1882.] on Climate in Town and Country. 25 



and cheerless gloom in winter. We suffer less, however, from exces- 

 sive solar intensity than continental cities between the same parallels 

 of latitude, owing to the very causes which plunge us into a more 

 miserable gloom in winter. Light-coloured walls neither make our 

 streets look cheerful nor feel hot. Such sad colours as brick, stone, 

 stucco, or paint give to our houses are soon changed to a grimy 

 neutral tint, powerless to reflect either solar light or heat. 



The darker the colour of the houses, the cooler the streets and 

 the hotter the rooms during sunshine, and vice versa. Whilst the 

 summer climate in our streets and houses is thus, to a considerable 

 extent controllable, that of winter, which depends so much on a clean 

 atmosphere, is still more so. All our towns are nearly at the sea- 

 level, a position favourable for air-, but not for sun- warmth. In our 

 large towns, however, we artificially create an impenetrable barrier 

 to solar radiation by throwing into the air the imperfectly burnt 

 products of bituminous coal. 



These products are of three kinds — soot, tar and steam. Every 

 ton of bituminous coal burnt in our grates gives off about 6 cwts. 

 of volatile but condensable products. The less perfect the combus- 

 tion the more tar and the less steam will be produced. If perfectly 

 burnt without any smoke, then about 9 cwts. of steam, occupying 

 27,359 cubic feet at 100° C, or 20,024 cubic feet at 0° C. will be sent 

 into the air. Now 33,333 tons of bituminous coal are, on the 

 average, daily consumed in London in winter, giving 667,460,000 

 cubic feet of steam at 0° C. 



This combustion of enormous quantities of bituminous coal acts 

 in the production of town fog in three ways : — 1st. By supplying 

 the basis of all fog — condensed watery particles. 2nd. By determining 

 the condensation of atmospheric moisture in the form of fog. 

 3rd. By coating the fog particles with tar, and thus making them 

 more persistent. 



All fogs have for their basis watery particles, and the greater 

 part even of the suspended matters visible in a ray of electric 

 light consists of these particles, for the air becomes nearly clear 

 when it is heated somewhat above 100° C. [Experiment shown]. 

 Everything therefore which increases the proportion of aqueous 

 vapour in town air tends to produce fog. But aqueous vapour alone 

 would probably never produce fog, for it condenses at once to large 

 particles, which rapidly fall as rain. When, however, solid or liquid 

 particles are present in the air, the minute spherules of fog are 

 produced. This was first shown by Messrs. Coulier and Mascart, in 

 1875, and their results have since been confirmed by Mr. Aitkin. 

 The speaker showed that air filtered through cotton wool, though 

 afterwards saturated with moisture, produced no fog when its 

 temperature was lowered ; but as soon as a small quantity of the 

 dusty air of the theatre was admitted fog was immediately formed, 

 whilst, when a little coal smoke was introduced, a dense and more 

 persistent fog was the result. 



