If the insulated prime conductor of a machine be well polished, and without corners or angles, it will retain its electric state very well, and will emit strong sparks upon the approach of any uninsu lated conductor. If the uninsulated con ductor be broad, round, and polished at the end, the sparks will he short and dense, and will produce a considerable sound ; if less broad, the spark will be long, crooked, and less sounding ; if the breadth be still more diminished, the con ductor begins to come under the deno mination of a pointed body, the electric matter passes to it from the prime con ductor, through a great space of air, with a hissing or rustling noise, and in a con tinual stream : a still greater sharpness enables the electricity to pass over a greater space, but silently, and nothing is seen but a small light upon the point. If a similar point issue from the prime con ductor, and the uninsulated conductor be round and polished, the same effects hap pen in like situations ; but if both be pointed, the electricity is more readily discharged : and in all these cases the ap pearance of the electric matter at the point of the prime conductor will be that which is peculiar to its electricity, a large divergent cone, if positive, or a small globular light or cone, if negative, and the light at the point presented to the prime conductor will be distinctive of the contrary electricity. Whether a pointed conductor be electrified positively or ne gatively, if the nose be brought near the point during the electrization, a wind will be felt blowing from the point, and the sense will be affected with a sulphureous or phosphoreal smell.
The reaction of the force by which the air is put into motion, is exerted on the pointed body. This is shewn by a pleas ing experiment with an electrified wire; thus, to the middle of the wire, or rather between two wires that lie in the same line, is affixed a centre.cap like those used in sea-compasses, so that the wire may easily be moved on a point in a hori zontal direction, as magnetical needles are : and the ends of the wire are pointed and bent contrary ways, to point in the direction of the tangent to the circle de scribed by them. Now if this wire, thus suspended on a point, be insulated and electrified, its sharp ends will become lu minous, and it will revolve in a direction contrary to that in which its ends are bent ; or if it be suspended on an uninsulated point, and brought near the electrified prime conductor, the same effect will fol low.
It may be thought strange that the air should issue from an electrified point, whether its electricity be positive or ne gative. It is easy to conceive that the is. suing out of the electric matter may cause the air to move in the same direction ; but it appears odd, that the electric matter rushing towards a point should cause the air to move directly contrary, that is to say, likewise from the point. It; however, the circumstance be examined more nar rowly, the difficulty will vanish. For it is highly probable that the electric mat ter passes too swiftly to excite any mo tion in the air, but that undulation where in sound consists ; to which may be add ed, that if the electric matter do act on the air to put it in motion, the air must react with an equal force ; and, therefore, that a current of air blown against the course of the electric matter must affect its appearance, by retarding the rays and deflecting those against which it struck obliquely : the contrary to which is, by experience, known to obtain ; for the lu minous cones are not sensibly affected by such 'treatment. The air being thus in.
different as to the motion of the electric matter, its motion may be shewn to depend on the established principles of electrici ty. The point is electrified either posi tively or negatively, and the air imme diately opposite and contiguous to the point, must, by the emission or exhaus tion of the electric matter, become strong ly possessed of an electric state of the same kind with that of the point : it is therefore, repelled and replaced by other air which is also electrified and repelled, by which means a constant stream is produced blowing from the point, and that equally, whether the elec. trization be positive or negative. And the point repelling the air must itself also be equally repelled in the contrary direc tion; whence the horizontal wire above described is turned, and that always one way, namely, contrary to that in which the air is moved, or to the direc tion of its bent points.
If an insulated conductor, free from points, be brought within a certain dis tance of the prime conductor or cylin der in an electric state, it will also ex hibit signs of electricity of the same kind; but if those signs be removed, by taking the spark, and the conductor taken from the prime conductor, it will exhibit signs of the contrary electricity. This is a very remarkable appearance, but may be accounted for, if two suppo sitions be admitted, viz. first, that the electric matter is attracted by conducting bodies ; and secondly, that the parts of the electric matter mutually repel each other, the forces of each power being in a certain inverted ratio of the dis tance.
For the electric matter, in an insulated and uniform conductor, will then be equal ly diffused through its whole mass, and the attraction which that conductor will exert on any mass of electric matter pre sented from without, must be the excess of the attractive force of the body over the repulsive force of the electricity it contains. 'Whence a given conductor will attract the electric matter the most pow erfully, when the quantity it already pos sesses is the least possible, and its attrac tive force will decrease as it becomes more saturated with electricity. Let two equal conductors, composed of like mat ter, be brought within a small distance of each other, then if the quantities of elec tricity they contain be equal, the attrac tions they mutually exert on those quan tities will be equal, and it will remain un disturbed in each body. But if one con ductor, A, contain more electricity than the other, B, the attractive power of B will be greatest, and will draw the elec tric matter from A, till an equilibrium is obtained. It follows, also, that in a num ber of conducting bodies, communicating with each other, the electric matter will be every where of the same density, if the greatest attractive force of the bodies be supposed equal; but if different bodies be supposed to attract the electric matter with different forces, as is most probable, the densities must vary with the forces. This may be called the natural state.