be described as two horseshoe electro-magnets placed opposite in horizontal position, their similar poles being towards one another, and having a small space between them in which rotates the armature ring." The machine contains other special features which would consume too much space to describe in detail.

Van der Weyde makes the following comparison between the Gramme and Brush machines. "In the

Gramme, the coils of the annular armature are, as in the Pacinotti machine, tapped in such a way that the whole of it is always in the circuit, even those parts which are over the neutral part of the ring; this unnecessarily increases the internal resistance of the current in the machine. Brush corrected this, by connecting the ends of the coils in such a way to the commutator, that those parts of the coils passing over the neutral parts of the magnets, in which no current is developed, are cut out from the circuit so as to diminish the internal total resistance. This adds to the efficiency of the machine." The Brush machine is one of the most popular machines in this country for electric lighting, and with certain modifications in the manner of winding has been adapted for electro-plating.

In response to a letter of inquiry addressed to the manufacturers of this machine, we have received, through the courtesy of Mr. G. W. Stockly, Vice-President of the Brush Electric Company, Cleveland, Ohio, the following reply:

"We have delayed sending to you the information you asked for, regarding the performance of our plating machines, in order that we might compare the theoretical figures of the work capable of being done by them with their actual work in practice. From the data thus collected, we are able to deduce the general rule (which we presume is what you wanted to know) that for each horse-power absorbed by the machines, we are able to deposit in suitable baths at least one pound per hour in each bath. The number of baths that can be run in series (with this amount being deposited in each) will be governed by the electro-motive force of the machine, the size of the plates in the bath, the character of the solution, the distance apart of the plates, etc. In the case

of our No. 8 light machine, wound suitably for copperplating and requiring about thirty-five horse-power to drive it, we could, with large surfaces of copper, both for anode and cathode, in an acid solution of sulphate of copper, with plates say an inch apart, with twenty baths in one series and suitable conducting wires, deposit about eight tons of copper per day of twenty-four hours.

"These figures will enable you to estimate the capacity of any one of our machines when wound for electro-plating. Any of our machines on the list inclosed can be wound for electro-plating, and, when so wound and run at their maximum capacity, absorb the same horse-power as when wound and used for electric light."

The accompanying cut, Fig. 72, represents the Weston machine. An iron ring or cylinder attached to an iron base forms the outer shell of the machine. The con

struction, which is not visible from the engraving, will be readily understood from the following brief description. From the interior of the cylinder above named, and pro

jecting radially towards the centre of the apparatus, are arranged a number of magnets (usually five), which consist of a core of iron to which are fastened a number of thin tempered steel plates, and they are wrapped with insulated copper wire, and so connected that the poles shall be alternately north and south. In the central space left between the inward ends of these magnets is arranged a shaft carried by bearings, which, to secure greater strength and perfect alignment, are cast on the iron disks or heads, which are accurately fitted and bolted to the ends of the cylinder. To the shaft is secured a series of armatures made in segments. The armatures are of iron, and are also wrapped with wire. When revolved, the outwardly projecting ends of these armatures will pass closely to, but without touching, the inwardly projecting ends of the magnets. The commutator is made in two pieces, and requires but two springs to carry the currents from all the armatures. These springs or brushes are clamped in sockets projecting from the front disk of the cylinder. An automatic switch or governor is attached to this machine for the purpose of preventing it from reversing by the polarization of the electrodes. The Weston machine is exceedingly compact in form, and has been extensively introduced for plating.

We have had the opportunity of noting the performance of one of these machines in the large electrotyping establishment of Messrs. Hanson Bros., Philadelphia, where it was introduced several years ago to take the place of thirty large cells of Smee battery, with which about 663 square feet of moulds could be covered with copper, of the usual thickness for electrotype shells, in ten hours. The Weston dynamo, consuming three horsepower, covers 100 square feet of moulds with copper of the required thickness in the same time, and without the

care and attention that the voltaic battery constantly demanded. Estimating the thickness of the copper shells atths of an inch, which is the average thickness, the surface above named will represent a weight of 27.72 pounds of copper; and, taking the cost of steam power at the usually accepted figure of four cents per hour per horse-power, the machine in question actually deposits 27.72 pounds of copper at an average cost of one dollar and twenty cents. This result is practically equivalent to the deposition of one pound of copper per hour per horse-power. The attention required by the machine is so trifling that the machinist in charge of the steam engine is able to look after it, without neglecting his other duties, hence no special charge for this item is made.

Fig. 73 shows the Arnoux-Hochhausen plating machine with a Siemens armature, as recently improved. To avoid undue heating of the armature coils, which is a serious source of trouble and of loss of power with many forms of the dynamo, these makers surround the armature with a water jacket in which a current of water is kept flowing. Another feature of the machine is an automatic switch for regulating the current according to the surface of the work in the bath, and for the purpose also of preventing the machine from "reversing" by the polarization of the electrodes.

The resistance board or "switch" with galvanometer shown in connection with the above is, in this or an analogous form, an indispensable adjunct to the dynamoelectric machine, for controlling the amount of current generated. It consists of a rectangular board of convenient size, to which is attached a series of brass or Germansilver wires of varying thicknesses, from very fine to thick. These wires are each attached at one end to a flat plate of German silver below, and are stretched over a pin