18 ELECTRIC INERTIA [CH. n. 



and many others had contributed. It is not too much 

 to say that up to the time of Crookes the phenomena 

 of the vacuum tube were shrouded in darkness, not- 

 withstanding much laborious and painstaking work 

 done both in this country and on the Continent in 

 connection with them ; but that since the researches 

 of Crookes in the seventies, the theoretical luminosity 

 of the vacuum tube has steadily increased, until now, 

 as Maxwell predicted, it is shedding light upon the 

 whole domain of electrical science, and even upon the 

 constitution of matter itself. 



