1881.] 



On the Refraction of Electricity. 



439 



incidence, would decrease or increase as the media in the refracting 

 and transmitting cells approached or receded in conducting power. 

 This was proved to be the case, first, by replacing the 1 per cent, 

 solution of copper sulphate in the refracting cell by a 2, 3, 5, and 10 per 

 cent, solution respectively, when analysers at i recorded respectively a 

 decreasing refraction as the media in the cells approached equality. 

 And, secondly, by placing a 5 per cent, solution of copper sulphate in 

 the refracting cell, and successively a concentrated solution of copper 

 sulphate, a concentrated solution of sodium chloride, and a dilute 

 solution (1 — 11) of oil of vitriol in the transmitting cell. Analysers 

 at i showed, in the case of the copper sulphate, a refraction of about 

 15°, in the case of the sodium chloride, 30°, and in that of the dilute 

 sulphuric acid, 40°. The order of the increase in refraction is here 

 the same as that of the conductivities of the liquids. 



Again, it was anticipated that the refraction would decrease as the 

 incidence decreased. This was proved to be true by setting the 

 diaphragms so that the angle of incidence should be 45°, 30°, and 15° 

 respectively. With a 5 per cent, solution of copper sulphate in the 

 refracting cell, and dilute sulphuric acid in the transmitting cell, a 

 refraction of about 35° was obtained when the incidence was 45°, 

 about 22° when at 30°, and about 7° when at 15°. 



Relation hetiveen Electric Incidence and Refraction. 

 That part of the electro- chemical method which has been already 

 described supplies three means of determining the bending of the 

 course of the energy on its passage into the refracting cell. First, by 

 the curvature of the ions on an analyser with the shorter edges of the 

 plate upright, and its length perpendicular to the electrodes. But the 

 practical impossibility of obtaining accurate measurements of these 

 curves, renders this plan only roughly quantitative. Secondly, by 

 placing an analyser at various angles to a right line joining the elec- 

 trodes, until it records a 'parallel distribution. This is the case when 

 the course of the energy is parallel with the sides of the analysing 

 plate, and the angle enclosed between the plate and the right line 

 referred to consequently expresses the amount of refraction. The 

 objections to this plan are twofold. It is very tedious, and it is also 

 difficult to determine with sufficient accuracy the angle of the plate as 

 it stands in the cell. The refraction numbers given above were 

 obtained by this second method, and for the last of the reasons just 

 mentioned I regard them only as approximately correct. The third 

 plan, based on the fact that the course of the influence, when parallel 

 to the sides of an analyser, is perpendicular to the boundary lines 

 of the ions set free, is the one I have employed for the more 

 accurate deter ruination of the relation between electric incidence and 

 refraction. 



