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Scientific American Supplement, No. 315, January 14, 1882试读：
THE ELECTRO-MAGNETIC APPARATUS OF DR．PACINOTTI.
In admiring the recent developments of electric science as evidenced by the number of important inventions which have during the past few years been given to the world, especially in those branches of applied science which deal more particularly with the generation of electricity and the production of the electric light, there is often too great a tendency to forget, or, at least, to pass over in comparative silence the claims which the great pioneer workers and discoverers undoubtedly have to a large share of the merit of this scientific development.
It is, of course, obviously impossible in anything approaching a retrospect of the science of magneto-electric induction or its application to illumination to pass slightly over the names of Oersted, of Ampère, of Davy, and of Faraday, but, in other respects, their work is too often lost sight of in the splendid modern developments of their discoveries．Again, there is another group of discoverer-inventors who occupy an intermediate position between the abstract discoverers above named and the inventors and adapters of still more recent times．To this group belong the names of Pixii and Saxton, Holmes and Nollet, Wilde, Varley, Siemens, Wheatstone, and Pacinotti, who was the first to discover a means of constructing a machine capable of giving a continuous current always in the same direction, and which has since proved itself to be the type of nearly all the direct current electric machines of the present day, and especially those such as the Gramme and Brush and De Meritens machines, in which the rotating armature is of annular form; and when it is considered what a large number of the well known electric generators are founded upon this discovery, it must be a matter of general gratification that the recent International Jury of the Paris Exhibition of Electricity awarded to Dr．Antonio Pacinotti one of their highest awards.
The original machine designed by Dr．Pacinotti in the year 1860, and which we illustrate on the present page, formed one of the most interesting exhibits in the Paris Exhibition, and conferred upon the Italian Section a very distinctive feature, and we cannot but think that while all were interested in examining it, there must have been many who could not help being impressed with the fact that it took something away from the originality of design in several of the machines exhibited in various parts of the building.
This very interesting machine was first illustrated and described by its inventor in theNuovo Cimento in the year 1864, under the title "A Description of a Small Electro-Magnetic Machine," and to this description we are indebted for the information and diagrams contained in this notice, but the perspective view is taken from the instrument itself in the Paris Exhibition.
In this very interesting historical communication the author commences by describing a new form of electro-magnet, consisting of an iron ring around which is wound (as in the Gramme machine) a single helix of insulated copper wire completely covering the ring, and the two ends of the annular helix being soldered together, an annular magnet is produced, enveloped in an insulated helix forming a closed circuit, the convolutions of which are all in the same direction．If in such a system any two points of the coil situated at opposite ends of the same diameter of the ring be connected respectively with the two poles of a voltaic battery, the electric current having two courses open to it, will divide into two portions traversing the coil around each half of the ring from one point of contact to the other, and the direction of the current, in each portion will be such as to magnetize the iron core, so that its magnetic poles will be situated at the points where the current enters and leaves the helix, and a straight line joining these points may be looked upon as the magnetic axis of the system．From this construction it is clear that, by varying the position of the points of contact of the battery wires and the coil, the position of the magnetic axis will be changed accordingly, and can be made to take up any diametrical position with respect to the ring, of which the two halves (separated by the diameter joining the points of contact of the battery wires with the coil) may be regarded as made up of two semicircular horseshoe electro-magnets having their similar poles joined．To this form of instrument the name "Transversal electro magnet" (Eletro calamita transversale) was given by its inventor, to whom is undoubtedly due the merit of having been the first to construct an electro-magnet the position of whose poles could be varied at will by means of a circular commutator.PACINOTTI ELECTRO-MAGNETIC MACHINE.—MADE IN 1860.
By applying the principle to an electro-magnetic engine, Dr．Pacinotti produced the machine which we illustrate on the present page．The armature consists of a turned ring of iron, having around its circumference sixteen teeth of equal size and at equal angular distance apart, as shown in Fig.1, forming between them as many spaces or notches, which are filled up by coiling within them helices of insulated copper wire,r r r, in a similar manner to that adopted in winding the Brush armature, and between them are fixed as many wooden wedges,m m, by which the helices are firmly held in their place．All the coils are wound round the ring in the same direction, and the terminating end of each coil is connected to the commencing end of the next or succeeding helix, and the junctions so made are attached to conducting wires which are gathered together close to the vertical shaft on which the armature ring is fixed, passing through holes at equal distances apart in a wooden collar fixed to the same shaft, and being attached at their lower extremities to the metallic contact pieces of the commutator,c, shown at the lower part of Fig.3, which is an elevation of the machine, while Fig.4 is a plan of the same apparatus.
The commutator consists of a small boxwood cylinder, carrying around its cylindrical surface two rows of eight holes, one above the other, in which are fitted sixteen contact pieces of brass which slightly project above the surface of the wood, the positions of those in the upper circle alternating or "breaking joint" with those in the lower, and each contact piece is in metallic connection with its corresponding conducting wire, and, therefore, with the junction of two of the helices on the armature．Against the edge of the commutator are pressed by means of adjustable levers two small brass contact rollers,k k, which are respectively connected with the positive and negative poles of the voltaic battery (either through or independent of the coils of a fixed electro-magnet, to which we shall presently refer), and the magnetic axis of the ring will lie in the same plane as the line joining the points of contact of the battery and rotating helix, this axis remaining nearly fixed notwithstanding the rotation of the iron ring in which the magnetism is induced.
In the apparatus figured in Figs.3 and 4, the armature rotates between the two vertical limbs, A B, of a fixed electro-magnet furnished with extended pole pieces, A A, B B (Fig.4), each of which embraces about six of the armature coils．The fixed electro-magnet is constructed of two vertical iron cylindrical bars, A and B, united at their lower extremities by a horizontal iron bar, F F, the one being rigidly and permanently attached to it, while the other is fastened to it by a screw, G, passing through a slot so that the distance of the pole pieces from one another and from the armature ring is capable of adjustment.
The connections of the machine, which are shown in Fig.3, are made as follows: The positive current, entering by the attachment screw,h, passes by a wire to the right hand commutator screw,l, to the right-hand roller,k, through the commutator to the ring, around which it traverses to the left-hand roller,k¹, and screw,l¹, to the magnet coil, A, and thence through the coil of the magnet, B, to the terminal screw,h, on the right hand of the figure．This method of coupling up is of very great historical interest, for it is the first instance on record of the magnet coils and armature of a machine being included in one circuit, giving to it the principle of construction of a dynamo-electric machine, and antedating in publication, by two years, the interesting machines of Siemens, Wheatstone, and Varley, and preceding them in construction by a still longer period.
With this apparatus Dr．Pacinotti made the following interesting experiments with the object of determining the amount of mechanical work produced by the machine (when worked as an electro-magnetic engine), and the corresponding consumption of the elements of the battery: Attached to the spindle of the machine was a small pulley, Q Q (Fig.3), for the purpose of driving, by means of a cord, another pulley on a horizontal spindle carrying a drum on which was wound a cord carrying a weight, and on the same spindle was also a brake and brake-wheel, the lever of which was loaded so as just to prevent the weight setting into motion the whole system, consisting of the two machines, when no current was flowing．In this condition, when the machine was set in motion by connecting the battery, the mechanical work expended in overcoming the friction of the brake was equal to that required to raise the weight; and, in order to obtain the total work done, all that was necessary was to multiply the weight lifted by the distance through which it was raised．The consumption of the battery was estimated at the same time by interposing in the circuit a sulphate of copper voltameter, of which the copper plate was weighed before and after the experiment．The following are some of the results obtained by Dr．Pacinotti in experimenting after the manner just described．With the current from a battery of four small Bunsen elements, the machine raised a weight of 3.2812 kilos to a height of 8.66 m．(allowing for friction), so that the mechanical work was represented by 28.45 m．During the experiment the positive plate of the voltameter lost in weight 0.224 gramme, the negative gaining 0.235 gramme, giving an average of chemical work performed in the voltameter of 0.229 gramme, and multiplying this figure by the ratio between the equivalent of zinc to that of copper, and by the number of the elements of the battery, the weight of zinc consumed in the battery was computed at 0.951 gramme, so that to produce one kilogrammeter of mechanical work 33 milligrammes of zinc would be consumed in the battery．In another experiment, made with five elements, the consumption of zinc was found to be 36 milligrammes for every kilogrammeter of mechanical work performed．In recording these experiments, Dr．Pacinotti points out that although these results do not show any special advantage in his machine over those of other construction, still they are very encouraging, when it is considered that the apparatus with which the experiments were made were full of defects of workmanship, the commutator, being eccentric to the axis, causing the contacts between it and the rollers to be very imperfect and unequal.
In his communication to theNuovo Cimento, Dr．Pacinotti states that the reasons which induced him to construct the apparatus on the principle which we have just described, were: (1) That according to this system the electric current is continuously traversing the coils of the armature, and the machine is kept in motion not by a series of intermittent impulses succeeding one another with greater or less rapidity, but by a constantly acting force producing a more uniform effect．(2) The annular form of the revolving armature contributes (together with the preceding method of continuous magnetization) to give regularity to its motion and at the same time reduces the loss of motive power, through mechanical shocks and friction, to a minimum．(3) In the annular system no attempt is made suddenly to magnetize and demagnetize the iron core of the rotating armature, as such changes of magnetization would be retarded by the setting up of extra currents, and also by the permanent residual magnetism which cannot be entirely eliminated from the iron; and with this annular construction such charges are not required, all that is necessary being that each portion of the iron of the ring should pass, in its rotation, through the various degrees of magnetization in succession, being subjected thereby to the influence of the electro-dynamic forces by which its motion is produced．(4) The polar extension pieces of the fixed electro-magnet, by embracing a sufficiently large number of the iron projecting pieces on the armature ring, continue to exercise an influence upon them almost up to the point at which their magnetization ceases when passing the neutral axis．(5) By the method of construction adopted, sparks, while being increased in number, are diminished in intensity, there being no powerful extra currents produced at the breaking of the circuit, and Dr．Pacinotti points out that when the machine is in rotation a continuous current is induced in the circuit which is opposed to that of the battery; and this leads to what, looked at by the light of the present state of electric science, is by far the most interesting part of Dr．Pacinotti's paper, published, as it was, more than seventeen years ago.
In the part to which we refer, Dr．Pacinotti states that it occurred to him that the value of the apparatus would be greatly increased if it could be altered from an electro-magnetic to a magneto-electric machine, so as to produce a continuous current．Thus, if the electro-magnet, A B (Figs.3 and 4), be replaced by a permanent magnet, and the annular armature were made to revolve, the apparatus would become a magneto-electric generator, which would produce a continuous induced current always in the same direction, and in analyzing the action of such a machine Dr．Pacinotti observes that, as the position of the magnetic field is fixed, and the iron armature with its coils rotates within it, the action may be regarded as the same as if the iron ring were made up of two fixed semicircular horseshoe magnets with their similar poles joined, and the coils were loose upon it and were caused to rotate over it, and this mode of expressing the phenomenon was exactly what we adopted when describing the Gramme machine, without having at that time seen what Dr．Pacinotti had written fifteen years before.
In explanation of the physical phenomena involved in the induction of the electric currents in the armature when the machine is in action as a generator, Dr．Pacinotti makes the following remarks: Let us trace the action of one of the coils in the various positions that it can assume in one complete revolution; starting from the position marked N, Fig.2, and moving toward S, an electric current will be developed in it in one direction while moving through the portion of the circle, Na, and after passing the point,a, and while passing through the arc,a S, the induced current will be in the opposite direction, which direction will be maintained until the point,b, is reached, after which the currents will be in the same direction as between N anda; and as all the coils are connected together, all the currents in a given direction will unite and give the combined current a direction indicated by the arrows in Fig.2, and in order to collect it (so as to transmit it into the external circuit), the most eminent position for the collectors will be at points on the commutator at opposite ends of a diameter which is perpendicular to the magnetic axis of the magnetic field．With reference to Fig.2, we imagine either that the two arrows to the right of the figure are incorrectly placed by the engraver, or that Dr．Pacinotti intended this diagram to express the direction of the current throughout the whole circuit, as if it started froma, and after traversing the external circuit entered again atb, thus completing the whole cycle made up of the external and internal circuits.
Dr．Pacinotti calls attention to the fact that the direction of the current generated by the machine is reversed by a reversal of the direction of rotation, as well as by a shifting of the position of the collectors from one side to the other of their neutral point, and concludes his most interesting communication by describing experiments made with it in order to convert it into a magneto-electric machine．"I brought," he says, "near to the coiled armature the opposite poles of two permanent magnets, and I also excited by the current from a battery the fixed electro-magnets (see Figs.3 and 4), and by mechanical means I rotated the annular armature on its axis．By both methods I obtained an induced electric current, which was continuous and always in the same direction, and which, as was indicated by a galvanometer, proved to be of considerable intensity, although it had traversed the sulphate of copper voltameter which was included in the circuit."
Dr．Pacinotti goes on to show that there would be an obvious advantage in constructing electric generating machines upon this principle, for by such a system electric currents can be produced which are continuous and in one direction without the necessity of the inconvenient and more or less inefficient mechanical arrangements for commutating the currents and sorting them, so as to collect and combine those in one direction, separating them from those which are in the opposite; and he also points our the reversibility of the apparatus, showing that as an electro-magnetic engine it is capable of converting a current of electricity into mechanical motion capable of performing work, while as a magneto-electric machine it is made to transform mechanical energy into an electric current, which in other apparatus, forming part of its external circuit, is capable of performing electric, chemical, or mechanical work.
All these statements are matters of everyday familiarity at the present day, but it must be remembered that they are records of experiments made twenty years ago, and as such they entitle their author to a very distinguished place among the pioneers of electric science, and it is somewhat remarkable that they did not lead him straight to the discovery of the "action and reaction" principle of dynamo-electric magnetic induction to which he approached so closely, and it is also a curious fact that so suggestive and remarkable a paper should have been written and published as far back as 1864, and that it should not have produced sooner than it did a revolution in electric science.—Engineering.
THE ELIAS ELECTROMOTOR.
We lately published a short description of a very interesting apparatus which may be considered in some sense as a prototype of the Gramme machine, although it has very considerable, indeed radical differences, and which, moreover, was constructed for a different purpose, the Elias machine being, in fact, an electromotor, while the Gramme machine is, it is almost unnecessary to say, an electric generator．This apparent resemblance makes it, however, necessary to describe the Elias machine, and to explain the difference between it and the Gramme．Its very early date (1842), moreover, gives it an exceptional interest．The figures on the previous page convey an exact idea of the model that was exhibited at the Paris Electrical Exhibition, and which was contributed by the Ecole Polytechnique of Delft in the Dutch Section．This model is almost identical with that illustrated and described in a pamphlet accompanying the exhibit．The perspective illustrations show the machine very clearly, and the section explains the construction still further．The apparatus consists of an exterior ring made of iron, about 14 in．in diameter and 1.5 in wide．It is divided into six equal sections by six small blocks which project from the inner face of the ring, and which act as so many magnetic poles．On each of the sections between the blocks is rolled a coil, of one thickness only, of copper wire about 0.04 in．in diameter, inclosed in an insulating casing of gutta percha, giving to the conductor thus protected a total thickness of 0.20 in.; this wire is coiled, as shown in the illustration．It forms twenty-nine turns in each section, and the direction of winding changes at each passage in front of a pole piece．The ends of the wire coinciding with the horizontal diameter of the ring are stripped of the gutta percha, and are connected to copper wires which are twisted together and around two copper rods, which are placed vertically, their lower ends entering two small cavities made in the base of the apparatus．The circuit is thus continuous with two ends at opposite points of the same diameter．The ring is about 1.1 in．thick, and is fixed, as shown, to two wooden columns, B B, by two blocks of copper,a.THE ELIAS ELECTROMOTOR.—MADE IN 1842.
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