Chemically Active Rays in the Sun's Atmosphere. 349 



Distance from 

 centre. 



Intensities. 



Radius =54. 



Scale 1. 



Scale 2. 



00 

 105 

 210 

 315 

 41-9 

 472 

 52-5 

 535 



1000 

 98-4 

 900 

 843 

 65-9 

 490 

 281 

 188 



1000 

 990 

 941 

 86 3 

 683 

 480 

 30-7 

 195 



I have tried to determine the relative intensities of the larger 

 sun-spots, their penumbrae, and the adjoining surface of the sun. 

 The mean of several observations showed the ratio of the inten- 

 sity of the spot to the adjoining parts of the sun's surface to be 

 0-067; that of the penumbra was 0-630*. 



If we take the distance from the centre as abscissa, the in- 

 tensity as ordinate, we obtain a curve showing the decrease of 

 the intensity from the centre of the sun's disk. The ordinates I 

 of the curve which agrees best with the observations have been 

 determined as follows for the distances E from the centre : — 



E = sin 0. 









Q 



I. 



Radius = 12. 









o / 



00 



1000 



1 



4 46-8 



1000 



2 



9 35-7 



99-4 



3 



14 28 6 



98-2 



4 



19 28-3 



96-4 



5 



24 37 5 



937 



6 



30 0-0 



89-8 



7 



35 41 2 



84-5 



8 



41 48-6 



770 



9 



48 35-4 



660 



10 



56 26 6 



51 



11 



66 26 6 



330 



12 



90 00 



13-5 



If we compare the above observations with those made by 

 Liais, Secchi, and others for the less-refrangible rays (i.e. the opti- 

 cally active heating rays), we see that the absorption for chemi- 

 cally active rays is considerably larger. 



* The observations must only be considered preliminary, and will be 

 repeated as soon as large sun-spots appear. Liais (I, c. p. 327) determines 

 the ratio of the intensity of light of a spot to the adjoining parts of the 

 sun's disk to be 0'091 for rays of mean refrangibility, and that of the pe- 

 numbra 0'5» 



