300 Dr. J. C. Bose. On the Influence of the Thickness of 



In the next series of observations, the rays were refracted from 

 air into glass. The electric beam was rendered parallel with the 

 help of a glass lens (f = 4 cm.). The beam was incident on the 

 plane face of the semi cylinder. As the cylinder itself focussed the 

 refracted beam, the objective hitherto nsed in conjunction with the 

 receiver was dispensed with. 



i. 



r. 



Mean value of r. 





40° 



18° 

 19 

 18 



18° 20' 



2-04 



50° 



22° 

 23 

 22° 30' 



22° 30' 



2-00 



65° 



25° 30' 

 26° 

 27 



2G° 10' 



2-05 



Mean value of /.i = 2 03 ( i). 



The different values of /i obtained are given below : — 



From total reflection from a single semi- cylinder, 2*08 .... (1) 



„ ,, ,, two semi-cylinders . . 2'04 .... (2) 



From refraction from glass into air , . 2-04 .... (3) 



,, air into glass 2"03 .... (4) 



The frequency of vibration was of the order 10 10 . 



The value of the optical index of the glass determined by the total 

 reflection method was found to be 



/<d == 1'53. 



" On the Influence of the Thickness of Air-space on Total 

 Reflection of Electric Radiation." By Jagadis Chunder 

 Bose, M.A., D.Sc. Professor of Physical Science, Presidency 

 College, Calcutta. Communicated by Lord Rayleigh,, 

 F.R.S. Received November 15, — Read November 25> 

 1897. 



In my preliminarj r experiments on the determination of the index 

 of refraction of various substances for electric radiation, I used a 



