20 THE WORLD'S LUMBER ROOM. 



all round him as he goes up and down Channel, and often 

 dares not close his eyes for many days and nights together, 

 and lives in a state of constant anxiety as long as the fog 

 lasts. 



But if the air were quite free from dust we should 

 also lose the clouds which make so large a part of the 

 beauty of our skies ; the artist would lose his mists and 

 atmospheric effects, and we should probably have no rain, 

 for when the moisture became more than the air could 

 hold, it would be deposited as dew upon every object 

 with which it might come in contact. Neither is this all 

 that the absence of dust would entail upon us. 



We might suppose that with no dust in the air we 

 should at least have more light; but while it is undoubtedly 

 true that the sunbeams show us the motes,- it is no less 

 true also that the motes and finer dust actually show us 

 the sunbeams, and that one is invisible without the other. 



A beam of sunlight or electric light if admitted into 

 a chamber of which the air is perfectly pure at once dis- 

 appears, and is replaced by pitchy blackness, except where 

 it strikes the wall or some other object. Balloonists tell 

 us that the higher they ascend the deeper becomes the 

 colour of the sky, until at the height of a few miles it 

 looks almost like a black canopy, because, though the 

 sun is shining in unclouded splendour, there is little or 

 no dust to scatter his light. The space between the stars 

 stellar space as it is called is, accordingly, absolute black- 

 ness, notwithstanding the blaze of light which passes through 

 it and becomes visible on striking our dusty atmosphere. 



This universal dust is kept out of our lungs, where 



