196 CLASSICS OF MODERN SCIENCE 

 formation of the magnet, and not by its mere virtual approximation, 

 that the momentary induced current was excited, the following experi- 

 ment was made. All the similar ends of the compound hollow helix 

 (34) were bound together by copper wire, forming two general 

 terminations, and these were connected with the galvanometer. The 

 soft iron cylinder (34) was removed, and a cyhndrical magnet three- 

 quarters of an inch in diameter and eight inches and a half in length, 

 used instead. One end of this magnet was introduced into the axis 

 of the helix and then, the galvanometer-needle being stationary, 

 the magnet was suddenly thrust in; immediately the needle was de- 

 flected in the same direction as if the magnet had been formed by 

 either of the two preceding processes (34, 36). Being left in, the 

 needle resumed its first position, and then the magnet being with- 

 drawn the needle was deflected in the opposite direction. These 

 eflfects were not great ; but by introducing and withdrawing the mag- 

 net, so that the impulse each time should be added to those previously 

 communicated to the needle, the latter could be made to vibrate 

 through an arc of 180° or more. 



40. In this experiment the magnet must not be passed entirely 

 through the helix, for then a second action occurs. When the magnet 

 is introduced the needle at the galvanometer is deflected in a certain 

 direction; but being in, whether it be pushed quite through or with- 

 drawn, the needle is deflected in a direction the reverse of that pre- 

 viously produced. When the magnet is passed in and through at one 

 continuous motion, the needle moves one way, is then suddenly 

 stopped, and finally moves the other way. 



41. If such a hollow helix as that described (34) be laid east and 

 west (or in any other constant position), and a magnet be retained east 

 and west, its marked pole always being one way ; then whichever end 

 of the helix the magnet goes in at, and consequently whichever pole of 

 the magnet enters first, still the needle is deflected the same way : on 

 the other hand, whichever direction is followed in withdrawing the 

 magnet, the deflection is constant, but contrary to that due to its en- 

 trance. 



57. The various experiments of this section prove, I think, most 

 completely the production of electricity from ordinary magnetism. 

 That its intensity should be very feeble and quantity small, cannot be 

 considered wonderful, when it is remembered that like thermo- 



