QO LIGHT SCIENCE FOR LEISURE HOURS. 



This is obvious, because those molecules of the air 

 which lie directly towards the moon's place are them- 

 selves suffering total eclipse from the sun's direct 

 light, and are illuminated by a rather less proportion 

 of prominence and coronal light than the observer 

 himself, whereas those molecules which lie in directions 

 far removed from the place of the eclipsed sun are 

 suffering either but a partial eclipse, or else, though 

 their eclipse be total, they are yet illuminated by 

 more lustrous portions of the corona and prominence- 

 matter. So that so far as atmospheric glare alone is 

 concerned, we should have, as I wrote in March 

 1870, a relatively ' dark region around the eclipsed 

 sun and a gradual increase of light with distance 

 from him.' 



The question which arises here, then, is this at 

 what distance from the eclipsed sun has the light of 

 the solar corona so diminished, and that of the atmo- 

 spheric glare so increased, that the latter light pre- 

 dominates over the former. This question is not only 

 exceedingly nice, but, as actually stated, it is wholly 

 unanswerable, unless as a matter of fact the real solar 

 corona has definite limits, recognisable perhaps by 

 more refined methods of observation than have yet 

 been applied. 



But although it is unlikely that the utmost actual 

 extension of the corona can be determined by means 

 of such appliances as are at present available, yet it 

 was possible last December to demonstrate the exten- 

 sion of the corona to a distance far exceeding the six 



