Henry Wilde to Faraday   c.15 January 1866

20 St. Anne’s Place, | Manchester,

To Michael Faraday Esq. D.C.L., F.R.S., &c.

Sir,

During the last two years I have been much engaged in some researches in electricity, and the results which I have at length obtained are of such an extraordinary character, and are so intimately connected with the department of natural knowledge in which you have so long and successfully laboured, but more especially with your famous discovery of magneto-electric induction, that I feel particularly anxious, for several reasons, (not the least of which is the great regard I have for you as the founder of the subject of my research), to give you a brief outline of the results of my investigations, in anticipation of the more extended publication of them through the medium of some of the scientific journals.

Referring to your communication in the Philosophical Magazine for June 1852. “On the Physical Character of the Lines of Magnetic Force.” paragraph 3273¹. when speaking of the remarkable and anomalous difference observed between the quantity of magnetic force in an electro helix, and in an iron core placed in its interior, you express your strong conviction, that, “In every point of view the magnet deserves the utmost exertions of the philosopher for the development of its nature, both as a magnet and also as a source of electricity,”. You will, I think, be gratified to learn, that I have had the good fortune to accomplish something towards the elucidation of these interesting phænomena when I tell you, firstly, that I have found out the cause of the difference observed between the magnetic force of an electro helix and its internal iron core. Secondly, that I have also discovered that an indefinitely small amount of magnetism is capable of producing an indefinitely large amount of dynamic electricity. And again, that an indefinitely small amount of dynamic electricity is capable of developing an indefinitely large amount of magnetism. Thirdly, that I have demonstrated, experimentally, that the magnet is the most powerful, as well as the most economical, source of electricity yet discovered and I have, besides, by means of the knowledge thus acquired, succeeded in constructing the most powerful generator of dynamic electricity which has been yet invented.

In pointing out an experimental distinction, which exists between the quantity of magnetism in an electro helix and its iron core, in the same paragraph (3273.)², you remark, “that an unchangeable magnet can never raise up a piece of soft iron to a state more than equal to its own, as measured by the moving wire. (3219.),” (3222.)³.

This observation, derived as it was from exact experiment, and having nearly all the rules of analogy to support it, is not absolutely true, but holds good only, under the conditions in which the experiment was made, for if one or more permanent magnets, of the horse shoe or other shape, form part of a magneto electric machine, and if the direct current from the machine be transmitted through the coils of a large electro magnet by means of a commutator, then will the electro magnet acquire a very much greater amount of magnetic force than that which is possessed by the permanent magnets of the magneto electric machine, notwithstanding the intermittent character of the magneto electric current. Again, when the electro magnet in its turn, forms part of an electro magnetic machine, the armature of which is driven at about the same speed as the one belonging [to] the magneto electric machine, a very much larger amount of dynamic electricity is obtained from the former, than what is obtained from the latter. Moreover, when the direct electric current evolved from the second machine, is transmitted simultaneously through the coils of a still larger electro magnet of a third machine, a still further, and very large increase of magnetism and electricity is obtained, and by extending the series of exciting machines, or increasing their dimensions, the quantity of magnetism and electricity evolved may be indefinitely increased.

Enclosed is a photograph, which has been taken from a perspective drawing of the machines as they are arranged for working, and by means of the letters marked thereon, I will endeavour to give you a general idea of their construction and mode of action, until a more particular description of them is completed. Should you then consider my researches of sufficient importance to merit your attention, I shall have great pleasure in forwarding to you, a fuller and better account of them before publication also.

The magneto electric and electro magnetic machines are constructed on precisely the same principle, with the exception of the magnetic arrangement for exciting the armatures, and as the latter machine is shewn on a much larger scale than the former, reference will be made to it more particularly.

A.A. Fig. 1. are the sides of an electro magnet formed of two plates of wrought iron enveloped with a large quantity of thick insulated copper wire. The upper ends of these plates are joined together by means of an iron bridge, which forms the top of the machine. The lower ends of the electro magnet are bolted to the cast iron sides B.B. of a compound cylinder of brass and iron B.C.B. the brass packings C.C. at the top and bottom of the cylinder, seperate [sic] the iron sides from one another, the latter, consequently, form the polar terminations of the electro magnet. The cylinder, as will be seen, is somewhat longer than the width of the electro magnet, and has a smooth and parallel hole bored through it from one end to the other. The length of the cylinder is five times the diameter of the bore, and as I have constructed many of them, for experimental purposes, with bores from one and a half to ten inches in diameter, I designate the different sizes of machines, from the bore or calibre of the magnet cylinder.

The armature D, represented in Fig. 2. without the coils, and in Fig. 3. complete, is made of cast iron, and is turned a small fraction of an inch less in diameter than the bore of the magnet cylinder. This armature is made to revolve concentrically, without touching the sides of the cylinder, in bearings provided for it in the brass crossheads E.E., by means of a strong leather belt G. The alternating currents generated by the revolution of the armature can be taken from it all in one direction, by means of two steel springs H.H. which are made to bear against the opposite sides of the commutator I. The currents of electricity can also be taken from the machine in alternate directions when required, by adjusting the springs so as to bear against the unbroken cylindrical part of each half of the commutator. The large electro-magnet is excited by the direct current from the small magneto-electric machine K, which stands on the wooden top of the electro-magnet, and is driven from the same driving shaft as that by which the electro-magnetic machine is driven.

In the following experiments, six small U shaped permanent magnets, eight inches long, and weighing about one pound each, were placed upon the cylinder of a one and a half inch magneto electric machine. Each magnet sustained a weight of about ten pounds, and the direct current from the machine was transmitted through the coils of the electro-magnet of a five inch electro magnetic machine, and the direct current from the latter, was, in like manner, transmitted simultaneously through the coils of the electro-magnet of a ten inch machine. This 10 inch machine is furnished with two armatures, one for producing quantity, and the other for producing intensity, effects.

The conductor on the quantity armature is 67 feet in length, and has a sectional area of 1.5 square inches.

The conductor coiled round the intensity armature is 376 feet in length, and has a sectional area of 0.25 of a square inch. These armatures are driven at a speed of 1500 revolutions per minute, and the armatures of the exciting machines at about 1800 revolutions per minute.

This combination of the machines, when in full action, is attended by the development of an amount of magnetism in the electro magnet of the ten inch machine, far exceeding anything which has hitherto been produced, together with the evolution of an amount of dynamic electricity from the quantity armature, so enormous, as to melt pieces of iron rod fifteen inches in length and a quarter of an inch in diameter. The electricity from the same armature will also melt fifteen inches of copper wire, one eighth of an inch in diameter.

When the intensity armature is placed in the machine, the electricity from it, will melt seven feet of No. 16 iron wire, which is about one sixteenth of an inch in diameter, and a length of 21 feet of the same wire, can be made bright red hot. Enclosed, are specimens of the different sized iron and copper wires so melted. All these, and the following results, are obtained from the alternating currents of the machine, without the intervention of the commutator.

The illuminating properties of this powerful arrangement are, as might be expected, of the most splendid description, for when the polar terminations of the intensity armature are connected with rods of gas carbon half an inch square, the light which bursts from the points is of great volume and of the most dazzling brilliancy, each of the carbons being made red hot for a length of an inch and a half from the points. When the carbons are fixed in the beautiful apparatus for regulating the electric light recently invented by M. Foucault⁴, behind which is placed a parabolic reflector twenty inches in diameter adjusted so as to cause the rays of light to diverge at a considerable angle, the light, when directed from the top of a lofty building, is sufficient to cast the shadows from the flames of all the street lamps upon the neighbouring walls for a distance of more than a quarter of a mile. When viewed from that distance, the light seems to fill the reflector completely, and is a very magnificent object to behold, the rays proceeding from it, having all the rich effulgence of sunshine.

A piece of the ordinary sensitized paper used for photographic printing, when exposed to the action of the light for five minutes, at a distance of five feet from the reflector, was blackened to the same degree as was a piece of the same sheet of paper after an exposure of ten minutes to the direct rays of the sun at noon on a very clear day in the middle of September last. Accept, Sir, the enclosed photograph of yourself, which has been printed by means of this light, from a negative taken at the Royal Institution by Mr Brothers⁵ of this city (by the light of burning magnesium)⁶, and who was kind enough to lend me the plate.

The extraordinary calorific and illuminating powers of the machine are all the more remarkable, from the fact, that they have their origin in the six small permanent magnets before mentioned, which are only capable of sustaining collectively, a weight of 60 pounds. while the electricity generated from the small magneto electric machine, is, of itself, incapable of heating to redness, the shortest length of iron wire, of the smallest size manufactured.

The evolution of so large a quantity of dynamic electricity from the ten inch machine is only obtained, as you would anticipate, by a correspondingly large expenditure of mechanical force. In the practical working of the machine, I have found, that it is not necessary to employ the combination of magneto electric and electro magnetic machines, as described, for exciting the large electro magnet, since a two and a half inch magneto electric machine, as shewn in the perspective drawing, answers the purpose very well, as by means of it, fully two thirds of the maximum amount of power from the armatures of the 10 inch machine can be obtained. The following are the principal dimensions of the 10in machine - Length of the magnet cylinder 50 inches. Total length of machine, 80 inches. Height, 60 inches. Width, 24 inches.- Weight of electro magnet without cylinder, about three tons.- cylinder one ton.- total weight of machine about 4½ tons.

With respect to the cause of the enormous increase of magnetism developed in the large electro magnet, amounting to considerably more than 1000 times that of the permanent magnets of the magneto electric machine, I find, that a considerable number of currents or waves require to be transmitted through the electro helices of the electro magnet, before the iron acquires its highest degree of magnetism. Moreover, the number of currents or waves necessary for producing this high degree of magnetism, is diminished as the power of the exciting machine is increased. I have also found, that a spark can be obtained from the electro helices of the large electro magnet of the 10 inch machine, twenty five seconds after all connection with the exciting machine is broken.

This part of my investigations is closely connected with some of your own, but more particularly with the subject of your Ninth Series of Researches⁷, and as I purpose making some observations thereon, as well as on the nature of time, and its influence in connection with the phenomena under notice, in my more extended communication, I will not trouble you at greater length with this part of the subject, nor with any further particulars of the construction of the machines. I am only sorry that they are not, at the present time, nearer London, or I might perhaps have had the pleasure of shewing them to you in operation, together with some other remarkable phenomena observed in connection with them, which I have reserved for a future communication.

I am, Sir, | Faithfully yours | H. Wilde.

Endorsed by Faraday: Received by post Tuesday 16 Jany 1866 MF⁸