Electricity.

Date:
[1829]
Catalogue details

Licence: Public Domain Mark

Credit: Electricity. Source: Wellcome Collection.

    145/150 page 155
    638. In the ease of steel, copper, and steel wires (so linked together), the steel wire on each side was ignited, while the copper wire remained unaltered. 639. In the chain of platinum, steel, and pla¬ tinum wires, the platinum wires were exclusively ignited, and the steel unignited'. 640. In that of steel, platinum, and steel, the intermediate link of platinum was ignited, and the steel wire on each end remained without ignition. 641. In a chain of gold, steel, and gold, the gold wires on each end were ignited and fused, and the intermediate steel was not ignited. 642. In one formed of steel, gold, and steel wires, the central one of gold was exclusively ignited. 643. Mr. Murray next tried spiral coils of platinum and steel, of various diameters, and found that they were ignited, though curvilinear, in the same manner as if the wires were not curved. 644. The preceding experiments seem to prove, that the caloric developed in galvanic action, has no relation with the medium in which the ignition takes place; and that it is evolved in some inverse ratio of the conducting properties of the uniting wire. 645. The phenomena of ignition in links of various metals united into a chain, seem con¬ nected with the passage of a material agent through them, displaying its powers in greater or less ignition, according as the passage is in¬ terrupted, or its fire more or less retarded, and, of course, as the amount of the resistance. The agent or agents, therefore, developed in transitu from pole to pole, will swell into igni¬ tion, if the conducting power of the medium traversed is low, or even burst its metalline con¬ fine, and expend its impetus in all the brilliancy of an intense combustion. The gold, platinum, and copper wires, were T^5th of an inch in dia¬ meter; and the steel the finest harpsichord wire. Description and Use of a very Sensible Electrometer, for indicating the Kind of Electricity which is applied to it. 646. Some years back, M. Behrens published the Description of an Electrometer, which in¬ dicates the kind of electricity that is presented to it; but it appears to have been forgotten, with the dry electrical columns, which formed an es¬ sential part of the apparatus. The electrical perpetual motion of Zamboni is similar to this electrometer, and M. Butzengeiger was employed to execute one of them, which we may proceed to describe. 647. A cylindrical vessel of glass about two inches and a half in diameter, and three and a half high, has fitted to it a brass cap, from which two small dry electrical columns descend into the vessel, and are attached to the cap by screws, so that the one has its positive and the other its negative pole, making a slight projection above the cap. Each column is composed of 400 discs of gold and silver paper, glued together, and three lines in diameter, so as to fill two tubes of varnished glass. Each of these , tubes is terminated below by a ring of brass, projecting a little, and rounded, which is in electrical com¬ munication with the discs. When the brass cap is in its place, the columns descend vertically, and the lower ring is one-fourth of an inch dis¬ tant from the bottom of the glass. The axes of the columns are one inch and seven lines dis¬ tant, but may be brought nearer one another. From the centre of the cap rises a tube of glass, varnished within and without, and within the tube is a brass wire kept in the axis by a cork, but touching the tube no where else. At the lower end of the brass wire is suspended a piece of gold leaf, two inches and a half long and three lines wide, exactly in the middle of the interval between the two columns, and parallel to their axis, if they are accurately vertical. At the upper end of the brass wire is a small brass ball, upon which may be screwed one of the discs of a condenser, as in the electrometer of Volta. By this arrangement, the electrical columns which Behrens had placed without the glass, which defends the gold leaf from the agitations of the air, are placed within the glass, so that their position is not only better preserved, but they are defended so completely from mois¬ ture, dust, &c., that, they retain the same elec¬ trical intensity. 648. This electrometer is used in the following manner:—The cap of metal is put in commu¬ nication with the ground by means of a metallic wire, and by touching the brass ball, any acci¬ dental electricity is discharged, which may be¬ long to this part of the apparatus. If the skin is dry, the touch of the finger is not suffi¬ cient. As the gold leaf is suspended between the columns, at the level of the rings of metal which terminate them, the one positively and the other negatively, the gold leaf is attracted equally on both sides, and remains quietly in the middle in its ordinary state; but if, by means of the metallic wire, we communicate to it the weakest degree of electricity, the lower extremity of the gold leaf is attracted hv the ring which possesses an electricity opposite to that which is communicated. Having come in con¬ tact with this ring, it is successively repelled and attracted by the opposite ring. This oscillatory motion continues till the gold leaf attaches itself to one of the columns, from which it may be easily detached by touching the brass wire, so as to dis¬ sipate its electricity, and by shaking the instru¬ ment. In order to determine the nature of the electricity, the upper poles of the two columns which project above the brass cap have the signs -}- and — upon them, and the electricity re¬ quired is that which is indicated by the sign of the column towards which the gold leaf first moves, or which it first touches, when the elec¬ tricity is stronger. 649. By this electrometer, strong and w^ak degrees of electricity may be equally well ex¬ amined. In the first case, the electrified body is made to approach slowly and at a distance the ball of the electrometer, till the gold leaf is put in motion towards one of the columns. If, for example, we bring an excited stick of sealing-wax to the distance of about three feet from the ball, we shall observe a motion of the gold leaf towards the column marked —. It we bring it to a less distance, it will strike the column, from which it may be easily detached,
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