Fig. 114
Fig. 115
One boy then touched the bare ends c and d to the tip of his tongue, while I touched repeatedly the binding post with b. There was, of course, no sensation. We now wound a portion of the wire upon the bundle of nails, laying on about fifty turns. (See [Fig. 114].) The tongue was now placed at T and b was touched a few times to the free binding post. A very decided shock was felt, not while the end of the wire was resting upon b, but at the instant of touching and again at breaking the connection. The shock was noticeably stronger at the instant of breaking than of making the connection. There was also a spark formed when the connection was broken, which did not appear before the coil was made. We next wound on more of the wire—about fifty more turns ([Fig. 115]). When now connections were made and broken at b the tongue at T felt a much more decided shock, and a larger spark occurred at b when the circuit was broken. Both the tongue and the spark indicate that the voltage is creeping up very rapidly in this series of experiments. We next connected two cells in series, then three, four, and finally five cells in place of the one. The spark grew larger and "fatter," as the boatmen say, with each addition of a cell. It was not pleasant to use the tongue in the experiment after the number of cells exceeded two. I removed the branch d from the wire b and connected it to the binding post, as shown in [Fig. 116]. I then removed the crystal from my watch and poured into it a little gasolene. I rubbed the ends of b and d together over this, and when they separated the spark which was produced would not light the gasolene. We had made a coil which produced a spark that looked like a miniature flame, but still was not hot enough to set fire to gasolene vapour. It simply needs more iron in the core and more turns of wire about it. Bringing the ends of the wires together and separating them is somewhat like drawing an arc with the arc light carbons. It requires a vastly higher voltage to make a spark jump across an air gap than it does to lead it across thus.
Fig. 116