24 Recent Advances in Electricity. 



effect was only obtained in one definite point on the circle — 

 a fact which indicates that there was not a continuous 

 spectrum, but one definite wave length. In his principal 

 experiment the wave length thus found was i'48 cm, 

 which was about double of the nearest distance between the 

 two outside balls. With a larger central ball, and a greater 

 distance between the two outside balls, the wave length was 

 found to be 2-36 cm. These lengths, one being about | in. 

 and the other about i in., are gigantic when compared with 

 wave-lengths of light, of which, roughly speaking, it takes 

 50,000 to make an inch. Another curious effect obtained by 

 Prof. Bose was that yarn wound regularly upon a flat spool of 

 wood acts upon the Hertzian rays in the same way that 

 tourmaline acts upon rays of light, that is to say, it transmits 

 only a portion of the incident radiation, and this transmitted 

 portion is polarised. The polarisation was tested by the usual 

 reflection test. 



To the general public the most interesting of recent 

 electrical discoveries is that of the Rontgen rays — rays 

 which, though they do not directly affect the eye, are 

 capable of affecting photographic paper, and also of pro- 

 ducing fluorescence in certain substances, especially in 

 platino-cyanides. Unlike rays of light and Hertz rays, they 

 cannot be refracted, and hence cannot be focussed by a lens. 

 The pictures which are obtained by their aid are accordingly 

 not images, but only shadows. Whatever sharpness they may 

 possess is due on the one hand to the smallness of the source 

 from which the rays proceed, and on the other to the nearness 

 of the object to the paper on which its shadow falls. Their chief 

 interest with the public lies in the fact that flesh is very trans- 

 parent to them, while bone is comparatively opaque, so that the 

 shadow of the skeleton is cast by the living body. Lenard 

 had previously found that when the cathode stream in a 

 Crookes' tube was directed against the side of the tube, some 

 influence, which might be regarded as a continuation of the 

 cathode rays, could be detected outside the tube. This 



