300 Professor Jagadis Chunder Bose [Jan. 29, 



There is an interesting speculation in reference to the possibility 

 of the sun emitting electric radiation. No such radiation has yet 

 been detected in sunlight. It may be that the electric rays are ab- 

 sorbed by the solar or the terrestrial atmosphere. As regards the 

 latter supposition, the experiment which I am able to exhibit on the 

 transparency of liquid air may be of interest. Professor Dewar has 

 kindly lent me this large bulb full of liquid air, which is equivalent 

 to a great thickness of ordinary air. This thick stratum allows the 

 radiation to pass through with the greatest facility, proving the high 

 transparency of the liquid air. 



Verification of the Laws of Reflection. 



A small plane metallic mirror is mounted on the platform of the 

 spectrometer-circle. The receiver is mounted on a radial arm. The 

 law of reflection is easily verified in the usual way. The second 

 mirror, which is curved, forms an invisible image of the source of 

 radiation. As I slowly rotate the cylindrical mirror, the invisible 

 image moves through space ; now it falls on the receiver, and there 

 is a strong response produced in the receiver. 



Refraction. 



Deviation of the electric ray by a prism may be shown by a prism 

 made of sulphur or ebonite. More interesting is the phenomenon of 

 total reflection. A pair of totally-reflecting prisms may be obtained 

 by cutting a cube of glass, which may be an ordinary paper-weight, 

 across a diagonal. The critical angle of a specimen of glass I found 

 to be 29°, and a right-angled isosceles prism of this material produces 

 total reflection in a very efficient manner. When the receiver is 

 placed opposite the radiator, and the prism interposed with one of its 

 faces perpendicular to the electric beam, there is not the slightest 

 action on the receiver. On turning the receiver through 90°, the re- 

 ceiver responds to the totally-reflected ray. 



Opacity due to multiple refraction and reflection, analogous to the 

 opacity of powdered glass to light, is shown by filling a long trough 

 with irregularly-shaped pieces of pitch, and interposing it between 

 the radiator and the receiver. The electric ray is unable to pass 

 through the heterogeneous media, owing to the multiplicity of re- 

 fractions and reflections, and the receiver remains unaffected. But 

 on restoring partial homogeneity by pouring in kerosene, which has 

 about the same refractive index as pitch, the radiation is easily 

 transmitted. 



Determination of the Index of Refraction. 



Accurate determination of the indices of refraction becomes im- 

 portant when lenses have to be constructed for rendering the electric 

 beam parallel. The index for electric radiation is often very diflierent 



