is carried round in the 
annual orbit, and therefore experiences a fubtration of 
aa? OF four entire revolutions, not contemplated by the 
contriver, or if contemplated not remedied; which fubtrac- 
tion, aéting in a direGtion contrary to that of the motion de- 
rived from the handle alone, makes the earth have four rota- 
tions in the year fewer than the index counts on the horary 
circle. The error thus occafioned in the indication of time, 
however, attaches fortunately to the h 
earth’s axis, the motion o 
the earth about its axis.’’ which affertion has hitherto been ge- 
nerally credited. Nay, to an accurate examiner it is evident, 
without an infpeétion o tt the means, that a corre& effet is not 
produced in counting time by the hour plate, for the circle 
of hours placed at the earth’s axis makes 91 revolutions 
only while i seieel makes 92 nearly. But this error is 
of fo m mportance in the motion of the handle as it 
would have been in the earth, or hour circle, while the two 
latter are correfpondent. The wheelwork, which contts- 
tutes the effectual part of the ratio between a year and a 
day, are — 4 
oS 365%, fo that the year is a 
civil, not a folar year, which a true ee requires. 
The wheel of 24 teeth, connef&ted with the earth’s axis, 
drives that of 18, on the arbor of which isa ee endlefs 
{crew acting with the eal wheel of 487, which wheel is 172 
a diameter, and » fo as to refift the power of the 
fcrew, which is fete itfelf obliged eg move, and the 
annual frame along with it, the a of —— of a circle in 
: 
ery 18 hours, or time 
a forward, and the third and fifth in a backward direction ; 
rt Smeael with the parallelifm is perfe&, but mien have been 
effe&ted with fewer wheels. 
35 
The wheelwork for the moon’s period is “> x 
12 
+33 
<= xX 
4 
of a day, the value of which train is 277 75 42™ 51.542, 
pe the error in exc This period, it will be 
obferved, is a nesiodic, t a fynodic revolution re- 
quired fome obfervation, as well as fkill in planetary calcula- 
tions, to afcertain firft how the chines volution, una- 
tion, is € e heelw that ers to iodi 
are placed upon the wheel that preferves the earth’s parallelifm, 
which wheel, we have faid, has a backward motion once in a 
civil year; it confequently carries its load of wheels round 
the earth once ina ear, In a re trograde direétion : but the 
laft wheel of the train, which has 153 teeth, is a ring in- 
dented on the interior circle, and moves concentric with the 
e€ pinion 
of 25, which aCtuates this wheel of 153, is annually carried 
backwards by the wheel of ae asi while its teeth are in 
action, and therefore the whee 153 has de mo- 
tion, arifing from the train fimply aS ridered, eectarded bY 
