The Evolution of the Sciences 



occur principally in the sun's equatorial zone, and 

 that periods of great spot frequency are also 

 characterised by great disturbance of the 

 chromosphere. It is, in general, difficult to 

 compare the spots, which are visible on the 

 surface of the disc, with the protuberances which 

 are only observed at the periphery; however, 

 it is now certain that both are in general simply 

 two aspects of a single disturbance. When we 

 observe a violent eruption at some point of the 

 eastern edge of the sun we are practically certain 

 to discover on the following day a sun spot at 

 the place to which the point has been transported 

 by the sun's rotation. Conversely a spot of 

 variable and tumultuous form, when it reaches 

 the western edge of the orb, is betrayed by the 

 upheaval of the chromosphere. It is also noticed 

 that the faculae, which are apparently elevated 

 regions of the photosphere, seem to coincide 

 with uprushes of practically pure hydrogen; 

 whereas the eruptions which cover the spots 

 would appear, from spectroscopic examination, 

 to consist of hydrogen shot through with numer- 

 ous metallic vapours. 



Our knowledge might have remained limited 



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