MODERN SCIENCE. 209 



the slow cooling and contraction of .incandescent gas-clouds, 

 after long and complicated calculations bearing on physical 

 and mechanical questions which the subject involved, Laplace 

 arrived at the conclusion that planets are condensations of 

 the solar atmosphere at first only rings of gaseous and 

 luminous matter detached from the nebula (sun) by the 

 contraction of the main body, then later^on condensed by 

 cooling into solid bodies (planets), which continue to revolve 

 around the sun, in the same orbits as those which they 

 occupied as vapours at starting. This theory is called 

 Laplace's NEBULAR HYPOTHESIS, and is the theory accepted 

 by most physicists and astronomers. It is in complete 

 harmony with the law. of evolution, of which Laplace is the 

 earliest scientific exponent and demonstrator. The law of 

 evolution, it is clear, accounts for all the phases through 

 which worlds must pass in the course of their birth, growth, 

 maturity, and decay. It was through this famous hypothesis 

 that evolutionism began to work its way throughout Europe 

 for the first time in a clear form, and to become familiar to 

 .scientific minds. The conception of slow natural develop- 

 ment, as opposed to that of sudden creation, steadily spread 

 after the publication of the " Mecanique Celeste." Laplace's 

 hypothesis is in the main a mathematical theory, and as such 

 it "explains a number of the most important facts of our 

 solar system." It may be added that spectroscopic astronomy 

 {see KirchhofT) has been adding a multitude of facts which 

 confirm and strengthen the theory more and more every 

 year. Thus, Laplace, in this as in other respects, advanced 

 the boundaries of science immensely, and must be re- 

 membered as one of the most profound philosophers of 

 modern times. 



17581840. Olbers discovered PALLAS (1802) and VESTA 

 (1807), anc * several comets; formulated the theory of ex- 

 plosion to account for meteorites a theory, however, which 

 is much opposed by other astronomers and particularly 

 Norman Lockyer. (See his meteoritic hypothesis.) 



1791 1865. Encke, by his accurate observations of the 

 comet which bears his name, and which returns every 3^ 

 years, formulated afresh the theory of the existence in spacs 



