There are four openings in the prime conductor: the lower one for the head of the supporting pillar; the one at the right for the attachment of the collecting apparatus; the one at the left for the stalk of a small brass ball; and the upper one for admitting the lower end of a large wooden ring, removable at pleasure. This last forms the peculiar feature of Winter's machine. It consists of a bent iron wire carefully covered all round with polished wood, and communicating by a brass pin at the foot of the stalk, on which it stands with the prime conductor. To receive the sparks from the machine, an appendage termed the spark-drawer is provided. This consists of a wooden pillar of the same height as the prime conductor, in the head of which a brass rod slides, with a large flat ball at the one end and a small ball at the other. All the fittings of the machine are of wood, no metal being used but for the prime and negative conductors. On using the machine, it is first necessary to connect the negative conductor by a wire or chain with the ground. As the plate is turned, — E. is developed on the rubbers, and led to the negative conductor; and E. is formed on the glass, which is collected by the points, and transferred to the prime conductor. If the negative conductor be insulated, the electric field would be limited to the space between the negative and prime conductors; hut when uninsulated, the floor and walls of the room form part of it, and the field now lies between the prime conductor and any surrounding object. If — E. is wanted, the negative conductor is insulated, and the prime conductor connected with the ground, when sparks of — E. are given off by the negative conductor.
The various forms of electric discharge through the air, or, as it is termed, disruptive discharge, can be well seen with Winter's machine. The negative conductor being con nected with the ground, with a two-foot plate, we may observe them in the following order. On turning the plate once or twice, a faint snapping sound is heard, and, when the room is darkened, a flickering spark is seen to be thrown out from the two-inch ball projecting from the prime conductor, which has the form of a bush, without leaves, with trunk, branches, and twigs, about 10 in. in height. This is one form of what is called the brush discharge. Its general direction is horizontal, or not much inclined from it, but it turns to the hand or other flat conductor brought near it. If it be received on a ball, its various branches concentrate on it. If the brush proceed from the end of a brass rod, instead of from a ball, it becomes very much diminished in size, and resembles a brush of feathers. The brush discharge, though apparently continuous, has been 'found by Wheatstone to consist of a series of successive brushes. When discharge is effected from a point, a star or glow of light marks its termination, while strong currents of air proceed from it, which are strong enough to blow away the flame of a candle. These currents accompany more or less the various forms of the brush discharge. The particles of air thus carry away the charge from a point to surrounding conductors, and hence a point is said to discharge itself by convection. If we connect the brass rod of the spark-drawer with the ground, or the negative conductor, and bring the fiat ball opposite to the small ball on the prime conductor, straight brilliant sparks pass between them so long as the distance does not much exceed 2 inches. Beyond that distance, the
sparks become somewhat crooked, and at about 4 in. the discharge begins to take the form of a brush. If, now, the ring be placed in the conductor, the sparks again pass with readiness, and the brush does not again take place till the ball of the spark-drawer is 11 or 12 in. off. The long sparks thus obtained with the aid of the ring are decidedly crooked or forked, with strongly marked lateral•,branches, which become all the more marked as they lengthen. It would thus seem that the spark has a tendency to break up into branches. When the striking distance is small, this is not perceptible; it is then straight and undivided. As the distance increases, it is crooked, with well-marked offshoots; and when the distance is too great, it splits up entirely into a bush or brush. !nig, hi; fillirrnenft 6-0 The ring is merely an extension of the prime conductor, and keeps down its electric density till a sufficient quantity of E. is collected, which can keep together in the form of a spark. Something similar occurs when water is driven out in spray from a small syringe, and in a jet from a large one, under an. equal head. All the forms of disruptive discharge are accompanied with the peculiar electric odor which arises the produc tion of ozone (q.v.).
We may now make a short reference to the experiments performed by the machine, illustrative of the general properties of electricity. A wooden head with hair on it illustrates, when placed on the prime conductor, electrical repulsion, by the hair stand ing on end. A spoon containing ether is held so as to receive a spark from the project ing ball, when the inflammation of the ether illustrates the heat of the spark. A man standing on an insulating stool (a stool with glass legs), with one hand on the conductor, can send sparks, with his other hand, to everything and everybody about him. This illustrates communication of E. by contact. A few pith-balls are inclosed in a glass jar, having its top and bottom of metal—the former in connection with the prime conductor, and the latter with the ground, when the pith-balls, by their rising and falling, show the attraction of unlike, and the repulsion of like electricities. A gas-jet may be lighted by a person wholly unconnected with the machine, and standing some 8 or 10 ft. from it. If the person so situated holds the blade of a knife or other point over the gas-burner, at a distance only short of touching, at each long spark from the machine, a small spark passes between the blade and the burner, and this ignites the gas. The reason is as follows: The body of the person in question is electrified negatively by the extensive prime conductor of the machine acting inductively. When the spark passes, the electric tension of the falls, and the negative E. of his body must return to the ground, and taking the easiest route, causes the spark in question. This is quite similar to what is known in thunder-storms as the back-stroke. A person in a prominent position, under a highly-charged cloud, experiences a violent, sometimes fatal shock at the same time as a flash of lightning, although the flash was not at all near him.