Chapter 5

The duration of the variable state is in proportion to the square of the length of the conductor, so that the difficulties increase very greatly as the wire is extended beyond ordinary limits. According to Prescott, "The duration of the variable condition in a wire of 500 miles is 250,000 times as long as in a wire of 1 mile."

In other words, a long line _retains a charge_, and time must be allowed for at least a falling off of the charge to a point indicated by the receiving instrument as zero.

In the construction of the line care was taken to insure the _lowest possible resistance_ through the circuit, even to the furnishing of the river cables with conductors weighing 500 lb. per mile.

Ground wires were placed on every tenth pole.

When the first 100 miles of wire had been strung, I was much encouraged to find that we could telegraph without any difficulty past the average provincial "ground," provided the terminal grounds were good.

When the western end of this remarkable wire reached Olean, N.Y., 400 miles from New York, my assistant, Mr. S.K. Dingle, proceeded to that town with a receiving instrument, and we made the first test.

I found that 800 words, or 20,000 impulses, per minute, could be transmitted in Morse characters over that circuit _without compensation_ for static.

In other words, the old Bain method was competent to telegraph 800 words per minute on the 400 miles of 1.5 ohm wire.

The trouble began, however, when the wire reached Cleveland, O., about 700 miles from New York.

Upon making a test at Cleveland, I found the signals made a continuous black line upon the chemical paper. I then placed both ends of the wire to earth through 3,000 ohms resistance, and introduced a small auxiliary battery between the chemical paper and earth.

The auxiliary or opposing battery was placed in the same circuit with the transmitting battery, and the currents which were transmitted from the latter through the receiving instrument reached the earth by passing directly through the opposing battery.

The circuit of the opposing battery was permanently completed, independently of the transmitting apparatus, through both branch conductors and artificial resistances.

The auxiliary battery at the receiving station normally maintained upon the main line a continuous electric current of a negative polarity, which did not produce a mark upon the chemical paper.

When the transmitting battery was applied thereto, the excessive electro-motive force of the latter overpowered the current from the auxiliary battery and exerted, by means of a positive current, an electro-chemical action upon the chemical receiving paper, producing a mark.

Immediately upon the interruption of the circuit of the transmitting battery, the unopposed current from the auxiliary battery at the receiving station flowed back through the paper and into the main line, thereby both neutralizing the residual or inductive current, which tended to flow through the receiving instrument, and serving to clear the main line from electro-static charge.

The following diagram illustrates my method:

Referring to this diagram, A and B respectively represent a transmitting and a receiving station of an automatic telegraph. These stations are united in the usual manner by a main line, L. At the transmitting station, A, is placed a transmitting battery, E, having its positive pole connected by a conductor, 2, with the metallic transmitting drum, T. The negative pole of the battery, E, is connected with the earth at G by a conductor, 1. A metallic transmitting stylus, t, rests upon the surface of the drum, T, and any well known or suitable mechanism may be employed for causing an automatic transmitting pattern slip, P, to pass between the stylus and the drum. The transmitting or pattern slip, P, is perforated with groups of apertures of varying lengths and intervals as required to represent the dispatch which it is desired to transmit, by an arbitrary system of signs, such, for example, as the Morse telegraphic code.

At the receiving station, B, is placed a recording apparatus, M, of any suitable or well known construction. A strip of chemically prepared paper, N, is caused to pass rapidly and uniformly between the drum, M', and the stylus, m, of this instrument in a well known manner. The drum, M', is connected with the earth by conductors, 4 and 3, between which is placed the auxiliary battery, E, the positive or marking pole of this battery being connected with the drum and the negative pole with the earth. The electro-motive force of the battery, E', is preferably made about one-third as great as that of the battery, E.

Extending from a point, o, in the main line, near the transmitting station, to the earth at G, is a branch conductor, l, containing an adjustable artificial resistance, R. A similar conductor, ll, extends from a point, o', near the receiving terminal of the line, L, to the conductor, 3, in which an artificial resistance, R', is also included, this resistance being preferably approximately equal to the resistance, R. The proportions of the resistance of the main line and the artificial resistances which I prefer to employ may be approximately indicated as follows: Assuming the resistance of the main line to be 900 ohms, the resistance, R, and R', should be each about 3,000 ohms. The main battery, E, should then comprise about 90 cells, and the auxiliary battery, E', 30 cells.

The operation of my improved system is as follows: While the apparatus is at rest a constant current from the battery, E', traverses the line, L, and the branch conductors, l, and ll, dividing itself between them, in inverse proportion to their respective resistances, in accordance with the well-known law of Ohm. When the transmitting pattern strip, P, is caused to pass between the roller, T, and the stylus, t, electric impulses will be transmitted upon the line, L, from the positive pole of the battery, E, which will traverse the main line, L, the two branch lines, l, and ll, and their included resistances, and also the receiving instrument, M. The greater portion of this current will, however, on account of the less resistance offered, traverse the receiving instrument, M, and the auxilary battery, E'. The current from the last-named battery will thus be neutralized and overpowered, and the excess of current from the main battery, E, will act upon the chemically prepared paper and record in the form of dots and dashes or like arbitrary characters the impulses which are transmitted.

Immediately on the cessation of each impulse, the auxiliary battery, E', again acts to send an impulse of positive polarity through the receiving paper and stylus in the reverse direction and through the line, L, which returns to the negative pole of the battery by way of the artificial resistances, R and R'. Such an impulse, following immediately upon the interruption of the circuit of the transmitting battery, acts to destroy the effect of the "tailing" or static discharge of the line, L, upon the receiving instrument, and also to neutralize the same throughout the line. By thus opposing the discharge of the line by a reverse current transmitted directly through the chemical paper, a sharply defined record will in all cases be obtained; and by transmitting the opposing impulse through the line, the latter will be placed in a condition to receive the next succeeding impulse and to record the same as a sharply defined character.

This arrangement was made on the New York-Cleveland circuit, and the characters were then clearly defined and of uniform distinctness. The speed of transmission on this circuit was from 1,000 to 2,000 words per minute.

Upon the completion of the wire to Chicago, total distance 1,050 miles, including six miles of No. 8 iron wire through the city, the maximum speed was found to be 1,200 words per minute, and to my surprise the speed was not affected by the substitution of an underground conductor for the overhead wire.

The underground conductor was a No. 16 copper wire weighing 67 pounds per mile, in a Patterson cable laid through an iron pipe.

I used 150 cells of large Fuller battery on the New York-Chicago circuit, and afterward with 200 cells in first class condition, transmitted 1,500 words, or 37,000 impulses, per minute from 49 Broadway, New York, to our test office at Thirty-ninth Street, Chicago.

The matter was always carefully counted, and the utmost care taken to obtain correct figures.

It may be mentioned as a curious fact that we not only send 1,200 words per minute through 1,050 miles of overhead wire and five miles of underground cable, but also through a second conductor in No. 2 cable back to Thirty-ninth Street, and then connected to a third underground conductor in No. 1 cable back to Chicago main office, in all about fifteen miles of underground, through which we sent 1,200 words per minute and had a splendid margin.--_Electrical World_.

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[ELECTRICAL REVIEW].

THEORY OF THE ACTION OF THE CARBON MICROPHONE--WHAT IS IT?

A careful examination of the opinions of scientific men given in the telephone cases--before Lord McLaren in Edinburgh and before Mr. Justice Fry in London--leads me to the conclusion that scientific men, at least those whose opinions I shall quote, are not agreed as to what is the action of the carbon microphone.

In the Edinburgh case, Sir Frederick Bramwell said: "The variations of the currents are effected so as to produce with remarkable fidelity the varied changes which occur, according as the carbon is compressed or relieved from compression by the gentle impacts of the air set in motion by the voice."

"The most prominent quality of carbon is its capability, under the most minute differences of pressure, to enormously increase or decrease the resistances of the circuit." "That the varying pressure of the black tension-regulator (Edison's) is sufficient to cause a change in the conducting power." Sir Frederick also said "he could not believe that the resistance was varied by a jolting motion; could not conceive a jolting motion producing variation and difference of pressure, and such an instrument could not be relied on, and therefore would be practically useless."

Sir William Thomson, in the same case, said: "The function of the carbon is to give rise to diminished resistance by pressure; it possesses the quality of, under slight degrees of pressure, decreasing the resistance to the passage of the electric current;" and, also, "the jolting motion would be a make-and-break, and the articulate sounds would be impaired. There can be no virtue in a speaking telephone having a jolting motion." "Delicacy of contact is a virtue; looseness of contact is a vice." "Looseness of contact is a great virtue in Hughes' microphone;" and "the elements which work advantages in Hughes' are detrimental to the good working of the articulating instrument."

Mr. Falconer King said: "There would be no advantage in having a jolting motion; the jolting motion would break the circuit and be a defect in the speaking telephone," and "you must have pressure and partially conducting substances."

Professor Fleeming Jenkin said, "The pressure of the carbons is what favors the transmission of sound."

All the above named scientific men agree that variations of a current passing through a carbon microphone are produced by _pressure_ of the carbons against one another, and they also agree that a jolting motion could not be relied upon to reproduce articulate speech.

Mr. Conrad Cooke said, "The first and most striking principle of Hughes' microphone is a shaking and variable contact between the two parts constituting the microphone." "The shaking and variable contact is produced by the movable portion being effected by sound." "Under Hughes' system, where gas carbon was used, the instruments could not possibly work upon the principle of pressure." "I am satisfied that it is not pressure in the sense of producing a change of resistance." "I do not think pressure has anything to do with it."

Professor Blyth said: "The Hughes microphone depends essentially upon the looseness or delicacy of contact." "I have heard articulate speech with such an instrument without a diaphragm." "There is no doubt that to a certain extent there must be a change in the number of points of surface contact when the pencil is moved." "The action of the Hughes microphone depends more or less upon the looseness or delicacy of the contact and upon the changes in the number of points of surface contact when the pencil is moved."

Mr. Oliver Heaviside, in _The Electrician_ of 10th February last, writes: "There should be no jolting or scraping." "Contacts, though light, should not be loose."

A writer, who signs "W.E.H.," in _The Electrician_ of 24th February last, says: "The variation of current arises from a variation of conductivity between the electrodes, consequent upon the variation of the closeness or pressure of contact;" and also, "there must be a variation of pressure between the electrodes when the transmitter is in action."

It seems, then, that some scientific men agree that variation of pressure is required to produce action in a microphone, and some of them admit that a microphone with loose contacts will transmit articulate speech, while others deny it, and some admit that a jolting or shaking motion of the parts of the microphone does not interfere with articulate speech, while others say such motion would break the circuit, and cannot be relied on.

I will now describe two microphones in which there is a shaking or jolting motion, and loose contacts, and no variation of pressure of the carbons against one another, and both of these microphones when used with an induction coil and battery give most excellent articulation. One of these microphones is made as follows: Two flat plates of carbon are secured to a block of cork, insulated from each other; into a hole of each carbon a pin of carbon fits loosely, projecting above the carbons; another flat piece of carbon, having two holes in it, bridges over the two lower carbons, being kept in its place by the pins of carbon which fit loosely in the holes in it, the bottom carbons being connected with the battery; a block of cork has a flat side of it cut out so as when secured to the lower cork the carbons will not come in contact with it, yet be close enough to it to keep the carbons from falling apart. The cork covering the carbons forms a dome.

Any good telephone receiver when used in connection with this microphone, reproduces articulate speech with remarkable distinctness, especially hissing sounds, and with a loud and full tone.

A description of this microphone was published in _La Lumiere Electrique_, of 15th April, 1882, and a drawing thereof on 29th April of same year.

Another form of microphone is made as follows: Two blocks of gas carbon, C, B, each about one and a half inches long and one inch square, having each a circular hole one and a quarter inches deep and half inch in diameter; these two blocks are embedded in a block of cork, C, about one-quarter of an inch apart, these holes facing each other, each block forming a terminal of the battery and induction coil; a pencil of carbon, C, P, about three-eighths of an inch in diameter, and two inches long, having a ring of ebonite, V, fixed around its center, is placed in the holes of the two fixed blocks; the ebonite ring fitting loosely in between the two blocks so as to prevent the pencil from touching the bottom of the holes in the blocks. The space between the blocks is closed with wax, W, to exclude the air, but not to touch the ring on the pencil. A block of cork fitting close to the carbon blocks on all sides is then firmly secured to the other block of cork. The microphone should lie horizontally or at a slight angle.

This microphone produces in any good telephone perfect articulation in a loud and full tone. In these microphones there is certainly "looseness and delicacy of contact," and there is a "jolting or shaking motion," and it does not seem possible that there can be any "pressure of one carbon against another."

I repeat the question I asked at the beginning of this communication, and hope that it may elicit from you, or some of our scientific men, an explanation of the theory of the action of this form of microphone.

W.C. BARNEY.

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THE DEMBINSKI MICROPHONIC TELEPHONE TRANSMITTER.

This apparatus, which is shown by Figs. 1, 2, and 3, consists of a wooden case, A, of oblong shape, closed by a lid fixed by hinges to the top or one side of the case. The lid is actually a frame for holding a piece of wire gauze, L L, through which the sound waves from the voice can pass. In the case a flat shallow box, E F (or several boxes), is placed, on the lid of which the carbon microphone, D C (Figs. 1 and 3), which is of the ordinary construction, is placed. The box is of thin wood, coated inside with petroleum lamp black, for the purpose of increasing the resonance. It is secured in two lateral slides, fixed to the case. The bottom of the box is pierced with two openings, resembling those in a violin (Fig. 2). Lengthwise across the bottom are stretched a series of brass spiral springs, G G G, which are tuned to a chromatic scale. On the bottom of the case a similar series of springs, not shown, are secured. The apparatus is provided with an induction coil, J, which is connected to the microphone, battery, and telephone receiver (which may be of any known description) in the usual manner.

The inventors claim that the use of the vibrating springs give to the transmitter an increased power over those at present in use. They state that the instrument has given very satisfactory results between Ostende and Arlon, a distance of 314 kilometers (about 200 miles). It does not appear, however, that microphones of the ordinary Gower-Bell type, for example, were tried in competition with the new invention, and in the absence of such tests the mere fact that very satisfactory results were obtained over a length of 200 miles proves very little. With reference to a statement that whistling could be very clearly heard, we may remark that experience has many times proved that the most indifferent form of transmitter will almost always respond well and even powerfully to such forms of vibration.--_Electrical Review_.

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NEW GAS LIGHTERS.

We are going to make known to our readers two new styles of electric lighters whose operation is sure and quick, and the use of which is just as economical as that of those quasi-incombustible little pieces of wood that we have been using for some years under the name of matches.

The first of these is a portable apparatus designed for lighting gas burners, and is based upon the calorific properties of the electric spark produced by the induction bobbin. Its internal arrangement is such as to permit of its being used with a pile of very limited power and dimensions. The apparatus has the form of a rod of a length that may be varied at will, according to the height of the burner to be lighted, and which terminates at its lower part in an ebonite handle about 4 centimeters in width by 20 in length (Fig. 1). This handle is divided into two parts, which are shown isolatedly in Fig. 2, and contains the pile and bobbin. The arrangement of the pile, A, is kept secret, and all that we can say of it is that zinc and chloride of silver are employed as a depolarizer. It is hermetically closed, and carries at one of its extremities a disk, B, and a brass ring, C, attached to its poles and designed to establish a communication between the pile and bobbin when the two parts of the apparatus are screwed together. To this end, two elastic pieces, D and E, fit against B and C and establish a contact. It is asserted that the pile is capable of being used 25,000 times before it is necessary to recharge it. H is an ebonite tube that incloses and protects the induction bobbin, K, whose induced wire communicates on the one hand with the brass tube, L, and on the other with an insulated central conductor, M, which terminates at a point very near the extremity of the brass tube. The currents induced in this wire produce a series of sparks between the tube, L, and the rod, M, which light the gas when the extremity of the apparatus is placed in proximity with the burner.

The ingenious and new part of the system lies in the mode of exciting the induced currents. When the extremity of the tube, L, is brought near the gas burner that is to be lighted, it is only necessary to shove the botton, F, from left to right in order to produce a _limited_ number of sparks sufficient to effect the lighting. The motion of the button has not for effect, as might be believed, the closing of the circuit of the pile upon the inducting circuit of the bobbin. In fact in its normal position, the vibrator is distant from its contact, and the closing of the circuit would produce no action. The motion of F produces a _mechanical_ motion of the spring of the vibrator, which latter acts for a few instants and produces a certain number of contacts that give rise to an equal number of sparks. Owing to this arrangement, the expenditure of electric energy required by each lighting is limited; and, an another hand, the vibrator, which would be incapable of operating if it had to be set in motion by the direct current from the pile, can be actuated _mechanically_. As the motion of the vibrator is derived from the hand of the operator, and not from the pile, it will be comprehended that the latter can, everything being equal, produce a larger number of lightings than an ordinary bobbin and vibrator.

Dr. Naret's _Fiat Lux_ (Fig. 3) is simpler in its operation, and cheaper of application, since it takes its current from the ordinary piles that supply domestic call-bells. It consists essentially of a fine platinum wire supported by a tilting device in connection with the two poles of a pile composed of three Leclanche elements. Upon exerting a vertical pressure on the button placed to the left of the apparatus, either directly or by means of a cord, we at the same time turn the cock and cause the platinum spiral to approach, and the latter then becomes incandescent as a consequence of the closing of the circuit of the pile. After the burner is lighted it is only necessary to leave the apparatus to itself. The cock remains open, the spiral recedes from the burner, the circuit opens anew, and the burner remains lighted until the gas is turned off. This device, then, is particularly appropriate in all cases where there is a pressing need of light, for a single maneuver suffices to open the cock and effect a lighting of the burner.--_La Nature_.

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DISTRIBUTION OF HEAT WHICH IS DEVELOPED BY FORGING.