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TUERMO-ELECTIilCITY; APPLICATION OF ELECTRO-MAGNETISM, &c. [Class X.
opposite to the axis of each roller, and on either side, areplaced two brushes of bristles. There is a double con-ductor connected by a curved brass rod hanging over thetop of the machine, similar in form to the conductor ofplate-glass machines, and also a simple means of tighten-ing or loosening the band, to correct the expansion andcontraction of the gutta-percha.
It is stated that the electricity given off appears to beof high intensity, and, under favourable states of theweather, nearly as much in quantity as that from an ordi-nary plate-glass machine. The machine exhibited, whenin good order, gave off sparks from about three-quartersof an inch to an inch in length.
This application of gutta-percha is quite new in prac-tice,* and indicates the discovery of a new motive power,which promises to be a means of obtaining a supply ofelectricity of almost unlimited extension : this applicationof gutta-percha opens a new field in electrical researchwell worth exploring. A Prize Medal was voted to Mr.Westmoreland.
Watkins and Hill (No. 659, p. 4GG*) exhibit an elec-trical machine with a glass plate of 3 feet in diameter,furnished with both positive and negative conductors;they also exhibit a dry pile apparatus, furnished with apair of Zaruboni’s dry electric piles, with a tangent screw,for the purpose of regulating the distance between thepiles, and their position with respect to the suspendedgold leaf. This is a beautiful instrument.
They also exhibit a delicate astatic galvanometer, forestimating minute currents of voltaic electricity; thelower needle is surrounded by a coil of wire 230 yards inlength and T i 0 th of an inch in thickness. It is furnishedwith a rack-work motion, and a microscope for reading.And they also exhibit Harris’s thermo-electrometer, forestimating small currents either of atmospheric or voltaicelectricity, by the heating of a line metallic wire.
Deleuil (France , No. I GO, pp. 1173—80) exhibits anelectrical machine for medical purposes, furnished withan arrangement to vary the strength of shocks. It issimple and effective in its operation.
Meinig (No. 437, p. 4G0) has exhibited hydro-electricchain batteries, consisting of the metallic combination ofvarious galvanic elements; so arranged as to be very port-able.
They are designed to be worn on the body for the pur-pose of effecting the cure of various chronic diseases bymeans of the electric current, which in its passage fromone pole to the other passes through that part of the bodyencircled by the chain.
In 1821, Lubeck , of Berlin, found that, if two metalsof different kinds be in any way brought into close con-tact, and heated at the points, a current of electricityflowed through the metals, which continued passing inthe same direction whilst the heat increased, ceased toflow when the temperature was constant, and flowed inthe opposite direction on the cooling of the metals;whence heat was found to be connected with electricity,and like other natural forces, capable of mutual reaction.
Suss (Prussia, No. 482, p. 1U78) exhibits a very largethermo-electric battery, with electro-magnet heating ap-paratus and apparatus for exhibiting chemical reactions.
A central ball of heated iron, 2^ inches in diameter,supported on a brass stand, radiates on five thermo-electriccombinations, each composed of many elements unitedby soldering, and are enclosed in brass cylinders about4 inches in diameter, and connected by copper rods witheach other, either directly or indirectly, or through a coilpassing round a core of soft iron. The circuit thus com-pleted, the magnetic power is developed. Each cylinderhas also a chamber for the reception of hot water or hotoil, whose radiation on a similar compound thermo-com-bination, placed as a diaphragm within the cylinder, de-velops the thermo-electric current. Honourable Mentionwas awarded by the Jury.
* The electric power of vulcanized caoutchouc is evenmore powerful than that of gutta-percha, and is excited withsingular facility.
Hoffmann and Ebkruardt (Prussia, No. 88, p. 1053)exhibit an apparatus for showing the action of the earth’smagnetism on electric currents, in illustration of the well-known experiments of Ampere , in which helices andframes of copper wire, delicately suspended, when in theact of transmitting the electric current, place themselvesin the magnetic meridian.
Application of Electro-Mapnetism to the movement ofMachines.
The great discovery of Professor Oersted in 1819, towhich we have before referred, opened a new field forphilosophic inquiry, and, especially for the application ofan active force, produced, without external influence, tothe movement of machines. This application, which hassince engaged the attention of scientific men, is prettywell represented in the Exhibition: although no greatpower has as yet been obtained, many important difficultiesin its practical application seem to have been overcome,particularly by Mr. IIjortii (Denmark , No. 47, pp. 1359,1360), and we cannot help flattering ourselves that theattainment of this mysterious motive force will soon befollowed by tlie making it available for practical purposes.
Joule (So. 440, pp. 461,462) exhibits an electro-mag-net, constructed of a plate of well-annealed wrought-iron,1 inch in thickness, 1 foot in breadth at the centre, and3 feet at the poles, which are 3 inches in breadth. Theiron is rendered magnetic by transmitting the voltaicelectricity through a bundle of copper wire (50 yards inlength and 1 cwt. in weight) with which it is enveloped;an armature, and a pair of tapered armatures, are alsoexhibited for the purpose of concentrating the magneticforce when the electro-magnet is excited by a feeblevoltaic current, and of directing the magnetic action toany required object. The superiority of this over otherelectro-magnets consists in the attainment of much greatermagnetic force from a given voltaic battery than hashitherto been procured. Its use is to magnetise bars ofsteel and compass-needles, to which it instantaneouslyimparts a larger and more regular dose of magnetism thancan be obtained by the usual means. It may also be em-ployed to exhibit the phenomena of magnetism anddiamagnetism.
Mr. Joule also exhibits a surface electro-magnet, con-sisting of a thick piece of wrought iron enveloped by abundle of copper wire. The exhibitor observes, that abattery of moderate power produces such a powerfulattraction between the above electro-magnet and itsarmature, that a weight of more than one ton is neces-sary to be applied in order to draw them asunder. Thisillustrates the extraordinary attractive power of ironwhen fully magnetized.
Harrison (No. 420, p. 455) exhibits an electro-mag-netic engine which acts on the principle of the inducedmagnetic power of a compound coil of insulated wireconveying the current to a series of plates of soft iron,and attracting them within a suitable aperture.
As there is only one body of wire in connection witheach coil, the retarding influence of the electro-magnetsacting upon each other, after the current from the bat-tery is cut off', is avoided, and by this arrangement theeffects of the secondary currents are much reduced. Thecoils are made of short lengths of wire, and the whole areenclosed in metallic cylinders: it is presumed that a con-siderable saving in the consumption of the battery materialsis effected. The advantages, Mr. Harrison says, are:—
1st. An almost unlimited power and length of stroke.
2nd. The greatest possible amount of power from thebattery, by reducing the influence of the secondarycurrent to a minimum.
3rd. Avoiding the retarding influence caused by theretention of magnetism in the ordinary method of appli-cation by magnets; and from the body of iron actedupon by the coils exposing a large surface, an instan-taneous and powerful induction of magnetism ensues, andthus the highest speed is obtained.
4th. By the employment of a compound conductingmaterial, a strong current of electricity is transmitted,and a much greater magnetic effect within the same spaceis obtained.