Scientific Memoirs/1/Part of a Lecture on Electro-Magnetism

Part of a Lecture on Electro- Magnetism, delivered to the Philosophical Society at Zurich, February the 18th, 1833; by the late Dr. R. Schulthess^[1].

From a work intitled "Ueber Electromagnetismus, nebst Angabe einer neuen durch electromagnetische Kräfte bewegten Maschine: Drey Vorlesungen von Dr. R. Schulthess. Zurich, 1835."

Though electro-magnetism from its intrinsic importance certainly is one of the most remarkable and interesting discoveries of modern times, yet it would create a much higher interest, and gain in popularity, if it could be rendered practically useful. For some time past I had been occupied with the idea, whether the power of electro-magnets, which without doubt might be infinitely increased, could be applied as a motive power for machinery. It was known from Van Moll's experiments, that when the electric current which runs through the spiral of an electro-magnet is rapidly reversed, the magnetic poles are likewise instantly reversed; and that a light iron keeper, which is supported from its poles, falls off at that moment, but is immediately re-attracted. The experiments of Henry and Ten Eyck showed that the power of such electro-magnets might be very greatly augmented. The thought struck me, that a considerably heavier keeper or armature might be suspended from such an electro-magnet, and that by the attraction and repulsion of the same a machine might be put in motion; at the same time the action of the gyrotrope, and thereby the reversion of the poles, might also be effected: and although the distance which the keeper would recede from the magnet could be but very inconsiderable, still I thought that the rapidity with which these motions would follow each other might in great measure compensate for this defect. I was, however, filled with mistrust on observing that this thought, which appeared to me so simple and natural, was not mentioned by any of the numerous natural philosophers who occupy themselves so assiduously with electro-magnetic experiments. I could not believe but that these notions must have struck them; but I was forced to suppose that they had either seen immediately the impracticability of them, or that, even if they had made some experiments upon the subject, they had met with insurmountable difficulties in its application. This long deterred me from making any experiments; but in the lecture which I gave before this Society on the 10th of December 1832, I could not refrain, when speaking of the powerful electro-magnets of Henry and Ten Eyck, from asking the question, "whether such a considerable power as that which is obtained by interrupting the electric current and then restoring it, could not be applied with advantage to mechanical science." After that lecture I considered the subject again, and thought I had convinced myself of its practicability; but that even if it were so, the result could not be very important, because the motion of the keeper must necessarily be very small. Notwithstanding, I had a more powerful electro-magnet made than any I had hitherto possessed, with which I intended to try the experiment; and I regarded the expense the less, as this apparatus appeared to me at the same time to be very appropriate for the evolution of the currents observed by Faraday; for this purpose the armature also must be covered with copper wire, and then each time the poles of the electro-magnet are reversed, a magneto-electric current circulates through this wire. In the mean time I found another method whereby the object I had in view might be effected, and which would allow a greater degree of motion to the armature: I thought I could effect this in the following manner. I placed on the table two cylindrical soft-iron horseshoes bound round with similar wires; so that when the electrical current was transmitted through both wires, the similar poles should lie opposite to each other: between these, and at a small distance from either, I placed a cylinder of soft iron, serving for a keeper; and then I expected to see the armature play to and fro between the two electro-magnets when I sent the electric current first round the one and then round the other electro-magnet. After several fruitless rough experiments it succeeded at last, and I therefore then instructed a turner to make an apparatus, that I might be able to repeat, by means of it, in a more easy and perfect manner, these yet very imperfect experiments. I had proceeded so far, when, on the 4th of January, I received the latest part of Baumgärtner's Zeitschrift, published at Vienna on the 17th of November 1832. I there observed a treatise, intitled, "Electro-magnetic Experiments of Salvatore Dal Negro, Professor of Natural Philosophy in the Imperial University at Padua," (translated from the Italian). The author says in the Introduction:

"Philosophers have already known for some time the power of electricity to make soft iron magnetic. In the year 1825, Sturgeon magnetized cylindrical horseshoes of soft iron by means of copper wires wound round them, connecting the ends of the wires with the plates of an electromotor. Professor Van Moll of Utrecht saw this experiment performed in the physical laboratory of the London University by Mr. Watkins, and he obtained on repetition those remarkable results described in Bibl. Univ., cah. 45. p. 19. This new method of communicating such great attractive power to iron created in me the desire of repeating the experiments, and principally of taking into consideration the application of this attractive power, which it appears may be infinitely increased, to some useful purpose. I give these experiments to the public in the conviction that a force so easily evolved and so very powerful justifies repeated and varied experiments. In my experiments the electromotors employed were without doubt smaller than any hitherto used, and these notwithstanding produced the same results: new circumstances and new laws were observed and discovered respecting the manner of increasing the magnetic power evolved by electromotors, of producing. in them currents now similar, and now different, sometimes in the same, sometimes in opposite directions, and by the success of these experiments of setting a lever in motion in different ways, and thus finally enriching natural philosophy with a new motive power."

It is easy to imagine with what avidity I read this notice, partly from joy at seeing my idea, of the practical application of which I still had many doubts, mentioned by another person, and partly somewhat vexed that the priority of my invention, if it really was as useful as my fancy made me think it, was snatched away from me. I therefore read with intense eagerness this paper; but my expectations were in a great measure disappointed; for it was only at the end that Dal Negro gave some short, and to me not altogether comprehensible hints concerning his experiments on the application of the power of electro-magnets to moving machinery, after having described a considerable number of other experiments, the principal object of which was to give with the least possible means to a soft-iron horseshoe the greatest possible magnetic power. He took seven different horseshoes, varying from 0·29 to 5 killogrammes^[2] in weight: the copper wire with which he enveloped them, in from 37 to 64 coils, had a diameter of 8·2 to 8·4 mill.; the zinc plates of the four different electromotors had surfaces = ¼, ¾, 2⅓, and 4⅖ square feet each; the dilute acid employed consisted of 160 of sulphuric acid and 160 of nitric acid in 1 of water. With these electro-magnets Dal Negro obtained remarkably powerful results. The largest, (weighing 5 killog., surrounded with 64 coils of copper wire of 8·4 millim. diameter,) with the armature weighing 2 killog., when connected with the largest electromotor, supported from 1 08 up to 1 1 7 killog. Dal Negro attributes the greatness of this effect principally to the weight of the armature, and also to the rounded form of this and also of the poles of the magnet; but he seems to think the great thickness of the wire, namely, 8·4 mill., of no moment. With this important particular the reader is not acquainted till the end of the paper, where a table of the diameter of the wires is added. He infers from his experiments, "that a temporary magnet (as he calls the electro-magnets) can only acquire a magnetic power proportional to its mass;" and says, "experience will show what is the smallest electro-motive surface required to give the maximum of power;" and adds, "these experiments will become the more necessary when electro-magnetic power has been applied to some useful purpose."

The following remarks of Dal Negro on the property of some pieces of iron either not to take any magnetism at all, or only to take it under certain circumstances from the inverted electric current, were to me very mysterious and enigmatical. He says:

I. (1.) "I had several cylindrical soft-iron horseshoes made, of different weight, and experimented with them according to Sturgeon's method; for the most part none of them were at all magnetic. Indeed, in a small bar of iron which was cut into four pieces, and the single pieces made into magnets of the above-mentioned size, only one of them became a powerful magnet; the others were little or not at all magnetic."

(2.) "In the same way curved square bars gave no appreciable results: it appears from this that the cylindrical form is essentially necessary to the development of this temporary magnetism. I also endeavoured, without success, to magnetize hollow cylinders."

(7.) "During the first experiments it often happened that when the weight which the magnet could support had reached its maximum, all on a sudden the horseshoe would become incapable of re-acquiring magnetism, not even so much as to be able to support the keeper again. Van Moll also appears to have observed this phænomenon."

"Fortunately it appeared that by continually weakening [abstumpfen](?) the same magnet, one is enabled to repeat the experiments, and each time make it support a considerable weight."

III. (5.) "It is remarkable that I did not observe with these two magnets (namely, the two strongest,) the phænomena mentioned in the first part of this treatise. No. (7). I am much inclined to believe that this depends upon the magnet being made to support the greatest possible weight for a longer or shorter time. But here I must not omit to mention, that often, when I removed from the magnets the helices which I had been using, either for the purpose of altering the number of coils or the thickness of the wire composing them, the magnets for several dags would not take up the least magnetism. On continuing these experiments I obtained the same phænomenon with the magnet C (weighing 0·29 killog.): the original coil had been removed, but immediately replaced by a smaller number of coils. To this magnet (even after 14 days had elapsed) I could in no way communicate any appreciable magnetic power."

To me these statements are very enigmatical; at least I have never observed anything similar in my own experiments; and not only different horseshoes of soft iron, but several varieties of hardened steel have always appeared to me very susceptible of electro-magnetism; steel of course in a less degree than iron, but notwithstanding much more so than I had expected from the observations of others. Every time when in my experiments no action was observed, or at most only a very feeble action, I found that either the circuit was somewhere interrupted, or the battery was too weak.

I was most interested by the last portion of Dal Negro's paper; it is as follows:

"As I had been successful in producing temporary magnets of very great power with very small electromotors, I endeavoured to apply this new power to moving machinery. I will now briefly state by what means I endeavoured to set a lever in motion. I first used a magnetic steel bar, placed vertically beneath one end of a temporary magnet: the bar vibrated from the attractions and repulsions which took place between its south pole and the north and south poles of the electro-magnet. In the same way a motion may be effected in a horizontal plane. I also set in motion a similar bar, by allowing a piece of iron, set free from the magnet at the moment when its power became = 0, to fall on one of its ends; after this it was immediately re-attracted. This can be effected in two ways; the one may be employed when a quick motion is to be produced, and the second when a greater force is wanted: in the first case the weight falls only just out of the power of the magnet's attraction; and the instant the weight has fallen upon the bar or lever, it is re-attracted by the magnet that the action may be repeated: this weight is always very small in comparison with that which the magnet can support whilst in contact. In the second case the whole weight which the magnet can carry is employed, and use is made of the force which draws it to the magnet. This can be done in several ways. One of them forms a very powerful electro-magnetic ram. I shall not fail to make known the action of this new machine, and hope thereby to satisfy those in particular who are endeavouring to set a machine in motion at the least possible expense."

I must confess that I cannot from this too short and uncertain description form any clear idea of Dal Negro's process, and I am therefore very curious to see his forthcoming paper. I could only clearly understand his fast method of setting a lever in motion, and I determined to make these experiments as soon as I had finished those which I had previously commenced. I hastened the completion of the apparatus so that I was enabled to exhibit it before the Mechanics' Society on the 18th of January. The construction of it is as follows (Plate VII.):

On a small board $A'A'$, resting on four feet, are placed the two similar electro-magnets $GG'$; each of them weighs about the 18th part of a pound, and is wound round with 80 convolutions of copper wire of 0·5 line in diameter, covered with silk: they can be made to recede from or approach each other, and are fixed in their places by wooden screws $JJ'$. The board has in the middle a hole $BB$, cut in it where the poles lie; in this a frame $EE$ is hung, made out of four laths joined together, forming an oblong, of which the long sides are vertical. Under the upper side, and parallel with it, is the iron cylinder or armature $KK'$. Fixed in the side laths, and about 112 inch below it, is placed a stout iron wire $F$ parallel with the cylinder and passing through the sides of the frame, and two pieces of wood $CC$ fixed in the under side of the board $A'A'$; this wire serves as an axis, which allows to the frame a pendulum-like motion. That part of the frame which is below the axis is twice as long as the upper part, and weights $OO$ may be placed on its base $E''E''$. The electric current was conveyed to the electro-magnets through a gyrotrope $PP$, standing on the board $AA$, which serves as a basis to the whole machine. The wires from the electromotors are connected with the two middle cups of mercury $dd'$, in each of which dips the central portion of a wire bent into the form of an anchor $QQ$. These two wires are fixed to a wooden bow, by the motion of which the alternate ends of the two bent wires dip either into the cups on the one side or into those on the other; into the one cup $d$, dip the wires from $f$, coming from the one plate of the electromotor; and into the other cup $d'$, those from the other plate. The motion of this bow is effected in a very simple way by means of the motion of the frame $EE'E''$, so that when the iron cylinder is attracted by the electro-magnet on the right hand, the bow of the gyrotrope is driven by the lower part of the frame to the left hand, by which motion the left-hand electro-magnet is brought into action. The working of this little self-acting apparatus is so quick and efficient, that another small machine, for instance, a wheel, might very easily be set in motion by it. Before the result was quite successful, there was still another difficulty to be overcome. It is a well-known fact that electro-magnets, when the connexion of the wires with the electromotors is interrupted, do not instantly lose all their magnetism, but are capable of carrying a considerable weight for some time. The bad effects which this remaining magnetism would have on the motion of the armature between the two electro-magnets would undoubtedly be greatly counteracted by the magnets being placed with the dissimilar poles opposite to each other. In this form of arrangement it is evident that the magnet in action would be much stronger, and assist in destroying the remaining weaker magnetism in the other magnet. There would therefore be a moment when the magnetism became $=0$, and at that moment I expected that the armature would be disengaged, and then be attracted to the active electro-magnet. However, this interval was of such momentary duration that the armature remained attached to the passive magnet. I then took, instead of the armature of soft iron, a steel magnet of exactly the same form and shape, and placed it so that its poles were always opposite to the similar poles of the electro-magnets; but even with this alteration the same result took place; it also happened when the electric current was sent at the same time, but in an opposite direction, to the other electro-magnet. As the power of the electro-magnet was considerably greater than that of the steel magnet, I could not expect to obtain more powerful effects than I had obtained with the soft iron. At last I determined to prevent any possible contact between the armature and the electro-magnets: this I effected by wrapping the armature up in paper, so as always to keep it at a small distance from the poles of the magnet. The result was now quite satisfactory. I also enveloped the steel magnet in the same way, and it appeared to me that with the first-mentioned armature the motion was quicker and more energetic than with the latter. If we consider that electro-magnets have already been made which were capable of carrying 20 cwt., and that there is no reason to doubt that they may be made infinitely more powerful, I think I may assert boldly that electro-magnetism may certainly be employed for the purpose of moving machines.

1. The translation has been communicated by E. Solly, jun., Esq.
2. [1 millimetre = ·03937 English inch.
   1 killogramme = 2 lbs. 3 oz. 5 dram.—Trans.]