64 A CENTURY'S PROGRESS IN ASTRONOMY. 



on the Sun. Thus a mighty conflict goes on 

 unceasingly between imprisoned and expand- 

 ing gases and vapours struggling to burst out, 

 and massive pressures holding them down. For 

 reasons we cannot fully understand, no equi- 

 librium is reached. For millions of years up- 

 rushes and down-rushes of the white-hot materials 

 have been proceeding on that bright photosphere 

 which gives us light, and looks a picture of 

 calm and quiescence. Above that is a com- 

 paratively thin rose-coloured layer, the chromo- 

 sphere, agitated with fiery ' prominences/ and 

 outside all these the coronal glory all alike 

 pointing to immeasurable activities." 



The following remark of Professor Newcomb 

 shows our inability to realise the solar activity. 

 " Suppose," he says, " every foot of space in a 

 whole country covered with 13 -inch cannon, 

 all pointed upward, and all discharged at once. 

 The result would compare with what is going 

 on inside the photosphere about as much as 

 a boy's popgun compares with the cannon." 



