of science, and a great impediment to the development of truth. To no part 

 of physical science do these observations apply with more force than to the 

 subject of the present discourse. That the phenomena of thunder and lightning 

 proceed from sudden and violent derangements of the electrical equilibrium of 

 the atmosphere or the clouds which float in it, may be regarded as certain ; and 

 that the laws which are observed to prevail among electrical phenomena offer 

 various analogies which afford explanations more or less plausible and proba- 

 ble, for some of the facts observed in thunder-storms, may be admitted. But 

 that any comprehensive and general principles have been established from 

 which the various atmospheric phenomena in which thunder and lightning are 

 exhibited, can be deduced in the same manner, and with the same clearness 

 and certainty, as the effects of common electricity have been deduced from the 

 theory of Dufaye, Summer, and Poisson, cannot be maintained. Under such 

 circumstances, both author and reader must patiently submit to the investiga- 

 tion of facts separated from theory or hypothesis ; and when these facts have 

 been clearly and fully stated, such general consequences as they justify may 

 be easily deduced from them, and the apparent discordances which, by com- 

 parison, may be apparent among them, will afford grounds for further observa- 

 tion and inquiry to those who devote their labor to such researches. 



COMMON THUNDER-CLOUDS. 



It is generally agreed that the formation of clouds is due to the partial con- 

 densation, in the upper regions of the air, of the vapors which have exhaled 

 from the surface of the earth. This condensation may be effected by any 

 cause which produces a diminution of temperature, and is, probably, in most 

 cases, the consequence of the mixture of two currents of air. charged with 

 vapor, and having different temperatures. The positive electricity which rises 

 into the atmosphere with the vapor, and which augments in intensity, as the 

 height increases, to the greatest elevation to which observation is extended, is 

 collected in the clouds thus formed ; and when the globules or vesicles com- 

 posing the cloud have collected together in sufficiently close proximity, the 

 cloud takes the nature of one continued conductor and the free electricity accu- 

 mulates on its surface in the same manner as on the conductor of an electrical 

 machine. The existence of positively-electrified clouds is, therefore, easily 

 conceived. 



If the electroscopic observations which indicate negatively-electrified clouds 

 be rightly interpreted, and the existence of such clouds be admitted, several 

 hypotheses have been proposed to explain them. 



If a cloud in its natural state, or feebly charged with positive electricity, ap- 

 proach another cloud strongly charged with the same electricity, the latter will 

 exercise upon it an inductive action, by which its natural electricities will be 

 decomposed, the positive electricity being repelled to the most remote part, and 

 the negative fluid being accumulated at the nearest part. If, under these cir- 

 cumstances, the most remote part be in contact with the earth, as it might be, 

 with the summit of a mountain, for example, the positive electricity will es- 

 cape to the earth, and the cloud will remain charged with negative electricity. 

 If any cause disengage this cloud from contact with the earth, it will float in 

 the atmosphere and afford an example of a negatively-electrified cloud. 



If two clouds, one or both of which are charged with electricity, approach 

 each other, the same phenomena must be evolved as when two conductors, 

 one or both of which are similarly charged, come together. If it happen (a 

 circumstance against which the chances are infinite), that the quantities of 

 electricity with which they are charged have the same relation as they w 



