82 THE NEW KNOWLEDGE. 



many memoirs that they constitute practically a history of 

 the relations of optics to electricity through the past fifty 

 years. Henri Becquerel, the son, was subjected to the train- 

 ing and influence of these honoured men, and it is little won- 

 der, then, that, through heredity and environment, he should 

 bear the face of one who sends his soul into the invisible 

 for that, in good solid truth, is what every true experi- 

 menter literally does. 



In due time he succeeded to the Professorship of Physics, 

 the chair of his father, and began his work in their laboratory 

 in the quaint old home of Cuvier in the Jardin des Plantes, 

 "a laboratory to which I had gone," he says, "from the 

 time I was able to walk." There he wrought nobly for the 

 credit of his name, until Rontgen's discovery of the X-rays 

 initiated an investigation which culminated in the discovery 

 of the Becquerel rays and radio-activity. 



Now, Becquerel did not discover his rays and their radio- 

 activity out of nothing. Every scientific discovery has a 

 genealogy of its own, going back to the primal ancestor of 

 all thoughts; no discovery comes into the world parentless 

 of previous conceptions. Here is a table showing a few 

 steps in the genealogy of the Becquerel rays: 



GENEALOGY OF THE RAYS. 



Cathode Rays. 



Lenard Rays I X-Rays 



S-Rays ! Niewenglowski's Rays. 



(?) N-Rays I Becquerel Rays. 



X-rays are in some way entangled with the phosphores- 

 cence in a Crookes' tube. Consequently, the discovery of 



