A HISTORY OF SCIENCE 



depths of space and gain such knowledge of stars and 

 nebulae as hitherto no one had more than dreamed of. 

 Then, in rapid sequence, a whole coterie of hitherto 

 unsuspected minor planets is discovered, stellar dis- 

 tances are measured, some members of the starry 

 galaxy are timed in their flight, the direction of move- 

 ment of the solar system itself is investigated, the 

 spectroscope reveals the chemical composition even of 

 suns that are unthinkably distant, and a tangible 

 theory is grasped of the universal cycle which includes 

 the birth and death of worlds. 



Similarly the new studies of the earth's surface re- 

 veal secrets of planetary formation hitherto quite in- 

 scrutable. It becomes known that the strata of the 

 earth's surface have been forming throughout untold 

 ages, and that successive populations differing utterly 

 from one another have peopled the earth in different 

 geological epochs. The entire point of view of thought- 

 ful men becomes changed in contemplating the his- 

 tory of the world in which we live albeit the newest 

 thought harks back to some extent to those days 

 when the inspired thinkers of early Greece dreamed 

 out the wonderful theories with which our earlier 

 chapters have made our readers familiar. 



In the region of natural philosophy progress is no 

 less pronounced and no less striking. It suffices here, 

 however, by way of anticipation, simply to name the 

 greatest generalization of the century in physical 

 science the doctrine of the conservation of energy. 



