216 ' FOGS. 



air that form the nuclei of fog and cloud particles, as these are 

 destroyed by combustion, and yet the air remains fog-producing. 

 No doubt these motes also play their part in condensation, but 

 their number is too small to be of importance. The fog and 

 cloud nuclei are a much finer form of dust, are quite invisible, 

 and though always present in our atmosphere are almost 

 unobserved. 



But more perfect combustion will remote the yellow character 

 from the fogs and make them purer and whiter by preventing the 

 production of smoke, which at present mixes with our town fogs 

 and aggravates their character. It is the smoke that prevents 

 them dissolving when they enter our rooms, like a well-conditioned 

 country fog does in a country house. 



We all know the saying of the Londoner, " The smuts are 

 falling ; there'll be rain shortly." This is how the circumstance 

 comes about :— The smoke-particles are good radiators, are soon 

 cooled, and form nuclei on which the vapour condenses. The 

 smoke-particles loaded with moisture are prevented from rising, 

 and descend into the streets. Therefore, it is perfectly true that 

 the falling of smuts indicates a saturated condition of the air. 



There is another point to consider with reference to our town 

 fogs — that is, the fact that sulphur, when burned, is an intensely 

 active fog-producer. Calculation shows that there are 200 tons of 

 sulphur burned with coal every winter's day in London. This, 

 together with the high fog-producing power of ammonia, accounts 

 for the density of London fogs. 



Before, however, condemning smoke and sulphur, we must 

 look for their good points. Like the good points in character, 

 they do not lie on the surface and annoy us as the bad ones do. 



Full consideration must be given to the value of smoke- 

 carbon, as a deodorizer ; so, too, to the powerful antiseptic pro- 

 perties of sulphurous acid, formed by the burning sulphur. The 

 air during fogs is still and stagnant. There is no current to clear 

 away the foul smells and noxious germs that float in the air, which 

 might be more noxious than they are, were it not for the suspended 

 soot and burned sulphur. 



