364 



Mr. Powell on Terrestrial Light and Heat. [Ma^> 



Incandescent iron. Rise in 30 seconds. Distance 7 inches. 



(10.) In the following set of experiments, the effect of hght 

 M'as observed with the instrument in its glass case, with an addi- 

 tional screen of plate glass several times replaced ; for (/ + h) 

 there were two screens to the lower bulb ; the outer one several 

 times replaced. 



Incandescent iron. Rise in SO seconds. Distance 7 inches. 



(11 .) I subsequently made a similar set of observations with a 

 ball of iron two inches in diameter. In the former case, the 

 values of (/) and of (/ + /') were not so taken as to be compara- 

 ble. In the present instance I attempted, by obtaining both 

 results under similar circumstances, to deduce the value of (A) 

 and the ratio as in former experiments. For this purpose, to 

 obtain (/) the instrument was employed without its case, but 

 with three screens of plate glass; and, as before, for (/ 4- A); 

 the nearest screen was 1"5 inch from the bulb; here there might 

 be some small cooling effect. After the experiment, the outer 



screen alone was found at all heated. 



■ni $ 



