Eclipses 



lunar atmosphere; it was universally accepted 

 that the appearances observed are caused by the 

 sur> itself, and that, in Arago's words, " we are 

 on the track of a third envelope situated above 

 the photosphere and consisting of dark or feebly 

 luminous clouds/' 



From this date every successive eclipse, 

 studied by numerous and well-equipped ex- 

 peditions, has contributed new results to science. 

 From 1860 the use of photography, due to 

 Warren de la Rue and to Secchi, has rendered 

 possible a precise comparative study of the 

 protuberances and of the corona observed from 

 different stations and consequently at different 

 moments. The eclipse of the 8th August 1868 

 marked the general application of spectroscopy 

 to the chemical analysis of the chromosphere 

 and of the protuberances, but it was also dis- 

 tinguished by a most important discovery. 

 M. Janssen was at Guntoor, in India, in order to 

 observe the spectrum lines of the protuberances ; 

 having been struck by the brilliant brightness 

 of these lines, it occurred to him that they might 

 perhaps be visible by daylight. The day follow- 

 ing, by directing the opening of his spectroscope 



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