^li Mxcitdt'ion of EkSirkttj hy various No/i-conduBfin,. 



XI. 



^» Account of EleSlrical Machines of cot ft der able Power, in luhich Silk is ufed inflead of 



E: 



Glafs, W. N. 



(LECTRICITY has been, in moft praftical cafes, excited or coUefted by the 

 fri£lion of various fubftances againft each other. In this procefs, which has not yet been 

 explained by reference to fimpler phenomena, it is 'a known condition, that one at leaft of 

 the fubftances rubbed muft be a non-condu£tor. Refin, lack, filk, baked wood, and 

 above all glafs, are the bodies which have hitherto been ufed. The durability and 

 unchangeable nature of glafs*, and its being very little if at all affefled by the atmofpherical 

 variations, are undoubtedly the caufes why it has obtained the preference. Its brittlenefs, 

 and the great cxpence of large plates or cylinders, are certainly among thofe reafons why 

 phiiofophical operators fliould be defirous of a fubflitute of lefs coft and danger. 



Dr. Ingenhoufz, the inventor of the plate machine, made a variety of experiments for 

 this purpofe. Pafteboard thoroughly dried and heated, and then foaked and varniflied. 

 with a folution of amber in linfeed oil, formed plates which were ftrongly eleftrified 

 when rubbed with a cat's flcin or hare's fkin. He tried baked wood boiled in linfeed oil, 

 but with lefs fuccefs. A cylinder of itrong Clk velvet, formed by ftrctching that fubftance 

 upon two circular wooden diflcg, was found to afford confiderable electrical force when 

 caufed to revolve againft a cufhion covered with hare's fkinf . And laftly, the fame 

 philofcpher contrived a portable apparatus for charging a jar by means of a rarniftied filk 

 ribband, expofed to the fri£lion of a rubber attached to the external coating, while the 

 oppofite eledtricity of the filk was taken off by a metallic part communicating with the 

 infidej. 



It was at the beginning of 1784 that M. "Walckiers de St. Amand undertook to 

 conftru£l a machine, in which a piece of filk was made to revolve inceflantly, and pafg 

 between two pair of rubbers. He made one of fmall dimenfions, and afterwards a larger 

 in which the filk was twenty-five feet in length, and five feet broad. In the following 

 year a machine of the fame kind was conftruded by M. Rouland, profeflbr and lefturer 

 in natural philofophy in the univerfity of Paris f As no accounts of either of thefe have 

 been publifhed in this country H, and the advantages and efFedls defcribed by the authors 



appear 



• Mr. C. Cuypers of Dclft aflirms that glafs becomes harder, and fitter for eleftrical purpofes, by long 

 expofure to the wann air of a room ; and Mr. Birch, of EiTex-ftrect, in a very extenfive cleftrical praflice, 

 found that glafs cylinders lo'e their power by long ufc, fo as to become of no value ; but he afcribes this change 

 to the ufe of the aurum mufivum on the cufliion. 



f Bakerian Lefture, Phil. Tranf. 1779. 



+ Nouvelles Experiences, &c. fur la Phyfique, par J. Ingenhoufz, F.R.S. &c. Paris, 17E5. 



^ Defcription des Machines eleftriques a tafl'ctas, par M. Rouland, &c. Amfterdam and Paris 17S5, oflavo, 

 3 5 pages, with one plate, of wliich PI. XVllI. is a copy. — The Report of the Parifian Academyon the Machine 

 of M. Walckiers, dated 25th March 1784, was fcparately printed in 29 pages OcStavo, with a coloiired plate. 

 The Report is copied in M. Rouland's pamphlet. 



IJ Some time after the conftruftioji of thefc machines, Mr. Edward Nairne, of Cornhill, whofe rcfearches 

 in this and other praftical departments of fciencc are well known, received an order to conftruft one of the fame 

 form, but found it impollibleby any adjufbnent to prevent the filk from running totally to one or the other end 



of 



