Chapter 4

Having got thus far in his devices for destroying induction from one line to another, Van Rysselberghe saw that, as an immediate consequence, it might be concluded that, if the telegraph currents were thus modified and graduated so that they produced no induction in a neighboring telephone line, they would produce no sound in the telephone if that instrument were itself joined up in the telegraph line. And such was found to be case. Why this is so will be more readily comprehended if it be remembered that a telephone is sensitive to the changes in the strength of the current if those changes occur with a frequency of some hundreds or in some cases thousands of times _per second_. On the other hand, currents vibrating with such rapidity as this are utterly incompetent to affect the moving parts of telegraphic instruments, which cannot at the most be worked so as to give more than 200 to 800 separate signals _per minute_.

The simplest arrangement for carrying out this method is shown in Fig. 1, which illustrates the arrangements at one end of a line. M is the Morse key for sending messages, and is shown as in its position of rest for receiving. The currents arriving from the line pass first through a "graduating" electromagnet, E2, of about 500 ohms resistance, then through the key, thence through the electromagnet, R, of the receiving Morse instrument, and so to the earth. A condenser, C, of 2 microfarads capacity is also introduced between the key and earth. There is a second "graduating" electromagnet, E1, of 500 ohms resistance introduced between the sending battery, B, and the key. When the key, M, is depressed in order to send a signal, the current from the battery must charge the condenser, C, and must magnetize the cores of the two electromagnets, E1 and E2, and is thereby retarded in rising to its full strength. Consequently no sound is heard in a telephone, T, inserted in the line-circuit. Neither the currents which start from one end nor those which start from the other will affect the telephones inserted in the line. And, if these currents do not affect telephones in the actual line, it is clear that they will not affect telephones in neighboring lines. Also the telephones so inserted in the main line might be used for speaking to one another, though the arrangement of the telephones in the same actual line would be inconvenient. Accordingly M. Van Rysselberghe has devised a further modification in which a separate branch taken from the telegraph line is made available for the telephone service. To understand this matter, one other fact must be explained. Telephonic conversation can be carried on, even though the actual metallic communication be severed by the insertion of a condenser. Indeed, in quite the early days of the Bell telephone, an operator in the States used a condenser in the telegraph line to enable him to talk through the wire. If a telephonic set at T1 (Fig. 2) communicate through the line to a distant station, T2, through a condenser, C, of a capacity of half a microfarad, conversation is still perfectly audible, provided the telephonic system is one that acts by induction currents. And since in this case the interposition of the condenser prevents any continuous flow of current through the line, no perceptible weakening will be felt if a shunt S, of as high a resistance as 500 ohms and of great electromagnetic rigidity, that is to say, having a high coefficient of self-induction, be placed across the circuit from line to earth. In this, as well as in the other figures, the telephones indicated are of the Bell pattern, and if set up as shown in Fig. 2, without any battery, would be used both as transmitter and receiver on Bell's original plan. But as a matter of fact any ordinary telephone might be used. In practice the Bell telephone is not advantageous as a transmitter, and has been abandoned except for receiving; the Blake, Ader, or some other modification of the microphone being used in conjunction with a separate battery. To avoid complication in the drawings, however, the simplest case is taken. And it must be understood that instead of the single instrument shown at T1 or T2, a complete set of telephonic instruments, including transmitter, battery, induction-coil, and receiver or receivers, may be substituted. And if a shunt, S, of 500 ohms placed across the circuit makes no difference to the talking in the telephones because of the interposition of the separating condenser, C, it will readily be understood that a telegraphic system properly "graduated," and having also a resistance of 500 ohms, will not affect the telephones if interposed in the place of S. This arrangement is shown in Fig. 3, where the "graduated" telegraph-set from Fig. 1 is intercalated into the telephonic system of Fig. 2, so that both work simultaneously, but independently, through a single line. The combined system at each end of the line will then consist of the telephone-set, T1, the telegraph instruments (comprising battery, B1, key, M1 and Morse receiver, R1), the "graduating" electromagnets, E1, and E2, the "graduating" condenser, C1, and the "separating" condenser, C2. It was found by actual experiments that the same arrangement was good for lines varying from 28 to 200 miles in length. A single wire between Brussels, Ghent, and Ostend is now regularly employed for transmission by telegraph of the ordinary messages and of the telemeteorographic signals between the two observatories at those places, and by telephone of verbal simultaneous correspondence, for one of the Ghent newspapers. A still more interesting arrangement is possible, and is indicated in Fig. 4. Here a separating condenser is introduced at the intermediate station at Ghent between earth and the line, which is thereby cut into two independent sections for telephonic purposes, while remaining for telegraphic purposes a single undivided line between Brussels and Ostend. Brussels can telegraph to Ostend, or Ostend to Brussels, and at the same time the wire can be used to telephone between Ghent and Ostend, or between Ghent and Brussels, or both sections may be simultaneously used.

It would appear, then, that M. Van Rysselberghe has made an advance of very extraordinary merit in devising these combinations. We have seen in recent years how duplex telegraphy superseded single working, only to be in turn superseded by the quadruplex system. Multiplex telegraphy of various kinds has been actively pursued, but chiefly on the other side of the Atlantic rather than in this country, where our fast-speed automatic system has proved quite adequate hitherto. Whether we shall see the adoption in the United Kingdom of Van Rysselberghe's system is, however, by no means certain. The essence of it consists in retarding the telegraphic signals to a degree quite incompatible with the fast-speed automatic transmission of telegraphic messages in which our Post Office system excels. We are not likely to spoil our telegraphic system for the sake of simultaneous telephony, unless there is something to be gained of much greater advantage than as yet appears.--_Nature._

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THE ELECTRIC MARIGRAPH.

For registering the height of the tide at every instant, hydrographic services generally adopt quite a simple marigraph. The apparatus consists in principle of a counterpoised float whose rising and falling motion, reduced to a tenth, by means of a system of toothed wheels, is transmitted to a pencil which moves in front of a vertical cylinder. This cylinder itself moves around its axis by means of a clockwork mechanism, and accomplishes one entire revolution every twenty-four hours. By this means is obtained a curve of the tide in which the times are taken for abscisses and the heights of the sea for ordinates. However little such marigraphs have had to be used, great defects have been recognized in them. When we come to change the sheet on the cylinder (and such change should be made at least once every fifteen days), there is an interruption in the curve. It is necessary, besides, to perform office work of the most detailed kind in order to refer to the same origin all these curves, which are intercrossed and often superposed in certain parts upon the original sheet. In order to render such a disentanglement possible, it is indispensable to mark by hand, at least once every twenty-four hours, upon each curve, the date of the day corresponding to it. It is equally useful to verify the exactness of the indications given by the apparatus by making readings several times a day on a scale of tides placed alongside of the float. Nine times out of ten the rise of the waves renders such readings very difficult and the control absolutely illusory.

All these conditions united, as well as others that we neglect in this brief discussion, necessitate a surveillance at every instant. The result is that these marigraphs must be installed in a special structure, very near the bank, so as to be reachable at all times, and that the indications that they give are always vitiated by error, since the operation is performed upon a level at which are exerted disturbing influences that are not found at a kilometer at sea. It were to be desired that the float could be isolated by placing it a certain distance from the shore, and transmit its indications, by meant of a play of currents, to a registering apparatus situated upon _terra firma_.

In the course of one of his lectures published in the December number (1883) of the _Elektrotechnische Zeitschrift_, Mr. Von Hefner-Alteneck tells us that such a desideratum has been supplied by the firm of Siemens & Halske. This marigraph, constructed on an order of the German Admiralty, gives the level of the sea every ten minutes with an approximation of 0.12 per cent., and that too for a difference of 8 meters between the highest and lowest sea. The apparatus consists, as we said above, of a float and registering device, connected with each other by means of a cable. This latter is formed of three ordinary conductors covered with gutta percha and surrounded with a leaden sheath, which latter is itself protected against accident by means of a strong covering of iron wire and hemp. The return is effected through the earth. We shall enter into details concerning each of these two apparatus in-succession, by beginning with the float, of which Fig. 1 gives a general view, and Fig. 2 a diagrammatic sketch. The float moves in a cast iron cylinder, having at its lower part a large number of apertures of small diameter, so that the motion of the waves does not perceptibly influence the level of the water in the interior of the cylinder. It is attached to a copper ribbon, B, whose other extremity is fixed to the drum, T. The ribbon winds around the latter in the rising motion of the float, owing to a spiral spring arranged so as to act upon the drum. The tension of this spring goes on increasing in measure as the float descends.

This difference in tension is utilized for balancing at every instant the weight of the ribbon unwound, and thus causing the float to immerse itself in the water to a constant degree. The ribbon, B, is provided throughout its length with equidistant apertures that exactly correspond to tappets that project from the circumference of the wheel, R. When the float moves its position, the wheel, R, begins to turn and carries along in doing so the pinion, w, which revolves over the toothed wheels, s1, s2, and s3. The thickness of w is equal to that of the three wheels, s1, s2, and s3, and a special spring secures at every instant an intimate contact between the pinion and the said wheels. These latter are insulated from each other and from the axle upon which they are keyed, and communicate, each of them, with conductors, I., II., and III. They are so formed and mounted that, in each of them, the tooth in one corresponds to the interspace in the two others. As a result of this, in the motion of the pinion, w, the latter is never in contact with but one of the three wheels, s1, s2, and s3.

If we add that the lines, I., II., and III. are united at the shore station with one of the poles of a pile whose other pole is connected with the earth, and that w communicates with the earth through the intermedium of R, and the body of the apparatus, it is easy to see that in a vertical motion of the float in one direction we shall have currents succeeding each other in the order I., II., III., I., II., etc., while the order will become III., II., I., III., II., etc., if the direction of the float's motion happen to change.

In order to understand how a variation in currents of this kind can be applied in general for producing a rotary motion in the two directions, it will only be necessary to refer to Figs. 3 and 4. The conductors, L1, L2, and L3 communicate with the bobbins of three electromagnets, E1, E2, and E3, whose poles are bent at right angles to the circumference of the wheel, R. There is never but one pole opposite a tooth. The distance between two consecutive poles must be equal to a multiple of the pitch increased (Fig. 3) or diminished (Fig. 4) by one-third thereof. It will be seen upon a simple inspection of the figures that R will revolve in the direction of the hands of a watch when the currents follow the order L1, L2, L3, etc., in the case shown in Fig. 3, while in the case shown in Fig. 4 the rotary motion will be in the contrary direction for this same order of currents. But, in both cases, and this is the important point, the direction of rotation changes when the order in the succession of currents; is inverted. Fig. 6 gives a perspective view of the registering apparatus, and Fig. 5 represents it in diagram. It will be at once seen that, the toothed wheel, r, is reduced to its simplest expression, since it consists of two teeth only. The electro-magnets are arranged at an angle of 120°, and for a change of current the wheel, r, describes an angle of 60°, that is to say, a sixth of a circumference. The motion of r is transmitted, by means of the pinion, d, and the wheel, e, to the wheel, T. For a one-meter variation in level the wheel, T, makes one complete revolution. It is divided into 100 equal parts, and each arc therefore corresponds to a difference of one centimeter in the level, and carries, engraved in projection, the corresponding number. As a consequence, there is upon the entire circumference a series of numbers from to 99. The axle upon which the wheel, T, is keyed is prolonged, on the side opposite e, by a threaded part, a, which actuates a stylet, g. This latter is held above by a rod, I, which is connected with a fork movable around a vertical axis, shown in Fig. 6. The rectilinear motion of g is 5 mm. for a variation of one meter in level. Its total travel is consequently 40 mm. The sheet of paper upon which the indications are taken, and which is shown of actual size in Fig. 7, winds around the drum, P, and receives its motion from the cylinder, W. This sheet is covered throughout its length with fine prepared paper that permits of taking the imprints by impression.

This stated, the play of the apparatus may be easily understood. Every ten minutes a regulating clock closes the circuit of the local pile, B2, and establishes a contact at C. The electro-magnet, E4, attracts its armature, and thus acts upon the lever, h, which presses the sheet of paper against the stylet in front that serves to mark the level of the lowest waters, and against the stylet, g, and the wheels, T and Z. In falling back, the lever, h, causes the advance, by one notch, of the ratchet wheel that is mounted at the extremity of the cylinder W, and thus displaces the sheet of paper a distance of 5 mm. The wheel, Z, carries engraved in projection upon its circumference the hours in Roman figures, and moves forward one division every 60 minutes. The motion of this wheel is likewise controlled by the cylinder, W.

It will be seen upon referring to Fig. 7, that there is obtained a very sharp curve marked by points. We have a general view on considering the curve itself, and the height in meters is read directly. The fractions of a meter, as well as the times, are in the margin. Thus, at the point, a, the apparatus gives at 3 o'clock and 20 minutes a height of tide of 4.28 m. above the level of the lowest water.

This apparatus might possibly operate well, and yet not be in accord with the real indications of the float, so it has been judged necessary to add to it the following control.

Every time the float reaches 3 meters above the level of the lowest tide, the circuit of one of the lines that is open at this moment (that of line I, for example) closes at C (Fig. 2), into this new circuit there is interposed a considerable resistance, W, so that the energy of the current is weakened to such a point that it in nowise influences the normal travel of the wheel, r. At the shore station, there is placed in deviation a galvanoscope, K, whose needle is deflected. It suffices, then, to take datum points upon the registering apparatus, upon the wheel, T, and the screw, a, in such a way as to ascertain the moment at which the stylet, g, is going to mark 3 meters. At this moment the circuit of the galvanoscope, K, is closed, and we ascertain whether there is a deviation of the needle.

As the sea generally rises to the height of 3 meters twice a day, it is possible to control the apparatus twice a day, and this is fully sufficient.

It always belongs to practice to judge of an invention. Mr. Von Hefner-Alteneck tells us that two of these apparatus have been set up--one of them a year ago in the port of Kiel, and the other more recently at the Isle of Wangeroog in the North Sea--and that both have behaved excellently since the very first day of their installation. We shall add nothing to this, since it is evidently the best eulogium that can be accorded them.--_La Lumiere Electrique._

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DELUNE & CO.'S SYSTEM OF LAYING UNDERGROUND CABLES.

In recent times considerable attention has been paid to the subject of laying telegraph cables underground, and various methods have been devised. In some cases the cables have been covered with an armor of iron, and in others they have been inclosed in cast-iron pipes. For telephonic service they are generally inclosed in leaden tubes. What this external envelope shall be that is to protect the wires from injury is a question of the highest importance, since not only the subject of protection is concerned, but also that of cost. It is therefore interesting to note the efforts that are being made in this line of electric industry.

Messrs. Delune & Co. have recently taken out a patent for an arrangement consisting of pipes made of beton. The annexed cuts, borrowed from _L'Electricite_, represent this new system. The pipes, which are provided with a longitudinal opening, are placed end to end and coupled with a cement sleeve. The cables are put in place by simply unwinding them as the work proceeds, and thus all that traction is done away with that they are submitted to when cast iron pipes are used. When once the cables are in place the longitudinal opening is stopped up with cement mortar, and in this way a very tight conduit is obtained whose hardness increases with time. The value of the system therefore depends, as in all cement work, on the care with which the manufacturing is done.

Experiments have been made with the system at Toulouse, by the Minister of Post Offices and Telegraphs, and at Lyons, by the General Society of Telephones. Here, as with all similar questions, no opinion can be pronounced until after a prolonged experience. But we cannot help setting forth the advantages that the system offers. These are, in the first place, a saving of about 50 per cent. over iron pipe, and in the second, a better insulation, and consequently a better protection of the currents against all kinds of disturbance, since a non-conducting mass of cement is here substituted for metal.

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ELECTRICITY APPLIED TO HORSE-SHOEING.

"There is nothing new but what has been forgotten," said Marie Antoinette to her milliner, Mdlle. Bertin, and what is true of fashion is also somewhat so of science. Shoeing restive horses by the aid of electricity is not new, experiments thereon having been performed as long ago as 1879 by Mr. Defoy, who operated with a small magneto machine.

But the two photographs reproduced in Figs. 1 and 2 have appeared to us curious enough to be submitted to our readers, as illustrating Mr. Defoy's method of operating with an unruly animal.

The battery used was a small Grenet bichromate of potash pile, which was easy to graduate on account of the depth to which the zinc could be immersed. This pile was connected with the inductor of a small Ruhmkorff coil, whose armature was connected with a snaffle-bit placed in the horse's mouth.

This bit was arranged as follows (Fig. 3): The two conductors, which were uncovered for a length of about three centimeters at their extremity, were placed opposite each other on the two joints of the snaffle, and about five or six centimeters apart. The mouth-pieces of the bit had previously been inclosed in a piece of rubber tubing, in order to insulate the extremities of the conductors and permit the recomposition of the current to take place through the animal's tongue or palate.

Each of the bare ends of the conductors was provided, under a circular brass ligature, with a small damp sponge, which, surrounding the mouth-piece, secured a perfect contact of each end of the circuit with the horse's mouth.

The horse having been led in, defended himself vigorously as long as an endeavor was made to remove his shoes by the ordinary method, but the current had acted scarcely fifteen seconds when it became possible to lift his feet and strike his shoes with the hammer.

The experimenter having taken care during this experiment to place the bobbin quite near the horse's ear, so that he could hear the humming of the interrupter, undertook a second experiment in the following way: Having detached the conductors from the armature, he placed himself in front of the horse (as shown in Fig. 2), and began to imitate the humming sound of the interrupter with his mouth. The animal at once assumed the stupefied position that the action of the current gave him in the first experiment, and allowed his feet to be lifted and shod without his even being held by the snaffle.

The horse was for ever after subdued, and yet his viciousness and his repugnance to shoeing were such that he could only be shod previously by confining his legs with a kicking-strap.

It should be noted that the action of the induction coil, mounted as this was, was very feeble and not very painful; and yet it was very disagreeable in the mouth, and gave in this case a shock with a sensation of light before the eyes, as we have found by experimenting upon ourselves.