I824.J 



Mr. Poivell on Solar Light and Heat. 



87 



Substituting these values in the formula (A), we have, with 

 the focus, the correction 



d s -^ a 55 901 1000 187^ 



a t • l~Ta — 45" X 5"87 — "532 ' 0I " 100 * 



With the diffuse rays, it becomes (C) 



d 1000 122 



T x ~ Tis ' or lOO* 

 (35.) To compare the heating effects, the following sets of 

 experiments were made : 



Focus. Rise in 30 seconds. Diffuse rays. Rise in 2 minutes. 



The ratios of these respective quantities in each case agree 

 very nearly among themselves. We may obtain the mean ratio 

 in each case by taking 



Mean 11-4 | 45 | 2-08 | 5*6 



Hence r ~ = ± | ^ .=? ~ 



Hence, since in each case, h — h x we obtain 



1000 



In the one case, ^ = ^x 



p A:, 1 1000 



1 



i 



And in the other,^ = - x — = — . 



(36.) Another set of experiments in which the coatings were 

 mutually changed, were as follows : 



