Ruhmkorff constructed, in the year 1848, the so-called spark-inducer named after him, the object of which was also to convert currents of low tension into hose of very high tension. With this coil and like coils of larger dimensions effects were produced, but only such as were afforded by the common forms of frictional electrical machines. All things considered, it is not a little surprising that while the invention of the Rhumkorff coil was still in its infancy, the wonderful output of Page’s apparatus was still, even in the year 1851, quite unknown in Europe. [Illustration: FIG. 5.] Fig. 5 represents the earlier form of the Ruhmkorff apparatus. It consisted of a bobbin of good insulating material; thoroughly dried wood, or better, hard rubber. The two end pieces of the bobbin were usually made of grooved glass discs, and were bound down to the bedplate of the apparatus by two wires. Inside the coil was the already often-mentioned bundle of iron wires. The primary or inducing wire was next wound upon the bobbin. As this wire had to carry currents of comparatively great strength, it consisted of only one or a few layers of thick wire. The circuit of this coil was completed as far as two terminals on the bedplate, first passing through an interruptor like what has already been described. Over the primary coil, and after a sufficient layer of insulation had been added, the secondary wire was wound. As this wire was destined for very small currents, it was of as fine wire as it was possible to wind. In order to obtain high potential it was necessary that the secondary should possess many turns. In the earlier coils a length of between 8 and 10 kilometres was used; in the coils now made this length has been increased to between 50 and 70 kilometres. The ends of the secondary coil were connected to terminals insulated on glass pillars. It was not nearly sufficient insulation for the secondary wire to be covered with silk, but every layer was well soaked with dissolved shellac, and then well dried as it should be. A condenser in connection with the primary coil was placed under or in the bedplate, which was usually a box. This condenser was, and is still, often made thus:—On both sides of a strip of paraffined paper, several metres long and of convenient breadth, tinfoil is stuck, at the same time leaving a sufficient margin of paper for insulation. The whole is then folded together suitably. The effect of the coil is substantially enhanced when the sheets of tinfoil are each connected to the circuit of the primary coil in such a way that the condenser is in shunt to the interruptor. In Fig. 6 is shown a newer form of Ruhmkorff’s coil, with an interruptor like the mercury contact-breaker which we have before described. According as the movable weight is raised or lowered, the oscillations of the lever, and consequently the induced currents, follow one another more slowly or more rapidly. [Sidenote: C. T. and E. B. Bright, 1855.]