In using this apparatus, eight pairs of Grove's battery will be quite sufficient to produce the effects, and the greatest care must be taken to avoid the shock, which is most severe and painful, and might do a great deal of harm to a weakly, sensitive, and nervous person. To avoid any accidents of this kind, the convenient arrangement at one end shown in Fig. 222 must be carefully attended to, and when manipulating with any part of the apparatus, if the battery is attached, the contact should first be broken by bringing the ivory (the non-conducting) part of the cylinder a (Fig. 222) in communication with the conductors, b b, where the wires from the battery are attached.
Fig. 222.
One end of Ruhmkorff's coil. b b. Connexion to receive the battery wires. a is the cylinder, one half of which is ivory and the other metal. In this position no shock can be received, because the electricity is cut off by the ivory from the coil.
First Experiment.
It is at the other extremity of the coil that the experiments are performed; for instance, if an exhausted globe is connected with the pillars b b (Fig. 223), and the connexion made with the battery, a beautiful faint blue light is apparent on one of the knobs and wires, and by reversing the current the light appears on the other knob and wire. This effect is supposed to resemble some of those magnificent streaks and undulations of coloured light called the Aurora Borealis; and, if the globe is removed from the foot, and screwed on to the air-pump plate, and a little alcohol, ether, naphtha, or turpentine placed on wool or tow is held to the air-pump screw, where the air usually rushes in, and the cock turned, so that the vacuum is destroyed, a quantity of the vapour will necessarily fill the globe; and if this is once more exhausted, it presents a different appearance, being full of coloured light (varying according to the spirit employed) but stratified and of a circular form. (Fig. 223.)
Fig. 223.
End of coil where the experiments are performed. b b. Connecting screws and wires passing to the exhausted globe, c. The screws are supported on insulating glass pillars, p p.