170 PHYSICAL SCIENCE 



have different values ranging from 60 to 95 per 

 cent, of the velocity of light. The ^ rays, then, 

 are negative corpuscles, or negative electrons. 



Magnetic and electric fields which are strong 

 enough to deflect considerably the /5 rays, produce 

 no effect on the easily absorbed a rays. R. J. 

 Strutt, now Lord Rayleigh, suggested in the year 

 1900, that the a rays were positively charged 

 particles, of mass greater than that of the negative 

 /5 particles, but it was not till some time after- 

 wards that their magnetic and electric deviations 

 were demonstrated experimentally, and shown to 

 be in the direction opposite to that observed with 

 /5 rays. The mass of the carriers in the a rays, 

 as calculated from the deviations, is the same as 

 that of helium atoms — more than four thousand 

 times that of the negative electrons — and the 

 positive charge associated with the particles is 

 found to be double that on a univalent ion. The 

 velocity is about one-tenth of that of light. 



The very penetrating or 7 rays have never 

 been deflected, and from this fact it has been 

 supposed that they are different in kind to the 

 other types, and, like the X-rays discovered by 

 Rontgen, consist of electro-magnetic waves similar 

 in nature to light but of shorter wave-length. On 

 the analogy of the cathode rays, we should expect 

 that such pulses would be started as a secondary 

 effect of the /5 rays. In 1903, Strutt published 

 experiments which show that, as with the a and 

 ^ rays, and also with the cathode rays, different 

 gases absorb the 7 rays in direct proportion to the 

 density. The absorption phenomena exhibited 

 by ordinary Rontgen rays are of an entirely 

 different kind. But very *'hard" Rontgen rays 



