THUNDER STORMS, 83 
off the redundancy upon any objects which may be in a 
fituation to receive it? One or the other feems neceflarily 
to follow, but the former is moft agreeable to dogtor 
Priefley’s experiment of the condenfed air in the tube a- 
bove mentioned, and is perfectly confonant with the ob- 
fervations of do€tor Franklin, Mr. Kinnerfley and others, 
that thunder clouds are generally in the negative ftate of 
ele€tricity*. But more upon this head hereafter. I would 
however obferve here, that many, and perhaps all other 
electric fubftances, even the moft firm and folid, as well 
as air, are liable to have their electric capacities thus di- 
verfified by heat, more particularly the tourmalin above 
mentioned. But as, in treating of the properties of this 
ftone, doctor Priefley has thought it deferving ofa diftine 
fection in his eleétric hiftory, to that I fhall refer the read- 
er for a particular account of them +; wherein he will find 
a difcovery made by Meflrs Canton and Wil/on, that thefe 
properties are not peculiar to the tourmalin, but that many 
gems have a natural difpofition to afford the fame appear- 
ances ; from whence we may conclude as above, by ana- 
logy, that all electric fubftances are, more cr lefs, affected 
in like manner, by the fame caufe. But to return to the 
fubjec&. 
If from the foregoing confiderations the reader fhould 
be fatisfied, that the electric capacity of air, in its con- 
denfed ftate in the lower regions of the atmofphere, is li- 
able to be diminifhed by a further condenfation, and that, 
ceteris paribus, it is increafed by heat et vice verfa; the 
folution:of the phenomena of thunder and lightening, to 
his fatisfa€tion, upon eleCtrical principles, will perhaps be 
no difficult tafk. 
For let us conceive a region of the atmofphere, extend- 
ing over a large tract of country, to be rarefied and heat- 
2 ed 
* Epitome of Phil. Tranf. Gent. Mag. Sept. 1773, page 447. Mr. Henley thinks cold 
eieGtrifies the atmofphere pofitively, and thence conjectures that heat electrifies it negatively. 
Wis conclufions are founded upon a courfe of experiments. 
+ Page 297. 
