XVI. On a self-acting apparatus for multiplying and maintaining electric charges, with applications to illustrate the voltaic theory

Abstract

In explaining the water-dropping collector for atmospheric electricity, in a lecture in the Royal Institution in 1860, I pointed out how, by disinsulating the water-jar and collecting the drops in an insulated vessel, a self-acting electric condenser is obtained. If, owing to elec­trified bodies in the neighbourhood, the potential in the air round the place where the stream breaks into drops is positive, the drops fall away negatively electrified; or vice versâ , if the air potential is negative, the drops fall away positively electrified. The stream of water descending does not in any way detract from the charges of the electrified bodies to which its electric action is due, provided always these bodies are kept properly insulated; but by the dynamical energy of fluid-motion, and work performed by gravity upon the descending drops, electricity may be unceasingly produced on the same principle as by the electrophorus. But, as in the electrophorus, there was no provision except good insulation for maintaining the charge of the electrified body or bodies from which the induction originates. This want is supplied by the following reciprocal arrangement, in which the body charged by the drops of water is made the inductor for another stream, the drops from which in their turn keep up the charge of the inductor of the first. To stems connected with the inside coatings of two Leyden phials are connected metal pieces, which, to avoid circumlocution, I shall call inductors and receivers. Each stem bears an inductor and a receiver the inductor of the first jar being vertically over the receiver of the second jar, and vice versâ . Each inductor consists of a vertical metal cylinder (fig. 1), open ah each end. Each receiver con­sists of a vertical metal cylinder open at each end, but partially stopped in its middle by a small funnel (fig. 1), with its narrow mouth pointing downwards, and situated a little below the middle of the cylinder. Two fine vertical streams of uninsulated water are arranged to break into drops, one as near as may be to the centre of each inductor. The drops fall along the remainder of the axis of the in­ductor, and thence downwards, along the upper part of the axis of the receiver of the other jar, until they meet the funnel. The water re-forms into drops at the fine mouth of the funnel, which fall along the lower part of the axis of the receiver and are carried off by a proper drain below" the apparatus. Suppose now a small positive charge of electricity be given to the first jar. Its inductor electrifies negatively each drop of water breaking away in its centre from the continuous uninsulated water above; all these drops give up their electricity to the second jar, when they meet the funnel in its receiver. The drops falling away from the lower fine mouth of the funnel carry away ex­cessively little electricity, however highly the jar may be charged; because the place where they break away is, as it were, in the in­terior of a conductor, and therefore has nearly zero electrification. The negative electrification thus produced in the second jar acts, through its inductor, on the receiver of the first jar, to augment the positive electrification of the first jar, and causes the negative elec­trification of the second jar to go on more rapidly, and so on. The dynamical value of the electrifications thus produced is drawn from the energy of the descending water, and is very approximately equal to the integral work done by gravity, against electric force on the drops in their path from the point where they break away from the uninsulated water above, to contact with the funnel of the receiver below. In the first part of this course each drop will be assisted downwards by electric repulsion from the inductively electrified water and tube above it; but below a certain point of its course the resultant electric force upon it will be upwards, and, according to the ordinary way of viewing the compo­sition of electric forces, may be regarded as being at first chiefly upward repulsion of the receiver diminished by downward repulsion from the water and tube, and latterly, the sum of upward repulsion of the receiver and upward attraction of the inductor. The potential method gives the integral amount, being the excess of work done against electric force, above work performed by electric force on each drop in its whole path. It is of course equal to m V, if m denote the quantity of electricity carried by each drop, as it breaks from the continuous water above, and V the potential of the inner coating of the lower jar, the potential of the uninsulated water being taken as zero. The practical limit to the charges acquired is either when one or other of them is so strong as to cause sparks to pass across some of the separating air-spaces, or to throw the drops of water out of their proper course and cause them to fall outside the receiver through which they ought to pass. It is curious, after commencing with no electricity except a feeble charge in one of the jars, only discoverable by a delicate electrometer, to see in the course of a few minutes a somewhat rapid succession of sparks pass in some part of the apparatus, or to see the drops of water scattered about over the lips of one or both the receivers.