422 THE POPULAR SCIENCE MONTHLY. 



of air which at once immensely rarefy all gaseous exhalations, but was 

 kept warm under a dome of glass, through which only the light of 

 heaven penetrated. Although not hermetically sealed, the circulation 

 of air in such a building, compared with that in the open air, is re- 

 duced over a hundred-thousandfold. 



I asked permission to make experiments for several days at 

 various hours of the day and night, which was readily granted. Now, 

 what was the result? The proportion of carbonic acid in the air in 

 the winter garden was almost as high as in the open air. This greatly 

 surprised me, but I hoped at any rate to have one of my traditional 

 ideas confirmed : I hoped to find less carbonic acid in the day than in 

 the night, supported by the fact that the green portions of plants 

 under the influence of light decompose carbonic acid and develop 

 oxygen. But even here I was disappointed. I generally found car- 

 bonic acid increasing from morning till evening, and decreasing from 

 night till morning. As this seemed really paradoxical, I doubled my 

 tests and care, but the result remained the same. At that time I 

 knew nothing of the large amount of carbonic acid of the air, in the 

 soil, the air of the ground, or I should probably have been less sur- 

 prised. 



One day it suddenly became clear to me why there was always 

 more carbonic acid by day than by night. I had been thinking only 

 of the turf, the shrubs, and trees, which consume carbonic acid and 

 produce oxygen, and not of the men and birds in the winter garden. 

 One day, when there were considerably more men at work there than 

 usual, the carbonic acid rose to the highest point, and sank again to 

 the average during the night. The production of carbonic acid by 

 the working and breathing of human beings was so much greater than 

 that consumed by the plants in the same time. 



The oxygen in the winter garden was rather higher than in the 

 open air; there it was about twenty-one per cent., and in the winter 

 garden twenty-two to twenty-three per cent. 



I did not make any experiments on ozone, for reasons which I will 

 give by-and-by. 



The amount of carbonic acid in the air in the winter garden can- 

 not be reckoned as telling for or against the hygienic value of vege- 

 tation in an inclosed space. Let us inquire, then, into the value of 

 the slight increase of oxygen. 



There is a wide-spread opinion that the breathing of air rich in 

 oxygen effects a more rapid transformation of matter, a more rapid 

 combustion, as we say, in the body. Even great inquirers and 

 thinkers have considered that we only eat and imbibe nourishment to 

 satiate the oxygen streaming through us, which woidd otherwise 

 consume us. We know now well enough that the quantity of oxygen 

 which we imbibe does not depend on the quantity in the air we 

 breathe, but far more on previous changes in and the amount of 



