LeVerrier on the constitution of the Solar System. 293 
the same values for these masses; if it shall not, some foreign 
cause must of necessity have been omitted. 
The question presented itself nearly in the following form. 
Would it be possible by assigning suitable masses to the known 
planets to satisfy all the observations? Or is there somewhere 
in our system a notable quantity of matter, which, as yet, has 
not been taken into account, and of which the consideration is 
indispensable 
he separate study of each one of the planets affords no 
answer to this question, whereas the comparison of all the results 
together enables us to decide with certainty. I will take then 
the new theory of Mars, and from my previous works, so much 
a8 is necessary to the end actually sought, but nothing more. 
The position. and small size of Mercury and Mars prevent 
them from exercising any important influence upon the bodies of 
our system. Observations upon Venus enable us to estimate the 
mass of Mercury as one five-millionth (ssz3572) of that of the 
sun; while the motion of the earth, deduced from observations 
of the sun, indicates the mass of Mars as one three-millionth 
(sastass) that of the sun. The uncertainty which may exist 
in these numbers has no influence upon that which follows. 
he mass of Venus is about one four-hundred-thousandth 
Gaassx) that of the sun. This result is obtained by severa 
methods; by the consideration of the displacement of the 
plane of the ecliptic; by the actual measurement of the period- 
teal perturbations of the earth from 1750 to 1810, and from 1811 
to 1850; and by the amount of the periodical inequalities of the 
lonvitude of Mercury. These results all confirm each other. 
he mass of’ the earth is one three-hundred-and-fifty-five- 
thousandth (sss'sa3) of that of the sun. This number is derived | 
from a comparison of the force of gravity upon the earth, with 
the full of our own planet toward the sun. : 
These being the data, the theory of Mars may be established 
the year 1672, at Paris by Cassini and Roémer, at Cayenne by 
it would be necessary to make equal to the tenth part of the 
value given above, 
