6 A Century of /Science 



gravitation, furnished for the Newtonian theory 

 the grandest confirmation known in the whole his- 

 tory of science. In Priestley's time, sidereal as- 

 tronomy was little more than the cataloguing of 

 such stars and nebula? as could be seen with the 

 telescopes then at command. Sixty years after the 

 discovery of oxygen the distance of no star had 

 been measured. In 1836, Auguste Comte assured 

 his readers that such a feat was impossible, that 

 the Newtonian theory could never be proved to ex- 

 tend through the interstellar spaces, and that the 

 matter of which stars are composed may be en- 

 tirely different in its properties from the matter 

 with which we are familiar. Within three years 

 the first part of this prophecy was disproved when 

 Bessel measured the distance of the star 61 Cygni ; 

 since then the study of the movements of double 

 and multiple stars has shown them conforming 

 to Newton's law ; and as for the matter of which 

 they are composed, we are introduced to a chapter 

 in science which even the boldest speculator of 

 half a century ago would have derided as a base- 

 less dream. The discovery of spectrum analysis 

 and the invention of the spectroscope, completed 

 in 1861 by Kirchhoff and Bunsen, have supplied 

 data for the creation of a stellar chemistry ; show- 

 ing us, for example, hydrogen in Sirius and the 



