38 LIGHT SCIENCE FOR LEISURE HOURS. 



moon, there springs suddenly into view a crown of 

 glory all round the moon's black disc, which has for 

 centuries perplexed astronomers. This appearance 

 the solar corona, as it is called had been supposed 

 until quite recently to be a solar atmosphere, other 

 interpretations having one by one been abandoned. 

 But then, the corona extends in appearance to a 

 distance at least half as great as the moon's apparent 

 diameter from the lunar disc. So that if in reality it 

 is due to a solar atmosphere, that atmosphere must be 

 at least half the sun's diameter in altitude that is, 

 upwards of four hundred thousand miles high. Now 

 our own atmosphere is probably not more than one 

 hundred miles high, so that the solar atmosphere 

 assuming the view we are considering to be correct 

 would be no less than four thousand times as high as 

 ours ; and on this account alone the pressure at its 

 base would enormously exceed the pressure of the air 

 we breathe. But this is not all. The pressure of our 

 air is due wholly to the earth's attraction, and would 

 be increased or diminished if the earth's attractive 

 force were increased or diminished. Now the sun 

 exerts an attractive force so vastly exceeding that 

 exerted by the earth, that if a man could be placed at 

 the sun's surface remaining uninjured by all other 

 circumstances' he would be crushed flat by his own 

 weight. We can see, therefore, that the atmosphere 

 of the sun would have its pressure enormously increased 

 through this cause also. Combining the two causes, it 

 is not too much to say that the pressure at the sun's 



