CHAP. ix. THE IMPORTANCE OF DUST. 81 



with perfect accuracy what would happen under the 

 supposed condition of the atmosphere, it is certain that 

 the total absence of dust would so fundamentally change 

 the meteorology of our globe as, not improbably, to ren- 

 der it uninhabitable by man, and equally unsuitable for 

 the larger portion of its existing animal and vegetable 

 life. 



Let us now briefly summarize what we owe to the 

 universality of dust, and especially to that most finely 

 divided portion of it which is constantly present in the 

 atmosphere up to the height of many miles. First of all 

 it gives us the pure blue of the sky, one of the most ex- 

 quisitely beautiful colors in nature. It gives us also the 

 glories of the sunset and the sunrise, and all those bril- 

 liant hues seen in high mountain regions. Half the 

 beauty of the world would vanish with the absence of 

 dust. But, what is far more important than the color 

 of sky and beauty of sunset, dust gives us also diffused 

 daylight, or skylight, that most equable, and soothing, 

 and useful, of all illuminating agencies. Without dust 

 the sky would appear absolutely black, and the stars 

 would be visible even at noonday. The sky itself would 

 therefore give us no light. We should have bright glar- 

 ing sunlight or intensely dark shadows, with hardly any 

 half-tones. From this cause alone the world would be 

 so totally different from what it is that all vegetable and 

 animal life would probably have developed into very 

 different forms, and even our own organization would 

 have been modified in order that we might enjoy life in 

 a world of such harsh and violent contrasts. 



In our houses we should have little light except when 

 the sun shone directly into them, and even then every 



