56 Prof. J. C. Bose on a Complete Apparatus for 



these little-known aether waves are now being gradually dis- 

 covered. Confining our attention to the electric waves, we 

 find that there are many important problems which may 

 perhaps be better attacked with these comparatively slow 

 vibrations ; among which may be mentioned the determina- 

 tion of the indices of refraction of various substances which 

 are opaque to visible light, but are transparent to the electric 

 ray ; the relation between the dielectric constant and the 

 refractive index when the rates of oscillation are made com- 

 parable in the two determinations ; the variation of the index 

 with the frequencies of vibration. Then there are the phe- 

 nomena of double refraction, polarization, and the magnetic 

 rotation of the electric ray ; the determination of the wave- 

 length, and other problems of a similar nature. 



The fascination of the subject drew me to its study, though 

 the investigations were rendered exceedingly difficult in 

 India from want of facility for making the necessary appa- 

 ratus. I ultimately succeeded in constructing a few instru- 

 ments with which I was able to obtain the values of the 

 indices of refraction of various substances for electric waves, 

 the wave-length of electric radiation, to demonstrate the 

 phenomena of double refraction and polarization of the 

 electric rays, and to find out certain substances which act as 

 electric tourmalines. The simplified apparatus with which 

 many of the properties of electromagnetic radiation may 

 be studied is here exhibited. This is a duplicate made by 

 Messrs. Elliott, Brothers, of the apparatus which I brought 

 from India. I also take this opportunity of thanking Mr. 

 Bolton, F.U.A.S., of the Mathematical Instrument Depart- 

 ment, Calcutta, for the divided circle in my apparatus. 



The following are the experiments which may be carried 

 out with this apparatus : — 



A. Verification of the laws of reflexion. 



1. Plane mirrors. 



2. Curved mirrors. 



B. Phenomena of refraction. 



1. Prisms. 



2. Total reflexion. 



3. Opacity caused by multiple refraction and reflexion. 



4. Determination of the indices of refraction. 



C. Selective absorption. 



1> Electrically-coloured media. 



