If an uninsulated conductor, which is broad, round and polished at the end, be presented to the prime conductor, a short and dense spark, accompanied with some noise, will be perceived; if the conductor be less broad, the spark will be longer, less dense, and attended with less noise; if the breadth be still more diminished, so that the conductor may come under the denomination of a point, the electric matter will pass to it, from the prime conductor, and through a greater space, with a hissing noise, and in a continual stream; a still greater sharpness will enable the electricity to pass over a yet more extended space, but unaccompanied by noise, and only a small light will be seen upon the point. The same result will arise if points of different acuteness be affixed to the prime conductor, instead of the uninsulated one: but if both be pointed, the electricity will be more readily discharged. In all the above cases, the appearance of the electric matter at the point, will indicate the kind of electricity from which it proceeds. A large divergent cone indicates positive electricity; a small globular light, that which is negative. Hence it is always easy to ascertain whether an insulated conductor be electrified positively or negatively, by presenting a point to it, as the light at the point is always definitive of the contrary electricity in the conductor. If a pointed conductor be electrified, either positively or negatively, and the face be brought near the point during the electrization, a wind will be felt blowing from the point, accompanied with a peculiar sensation, commonly called _the spider’s web_. It is remarkable that the current of air is always in the same direction, whether the point throws off or receives electricity. The re-action of the force, by which the air is put in motion, is exerted upon the pointed body. This is shewn by a very pleasing experiment called the electric fly. This fly is composed of four small wires, fastened into a metallic cap, similar to those used in sea-compasses, so that the wires may easily move upon a point, in a horizontal direction. They should be exactly balanced, and have their ends, which must be very sharp, all bent in the same direction. Now if this fly be placed on an insulated point and electrified, its sharp ends will become luminous in the dark, and it will revolve in a direction contrary to that in which the ends are bent; or if it be placed on an uninsulated point and brought near the electrified prime conductor, the same effect will follow.