eriodic time of Venus is in the same
proportion to the square of the periodic time of the earth as the cube
of her distance is to the cube of the earth's distance. Our next nearest
planet is Mars, and observations on this planet at its opposition to the
sun, invariably give a larger parallax for the sun--Venus giving 8.5776"
while Mars gives about 10". It is true that the first is obtained under
more favorable circumstances; but this does not prove the last to be
incorrect. It is well known that the British Nautical Almanac contains a
list of stars lying in the path of the planet Mars about opposition,
(for the very purpose of obtaining a correct parallax,) that minute
differences of declination may be detected by simultaneous observations
in places having great differences of latitude. Yet strange to say, the
result is discredited when not conformable to the parallax given by
Venus. If then, we cannot trust the parallax of Mars, _a fortiori_, how
can we trust the parallax of Jupiter, and say that his mean distance
exactly corresponds to his periodic time? Let us suppose, for instance,
that the radius vector of Jupiter fell short of that indicated by
analogy by 10,000 miles, we say that it would be extremely difficult,
nay, utterly impossible, to detect it by instrumental means. Let not
astronomers, therefore, be too sure that there is not a modifying cause,
independent of gravitation, which they will yet have to recognize. The
moon's distance is about one-fourth of a million of miles, and Neptune's
2854 millions, or in the ratio of 10,000 to 1; yet even the moon's
parallax is not trusted in determining her mass, how then shall we
determine the parallax of Neptune? It is therefore _possible_ that the
effective action of the sun is in some small degree different, on the
different planets, whether due to the action of the ether, to the
similarity or dissimilarity of material elements, to the temperature of
the different bodies, or to all combined, is a question yet to be
considered.

As another evidence of the necessity of modifying the strict wording of
the Newtonian law, it is found that the disturbing action of Jupiter on
different bodies, gives different values for the mass of Jupiter. The
mass deduced from Jupiter's action on his satellites, is different from
that derived from the perturbations of Saturn, and this last does not
correspond with that given by Juno: Vesta also gives a different mass
from the comet of En