ELECTRICITY. 



413 



Hiktory. 



Eiperi- 

 menttof 

 Sir Isaac 

 Newton. 



Born 1642, 

 Djed 1727. 



Discoveries 

 of Mr 

 H-iwksbcc. 



with a push or puff like wind. This light and crack- 

 ling seems in some degree to represent thunder and light- 

 ning." 



Sir Isaac Newton is entitled to be mentioned in a 

 history of electricity, more from the splendour of his 

 name than from the contributions which he made to the 

 progress of the science. He found, that when the up- 

 per surface of a plate of glass was excited by friction, 

 light bodies were attracted to the opposite side ; and 

 in the History of the Royal Society, he has recorded 

 the few experiments which he made upon this subject. 

 In the 8th and 27th queries at the end of his Optics, he 

 has introduced the subject of electricity in such a man- 

 ner, as to convey some notion of the theoretical views 

 which he had been led to form. " A globe of glass," 

 says he, " about 8 or 10 inches in diameter, being put 

 into a frame, where it may be swiftly turned round its 

 axis, will, in turning, shine where it rubs against the 

 palm of one's hand applied to it. And if at the same 

 time a piece of white paper, or a white cloth, or the end 

 of one's ringer, be held at the distance of about a quar- 

 ter of an inch, or half an inch from that part of the 

 glass where it is most in motion, the electric vapour, 

 which is excited by the friction of the glass against the 

 hand, will, by dashing against the white paper, cloth, or 

 ringer, be put into such an agitation as to emit light, 

 and make the white paper, cloth, or finger, appear livid 

 like a glow worm ; and in rushing out of the glass, will 

 sometimes push against the finger so as to be felt. And 

 the same things have been found, by rubbing along a 

 large cylinder, or glass, or amber, with a paper held in 

 one's hand, and continuing the friction till the glass 

 grew warm." " Let him also tell me," says he in the 

 27th query, " how an electric body can by friction emit 

 an exhalation so rare and subtile, and yet so potent, as 

 by its emission to cause no sensible diminution of the 

 weight of the electric body, and to be expanded through 

 a sphere whose diameter is above two feet, and yet to 

 be able to agitate and carry up leaf copper, or leaf gold, 

 at the distance of above a foot from the electric body ':" 



The subject of electricity, as well as other branches 

 of natural philosophy, were about this time cultivated 

 with assiduity by our countryman Mr Hawksbee. So 

 early as the year 1705, he ascertained that light was 

 produced by shaking mercury in gla--s vessels, and that 

 the light became more brilliant when the air was re- 

 duced to half its density. He observed a similar light, 

 when amber or glass was rub!>ed against flannel, glass 

 against oyster shells, woollen against woollen, or glass 

 against glass ; but he was not at thi.s time aware, that 

 the phenomenon was electrical. In the course of his 

 experiments, he found that sugar and calomel when 

 broken produced light ; that mercury in a varnished 

 vessel, shaken under an exhausted receiver, also exliibi- 

 (! light ; and that an exhausted glass globe rubbed by 

 the hand became luminous, the light being diminished 

 by the admission of the air, but appearing on the point 

 of his finger, or other bodies, when brought near the 

 globe. The experiments of Mr Hawksbee on electrical 

 attraction and repulsion, were made with a pretty large 

 glass cylinder, turned by a winch, ;md rubbed by his 

 hand. Seven threads tied round a wire hoop, were 

 attracted towards the axis of the cylinder, and this 

 effect continued about four minutes after excitation. 

 He afterwards found that the threads, when attracted 

 by the cylinder, were repelled by his finger at a cer- 

 tain distance, and attracted by it when the distance was 

 less. He observed also, that threads tied to the axis of 

 the cylinder, diverged in all directions when the cylin- 

 der was excited, and were repelled by the finger when 



held on the opposite side of the glass. When the globe History. ^ 

 was at rest and unexcited, the threads were moved by ^"7""^"^ 

 the approach of an excited electric, excepting during of Hawk* 

 moist weather. tee. 



When an exhausted globe was held within the efflu- 

 vije of an excited one, he observed a light in the for- 

 mer, which gradually vanished when it was brought to 

 rest, but which re-appeared when the exhausted globe 

 was put in motion. Upon presenting an exhausted 

 tube to the effluvia of an excited globe, he perceived 

 what he calls an interrupted flashing light. The ex- 

 periments of Mr Hawksbee on the great subtlety of elec- 

 tric light, are extremely interesting. He lined more 

 than half of the inside of a glass globe with sealing- 

 wax, which in some places Was one-eighth of an inch 

 thick, and where it was thinnest it would just permit a 

 candle to be seen through it in the dark. When this 

 globe was exhausted and excited while in motion bv 

 his hand, Mr Hawksbee saw the shape and figure of all 

 the parts of his hand as distinctly upon the concave su- 

 perficies of the wax within, as if no wax whatever had 

 intervened between his eye and his hand. The same 

 result was obtained, when pitch was substituted for 

 sealing-wax. Melted flowers of sulphur did not pro- 

 duce the same effect ; but common sulphur gave the 

 same result as sealing-wax. When the quantity of 

 common sulphur was large, the light within the globe 

 was sometimes as great, but the shape of his fingers was 

 not so distinctly seen as before. If a small portion of 

 air was admitted into the globe when partially linerj 

 with sealing-wax, the light completely disappeared on 

 the part covered with the wax, but not on that which 

 was uncovered. When the globe was full of air, the at- 

 tractive power of the coated part exceeded that of the 

 uncoated part. Upon again exhausting the globe, the 

 co.ited parts attracted bodies placed near the outside of 

 the glass, but refused to exercise this force when the 

 wax was removed. 



Mr Hawksbee's attention was next directed to the 

 electricity produced by globes of sealing-wax, rosin, 

 and sulphur, having a globe of wood in their centre. 

 The globular wax gave, in general, the same kind of 

 electricity as glass, only differing from it in degree ; but 

 he could not make any of the electrical light adhere to 

 his fingers, when it was placed near the excited wax. It 

 was with great difficulty that he could excite the globe 

 of sulphur, whereas a more powerful effect was produ- 

 ced with the globe of rosin, (which had a little brick dust 

 mixed with it.) than with the sealing-wax. The sulphur 

 exhibited very little light in the dark, and the rosin 

 none. Mr Hawksbee endeavoured in vain to obtain 

 electricity from brass ; and from his attempting to ex- 

 plain this, by supposing that a small degree of attrition 

 is not capable of " putting the parts into such a mo- 

 tion as to produce an electrical quality, owing to the 

 firmness with which they adhere," it is evident, that he 

 was unacquainted with the distinction between elec- 

 tric* and non- electrics. 



After a considerable interval, during which electri- Discoveries 

 city received no accessions, the subject was taken up of Mr Ste- 

 by Mr Stephen Gray^, a pensioner at the Charter House, phcn Gray, 

 who enriched the science with the most important dis- 

 coveries. Prior to the year 1728, Mr Gray had repeat- 

 edly observed, that a down feather, tied to the end of a 

 small stick, would cling to the stick after it was with- 

 drawn from an excited tube, as if electricity had been 

 communicated to the stick or to the feather. Hence he 

 was led to the experiment of exciting the feather by 

 drawing it between his fingers, and trying this, with a 

 variety of other bodies, he discovered that feathers. 



