68 



Sir W Thomson on an Apparatus 



[June 20, 



the inductor of tlie first jar being vertically over the receiver of the 

 second jar, and vice versa. Each inductor consists of a vertical metal 

 cylinder (fig. 1), open at each end. Each receiver con- 

 sists 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 in- 

 ductor, 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 fuunel, which fall along the lower part of the axis of 

 the receiver and are carried ofi" 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 ex- 

 cessively little electricity, however highly the jar may be charged; 

 because the place where they break away is, as it were, in the in- 

 terior 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 elec- 

 trification 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 compo- 

 sition 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 hy electric force on each drop in its whole 

 path. It is of course equal to m Y, if m denote the quantity of elec- 



