Page:Popular Science Monthly Volume 87.djvu/250

246 Inquiry in Pittsburgh among metal workers developed the fact that metal work in a smoky city lasts only half as long as in one free from smoke.

It is hardly necessary to point out that smoke damages the interior decorations of a building or home, limits interior decorators in the use of colors and materials and in every way tends to render artistic effects gloomy and depressing.

Cities very properly hold favorable climatic conditions as a very desirable asset, as is evidenced by the records of rainfall, temperature, fog and hours of sunshine which appear in the year books of the chambers of commerce and boards of trade of the different cities. Cities which have smoky atmospheres are under a severe handicap in this regard.

In the first place, while smoke is not a cause of fog, it intensifies a fog when it is once formed and accordingly causes it to persist longer. In consequence of this there are fewer hours of sunshine in smoky cities than in cities which are practically free from smoke. Again, the sunshine is less intense in smoky cities, the light of short wave lengths, or the blue light, suffering the greater depletion. Not only is this true, but daylight, which depends entirely upon diffused light from the sky, is depleted by the smoke in greater proportion than the direct sunlight.

Experiments carried on by the Smoke Investigation of the Mellon Institute in Pittsburgh and Sewickley, a small residential town on the Ohio River, about twelve miles northwest of Pittsburgh, during 1913, revealed that Pittsburgh had 25 per cent. less sunlight and 40 per cent. less daylight than Sewickley. It was also found that the limit of visibility in the business section of Pittsburgh was about one tenth the limit in the open country. It is well known that the frequency of intense fogs in London has decreased and the hours of sunshine increased since 1890, due to a mitigation of the smoke nuisance. The same was true of Pittsburgh between 1885 and 1895, when the use of natural gas for manufacturing and domestic purposes was quite general.

A number of studies have been made of the effect of soot on vegetation. Cohen and Euston, as a result of their researches in Leeds, England, declared that soot may exert a detrimental effect on the growth of plants in three ways, namely, by blocking up the stomata and thus impeding the process of transpiration; by coating the leaf and so reducing the intensity of sunlight, and at the same time affecting the assimilation of carbon dioxide; and lastly, by the corrosive effect of the acid it contains. Experiments they carried on went to show that the power of assimilation of laurel leaves had a definite relation to atmospheric