504 THUNDER-STORMS. 



a series of two or more clouds, situate at different elevations, one below the 

 other ; avid that sometimes the lowest of the series is not far removed from the 

 suriace of the earth. 



Saussure states that he never witnessed lightning to proceed from a solitary 

 cloud. In observations on the Col de Geant, when a single cloud, however 

 dense and dark it might be, was seen upon the summit, no thunder was ever 

 heard to issue from it ; but whenever two strata of two such clouds were formed, 

 one below the other, or if clouds ascended from the plain and approached that 

 collected round the summit, the encounter was attended by a storm of thunder, 

 hail, and rain. 



Such is the negative testimony of Franklin and Saussure against the fact of 

 thunder proceeding from solitary clouds. Franklin is even more circumstan- 

 tial than Saussure, and maintains that thunder never proceeds from any save a 

 cloud of great magnitude, below which are placed a series of smaller clouds, 

 identical in fact, with the adscititious clouds of Beccaria. 



Negative evidence is, however, not conclusive against a fact, unless the wit- 

 ness be actually present at the time and place of its alleged occurrence. Had 

 the eminent philosophers above mentioned consulted the records of science, 

 their persuasion of the impossibility of thunder issuing from a single cloud 

 would have been shaken. It is related in a memoir of the academician 

 Marcordle of Toulouse, that on the 12th of September, 1747, the heavens being 

 generally cloudless, a single small cloud was seen, from which thunder rolled 

 and lightning issued, by which a female by name Bordenare was killed. 



In his meteorological observations made at Denainvilliers, Duhamel de Mon- 

 ceau relates that on the 30th of July, 1764, at half past rive, A. M., in bright 

 sunshine and a clear sky, there appeared a small dark solitary cloud, from 

 which thunder and lightning proceeded, by which an elm-tree near the chateau 

 was stricken. 



Similar observations of lightning having issued, followed by thunder, from 

 solitary clouds, have been recorded by Bergman and by Captain Hossard, al- 

 ready mentioned. 



M. Duperrey, who commanded the French corvette Uranie, relates that being 

 in the straits of Bombay, in November, 1818, he saw a small white cloud in a 

 clear sky, from which lightning issued in all directions. It ascended slowly 

 in the heavens in a direction opposed to the wind, and was at a great distance 

 from all other clouds, which appeared to be fixed upon the horizon. This 

 cloud was round in its form, and did not exceed the apparent magnitude of the 

 sun. Zigzag lightning issued from it, followed by thunder which resembled 

 the irregular discharge of musketry from a battalion commanded to fire at 

 pleasure. This phenomenon lasted for about thirty seconds, and the cloud 

 completely disappeared with the last detonations. 



feuch are the evidences on the question whether the presence and proximity 

 of a plurality of clouds be essential to the development of the phenomena of 

 thunder and lightning. The analogies offered by common electricity favor the 

 supposition that two or more clouds are essential ; and for this very reason the 

 greater should be the caution for receiving the testimony of observers. It is 

 difficult for those whose minds are prepossessed by theory to observe and re- 

 cord facts and appearances as they are ; there is a disposition sometimes 

 perhaps often to see them as it is supposed they ought to be, and consequent- ( 

 ly the testimony of the ignorant is frequently more deserving of attention than \ 

 that of the better informed. Be this as it may, the subject is one well worthy < 

 of attention, and all persons, who happen to be located in regions where these ( 

 ? phenomena prevail, will have it in their power to contribute to the real advance- ( 

 s incut of science, by carefully and accurately noting down what passes above < 



