106 LIGHT SCIENCE FOR LEISURE HOURS. 



by the sun. But these vapours are such as we should 

 be rather startled to find in our own atmosphere. We 

 breathe the vapour of water without inconvenience, 

 unless it is present in too great quantities ; but if we 

 could imagine for a moment that there were breathing 

 creatures on the sun, these must be able to inhale 

 without injury the vapour of iron, copper, zinc, and 

 others of our familiar metallic elements. For the solar 

 atmosphere, to a depth of a few hundred miles, is 

 loaded with these vapours, all glowing with intensity 

 of heat. 



But how, it will be asked, can a fact of this sort 

 become known to astronomers? It seems incredible 

 that an observer on the sun, even if armed with the 

 most powerful instruments used by terrestrial astro- 

 nomers, could ascertain that the lower strata of our air 

 are loaded with the vapour of water. How then can 

 the terrestrial observer learn that the lower strata of 

 the solar atmosphere are loaded with such and such 

 vapours ? 



The telescope, as I have said, can teach nothing. 

 But the spectroscope can not only teach us this lesson 

 about the solar atmosphere, but it has been teaching 

 men that lesson for more than half a century, though 

 the lesson has only of late been understood. The sun's 

 light, shining through the complex atmosphere of 

 glowing vapours, is deprived of certain of its rays by 

 the absorbing power of these vapours ; and, accordingly,, 

 when that light is spread out into the rainbow-tinted 

 streak called the solar spectrum, those rays are found 



