C. C. Hutchins — Irregular Reflection. 379 



the total reflection. We must know what the galvanometer 

 deflection would be provided the thermograph received direct 

 sunlight. To this end a brass plate having a small hole at its 

 center is put in the path of the sunbeam near the heliostat, 

 and the galvanometer deflection produced by the sun so 

 reduced is observed. We may calculate the deflection for the 

 unreduced sun and the albedo as follows : 



Let L == distance of small hole to thermal junction. 



I = dist. ot body under experiment to thermal junction. 



d — sun's apparent diameter. 



G= galvanometer deflection by reduced sun. 



g - " " " body. 



M= diameter of small hole. 



m= " " body. 



'Now on the supposition that the body in the form of a flat 

 disc reflects in accordance with the sine law, and that m is not 

 large in comparison with I, the whole interior of a hemisphere 

 having the body at its center would be uniformally illuminated, 

 and were the total reflection received by this hemisphere 

 received by the thermograph the galvanometer deflection 

 would be 



2irF 



■(?)' 



'9 



The deflection by the unreduced sun would be 

 (L sin elf 



and consequently the albedo, 



(*■*"*>' (if)' g 



2M 2 r ' g 



The following were the dimensions of the constants : 



L = 640 cm 

 I = 57'5 



d = 



M= 0-1567 

 m— 4-00 



For present purposes d may also be considered constant, 

 and the above reduces to K . ^, in which log K = 9*9417. 



