Page:Popular Science Monthly Volume 23.djvu/40

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and estimating the spores deposited by those volumes, and from this deducing the number of spores contained in a cubic metre of air. Repeating these measurements every day and every hour for several years, and taking care to notice all the anterior or concomitant meteorological

PSM V23 D040 Pollen and dust in the atmosphere.jpg
Fig. 2.—Pollen and Dust in the Atmosphere.

conditions, he succeeded in defining the influence of the seasons, and of temperature, dryness, and moisture in the progress of the phenomenon.

This method, applied at the Montsouris Observatory, shows that the number of mold-spores is weak in January and February, diminishes in March, and rises in April; the increase is very sensible in May, and the maximum is reached in June. The number then diminishes slowly till October, considerably in November, and reaches a minimum in December.

It may be said, generally, for the locality where the experiments were made, that a cubic metre of air contains on the average seven thousand mold-spores in December, January, and February; twelve thousand in May; thirty-five thousand in June; twenty-three thousand in August; fourteen thousand in October, and eight thousand in November. If, instead of considering the means of several years, we