of the Solar Spectrum. 245 



values for w and e, namely those belonging to the Fraunhofer's 

 lineB, w = mO, e= 1-526; 



secondly, those belonging to the Fraunhofer's line F, 



m; = 485, e = l-536; 

 and finally, those belonging to the Fraunhofer's line H, 



m; = 396, e = 1-546 



(multiplying the real value of w with 1000000, in order to 



avoid the decimal places), we obtain three equations, from which 



the following values of a, b, and c are derived : — 



ffl= 1391460, 



i= -1796460, 



c= 580000. 



Substituting these numbers in equation (1), we get 



w; = 1391460 -1796460e + 580000e^ . . (2) 

 From this equation the undular length of the extreme thermal 

 rays of the solar spectrum is obtained by substituting for e the 

 index of refraction 1 "506 : we get then 



m; = 1770; 

 or, rather, redividing by lOOOOOO, 



«; = 0-001 77. 

 The same result may be obtained more easily and clearly in 

 a graphic manner. In fig. 2, the hne R S represents the 

 Fig. 2. 



O'OOIS 

 0-0016 

 0'0014 



solar spectrum produced by a prism of crown-glass on the same 



