72 THE NEW KNOWLEDGE. 



POWER TO PENETRATE MATTER. 



It was at first supposed that solid bodies were absolutely 

 impenetrable to these corpuscles. Nowadays, however, we 

 know that this is not so. Lenard has made a tube which 

 has in it a small window of aluminum foil, and on shoot- 

 ing the corpuscles against this window, he found that they 

 passed straight through it, and so got outside the tube, 

 where they could be more easily investigated. Cathode 

 rays which have passed through the glass bulb into the 

 outer air are consequently called Lenard rays. 



LENARD RAYS. 



It will be understood that these rays consist simply of 

 corpuscles which have passed through an aluminum window, 

 and are in no way different from corpuscles in general or 

 from the cathode rays within the tube. They have turned 

 out to be very useful, however, in determining the Law of 

 Absorption. The absorption of ordinary light by different 

 substances bears no relation to the density, or weight, of 

 the absorbing medium. Hea vy materials, like iron or glass, 

 light bodies, such as cork or water, may be transparent or 

 opaque to ordinary light, as the case may be. On- the 

 other hand, in the absorption of corpuscles in the Lenard 

 rays very different phenomena appear. 



A given thickness of material, whether gas, liquid or solid, 

 absorbs these rays simply in proportion to its density, 

 and entirely independently of any other property. Thus, 

 though the density of the lightest substance is only one 

 sixty-millionth of the heaviest, throughout this enormous 

 range all substances, including air, carbonic acid gas, paper, 

 copper, glass and gold, absorb these rays in direct propor- 

 tion to the relative weight of the substances involved. 



v 



