Orr NATURE OF THE RADIATIONS [CH. 
discharge passes through it. The « rays correspond to the canal 
rays, discovered by Goldstein, which have been shown by Wien to 
consist of positively charged bodies projected with great velocity. 
The @ rays are the same as the cathode rays, while the y rays in 
some respects resemble the Rontgen rays. In a vacuum tube, 
a large amount of electric energy is expended to produce the rays, 
but, in the radio-active bodies, the rays are emitted spontaneously 
and at a rate uninfluenced by any chemical or physical agency. 
The a and 8 rays from the active bodies are projected with much 
greater velocity than the corresponding rays in a vacuum tube, 
while the y rays are of much greater penetrating power than 
Rontgen rays. 
The effect of a magnetic field on a pencil of rays from a 
radio-active substance giving out the three kinds of rays is very well 
illustrated in Fig. 207. 
Some radium is placed in the bottom of a narrow cylindrical 
lead vessel R. A narrow pencil 
of rays consisting of a, 8, and 
ry rays escapes from the open- 
ing. If a strong uniform 
magnetic field is applied at 
right angles to the plane of 
the paper, and directed towards 
the paper, the three types of 

rays are separated from one 
another. The y rays continue 

in a straight line without any 
deviation. The § rays are 
deflected to the right, deserib- 
ing circular orbits the radius of which varies within wide limits. 
If the photographic plate AC is placed under the radium vessel, 
the 8 rays produce a diffuse photographic impression on the right 
of the vessel R. The a rays are bent in the direction opposite to 
that of the 8 rays and describe a portion of the arc of a circle of 
large radius, but they are rapidly absorbed after traversing a 
distance of a few centimetres from the vessel R. The amount 

1 This method of illustration is due to Mme Curie, These présentée & la Faculté 
des Sciences de Paris, 1903. 
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