tips, which have the form either of buttons, from 1 to 1 inch in diameter, or of segments of balls and plates, from 1 to 3 inches in diameter, or of square rods, from 1 to 3 inches long, and to 1 inch wide. These, to prevent oxidation, are covered with platinum plate, and then with a layer of flannel concealed by linen. The conductors are protected by cork coverings, from to of an inch thick, which are secured to the metal plate by linen binding.

Lately, Fromhold has described an apparatus in a short paper,' which, so far as we can judge, is an improvement in the construction, since we can, by the use of it, not only obtain currents of a desired intensity, but of any quantity, for therapeutical purposes.

6. Fromhold's apparatus has the following construction: Its base has a length of 24", and a breadth of 13", and is furnished on each of its longer sides with a prominence for the reception of a wooden column, 21" high, having a slit below, 3"" wide. There is glued to the bottom, and secured by screws, a second board, pierced with 32 holes, which are for the reception of 32 battery-glasses. A similar board, serving as a point of support for the glasses, may be secured by means of two screws, which pass through the slits in the columns, at any height, even as far up as the edge of the glasses, and allow in this way an open view of these from all sides. (See Fig. 6.)

The 32 glasses, each of which has an outer diameter of about 2 inches, and a height of 8 inches, are arranged in 4 rows, and serve for the reception of the zinc-lead-platinum elements already described. The electro-motor metals are secured to a wooden frame, of the dimensions of the bottom board, which is divided lengthwise into four parts, and carries on its middle cross-piece the dial (Remak's current selector) and the commutator. The four longitudinal divisions are so divided, by means of cross-sticks or saddles,

Der constante galvanische Strom modificirbar in seinem Intensitäts- und Quantitätswerth, Pesth, 1867.

that each saddle comes exactly over the middle of a batteryThe entire frame is elevated when the metals are

glass.

lifted from the fluid, and is lowered when these are allowed to sink into the fluid consisting of acid water, and this rising and sinking take place by means of a windlass. This consists of an iron rod passing from one column to the other, which holds on both of its inner ends a metallic disk of 3 inches diameter, and a cog-wheel where it passes at right angles through the column. This wheel is moved by means of an endless vertical screw, which turns it completely on its axis by 40 revolutions, and is held fast, through the friction, at any height. The dial-plate, which receives on its lower surface the conducting wires of all the positive poles, con

sists of a horizontal disk, 5 inches in diameter, of well-dried wood, which has on its surface 32 numbers, corresponding to the 32 elements, and of an indicator which can be moved without disturbing the apparatus from 1 to 32. Connected with this battery, as with Remak's, there is a commutator, and in place of the magnet-needle there is, separated from the apparatus, a tangent box-compass which is intercalated. in the course of the current.

The power which this apparatus has of delivering currents of greater intensity and quantity, results from the possibility of introducing a greater or less number of elements, and of sinking them more or less deeply into the fluid: moreover, all possible modifications may be resorted to according to the various therapeutical indications or surgical demands. This battery also produces, by the slow sinking of the electro-motor metals into the fluid, a gradual increase of the quantity, and through the slow moving of the index from lower to higher numbers a gradual increase of the intensity -advantages which Fromhold considers of great service in therapeutics.

Deserving of special notice is

7. Thomsen's Polarization Battery,' because it has the advantage over all other batteries of producing sufficient electro-motor power by the use of one galvanic element, which takes up very little room, because, though the first cost is considerable, the expense of operating it is light, and because, with certain modifications, it may serve as a transportable battery for medicinal purposes. The theory which lies at the foundation of the construction of the apparatus is the following: When we touch the poles of a galvanic element to two platinum plates, which are dipped into dilute sulphuric acid, and then remove the element and con

1 Die Polarisations-Batterie, ein neuer Apparat zur Hervorbringen eines continuirlichen electrischen Stromes von hoher Spannung und constanter Stärke mit Hülfe eines einzelnen galvanischen Elements von Julius Thomsen, Hamburg, 1865.

nect the platinum plates by means of a metallic wire, there arises an electric current, which runs in an opposite direction to the current which produced this condition-the platinum plates are then polarized; during the short time of contact there was formed an invisible film of the constituents of the water on the platinum plates-hydrogen on the plate which was in connection with the zinc pole, and oxygen on the plate in connection with the copper pole. The current has naturally only a short duration, since the hydrogen and oxygen quickly unite again, but we may, in a very short time, in this way charge a large number of plates, and obtain, if we unite these into a battery, an electrical current of very high tension. The strength of the current decreases, however, very quickly, unless we take care to charge the individual cells without breaking their connection with one another, and this is done by so arranging the platinum plates, as in a battery, and the connection of the polarizing element with each platinum pair, that the already present charge will be increased by the action of the charging cur

rent.

The polarization-battery consists of three principal parts: 1. The battery proper; 2. The galvanic element, which charges; 3. The distributing apparatus, through which the current produced by the element is conducted from one to another of the different cells of the battery. 1. The battery is formed of two open wooden chests, each of which is divided by means of 26 platinum plates secured in its walls, into 25 cells, so that-and this is a peculiarity of this battery-the plates themselves form partition walls between the cells, and the two sides of a plate belong to two different cells. 2. As the galvanic element must be able easily to decompose water, it is best to use a zinc-platinum or a zinc-carbon element with nitric or chromic acid. 3. The distributing apparatus consists of a flat ring, composed of insulating material, into which a number of short, radiating, metallic rods are secured, as many in number as the battery

cells. Each of these is combined by means of a fine silver or copper wire with a platinum plate in the battery. Through the middle of the ring passes a vertical axis, which carries above two isolated arms alongside of one another, which stand in connection with two wooden clamps, serving for the reception of the conducting wires from the galvanic element. The two arms represent the two poles of the element; each is supplied with a spring, and they stand so far apart that, when one touches one metallic rod of the ring, the other is also in contact with the next. If the axis is now turned, which may be done by means of clock-work, a weight, or an electro-magnetic contrivance moved by a galvanic element (which causes a revolution in at most two or three seconds), each plate will become loaded one after the other with hydrogen on one side and oxygen on the other. After a single turning round of the axis all the plates are charged, and the battery is in a condition to begin its action. The intensity of the current is regulated through the polarizing element, and this again through the rheostat, i. e., an apparatus that enables us at pleasure to increase the conducting resistance by intercalating a longer or shorter metallic wire. The entire apparatus, exclusive of the galvanic element, is enclosed in a polished wooden chest 13 feet long, 1 foot wide, and foot high.

II. INDUCTION APPARATUS.

Among the magneto-electrical induction apparatuses we will mention:

8. The apparatus of Pixii. In this the electrical current is induced by means of a steel magnet rotating vertically on its axis, above the poles of which are two iron rods wound with connecting spirals. The magnet rotates, while the induction spirals remain immovable.

In all the later constructed apparatuses the magnet is immovable, and the horse-shoe shaped soft iron, either with the induction spiral or without it, is movable. To the in