1895.] J. C. Bose — Polarisation of Electric Bays. 291 



EXPLANATION OF PLATES. 

 PLATE III. 

 Fig. 1. Lambrachaeus remifer, <f. 

 „ 2. Physachaeus ctenurus, $ ; 2a. abdomen of 2 x 4 ; 2b. abdomen of 



6 x 4. 

 „ 3. Physachaeus tonsor, ? 

 „ 4. 4a. Grypachaeus hyalinus, ? . 



PLATE IV. 



Pig. 1. la. Inachoides dolichorhynchus, <?. 



„ 2. 2a. Apocremnus indicus, <f . 



„ 3. Naxia investigatoris, <?. 



„ 4. Macrocoeloma nummifer, cf. 



„ 5. Maia gibba, cf . 



PLATE V. 



Pig. 1. Achaeus cadelli, <f . 



„ 2. 2a. Chorilibinia andamanica. 



„ 3. Callodes malabaricus, ? . 



„ 4. 4a. Paratymolus hastatus, ? 



On Polarisation of Electric Bays by Double Befracting Crystals. — By Prof. 

 J. C. Bose, b.a., (Cantab.) B. Sc. (Lond.) 



[Read 1st May.] 



Plate VI. 



A ray of ordinary light incident on a crystal of Iceland spar is 

 generally bifurcated after transmission, and the two emergent rays 

 are found polarised in planes at right angles to each other. The object 

 of the present inquiry is to find natural substances which would polarise 

 the transmitted electrical ray. It was thought that the analogy be- 

 tween electric radiation and light would be rendered more complete, 

 if the classes of substance which polarise light were also found to 

 polarise the electric ray. The identity of the two phenomena may 

 be regarded as established, if the same specimen is found to polarise 

 both the luminous and electric rays. 



As the wave length of an electrical ray is very large compared with 



that of visible light, one would think very large crystals, much larger 



than what occur in nature, would be required to show polarisation 



of electric rays. By working with electric radiations having very 



J. n. 37 



