gas-carbon; above this carbon a saturated solution of water and sal ammonia is poured up to two-thirds the height of the tube,

FIG. 8.

GALVANO-FARADIC COMPANY'S GALVANIC BATTERY.
(Piece cut away, showing cells.)

At the bottom of a glass tube, of the dimensions of a test-tube, is a platinum wire melted into it, extending as well inside as outside. The tube is filled one-third of its height with prepared

FIG. 9.

by which means the porous jar, as required in a Leclanche battery, becomes unnecessary. The upper part of the tube is

coated on the inside to prevent the solution from adhering to the glass, and so as not to form crystals of sal ammonia, which,

B

FIG. 10.

by capillary attraction, would further soak up the solution and cause these crystals to rise over the upper edge of the tube. The tube is closed loosely on the top by means of a rubber stopper in which a rod is fastened connecting the zinc, so as not to be moved up or down.

b); but only one must remain connected at a time; the second cord-pin only serves to act, when an alteration of the number of elements is required, in which case the connected pin remains connected until the desired new connection is completed by means of the disconnected cord. In this manner any desired connection or any alteration in the number of elements, as well as any desired current-fluctuations, can be produced without causing an entire interruption."

The Galvano-Faradic Company have recently made a most excellent modification of the celebrated Brenner battery, by which the cumbersome table of the original battery is done away with, and a neat glass case substituted. These batteries are furnished with a most complete set of rheostats, galvanometer, current-selector, etc., in a very small space.

Pülvermacher's chain consists of a number of alternate slips of copper and zinc wired together in the form of a chain. When these are immersed in dilute acetic acid, a mild current is generated. These chains have been worn about paralyzed limbs, and the action sometimes has been sufficient to vesicate the part. Numerous disks, "galvanic insoles," etc., have been lauded by different physicians. Garret's disks will be hereafter alluded to.

CHAPTER II.

THE INDUCED CURRENT.

General Laws of the Induced Current.-Theory of Induction.-Rotary and Chemico-Magnetic Batteries.-Induction Apparatus.-Galvano-Faradic Company's Apparatus.-Curt W. Meyer's Apparatus.

THE second division of current electricity is the induced, or faradic current; but, before we go further, it will be advisable to consider briefly the theory of induction.

It was Faraday who discovered that, at the moment of opening and closing a galvanic circuit, a current was produced in another conductor placed near that of the battery, and that this current ran in the opposite direction to the primary one. This current is but instantaneous, however, and only renewed on the closure or opening of the circuit, to disappear again on the instant, and reappear as often as the connection is made or broken, for, during this interval, or during all the time that the first current flows, the new one does not exist. A current of this kind is called the induced, or secondary current, in opposition to the inducing, or primary one. This current was called by Duchenne faradism, in honor of Faraday, its discoverer; whence have come into use the terms faradic or faradaic, and faradization, a term suggested in analogy with galvanization.

In the production of the current by the magneto-electric machine, a bar of soft iron is magnetized and demagnetized, and this induces in a parallel wire a vibratory or to-and-fro current, which is more magnetic than the inducing current.

The currents produced by the rotatory machine are broken in the interval between the interruptions, and are barely appreciable on account of their brevity.