Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.

The coil or helix of all these machines, that are useful, is made pretty much on the same principle. A stout copper wire is well covered with cotton thread and varnish, for perfect insula- tion ; and then some ten to fifteen yards of this is first wound into a coil, (which forms the inside of the helix of every such machine,) so as to allow the two ends of this coarse wire coil, which is but a part of the helix, to connect with the galvanic battery. This is termed the inducing wire, and the current of the battery when passing through this inner and stouter wire is designated the inducing current. Indeed, this current does in- duce the additional power from two sources — the one from a bundle of soft iron wires or a piece of soft iron that is placed within the central cylindrical cavity in the helix, and the other power from the outer and second coil of the helix, that will soon be described. But to understand as we go. If, now, into the interior of this primary coil of wire there is inserted the piece of soft iron or the bundle of wires while the current flows through the coil, the wire or iron is magnetized by the power of the cur- rent that is only passing from the battery through the helix and back to the battery. This is proved by the visible effects on a common magnetic needle placed under the wire, but very close to it; or it is seen the better by a galvanometer, so arranged that the current passes through this instrument, when it is found to be very decidedly increased, because there is added to the primary current of the battery the induced current from mag- netic induction. To finish the helix as it is, or should be, there is wound on or over the bobbin of coarse copper wire, that we have just been experimenting with, a second coil of fine copper wire of good quality, that is also well covered with silk or cotton thread and varnish, for perfect insulation : of this there should be at least five hundred to fifteen hundred feet, closely laid in the same direction over the coarse inducing wire. When thus completed, the two ends of the primary or coarse inducing wire lead to, and connect with, the battery. The two ends of the outer sec- ondary fine induction wire lead to binding screws, with which the electrodes and conductors can be adjusted so as to lead to the patient.