514 



ELECTRICITY. 



tnaial drawing and description of this machine will In- found 

 in Roier' Obte notions tur la Physique, 1788, vol. xxxiii. 

 p. 367 371. 



StCT. III. On Elcdrifyi*g Machinei made of other Siib- 

 staticcs than Polished Glass. 



PtKttcal 



K-ity. 



On dfC'.n- 



ALTIIOI'OII we have now de-cril>ed the most valuable 

 and powerful electrifying.' machines, yet s, m u- of our 

 readers may be interested with an account of other elec- 

 trifying machine* made of other Substances, and smiic 

 of which can be constructed at very little expcnce, and 

 without the necessity of any accurate workmanship. 



1. Description of the SUJt Machine ofM. Jf'alckiert dc 

 St Anianil. 



S0km- This machine, of which we have given a drawing in 



Ainerf M. Plate CCXIA'III. Fig. 6. was invented by M. \\ 

 Wkldricn rrs O f Brussels. Upon a wooden frame RBHH, is sup- 

 ported two large cylinders A, A, six feet Ions, and * v 

 feet in diameter, which have a motion of rotation by means 

 CCXLVIII. of the winches C, C, C, C, about 8 or 10 inches in radi- 

 Fig. 6. us. These cylinders are made of wood, and are covered 

 with woollen serge. Around these two cylinders is 

 ced a web of varnished silk, about 5 feet wide, and '_'"> 

 feet long, halt' its length, or the distance N-twcen the two 

 exterior circumferences of the cylinders A, A, being 12^ 

 feet. The cushions E, between which the silk moves 

 during the revolution of the cylinders, are 7 feet long 

 and 2 inches in diameter, and covered by catskin or 

 hareskin, and can be brought together or separated by 

 screws, so as to increase or diminish the friction. In the 

 interval of two feet between the upper and under part 

 of the silk, and at an equal distance from the two cylin- 

 ders, is placed the conductor FG, which is suspended by 

 silk strings HH, from the frame of the machine. It is 

 about 7 inches in diameter, and extends a little beyond 

 the silk on both sides. This conductor is furnished 

 with a number of points, on the upper and under side of 

 it, for receiving the electricity from the silk. The dis- 

 tance of the cylinders may be increased or diminished 

 by means of a wedge I. The machine is moved by four 

 men, each of whom mounts upon the boxes L, L, L, L, in 

 order to reach the handles C, C, C, C. As this machine 

 obviously produces negative electricity, it can be made to 

 give positive electricity by advancing the cushions into 

 the middle between the cylinders, and supporting them 

 by silk cords like the conductor, and by making the 

 silk itself communicate with the ground. 



This machine is said to have been so powerful, that 

 no person durst take a spark from it, unless with the el- 

 bow or the shoulder. Even in seasons the most unfa- 

 vourable for the production of electricity, the sparks ex- 

 tended to fifteen inches from the conductor. 



2. Description of Roultind's Silk Machine. 



RouIancTs This machine, constructed by M. Rouland, Profes- 

 ilk m- gor of Natural Philosophy in the University of Paris, is 

 **""* rather an improvement upon that of \Valckicrs than a 



new machine. The rubbers employed by M. Rouland, 

 are tubes of tin covered with catskin ; and, instead of 

 two rows of points upon the upper and under side of 

 the conductor, which often tear the silk, he employed 

 two plates of brass, which were fixed upon the conduc- 

 tor, and stood at the distance of half an inch from the 

 ;lk. In other respects this machine does not differ 

 from that of M. Walckiers, excepting in the construc- 

 tion of the frame-work. See Rouland, Description des 

 Machines a Taffetas, 8 Amsterdam, 1785. 



- 





t'C... 



3. Iiigenhouts's Portable Ribbon Machine. 



This machine is nothing more than a varnished rib- 

 bon suspended upon a fixed pin or nail, and excited 

 with a rublx-r of catskin. A small Ley den phial is 

 hclil near the rubber, and collects negative electricity m^int. 

 from the silk. 



4-. Ingcnlionsz's Electrifying Machine of Pasteboard 



m. 



On account of the fireat cxpcnce of making a \ rry pow- 

 erful electrifying machine of plate gla.-s, Dr Ingcnhoiis/ 

 employe*! three pasteboard discs, four feet in diamctir. 

 Having soaked them in copal or amber varnish i, 

 veil in linseed oil. he covered them with a thick coat 

 of the same varnish, and dried them by the heat of a 

 del-man stove. When the varni.sh had become \er\ 

 hard, lie found that they were capable of a very power- 

 ful excitation by a rubber made of eat'- or hare skin. 

 These discs were then placed in a frame, which v 

 constructed a-; to hold t\\elxe of them. 

 t\M> -quare pillars of wood, about five feet Ing! 

 three inches broad, joined together ahou 

 a transverse piece of wood. In the middle of the two 

 pillars was a hole about an inch and a half in diameter, 

 m; 'ile to receive a wooden axis. The pasteboard 

 were then put upon this axis, and between each two 

 was placed a flat board, three inches* broad, co- 

 vered on both sides with flannel, and then with hare- 

 s-kin. The two square pillars were also covered with 

 flannel and with hareskin. Wl>en the three discs were 

 placed in the machine, Dr lugcnhousz received sparky 

 about one and two feet long from the front surface of 

 the first disc, by approaching his knuckle to it. He 

 then applied a tin conductor, about six feet long, and 

 six inches in diameter, 'divided into two branches, on 

 tiie extremitic.- of which was a thick silver lace fringe 

 instead of points. Sparks, about four or five inches 

 long, and extremely brilliant and strong, were received 

 from tliis conductor. See Phil. Trans. 1779, vol. bcix. 

 p. 659. 



5. Electrifying Machines made of Wood. 



M. P. Ammersin constructed electrifying machines Electrifying 

 made of a cylinder of wood, prepared by boiling it in machines 

 lintseed oil ; and he obtained positive or negative elec- Iuluic ot 

 tricity, according as he employed a rubber of silk or w 

 of wool. Professor Pickcl at Wurtzburg, and Mr 

 Kohlreif of St Petersburg, employed discs of well dried 

 wood. Mr Kohlreif constructed a machine, in which 

 he could substitute a plate of glass, or n plate of wood, 

 according as he wished to have positive or negative 

 electricity. The rubbers for the wooden plate were 

 covered with fine i'ur from rats and moles. 



6. Van Marvin's Macliine consisting (f Cum Lac and 

 Mercury. 



Van Marum constructed an electrifying machine that Van Mn. 

 had a disc of gum lac, the inferior part of which was ruu ' s ""' 

 immersed in a vessel containing mercury, and was ex- 

 cited while in motion by the friction of the mercury. gui 

 Van Marum found that the gum Lie was much less at- ;i!U . u.i.jcu. 

 fected than glass with the moisture of the atmosphere. 17. 



7. Lichtcnbtrg's Electrifying Mac: 



M. Lichtenberg constructed a machine which con- Licluen- 

 sinted principally of a drum or cylinder of wood cover- beiy 

 ed with block woollen cloth. Above this cylinder he trifying un- 

 placed a cushion lined with catokin, which rubbed clunc - 



