Chapter 5

He admitted that the rights and interests of the work were all carefully guarded by the terms of the resolution, and that the company was not called upon to lay out any of its means for the promotion of the scheme. But notwithstanding all this, he did not feel, as a conscientious man, that he could, without further examination, give his vote for the resolution. He knew that this idea of Mr. Morse, however plausible it might appear to theorists and dreamers, and so-called men of science, was regarded by all practical people as destined, like many other similar projects, to certain failure, and must consequently result in loss and possibly ruin to Mr. Morse. For one, he felt conscientiously scrupulous in giving a vote which would aid or tempt a visionary enthusiast to ruin himself.

Fortunately, the views of this cautious, practical man did not prevail. A few words from the mover of the resolution, Mr. Nicholas, who still lives to behold the wonders he helped to create, and from Mr. Kennedy, without whose aid the appropriation would not have passed the House of Representatives, relieved the other directors from all fear of contributing to Mr. Morse's ruin, and the resolution was adopted. Of the President and thirty directors who took part in this transaction, only three, Samuel W. Smith, John Spear Nicholas, and the writer, survive. Under it Morse at once entered upon that test of his invention whose fruits are now enjoyed by the people of all the continents.

It was not, however, until the spring of 1844 that he had his line and its appointments in such a condition as to allow the transmission of messages between the two cities, and it was in May of that year that the incident occurred which has chiefly led to the writing of this paper.

MR. LATROBE'S RECOLLECTIONS.

MY DEAR MR. POE: Agreeably to my promise, this morning I put on paper my recollection of the introduction of the magnetic telegraph between Baltimore and Washington. I was counsel of the Baltimore & Ohio Railroad Co. at the time, and calling on Mr. Louis McLane, the President, on some professional matter, was asked in the course of conversation whether I knew anything about an electric telegraph which the inventor, who had obtained an appropriation from Congress, wanted to lay down on the Washington branch of the road. He said he expected Mr. Morse, the inventor, to call on him, when he would introduce me to him, and would be glad if I took an opportunity to go over the subject with him and afterward let him, Mr. McLane, know what I thought about it. While we were yet speaking, Mr. Morse made his appearance, and when Mr. McLane introduced me he referred to the fact that, as I had been educated at West Point, I might the more readily understand the scientific bearings of Mr. Morse's invention. The President's office being no place for prolonged conversation, it was agreed that Mr. Morse should take tea at my dwelling, when we would go over the whole subject. We met accordingly, and it was late in the night before we parted. Mr. Morse went over the history of his invention from the beginning with an interest and enthusiasm that had survived the wearying toil of an application to Congress, and with the aid of diagrams drawn on the instant made me master of the matter, and wrote for me the telegraphic alphabet which is still in use over the world. Not a small part of what Mr. Morse said on this occasion had reference to the future of his invention, its influence upon communities and individuals, and I remember regarding as the wild speculations of an active imagination what he prophesied in this connection, and which I have lived to see even more than realized. Nor was his conversation confined to his invention. A distinguished artist, an educated gentleman, an observant traveler, it was delightful to hear him talk, and at this late day I recall few more pleasant evenings than the only one I passed in his company.

Of course, my first visit the next morning was to Mr. McLane to make my report. By this time I had become almost as enthusiastic as Mr. Morse himself, and repeated what had passed between us. I soon saw that Mr. McLane was becoming as eager for the construction of the line to Washington as Mr. Morse could desire. He entered warmly into the spirit of the thing, and laughed heartily, if not incredulously, when I told him that although he had been Minister to England, Secretary of State, and Secretary of the Treasury, his name would be forgotten, while that of Morse would never cease to be remembered with gratitude and praise. We then considered the question as to the right of the company to permit the line to be laid in the bed of the road--the plan of construction at that time being to bury in a trench some eight or ten inches deep a half inch leaden tube containing the wrapped wire that was to form the electric circuit. About this there was, in my opinion, no doubt, and it was not long after that the work of construction commenced. I met Mr. Morse from time to time while he lived, and often recurred to the evening's discussion at my house in Baltimore.

The above is the substance of what I have more than once related to other persons. I hope you will persist in your design of putting on paper your own very interesting recollections in this connection, and if what I have contributed of mine is of service to you, I shall be much pleased.

Most truly yours, JOHN H.B. LATROBE. March 3, 1881.

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THE KRAVOGL ELECTRIC MOTOR.

At the origin of every science, of whatever nature it may be, there is always a fruitless period, of greater or less length, characterized by the warfare of a few superior minds against general apathy. The finest discoveries pass unperceived, so to speak, since they cannot cross the limits of a narrow circle; and it often happens that they fall into oblivion before they have been seriously judged. Meanwhile, a slow progress is imperceptibly made, and, in measure as theoretical principles more clearly disengage themselves, a few industrial applications spring up and have the effect of awakening curiosity. An impulse is thus given, and from this moment a movement in advance goes on increasing at a headlong pace from day to day.

With electricity this period has been of comparatively short duration, since scarcely a century and a half separate us from the first experiments made in this line of research. Now that it has truly taken its place in a rank with the other sciences, we like to go back to the hesitations of the first hour, and trace, step by step, the history of the progress made, so as to assign to each one that portion of the merit that belongs to him in the common work. When we thus cast a retrospective glance we find ourselves in the presence of one strange fact, and that is the simultaneousness of discoveries. That an absolutely original idea, fertile in practical consequences, should rise at a given moment in a fine brain is well; we admire the discovery, and, in spite of us, a little surprise mingles with our admiration. But is it not a truly curious thing that _several_ individuals should have had at nearly the same time that idea that was so astonishing in one? This, however, is a fact that the history of electrical inventions offers more than one example of. No one ignores the fact that the invention of the telephone gave rise to a notorious lawsuit, two inventors having had this ingenious apparatus patented on the same day and at nearly the same hour. This is one example among a thousand. In the history of dynamo-electric machines it is an equally delicate matter to fix upon the one to whom belongs the honor of having first clearly conceived the possibility of engendering continuous currents.

We do not wish to take up this debate nor to go over the history of the question again. Every one knows that the first continuous current electric generator whose form was practical is due to Zenobius Gramme, and dates back to July, 1871, an epoch at which appeared a memoir (entitled "Note upon a magneto-electric machine that produces continuous currents") that was read to the Academy of Sciences by Mr. Jamin. Ten years previous, Pacinotti had had a glimpse of the phenomenon, and of its practical realization, but was unfortunately unable to appreciate the importance of his discovery and the benefit that might be reaped from it. It is of slight consequence whether Gramme knew of this experiment or not, for the glory that attaches to his name could not be diminished for all that. But an interesting fact that we propose to dwell upon now has recently been brought to light in an electrical review published at Vienna.[1] It results from documents whose authenticity cannot be doubted that, as far back as 1867, Mr. L. Pfaundler, a professor at Innsbruck, very clearly announced the reversibility of a magneto-electric motor constructed by Kravogl, a mechanician of the same place, and that he succeeded some time before Gramme in obtaining continuous currents.

[Footnote 1: _Zeitschrift des Electrotechnischen Vereines_ in _Wien_, July, 1883.]

The Kravogl motor that figured at the Universal Exhibition of 1867 is but little known, and it is now very difficult to obtain drawings of it. What is certain is that this motor is an application of the properties of the solenoid, and, from this standpoint, resembles the Bessolo motor that was patented in 1855. We may figure the apparatus to our mind very well if we suppose that in the Gramme ring a half and almost two-thirds of the core are removed, and the spirals are movable around the said core. If a current be sent into a portion of the spirals only, and in such a way that only half of the core be exposed, the latter will move with respect to the bobbin or the bobbin with respect to the core, according as we suppose the solenoid or the bobbin fixed. In the first case we have a Bessolo motor, and in the second a Kravogl one.

In order to obtain a continuous motion it is only necessary to allow the current to circulate successively in the different portions of the solenoid. It is difficult to keep the core in place, since it is unreachable, being placed in the interior of the bobbin. Kravogl solved this difficulty by constructing a hollow core into which he poured melted lead. This heavy piece, mounted upon rollers, assumed a position of equilibrium that resulted from its weight, from friction, and from magnetic attraction. But for a current of given intensity this position, once reached, did not vary, and so necessitated a simple adjustment of the rubbers. Under such circumstances, with a somewhat large number of sections, the polarity of the core was nearly constant. The spirals as a whole were attached to a soft iron armature that had the effect of closing up the lines of forces and forming a shell, so to speak.

Like Bessolo, Kravogl never thought of making anything but a motor, and did not perceive that his machine was reversible. It results from some correspondence between Dr. A. Von Waltenhofen and Mr. L. Pfaundler at this epoch that the latter clearly saw the possibility of utilizing this motor as a current generator. Under date of November 9, 1867, he wrote, in speaking of the Kravogl motor, which had just been taken to Innsbruck in order to send it to Paris. "I regret that I shall not be able to see it any more, for I should have liked to try to make it act in an opposite direction, that is to say, to produce a current or an electric light by means of mechanical work." A little more than two years later these experiments were carried out on a larger motor constructed by Kravogl in 1869, and Mr. Pfaundler was enabled to write as follows: "Upon running the machine by hand we obtain a current whose energy is that of one Bunsen element." This letter is dated February 11, 1870, that is to say, it is a year anterior to the note of Gramme.

In the presence of the historic interest that attaches to the question, we do not think it will be out of place to reproduce here the considerations that guided Prof. Pfaundler in the researches that led him to convert the Kravogl motor into a dynamo-electric machine. Let us consider two magnetized bars, _db_ and _bd'_, placed end to end and surrounded by a cylindrical armature forming a shell, this armature being likewise supposed to be a permanent magnet and to present poles of contrary direction opposite the poles of the bars. For the sake of greater simplicity this shell is represented by a part only in the figure, _s n n s_. If, into a magnetic field thus formed, we pass a spiral from left to right, the spiral will be traversed by a current whose direction will change according to the way in which the moving is done. It is only necessary to apply Lenz's law to see that a reversal of the currents will occur at the points, _a_ and _c_, the direction of the current being represented by arrows in the figure. If we suppose a continual displacement of the spirals from left to right, we shall collect a continuous current by placing two rubbers at _a_ and _c_. Either the core or the shell may be replaced by a piece of soft iron. In such a case this piece will move with the spiral and keep its poles that are developed by induction fixed in space. From this, in order to reach a dynamo-electric machine it is necessary to try to develop the energy of the magnetic field by the action of the current itself. If we suppose the core to be of soft iron, and make a closer study of the action of the current as regards the polarity that occurs under the influence of the poles, _s_, _n_, _s_, we shall see that from _d_ to _a_ and from _b_ to _c_ the current is contrary, while that from _a_ to _b_ and from _c_ to _d'_ it is favorable to the development of such polarity. In short, with a spiral moving from _d_ to _d'_ the resulting effect is _nil_, a fact, moreover, that is self-evident. Under such circumstances, if we suppose the shell, as well as the core, to be of soft iron, we shall obtain a feeble current due to the presence of remanent magnetism; but this magnetism will not be able to continue increasing under the influence of the current. To solve this difficulty two means present themselves: (1) to cause a, favorable magnetic current and act upon the armature, and (2) to suppress such portions of the current in the spirals as are injurious in effect. The first solution was thought of by Gramme in 1871, and is represented diagramatically in Fig. 2. The second is due to Prof. Pfaundler, and dates back to 1870. The core is cut through the center (Fig. 3), and the portion to the right is suppressed; the current is interrupted between _da_ and _cd'_, and is closed only between _a_ and _c_ (_v_, Fig. 1). It results from this arrangement that, under the action of the current, the polarity due to remanent magnetism does nothing but increase. It suffices then for but little remanent magnetism to prime the machine; the polarity of the shell continues to increase, and the energy of the magnetic field, and consequently of the current, has for a limit only the saturation of the soft iron. If, now, we curve the core, the spirals, and the armature into a circle, we have a Gramme or a Pfaundler machine, according as we consider Fig. 2 or Fig. 3.

This latter apparatus has in this case the form shown in Fig. 4.

The spiral, _s m b_, is movable, and the core, N _o s_, is kept in a position of equilibrium by virtue of its weight, and is provided with rollers. For the sake of greater clearness, the front part of the armature is supposed to be removed. The current does not circulate in the spirals to the right of the diameter, W O, which latter is not absolutely vertical. The position of the rubbers and armature is regulated once for all. We do not know just what were the means devised by Kravogl to suppress the current in the spheres to the right. At all events, it is probable that the system has grown old since Gramme invented his collector. In the application of the Kravogl motor to the generation of continuous currents, Professor Pfaundler now proposes to ingeniously utilize the Gramme collector. In such a case the arrangement shown in Fig. 5 would be adopted. Let us suppose an ordinary collector having as many plates as there are sections in the ring, these plates being connected as usual with the entrance and exit wires of the sections. The diametrically opposite touches that are in the line, W O, are divided, and one of the halves is connected at the entrance, _c a'_ (Fig. 4), with the corresponding section, while the other communicates with the exit, _c' a_, of the neighboring section. Each of these halves is prolonged by a piece of metal bent into the form of an arc of a circle and embracing a little less than a semi-circumference. Between these prolongations there is an insulating part. In the rotary motion of the spiral, at least one of the touches is always outside of the arc comprised between the brushes, R. In order to secure a continuity of the circuit in the effective arc, W S_ o_, it is only necessary to arrange a rubber, M, in such a way as to establish a communication between the two parts of the divided touch as soon as this latter enters the arc under consideration.

In order to produce a current in the direction of the arrows shown in Fig. 4, the spiral and axle must revolve from right to left. In this case the rubber, M, occupies the position shown in the same figure, the brushes embracing an arc of a little less than 180°. As soon as the lower touch comes in contact with the brush, R, when the revolution is being effected from left to right, the rubber, M, establishes a communication between the two halves that have until now been isolated, and the current is no longer interrupted. The second touch during this time is at any point whatever of the arc, W N _o_, and the spirals corresponding to the latter arc outside of the circuit. In short, thanks to the rubber, M, we have an ordinary Gramme collector in that portion of the circuit comprised between the brushes, and a collector with a breakage of the circuit in the portion to the right.

This type of machine is entirely theoretical. In the apparatus used for Prof. Pfaundler's experiments in 1870, the armature revolved with the solenoid. The core and armature were of soft iron, and the core was arranged in a manner analogous to the preceding, and remained in place under the action of its weight, and the shell, forming a complete circle, revolved with poles fixed in space.

Practically, the machine that we have just described would prove inconvenient to realize, and would present serious inconveniences. In the first place, it seems to us quite difficult to transmit the motion of the solenoid to the axle, supposing the former to revolve within the armature. In the second place, considerable friction would surely occur between the spirals and core, and the axle, being submitted to a lateral stress, would be placed in a poor condition for work. It is even allowable to doubt whether such a type could be practically got up. At all events, no trial has as yet been made of it.

Compared with the Gramme machine, from an absolutely theoretical point of view, the Pfaundler apparatus presents undoubted advantages. A theoretically perfect dynamo electric machine would be one in which there was a complete reciprocity between the magnetizing action of the current and the inductive action of the magnetic field. Now, such is not the case in the Gramme machine. In this apparatus the soft iron core is at the same time a magnet through favorable induction and a disadvantageous electro-magnet. This double polarization is only remedied to a certain extent by the adjustment of the brushes. In the Pfaundler machine, on the contrary, the electro-magnetism and magnetism through induction act in the same direction, and concur in effecting a polarization that favors the production of the current. Looked at it in this light, the latter machine more nearly approaches the type of perfection than does that of Gramme.

But we must not forget that such qualities are purely theoretical. In practice the best machine is that in which the copper is best utilized, that is to say, that which with a given weight of this metal furnishes the most work. Now, this is certainly not the case in the Pfaundler machine, for here half or more than half of the ring is inert--a defect which is apparent at first sight. It results from this that as soon as we propose to obtain an electromotive force, however slight it be, we must get it with machines of large dimensions. Now, it is permissible to believe that under such circumstances (taking into consideration the complication of mechanical means that the construction of such apparatus necessitates, and the great friction that occurs) it would be impossible to obtain practical rotary velocities. Comparing his machine with Gramme's, Prof. Pfaundler expresses the idea that between them there is the same analogy as there is between a constant pressure and an expansion engine. With cylinders of equal diameters the work performed by the former of these is greater than that done by the second, but in the latter the expansive force of the steam is better utilized. This comparison seems to us to be more ingenious than exact. Would it not be coming nearer to the truth if we were to suppose a case of a hydraulic motor whose performance continued diminishing with the height of the fall, and would it not be advantageous under such circumstances to utilize only a portion of the fall for the purpose of increasing the motor's performance?

This machine, however, as before stated, has never as yet been constructed, so that experimental data relative to its mode of working are wanting. It is especially interesting as regards its origin, which dates back to an epoch at which researches on the dynamo electric machine were at their heat. It is in its historical aspect that it is proper to regard it, and it is from such a point of view that we have deemed it well to say a few words about it in this place.--_La Lumiere Electrique._

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BORNHARDT'S ELECTRIC MACHINE FOR BLASTING IN MINES.

We shall not attempt to pass in review the several apparatus that have hitherto been devised for igniting blasts in mining operations, but shall simply describe in this place a machine recently invented for this purpose by Mr. Bornhardt, an engineer to the Grand Duke of Brunswick.

This apparatus (shown in the accompanying engravings) consists essentially of two hard-rubber disks, A (Figs. 2 and 3), keyed to an iron axle, and of two rubbers, B, that are formed of skin and are held against the disks by small springs, R; motion is communicated to the axle, _a_, by means of a pair of gearings, _a_ and _b_, and a crank, _f_.

Each disk revolves between two metallic rings, _c_, provided with points that attract and collect in Leyden jars, D, the electricity produced by the friction. For discharging the condensers there is employed a manipulator formed of a rod, mm, which can be acted upon, from the exterior, by means of a button, _k_. Upon bringing the ball, _m_, of the rod in contact with the ball, _p_, of the condenser, the lever (which then takes the position shown by the dotted line) continues to remain in connection with a small ring, _q_, through a special spring. Another ring, _t_, is connected in the same way with the external armature of the condenser. Upon connecting the rings, _p_ and _t_, by a wire to which cartridges are attached, any number of the latter may be ignited.