396 Prof. Tyndall on Calorescence. 



quantity of heat transmitted by the pure liquid to the pile was 

 determined. The same cell was afterwards filled with the opake 

 solution, the transmission through which was also determined. 

 Calling the transmission through the transparent liquid 100, 

 the foregoing Table gives the transmission through the opake. 

 The results, it is plain, refer solely to the iodine dissolved in the 

 bisulphide, — the transmission 100, for example, indicating, not 

 that the solution itself, but that the body dissolved is, within 

 the limits of error, perfectly diathermic to the radiation from the 

 first four sources. 



The layer of liquid employed in these last experiments was 

 not sufficiently thick to quench utterly the luminous radiation 

 from the electric lamp. A cell was therefore constructed whose 

 parallel faces were 2*3 inches apart, and which, when filled with 

 the solution of iodine, allowed no trace of the most highly con- 

 centrated luminous beam to pass through it. Five pairs of 

 experiments executed with this cell yielded the following re- 

 sults : — 



Radiation from Electric Light ; battery 40 cells. 



Deflection, 



o o 



{Through transparent bisulphide . . 47*0; 46-0 



Through opake solution .... 42*3 ; 43*5 



{Through transparent bisulphide . . 44*0 ; 43*7 



Through opake solution . . . . 41 -2 ; 40*0 



Through transparent bisulphide . . 42*0; 43*0 



Calling the transmission through the transparent liquid 100, 

 and taking the mean of all these determinations, the transmis- 

 sion through the opake solution is found by calculation to be 

 86*8. An absorption of 132 per cent, is therefore to be set 

 down to the iodine. This was the result with a battery of forty 

 cells ; subsequent experiments with a battery of fifty cells made 

 the transmission 89, and the absorption 11. 



Considering the transparency of the iodine for heat emitted 

 by all sources heated up to incandescence, as exhibited in Table 

 III., it may be inferred that the above absorption of 11 per 

 cent, represents the calorific intensity of the luminous rays alone. 

 By the method of filtering, therefore, we make the invisible 

 radiation of the electric light eight times the visible. Compu- 

 ting, by means of a proper scale, the area of the spaces A B C D, 

 CDE (fig. 3), the former, which represents the invisible emis- 

 sion, is found to be 7'7 times the latter. Prismatic analysis, 

 therefore, and the method of filtering yield almost exactly the 

 same result. 



[To be continued.] 



