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THIS is a magneto-electric machine, invented by M. Gramme, of Paris. It was first submitted to the Academy of Sciences in July 1871, when it elicited warm commendation from several members of that learned body. The novelty of its leading features is such as to excite the interest of the scientific enquirer, while its practical bearings strongly urge it on the notice of certain classes of specialists.

It has been introduced into this country by M. Werdermann, an eminent chemist, and has been exhibited for several weeks to various parties in the Engineering Works of Messrs. Whieldon and Cooke, Westminster Bridge Road. Public attention seems to be awakening to the advantages derivable from it, and no doubt further enquiry will be made into its characteristic merits, when, if it answer the expectations already entertained by many, it must play an important role in the development of the practical applications of electricity, and may indeed eventually supersede the machines actually in use. We intend in this paper to give as full an account of this new apparatus as the limits which have been prescribed to us will permit. ‘

It is only about forty years since the principle of induction was discovered by that indefatigable researcher, Faraday; and the progress made in this new branch of electricity during the four decades in question, is quite astonishing. There is scarcely a parallel for it in the history of science. Nor has there been a halt in the onward movement; every year has brought its contribution—sometimes in the shape of a new application, occasionally in the extension of a principle, but generally in the introduction of more or less valuable improvements. Fara— day’s discovery threw open a very extensive region for exploration; and one too which promised to be amply remunerative. Accordingly, we find many labourers in the field even from an early hour. Some centred their attention upon the inductive action of voltaic currents, and among the most successful of these as candidates for fame and fortune was Ruhmkorfi'. Others devoted their thoughts to the magneto-electric spark, and devised apparatuses, which, in their days, startled the scientific world. But such is the discarding nature of progress that the beautiful contrivances of Pixii, Saxton, and Clarke, are now objects more of curiosity than utility, and are therefore relegated to collections of physical instruments. These expensive toys, as they were called, have been succeeded by machines which produce veritable streams of electricity. These changes have been effected rapidly indeed, but not per salt'wm ; and it is as instructive as entertaining to follow up the steps which have led to these results.

The rationale of voltaic induction, as determined by the labours of Faraday, is that a current which begins or finishes generates in a neighbouring conductor currents whose directions may in every case be determined by Lenz’s law. The transition from this to magneto-electric induction was comparatively easy, as Ampere had many years before propounded to the Academy of Sciences his famous electro-dynamic theory, which virtually identified magnetism and electricity. Experiment proved the accuracy of the Ampérian theory, and Faraday was the first to elicit the spark from the magnet. Every tyro in science knows that the introduction of a magnet within a hollow coil produces an inverse current in the wire, as indicated by the oscillations of the galvanometer needle. These effects may be rendered much more striking by inserting within .the coil a bar or a cylinder of soft iron, and then approaching and withdrawing a pole of a magnet. The pole acts inductively on the soft iron; the variation of distance augments or decreases its magnetic condition, and this fluctuation suffices to generate the induced current. The strength and continuance of the latter depend on the velocity and duration of the movement. It may be interesting to vary these experiments by winding a few turns of copper wire—the free ends of which are connected with a galvanometer—on a soft-iron bar, whose middle section is at right angles to a steel magnet, and then moving the helix from the centre to either extremity ‘and back again, when it will be noticed that in the first case the currents are in the same direction, and if we call them direct, those in the second will be inverse.

Gauss and Weber were the first to utilise Faraday’s discovery; they transmitted telegraphic signals byraising or depressing a wooden bobbin, wound with copper wire, through the centre of which passed two or three vertically placed bar mag

nets, with similar poles joined together. In Pixii’s apparatus, which was invented about the time of these Gottingen experiments the magnet rotated before the coil. Later on, Saxton and Clarke improved upon this by fixing the magnet, and causing the double bobbin, which is much lighter, to rotate before it. Attention was now drawn to the production of copious magnetocurrents. A new impetus was given; a great question was proposed, and a solution required. Genius and skill went to work, and it was not until several years had elapsed that the knot was severed. One of the most ardent and successful investigators of this subject was Professor Holmes. He struggled against difficulties and prejudices, and had at last the satisfaction of exalting the tiny spark of Faraday into a brilliant star,* and of giving to our coasts beacon-lights whose vivid flashes may be distinguished far out at sea by the storm-beaten mariner.

Mr. Wilde combined all valuable anterior facts and principles into a machine of unprecedented power. He rejected the coils of Clarke, and adopted the armature of Siemens, in which the transversal was replaced by the longitudinal system of winding the wires around the iron cores. The current from the upper armature, which revolved between the poles of permanent magnets, was transmitted round large electro-magnets, which, by their action on a second armature, produced the useful current.

The mutual action principle was the next valuable discovery in magneto-electricity. It seems tohave occurred simultaneously _ to Siemens and VVheatstone, and consists in building up a powerful magazine from the very small amount of magnetism that remains in soft-iron when once a galvanic current has been sent round it. This beautiful principle was embodied by Ladd in his apparatus, to which a silver medal was awarded at the Paris exhibition of 1867.

However satisfactory were the effects obtained from all these machines, there was yet room for several improvements. The currents were instantaneous in duration, and alternately in opposite directions. This made no material difference in the production of electric light; but in electro-metallurgy it required a commutator, which is not always a convenient appendage. These imperfections were finally removed by the Gramme machine, in which we have absolutely continuous currents, and all in the same direction. This invention is thus among the most important of this prolific age ; it marks a new era in the annals of science. ‘

We have already stated that its introduction into this country is due to the diligence and enterprise of M. Werdermann ; and

' “Michael Faraday,” by Dr. Gladstone.

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