Meteorological essays / by François Arago ... with an introduction, by Baron Alexander von Humboldt. Tr. under the superintendence of Colonel Sabine.

François Arago

Date:: 1855

Credit: Meteorological essays / by François Arago ... with an introduction, by Baron Alexander von Humboldt. Tr. under the superintendence of Colonel Sabine. Source: Wellcome Collection.

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$Tlie above remarks are tlie substance of what bas been said on tbe siibject by an autlior (Beccaria)^ wlio llved in a country (the plain aronnd Turin) alinost entirely surrounded by higli mountains. In order to juclge how far tliey apply generally and how far only locally, we ought to be able to compare with them the description of the commencement, progress, and full development of a storm in a country without mountains.* No one will doubt that there is something local in some of the circumstances attendant on the formation and development of storm clouds, in reading the foUowing description, given by ]\I. Antoine d’Abbadie, of thunder-clouds of frequent occurrence in Abyssinia. Storm-clouds in Ethiopia bave,” he says, “ always a plain or uniform surface on their inner side, and a checkered surface on theh* outer side, and are, generally speaking, far from being very dense ; sometimes clouds in which strong manifestations of electricity take place are so thin that stars can be seen through them.” M. d’Abbadie remarks further that tliese clouds bave a tendency to cluster round lofty peaks, by which they appear to be attracted. Let us add to these different remarks that storm-clouds are often diverted from the direction in which the wind would carry them to follow the course of rivers. Mr. Sturgeon mentions having often observed this to take place at the junction of the Thames and Medway. In ail that Beccaria bas said of the graduai disappearance of the many and great undulations in storm-clouds as they rise from the horizon to the zénith, he spoke only of their under surface, as alone visible from his observatory at Turin. I should be unable to speak of their uj>per surface, if I had not thought of Consulting on the subject ofhcers of the Etat Major, formerly pupils of the Ecole Polytechnique, who hav- ing been recently engaged in covering the Pyrenees with their admirable net-work of triangulation, were likely to hâve had frequent opportunities of seeing thunderstorms beneath them.f * St. Lambert, in his poem “ Les Saisons,” begins the description of a thunderstorm by two lines, in which he speaks of clouds rising from two opposite points of the horizon : — “ On voit à l’horizon de deux points opposes Des nuages monter dans les airs embrasés.” Is he describing a local phenomenon ? t I have to address my especial thanks to two officers of high merit.$