14 Art. 10. -S. Kinoshita and H. Ikeuti : 



When a photographie plate was plaeed in contact with a flat 

 piece of glass coated witli the active deposit of radium and thus 

 exposed to the a rays coming out of the source of large area, a con- 

 siderable proportion of then* tracks seemed to have sufïered large 

 deflexions. This is not in conformity with tlie result just stated. 

 It appears likely that inost, if not all, of the tracks which look as 

 if they were deflected are only apparently so. This view is sup- 

 ported by the fact that there were as many tracks showing large 

 deflexions as small ones. 



Experiments made with tlie object of flnding if the magnetic 

 field has any influence upon the a ray tracks gave negative results. 

 In a field of ten thousand gauss, up to whicli the experiment was 

 extended, an « particle with a velocit}^ of 10" cm. per sec. (one-half 

 of the initial velocity of the a particles from I'adium C) will describe 

 a path for which the radius of curvatui-e is as great as 20 centi- 

 metres. It would not be possible to recognize such a slight curva- 

 ture, as the track under examination is only 52 // at most in 

 length. 



10. The 'photographic action of ß particles. It has long been 

 known that ß rays possess the property of acting on a photographic 

 plate; but owing to difficulties involved in the experiments, very 

 little is known about the efïect of an individual ß particle. 



When the a and ß rays from the active deposit of radium were 

 allowed to fall separately upon two areas on a thinly coated plate, 

 the photometric density produced by the ß rays was, for an equal 

 number of the particles, found to be one-sixth to one-eighth of that 

 produced by the a ra^^s. Therefore in going a unit distance through 

 the emulsion film, a ß particle brings out at most the above frac- 

 tion only of the silver grains which an « particle would, the actual 

 path of the ß particle being, on account of deflexions, greater than 

 the tliickness of the film. It is thus to be anticipated that the 

 silver grains acted on by a ß particle follow one another with too 

 wide intervals to present themselves as the track of the particle, 

 much more so when the liability of the particle in suffering deflex- 

 ions through matter is considered. The difference shown by the 

 tracks in air of a and ß particles in the photograph obtained by 



