66 Sir John Conroy. On the Amount of Luminous and 



These values are contained in Table IX, column 3 ; they agree more 

 closely with the observed values contained in column 4 than those 

 calculated on the assumption that there was no absorption. The 

 deflections of the galvanometer, however, were so small, and therefore 

 the difference between the two sets of calculated values for the deflec- 

 tions, and the observed values, so slight, that no very definite con- 

 clusions can be drawn from them ; they seem, however, to show that 

 some absorption did take place, and to about the same amount as 

 stated by Professor Tyndall. 



Table IX. 



Distances of 

 lamp. 



Deflection of galvanometer. 



Calculated. 



Observed. 



cm. 









150 







4' 14 



160 



3-64 



3-62 



3 63 



200 



2-33 



2-28 



2 34 



210 



2-11 



205 



2-06 



220 



1-92 



1 -86 



1 -83 



230 



1-76 



1-70 



1-72 



In the experiments made with Cell IV, the radiation from the lamp 

 had to traverse about 15 cm. of air when the cell was interposed 

 between the lamp and the pile, and about 215 cm. when the cell was 

 removed. The absorption in the former case must, according to 

 Professor Tyndall's experiments, have been insensible, and in the 

 latter case have amounted to about 9'7 per cent. ; assuming that the 

 absorption is proportional to the length of air traversed, an assumption 

 which in all probability is not strictly true. 



Calling the total amount of radiation from the lamp, 100, the ex- 

 pression for K under the given conditions is = 1*751. 



Thus, allowing for the absorption due to the aqueous vapour, and to 

 the loss which the light suffered in passing through the cell, it appears 

 that the total radiation from the lamp consisted of 1'75 per cent, 

 luminous and 98*25 per cent, non-luminous radiation : a somewhat 

 smaller value for the percentage of luminous radiation than that 

 found by Julius Thomsen. 



Conclusion. 



These experiments show : — 



(1.) That 3 mm. of glass and 10 cm. of water transmit a small 



