62 Sir John Conroy. On the Amount of Luminous and 



The amount of light transmitted by the four cells was determined, 

 the photometric arrangement used being the one described in the 

 ' Philosophical Transactions,' A, vol. 180, 1889, p. 248. It consisted 

 essentially of a small Argand gas burner and of two mirrors, so placed 

 that they reflected the light of the lamp towards each other. The 

 photometer was placed between them, and the cell between the 

 photometer and one of the mirrors, and six readings made of the 

 position in which there was equality of illumination; the cell was 

 then placed on the other side of the photometer, and six more read- 

 ings made of the new position of equality of illumination ; from these 

 measurements the value of the coefficient of transparency, was 



calculated by the expression (loc. cit., p. 250) k = ^ ~ x . x b e i n g 



x 2 (x — x Y ) 



the distance between the two images of the lamp, x 1 and x 2 the two 

 positions of the photometer in which there was equality of illumina- 

 tion, the optical shortening of the path of the light due to its passage 

 through the glass and water being, of course, allowed for. 

 Table V gives these results. 



Table V. 





x x . 



x — Xi. 



a?2- 



x — x. 2 . 



Per cent, of 

 incident light 

 transmitted. 



Cell I 



185-5 



199-1 



199 -3 



185 3 



86-62 





186-0 



198-6 



199-0 



185 -6 



87-35 





185-5 



199-1 



199-1 



185 5 



86 -80 











Mean . . 



86-92 



Cell II 



184-7 



198-9 



199-2 



184-4 



85 -96 





184-8 



198-8 



199-1 



184-5 



86-14 





185-2 



198 -4 



199-3 



184-3 



86-32 











Mean. . 



86-14 



Cell III 



182-9 



199-4 



198-1 



184-2 



85 -29 





182-7 



199 -2 



198-6 



183 -7 



84-84 





182-7 



199-2 



198-6 



183-7 



85-11 











Mean . . 



85 -08 



Cell IV 



182 "3 



198-7 



198-6 



182-4 



84-26 





182-8 



198-2 



198-3 



182-7 



84 98 





182-9 



198-1 



198-6 



182-4 



84-80 











Mean . . 



84-68 



The table shows that the loss of light increased from 13'1 per cent, 

 with Cell I to 15*3 per cent, with Cell IY ; the loss being due to 



