[The popular notion]

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THE POPULAR notion, which regards the night air of the dog-days as unhealthy, is one that has often been derided, but it is, nevertheless, substantially correct. At that season of the year, the atmosphere is full of poisonous exhalations from decayed matter. These exhalations, though generated most freely in the day time, under the influence of a fervid sun, are borne upward into the higher regions of the air, by the current which the sun's rarefaction creates, and are, therefore, comparatively innoxious. But the night exhalations, though less dense, are, from the absence of such a current, left on the surface of the earth, where being inhaled, they produce fevers, which are frequently of the most dangerous type. Persons accustomed to well-drained towns and cities, where these exhalations are less perilous than in the country, frequently bring on themselves serious illness, by walking in the night air, out of town, or by sleeping with open windows in localities where these exhalations abound. Many a fair young girl, tempted by a beautiful moonlight, has, at this season, lingered out, unbonneted, till late at night, and so imbibed the seeds of a disease, which, in a few weeks, sometimes in a few days, has carried her to the grave.