No DUST, NO CLOUDS OR FOG. 19 



forms round some minute particle of matter, and when our 

 breath becomes visible, it is a proof that the air we are 

 breathing is not only cold, but more or less dusty. 



Microscopic meteorites are often found in the centre 

 of hailstones, as if the ice had crystallised upon them ; 

 but the invisible dust produced by a gas-jet, a clear fire, 

 the heating of the hundredth part of a grain of iron, or 

 a fragment of glass, is quite enough to cause steam to 

 condense into a cloud ; while common salt burnt in a 

 spirit-lamp produces intense fog, as soon as the steam is 

 admitted, and burnt sulphur gives a fog so dense that it 

 is impossible to see through a thickness of even two inches. 



As it is calculated that more than two hundred tons 

 of sulphur are burnt daily in London with the coal during 

 winter, this alone, without the suspended soot, would 

 be enough to account for much of our fog. Happily the 

 human furnaces are so constructed as to consume their 

 own smoke, otherwise, since eight hundred tons of carbon 

 as well as nearly 2,000,000 pints of water, are said to be 

 discharged daily, from the lungs of Londoners alone, the 

 consequences would be dismal indeed. 



Still, even when we have got rid ot our smoke, we 

 shall not be free from fog, though we shall see no more 

 of the "pea-soup" variety. Fogs, as we know, prevail 

 out at sea, and even high up among the mountains, where 

 there is certainly no smoke, though there is dust ; and 

 as long as the air is dusty fogs there will be. 



Well, we should most of us be willing enough to dis 

 pense with them ; some of us, indeed, would be more than 

 willing, especially the sailor, who has fog-horns sounding 



