7 Do

PLATE XL.

Fig. 552. A. A spark passing between a negativeand a neutral bail; li, between a neutral and a positiveball; O, between a negative and a positive ball. ]),two sparks between a negative and a positive cy-linder, each of the same form as if it were passingsingly from the end of a charged to the side of a neu-tral cylinder. From Mr. Nicholson. P.071.

Fig. 553 . A compound galvanic circuit, formed byportions of an acid, pieces of zinc, and wires of silver;the arrows show the directions of the electric current.P. 670.

Fig. 551. A compound galvanic circuit, formed bvan acid, charcoal and water, the water and the acidcommunicating by a small siphon. P. 070.

Fig. 555. A compound galvanic circuit, formed byportions of an alkaline stdfurct, and water, andpieces of eopper: the liquids being connected by asiphon. P. 076.

Fig. 556. A simple galvanic circuit, formed by wiresof zinc and silver, or platina, the lower ends being im-mersed in an acid, and the upper being brought intocontact at pleasure. P. 070.

Fig. 557 A galvanic battery, in the form of atrough, composed of plates of zinc, silvered on oneside, with vacant spaces for che reception of an acid:the letters show the order of the elements, and thearrows the direction of the current, from the positivewire ■+• to the negative wire —. 1’. 677.

F'ig. 550. An electrical machine, on Nairne’s con-struction. A, the cylinder of glass; K, the cushion,or rubber; C, the silk Hap; 1), the negative conduc-tor; 15, the positive conductor; F, a hall connectedwith the internal coating of a glass jar, contained inthe conductor. The conductors are insulated by var-nished rods of glass. P. 080.

Fig. 559. A plate machine. 7. and B, the rubbers,which are usually double ; (_' I), double flaps of oiledsilk, for colilining the electricity ; 15, the conductor. P.680.

F'ig. 560. An electrophorus. A, the cake of resin;B, the plate of metal; C, die hall for taking die spark ;D, the handle of glass. P. 081.

F'ig. 501. A condenser, as arranged by Mr. Cavallo,under the name of a collector: the middle plate is in-sulated : the two outward plates communicate withthe earth ; they stand near the first plate when theelectricity is imparted to it, and are afterwards re-moved by means of their hinges. P. 681.

Fig. 562. Mr. Cavallo’s multiplier. The electri-

city being first communicated to the insulated plate A,the moveable plate P is brought near it, while the wireC touches the pin D so as to form a communication■with the earth; the plate B is then made to commu-nicate with F., which is insulated, and stands near theplate F, which enables it to receive almost the wholeof the electricity brought at each alternation by P ,and when tiie plate F is removed from tbc neighbour-hood of K, this plate becomes strongly charged. P.682.

Fig. 563. A revolving doubler, on the principle ofMr. Bennet’s instrument. The fixed and insulatedplate A first receives the electricity, and when themoveable plate B stands opposite to it, it receives bya wire from the stand of the instrument C the oppositeelectricity; when it is brought opposite to 1), tinsplate is made to communicate witii the stand by thewire F., and acquires a charge similar and nearly equaltojtliat of A. When B conies again to A, the wire Fforming a communication between A, and I), nearlythe whole charge of both these plates is brought into

A, and B receives a charge almost twice as great as atfirst. P. 682.

F’ig. 564. Mr. Coulomb’s electrical balance. Theneedle A is made of silk, covered with sealing wax; itsupports, at the end B, a hall of the pith of elder*another similar bull being fixed at C; the force of at-traction or repulsion is ascertained by the torsion ofthe wire A I), which is measured by a graduatedcircle 15. P. 683.

F'ig. 565. Mr. Henley’s quadrant electrometer; it ismade of box wood, supported by metal; the ball is ofcork, the graduated arc of ivory. P. 683.

Fig. 566. A, Mr. Bennet’s gold leaf electrometer;

B, a piece of excited sealing wax held over it, for dis-tinguishing the electricity. Instead of the pieces ofgold leaf C, we may substitute Mr. Cavallo’s pith balls1), or the straws E, employed by Volta. P. 683.

F'ig. 567. Mr. Lane’s discharging electrometer.The distance of the balls A, B is measured by the turnsof the screw on the scale C; ami the parts of a turnare ascertained by the graduated circle]). P. 683.

Fig.508. A discharger for a battery. When therepulsion of the bulls A, B, becomes greater than theweight of a wire which passes through a perforation inthe halls, they separate, and the hull C, descendingto I), forms a communication, which completes thecircuit, so that the shock passes through any substancel laced at 15. P.683.