795 



PLATE XL. 



Fig. 552. A. A spark passiiij; between a negti'ive 

 Slid a neutral h-M ; B, 'ictween a neutral and a positive 

 ball; C, beHveen a negative and a pobitive ball. D, 

 two spark* between a negative and a positive cy- 

 linder, each of tlie same form as if it were passing 

 sini:!^ frn:ii the end of ji charged to the side of a neu- 

 tral cylinder. From Mr. Nicholson. 1'. 671. 



Fig. 553. A com|)Ound galvanic circuit, formed by 

 portionsof an acid, pieces of zinc, and wires of silver; 

 the arrows show the directions of the electric current. 

 P. 676. 



Fit'. 55*. A compound galvanic circuit, formed by 

 •n acid, charcoal and watci , the water and the acid 

 coniaiuiiicatini!; by a small siphon. P. 676. 



Fig. 555. A compoinid galvanic circuit, formed by 

 portioiis of an alkaline sulfurct, and water, and 

 {)ieces of c )pper: the liquids being connected by a 

 siphon, p. 676. 



Fig. 556. A simple galvanic circuit, formed by wires 

 of zinc aijd sjU er, or platina, the lovwer ends being im- 

 mersed in an aci:i, and tlie upper being brought into 

 contact at pH asure. P. 676. 



Fij. 557 A galvanic battery, in the form of a 

 trough, composed of plates of zinc, silvered on one 

 side, with vax;ant •ipaces f >r rhe reception of an acid : 

 the letters show the order of the elements, and the 

 arrows the dirt clion of the current, from Che positive 

 wire + to the negative wire — . P. 677. 



Fig. 558. An electrical machine, on Xairnc's con- 

 struction. A, the cylinder of glass; B, the cushion, 

 or'rubber; C, the silk flap; D, the negative conduc- 

 tor; E, the i)ositive conductor; F, a ball connected 

 with the internal coating of a glass jar, contained in 

 the conductor. The conductors are insulated by var- 

 nished rods of glass. P. OiiO. 



Fig. 559. A plate machine. A and B, the rubbers, 

 which .ire usually doubU; ; C I), double flaps of oiled 

 silk, for confining the electricity ; K, the conductor. P. 

 680. 



Fig. 560. An rlcctrophorus. A, the cake of resin; 

 B, the plate of metal ; C, the ball for taking the spark : 

 D, the ha idle of glass. P. 681. 



Fig. 561. A condenser, as arranged by Mr. Cavallo, 

 under the name of a collector : the middle plate is in- 

 sulated : the two outward platcp communicate with 

 the earth ; they stand near the first plate when the 

 electricity is imparted to it, and are afterwards re- 

 moved by means of their hinges. P. 681. 



F^ 562. Mr. Cavallo's multiplier. The electri- 



city being first communicated to the insulated piate A, 

 the moveable pLate B is brought near it, while the wire 

 C touches the pin D so as to form a communicatioo 

 with the earth; the plate B is then made to commu- 

 nicate with E, which is insulated, and stands near the 

 plate F, which enables it to receive ahnosr the whole 

 of the electricity brought at eacii alternation by B ; 

 and when the plate Fis removed from tlie neighbour- 

 hood of E, this plate becomes strongly charged. P. 

 682. 



Fig. 563. A revolving deubler, on the principle of 

 Mr. Bcnnet's instrument. The fixed and insulated 

 plate A first receives the electricity, and "hen the 

 moveable piate B stands opposite to it, it receives by 

 a wire from the stand of the instrument C the opposite 

 electricity; wlien it is brought oppisitc to D, this 

 plate is made to communicate witii the stand by the 

 wire E, and acquires a charge similar and nearly equal 

 to^that of A. M'hen B comes again to A, the wire F 

 forming a communication between A, and D, nearly 

 the wliole charge of both these plates is brought into 



A, and B receives a charge almost twice as great as at 

 first. P. 682. 



Fig. 564. Mr. Coulomb's electrical balance. The 

 needle A is made of silk, covered with sealing wax; it, 

 supports, at the end B, a ball of the pith of elder' 

 another similar ball being fixed at C; the force of at- 

 traction or repulsion is. ascertained by the torsion of 

 the wire AD, which is measured by a graduated 

 circle E. P. 683. 



Fig. 565. Mr. Henley's quadrant electrometer; it is 

 made of box wood, sui^i^orted by mttal; tlie ball is of 

 cork, the graduated arc of iviiry. P. 683. 



Fig 566. A, Mr. Beniiet's gold leaf electrometer; 



B, a piece of excited scaling wax held over it, for dis- 

 tinguishing the electricity. Instead of the pieces of 

 fiold leaf C,, we may substitute Mr. CavalloVpith balls 

 D, or the straws E, employed by Volta, r. 683. i ,: 



Fig. 5fi7. ■ Mr. Lane's discharging electrometer." 

 The djstaiice ofthe fcalls A,JJ is trtt'asUrid by'thetufn^ 

 of the screw on the scale C ; and the parts of a turn 

 are ascertainud by the graduated circle D. P. 683. 



Fig. 568. A discharger for a battery. When the 

 repulsion of the balls A, B, becomes greater th.an the 

 weight (if a wire which passes through a perforation in 

 the ball-', tliey separate, and the ball C, descending 

 to D, forms a communication, ^vbich completes the 

 circn t, so that the shock passes tbrough any luhitancc 

 1 Uc€d at £, P. 083. 



