gO INVISIBLE LINES IN THE SUN'S SPECTRUM. [MEMOIR III. 



were subsequently called. The lines D, E, F were, how- 

 ever, afterwards photographed by my son, Henry Draper, 

 and so the argument fell to the ground.) 



In 1834, when my attention was first drawn to these 

 subjects, and I began to make prismatic analyses by the 

 aid of sensitive paper, some of my earliest attempts were 

 directed to the detection of these fixed lines. At that 

 time I was employing sensitive paper, made with bro- 

 mide of silver, precisely as has been subsequently done 

 in Europe a number of the results were published in 

 the American journals during the year 1837. In the de- 

 tection of the fixed lines I failed at that time entirely ; 

 but the bromuretted paper enabled me at that early pe- 

 riod, when the attention of no other chemist was as yet 

 turned to these matters, to trace the blackening action 

 from far beyond the confines of the violet, down almost 

 to the other end of the spectrum. I distinctly made out 

 that the dark rays underwent interference, after the man- 

 ner of their luminous companions, a result originally due 

 to Arago, and printed some long papers in proof of the 

 physical independence of the chemical rays and light and 

 heat throughout the spectrum. 



