The Evolution of the Sciences 



along the periphery of the sun, he had the satis- 

 faction of perceiving the bright rays of the 

 protuberances. From that day the study of 

 solar eruptions ceased to be at the mercy of 

 eclipses ; it could be carried out in any situation 

 wherever the sun was visible. However, we 

 must not forget that only the most intense 

 radiations, such as those of hydrogen and helium, 

 are suited for these daily observations. The 

 multitude of less bright rays of the chromosphere 

 and of the protuberances, especially those situ- 

 ated in the violet and the ultra-violet, can only 

 be observed on the occasion of an eclipse. 



From the time of M. Janssen's discovery the 

 observations made during eclipses have been 

 concentrated on the corona, because owing to 

 its feeble brightness the corona evades daily 

 observation, its weak radiance being drowned 

 by the intense light of the photosphere diffused 

 by our atmosphere. 



Let us see what the succession of eclipses 

 has taught us on this subject. 



The corona appears to consist of two distinct 

 parts which interpenetrate each other more or 



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