Examination of the Theory of a Resisting Medium. 17 
Jive 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) 
ercury, ; : é i : ZoBsTTT 
Venus, . ; : ‘ aUse7T 
The Earth, . : ; ‘ : 35a038 
ars, + . . : : . E5ab320 
Jupiter, . ‘ : . : : TOTS 
Saturn, . ; : $ . - 35TF 
nus TT31T 
Pontecoulant, from the same unit, gives the several masses of the 
same planets thus: 
M 
ercury, : ; ; i -  "TeseTEs 
Venus, . : : : : : eet Sree 
e Earth, . . ‘ ° eLETES 
Mars, . . . . 20U0a37 
Jupiter, ; ‘ ; : eee oa 
Saturn, . é : 2 : s¥Iz 
nu ; Le 
; : ; : : 
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) 
upiter, . . . . . . Tot ou v 
turn, - . . . . * 350 1g 
The Earth 
’ . . . . . 357T30T ' 
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 a 
German geometrician, Rosenberg, on the contrary, has announced 
(58) Laplace, Systéme du Monde, p. 210. 
(59) Théorie Analytique du Systéme " Monde, tome 3, p. 341, et suiy 
(60) Connaissance des Tems, pour l’an 
Vou. AAAI —No. 1. 
