150 Remarks on Drs Enfield’s Institutes 
editions concerning the retrogradation of the primary plau- 
ents; and, should, “like them, have been rectified or struck 
out. All that can be said with truth is, that during the spe- 
cified interval the motion of the secondary is retrograde 
relatively to its. primary; and even this statement can 
scarcely be oubares to the satellites of Herschel.* 
Prop. 114.“ The greatest elongations of a satellite on 
each side are Soe This proposition has several excep- 
tions. The orbits of the third and fourth satellites of Ju- 
plter have a very sensible excentricity ; and the same is true 
of the fourth (now more generally numbered as the. sixth) 
satellite of Saturn. See Laplace: Syst. du Monde. © ‘The 
latter, according to Delambre, (Ast, If. eed has an ellip- 
ticity nearly equal to that of our moon. 
Prop. 123. Several of the particulars inserted:i in the an- 
nexed heli from Sir I. Newton, have now become ob- 
solete. In particular, the ¢ s of matter in Jupiter 
and Saturn, instead. of being to to that i in the sun in the ratios 
= 1100 and 2360, are now inom to be in the ratios of 
p- 135, is Soemviod on the erroneous shenty: ob retro- 
eon previously laid down; and therefore should - 
heen: corrected. 
_ Prop. 155. The demonstration of this panpenieiteiii in 
Br fallacious. It is said to be contrary to prop. 51. cor. of 
ok I, that the centre of gravity of two gravitating bod- 
ies should: move; and is inferred that if one of the bodies 
is. projected in any direction, the other must acquire (by 
hat means we are not told) an equal motion in the oppo- 
site direction. - Now this is so far from following as a ne- 
cessary ice, that the other body will not in fact 
apis wry: such motion 3 and ifs a prdjeecie rales 0 
i os not taltempied, in the general list of corrections ipenst ne p. 
6, _ rectify the periodical times of ot satellites of Hers ; for with 
oe ie exception of the second and fourth their distances from helt wimary 
Ww holly 
vig yet fully ascertained. His last pestle of the sy —— ~ neem 
of | the second and fourth, ares . the Phil los. Trans. for 1815, is as dis ee 
Ge IV. 134.1 . so 
€ Pe ipation of their orbits ti to the ecliptic he finds t o be 78° 53'.— 
oo wee penpendioulrity than has been leretotoe hae ol 
yeti < ere + Mee. Céleste. Parts ls eb. Oe Sook 
