Page:Popular Science Monthly Volume 60.djvu/535

Rh in following the subject further to papers already published by me on the subject.

With these possible exceptions we can say: that during calms those life phenomena which are due to excessive vitality are deficient in number. If these theses have been sufficiently defended, and figures are not in existence with which to refute them, the next logical question would be, 'Why?'

Two hypotheses may, I believe, be presented in answer. The first is based upon the general facts bearing upon ventilation, and the second upon those of atmospheric electricity. The first would only be applicable to the conditions of large cities—and I will again call attention to the fact that all the data of the present problem were for New York City—while the second would be valid for any spot on the earth's surface. In discussing the first I would call attention to the fact that combustion of any sort, whether within the lungs of animal organisms or in the ordinary processes of burning, depletes the air of its oxygen and surcharges it with carbonic acid gas. If the normal proportions of oxygen are to be maintained in the immediate vicinity of such combustion, fresh air must by some means be brought in to take the place of that, the normal mixture of which has been disturbed. We are quite familiar with these facts in their bearing upon the ventilation of buildings, but there is no difference except that of magnitude between a building in which the air is being robbed of its oxygen through combustion, and a city in which the same process is going on.

Three million animal organisms (not all human) and half as many more fires, all without adequate vegetable organisms to reverse the process should, we would argue, make tremendous inroads upon the atmospheric stock of oxygen. That this is true has been demonstrated by Dr. J. B. Cohen in an article appearing in the Smithsonian Reports for 1895, p. 573. He there shows that the proportion of carbonic acid gas varies to a very marked degree in the center of the city of Manchester, England; that the variation extends from the normal amount at times, to more than four times that amount at others, the average being nearly three times the normal. Although he makes no reference to the fact, it is, I believe, safe to assume that these variations bear a fixed relation to wind movements. Certainly when the wind was very violent, no considerable difference could exist between the composition of the atmosphere in a great center of population and in the surrounding country where the normal mixture of gases would be found. It is safe also to assume that what was true for Manchester would be for New York City, and to assume at least as a working hypothesis that