Eight-Year Cycle in Relation to Physical Cause 117 



will appear: one directly opposite the cathode on the 

 wall of the tube and the other on the cathode itself. 

 The shadow on the wall is explained by the intercepting 

 of the cathode rays which would otherwise produce a 

 fluorescence on the wall. . The shadow on the cathode 

 is due to the intercepting of positively charged mole- 

 cules mo\'ing in the direction of the cathode. These are 

 the positive or anode rays: 



(1) The positive rays are positively charged mole- 



cules of the gas in the discharge tube stream- 

 ing in the direction of the cathode. 



(2) They light up a fluorescent screen. 



(3) The size of the positively charged molecules is 



comparable with the size of the molecules 

 of the gas, and they are much larger than the 

 negatively charged particles in the cathode 

 stream. The mass of the electrons is only 

 about 1 /1800th of that of a hydrogen atom, 

 while its radius is only about 1/50, 000th 

 that of an atom. 



(4) The positive ra^^s are deflected both by a mag- 



netic and an electrostatic field. 



(5) They produce ionization of gases through which 



they pass. 



(6) The gaseous ions may become nuclei for the 



condensation of water vapor. - 



There is a principle in physics known as the prin- 

 ciple of reversibility which has been the means of a 

 number of important discoveries. If a set of forces 

 can produce an observed change, it is in order, accord- 



