46 AI.OIS RIEHL 



philosophy found itself, in Helmholtz's words, 

 once more upon a healthy footing in Kant. 

 From its position here it first proceeded to a 

 fresh self-examination. Meanwhile natural 

 science had issued in discoveries and views of 

 philosophical significance, among others the 

 discovery of the Conservation of Energy — the 

 principle which made it possible for the first 

 time to combine all the parts of physics into 

 a single system. The idea of development 

 had been applied to the investigation of or- 

 ganic nature in the doctrine of the Origin of 

 Species. In proportion as scientific research 

 assumed exacter forms it became more and 

 more conscious of the conditions under which 

 it labored. A physiologist of repute spoke of 

 "the limits of our knowledge of nature." Be- 

 tween a natural science grown critical and a 

 philosophy which had made it its principal bus- 

 iness to examine the sources and determine 

 the limits of knowledge a rapprochement, 

 which was soon to develop into an alliance, 

 became feasible. Mathematicians and physi- 

 cists of standing, Ludwig Boltzmann, Henri 

 Poincare, Ernst Mach and others, following 



