THE SPIRIT-RAPPERS 



merely new tools but new senses. Every new in- 

 strument, every new discovery in experimental 

 science, represents, as Herbert Spencer long ago 

 pointed out, either a great widening of our original 

 six senses or the creation of new ones. Every dis- 

 covery brings with it a new weapon of scientific 

 conquest. The last four or five years have offered 

 a number of beautiful examples. We may select 

 one of a special import: 



Early in 1896 that is, a few months after Pro- 

 fessor Rontgen's amazing announcement of the 

 performances of the X-rays Professor Becquerel, 

 of the Natural History Museum, in Paris, followed 

 with another of an even more puzzling nature. 

 Studying the action of the salts of a rare and very 

 heavy mineral, uranium, Professor Becquerel ob- 

 served that these substances give off an invisible 

 radiation which, like the Rontgen rays, traverse 

 metals and other bodies opaque to light, as well as 

 glass and other transparent substance. 



This was the first found of the so-called "radio- 

 active" substances, of which the much-discussed 

 radium is now the most notable. Nothing within 

 a century has proven so great a puzzle to the scien- 

 tific world a puzzle, because these substances 

 seemed, in the beginning, to disprove the first prin- 

 ciples of natural science. They were endowed 

 with tremendous energy, yet what was the source 



395 



