Voltaic Induction. 39 



other end, 6, so as to form a perfect metallic communication, through 

 the coil, between the magnet and armature. From each of these 

 portions of the instrument proceeds a conducting wire, c, d. The 

 connections at a and b being preserved, if the armature be made to 

 slide from the magnet, very brilliant sparks appear between the latter, 

 at the last point of contact ; and the wires c, d, if taken into the mouth 

 at the time of separation, will communicate very unpleasant shocks, or 

 if brought close together, furnish a small but vivid spark. Yet the 

 current actually passing through these wires, scarcely admits of detec- 

 tion, even by the galvanic multiplier. As, however, the effect varies 

 with the magnetic intensity, length of coil, &c, the observation will be 

 best sustained bj- an appeal to experiment. The magnet, coil, ar- 

 mature, and galvanic multiplier being the same in all cases, the fol- 

 lowing results were obtained. 



1. One half the coil, moved downwards between the poles, gave, 

 alone, a declination of 12°. 



2. One half the coil, moved downwards between the poles, with 

 the armature, gave, alone, a declination of 70°. 



3. One half the coil, moved downwards between the poles, and 

 arranged as in fig. 6, gave, alone, a declination of 5°. 



Here it will be seen that a current, equal to 70° when the arma- 

 ture merely passes through the coil, becomes diminished to T f ? by 

 merely making the magnet form a part of the circuit, as shown in fig. 

 6. That the armature contributes nothing to this effect is shown by 

 the fact, that an equal reduction takes place when the end of the 

 coil, a, is separated from the armature and made to touch the mag- 

 net, so that upon breaking off the contact of the armature, this end 

 also becomes removed. The result, therefore, clearly depends upon 

 breaking off the circulation in the magnet and throwing it suddenly into 

 the wires c, d> — It is easy to perceive why this arrangement should 

 furnish a smaller current than even the coil alone ; since, up to the 

 period when the armature leaves the magnet, a close circuit exists 

 and the wires c, J, cannot possibly receive any portion. After this 

 separation the coil alone acts, but as its position is then necessarily 

 lower down than when it is used alone, so the resultant current must 

 be less. What then produces the shock, by this arrangement, when 

 the wires c d are taken into the mouth, or the spark, when they are 

 close to each other ? The galvanometer shows that there is scarcely 

 any fluid circulating through them at the time. The result of my 

 observation upon the three positions, establishes the fact, that the 



