shape represents the latest form of the lamp first described, and patented by him in 1878, which, like the Edison lamp of that date, was intended for metallic incandescence. The filament employed in the improved Lane-Fox lamp is made from grass fibre, preferably that known as French whisk or bass broom, and used in making certain kinds of carpet brushes. The fibre is first cleaned by boiling in a strong solution of caustic soda or potash, and the outer skin scraped off. The soda or potash is then boiled out of it, and a number of fibres are stretched round a mold or shape of plumbago, and are then baked in a plumbago crucible at a white heat. After being baked in this manner, the fibres are furthur carbonized by depositing carbon upon them from a rich hydrocarbon gas, such as benzole. Instead of employing the electric current in this operation, Mr. Lane-Fox carbonizes his filaments by raising the benzole receptacle to a white heat in a furnace. His light, like the others, is produced in an exhausted glass bulb.

The Bernstein incandescent lamp was a lamp of low resistance. Its carbon was hollow and presented a large surface for incandescence, hence its property of giving light with a current of very low tension. But it was very frail, and liable at the slightest jar to break, and was not, under the most favorable conditions, of long life. The company controlling this invention after a time adopted the ordinary carbon loop and an approach to the higher resistance of ordinary incandescent lamps was made.

The Brush-Swan incandescent lamp is only an imitation of the English Swan lamp, already mentioned.

The Crookes incandescent lamp is another variety, which, however, is not known in this country, being in use principally in England. Mr. Crookes, the inventor, may be called the father of the high vacuum in the glass globes used in the incandescent systems, for without his experiments and investigations in this direction, both Edison and the other inventors of incandescent lamps would have found their road to success a far more difficult one than it has been. Crookes lamps are quite largely used in England. For his filaments he uses a homogeneous structureless cellulose, which he has made or invented. This is produced from cotton dissolved in ammonium cuperate, the material being afterwards deposited in sheets of any thickness desired. The substance

is a new and very interesting product, presenting the appearance of an almost transparent horn-like sheet. This material, after being dried, is cut into threads of uniform cross sections. These are cut to the desired length, and molded into the form of the filaments that may be desired and then carbonized at a high temperature, giving a filament thoroughly homogeneous and of uniform conducting power, not subject to warping or twisting under the action of heat because of the absolute uniformity of substance and absence of fibrous structure, which Edison, as we have shown, at first regarded as a necessary condition of structure for the carbon filament.

The Stanley and Thompson lamp is the joint invention of William Stanley, Jr., of Englewood, N. J., and Edward P. Thompson, M. E., of New York, and it is now manufactured under rights owned by the Union Switch and Signal Company, of Pittsburgh, Pa. The principal part of the invention consists in such a chemical treatment of animal substances that they may be used as the carbonizable material from which the carbon filaments are manufactured, in a dense flexible and elastic condition. It is well known that all forms of animal matter, such as catgut, skin, silk, hoofs of animals, etc., becomes disintegrated into a fine powder during the process of destructive distillation. This is due to the presence of a large quantity of water and nitrogen, which, under the influence of heat, causes a rupture of the natural structure of the material. It is found, however, that by soaking these materials in a solution of soluble carbon compound, such as sugar, starch, etc., in dilute sulphuric acid, for several weeks, the chemical nature of the substance becomes radically different. This mixture of chemicals is not washed away, but the prepared filaments are simply dried and put into the furnace after being wound upon suitable forming blocks. During the heating of the filaments the chemicals slowly continue their action, so that the structure is not only not destroyed, but, also, the pores are filled with all the carbon from the carbon compound which is put into solution in the dilute sulphuric acid. Another important part of the invention is that of being able to carbonize a large number of carbon filaments in a very small space. The prepared filament is wound helically upon a block whose cross-sectional shape is that which it is desired the carbon filament shall be.

The two ends are held temporarily by wax and then a ligature, such as ordinary string or cord is wound helically at right angles to the winding of the filament and the ends are tied. This ligature serves to hold the filament upon the block permanently and yet allows the latter to shrink. The shrinkage is allowed to take place also by severing the filament along one end of the forming block. The Stanley and Thompson lamp was among the four standard lamps exhibited at the International Electrical Exhibition at Philadelphia in 1884, and this description is a brief of a valuable paper on the "Chemistry of the Carbon Filament," by Edward P. Thompson, M. E., read at the Philadelphia meeting of the American Institute of Electrical Engineers. American Electrical Directory, (1885).

STORAGE BATTERIES,

What are known as secondary currents of electricity were observed at the very beginning of the present century, and almost immediately succeeding the invention of the electric battery by Volta. One of the earliest methods of measuring a current of electricity was by plunging conductors, connected with the terminals of a voltaic battery, into a vessel containing slightly acidulated water, and collecting the gases evolved, whose volume was an indication of the quantity of electricity given off by the battery. Gautherot, a French scientist, discovered as early as 1801, that if the terminals used in the water were of platinum or silver, after the battery had been removed these terminals possessed the property of giving off, from themselves, a feeble current of short duration, if connection were made between the two sides. In 1803, Ritter, of Jena, observed the same phenomenon with the terminals of gold wire, and constructed the first secondary battery by piling a series of golden plates one on top of the other, separated by bits of woolen cloth, wetted in salt water. Inactive itself, this battery, after having been submitted to the action of a voltaic battery whose elements were greater in number than its own, was capable of giving off, during a few seconds, a current in the opposite direction to that of the voltaic battery; this current received the name of "secondary current."

After the announcement of the discovery the phenomena were investigated and explained correctly by such scientists as Volta, Marianini and Becquerel, who demonstrated that this current came from the formation of acid and basic deposits on the metallic discs, caused by the decomposition of the primary current of the salt with which the bits of cloth were soaked. It

remained, however, for the distinguished Frenchman, Gaston Plante, to fully investigate and make clear the principles governing the phenomena. He commenced his researches in 1855 and investigated with zeal and patience until 1879, when he published the result of his work. He made secondary batteries in many forms and of many metals, and finally concluded that lead was the best material. He took of the sheet lead of commerce two sheets of equal size, each having a tail piece in one corner. Laying one sheet on a table he placed the second over it, with its tail at the opposite end to that of the first sheet, separating the two sheets by strips of hard rubber, so they would not touch. Then he rolled them up into a scroll. This was then placed in a glass vessel, the tail pieces pulled through the cover and the vessel filled with water, slightly acidulated with sulphuric acid, so as to make it a better conductor. When the current from a battery of two or three Bunsen cells was connected with these tail pieces, the water in the battery was decomposed, oxygen going to the positive anode and hydrogen to the negative cathode. As commercial lead has a slight coating of oxide of lead on its surface, this oxide on the anode was made a peroxide by the addition of oxygen, and the oxide coating on the cathode was reduced to metallic lead in fine granular form by the action of hydrogen. By charging his battery, first in one direction, and then, after discharging it, charging it again in the opposite direction, and repeating this for a considerable time, it was found the coatings on the plate grew thicker and thicker, until a point was reached beyond which no additional storage strength could be gained, when the plates were "formed." These plates were capable of holding considerable charges. M. Plante never took out a patent. M. Faure, another Frenchman, conceived the idea of painting the lead plates with a paste made of red oxide of lead, covering them with felt to keep the paste in place, and in that condition putting them in the acidulated water, just as Plante did. He can thus spread on more of a coating than would be formed on the plates by a life-time of charging and recharging. Hence his battery (which he has patented in Europe and America) is proportionately stronger than Plante's, and has been put to practical use. It is thus evident that the Faure battery is nothing more than the old Plante battery, the claim of its patentee resting solely upon the method of preparing