MIM..IU III.] IN VISIT, I. K LINKS IN THK SUN'S SPECTRUM. 79 



had taken the precaution to deposit with the Academy 

 a scaled envelope containing an account of their discov- 

 ITV, not knowing that it had been made and published 

 long previously in America. 



Hereupon M. E. Becquerel communicated to the same 

 Academy a criticism on their paper. In this he remarks: 

 "M. Draper, in examining the image produced by the 

 action of the spectrum on plates of iodized silver, an- 

 nounced before those gentlemen the existence of protect- 

 ing rays antagonizing the action of the solar rays, and 

 even acting negatively on iodide of silver." He strength- 

 ened his views by adding some observations that had 

 been made by Sir J. Herschel, who did not assent to the 

 existence of this protecting action, but thought that the 

 daguerreotype impressions could be explained on New- 

 ton's theory of the colors of thin plates. 



Herschel had made some investigations on the distri- 

 bution of heat in the spectrum, using paper blackened on 

 one side and moistened with alcohol on the other. He 

 obtained a series of spots or patches, commencing above 

 the yellow and extending far below the red. Some writ- 

 ers on this subject have considered that these observa- 

 tions imply a discovery of the lines a, )3, 7 ; they forget, 

 however, that Herschel did not use a slit, but the direct 

 image of the sun an image which was more than a 



o o 



quarter of an inch in diameter, as I know from the speci- 

 mens he sent me, and which are still in my possession. 

 Under such circumstances it was physically impossible 

 that these or any other of the fixed lines should be seen. 

 As I had thus been unsuccessful in obtaining impres- 

 sions of the fixed lines D and E once only I thought I 

 perceived a line corresponding to Frauuhofer's F, but it 

 was exceedingly faint and on the whole doubtful I sup- 

 posed that this furnished an argument for the physical 

 independence of the luminous and actinic rays, as they 



