Chapter 7

It will be seen that the Thury armature resembles, in the system of winding, those of the Siemens machines and their derivatives. But it differs from these, however, in the details connected with the coupling of the wires, from the very fact that the features of a two-pole machine are not found exactly in a multipolar one.

This latter kind of machine is considered advantageous by its inventors, in that there is no need of revolving it with much velocity. It must not be forgotten, however, that although we reduce the velocity by this mode of construction, we are, on another hand, obliged to increase the size of the machine, so that, according to the circumstances under which we chanced to be placed, the advantage may now be on the one side and now on the other.

It goes without saying that Fig. 4 is essentially diagrammatic, and is designed to give a clearer idea of the mode of winding the armature. In practice the number of the frames, and consequently that of the plates of the conductor, is much greater, and the arrangement that we have described is repeated a certain number of times, the conducter always forming a circuit that is closed upon itself.

The Thury machines are constructed in different styles. No. 1 is a 100-lamp (16 candles and 100 volts) machine, and Nos. 2 and 3 are nominally 250-lamp ones, but may be more. Their weight is 1,100 kilogrammes, and their velocity, for 100 volts, is from 400 to 500 revolutions, according to the mode of coupling.

A later type, now in course of construction, is to furnish from 750 to 2,000 lamps, with 250 revolutions, for 100 volts, and is not to weigh more than 2,000 kilogrammes. Let us add that Messrs. Meuron and Cuenod, the manufacturers, have likewise applied their mode of winding to conductors arranged radially upon the surface of a circle. Fig. 5 shows this arrangement.

In this case the inductors will, it is unnecessary to say, be arranged laterally as in all flat ring machines. The arrangement will recall, for example, that of the Victoria machines (Brush-Mordey).

We do not think that the inventors have applied this radial arrangement practically, for it does not appear to be advantageous. The parts of conductors which are perpendicular to the radius, and which can be only inert (even if they do not become the seat of disadvantageous currents), have, in fact, too great an importance with respect to the radial parts.--_A. Guerout, in La Lumiere Electrique_.

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BREGUET'S TELEPHONE.

Prof. G. Forbes gives the following description: The instrument which I call Breguét's telephone is founded upon the instrument which was described by Lipmann, called the capillary electrometer. The phenomenon may be shown in a variety of ways. One of the easiest methods to show it is by taking a long glass tube and bending it into two glasses of dilute acid, and, the tube being filled with acid itself, a piece of mercury is placed in the center of the tube. Then if one pole of a battery is connected with one vessel of acid, and the other pole of the battery is connected with the other vessel of acid, at the moment of connection the bit of mercury will be seen to travel to the right or left, according to the direction of the current. M. Lipmann explained the action by showing that the electro-motive force which is generated tends to alter the convexity of the surface of the mercury. The surface of the mercury, looked at from one side, has a convex form, which is altered by the electro-motive force set up when connection is made with the battery. The equilibrium of the mercury is dependent upon the convexity, and consequently when the convexity is disturbed the mercury moves to one side or the other. Lipmann also showed that if a tube containing a bit of mercury, and tapering to a point, is taken and dipped into acid, and then the tube filled with acid, on one pole of a battery being dipped into the tube and another into the acid the mercury will move up or down, showing similar action to that which I have just described.

Lipmann further showed the reverse effect, that if a piece of mercury be forcibly pressed, so as to alter the convexity of its surface, such as by bringing it into a narrower part of the tube, then there is an electro-motive force produced.

It occurred to me, and no doubt it did to Breguet also, that if we speak either against the surface of the glass tube, and caused the tube to vibrate, or if the mercury were caused to vibrate in the manner I have shown, we ought to be able to introduce a varying current in the wires which might have sufficient electro-motive force to produce audible speech in a Bell telephone. Further, the same instrument, since varying electro-motive force affected the drop of mercury and produced varying displacement, ought also to act as a receiving instrument, and should vibrate in accordance with the currents that arrive. My experiments have only been in the way of using the instrument as a transmitter; but Breguét, I find, used it as a receiver as well as a transmitter, though I am not aware that M. Breguet made any actual experiments so as to produce articulate speech. I presume that this was done, although I have not come across any description of the experiments, and it was for that reason that I thought possibly some account of my own experiments might be interesting to the members of the Society. The first tubes that I used were bits of glass tube about a centimeter diameter, and simply drawn out to a tapering point. I have the tubes here. The first experiment I tried was by tapping the glass tube so as to mechanically shift the position of the mercury, and by listening on the telephone for the effect. For a long time, at least an hour, I could get no effect at all. At last I got a sound, but could not understand how it was that at one time of tapping I could not hear, while at another time it was quite loud.

At the top I always got sound, but at the side I got no sound, although the mercury was shaking. I then tried to see how feeble a current was audible in the telephone. An assistant tapped the tube while I stood out of the way, and where I could not see. I got him to tap it gentler and gentler, and could hear the most feeble tap. A pellet of paper was next dropped from various heights down to an inch, and each tap was perfectly audible in the telephone. I tried many methods, and one, purely accidentally chosen, was a piece of glass tube which I had drawn out into a tube about 2 mm. diameter, and then nearly closed the end of it. I have that tube here, and you will see what an ill-shapen and ugly-looking tube it is, but it is one of the best tubes I ever got; and finally, I found that small bits of thermometer tube, which were simply closed at their ends with a blow-pipe, gave very good results, and I was able to make them useful for various purposes. I then tried mounting a tube on the end of a speaking-trumpet and speaking to the mercury, but got no effect. In every place where I attached the glass tube itself to a sounding-board I got a very accurate reproduction. I put one on a piece of ferrotype plate, and that gave really the best result I ever got. The tube was fastened with sealing-wax, and with it I got excellent speech heard in a Bell receiver. I tried putting in a large number of these tubes, all in quantity, on the bottom of a ferrotype plate, but with no advantage. I have not yet tried putting them in series, one behind the other, so as to increase the electro-motive force, but I think that probably would be an improvement; of course it would require many vessels of acidulated water to dip into. The most distinct articulate speech was obtained from an ordinary ferrotype telephone plate, secured at the edges, and one of the glass tubes you see here attached to it.

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MUNRO'S TELEPHONIC EXPERIMENTS.

Mr. J. Munro, whose name is well known not only as a very clear writer upon electrical subjects, but as an original investigator, has recently, with the assistance of Mr. Benjamin Warwick, been conducting a most interesting experimental investigation of the action of the microphone as a telephonic transmitter, with the result of proving that metals may advantageously be employed in the place of carbon in a transmitting instrument, a practical development of one of the very earliest of Professor Hughes' microphones. The fact that metallic electrodes can practically be employed in microphonic transmitters has been denied of late with so much assurance and in such high quarters, that Mr. Munro's successful applications of that portion of Professor Hughes' discovery possess an especial interest, and must to a considerable extent affect the aspect of litigation in future contests in which the discovery of the microphone and the invention of the carbon transmitter are vital points at issue.

In investigating the properties of metallic conductors employed in the construction of microphones, Mr. Munro's first experiments were made with wires. These, in some cases, were caused by the action of a diaphragm, to rub the one on the other in such a manner as to make the point of contact vary (under the influence of the vibrations of the diaphragms) on one side or other of a position of normal potential, so that by the movement of a wire attached to a vibrating tympan along a fixed wire conveying a current from a battery, and thereby shunting the current at various positions along the length of the fixed wire, the strength of the current in the derived circuit, in which was included a suitable receiver, was varied accordingly. In other experiments mercury was employed, either as a sliding-drop, inclosing the fixed wire, or as an oscillating column; but these experiments, though instructive and interesting, did not for various reasons give encouraging results with a view to the practical application of the principle.

They, however, led Mr. Munro to proceed with compound wire structures, such as gratings resting upon or rubbing against one another, and one of the first experiments in this direction proved very successful, and led Mr. Munro to the construction of his gauze telephone, which is the most characteristic and efficient of his practical apparatus.

This instrument consists essentially of two pieces of iron-wire gauze, the one fixed in a vertical plane, and the other resting more or less lightly against it, the pressure between them being regulated by an adjustable spring or weight. These gauze plates are so connected in a telephonic circuit as to constitute the electrodes of a microphone; for touching one another lightly in several points, they allow the current to be transmitted between them in inverse proportion to the resistance offered to it in its passage from one to the other. Under the influence of sonorous vibrations the one plate dances more or less on the other, thus varying the resistance; and very perfect articulation is produced in a telephonic receiver included in the circuit. The gauze transmitter so constructed may be fixed within a wall-box with or without a mouthpiece; but as the sound waves acting directly upon the gauze plates set them into agitation through their sympathetic vibration or by direct impact, no sort of diaphragm or equivalent device is necessary, and none is employed.

A convenient form of this apparatus is shown in Fig. 1, and to which the name of "The Lyre Telephone" has been given from its resemblance to that impossible musical instrument. In this apparatus, G¹ is a plate of iron wire gauze stretched vertically between two horizontal wires attached to a lyre-shaped framework of mahogany; against the plate rests the smaller plate, G², the normal pressure between them being regulated by an adjustable spring acting in opposition to a weighted lever, W. The two plates are connected respectively with the attachment screws, X and Y, by which the instrument is placed in a circuit with a battery and telephonic circuit.

A modification of this apparatus is shown in the diagram sketch, Fig. 2, which will probably be a more practical form. In this instrument the electrodes consist of two circular disks of iron wire gauze of different diameters, the larger disk, G¹, which is fixed, being pierced with holes of smaller diameter than the smaller disk, G². In the diagram the two disks are shown separated for the purpose of explanation, but in reality they rest the one against the other; the smaller and movable disk, G², is held up against G¹ with greater or less pressure by the spiral spring, S, the tension of which can be adjusted by a screw or other suitable device at N. This form of the apparatus is more suitable for inclosure in a wall box with or without a mouthpiece, but it does not require the employment of any kind of diaphragm or tympan. Mr. Munro can employ with all his instruments an induction coil for installations where the resistance of the line wire makes it desirable to do so; the microphone and battery being included in the primary circuit and the telephones in the secondary.

Fig. 3 is an ingenious arrangement devised by Mr. Munro, in which the adjusting spring or weight is substituted by a magnet which may be either a permanent or an electro-magnet. The figure shows an arrangement in which the fixed gauze, g¹, is perforated as in the apparatus illustrated in Fig. 2, and the movable electrode, g, is bent or dished so as to press upon g¹ around its edge. E is a magnet which by its attractive influence upon g holds t up against g¹ with a pressure dependent upon its magnetic intensity and upon its distance from the gauze. By making E an electro-magnet, and including its coil in the telephonic circuit, an instrument may be constructed in which the normal pressure between the electrodes can be automatically adjusted to the strength of the current, and in cases where an induction coil is employed the magnet, E, may be the core of such a coil.

Fig. 4 illustrates an apparatus devised by Mr. Munro, and to which the name thermo-microphone might be given, as it is a microphone in which thermo-electric currents are employed in the place of voltaic currents, its special feature of interest lying in the fact that the heated junction of the thermo-electric couple is identical with the microphone contacts of the two electrodes. In this very elegant experiment a piece of iron wire gauze, G, is supported in a horizontal position by a light metallic support, B. To another support. A, is loosely hinged a frame, which at its further extremity carries a little coil of German silver wire, C, which by its weight rests upon the center of the gauze plate, G; and in contact therewith, and to increase the pressure of contact, a little bar weight is laid within the convolutions of the core. The two electrodes, the gauze, and the coil are connected, as shown, to a receiving telephone, T. Upon the application of heat, as from the flame of a spirit lamp placed below, a thermo-electric current is set up throughout the circuit; in this condition the apparatus becomes a very perfect microphone, and when the pressure between the electrodes is properly adjusted it is a very efficient telephonic transmitter, transmitting articulate speech and musical sounds with remarkable clearness and fidelity.

Mr. Munro is, with the aid of Mr. Warwick's manipulative skill, extending this portion of his investigation further by experimenting with gauzes and coils of various metals forming other couples in the thermo-electric series, as well as with iron and other gauzes electrotyped with bismuth and other metals, and we hope in due time to lay the results of those experiments before our readers.

Mr. Munro has, moreover, observed that if two pieces of gauze of identical material and in microphonic contact be heated, a peculiar sighing sound is heard in a telephone connected with them and with a battery, and he attributes this phenomenon to the electrical discharge between the gauze plates being facilitated and increased by the action of heat, but we are rather inclined to trace the effect to the mechanical action of the one gauze moving over the other under the influence of expansion and contraction of the metals by the variable temperature of the flame and convection currents of heated air, such movement producing the sounds just as would be produced if one of the electrodes of an ordinary microphone were as delicately moved by the hand or other agent.

Figs. 5 and 6 illustrate another and distinct form of metallic microphone transmitter designed by Mr. Munro and Mr. Warwick, in which a small chain, preferably of iron, forms the microphonic portion of the apparatus. In Fig. 5, A is a plate of sonorous wood forming a diaphragm or collector of the sonorous waves; to the back of this is attached a short length of chain, C, the opposite ends of which are by the wires, X and Y, included in the telephonic circuit. The points of junction of the links with one another constitute the variable microphonic contacts, and the normal pressure between them is adjusted by the spiral spring, S, the tension of which may be varied by the cord and winding pin, B. Fig. 6 is the section of a transmitter constructed upon this principle, and in which two chains, c and c', are employed attached at one end by a wire, f, to a diaphragm mouthpiece, N, and at their opposite extremities to the adjusting springs, s and s'; an induction coil, D, may be employed if the resistance of the line render it advantageous.

Fig. 7 is a form of pencil microphone experimented with by Mr. Munro, which differs from some of the Hughes' transmitters adopted by Crossley, Gower, Ader, and many others only in the material of which it is composed, Mr. Munro's being of cast iron, while the others to which we have referred are of carbon rods such as are used in electric lighting. In Fig. 7 a light cast-iron bar, i², of the form shown, is supported in holes drilled in two blocks of cast iron, i i', and the pressure between the bar and the blocks can be adjusted by a regulating spring, s. In connection with this apparatus Mr. Munro has observed that rust has no appreciable effect upon the efficiency of the instrument unless it be to such an extent as to cause the two to adhere, or to be "rusted up" together.

We now come to another class of metallic transmitters with which Mr. Munro and his associate have been making experiments, and to which he has given the name "Grain transmitter," since it consists of a box having metallic sides, e e', to which terminal screws, t t', are attached and filled in between with iron or brass filings, granules of spongy iron, or indeed small metallic particles in any form; one of the most efficient transmitters being a box such as is shown in Fig. 8, filled with a quantity of ¼ in. screws.

The results of Mr. Munro's experiments have led him to the opinion that the action of the microphone must be attributed to the action of sonorous vibrations upon the air or gaseous medium separating the so-called contact-points of the electrodes, and that across these spaces, or films of gaseous matter, silent electrical discharges take place, the strengths of which, being determined by the thickness of the gaseous strata through which they pass, vary with the motion of the electrodes; and as, according to this hypothesis, the distances of the electrodes from one another is determined by the sound-waves, the sound in that way controls the current.--_Engineering_.

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APPARATUS FOR MANEUVRING BICHROMATE OF POTASSA PILES FROM A DISTANCE.

Bichromate of potassa piles, especially those single liquid ones that are applied to domestic lighting, all present the grave defect of consuming almost as much zinc in open as in closed circuit, and of becoming rapidly exhausted if care be not taken to remove the zinc from the liquid when the battery is not in use. This operation, which is a purely mechanical one, has hitherto required the pile to be located near the place where it was to be used, or to have at one's disposal a system of mechanical transmission that was complicated and not very ornamental.

In order to do away with this inconvenience, which is inherent to all bichromate piles, Mr. G. Mareschal has invented and had constructed an ingenious system that we shall now describe.

Mr. Mareschal's plan consists in suspending the frame that carries all the battery zincs (Fig. 1) from the extremity of a horizontal beam, and balancing them by means of weights at the other extremity.

The system, being balanced, the lifting or immersion of the zincs then only requires a slight mechanical power, such as may be obtained from an ordinary kitchen jack through a combination that will be readily understood upon reference to Fig. 2. The axis, M, of the jack, on revolving, carries along a crank, MD, to which is fixed a connecting-rod, A, whose other extremity is attached to the horizontal beam that supports the zincs and counterpoises. If the axle, M, be given a continuous revolution, it will communicate to the rod, A, an upward and downward motion that will be transmitted to the beam and produce an alternate immersion and emersion of the zincs.

Upon stopping the jack at certain properly selected positions of the rod, MD, the zincs may, at will, be kept immersed in the liquids, or _vice versa_. This is brought about by Mr. Mareschal in the following way: The jack carries along in its motion a horizontal fly-wheel, V, against whose rim there bears an iron shoe, F, placed opposite an electro-magnet, E. In the ordinary position, this shoe, which is fixed to a spring, bears against the felly of the wheel and stops the jack through friction. When a current is sent into the electro-magnet, E, the brake shoe, F, is attracted, leaves the fly wheel, and sets free the jack, which continues to revolve until the current ceases to pass into the electro.

The problem, then, is reduced to sending a current into the electro and in shutting it off at the proper moment. This result is obtained very simply by means of an auxiliary Leclauche pile. (The piles got up for house bells will answer.) The current from this pile is cut off from the electro, F, by means of a button, B, when it is desired to light or extinguish the lamps. In a position of rest, for example, the crank, MD, is vertical, as shown in the diagram to the right in Fig. 2. The circuit is open between M and N through the effect of the small rod, C, which separates the spring, R, from the spring, R'. As soon as the circuit has been closed, be it only for an instant, the crank leaves its vertical position, the rod, C, quits the bend, S, and the spring, R, by virtue of its elasticity, touches the spring, R', and continues its contact until the crank, MD, having made a half revolution, the rod, C', repulses the spring, R, and breaks the circuit anew. The brake then acts, and the crank stops after making a revolution of 180°, and immersing the zincs to a maximum depth. In order to extinguish the lamp, it is only necessary to press the button, B, again. The axle, M, will then make another half revolution, and, when it stops, the zinks will be entirely out of the liquid. The depth of immersion is regulated by fixing the crank-pin. D, in the apertures, T1, or T2, of the connecting rod. This permits the travel, and consequently the degree of immersion, to be varied.