S. P. Langley on the Selective Absorption of Solar Energy. 177 



therefore, of the original unknown heat of the ray, which we 

 will represent by E, reached the observer at noon, producing 

 a deflection of 17, or -895 E = 17, giving 



E = 



17 



•895 



= 19-0: 



that is, had our instrument been placed outside the atmosphere 

 at that time, it would have indicated a deflection of 19 instead 

 of 17. 



By a similar process we find that the coefficient of trans- 

 mission for the violet ray is *923; from which we see that the 

 ultra-red ray is transmitted with greater facility than the 

 violet. The amount of this violet radiation transmitted by the 

 whole depth of atmosphere at noon was *538, from which its 



4*5 

 energy outside the atmosphere was -^^ = 8*4. 



The table below gives the coefficients of transmission &c. 

 for these and other points in the spectrum where measure- 

 ments were taken on this day. The first column gives the 

 deviation of the observed ray in the spectrum of the prism 

 used; the second and third columns the deflections obtained 

 with the galvanometer at noon and in the afternoon respec- 

 tively; the fourth column the coefficient of transmission (for 

 an atmosphere supporting one decimetre of mercury); the fifth 

 the transmission of the whole depth of atmosphere at noon, 

 obtained by raising the coefficient of transmission to the 7*74 

 power ; and the last the computed energy outside the atmo- 

 sphere expressed in galvanometer-deflections. 



Deviation. 



o i d v 



53 00 0-02 



52 00 0-21 



51 00 0-96 



50 00 4-5 



49 30 7-3 



49 00 13 



48 00 43 



47 30 72 



46 45 158 



46 12 209 



45 53 175 



45 28 122 



44 30 17 



Table VIII. 







d 2 . 



t 



<** 



E. 



000 









000 









009 



•925 



•549 



1-8 



0-39 



•923 



•538 



8-4 



3 : 6" 



•953 



•689 



18 : 9 



125 



•960 



•731 



58-8 



38 



•979 



•850 



84-7 



109 



•988 



•910 



173-7 



134 



•986 



•894 



233-8 



107 



•984 



•883 



198-3 



79 



•986 



•895 



136-2 



11 



•986 



•895 



190 



Similar reductions have been made for each day's observa- 

 tion, the result from each being confirmatory of the statement 

 here (see column t Mipt ) that the atmospheric absorption dimi- 



