ORRERY. 
whole 
tranfmatation of the eriodie. into a Gunde Lass be 
dah 4 
rror 2 
will exprefs the number 
y the train of wielaoe exclufively : 
unity, the effe& of one retrograde revolution in a year, pro- 
duced by the wheel of parallelifm, we fhall have 12. 368628 
for the number of lunations in the fame time, by which, i 
4 
ceflive conjunctions of the moon ic 
ana true one, as taken from the aftronomical tables, by 
20.51 
The wheels for the motion of the moon’s nodes plate, are 
93 X= oe the retrograde period of which is 93 — 
183 years, or 6793% 15° 36™ (fee Nomsers seed 
which period is tao te by 4) 
nd, air of intermediate wheels of 
eth each. re coke on the fame arbor, com mu- 
nicates its motion to the wheel 93, which revolves once ina 
year, and 5 , or five teeth more, which excefs above one 
revolution, in a retrograde direGtion, as it regards the 
moon’? 8 motion in her orbit, amounts to an entire backward 
is ~ — xX 8 6 which at firft 
black ed cap, is > 6 = 51 
wheel of 
each lunation ; when the train is reduced to the a form 
a the 560 reprefents the lunar wheel 28, and the 516 the 
wheel of 86 on the annual bar, and to afcertain how much the 
by the saris tranfpofition of the 
latter, we muft fay as 3654°: 51 95 3035 342 wed 
fo that in each month the produ@ (ahich may be called t 
wheel) 560 is accelerated, as much as if 516 had bees 
Vou. XXV. 
ys 560 
516 + 42 = 558, and the whole value of the train 22> 
without tranfpofition : but to make the parallelifm complete, 
the produéts of the drivers and of the =_ ‘wheels ought to 
have been alike, which they are not by 3 ; the deviation 
from perfet accuracy is, however, ‘of lefs moment than it 
would have been ‘in one of the planetary periods, becaufe the 
cap is eafily adjuftable whenever the error becomes fenfible. 
After this patina and report of Graham’s portion 
of the orrery, which is the moft effential part, it will ap- 
pear remarkable to the eee that the inventor fhould have 
gai aie as =~ credit from his expenfive and cumberfome 
n ine, in which neither accuracy nor 
fipliciy fae been attained, as if he had contrived a perfe& 
reprefentation of th a ’s and moon’s ana in the 
eft an oft accu anbeaer but the feems to 
have been, that the complex y of the conftruétion has 
hitherto fo puzzled every examiner oF i its internal mechanifm, 
that all attempts to afcertain the 3 correfponding to 
the wheelwork employed therein have proved ineffeétual, 
until we undertook to difclofe the value ‘7 each train by 
yftematic rules, that we truft are intelligible by ordinary 
readers; and we beg to avow our difinterefted love of truth, 
"by afferting that, fo far as we have examined this machine, 
it “ has paffed ie more than it is worth. 
he intramentmaker hom Dr. De- 
added dale - his own to 
fo} 
(m7) 
mpre 
we have faid, Rowle e is “familia among the 
the 
apn which 
of mechanifm ; they neither of them 
ufeful maxim, "that ** more means are not nece 
n end ;’ 
e a new iia with all its ans parts as a 
eloG than to adopt the ideas and calculations of another 
artift, an 
o 
took to introduce into oy ’*s machinery the wheelwork 
for the fun and inferior planet 
We will begin with er of the fun, which is 
4 BY By, 4, & 
, * 6% 0% vi x oe but we may omit the portion 
26 24 
=X ay being of no valuein the calculation, and ferving 
only te transfer the motion. communicated to them; then 
the remaining or effeCtive portion of the wheelwork sil be 
94. 12 60 94 12 _ 
7x Be x wer xX aS 314, which are fo many 
ays by reafon of the fingle {crew denoted by unity -revolv- 
ing in a day, and this would have been the exa@ Pe iod of 
4 Fo rotation 
