08 
Professor .Leslie on Electrical Theories: 
at some distance from the walls *. This would be particularly 
advisable in powder-houses ; and though to divert or dissipate 
the storm is an idea wholly chimerical, we may yet lessen the 
real danger, and mitigate the fated stroke. 
It may now be proper to give an abstract of the principles 
which have occurred in the course of this inquiry. Electricity 
is a state or condition of which every species of matter is sus- 
ceptible. It is of two kinds, attended with opposite effects : 
The one disposes bodies to emit their light, and perhaps dimi- 
nishes their capacity for heat ; the other disposes bodies to ab- 
sorb light, and perhaps increases their capacity for heat f. Bo- 
dies similarly electrified repel each other ; those dissimilarly 
electrified attract each other. Substances in the vicinity of an 
electrified body, at least their proximate portions, assume an op- 
posite electricity, which is the more intense, in proportion to their 
nearness and their extent. But to the contiguous substances, 
the electrified body communicates a part of its own electricity. 
Even a distant substance may acquire the same electricity from 
the successive appulses of the intervening air : And the acute 
form has the property of accelerating prodigiously the motion 
of this aerial current. The celerity with which electricity is 
communicated depends on the quality of the conducting sub- 
stance and the difference between the proximate intensities, 
and is therefore the greatest through thick and short conduct- 
ors. In the case of compound conductors, that celerity will 
be in the ratio compounded of the conducting power of each, 
and the reciprocals of their lengths. During the time of the 
electrical communication, the particles of the conducting sub- 
stance are actuated by a mutual repulsion, which is proportional 
* As copper conducts electricity with much greater swiftness than lead , perhaps 
the best mode icould be to make the gutters and discharging pipes of that metal. To, 
save ships , ribands of copper should be extended from the masts to the keel. 
■f Hence, perhaps, the reason why electricity sometimes vitrifies stones, and 
calcines metals. There is one experiment, however, that has not hitherto been 
properly explained 2 It is, that if the ball of a thermometer be held opposite to an 
electrified point, the mercury will rise two or three degrees. For the air that 
streams upon the ball is accumulated, and consequently suffers a condensation, 
which, according to general analogy, must be attended with a diminution of capa- 
city for heat s 
