THUNDERSTORMS. 601 



THUNDER-STORMS. 



SINCE the epoch of the memorable experiments of Franklin, meteorologists, 

 in all parts of the world where physical science is cultivated, have observed 

 with increased interest the phenomena of thunder-storms. Although a great 

 body of facts have been, by such means, accumulated, the general conclu- 

 sions deducible from them are few ; nor are even these few invariably sus- 

 tained by that consistency, and harmony of effects which are necessary, to 

 command universal assent. Indeed, the facts themselves, on which, alone, any 

 safe and certain generalization could be based, were isolated, and scattered 

 through the memoirs of the various scientific bodies to which their observers 

 had originally consigned them ; and many of the most important and valuable 

 observations remained in unpublished memoranda, or were incidentally men- 

 tioned in the narratives of voyagers and travellers, where they were little like- 

 ly to attract the attention of those who, alone, are capable of estimating their 

 value, until, by the indefatigable zeal of M. Arago they were collected, ar- 

 ranged, and compared, and presented to the world, invested with all those 

 charms of style which render the productions of that philosopher so universal- 

 ly .attractive.* It is natural that the impatient student should desire to be supplied 

 with clear and comprehensive principles, and be relieved from the tedious de- 

 tails of particular observations and experiments ; that facts should be laid before 

 him in extensive groups and classes, so as to suggest easy and obvious gener- 

 alizations. It is equally natural that the authors of elementary and general 

 treatises should desire, in every case, to present the scientific truths in concise 

 and general propositions, connected together by distinct logical relations. The 

 temptation to yield to this disposition by presenting all physical problems as 

 completely resolved, and all elementary questions as completely exhausted 

 of laying down sweeping conclusions and general principles, on matters which , 

 are, m fact, surrounded with difficulty and doubt is most hurtful to the progress ( 



* See Notice eur le Tonncrre dans 1'Annuaire du Bureau dea Longitudes pour 1'An i.838. v 



