MACHINE, ELECTRIC. 



is a compounded conductor ; and the 

 prime conductor, which is destined to re- 

 ceive and convey the electricity, in mak- 

 ing- experiments. The first electrical ap- 

 paratus consisted of a tube of glass, or a 

 stick of sealing-wax, rubbed by the hand. 

 Glass globes, whirled quickly on an axis, 

 Were substituted as an improvement, and 

 the rubber was still the hand : but subse- 

 quently a round concave cushion These 

 were succeeded by glass cylinders, which 

 are cheap, sate, and considerably power- 

 ful; but the present fashion determines 

 in favour of flat glass plates, on account 

 of the advantage of a large surface, rub- 

 bed by two or more pairs of cushions, 

 and the equality of pressure, which causes 

 the supply of electricity to be steady and 

 without undulation, as to its quantity. 

 Machines of very great power (see " Ni- 

 cholson's Journal," quarto), have been 

 mude by M. Walckiers, consisting of an 

 endless web or jack-towel of silk, passing 

 between two pair of cylindrical rubbers, 

 faced with cat skin ; the electricity being 

 communicated to a prime conductor, ly- 

 ing between the parallel pieces of the 

 silk. 



The rubber is usually a piece of wood 

 fitted to the surface intended to be sub- 

 jected to friction, and covered first with 

 two or three thicknesses of elastic cloth, 

 then with smooth leather, and lastly with 

 a flap of silk, pasted upon the edge at 

 which the glass in its rotation arrives, and 

 passing loose over the face of the cushion, 

 and thence upon the surface of the glass, 

 as far as the commencement of the prime 

 conductor. Its use has been explained 

 under the article EXCITATION. 



In fig 1, Plate Machine Electric, \ re- 

 presents the glass cylinder of a machine, 

 turned by, B, the handle. Its surface 

 rubs against, C, the cushion, which pro- 

 ce d, I), the sill flap, and the electricity 

 is conveyed to E, the prime conductor. 

 The supports of the cylinder, the cushion, 

 and (indispensably) f>f the prime con- 

 ductor, are made of glass or baked wood, 

 in order that the electricity may not be 

 conveyed to the earth, unless when the 

 operator chooses to make the communi- 

 cation by some conducting body. A prime 

 conductor is sometimes applied to the 

 rubber. 



Though we have produced as strong 

 an excitation as we have ever heard of, 

 by the amalgam of mercury and zinc, 

 with a little tallow, as mentioned under 

 the article EXCITATION, yet as many 

 electricians, particularly the experienced 

 Mr. Cuthbertson, prefers tin and zinc, 



and it is probable that this mixture may 

 afford a speedier oxydation, we shall 

 give his receipt. 



Melt two parts of tin and zAnc in a cru- 

 cible, and pour them on two parts of mer- 

 cury in a wooden box made for that pur- 

 pose, which close and agitate till the 

 metals are cold. Then pulverize the 

 granulated muss very finely, and make it 

 into a paste with hog's lard 



Fig. 2, shows the plate machine, with 

 Nicholson's cylinder improvements for 

 changing the two states at pleasure, as 

 adapted by Dr. Von Marum, of Haerlem. 



The glass plate, G G, is fastened to the 

 axis, B B, by means of a screw on the 

 axis passing through a hole in the centre 

 of the plate, and secured by a nut, C, on 

 the opposite side. The axis is supported 

 by a .single pillar, A, which for this pur- 

 pose is provided with a bearing piece, 

 K, on which are two brass collar pieces, 

 that carry the axis; and on the end of the 

 axis, opposite the glass, is a counterpoise, 

 O, of leaii, to prevent too great a friction 

 in the collar nearest the handle. The 

 arc of the conductor, E E, which carries 

 the two small receiving conductors, F F, 

 is fixed to an axis turning in the ball, H. 

 On the other side of the plate is the other 

 arc, 1, of brass wire, fixed in the bearing 

 piece, K, but so as to admit of being 

 turned round like the arc EE. P is a 

 copper tube, moving like a radius on the 

 stem of the ball, S, which, being screwed 

 into the conductor, H, serves to confine 

 the arm, P, in any position that may be 

 required. The dissipation of electricity 

 along the glass supports is prevented by 

 a kind of cap, T, of mahogany, which 

 affords an electrical well or cavity under- 

 neath, and likewise effectually covers the 

 metallic cap into which the glass is ce- 

 mented. The lower extremity of the pil- 

 lar is guarded in the same manner by a 

 hollow piece or ring of mahogany, V. 

 The three glass pillars are set in sliding 

 pieces, WWW, adjustable by screws; at 

 each extremity of the horizontal diame- 

 ter of the plate are two rubbers, X, one 

 on each side, pressed regularly and uni- 

 formly against the plate by means of a 

 spring, Y, the force of pressure of which 

 is regulated by means of a screw. To 

 these rubbers are attached silk flaps, ZZ, 

 those of one pair of rubbers descending, 

 and those of the other pair ascending, in 

 the direction in which the plate is work- 

 ed. A piece of fine dry writing paper, at, 

 long as the rubber, and half an inch 

 broader, so as to cover the seam that fas- 

 tens the silk to the leather, allows greater 



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