434 ^■^''^ EleHric Charge NaturJ and Artijidal. 



which have been dlftinguiflied by the terms pofitive and negative eletlricify. Thefe alge- 

 braical terms are well fuitecl to dcfcribe either two ditTerent fluids, or two dillerent ftates of 

 the fame fluid ; for it is well known by experiment, that elcdlricity, under thefe different 

 forms, has the property (like pofitive and negative quantities in algebraical coniputatious) of 

 deftroying the eflii:£ls of each other, when united in equal quantities. 



The enquiries hitherto made upon the fubjecl of this paper, have in general been con- 

 fined to what relates to the operation of one fluid only ; but in thefe experiments the joint 

 operations of the pofitive and negative eleiSlricities are confidered, to which probably many- 

 appearances, that have hitherto occafioned much controverfy araong(t-ele6lricians iefpe£ling 

 the forms of conduftors, may be afcribed. 



It is a known facl in cledlricity, that if the furfaces of two metallic bodies be placed op- 

 pofite and near to each other, the one infulated, and the other conneiSbed with the eartli ; if 

 a thin plate of any eleftric fubflance be introduced between thefe furfaces, and extending 

 beyond their extremities, if ele£lricity be then communicated to the eleflric by means of 

 the infulated metallic fubflance, the other metallic fubflance conncfted with the eartli has 

 the power of putting the fide of the eleilric with which it is in contaQ into the oppofite 

 ftate of eleflricity ; and the pofitive and negative eleQricities on the oppofite furfaces of the 

 ele£lric, by their attraftive powers, retain each otlier in their refpeclive fituations And, 

 in folid clc£lrics, even after the removal of the metallic fubftances, if the fame, or other 

 condu£ling fubftances, having a conducing communication between them, be applied again 

 to the oppoGte fides of. the charged eleftric, . all electricity will difappear, Clcntly, or with 

 an explofion. Thefe are tlie phenomena of the eleflxic jar. 



It is alfo well known, that if a body of atmofpheric air, included between metallic fur- 

 faces, be the eieclric employed in the experiment above defcribcd, . fimilar efl^efts will be 

 produced. 



Hence it maybe inferred, that the effe£ls of lightning may arife from the difcharge of 

 large bodies of ele£lrified air ; the upper furface of which will be in one ftate of electricity, 

 and the furface adjoining the earth and terreftrial bodies will be in the oppofite ftate ; and 

 when thefe bodies of charged air pafs over lofty buildings capable of forming a conducting 

 communication between their oppofite furfaces, the explofion of lightning takes place. 



The lower furface of a body of charged air may extend over the whole, over a part, or 

 over no part, of a building, at the time it is -ftruck by lightning ; the building forming 

 only a part of the conducting communication. 



Buildings in general have many metallic fubftances belonging to thera : it is to thefe fub- 

 ftances, and to their imperfe£l connedtion with the earth, that moft of the mifchief that 

 arifes from the eflcCls of lightning is generally afcribed. To prevent this mifchief, metallic 

 condudiors have been attached to buildings. 



The advantage expefled from thefe conduflors is founded upon a fuppofitlon, that the 

 natter of lightning will always prefer, in its pafTage to the earth, a continued conduifling 

 fubftance to one that is broken or interrupted by non-condufling fubftances ; and therefore 

 it is fuppofed that a conductor, conftrudled of a perfeiStly continued metallic fubftance, and 

 extending from above the upper furface of a building into the earth, below its foundation, 

 will receive and convey the matter of lightning into the earth, and prevent the mifchief 



that 



