[76] These phenomena excite more interest in consequence of the employment, for medical purposes, of an apparatus originally contrived by Callan, but since ingeniously modified by our countryman, Dr. Page, into a form which has been designated as the electrotome. A coil of coarse copper wire, covered with cotton, like bonnet wire, is wound about a wooden cylinder. Around the coil thus formed, a coil of fine copper wire similarly covered is wound, leaving the extremities accessible. One end of the coarse coil communicating constantly with one pole of a galvanic battery, the other end is left free; so that by scraping with it the teeth of a rasp attached to the other pole, a rapid closing and opening of the circuit may be effected. Under these circumstances, an observer, holding the ends of the fine coil, receives shocks more or less severe, according to the construction of the battery, the energy of the agents employed to excite it, or the total weight and relative dimensions of the coils as to length and sectional area. Agreeably to the received doctrine, the shocks thus produced are owing to secondary currents caused by dynamic induction. Agreeably to the hypothesis which I have advanced, the atoms of the coarse wire, polarized by waves proceeding from the poles of the battery, induce a corresponding polarization of the atoms of the fine wire; the aggregate polarity imparted being as the number of atoms in the former to the number of atoms in the latter: or (to use an equivalent ratio) as the weight of the coarse, to the weight of the fine wire. But as on breaking the circuit through the coarse wire, the ethereo-ponderable atoms in both wires resume their neutral positions, while this requires each circuit to be run through within the same minute interval, the velocities of their respective waves will be inversely as their sectional areas and directly as their lengths: in other words, the velocity in the fine wire will be as much greater as the channel which it affords is narrower and longer. The cylinder included within the coils as above stated being removed, a cylindrical space is vacated. If into the cavity thus made iron rods, like knitting needles, be introduced, one after the other, while the apparatus is in operation, the shocks increase in severity as the number augments; so that from being supportable they may be rendered intolerable. The shock takes place without the presence of iron, but is much increased by its assistance.[77]
These facts appear to me to justify a surmise that the ethereo-ponderable atoms of iron, in becoming magnetized and demagnetized, co-operate with the ethereo-ponderable atoms of the copper coils in the induction of secondary undulations. It is conceived that these may be owing to the intestinal change attended by sound, as above stated, (73;) this being caused by a sudden approximation of the poles of the atoms, previously moved apart by the influence of the galvanized coil. But if this sudden coming together of the previously separated poles of atoms within a magnetized cylinder of iron, can contribute to the energy of secondary waves, it is consistent to infer that these waves owe their origin to an analogous approximation of the separated poles of the cupreous atoms, forming the finer coil, in which the secondary undulations may be created without the presence of iron. Of course, this reasoning will apply to all cases in which the phenomena hitherto attributed to Farradian currents are the result of dynamic induction.
Thus it appears that the polarization of magnets, and that created and sustained when a galvanized coil or helix acts upon another in proximity, have the same relation to galvanic discharges that the charges upon insulated surfaces have to their appropriate discharges. The permanent magnetism of steel seems to have some analogy with the charge upon a coated pane, while we may consider as analogous with the charges upon insulated conductors, already adverted to, (61, 62,) that state of the ethereo-ponderable particles, (38,) of a wire helix, which state, resulting from the influence of an included magnet, or neighbouring galvanized coil, and being discharged on a change of relative position, or breach of the galvanizing circuit, is productive of spark, shock, ignition, or electrolysis, as exemplified by Callan’s coil, Page’s electrotome, or the magneto-electric machine.
[77] Agreeably to the usual construction, the cylinder about which the inner coarse wire coil is wound is originally of iron, so that there is as much of this metal contained as it can hold. Various contrivances are resorted to for the closing and opening of the circuit, which are more ingenious and convenient than scraping a rasp, as above described.
[78] American Journal of Science, vol. x. p. 121, 1826.
[79] It is well known that if a rod of iron be included in a coil of coated copper wire, on making the coil the medium of a voltaic discharge, the wire is magnetized. Agreeably to a communication from Joule, in the L. & E. Phil. Mag. & Jour. for Feb,, 1847, the bar is at the same time lengthened, without any augmentation of bulk, so that its other dimensions must be lessened in proportion to the elongation.
All these facts tend to prove that a change in the relative position of the constituent ethereo-ponderable atoms of iron accompanies its magnetization, either as an immediate cause or as a collateral effect.
[80] To the tune of Moore’s “Canadian Boat Song.”
[81] See paragraph 410.
[82] See paragraph 449.