Examination of the Theory of a Resisting Medium. 17 
five since Clairaut penned his suggestion. ‘The masses of the sev- 
eral planets, upon which so much, depends in these investigations, 
appear more or less imperfectly known. Laplace gives the follow- 
ing table of them, that of the sun being taken for unity.(58) 
Mercury, : : : he ig BOESTIS 
Venus, . : : A 4 : a 
The Earth, . : ; : é asesee 
Mars sah. ; L R ‘ aa 
Jupiter, . ‘ : ; : : oo 
Saturn, . : : : : : a 
Uranus, : : : : : coh 
Pontecoulant, from the same unit, gives the several masses of the 
same planets thus: 
Mercury, : : , a ere TooSTO 
Venus, . ss A : a & aease 
The Earth, . : aires : Snes 
Warsi ere : é ‘ : Sendase 
Jupiter, - : : ; : TUEa TET 
Saturn, B ‘ é 4 : : aise 
Uranus, 3 . l : aa 
These values, says our author, appear to us the most exact which 
have hitherto been obtained of the planetary masses. It will be 
observed that these two tables agree only in the masses of Saturn 
and Uranus ; and of these Pontecoulant says it is very probable they 
need correcting, and that observations to determine that fact are 
in progress.(59) This was in 1834. Since that period this great 
geometrician has had cause to change his views in relation to some 
of these values. In calculating the perturbations of Halley’s comet, 
he has made use of the following values, namely :(60) 
Jupiter, . BV Ne s : 2 575,05 
Saturn, . ‘ A , i if eed 
The Earth,  . : : é 0) pedese 
These values, it will be seen, do not accord with those in either 
of the above tables. In the calculations here referred to, the action 
of Venus, Mercury and Mars was neglected as insensible. But 2 
German geometrician, Rosenberg, on the contrary, has announced - 
(58) Laplace, Systéme du Monde, p. 210- 
(59) Théorie Analytique du Systéme du Monde, tome 3, p. 341, et suiv. 
(60) Connaissance des Tems, pour l’an 1838. 
Vou. XX XIII.—WNo. 1. 3 
