120 Philosophy of Storms. 



These opinions I esteem as of the utmost importance ; but that 

 is a reason which makes me the rather desirous to decHne enter- 

 ing upon their consideration ; inasmuch as upon many of their 

 connected points I have formed no decided notion, but am con- 

 strained by ignorance and the contrast of facts, to hold my judg- 

 ment as yet in suspense. It is indeed to me an annoying matter 

 to find how many subjects there are in electrical science, on which 

 if I were asked for "an opinion, I should have to say I cannot 

 tell — I do not know ; but, on the other hand, it is encouraging 

 to think that these are they which if pursued industriously, ex- 

 perimentally, and thoughtfully, will lead to new discoveries. 

 Such a subject, for instance, occurs in the currents produced by 

 dynamic induction, which you say it will be admitted do not 

 require for their production intervening ponderable atoms. For 

 my own part, I more than half incline to think they do require 

 these intervening particles, i. e. when any particles intervene, 

 (1729, 1733, 1735.) But on this question, as on many others, I 

 have not yet made up my mind. Allow me therefore here to 

 conclude my letter, and believe me to be, with the highest esteem 

 and respect, my dear sir, your obliged and faithful servant, 



M. Faraday. 



Royal Institution, April 18, 1840. 



Art. XV. — Brief Synopsis of the Principles of James P. Espy's 

 Philosophy of Storms.* 



(Communicated for this Journal.) 



When the air near the surface of the earth becomes more heat- 

 ed or more highly charged with aqueous vapor, which is only 

 five eighths of the specific gravity of atmospheric air, its equilib- 

 rium is unstable, and up-moving columns or streams will be 

 formed. 



As these columns rise, their upper parts will come under less 

 pressure, and the air will therefore expand ; as it expands, it will 

 grow colder about one degree and a quarter for every hundred 

 yards of its ascent, as is demonstrated by experiments on the 

 Nephelescope. 



* Copious facts going to establish the principles contained in this Synopsis, are 

 given in Mr. Espy's Lectures. 



