160 LAPLACE. 



uumerical results will enable those who are disposed to iustitnte a com- 

 plete comparison between the two rival theories of light to derive from 

 the Mccanique Celeste the materials of several interesting relations. 



Is light an emanation from the sun ? Does this body launch out inces- 

 santly in every direction a part of its own substance? Is it gradually 

 diminishing in volume and mass! The attraction exercised by the sun 

 ui)()n the earth will, in that case, gradually become less and less consid- 

 erable. The radius of the terrestrial orbit, on the other hand, cannot 

 fail to increase, and a corresponding effect will be produced on the length 

 of the year. 



This is the conclusion Avhich suggests itself to every person upon a 

 first ghmce at the subject. By applying analysis to the question, and 

 then proceeding to numerical computations, founded upon the most trust- 

 worthy results of observation relative to the length of the year in dif- 

 ferent ages, Laplace has proved that an incessant emission of light, go- 

 ing 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 tohimself anything vague 

 or indefinite. His constant object w?.s the explanation of the great 

 phenomena of nature, according to the inflexible principles of mathemat- 

 ical analysis. No philosopher, no mathematician, could have main- 

 tained himself more cautiously on his guard against a propensity to 

 hasty speculation. No i)erson dreaded more the scientific errors which 

 the imagination gives birth to, when it ceases to remain within the limits 

 of facts, of calculation, and of analogy. Once, and once only, did 

 Laplace launch forward, like Keiiler, like Descartes, like Leibnitz, like 

 Buff on, into the region of conjectures. His conception was not then less 

 than a cosmogony. 



All the planets revolve around the sun, from west to east, and in planes 

 which include angles of inconsiderable magnitude. The satellites revolve 

 around their respective primaries in the same direction as that in which 

 the planets revolve around the sun, that is to say, from west to east. 



The planets and satellites which have been found to have a rotatory 

 motion, turn also upon their axe^ from west to east. Finally, the rota- 

 tion of the sun is also directe*! from west to east. We have here, then, 

 an assemblage of forty-three movements, all operating in the same di- 

 rection. By the calculus of probabilities, the odds are four thousand 

 millions to one that this co-incidence in the direction of so many move- 

 ments is not the effect of accident. 



It was Buffbn, I think, who first attempted to explain this singular 

 feature of our solar system. Having wished in the explanation of phe- 

 nomena to avoid all recourse to causes which were not warranted by na- 

 ture, the celebrated academician investigated a physical origin of the 

 system in what was common to the movements of so many bodies differ- 

 ing in magnitude, in form, and in distance from the principal center of 

 attraction. lie imagined that he discovered such an origin by making 



