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



If we take into account the electric radiation only, it would 

 no doubt be found that radiations haying different wave- 

 lengths are unequally absorbed by different substances. 



Phenomena of Interference. 



Determination of the Wave-Lengths by Diffraction Gratings. 

 — In a paper read before the Royal Society in June last 

 (vide Proceedings of the Royal Society, vol. Ix.) I have given 

 an account of a method of obtaining pure spectra of electric 

 radiation by means of curved gratings. The experiment was 

 carried out with a large apparatus. The spectrum obtained 

 was well defined, and appeared to be linear, and not conti- 

 nuous. I had not time to adapt the experiment to this small 

 apparatus, but I think it would not be difficult to do so. 



Double Refraction and Polarization. 



The spectrometer circle is removed, and an ordinary stand 

 for mounting the receiver substituted. By fitting the lens- 

 Fig. 8. — Polarization Apparatus. 



K, the Crystal-Holder. S, a Piece of Stratified Eock. C, a Crystal. 

 J, the" Jute Polarizer. W, the Wire-Grating Polarizer. D, the 

 Vertical Graduated Disk, by which the Eotation is measured. 



tube the electric beam is made parallel. At the end of the 

 lens-tube there is a slot in which is dropped the wire-grating 

 polarizer. A crystal-holder provided with three sliding jaws 

 is fitted on to the lens-tube, and is capable of rotation round 

 an axis parallel to the direction of the electric ray. 



