392 Royal Society : — Sir W. Thomson on an Apparatus 



■Fig. 1. 



other stream, the drops from which in their turn 

 keep up the charge of the inductor of the first. 



To stems connected with the iuside 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 re- 

 ceiver, the inductor of the 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 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 cylin- 

 der. 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, w T hen 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 elec- 

 trification thus produced in the second jar acts, through its in- 

 ductor, on the receiver of the first jar, to augment the positive 

 electrification of the first jar, and causes the negative electrifica- 

 tion 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 approxi- 

 mately 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 induc- 

 tively electrified water and tube above it; but below a certain 

 point of its course the resultant electric force upon it will be up- 

 wards, 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 repul- 

 sion from the water and tube, and latterly the sum of upward 



