ELECTRICITY AND MAGNETISM 



on the surrounding walls of the tube near the negative 

 pole, or cathode, appeared a greenish phosphorescence. 

 This discovery was soon being investigated by a num- 

 ber of other scientists, among others Hittorf, Gold- 

 stein, and Professor (now Sir William) Crookes. The 

 explanations given of this phenomenon by Professor 

 Crookes concern us here more particularly, inasmuch 

 as his views did not accord exactly with those held by 

 the other two scientists, and as his researches were more 

 directly concerned in the discovery of the Rontgen 

 rays. He held that the heat and phosphorescence 

 produced in a low-pressure tube were caused by streams 

 of particles, projected from the cathode with great 

 velocity, striking the sides of the glass tube. The 

 composition of the glass seemed to enter into this 

 phosphorescence also, for while lead glass produced 

 blue phosphorescence, soda glass produced a yellowish 

 green. The composition of the glass seemed to be 

 changed by a long-continued pelting of these particles, 

 the phosphorescence after a time losing its initial 

 brilliancy, caused by the glass becoming "tired," as 

 Professor Crookes said. Thus when some opaque sub- 

 stance, such as iron, is placed between the cathode and 

 the sides of the glass tube so that it casts a shadow in 

 a certain spot on the glass for some little time, it is 



moving the opaque substance or chan 

 its position that the area of glass at first covered by 

 the shadow now responded to the rays in a different 

 manner from the surrounding glass. 



The peculiar rays, now known as the cathode rays, 

 not only cast a shadow, but are deflected by a magnet, 

 so that the position of the phosphorescence on the sides 



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