In the last half of the century the production of electrotype plates for printing in books, and for the production of rollers for printing fabrics, and the extensive art of electro-plating with gold, silver, nickel and copper, has grown to enormous proportions, but the fundamental principles have not materially changed. The dynamo, however, has generally supplanted the voltaic battery in this art. The deposition of silver and gold on baser metals not only increases the ornamental effect, but prevents oxidation. Silver plated goods for the table and articles of vertu are to be found everywhere. Nickel is employed for cheaper ornamental effect, and copper finds a large application for electrotypes for printing and for coating iron castings as a protection against rust. In Fig. 71, which shows the interior of an electro-plating establishment, the dynamo is shown on the right connected by wires with two horizontal rods running along the wall and across the various tanks containing the plating solution. On the tanks are rods supporting the articles to be plated, which are suspended in the solution. Similar rods support the opposite electrodes of the tank. Wires connect these rods to the rods on the side of the wall, and to the opposite poles of the dynamo. [Illustration: FIG. 72.--EDISON’S ELECTRIC PEN.] _The electric pen of Edison_, brought out in 1876 (U. S. Pat. No. 196,747, Nov. 6, 1877), is one of the simple applications of electricity, which for a number of years was in quite general use for making manifold copies of manuscript. In the illustration, Fig. 72, this is shown. It comprises a stylus _b_ reciprocated in a tube _a_ by the vibratory action of an armature _k_ over the poles of an electro-magnet, supplied with a suitable current and vibrating contacts _l h_. The stylus was rapidly reciprocated, and as the operator traced the letters on the paper, the stylus produced a continuous trail of punctures which permitted the paper to be used as a stencil to make any number of copies. It has, however, been rotated out of existence by manifolding carbon paper, and the almost universal use of the typewriter. [Illustration: FIG. 73.--ELECTRIC CAUTERY.] _Electricity in Medicine._--The superstitious mind is prone to resort to mysterious agencies for the cure of diseases, and for many years men of no scientific knowledge whatever have been employing this seductive instrumentality for all the ills that flesh is heir to. That it has valuable therapeutic qualities when rightly applied no intelligent person will doubt, and it is unfortunate that for the most part it has been in the hands of charlatans who sell their wares, and rely upon a faith-cure principle for the result. Still there have been intelligent experimenters in this field, and it is one of much promise for further research.