54 LIFE AND WORK OF SIR JAGADIS C. BOSE 



and opaque, and some midway translucent, as it were. 

 Experiment immediately justified these anticipations, 

 although, as a physicist would be prepared to expect, with 

 different media than for ordinary light. Thus a sheet of 

 water is opaque to the electric waves, while glass and 

 pitch turned out alike to be transparent to them. 



The next question is naturally Can these waves be 

 reflected, like light ? With big plane mirrors, sheets of 

 zinc and other metal, reflection was found to take place ; 

 but not with the precision of optical phenomena, in which 

 the angle of reflection is exactly equal to the angle of inci- 

 dence, whereas here the reflection was spread out. But 

 this too was only what was to be expected from the large 

 size of waves. Indeed, though light is propagated recti- 

 linearly, a certain curl of its waves inwards on passing an 

 obstacle has long been known to take place ; and this 

 ' diffraction ' has been beautifully investigated, experi- 

 mentally and mathematically. On the great scale of Hertz's 

 waves, comparable to those of sound indeed far surpassing 

 these, since ranging from several metres, the shortest he 

 produced, up to two hundred yards, or thence again to even 

 a mile it was natural that their rectilinear propagation 

 should be but relative, and that they should curl round 

 corners, just as sound-waves do. 



Hertz next tested whether Newton's classic experiment 

 the refraction of light by the prism could be repeated 

 with his new rays. But for their immense and spreading 

 magnitude, a correspondingly large prism was needed, on 

 a scale beyond that of glass-casting. Still, Hertz rose to 

 the occasion, and cast a gigantic prism with some two tons 

 of pitch. Experiment rewarded him : the electric rays 

 were unmistakably bent towards the base ; and though his 

 measurements with such long and curling waves were 

 naturally but a first and rough appproximation, the great 

 thing was proved the expected refraction did take place, 

 and that very appreciably. Thus encouraged, Hertz set to 

 testing whether his electric rays could not also be polarised, 



