10 Professor Leslie on Electrical Theories. 
tion ; and hence the actual impelling force will gradually lessen 
with the distance ; and, in electrical experiments performed in 
the common atmosphere, the fl ow will be found not sensibly to 
extend many inches. It is also evident, that the source of all 
this motion is the maximum attraction BS, which must deter- 
mine both the velocity and the quantity of the aerial current. 
But, besides the celerity of the stream, there are other cir- 
cumstances which favour the electrical communication. The par- 
ticles of air that environ the electrified body are repelled from 
it with considerable force, which is greatly increased by the di- 
vergency of their motion ; for, as they continually become rarer, 
their elasticity is diminished, and consequently they are impelled 
by the excess of the elasticity of the succeeding particles. Hence 
these particles will move towards A with more velocity than other 
particles of air, and thus a much larger proportion of them will 
be brought within the sphere of the ball's action. They will 
then receive new accessions to their motion, from the attractive 
forces which are exerted upon them alone. A sort of selection 
even will take place ; for, as the convergency near the ball is 
greater, the elasticity of the air will there be much increased, 
which, though it will, in some measure, retard the progress of 
the electrified particles, yet will it have a much greater effect in 
obstructing the approach of the others, since the impulsion of 
these becomes now considerably inferior to that of the others. 
After the particles have successively arrived into the situation B, 
they will acquire the electricity of the metallic substance, and be re- 
pelled with the same forces with which they were before attracted. 
In consequence of the unequal actions, a particle at the distance 
B will press upon the contiguous one, with the difference TS of 
the repulsions. In the same manner, a particle at the distance 
C will press upon a preceding particle with the force RU, which 
will also be communicated to the distant portions of the air. It 
must follow, therefore, that all the particles of the atmosphere 
will indiscriminately tend from A. But this tendency is dimi- 
nished by the action of another cause : for, as the particles di- 
verge from it, they become perpetually rarer, and their elasticity 
weakened, and consequently they will be more and more pressed 
by the remoter atmosphere in an opposite direction. The cele- 
