ELECTRICAL MACHIVi:. 



which differs in tome respect* from the solar spectrum ; but tn the 

 case of the electric light, the fpeotnim Taries with the material of 

 which the electrode! are composed. 



The light produced by the magneto-electric machine [MAUNETO- 

 BUOTRICITT] hu lately been applied to the illumination of light- 

 houses. The South Foreland lighthouse, near Dover, u thus furnished. 

 The lighthouse U placed on a high cliff, and the light is visible at the 

 distance of above 27 miles, and can be soen from the lantern* of the 

 lighthouses of the coast of France. 



ELECTRICAL MACHINE. An apparatus (or furnishing supplies 

 of electricity. There are two prinvi|>al forms of this instrument in 

 general use, namely, the ct/Hmlrr and the plate machine. The former will 

 be described uuder ELECTRICITY, COMMON ; the latter, in its simplest 

 form, is represented in the annexed figure. It consists of a duo of plate 

 glass, o, moving upon a central horizontal axis with two pair of rub- 

 bers or cushions, B, grasping the plate, proceeding from which nro 

 flaps of oiled xilk, also attached, by means of threads, to fixed points, 

 to prevent the plate from dragging them too much : r, in the prime 

 conductor, insulated by means of a glass stem. When this machine is 

 in good order it furnishes an abundant supply of vitreous electricity. 

 A method of insulating the rubber so as to obtain negative electricity 

 has been contrived by Sir W. Snow Harris, and is described in hi* 



' Rudimentary Electricity.' Plate machines of great power have within 

 the last few years been erected in London ; that at the Polytechnic 

 Institution wan 7 feet in diameter, and wag turned by a small steam 

 engine, while that at the Panopticon, in Leicester Square, was 11 feet 

 in diameter. 



A good deal of attention has lately been excited by a new method of 

 mounting plate machines, invented by Winter, of Vienna. There is 

 only one pair of rubbers, and they are large and peculiar in shape ; but 

 the most curious feature of the machine is a stem rising vertically from 

 the prime conductor, and carrying at its top a large wooden ring lined 

 within with metal. The effect of this new arrangement is greatly to 

 increase the striking-distance of the sparks ; but then it must be borne 

 in mind that the sparks are less frequent than in the ordinary plate 

 machine. This method of mounting does not, criteria paribut, increase 

 the quantity of electricity, but only the size of the sparks and their 

 striking distance. Some of the Edinburgh instrument makers have 

 adopted this method of mounting, but the London maker* do not 

 seem disposed to favour it. The reader interested in the subject will 

 find a full account of the method, with figures and measurements, hi 

 the second edition of Frick's ' Physikalische Technik,' Braunschweig, 

 1856, p. 348. 



The Hydro- Electric Machine is a powerful source of electricity. It 

 originated hi 1840, in the observation of a workman who was in charge 

 of a fixed steam-engine at Sighill, near Newcastle. A leak in the 

 cement about the safety valve led to a considerable escape of steam, 

 and the engine-man, in attempting to adjust the weight of the valve, 

 noticed a strong electric spark proceeding from the metal-work of the 

 boiler, and from the boiler iUelf, if he attempted to touch it while 

 steam was escaping, especially if one hand were immersed in the 

 vapour. Mr. Armstrong (now Sir Charles), of Newcastle, examined the 

 phenomenon, and by means of an insulated brass rod, with a metallic 

 plate at one end and a ball at the other, the former being immersed in 

 the escaping vapour and the latter held near the boiler, sixty or seventy 

 parks per minute were obtained. Armstrong's hydro-electric machine 

 was based on this result. It consists of a steam-boiler insulated on stout 

 pillars of glass, and of a large number of bent iron tubes, terminating in 

 wooden jets, through which the steam issues with considerable force : 

 projecting from the boiler is a conductor, terminating in a knob, 

 while immediately in front of the jets is a metallic case, containing 

 several rows of points for receiving and carrying off the opposite 

 electricity of the steam, for if it were allowed to return upon the 

 boiler the electrical forces would be neutralised. Faraday has shown 

 that the electricity produced by this machine docs not depend 



nn the issue of steam through small orifices, nor on any 



physical change due to evaporation or condensation, but is the result 



of the friction of the condensed particles of water which ore driven 

 by the steam through the jets, which particles act the part of the. 

 glass plate in the common machine, and give out vitreous electricity, 

 while the wooden jets and pipes act as rubbers and give out resinous 

 electricity. In fact the friction of the steam is the source of tin- 

 electricity ; the escaping steam exhibits positive and the boiler negative 

 electricity : it is remarkable that a small quantity of oil r of tur- 

 pentine in the exit pipe reverses these electrical states. Wood seems 

 to be the best material for the orifice of the jet; ivory one of the 

 mni 



Another electrical apparatus depending on friction is the ELECTRO- 

 PHOBUS, and will be described under that head. 



Rhumkorff's Magneto-electric induction coil is a powerful source of 

 electricity, but the proper place for its description will be found under 

 MAONBTO-ELECTRICITY. 



ELECTRICAL, or ELECTRIC TELEGRAPH. [TELEGRAPH.] 



ELECTRICAL TIME BALL. [TiMR BALL.] 



ELECTRICITY. A subtle imponderable agent pervading all 

 .matter apparently without affecting its volume or temperature, and 

 without displaying its presence in any way when in the latent state ; 

 but when excited, its effects may be displayed either in a ludden, 

 violent, and destructive manner, or as a less energetic In 

 force. The remarkable differences in the numerous and varied pheno- 

 mena of electricity depend chiefly on the modes in which 

 developed, whether by mechanical power or by chemical a< -ri..n, l.y 

 magnetic or calorific influence, or in certain cases by the animal will. 

 Thus when the force is excited by means of friction, as with the 

 ordinary electrical machine, it is called COMMON or FRIOTIONAI. : 

 TRICITV, or in honour of one of the great investigators of this liraneh 

 of knowledge, FRANKLINIC ELECTRICITY. A second modification of 

 electricity is MAGNETISM, which like common electricity is a polar 

 force, operating on every description of matter, but commonly exhibit- 

 ing its properties in bars or needles of steel known as m.'/< it. Tin- 

 third branch of electrical science is due to chemical action, as when 

 two dissimilar metals are brought into contact in a liquid which acts 

 upon one of them, in which case there is develo[>ed an electric current 

 known as GALVANISM, or VOLTAIC ELECTRICITY, in honour of the 

 founder and great improver of this branch of science, namely, Galvani 

 and Volta. Fourthly, there is THERMO-ELECTRICITY, in which a cut rent 

 is produced by the action of heat upon certain metallic arrangements. 

 Fifthly. Certain fishes, such as the torpedo and the electrical eel, are 

 furnished with an apparatus capable of producing electricity, whie.li 

 for distinction's sake, is termed ANIMAL ELECTRICITY. The influence 

 of an electric current on the magnet, or the magnetic relations of the 

 voltaic current, present a large class of important phenomena vhi.-li 

 are included under ELECTRO-MAGNETISM, while the electrieal pheno- 

 mena produced by magnetism form the branch of science known as 

 MAGNETO-ELECTRICITY. 



Science does not now pretend to explain why electricity is oa|mlil<- 

 of being excited from its neutral condition by any of the means above 

 indicated, any more than the iii.nl,- of its existence in matter. She 

 does not pretend to decide whether electricity be a material agent, or 

 only a property of matter, or whether, like light and heat, it is supposed 

 to be due to the vibrations of on ether. For the sake of convenience, 

 however, electricity is assumed to be a physical agent, having the pro- 

 perties of an elastic fluid, -and hence capable of being held in equili- 

 brium by the mutual action and re-netion of antagonistic forces, or of 

 moving in definite directions and forming currents of greater or less 

 intensity. Hence the modes of investigation and the method of classi- 

 fication have had reforenee to the mechanical science*, the varied phc- 



