ELECTRICITY. 



519 



Klectritity. 



' 



Morgan's 



Conductors 

 foi ships, 



Precautions 

 during 

 Ktorxu. 



Korm of 

 cjvs. 



edifice. All the metallic parts on the roof of the 

 house should be connected with the rod, and the con- 

 ductor should pass to the ground by the shortest pos- 

 gible path. Mr Morgan has very judiciously proposed 

 to attach to the sides of the foundation of each parti- 

 tion wall a stripe of lead connected with a similar stripe 

 going round the whole of the foundation of the build- 

 ing. From these horizontal stripes, a perpendicular 

 stripe should rise on each side of the house, and, being 

 connected with the water-pipes, Ike. should be continued 

 to the roof to another set of horizontal stripes, the very 

 same as those below. The top of the house should 

 then be surrounded with a stripe, continued over every 

 edge and prominence up to the top of the chimney. 

 In order to insulate conductors, the iron or copper sta- 

 ples which fasten them to the walls should be consi- 

 derably larger than the rod, and should be covered with 

 two or three folds of woollen cloth besmeared with 

 melted pitch. 



For the protection of ships, chains have been fre- 

 quently employed, and they are particularly conveni- 

 ent, on account of their great flexibility. The con- 

 ducting power, however, of the metal, is greatly dimi- 

 nished, by being t'omu-d into separate links ; and it is 

 therefore better to have the conductor made of rods. 

 These rods should be connected with stripes of metal 

 encircling the deck, continued mir the bottom or bides 

 of the keel, and connected with others embracing the 

 M'.l.'s of the ship. If the ship is copper Ixrttomed, it 

 will be sufficient to form a connection with the copper. 



The best precautions for personal security, in the time 

 of a thunder-storm, is to avoid taking shelter under 

 trees, houses, and all other elevated bodies, and to 

 keep at a distance from streams and pools of water. 

 Within the bouse, the middle of the room is the safest 

 situation, so as to In- at a distance, from the gable end 

 of the house, from the bell-wires, and from the gild- 

 ings on the wall. See Franklin's Is/lrrs, p. 121. W;it- 

 *on, Phil. Trtnix. ITIil, p. _>()!. Wilson, Id. p. <_'!( i ; 

 Id. 1773, p. 48; Id. 1778, p. tag, <M> ; Id. 176<>, p. 

 100. Id. 1770, p. 188. I....... M,HI. Acad. 1770, 



p. 53. Id. 1773, p. 5;>f>. Id. \ 770, p. 472, 588. Phil. 

 Trans. 177.% p. 42. Henley, Id. 1774, p. 133. Nairne, 

 Id. 1778, p. 823. Hlagden, Id. 1782, p. 355. Patter- 

 son, Trans. Amer. Phil Stic. vol. iii. p. 321. Regnier, 

 Mem. Instil, vol. iv. Stanhope, Phil. Trout. 1787, 

 p. 30. Bertholon, De I' Klectriciti- dcs Meteores, torn. i. 

 p. 193. Cuthbertson's Practical Electricity, p. 79 85. 

 Morgan's Lectures, vol. ii. p. 297. 



BOOK II. 



ON MACHINES FOR ACCUMULATING AND DISCHARGING 

 ELECTRICITY. 



SECT. I. On the Construction of Jars and Coaled 



let. 



IM our Section on the Accumulation of Electricity, we 

 have already given a general account of the I.evden 

 jar, and of electrical batteries, and shall therefore 'con- 

 fine ourselves, at present, to some practical remarks on 

 the construction and use of these instruments. 



The be.,t form of a jar is that of a cylinder, having 

 its mouth sufficiently large to admit the hand, for the 

 purpose of coating, cleaning, and repairing it. With 

 this view, jars completely cylindrical were for some 

 time employed, particularly by Mr Cuthbertson ; but 

 he afterwards found that it was better to have them a 



little contracted at the mouth. Dr Eobison prefers Piactieal 

 bottles of a globular form, and he frequently used the Electricity. 

 balloons employed in distillation. 



The glass of which the jars are made should have np Thickness 

 more thickness than what is necessary to prevent them of the glass. 

 from being broken by a spontaneous discharge ; for Mr 

 Cavendish has found that the quantity of electricity 

 necessary to charge different coated jars of the same ex- 

 tent, is inversely as the thickness of the jars. 



The best method of coating jars, is to line them both Method of 

 on the outside and the inside with tinfoil, which may coatingjars. 

 be made to adhere to the glass by gum water. When 

 the jars, however, will not admit of being lined with 

 tinfoil, or when tinfoil is not to be got, a coating of 

 brass filings may be laid on with gum water, or a quan- 

 tity of gold leaf or Dutch metal may be placed in the 

 jar, so as not to rise higher than the external coating. 

 When the jar has a globular form, it should be coated 

 by cutting the tinfoil into gores or joints, in the same 

 manner as terrestrial and celestial globes are covered. 

 A coated jar is shewn in Plate CCXLIII. Fig. 5. 



As jars are very often broken by the spontane- Brooke's 

 ous discharge through the glass, Mr Brooke propo- method of 

 set), as the result of experiment, that the tinfoil should coatin S- 

 be first pasted upon common writing paper. When 

 this precaution was taken, he very seldom had any of 

 liis jars broken. 



For the .purpose of preventing the charge of the jar 

 from being dissipated, it is of great advantage to cover 

 the uncoated part with melted sealing-wax or with 

 varnish, to prevent the deposition of moisture from the 

 atmosphere. 



In order that the jar may retain its cliarge for a con- Jar for rc - 

 siderable time, it is constructed, as in Plate CCXLVII. 

 Fig. 1. where it is shewn suspended at the end C of the 

 conductor. After being coated in the usual manner, 

 a glass tube ah, reaching to the bottom, is cemented into 

 the cap. The inside of this tube is covered -with tin- ' 

 foil rather more than half its length from the bottom, 

 and this lining communicates with the inner coating 

 of the jar. A wire c, blunted at the lower end, and 

 half the length of the tube, is placed loosely in a hole 

 in the brass cap, so that when the jar has the position 

 in the Figure, the wire c forms a communication be- 

 tween the brass cap and the inside coating ; but when this 

 wire is drawn up or taken out, there is no communication 

 of the internal coating either with the brass cap or with 

 the external air. The phial will consequently retain 

 its charge, and may be carried about in the pocket till 

 it is needed. 



M. Cavallo has invented a curious instrument, which Cavalfo's 

 he calls a self-charging phial. It consists of a glass self-char- 

 tube 18 inches long, and l inches in diameter. Coat gins P hia1 ' 

 the inside of it with tinfoil over half its length, place 

 a cork into the aperture of the coated end, and let a 

 knobbed wire pass through the cork to the coating. If 

 this tube is now held by the uncoated part with one 

 hand, while the outside of the coated part is rubbed by 

 the other hand, and if the rubbing nand, after every 

 three or four strokes, is made to touch the knob, it will 

 communicate to it a spark, and the inside coating will 

 thus be gradually charged. If the outside of the coat- 

 ed end is now grasped with one hand, while the other 

 touches the knob, a shock will be experienced. 



Dr Ko'i.i.son informs us, that he constructed a very Dr Rolri- 

 fine electric phial for the pocket, by forming tin plate son's pta- 

 into somewhat of a phial shape with a long neck. It We jar. 

 was next i oated with sealing-wax, about T ' a of an inch 

 thick, quite to the end of the neck. The sealing-wax 



