39* Professor Leslie on Electrical Theories. 
of discharge through AB will be the same with that through 
AE, which terminates in a neutral point E at a certain distance, 
BE beyond the former, and determined by the proximate sur- 
face of B, and the density of the air, and affected in some de- 
gree by the obstruction to the current occasioned by the dis- 
tance BO, The same investigation will apply, if we suppose 
conductors to proceed from the two coatings, and brought near 
each other ; for the effect will be the same as if they were con- 
tinuous, and a certain addition made to the length of each. 
We have talked of the quantity and intensity of electricity *. 
But such language may be held, whether we consider electricity 
as a substance, or as a quality only. In the same manner, we 
speak of the motion of bodies, of its communication from one to 
another, of its distribution, &c. ; yet no person ever imagines 
that motion has any independent existence. 
These deductions are confirmed by experiment, as far as the 
nature of the subject will admit. Thus, if a slip of paper, suf- 
ficient to discharge a Leyden phial in about a quarter of an hour, 
be rubbed slightly with charcoal dust, it will perform the effect 
in ten seconds. If now reduced to one-half its breadth, it will 
require about double the time ; and, if again shortened to one- 
half its length, the time will be nearly the same as at first. If 
the charcoal dust be gradually strewed thicker, the discharge 
will become more and more rapid, till the interval can no longer 
be distinguished. But though the sense of sight now fails us, 
the impression made upon the ear may direct our judgment. 
For such is the peculiar structure of the organ of hearing, that 
the loudness of sound depends not so much on the quantity of 
aerial impulse, as on the rapidity of the concussion. 
* Compare the noise of a discharge of a file of musquetry with the sound of 
the explosion of a single cannon. Pulvis fulminans is brought to a fluid mass before 
it inflames, while in gunpowder the fire is comparatively slowly communicated 
through the contiguous grains : And though the expansive force of the former be 
inferior, it occasions a much sharper and louder explosion. The sound of a can- 
non, heard at some distance, seems not only fainter but flatter ; because every in- 
termediate point becomes the centre of new aerial undulations, which, mingling with 
the primary ones, prolong and blunt the impression made on the ear. For the 
same reason, the notes of a musical composition become mellowed in their pro- 
gress through the air. 
