FIRST RESEARCHES IN PHYSICS 59 



scope and polarimeter ; rotation of plane of 

 polarisation. 



Fully to summarise the results of this comprehensive 

 experimental inquiry is here impossible : enough to borrow 

 from a recent retrospect of it by an eminent American 

 physicist, Dr. Kunz of Illinois University : 



Bose showed that these short electrical waves have the same 

 properties as a beam of light, exhibiting reflection, refraction, 

 even total reflection, double refraction, polarisation and rotation 

 of the plane of polarisation. The thinnest film of air is sufficient 

 to produce total reflection of visible light with its extremely 

 short wave-lengths ; but with Bose's short electric waves, the 

 critical thickness of the air-space was determined by the 

 refracting power of the prism, and by the wave-length of the 

 electric oscillations. He found a special crystal, Nemalite, which 

 exhibits the polarisation of electric waves in the very same 

 manner as a beam of light is polarised by selective absorption in 

 crystals like Tourmaline, which Bose found to be due to their 

 different electric conductivity in two directions. The rotation 

 of the plane of polarisation was demonstrated by means of a con- 

 trivance twisted like a rope, and the rotation could be produced 

 to left or right, just as different sorts of sugar rotate the plane 

 of polarisation of ordinary light towards one direction or the other. 

 The index of refraction of these electrical waves was determined 

 for different materials ; and a difficulty was eliminated which 

 presented itself in Maxwell's theory, as to the relation between 

 the index of refraction of light and the dielectric constant of 

 insulators. Bose also measured the wave length of the various 

 oscillations. In order to produce the short electrical oscillations, 

 to detect them and to study their optical properties, he had to 

 invent a large number of new apparatus and instruments ; 

 and he has indeed enriched physics by a number of apparatus 

 distinguished by simplicity, directness, and ingenuity. 



So far the American physicist. But for the conclusion 

 of this chapter we may best quote one of Bose's own 

 passages, which better unveils the spirit which lies behind 

 research : in fact the part of the scientific imagination 

 which ever unifies reason and experiment alike. 



