Ground connections may be made with a one inch galvanized iron pipe driven about 8 feet or until it reaches permanently moist earth, and extending at least 7 feet above ground. The ground wire should be securely soldered to a brass plug firmly screwed into the pipe, and both strongly stapled to the pole so there will be little danger of the connection being broken.

A good ground is important, as the efficiency of the protection would be impaired if the ground connection were poor. Wherever the earth is dry and a good ground cannot surely be obtained, an excavation 4 or 5 feet deep should be made, and after placing the copper ground plate or iron pipe in the hole, it should be filled with crushed coke or charcoal about pea size. This improves the electrical connection between pipe or plate and earth.

Ques. Does lightning often strike telephone or electric light lines?

Ans. No, the lines become charged to a high pressure by induction from lightning flashes or from the passing of clouds that are highly charged.

CHAPTER XLIV
STORAGE BATTERIES

Introduction.—The practical development of the storage battery is comparatively recent, although a knowledge of the phenomena upon which its actions are based, dates back to 1801. In 1800, the year made memorable by Volta's discovery of the galvanic battery, Nicholson and Carlisle found that a current from Volta's cell could decompose water.

In 1801, Gautherot discovered that if two plates of platinum or silver, immersed in a suitable electrolyte, be connected to the terminals of an active primary cell and current be allowed to flow, a small current could be obtained on an outside circuit connecting these two electrodes as soon as the primary battery had been disconnected.

Erman found that the positive pole of such a cell, was the pole which had been connected to the positive pole of the battery.

In 1803, Ritter observed, with gold wire, the same phenomenon as Gautherot, and constructed the first secondary battery, by superposing plates of gold, separated by cloth discs, moistened with ammonia.

Volta, Davy, Marianini, and others added somewhat to the knowledge on the subject, and in 1837, Schoenbein found that peroxide of lead could be used in secondary batteries.

Sir William Grove next came forward with the discovery that metal plates, with a layer of oxide on them, acted better than the plain metallic plates, and Wheatstone and Siemens found still later that peroxide of lead was the best for such purposes.

In 1842, Grove constructed a gas battery, in which the electromotive force came from the oxygen and hydrogen evolved in the electrolysis of water acidulated with sulphuric acid. By means of fifty such cells, he obtained an arc light.

Michael Faraday, when electrolyzing a solution of lead acetate, found that peroxide was produced at the positive, and metallic lead at the negative pole, and in his "Experimental Researches," he comments on the high conductivity of lead peroxide, and its power of readily giving up its oxygen. Although he made no apparent use of this discovery, it may be considered as the next important step in the development of the storage battery.

According to Niblett, Wheatstone, de la Rue, and Niaudet were well aware that peroxide of lead was a powerful depolarizer, but nobody appears to have made use of this fact until 1860, when M. Gaston Plante constructed his well known cell with coiled plates. Plante's researches extended up to 1879, and practically determined the state of the art.

Fig. 1,046.—One plate or "grid" of a type of storage cell constructed by inserting buttons or ribbons of the proper chemical substances in perforations. Some such cells use crimped ribbons of metallic lead for inserting in the perforations, others pure red lead or other suitable material.