56 LIFE AND WORK OF SIR JAGADIS C, BOSE 



the discharge, and the second by the use of platinum-covered 

 surfaces, from and to which the alternating sparks could 

 pass without roughening or oxidation. Bose's radiators, 

 instead of being disordered by specks of dust, as previous 

 workers had found, continued to emit their sparks, and 

 these their waves, so steadily as to be uninterrupted even 

 when a jet of air mingled with street-dust was turned upon 

 it. Bose also used for his radiator a sphere surrounded 

 by two hollow hemispheres. This device increased the 

 energy of radiation. 



Further advance of the determination of the optical 

 properties of electric radiation by quantitative measure- 

 ments have been retarded, since on account of the large 

 size of the waves their strictly linear propagation could not 

 be secured. Bose was able to produce extremely short 

 waves, which largely filled up the gap between the infra- 

 red rays and Hertz's long electric waves. 



For this purpose, the whole of the radiating part of 

 the apparatus was enclosed within double metal walls 

 to cut off stray radiation : the outer of copper to prevent 

 the escape of the electric rays, and the inner of soft iron as 

 a shield to cut off the magnetic disturbance. 



The next problem before experimenters was to im- 

 prove upon Hertz's receiver. Here the initiative was 

 afforded by Professor Branly, of the Catholic University 

 College of Paris, whose ' radio-conductor ' has since become 

 so well known. In principle it is merely a slender tube 

 containing metal filings, in which, although themselves 

 good conductors, there is yet considerable resistance, since 

 their contacts are comparatively few, and these variably 

 imperfect. But Branly found that the Hertzian waves, 

 which could not but produce considerable induction in 

 the filings, enormously reduced their resistance, some- 

 times even to a millionth. Hence it followed that the 

 apparatus could be used as the needed improved receiver, 

 'since detecting the electric rays more finely and more 

 clearly than did the first receiver of Hertz. After the 



