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LV. Description of a new Electrical Machine. 

 By W. H. Barlow, Esq., F.R.S., M. Inst. C.E. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, Derby, April 0, 1850. 



THE following short description of a new electrical ma- 

 chine may not be uninteresting to some of your readers. 



The highly electric properties of gutta percha have been 

 commented upon by Dr. Faraday; but I believe it is not 

 generally known that this material affords the means of pro- 

 ducing in a very simple manner an amount of electricity as 

 great as that of the common electrical machine. 



There is a description of gutta percha sold which is thinner 

 than common paper, about three feet wide, and in long lengths. 

 If a sheet of this substance, of about four or five feet superficial 

 area, be laid on a surface or held against the wall of a room 

 and rubbed with the hand or a silk handkerchief, and then 

 carefully removed by the extreme edges and held suspended 

 in the air, it will give off a brush-like spark of several inches 

 in length to the knob of any conducting surface presented to it. 



A similar effect may be produced by causing the sheet of 

 gutta percha to be passed once over one, or between two rub- 

 bing surfaces; but in order to obtain the best effect, certain 

 conditions appear necessary, which I will here only describe 

 as I have found them, without occupying space in your valu- 

 able Journal to enter into the cause of the effects produced. 



If ab be any surface, Fig. 1. 

 such as that of a common 

 table, and cdf be a sheet 

 of gutta percha made to 

 pass over it in the direc- 

 tion exhibited by the ar- / -/ 



row, so as to produce /~\4 ^__J^— -^~^ ,_ 9 



friction at d, then the best / R Z^=^rrrrr^-- 



effect is exhibited when \^h^ — — — — -* 



<7/Yorms an angle of about / 



10° with the surface ab: J 



ifitbebroughttoasmaller / 



le as dg, or a larger c ' 

 one as de, the amount of 



electricity excited is not so great ; but a still greater effect is 

 produced if another rubber be applied outside the gutta percha 

 at d; and if the surface of ab and the cushion R be of silk 

 or horsehair, and the pressure and speed of rubbing mode- 

 rate, the amount of electricity excited is very considerable. 

 Having found these effects to be constant, it occurred to me 



