1910.] SEE— PLANETS. 223 



planets at the great distance of the fixed stars, while the double 

 and multiple stars constitute systems of very different character. 

 There was, therefore, no direct observational evidence that plane- 

 tary formation was a part of the usual order of nature. The 

 process by which our solar system arose was involved in great doubt 

 and obscurity, and could not be definitely made out, notwithstanding 

 the labors of many eminent mathematicians during the past century. 

 No longer ago than 1906 the late Professor Newcomb declared^ 

 that he still retained " a little incredulity as to our power in the 

 present state of science to reach even a high degree of probability 

 in cosmogony." 



I have recently shown that the principal difficulty in all the 

 efforts of mathematicians for solving the problems of cosmogony 

 has arisen from false premises which had come down from the 

 days of Laplace, and thus vitiated all our reasoning. It had been 

 uniformly assumed that the planets were thrown off from the sun, 

 and that this process of detachment by rotation of the central mass 

 had set them revolving in orbits of small eccentricity. Laplace's 

 postulates in some form or other had been assumed by all investi- 

 gators since 1796. And it is curious to notice that Laplace in turn 

 had merely extended the conceptions developed by Newton in his 

 treatment of the problem of the figure of equilibrium of a rotating 

 mass of fluid. 



For, in establishing the theory of universal gravitation, in 1686, 

 Newton had correctly explained the figures of the earth and other 

 planets as due to the effect of gravitational attraction combined 

 with the centrifugal force due to axial rotation, thvis giving various 

 degrees of oblateness depending on the intensity of the forces, and 

 the heterogeneity of the planetary masses. These results followed 

 from the theory of gravitation, and Newton had applied to them 

 the same masterly reasoning which he usually exhibited in the 

 treatment of mathematical problems. 



Not long after the epoch of Newton the problem of the deter- 

 mination of the figures of equilibrium of rotating masses of fluid 

 was considerably improved by the researches of Maclaurin, while 

 subsequently Laplace himself extended and confirmed the results 



* In Popular Astronomy for November, 1906, p. 572. 



