I Acknowledge It Is Very Difficult To Explain, In The Present State Of Meteorology, Why It Hails At Philadelphia, At

Rome, and at Montpelier, during the hottest months, the mean temperature of which attains 25 or 26 degrees; while the

Same phenomenon is not observed at Cumana, at La Guayra, and in general, in the equatorial plains. In the United States, and in the south of Europe, the heat of the plains (from 40 to 43 degrees latitude) is nearly the same as within the tropics; and according to my researches the decrement of caloric equally varies but little. If then the absence of hail within the torrid zone, at the level of the sea, be produced by the melting of the hailstones in crossing the lower strata of the air, we must suppose that these hail-stones, at the moment of their formation, are larger in the temperate than in the torrid zone. We yet know so little of the conditions under which water congeals in a stormy cloud in our climates, that we cannot judge whether the same conditions be fulfilled on the equator above the plains. The clouds in which we hear the rattling of the hailstones against one another before they fall, and which move horizontally, have always appeared to me of little elevation; and at these small heights we may conceive that extraordinary refrigerations are caused by the dilatation of the ascending air, of which the capacity for caloric augments; by currents of cold air coming from a higher latitude, and above all, according to M. Gay Lussac, by the radiation from the upper surface of the clouds. I shall have occasion to return to this subject when speaking of the different forms under which hail and hoar-frost appear on the Andes, at two thousand and two thousand six hundred toises of height; and when examining the question whether we may consider the stratum of clouds that envelops the mountains as a horizontal continuation of the stratum which we see immediately above us in the plains.

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