on the Temperature of the Sun. 547 



Another proof of the rule which has just been indicated 

 can be given. If from different curves we deduce the values 

 of y which correspond to one and the same value of e, we 

 have, obviously, different numbers. As, for example, we have 

 for 6=2-7 :— 



September 28 174*0 



29 163-3 



30 164-0 



October 2 160'0 



„ 18 175-0 



„ 19 169-0 



„ 21 172-2 



10 172-4 



November 1 164*0 



December 10 168-0 



„ 17 180-0 



„ 22 162-2 



The arithmetic mean of these values is y — 168*7 ; and if we 

 determine the mean value of b corresponding to e =2*7, we 

 obtain the number 



6=0-86. 



By making 6 1 = 0*86 — 0-08 = 0*78, and by substituting the 

 values of y, of b, and of e in the formula y = ab\, we obtain 



a=330, 



a value which is very near the mean 323. If, instead of 

 b-L — 0*78, we had taken the values 0*75 and 0*80, we should 

 have had respectively the values 308 and 367 for a, which 

 shows that a very slight difference in the value of the coeffi- 

 cient of absorption b is sufficient to give very different values 

 for a ; but that proves also that the method followed in deter- 

 mining the mean value of a is very appropriate, since the ex- 

 treme values amongst those of which the mean has been taken 

 are nearer to the latter than those which are obtained by vary- 

 ing the coefficient of absorption 2 or 3 hundredths. 



We can therefore confidently assume that the value a = 323 

 represents the solar constant expressed in scale-divisions of the 

 galvanometer employed when there was a resistance of sixteen 

 Siemens units in the circuit, in addition to that offered by the 

 pile No. 1, the rheophores, and the wire of the galvanometer. 



It is now only necessary to determine what the value of a 

 signifies, in order to be able to compare the thermal effect 

 produced by the radiation of the sun with that produced by 

 the radiation from the artificial sources, and so determine in 

 the end the effective temperature of the sun. 



