DRY PILE, a very interesting form of gal yank battery, invented by De Luc, so named from the fact of its requiring merely a slight moisture among its leaves. Various kinds of dry piles are constructed. A very excellent one, Zamboni's dry pile, is made in the follow ing way: Some sheets of ((silver° paper, cov ered on one side with zinc foil, are moistened on the back with honey or glycerine and water, and then rubbed over with very finely-powdered black oxide of manganese. These are laid one on the top of the other, the silvered side of one being in contact with the oxide of manganese of the next. They are then cut with a punch into discs of about an inch in diameter and they are put into a glass tube, care being taken that the order just mentioned is preserved. The tube is varnished with shellac inside and out and is fitted at each end with a brass cap through which passed a brass piston which is set down firmly against the paper discs in the tube and furnished with an outer knob. From 1,000 to 2,000 discs may be used. The knob at the oxide-of-manganese end will be found posi tively electrified, the other negatively. A pile containing 2,000 discs will charge a Leyden jar. A pile of 40,000 discs was strong enough to emit a succession of sparks three-fiftieths of an inch in length, to charge a Leyden jar of 50 square inches capacity, and thence to fuse one inch of fine platinum wire. The honey with which the paper is saturated is intended for a hygrometric substance. If the pile be care fully kept it will preserve its power for many years. A pile of this type with 20,000 discs has kept a pendulum vibrating between two bells so as to keep up a perpetual ringing for several years. If it be artificially dried it
loses it, but will frequently regain it when a sufficient amount of moisture has-been absorbed from the air. Its action is similar to that of a galvanic battery, but seems to have no chemical effect, as saline solutions subjected to its cur rent for several days remain unchanged; and the most delicate vegetable coloring matters are unaffected. An examination of the pile shows that it resembles a conductor, neutral at the centre, one extreme negative and the other posi tive. The activity of the instrument is in creased by artificial heat and is more marked in summer than in winter. The principle of the dry pile is made use of in Bohnenberger's elec troscope. Two short dry piles are set side by side an inch or so apart, with opposite poles uppermost, the whole being covered with a bell glass. Through the top of the bell glass passes a rod having a knob at its upper extrem ity and a strip of gold leaf at its lower end, hanging between the poles of the dry piles. Then any substance even feebly electric is brought close to the knob, the gold leaf in stantly announces its electrical nature, whether positive or negative, by flying to the pile which presents the opposite phase of electrification. This electroscope is regarded as more sensi tive than any other. See ELECTRIC BArrEav; ELECTRICITY ; ELECTRIC STORAGE BATTERY.