416 



ELECTRICITY. 



Hjorr 



Discoveries 

 Dr 



Uiedi79o' 



thi time invented at Leyden for die purpose of accu- 



i: i:itidcrnblc quantities of electricity. Heen- 



dtMv ourv 1 in vain to give a theory of its operations ; but 

 In- '>t lined a immlMT of curious results, which, though 

 of importance at the time when he wrote, could not 

 with propriety In* introduced into a short history of 

 electricity. Or Watson was now at the head of a small 

 party of I n^li>li philosopher*, who associated them- 

 selves for the purpose of making a series of experi- 

 ment-- on the distance to which the electric shock could 

 be carried, and on the velocity of its motion. On the 

 14th and 18th of July 1747, they conveyed die shock 

 across the Thames at Westminster bridge, by an iron 

 wire, the water of the river forming part of the chain 

 of communication. One of die party held a wire in one 

 kind, which communicated with the phial, and recei- 

 ved the shock by dipping an iron rod in the river. On 

 the '2+th of July, at two different places, they forced 

 the electric shock to make a circuit of two miles at die 

 New River at Stoke Newington. At one of these places, 

 the distance by land was 800 feet, and by water 2000 ; 

 in die other, the distance by land was 2800, and 8000 

 by water. In odier experiments, they found dial mea- 

 dow-ground, covered widi grass, conducted die elec- 

 tricity well ; and dial dry, gravelly ground, was as 

 good a conductor as water. On the 14th of August 

 1747, in die driest weather, die association assembled 

 on Shooter's Hill, for the purpose of performing a very 

 magnificent experiment. The wire which communicated 

 with die iron rod that made the discharge, was support- 

 ed by rods of baked wood, and was 6732 feet long. The 

 wire communicating with die phial was supported in a 

 similar manner, and was 3868 feet in length ; the dis- 

 tance of the observers being about two miles. Al- 

 though die circuit was four miles, two of water and 

 two of dry ground, yet no time appeared to elapse du- 

 ring die passage of the shock ; so that there was every 

 reason to consider it as instantaneous. In another ex- 

 periment of the same kind, where the whole length of 

 the wire was 12,276, die same result was obtained. 

 Alter die completion of these experiments, Dr Wat- 

 son commenced his individual labours. He discovered 

 dial glass tubes and globes did not contain die electri- 

 cal power in diemselves, but were merely movers, or, 

 as he calls it, determiners of that power ; and, before 

 any notice of Dr Franklin's celebrated discovery had 

 reached England, Dr Watson had communicated to the 

 Royal Society of London a dieory of positive and ne- 

 gative electricity. 



While electricity was making such progress in Eng- 

 land, Dr Franklin was busily occupied with the same 

 8U ^ ) J ect i* 1 America. The extent and brilliancy of his 

 discoveries gave a form and dignity to the science of 

 electricity which it had never before possessed, and 

 raisI dieir audior to a high rank among die dibtin- 

 guished philosophers of die eighteenth century. His 

 earliest discoveries were communicated to his friend .Mr 

 C'ollinson of the Koyal .Society, on the 28di July 1747, 

 and the letters which contained them were speedily 

 translated into die different lang uatfcs of Europe. These 

 discoveries related to almost every branch of electricity; 

 but the most important may be reduced to diree. 1st, 

 I li^ discovery of plus and minus electricity. 2d, His 

 explanation of die Leyden phial. 3d, His discovery of 

 die identity of lightning and electricity. 



1. Dr Franklin had observed, like Dr Watson, that 

 electricity was not created by die friction of the glass, 

 but was merely collected by dial operation from neigh- 

 bouring non-electrics. He bad likewise noticed, dial 



no person could electrify himself, even when standing Hiwaiy. 

 upon wax or glass, as the tube which he rubbed could S "~"V" 1 ^ 

 communicate to him no more electric matter th:m it 

 had received from him during excitation; and he hud 

 seen, that when two persons stood 11)1011 wax, they l>oih 

 seemed to be electrified when one of them rubbed the 

 tube and the other took the fire from it ; and dial die 

 spark betwivn them was stronger when they touched 

 one another after that operation, tlian when any other 

 person touched one of them. Hence Franklin was led 

 to conclude, that the electric matter was conveyed from 

 de person who excited die tube to the ]>erson who 

 touched it; and he therefore supposed that he who 

 touched the tube received an additional quantity of 

 electricity to what he had naturally, or was electrified 

 pint or positively, while die in-rson that excited the 

 tnhc WHS deprived of a part ot his natural quantity of 

 the electric fluid, or was electrified minus or negalioely. 

 According to this system, therefore, every body has a 

 natural quantity of electricity; and this body may be 

 excited eidier by increasing or diminishing that natural 

 quantity. 



2. This simple dieory found a ready and a beauti- |., V1 ], i( 

 ful application in the explanation of die Leyden phial, 

 This apparatus, which was discovered by Muschen- 

 broek, is nothing more than a glass jar coated both on 

 the outside and inside to widiin a certain distance of 

 die top with a conducting substance, such as tin-foil. 

 If the internal coating is connected by a wire with an 

 excited tube, or with the electrified conductor of an 

 electrical machine, while the external coating is con. 

 nected with the ground, or widi any conducting sub- 

 stance, a great quantity of electric matter may be accu- 

 mulated in die jar. If a communication is now made 

 by means of a conductor between die internal and ex- 

 ternal coating, a loud snap is heard, and a brilliant 

 spark emitted ; and if the conductor is a living being, 

 he will receive a severe shock in his arm and heart, 

 proportional to the coated surface of the jar, or rather 

 to die quantity of electricity which lias been collected. 

 \Vhen the phial is thus ditchareed,the accumulated elec- 

 tricity has escaped, and the phial is in the same state in 

 which it was before die commencement of die experi- 

 ment. When the electric shock was first discovered, 

 the philosophers themselves were thrown into such a 

 tumult of wonder and surprise, that they published the 

 most ridiculous and exaggerated accounts of the effects 

 which it produced. Muschenbroek received such a con- 

 cussion in his arms, shoulder, and heart, that he lost his 

 breadi, and required two days to recover from the ef- 

 fects of the blow and the terror, and declared that die 

 kingdom of France would not induce him to take another 

 shock M. Allamand lost die use of his breath for some 

 moments, and afterwards experienced along his right 

 arm such an acute pain, dial he apprehended serious 

 consequences from it. Mr Winkler tells us, that his 

 body was thrown into such convulsions, and his blood 

 into such an agitation, that he employed cooling medi- 

 cines to keep off fever. At anodier time, he bled co- 

 piously at die nose; and the same effect was produced 

 upon his wife, who was almost deprived of die power 

 of walking. These remarkable effects of die electric 

 fluid excited the attention of all classes of people. The 

 learned and the vulgar were equally desirous to expe- 

 rience the singular sensation; and crowds of half-taught 

 electricians wandered through every part of Europe to 

 gratify die universal curiosity. It was only the curiosi- 

 tv of 'the unlearned, however, that was satisfied. The 

 electrical philosophers endeavoured in vain to account 





