VACUUIM TUBES. I5I 



cile a purely electrical explanation of the phenomenon with 

 its apparent indifference to the question of insulation. As an 

 example of this indifference it may be stated that the light 

 can be produced about as readily with the globe held in con- 

 tact in various ways with a water spigot as when the observer 

 stands on an insulated stool. 



Neither theory, therefore, seems satisfactory, and the cause 

 of the light, at least so far as can be gleaned from the litera- 

 ture at hand, still remains an open question. 



