Eight-Year Cycle in Relation to Physical Cause 115 



electrically charged body may be observed, 

 under proper conditions, by the movement 

 of the light upon the screen when the rays 

 are subjected to a magnetic or an electro- 

 static influence. 



The very great importance for our purpose 

 of the magnetic and electric deflectibility 

 of these rays will be pointed out later on. 



(5) They ionize gases through which they pass and 



consequently render the gases conductors of 

 electricity. 



We have seen that cathode rays are com- 

 posed of negatively charged particles which 

 have recently been called electrons. The 

 theory of ionization by the cathode rays 

 is that the passage of the rays separates the 

 gas into molecules which because of the 

 acti\dty of the rays have individually gained 

 or lost one or more electrons. These mole- 

 cules, which in this state are known as gaseous 

 ions, become carriers of electric current. 



(6) The gaseous ions produced by cathode rays 



may become nuclei for the condensation of 

 water vapor. 



Sir J. J. Thomson's treatise was not the only piece of 

 epoch-making research that grew out of the investigation 

 of cathode rays. In Germany, at the University of 

 Wiirzburg, Professor Roentgen, in 1895, was at work 

 upon the problem of cathode rays when he made the 

 discovery of the rays, subsequently called X-rays or 

 Roentgen rays, which were ahnost immediately put to 



