DRY PILE. A voltaic pile or battery con sisting of a number of disk- of paper covered with zinc foil on one side and gilt or black oxide of manganese on the other. Various modifica tions of the above form are also known by the same name. Following the invention of Volta (see VOLTAIC CELL OF BATTERY I. liehreli-1. I803. constructed a pile in which paper was used instead of moistened cloth, in consequence of which it was called a dry pile. The term dry pile is really a misnomer, as the pile is inactive unless the paper contains a certain amount of moisture. Behrens% construction was modified and improved by Zamhoni. by whose name the dry pile is often known. In this apparatus the pile was made of so-called silver paper and paper which had been rubbed with manganese peroxide. The couples were made of small disks of tl c paper so treated. placed together with their coated side, outward, and these were piled tip to the number of a thousand or more, each couple or facing in the same direction. The entire pile was then firmly pressed into a glass tube varnished with shellac, and finally coNered on the ends with brass caps. These have been ninth. with as many as 20,0o0 pairs of disks and capable of charging a thin Leyden jar of 350 square vent iineters surface in ten minutes to such an extent that its discharge melted 2.5 eenti meter, of platinum wire c f vs.i millimeters diame ter.
The dry pile was employed by Behrens and Bohnenberger in the construction of a very deli• cat'. gold-leaf electroseope. commonly known by
the latter's name. nu' this purpose the dry pile was in columns connected togeth er below, so that the poles were at the upper ends. 1% Cell I 'WM.' a -angles gold leaf was sus pended. As one pile is positive and the other negative, a very slight charge given to the gold leaf is sufficient to make it MO Ve toward one of the poles of the dry pile. The dry pile has also been applied to the construction of a 'perpetual motion' electric pendulum, in which ease it is divided into two column-, in the same way as in the electroscope just described. and between them a very light pendulum rod is balanced on knife-edges. In the upper end of the rod is a light metal ring which oscillates betw•(at the t NA 0 pales. The pendulum iucl apes first to one side and the ring touches one pole. at which it is charged. The pendulum is then repelled and carries it to the pole, where the charge in neutralized, and it receives a charge of the opposite polarity, which reverses its motion. This action is repeated indefinitely. Snell a pendulum has been in continuous motion in the University of Innsbruck since 18.2.3. The period of it oscillation varies slightly with tie humidity of the atmosphere. The energy expended i- ex ceedingly minute. as no pile can generate a sensible current except by a corresponding con sumption of its materials in the shape of chemical action. See VOLTAIC CELL OR R.\TTEEtY.