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



crossed by hundreds of minuter lines, so that it was im- 

 possible to count them. If nearly six hundred have been 

 counted between A and H, I should think there must be 

 quite as many between H and P. In speaking of these 

 lines as though they were strong individual ones, the 

 statement is to be taken with some limitation. It is 

 quite likely that each of these bolder lines is made up 

 of a great number that are excessively narrow and close 

 together. 



If the absorptive action of the sun's atmosphere be the 

 cause of this phenomenon, that action must take place 

 much more powerfully on the more refrangible and ex- 

 tra-spectral region. The lines exhibited there are bold 

 and strongly developed ; they are crowded in groups to- 

 gether. 



(Scarcely was the paper from which the foregoing ex- 

 tracts are made published in the Philosophical Magazine, 

 when I learned that in France M. E. Becquerel had al- 

 ready photographed the more refrangible lines, and pub- 

 lished statements to that effect. But he had not ob- 

 served those in the less refrangible regions, designated 

 by me a, ]3, y. 



In fact, the process I was using was one I had recently 

 discovered: it consisted in permitting the daylight to 

 fall along with the sun rays on the photographic surface. 

 The daylight and the sunlight antagonized each other, 

 and these hitherto undiscovered lines made their appear- 

 ance as positive photographs. The peculiarities of this 

 singular and interesting process I will describe hereafter 

 in one of these memoirs. 



In 1846, MM. Foucault and Fizeau, having repeated the 

 experiment thus originally made by me, presented a com- 

 munication to the French Academy of Sciences. They 

 had observed the antagonizing action above described, 

 and had seen the ultra spectrum heat lines a, ]3, y. They 



