Page:Electricity (1912) Kapp.djvu/110

106 charge which they carry forward and give up to B and A respectively, again increasing the original charge. Thus at each half revolution of the internal carrier the charges on the outer segments are increased, the process being cumulative, but also in this case limited by the dispersion of electricity, which, with an increasing potential difference, eventually reaches so high a value that the charge brought in each half revolution by the carrier just balances the leakage of electricity during the time it takes to perform the half revolution. The faster we twirl the knob, the shorter is this time, and the smaller the leakage per half revolution. By twirling faster a higher potential between the outer segments can be attained. This means in the electric gas-lighter a more vigorous and effective spark.

When it is required to accumulate large charges and to produce spark discharges of considerable magnitude, machines on a larger scale must be used. These are known under the name of "influence machines." Such machines have been constructed by Toepler, Holtz, Voss and others, but the type most commonly used in England is that designed by Wimshurst, of which Fig. 5 is a diagrammatic representation. Two discs of highly insulating