412 



ELECTRICITY. 



I U lory. 



GMKBdi'f 



hypothecs. 



DeMtnes' 



hypothesis. 



Experi- 

 nenu> of 

 Boyle- 

 A. D. 1670. 



Born 1627, 

 Died 1691. 



He also remarks, that glass, Ulc, and crystal, and all 

 other electrical bodies, lost their faculty of attraction 

 after being burned or routed. Even in this early stage 

 of discovery, Dr (iilbert could not retrain from gene- 

 ralising the few observations which he Imd nude. He 

 conceived that electrical attraction was .similar to the 

 attraction of cohesion, ami that it was occasioned by the 

 effluvia- of the electric body being excited by friction. 



Other hypotheses were about this time proposed, to 

 explain the phenomena of electric attraction. The Je- 

 suit Cabirus supposed that the streams which issue from 

 amber, when heated by rubbing, " discuss and expel 

 the neighbouring air ; which, after it has been driven 

 off a little way, make*, as it were, a small whirlwind, 

 because of the resistance it finds from the remoter air, 

 which has not been wrought on by the electrical 

 steams ; and that these shrinking back swiftly enough 

 to the amber, do, in their returns, bring along with 

 them such light bodies as they meet with in the way." 



According to the hypothesis of Sir Kenelm Digby, 

 embraced by Dr Browne, the amber " being chafed 

 or heated, is made to emit certain rays or files of unc- 

 tuous steams, which, when they come to be a little 

 cooled by the external air, are somewhat condensed, 

 and having lost their former agitation, shrink back to 

 the body whence they sallied out, and carry with them 

 those light bodies that their farther ends happen to ad- 

 here to, at the time of their retraction. As when a 

 drop of oil or syrup hangs from the end of a small stick, 

 if that be dextrously and cautiously struck, the viscous 

 substance will, by that impulse, be stretched out, and 

 presently retreating, will bring along with it the dust 

 of other light bodies that chanced to stick to the re- 

 moter parts of it." 



The learned Gassendi has adopted the same hypo- 

 thesis as the preceding, and he supposes that " these 

 electrical rays being emitted several ways, and conse- 

 quently crossing one another, get into the pores of the 

 straw, or other light body to be attracted, and, by means 

 of their decussation, take the faster hold of it, and 

 have the greater force to carry it along with them, when 

 they shrink back to the amber whence they are emit- 

 ted." 



As the preceding hypotheses were unapplicable to 

 glass, which had not the property of emitting effluvia? 

 when heated, Descartes attempted to account for elec- 

 trical attractions, by supposing certain particles shaped 

 like small pieces of ribbon, to be harboured in the 

 pores or crevices of glass, and to be emitted by fric- 

 tion, like the effluvia of amber. 



The ingenious Mr Boyle, to whom some of the other 

 physical sciences owe such lasting obligations, directed 

 much of his attention to the subject of electricity, and 

 has left us an account of his experiments, in a small 

 work, entitled Experiment* and ^oles about the Mecha- 

 nical Origin and Production of LLctricity, Lond. 1675. 

 He found that the hard transparent cake which re- 

 mained after slowly evaporating the fourth part of good 

 turpentine, was electrical, and that the same property 

 was possessed by the dry mass which remained after dis- 

 tilling a mixture of petroleum, and strong spirit of 

 nitre by glass of antimony glass of lead caput 

 mortuum of amber the cornelian and the emerald, 

 the two Ia*t of which hud been supposed incapable of 

 electrical excit: tion. Mr Boyle also made experiments 

 with the diamond, and remarks that he never found 

 any electric of the same bulk so vigorous as a rough 

 diamond, with which be moved a needle about three 



minute* after he had ccaed to cliafe it. The Miperio- 

 rity of rough to polished diamonds he ascribes to the 

 loss of " fffluvial matter," during the operation of cut- 

 ting and polishing. Me found also that the electricity 

 of all Innlio is increased by lersiun, us he calls it, or by 

 wiping them before they are excited, which he su|>i 

 tn ivimixe whatever may tend to choke the jxu-es ot' 

 the amber. In order to determine if the electrical in- 

 fluence was conveyed bv the intervention of the air, 

 lie Mitpcndcd a large piece of amber, well excited, 

 in a small glass receiver, and over a light body, and 

 iir'tiT rapidly exhausting the receiver, the suspended 

 amber was let down, till it came near the straw or 

 feather, which was always attracted by the amber. In 

 order to determine if an excited electric was acted upoa 

 by other bodies, he suspended his large piece of amber 

 by a silken thread, and having exciteil it by a pin- 

 cushion covered with a black woollen stuff, he allowed 

 the amber to hang freely at the end of the string. As 

 soon as the cushion held steadily was brought near 

 the suspended amber, it was drawn aside, and, when 

 the cushion was removed, it returned to its former po- 

 sition. " This power of approaching the cushion," 

 says Mr Boyle, " was so durable on our vigorous 

 piece of amber, that, by once chafing it, I was able to 

 make it follow the cushion no less than ten or twelve 

 times. Whether from such experiments one may ar- 

 gue that 'tis but as 'twere by accident that amber at- 

 tracts another body and not this the amber ; and whe- 

 ther these ought to make us question if electrics may, 

 with so much propriety as has been hitherto generally 

 supposed, be said to attract, are doubts that my design 

 does not here oblige me to examine." Like all his pre 

 decessors, Mr Boyle could not refrain from speculating 

 on the causes of electrical phenomena. He supports 

 the hypothesis of emitted and retracted effluvite, and re- 

 plies to the objection of Descartes, by remarking that a 

 " stinking odour" is actually emitted by glass, when 

 two pieces of it are dextrously rubbed together. 



While Mr Boyle was engaged in these experiments 

 in England, the celebrated Otto Guericke, Burgomaster 

 of Magdeburg, was successfully occupied with the same 

 subject. Having filled a glass globe with melted sul- 

 phur, and afterwards removed the glass, he mounted 

 his sphere of sulphur upon an axis, and performed 

 many electrical experiments, with a new degree of fa- 

 cility. He observed the sound and the light which ac- 

 companied the excitation of the globe; he discovered, 

 by means of a feather suspended near his globe, that a 

 body, when once attracted by an excited electric, was 

 afterwards repelled, till it had been touched by some 

 other body ; and that bodies, placed on an electric at- 

 mosphere, receive an electricity opposite to that of the 

 atmosphere. This interesting result was obtained by 

 suspending threads near the excited globe. He found 

 that these threads were often repelled by his finger, and 

 that a feather, when repelled by the globe, always 

 turned the same side towards it. 



The existence of electric light was discovered about 

 the same time, in England, by Dr Wall. Having procu- 

 red a long and tapering piece of amber, he drew it swift- 

 ly through a piece of woollen cloth, and he heard a 

 pnxligious number of little cracklings, each of which 

 was accompanied with a small flash of light ; but, by 

 holding his finger at a little distance from the am- 

 ber, he heard a loud snap, and saw it succeeded 

 by a great flash of light. " It strikes the finger," 

 says Dr Wall, " very sensibly, wheresoever applied. 



Hutorv. 



Boylo'i hy. 

 pothesu. 



Labours of 

 Otto tiue- 

 ricke. 



Experi- 

 ments of 

 Dr Watt. 



