The Evolution of the Sciences 



They change their object from day to day with 

 the consequence that programmes must con- 

 stantly be recast, courses altered and habits 

 abandoned. This is no great matter, or 

 rather it is the very condition of progress 

 and life. But there is another important cir- 

 cumstance to be considered. As living cells 

 are modified by division, so the sciences acquire 

 new life and growth by the creation of mixed 

 sciences. 



First we have physical astronomy. Thanks 

 to the immortal labours of Kepler, Newton and 

 Laplace, astronomy has reached a higher degree 

 of perfection than any of the other sciences 

 based on observation. The laws governing our 

 system are known with absolute certainty, as 

 everyone can see for himself from the astrono- 

 mical predictions, which fix beforehand to a 

 fraction of a second the motions of the various 

 planets; and it was reasonable to speak of 

 celestial mechanics in the case of a science 

 whose entire content could be treated deductively. 

 But that is not the whole of astronomy; there 

 is also a celestial physics and chemistry. What is 



the nature of these stars which the old astronomy 



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