THE ORIGIN OF THE PLANETARY SYSTEM. 357 



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 Mecanique Celeste 

 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 



