THE ORIGIN OF THE PLANETARY SYSTEM. 3957 
of double refraction which it is subject to in the course 
of its passage through certain crystals, with the action of 
attractive and repulsive forces, should not have aban- 
doned this route, before he recognized the impossibility 
of arriving by the same path, at plausible explanations 
of the phenomena of diffraction and polarization. In 
other respects, the care which Laplace always employed 
in pursuing his researches, as far as possible, to their 
numerical results, will enable those who are disposed to 
institute a complete comparison between the two rival 
theories of light, to derive from the Mécanique Céleste 
the materials of several interesting relations. 
Is light an emanation from the sun? Does this body 
launch out incessantly in every direction a part of its 
own substance? Is it gradually diminishing in volume 
and mass? The attraction exercised by the sun upon 
the earth will, in that case, gradually become less and 
less considerable. The radius of the terrestrial orbit, on 
the other hand, cannot fail to increase, and a correspond- 
ing effect will be produced on the length of the year. 
This is the conclusion which suggests itself to every 
person upon a first glance at the subject. By applying 
analysis to the question, and then proceeding to numer- 
ical computations, founded upon the most trustworthy, 
results of observation relative to the length of the year 
in different ages, Laplace has proved that an incessant 
emission of light, going on for a period of two thousand 
years, has not diminished the mass of the sun by the 
two-millionth part of its original value. 
Our illustrious countryman never proposed to himself 
any thing vague or indefinite. His constant object was 
the explanation of the great phenomena of nature, ac- 
cording to the inflexible principles of mathematical 
