440 



Mr. A. Tribe. 



[June 16, 



I employed for this purpose four similar electrolytic cells of the 

 shape and dimensions given in p. 436. Pairs of porous plates were 

 set across each of these cells, as before described, so as to give in one 

 case an incident angle of 45° ; in the second, 37-^° ; in the third, 30° ; 

 and in the fourth, 15°. Dilute sulphuric acid (1 to 11) was used in 

 the transmitting cell, and a 5 per cent, solution of copper sulphate in 

 the refracting cell. The current generally used was three Webers, 

 though variations in this respect were found not to affect the refraction. 

 The time of each determination was five minutes. The analysers 

 employed were squares (24 millims. the side) of sheet silver, and disks 

 of the same material 24 millims. in diameter. These were immersed 

 horizontally in the centre of the refracting cell, the squares in such a 

 way that their edges were parallel with the respective sides and ends 

 of the rectangular electrolytic cell ; the disks, so that a line passing 

 through their centres was coincident with a line joining the electrodes. 



As it has been already shown that the course of the energy in the 

 transmitting and refracting cells was in the same horizontal plane, it 

 was to be anticipated that the boundary lines of the ions on the 

 analysers placed in the positions just described would be straight. 

 Such is the case with the boundary of the negative ion, which conse- 

 quently is taken for purposes of measurement. 



Were the course of the energy in the inner cell identical with that in 

 the transmitting cell, the boundary lines, in accordance with the rule 

 in /3, would be perpendicular to a right line joining the electrodes, and 

 this might be named the zero line, or line of no refraction. And were 

 the analysers in the position described, the zero line would be perpen- 

 dicular to the central line on the disks and to the edges of the squares, 

 which are parallel with the sides of the cell. It follows that, were the 

 course of the energy diverted from a right line joining the electrodes 

 (its original course), the boundary line of the ion would deviate pari 

 passu from the line of no refraction. The numbers expressing this 

 obliquity or amount of refraction in five series of trials are given in 

 the annexed table. In Series I, II, III, square analysers were used, 

 and for IV and V the disks already described. 









Deviation. 







Angle of 













incidence. 















I. 



II. 



III. 



IY. 



y. 



o 



o 



o 



o 



o 





15 



9 



9 



9 



10 



9 



30 



19 



20 



19 



19 



20 



S7h 



27 



26 



25 



26 



25 



45 



31 



31 



33 



33 



32 



