26 SEVENTH REPORT—1837. 
or breaks battery connexion with the extremities of helix A. The — 
helices, bar, and wires, are enclosed, permanently, in a strong deal 
case, upon which are screwed the copper cylinders S and T, the | 
fulerum C upon which Z E moves, and the cups of mercury H, K, N, 
O, P. By sliding a small wedge under the extremity of the lever E, 
the knob D more nearly approaches the bar W W, and being more 
easily, is, therefore, with greater frequency attracted by it, as the time 
necessary for intense magnetization is not then required; a spring 
also sliding under E lightens the latter, and without bringing the 
knob nearer to W W, renders its attraction more easy: both wedge 
and spring will be found useful. 
Since battery connexion is broken by the apparatus itself, and at 
the moment the magnetism and excitement of the helix have reached 
their highest intensity, the circumstances are, in consequence, most 
favourable for the production of the desired effect; hence, to break 
connexion more rapidly, either by a separate mechanism, or by regula- 
ting the wedge and spring of the apparatus itself, though it increase the 
number, cannot augment the violence of the shocks. This was shown 
by experiment ; and it was said to be in accordance with the belief 
of Dr. Faraday, who says, (Phil. Trans. 1832,) “that a magnet, even 
of soft iron, does not arrive at its fullest intensity in an instant.” The 
mercury cups are arranged so that the experimenter may connect the 
extremities of the helices, the cylinders, and the battery, as he pleases. 
That contact, when broken, may be broken with great rapidity, the 
wire E is attached to the longer arm of the lever. 
It is said, Mr. M‘Gauley continued, that mere metallic contact, 
without mercury cups, is sufficient, and he hoped it was so; but he 
had reason, from experiment, to fear, that a pressure of the metals, 
incompatible with the delicate action of the machine, would be re- 
quired. Besides many, and he was induced to hope important dif- 
ferences between this and other contrivances, he thought it right to 
remark, in anticipation of what perhaps might be said, that the coils 
used by Dr. Faraday and Professor Jacobi were not the same as the 
present ; and the importance even of the manner of coiling the wire, 
may be inferred from the fact, that out of four arrangements, the 
same in every respect except the coiling of the wire, none was at all 
comparable in effect with the one exhibited. Dr, Faraday’s coils, as 
they were nearly of the same length,—(paper read before the Royal 
Society, Jan. 29, 1835: Atheneum, No. $91)—must have been placed 
beside each other in the same stratum on the bar; and Jacobi (Seien-- 
tific Memoirs, part 4) coiled the wires together in one helix. 
That the action of the apparatus was very great, was, he observed, 
manifest to all present; and he had not known any person, when it — 
was in order, as it then was, able to retain the hands, wetted with © 
water, on the cylinders for an instant; nor, very frequently, the hands — 
even unwetted. With this apparatus we have a very convenient means — 
of trying the beautiful experiment of Dr. Faraday, repeated by Jacobi. 
They found that when two wires were coiled .in a parallel direction, 
and the extremities of one of them united, the spark and shock were 
a ee 
Gay ea 
