Professor Leslie on Electrical Theories. IS 
It may be urged, that this solution supposes that a part of 
the surface of a body will coincide with a segment of a sphere ; 
whereas every substance in nature is full of asperities. But it 
must, at the same time, be observed, that no absolute contact 
can ever take place ; and that the nearest approach which can 
be made, is limited by the repulsion which the body would ex- 
ert, and that, in this situation, when the asperities are minute,, 
the forces of the various particles mingle, modifying each other, 
produce the same effect as if they had been disposed in the most 
perfect uniformity. It. is thus that the rays of light are reflected 
from the polished surface of a mirror, with scarce any dissipa- 
tion ; and, for the same reason, an acute shaped metallic body 
will occasion, when electrified, the same celerity and extent of 
aerial stream, as if it had been absolutely smooth. Nor does the 
investigation require that the electrical virtue shall reside in 
the mere surface ; it is sufficient if it be confined to an exceed- 
ingly thin external sheik 
The effect will often be nearly the same, whether the point 
be turned towards the prime conductor, or be held in an oppo- 
site direction. In the former case, the motion with which the 
air flows from the conductor, conspires indeed with the action of 
the point, and, in the latter, it weakens that action. But as the 
parts of the stream proceed diverging, they become in some 
measure attenuated ; which occasions a diminution of their elas- 
ticity, and consequently an opposite pressure. And, hence 
the velocity will be continually diminished, and, at a certain dis- 
tance, it will become so small, that, though sufficient to renew 
the air about the point, it will hardly have any effect on its 
action. This will be found to agree with experiment *. 
The foregoing principles will enable us to determine the ef- 
fect of compound points, which seems inexplicable from the com- 
mon notions. Let A and B, (PL I. Fig. 3.), be two tapered wires, 
whose points are placed opposite and near to each other. The 
* Writers on Electricity suppose a portion of redundant fluid to collect on the 
surface in a thin settled stratum, which, from analogy, they term an electric atmo- 
sphere. This expression I have carefully avoided, as it refers to an idea essen- 
tially different from mine. Electric atmospheres have no connection whatever 
with the ambient air, and are believed to take place equally in vacuo ,— But the 
whole hypothesis seems to be a baseless fabric. 
