516 



ELECTRICITY. 



ployed instead of iin electrical machine. Mr Singer 

 Klttuichy. informs u, tluit about '-'0 sparks from the uppr con- 

 "* tluctor, when raited, is sufficient to charge a Lcydcn 

 phial of a moderate size. 



Sometimes the resinou* plate of the electrophorus is 

 placed upon a plate of glass. 



Dr Ingcnhousz informs us, that the electricity pro- 

 duced l>y the fectrophorus may be varied liy transfer- 

 ring alternately the upper conductor from one resinous 

 cake to another, and touching it after it is placed on the 

 cakes. By this method, both cakes continually acquire 

 more and more electricity, so that the upper eumluctor 

 returns from either plate quite overcharged, and Ley- 

 den phials may be charged by it so very strongly that 

 they may be broken by the charge. The' condnetor 

 returns from one cake in a positive and from the other 

 in a negative state. This method of increasing the electri- 

 cities, was communicated to Dr Ingenhousz by Dr 

 Klincock of the I nivcrsity of Prague. 



See Volta in Rozier's Journal, vol. viii. 2Sth Sept. 

 1776; Henley, Phil. Trout. 1776, p. 51:!, 1,1. 177S. p. 

 1019; A.chard,Mem.Aca:i. 11,-rl. 177'>,p. I-"-' ; Cavallo, 

 Phil. Trans. 1777, p. 116', 388; Ingenious*. Phil. 

 Trans. 1778, p. I(ti7 ; Robert in Rozier's Journal, vol. 

 xxxvii. p. 18:5; Hobison's System of Mechanical Plnlo- 

 tophi/, vol. iv. now in the press; and Singer's Elements 

 of Electricity, p. 121 120'. 



CHAP. III. 



On Electrical Kites, Thunder Rods, and Conductors 

 for collecting the Electricity of the Atmosphere. 



WE have already seen in our History of Electricity, 

 and in the Section upon the Electricity of the Atmo- 

 sphere, that lightning is identical with electricity, and 

 that all the experiments made with a common electrify- 

 ing machine may also be made with the electricity which 

 is brought down from the atmosphere. The instrument* 

 which have been used for this purpose are electrical kite?, 

 for bringing it down from the higher regions of the at- 

 mosphere ; thunder rods for collecting it from the lower 

 strata; arid conductors for carrying it off to the ground. 

 The terms thunder rods and conductors are generally 

 employed as synonymous; but in the present Chapter we 

 have given the name of thunder rods to those instru- 

 ments which are employed for collecting electricity for 

 the purposes of experiment, 



SECT. I. On Electrical Kite*. 



Construe- THE electrical kite constructed by Dr Franklin eon- 

 uon of ^ sisted of two light stripes of cedar wood put together 

 F ""^"*' in the form of a cross, the arms being so long as to ex- 

 tend to the corners of a large thin silk handkerchief 

 when properly stretched out ; the corners of the hand- 

 kerchief were then tied to the extremities of the cross, 

 so as to form the body of the kite. It was then sup- 

 plied with a tail, a loop, and a string, and was better 

 able to withstand the resistance of a thunder storm than 

 if it had been made of paper To the top of the up- 

 right stick of the cross, Dr Franklin fixed a sharp point- 

 ed wire, which rose to more than a foot above the wood. 

 To the lower end of the Mrin:.' made of twine, he tied 

 a silk ribbon, and fastened a key at the junction of the 

 silk and the twine. The kite "is then raised during a 

 thunder storm, and the person who holds the string 

 stands within a door, or window, or under cover, so 



that the nilk ribbon may not be wrt, nd w that the Pitfcl 



string does not touch the frame of the dour (.r window. Electricity.^ 

 When the kite and the string are wetted I y the rain, tile """"Y" 

 electricity will stream out from the ke\ w hen the 

 knuckle is presented to it, and a l.c\dcn jar or u battery 

 may be readily charged. 



. 



In our account of the experiments made by M. Ro- 

 mas, we have already given a general description of tl.. 

 electrical kite which lie employed. The twine stru 

 employed l>y Dr Franklin, wa> obviously unfit to con- 

 duct the electricity of the atmosphere until it had i 

 wetted 1>\ the rain In order to obviate this and other 

 defects. Si. Romas made tlie string of twine twisted 

 round with a eop|>er wire. Having formed a prettr 

 stout thread of good hemp, lie doubled it, and twistid 

 the two threads and the metallic wire at the same time, 

 so as to form only one string. In this manner, ths 

 string acquired a degree of strength, which rendered it 

 capable of resisting the rough usage to which it must 

 irily be subjected. In this state, he took another 

 hempen cord, and twined it round the string, but at in- 

 tervals of two feet he sewed it to the other thread 

 that if it should be broken by any accident, the conti- 

 nuity of the cord would not l>e broken for any consi- 

 derable extent. Having received a severe shock from 

 the lightning when he was raising the kite, M. Romas 

 contrived to elevate it without touching the cord. This 

 he effected by means of a small chariot, with which 

 he could let out the string as rapidly or slowly as he 

 chose. 



Mr Cavallo, in his experiments on atmospherical elec- rv.illnS 

 tricity, generally used school-boys' kites, about 4 feet t1t ' ctric ** 

 high, and 2 feet wide, the strings being formed, like 

 that of Romas, of threads of common twine and copper 

 wire, such as is used for trimming. In order to pro- 

 tect himself from danger, he usually hung a chain 

 from the string, the end of which fell to the ground ; 

 and at other times he stood upon an insulating stool. 

 When the kite was raised, he commonly brought the 

 string through a window, and fastened it to a strong 

 silk lace, the end of which was generally tied to a heavy 

 chain in the room. By means of a small prime conduc- 

 tor standing upon a table, and connected with the string 

 by a wire, he observed the character of tlic electricity 

 which was brought down. 



Mr Cuthbertson, in his Practical Electricity, has given Cuthb*rti 

 a drawing of the apparatus which he employed in rais- son's clec- 

 ing electrical kites, and which does not differ essential- ^cal kit*. 

 ly from those which we have described. The string of 

 the kite is coiled round a horizontal axis, supported 

 upon three mahogany legs; and round a drum, on a 

 thicker part of the same axis, is coiled a silk cord, the 

 other end of which is again coiled round another axis 

 or reel 20 or 25 feet distant, which is moved by a winch ; 

 by turning this winch, the string of the kite can be 

 lengthened or shortened at pleasure without any dan- 

 ger. 



Mr Cuthbertson sometimes used three kites all con- 

 nected with one another ; and on one occasion, when 

 he could obtain no electricity with a kite having a string 

 500 feet long, he succeeded by adding other two, each 

 of which had strings 500 feet in length. For farther 

 information on the construction of kites, see Franklin's 

 Letters, p. 90, or Phi*. Tran . 1751, p. 565 ; Romas, 

 Mem. di ,SVirM.v Elrnngers, torn iv. page 514, &C. ; Her- 

 tholon, De I' Electricity des Mettorcs, torn. i. p. 51, 53; 

 Cavallo, /V/. Trans. 177, p 4<>7 ; Id. 1777, p. 48; 

 and Cuthbcrtson's Practical Electricity, p. 2372**. 

 Loud. 1807. 



