SOME PHYSICAL PROBLEMS 



the leading investigators have postulated tentative 

 hypotheses which at least serve as a working basis 

 until they are either confirmed or supplanted. On one 

 point, however, there seems to be unanimity of opinion 

 there seems to be little question that there are at least 

 three different kinds of rays produced by radio-active 

 substances. According to Sir William Crookes, the 

 first of these are free electrons, or matter in an ultra- 

 gaseous state, as shown in the cathode stream. These 

 particles are extremely minute. They carry a negative 

 charge of electricity, and are identified with the electric 

 corpuscles of Thompson. Rays of the second kind are 

 comparable in size to the hydrogen atom, and are pos- 

 itively electrified. These are easily checked by ma- 

 terial obstructions, although they render the air a con- 

 ductor and affect photographic plates. The third are 

 very penetrating rays, which are not deflected by elec- 

 tricity and which are seemingly identical with Roentgen 

 rays. Professor E. Rutherford has named these rays 

 beta (/3), alpha (a), and gamma (7) rays respectively. 

 Of these the beta rays are deviated strongly by the 

 magnetic field, the alpha much less so very slightly, 

 in fact while the gamma rays are not affected at all. 

 The action of these three different sets of rays upon 

 certain substances is not the same, the beta and gamma 

 rays acting strongly upon barium platinocyanide, but 

 feebly on Sidot's blende, while the alpha rays act ex- 

 actly the reverse of this, acting strongly on Sidot's 

 blende. 



If a surface is coated with Sidot's blende and held 

 near a piece of radium nitrate, the coated surface be- 

 gins to glow. If now it is examined with a lens, brill- 



103 



