ELECTRICITY. 



505 



Descriptive 

 Electricity. 



Beixaria's 

 esperi- 



Variation 

 f the nee- 

 dle produ- 

 ced by elec- 

 tticity. 



tcmpawet 



destroyed 

 by light- 

 ning. 



Iroi wirtt 

 rendered 

 magnetic by 

 lightning- 



Ex peri- 

 menu of 

 Van Ma- 

 rum. 



riments, the needle was sometimes finely blued, like the 

 spring of a watch. 



Beccaria repeated the experiments of Franklin, and 

 found that lightning always gave polarity to the mag- 

 netic needle, and to all bodies, such as bricks, &c. that 

 have any iron in their composition ; and by observing 

 the way in which these poles lie, he was thus enabled 

 to ascertain the direction in which they were struck by 

 the lightning. Hence he has conjectured, that a regu- 

 lar and constant circulation of the whole mass of the 

 electric fluid from north to south may be the cause of 

 magnetism in general. 



Mr Benjamin Robins having had occasion to compare 

 two compasses of a different make, one of them having 

 a bare needle, and the other a chart like mariners' com- 

 passes, he accidentally wiped off with his finger some 

 dust which lay upon the glass of the former, and was 

 surprised to observe tliat the needle was thrown into 

 a disorderly motion, partly horizontal and partly dip- 

 ping. This disturbance he found to be owing to the 

 electrical excitation of the glass by the slight friction 

 which it received from his finger. By rubbing the 

 glass with his finger, or with a bit of muslin or paper, 

 either end of the needle was attracted by the part thus 

 excited, and when the needle had for some time adhe- 

 red to the glass, and afterwards dropped loose, its vi- 

 brations were not bisected, as usual, by that point 

 where the needle should have rested. At the end of 

 1 5 minutes the electricity was generally dissipated, and 

 the needle obeyed the magnetic force. By moistening 

 the surface of the glass, or putting a wet finger upon 

 it, the electricity could, at any time, be removed. 



On the 9th of January 17*9;. the ship Dover, Captain 

 Waddel, bound from N'ew York to London, was struck 

 and considerably damaged by lightning, in West Long. 

 22 1 5', and North Lat. 47 Stf. There were four com- 

 passes in 'he ship, one of them in a brass box, and three in 

 wooden boxes, and all of them were in good order be- 

 fore the storm. After the ship was struck with the 

 lightning, however, Captain Waddel observed that all 

 the needles had lost their virtue. The hanging com- 

 pass in the cabin was 'not so much injured as the re^t. 

 The needles were at first nearly reversed, but after a 

 little while they moved about in every direction, and 

 were of no use. Mr Gowin Knight examined the com- 

 pass, and observed that the outward case wag joined to- 

 gether by pieces of iron wire, 16 of which were found 

 in the sides of the box, and 10 in the bottom. Mr 

 Knight applied a small needle to each of these wires, 

 and found that the lightning had made them strong- 

 ly magnetical, particularly those that had joined the 

 sides. 



If a steel wire is placed in a perpendicular direction, 

 and a strong charge of electricity sent through it, it 

 will be magnetized, and the lower end will be the north 

 pole ; if this end is now placed uppermost, and another 

 charge passed through it, it will either destroy its mag- 

 netism altogether, or reverse its poles. The polarity or a 

 natural magnet may also be destroyed, by transmitting 

 through it a powerful shock. 



The most accurate experiments, however.on the mag- 

 netic effects of electricity, were made by M. Van Ma- 

 rum with a battery of 1 . "5 jars, containing 130 square 

 feet of coated Mirt'aie, and with watch spring needles 

 from 3 to <) inches long, and also with steel bars 9 

 ii:rln-s in length, between -J. and f an inch in breadth, 

 and nearly a line in thickness. When the needle or 

 bar was placed horizontally in the plane of the magne- 



VOL. VIII. PART II. 



tic meridian, the north end of the bar acquired north Oeseriptir* 

 polarity, and the south end south polarity, in whatever Ele ' ^ 

 way the shock was communicated. When the bars had K ~ e ^"^ 

 some degree of polarity before the shock, it was either di- rae nts of 

 minished or reversed after it. When the needle or bar Van Ma- 

 received the shock in a vertical position, its lowest end 

 became the north pole, whether it was magnetic or not 

 before the experiment. In general, the degree of mag- 

 netism which was communicated, was as strong in a ho- 

 rizontal as in a vertical position. 



When the needle or bar was laid in the magnetic 

 equator, it never acquired any magnetism in whatever 

 way it received the shock, excepting when it was given 

 through its width, and then the needle became consi- 

 derably magnetical, the end wliich lay towards the west 

 being the north pole, and the opposite end the south 

 pole. 



When the shock was so powerful as to make the 

 needle hot, no perceptible magnetism was acquired. 



When a magnetic bar, or a natural magnet, received 

 the electric shock, its power was always diminished in 

 whatever direction it was given. 



See Franklin's Lttters, p. 90. Phil. Trans. 1751, p. 

 289, or Priestley's History of Electricity, p. 178, 179. 

 Beccaria Lettere -felt Eletlricismo, p. 252, 262, or Priest- 

 ley's Hitt. p. 351. Robins, Pkil. Tnns. I7*G, vol. xliv. 

 p 242. Waddel, Phil. Trans. 1749, vol. xlvi. p. 111. 

 Knight, Phil. Trans. 17*9, vol xlvi. p. 113. 



SECT. IV. On the Effects of Electricity upon Animal 

 Bodies. 



WHEN the effects of the electric shock were first ex- 



Qn 



n e 



hibited, the most sanguine hopes were entertained that f Kt& O f 

 electricity would become a powerful agent in the cure electricity 

 of diseases. A fluid, indeed, so powerful and penetra- uponanimd 

 ting, which could be sent at pleasure through any part 

 of the human body, and in any given quantity, might 

 well be supposed capable of restoring to action and vi- 

 gour the disordered functions of the animal frame ; and 

 had this investigation been left in the hands of those 

 eminent men who were engaged in advancing the pro- 

 gress of electricity, science would never have been de- 

 graded by those gross impositions which have been 

 practised upon the credulous. 



We have already seen, in our History of Electricity, 

 that several respectable individuals were for a while 

 misled, by a number of absurd experiments said to 

 have been made at Venice and Bologna. A diligent 

 and careful inquiry, however, proved them to be false ; 

 and since that time, it has been only among a number 

 of wandering empirics, or among a few ignorant prac- 

 titioners, that the panaceal power of the electric fluid 

 has been acknowledged. 



In these general remarks, we must not be understood 

 as censuring, in the smallest degree, the cautious ap- 

 plication of electricity, in some particular cases of dis- 

 ease. It were unphilosophical to maintain, that cures 

 cannot be performed by this powerful agent ; but the 

 skilful and prudent physician will only admit its effi- 

 cacy when he has seen it established by a cautious and 

 impartial induction of well authenticated facts. 



So late as the year 1 785, there appeared a work by . 

 the Abbe Bertholon, entitled, De I'Elcclricilt Hit corps ^ Abb* 

 liiimain dans I' Hat de Sante et de Mnta/tir, in 2 vols 8vo. BerthoUn. 

 This work was crowned by the Academy of Sciences at 

 Lyons, and its respectable author, who has cultivated, 

 with assiduity, several branches of physics, was professor 

 3s 



