Cooley's Cyclopaedia of Practical Receipts Volume Ii Part 19

Shortly after Faraday's discovery in 1830 of electrical induction, or the power of a bar of magnetised steel to set up in a certain direction a current of electricity in a coil of insulated wire when introduced into it, Pixu, reducing the result of Faraday's researches to practice, constructed an instrument, which appears to have been the first dynamic magneto-electric machine. By Pixu's contrivance a current of electricity was generated by means of the poles of a permanent horseshoe magnet being made to revolve across those of an electro, or temporary magnet, the induced electricity set up in which in its turn established in the surrounding helix a current of electricity, which being made to escape by the terminals or ends of the wire coils could be applied to practical use.

The dynamic electro-magnetic machines of Saxton and Clarke, which succeeded Pixu's, may be regarded as modifications of this latter, since they differed only in the arrangement of their parts and mode of action.

All three machines were chiefly in use in chemical and physical laboratories, whence they have gradually been supplanted by the far more useful Ruhmkorff's coil, a very powerful variety of the electro-magnetic instrument. In a small form Clarke's is now chiefly used for medical purposes. That electro-magnetic machines, as cheaper and more convenient sources of electric force, should have been applied to the purposes of telegraphy, will be an obvious inference.

Among the most important and effective of the various instruments for attaining this end, it will suffice to mention the magneto-electric machine of Messrs Siemens and Halske, first brought into use in 1854.

Except, however, in the case of short distances, or with telegraphs belonging to private persons or commercial firms, these instruments have not met with very general adoption. This is owing to the great tension of the induced current, and the consequent difficulty of insulating the wire, particularly for long distances, objections from which the old galvanic apparatus is in a much greater measure free. Mr Henley was the first to use the dynamic magneto-electric machine for working the electric telegraph soon after this instrument had been adopted in England; but as we have seen, the method, except in the cases quoted, have been in great measure abandoned. A large magneto-electric machine has lately been invented by Wheatstone, the induced spark from which is used for firing mines.

The first electro-magnetic machine used for lighting purposes appears to have been one that was the joint invention of MM. Nollet and Van Malderen, of Brussels, a circ.u.mstance to which it probably owes its name of the 'Alliance Machine.'

Nollet, who brought out his invention (which is a modification of Clarke's) in 1850, originally designed it for the electrolysis of water, the hydrogen resulting from which it was proposed to pa.s.s through camphine, or some other hydro-carbon illuminant, and to burn as gas.

Additionally it was designed to use the hydrogen as a source of motive power by exploding it in a suitably constructed engine. Owing to the improvements, however, effected in the machine by Van Malderen, by which it became a powerful generator of magneto-electricity, this purpose was abandoned. 'The Alliance Machine' consists of a cast-iron frame, on the circ.u.mference of which 40 powerful horseshoe magnets, each capable of supporting a weight of 120 to 130 lbs., are fixed, in eight series of 5 magnets each. A number of circular metal discs, around the circ.u.mference of which are attached sixteen bobbins of insulated wire fixed to a horizontal shelf turned by a pulley, are in such a position with regard to the magnets, that with each revolution of the shaft each bobbin pa.s.ses sixteen alternate poles of the magnets, and will have had sixteen alternate currents set up or induced in it. Until replaced by the later and smaller magneto-electric machine, the 'Alliance' has been the one mostly employed for the production of the electric light in France, and it is still in use in the lighthouses of Heve and Grisnez, as well as in those of many other places in that country. In 1856 Mr Holmes took out a patent for a machine, which differs from Nollet's in increasing the number of bobbins by arranging them in concentric circles between two bra.s.s discs. By this device the bobbins revolve more quickly in succession in front of the poles of the magnets, a plan which ensures the generation of a greater number of currents for every revolution.

Like the first application of Nollet's, Holmes' machine was used for lighthouse illumination. It was in work from December, 1858, until June, 1862, at the South Foreland lighthouse, since which time it has been removed to Dungeness, in the lighthouse of which station it has been in use ever since.

When applied to lighting purposes, both the 'Alliance' and Holmes', and the other machines named, are worked in conjunction with the carbon points, which when arranged with proper machinery const.i.tute the electric lamp.

Wild's and Ladd's are powerful dynamic magneto-electric instruments, capable of yielding large quant.i.ties of the electric fluid.

Artificial illumination by means of electricity has, however, been more or less occasionally practised for other than lighthouse purposes.

For instance, in 1854, during the building of the Napoleon Docks at Rouen, when 800 workmen were engaged nightly for four hours, the electric light was used for several nights with perfect success, the men being able to carry on their work at a distance of more than 100 yards from the source of the light.

In 1862 and 1863 it was frequently employed in Spain during the night in the construction of railways. During the late Franco-German war in 1870 it was applied to submarine illumination, and more lately it has been used in a series of street illumination in St Petersburg.

The electric light apparatus was placed on the tower of the Admiralty Buildings of that city, and by means of it three of the larger streets were illuminated at night from 7 until 10 o'clock. In this latter case, as well as in that of the Rouen Docks, the lamps were supplied with the electric current generated in batteries.

It may be said, however, to have been only within the last two years that the question of electric lighting has developed into a burning one, and that the light itself has become so much more generally and extensively adopted.

This new era in the history of artificial illumination may be said to date from the introduction of two forms of dynamic magneto-electric apparatus, the one invented by Dr Siemens, the eminent telegraphic engineer, the other by M. Gramme, of Paris, who, from having been formerly a journeyman carpenter, has now become the head of a manufacture which forms a most important branch of scientific industry.

In the apparatus of Gramme and Siemens three marked features and improvements over the older machines have been achieved:--

1. A great reduction in size, and, consequently, in cost, and requisite s.p.a.ce for the machine.

2. The method of generating large quant.i.ties of electricity by the mutual action between the different parts of the same machine, and the induction therein set up.[14]

[Footnote 14: This discovery was made independently and nearly simultaneously by Drs Siemens and Sir Charles Wheatstone.]

3. The production of the electric current at a much less expenditure of motive power.

On this latter point Professor Tyndall, in his report to the elder brethren of the Trinity House, states that magneto-electric machines of old construction cost ten times more, occupied twenty-five times the s.p.a.ce, and weighed fourteen times as much as the recent machines, while they produced only one-fifth of the light with practically the same driving power; which in effect amounts to this--that taking illuminating effect in each case into consideration, the new machines cost one-fiftieth, and are, as regards s.p.a.ce occupied, 125 times more advantageous than the earlier forms.

In all the older and larger machines the current of electricity, as it was given off from the wire and pa.s.sed through the carbon points, was alternate, or first in one direction and then in the opposite--that is, it was a momentary current, first positive and then negative.

In Siemens' machine, and in one form of Gramme's, the current is direct--that is, it pursues one uniform course in its pa.s.sage through the carbon points of the lamp, and in its circuit from the terminal of one wire to that of the other.

Scientific opinion is somewhat at variance as to the disadvantages of the indirect current; many electricians consider that it causes the partial destruction of the contacts, and sets up unnecessary heat in the machine.

In magneto-electric machines employed in electro-metallurgic operations, it is essential the current should be a direct one.

In the Gramme machine the electro-magnet consists of a ring composed of soft iron wire attached to a horizontal spindle or axis, which latter is turned by an endless strap revolving on a pulley. Around this iron ring are wound a number of coils, each having 300 turns, of insulated copper wire, each coil being bent inside the ring, and fixed to an insulated piece of bra.s.s.

The wire being continuous, each coil is connected with the adjacent one, the whole of the coils thus forming a single conductor. The series of pieces of bra.s.s to which the wire is soldered are formed into a circle, which surrounds the axis of the machine, each piece of bra.s.s being insulated from its neighbour. The iron-wire ring with its attachments is so arranged, that when the shaft or axis to which it is fixed is turned, it revolves between the poles of a powerful horseshoe magnet in the same plane with it. As it turns the ring gives rise in the coils to two different and diverse currents of electricity, one in one half of the coils around the ring, and the other in the other half.

These currents are made to pa.s.s to the circle composed of the insulated pieces of bra.s.s, which are arranged radially to the axis of the machine.

Two bra.s.s brushes press against these insulated bra.s.s radii, one on each side.

These brushes are connected one to each terminal of the machine, and so contrived as always to be in contact with the coils, not becoming insulated from one coil until contact is established with the next one, an arrangement which gives rise to a continuous current of electricity always, and in the same direction.

The Gramme, although of very small dimensions, is an extremely powerful machine. It easily decomposes water, and will heat an iron wire 8 inches in length and a 25th of an inch in diameter to redness.

The following description of the Siemens magneto-electric machine is from a paper read some few months back at the Society of Arts by Dr Paget Higgs, and is extracted from the journal published by that body:

"In the latest form of construction of the Siemens magneto-electric machine the armature, as the revolving coil may be called, consists of several lengths of insulated copper wire, coiled in several convolutions upon a cylinder. The whole surface of the cylinder is covered with wire, laid on in sections, each convolution being parallel to its longitudinal axis. For about two thirds of its surface the wire cylinder is surrounded by curved iron bars, there being just sufficient s.p.a.ce left between these curved iron bars and the wire cylinder to allow of its free rotation. The curved iron bars are prolongations of the cores of large, flat electro-magnets; the coils of these electro-magnets and the wire on the cylinder (from brush to brush) form a continuous electrical circuit. On revolving the cylinder (which is supported on a longitudinal axis in suitable bearings, the axis carrying a pulley) an initially weak current is generated into its wires by their pa.s.sage through the magnetic field, formed by the residual magnetism of the iron coils of the electro-magnets, and the current being directed into the coils of the electro-magnets, increases the magnetism of the cores, which again induce a stronger current in the wire cylinder. This material action may continue until the iron has attained its limit of magnetisation. The maximum magnetic power acting upon each convolution is attained at every revolution of the armature, when the convolution pa.s.ses through the centre of both magnetic fields, and gradually falls to zero as the convolution becomes perpendicular to that position. Each convolution has, therefore, a neutral position, and a convolution leaving that position on the one side of the axis and advancing towards the north pole of the electro-magnet would be subject to a direct induced current, and that portion of the convolution on the opposite side of the axis would be traversed by a current of opposite direction as regards a given point, but of the same direction as regards circuit. Each of the sections of wire coiled upon the cylinder consists of two separate coils, leaving four ends; two of these ends are connected to each of the segments of a circular commutator divided into parts. But all the coils are connected to the several segments of commutator in such a manner that the whole of the double sections form a continuous circuit, but not one continuous helix. Two brushes placed tangentially to the segments of the commutator collect the electric currents; these brushes are connected one to each electro-magnet, and the two free ends of the electro-magnet coils are connected to the conducting wires leading to the lamp.

"The dimensions, weight, number of revolutions made by the armature, light equivalent in normal candles, and horse-power required for driving, are for the three sizes of machines as follows:--

+----------------------+-------+------------+--------+------------+ Dimension in Inches. Weight Revolutions Candles' Horse Power. +-------+------+-------+in lbs. of cylinder. Light. Length. Width. Height. +-------+------+-------+-------+------------+--------+------------+ 25 21 88 298 1100 1,000 1-1/2 to 2 29 26 95 419 650 6,000 3-1/4 to 4 44 283 126 1279 480 14,000 9 to 10 +-------+------+-------+-------+------------+--------+------------+

"In the lamp which it is preferred to use with the Siemens machine, the points of the carbons after being separated are brought together again by the gravitation of the top carbon and its holder. The descent of the top carbon actuates by means of the straight rack it carries at its lower end, a large pinion, the spindle of which carries a small pinion, gearing into a second neck attached to the lower carbon holder, the superior weight of the top carbon and holder, in conjunction with the multiplying ratio of the two pinions, producing a continual tendency of the carbons to approach each other. The large and small pinions are connected to each other, and to the spindle that carries them, by an arrangement of friction discs, and the object of this construction is to allow of the two racks being moved equally and simultaneously up or down for the purpose of focussing the light when required. This movement is effected by means of bevelled gearing, and actuated by a milled head, which can be pressed into position when required. On the spindle carrying the large and small pinions and the friction discs is placed a toothed wheel, connected with the spindle by a pawl and ratchet.

"This wheel is the first of a train of wheels and pinions driving a regulating fly in the usual way. The pawl and ratchet are provided to allow of the rapid distancing of the carbon holders when it becomes necessary to introduce fresh carbons. The spindle of the fly also carries a small finely-toothed ratchet wheel. This ratchet wheel is actuated by a spring pawl, carried at the end of a lever, which lever is the continuation of the armature of the electro-magnet, in such a manner that when the armature is attracted by the electro-magnet, the spring pawl engages in the teeth of the ratchet wheel, and causes the wheels in gearing therewith to act upon the racks of the carbon holders to draw them apart.

"The action of the lamp is as follows:--The current pa.s.ses from the conductor to the top carbon holder, thence through the carbons to the bottom carbon holder, then to the coils of the electro-magnet situated in the base of the lamp. From the coils of the electro-magnet the circuit is completed to the other conductor. Upon the current pa.s.sing through the circuit, the armature of the electro-magnet is attracted, and the abutment from the armature lever caused to short-circuit the coils of the electro-magnet, releasing the armature. The armature being released, the short-circuit is removed from the coils of the electro-magnet, and the cycle of movement repeated; in this manner an oscillatory motion is given to the armature lever, which by the spring pawl actuates the ratchet wheel, the train of clockwork, and the racks of the carbon holders, forcing the carbons apart until the distance between their points sufficiently weakens the current, so that it no longer attracts the armature of the electro-magnet. Thus, by the combined action of gravitation of the top carbon in drawing the carbons together, and of the current to separate the carbons when they approach too closely, a working distance is maintained between the points with perfect automatism."

Siemens' lamp is at the present time employed in the Lizard Lighthouse, in Messrs Siemens' Engineering Works in England and Wales, as well as in other localities or buildings requiring powerfully lighting up.

An interesting ill.u.s.tration of the value of the electric light to the sailor is furnished by the 'Telegraph Journal' of April 5th, 1878. This publication contains a letter from the captain of the S.S. 'Faraday,'

narrating how that vessel was by its means prevented from running into another vessel during a dense fog.

Siemens' magneto-electric apparatus and lamp were used on the occasion above referred to.

In every form of contrivance for electrical illumination the lamp or lighting apparatus consists of carbon points separated by a very slight interval, through which the current of electricity pa.s.ses by means of terminal wires attached to the dynamo-electrical machine.

The lighting effect is produced by the pa.s.sage of the electric spark through the small gap which separates the carbon points, in which interval extremely minute but solid particles of carbon, given off by the points, are heated up to incandescence in the path of the spark, and thus give rise to the intensely luminous focus known as 'the electric light.' The brilliancy of the light of course depends upon the quant.i.ty of electricity employed.

A very large number and variety of designs and patents for electric lamps have made their appearance in England, America, France, and Russia within the period following the invention of the small, powerful, and economic dynamo-electric machines of Siemens and Gramme.

The lighting apparatus generally attached to and worked by that variety of Gramme's machine generating the continuous current is that known as the 'Serrin Lamp.' Two carbon electrodes placed vertically one above the other (the positive being the upper one) are fixed on bra.s.s holders, which are so connected by a suitably contrived clockwork movement, combined with the working of an electro-magnet in connection with the electric circuit, as to maintain the two carbon poles during their combustion at the necessary distance from each other. Serrin's lamp differs in detail from Siemens', but, like this latter, is automatic in principle. In Paris it was the one in general use until the introduction of the Jablochkoff candle, and, with the Duboscq lamp, may be looked upon as the precursor of the various lamps and regulators now employed in electric lighting. Serrin's lamp or regulator, with some slight modification in the machinery, is also used in the Lontin system of electric illumination, by which separate lights are supplied by separate circuits of electricity. Lontin's method is that by which the Gaiety Theatre in the Strand is lighted; and is also used at the Western Railway Station (Gare, St Lazare) at Paris. The Jablochkoff candle, which in Paris has lately superseded the Serrin lamp, probably because its use renders unnecessary the use of automatic machinery, is the invention of a Russian engineer, whose name it bears.

It consists of two sticks of gas carbon, about 9 inches long and 1/5th of an inch thick, which are placed vertically side by side, and insulated from one another by a very thin strip of kaolin or china clay (a silicate of alumina and potash), the whole forming a candle. Each carbon rod is connected with one of the terminal wires of a Gramme dynamo-electric machine, the electric current from which, however, not being continuous, sets up an alternate current between the tips or poles of the candles, which are gradually consumed like an ordinary taper, and with this only difference in action between Serrin's and Siemens' lamps, that whereas in these latter the spark pa.s.ses from the top to the bottom carbon point, in the Jablochkoff candle it jumps from side to side. The inventor contends that the kaolin by becoming heated diminishes the resistance of the circuit, and thus permits of the pa.s.sage of the electric spark more easily through the carbons, and also, we believe, a.s.serts that the kaolin being electrolytically decomposed as the carbons are consumed, becomes converted into silica, which melts and drops down, whilst the aluminium liberated contributes luminosity during combustion to the flame.

One of the chief advantages, however, claimed by M. Jablochkoff is, that he can divide the circuit into a number of different lights, as the resistance of the circuit is uniform.

A large number of Jablochkoff candles are employed in the celebrated 'Magasins du Louvre,' one of the most extensive commercial establishments in Paris for the sale of silks, ribbons, gloves, &c., and clothing of every description.

The pure white light diffused by electricity admirably adapts it for viewing colours of all kinds at night, whether seen in pictures or on fabrics and raiments, and more particularly blues and greens, the hues of which are frequently indistinguishable from each other by gaslight. The candle is also used to light the courtyard of the Hotel du Louvre, a large building contiguous to, and with its apartments running over, the Magasins, as well as in several shops.