The Technical World, March, 1905, page 71:
cover

Wireless  Telephony
ELSEWHERE in this issue will be found a description of the various wireless telephone systems which have been proposed, together with a brief history of the general subject, by A. Frederick Collins. The first suggestion of a wireless system was by A. G. Bell in 1880. Professor Bell conceived the idea--after the discovery of the variation in resistance of the selenium cell according to the variation in light thrown upon it--that this principle might be used to reproduce spoken words, and such proved to be the case. The speaking arc is another very interesting experiment described; but, as both of these methods depend upon an uninterrupted visual line and more or less accurate alignment of apparatus, it is hardly possible that they can attain much practical importance or be operated over very great distances. In a recent article Mr. Tesla states that "within a few years a simple and inexpensive device, readily carried about, will enable one to receive on land or sea the principal news, to hear a speech, a lecture, a song, or play of a musical instrument conveyed from any other region of the globe." Aside, however, from this prophecy, wireless telephony offers an interesting field for research and experiment, although after 25 years much still remains to be done to place it on a sound commercial footing.

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W i r e l e s s    T e l e p h o n y

By  A.  Frederick  Collins

Author  of  "Wireless  Telegraphy,  Its  History,  Theory,  and  Practice"
Ruhmer Receiver Ruhmer Receiver THE transmission of intelligence by use of the electric current has reached, in its broadest sense, its final stage of development.
    Intercommunication by means of an electrical disturbance set up for the purpose of propagating energy representing the alphabetic code or articulate speech, may be divided into four general classes -- namely -- Telegraphy with wires, Telephony with wires, Telegraphy without wires, and Telephony without wires. These principal classes, again, it is evident, may be subdivided into many branches; but there can be no further evolution in the art of sending and receiving messages by electrical methods, where instruments are interposed between those who are to be brought into mental relationship with one another.
    This is not to say that each of the fore-named systems approximates in its present state anything like perfection, for all are more or less crude in practice if not in theory; but any improvements that may be made in the future must differ from present attainments in degree and not in kind. Hence the raison d'être of the numerous arrangements for wire; and when wireless telegraphy made its spectacular debut a few years ago, there seemed to the casual observer no good and valid reason why speech propagation and reception without wires should not be considered as already at hand. To the investigator, however, it was soon revealed that history was repeating itself, and that wireless systems of telegraphy and telephony were as different in all their phases as were their predecessors which utilized the connecting wire. A brief analysis of these differences that mark so clearly the dividing line between the four great classes enumerated, will assist materially to an understanding of the fundamental principles of wireless telephony. Bell Transmitter

Evolution  of  Electrical  Communication

    When Morse took up the study of telegraphy, a working knowledge of the laws of electricity had not as yet been very accurately deduced. Induced and alternating currents had been explained by Henry and Faraday, but their usefulness remained to be indicated. It was well known, however, that a direct current traversing a wire was capable of energizing an electro-magnet; and from this fact Morse conceived the idea of the relay--the device that made telegraphy a commercial factor.
    Although nearly half a century elapsed before Bell made his successful essay to produce a speaking telephone, electricity had not made so much progress as might have been expected. Reis had attempted to construct a telephone by utilizing a rapidly intermittent current, and these futile trials led Bell to believe that such a method was impracticable. Experimenting with steel reeds vibrating over magnets, he produced currents of varying strength--termed "undulatory currents" in virtue of their wavelike characteristics--and this formed the basic principle of the telephone.
    In Marconi's wireless telegraphy, any kind of low-voltage current may be transformed into one of high potential and frequency; but in this system the oscillations of the transmitter emit their energy in the form of a train of waves with long intervals of time between them, and these oscillations, therefore, are not at all adapted to the transmission of voice undulations. Bell Receiver

Methods  of  Speech  Transmission

    There are several methods whereby articulate speech can be transformed into electric current waves, which may, in turn, be propagated by the ether through air, earth, or water.
    The first of these methods consists in the use of a battery and a telephone transmitter connected in series with terminals embedded in the earth or immersed in water. When the undulatory current flows through the circuit thus formed, the larger portion of its energy is dissipated, flowing out in curved stream lines, owing to the great cross-section of the earth, and extending to considerable distances. Now, if a complementary equipment consisting of a telephone receiver is likewise placed in contact with the earth by having its terminals similarly grounded, when the energy impinges upon these the current then flows through the receiver, and speech may be accurately reproduced.
    A second method, ideal in its simplicity, is accomplished by electro-magnetic induction. Everyone knows that when a current flows through the primary of an induction coil, alternating currents are set up in the secondary coil by what is called "induction;" but not everyone knows that the coils may be widely separated before the limits of the inductive influence will be reached. If, for instance, a telephone transmitter and a source of electromotive force approximating 25 volts are included in the circuit of a coil of wire having, say, 25 turns and a diameter of feet, and if a telephone receiver is included in a coil of wire having 60 turns and a diameter of 3 feet, words spoken into the transmitter can be distinctly heard in the receiver when the two instruments are separated a distance of 100 feet--providing, of course, that the coils have their planes parallel with each other. This is the "inductivity method;" and like the one previously described, it is operated by a low-voltage direct current.

The  Bell  Photophone  or  Radiophone

    The invention of the telephone receiver led to many interesting experiments and to many curious discoveries. Prof. Alexander Graham Bell, in working with his new telephone, devised an apparatus for telephoning on a beam of light. This instrument, which he named the "photophone" or "radiophone," involved the use of selenium, a substance possessing the very remarkable property, under the action of light, of varying in electrical resistivity and its reciprocal, when fused in between two connecting wires of platinum or silver.
    This apparatus is shown in the diagram, Fig. 1. The transmitter used by Bell was not electrical--for the transmitter, as we know it, had not been invented. Bell's transmitter comprised the mouthpiece 1, a shell 2 supporting a thin metal diaphragm 3, and, attached to the latter, a small concave mirror 4. A plane mirror 5, a convex condensing lens 6, and a projecting lens 7, all of which were suitably mounted on a frame, completed the apparatus for transforming the air vibrations produced by the voice into light variations of the projected beam. Figure 1
    The receiver was formed of a parabolic mirror 8 of large diameter, in the focus of which a selenium cell 9 was adjusted. The terminals of the conducting wires or electrodes of the cell led through insulated bushings in the reflector, to the back, where they were connected in series with a battery 10 and a telephone receiver 11.
    When the radiophone is in operation, the successive transformations take place in the following manner:--The light from the sun is reflected by the plane mirror 5 to the condensing lens 6, where its rays are focused on the concave mirror 4. From the latter, the light is reflected to the lens 7, whence it is propagated through the intervening space to the large parabolic reflector 8, whereby its diffused waves are collected and concentrated to a pencil point on the selenium cell 9. It is evident that any changes in the intensity of the light will alter the electrical resistance of the selenium cell, consequently causing variations in the current from the battery 10, and finally affecting the telephone 11.
    When words are spoken into the transmitter, this is precisely what takes place, for the movements of the diaphragm of the transmitter cause the concave mirror to vibrate in unison with it, and every change is thus indicated at the receiving end in virtue of these fluctuations.

The  Ruhmer  System
Ruhmer System
Mobile Tender Ruhmer
    While the distance to which Bell was able to propagate the light variations representing the human voice, was not more than a few hundred feet, recent improvements in the system by Herr Ernest Ruhmer have resulted in the transmission of speech a distance of several miles. This was made possible through the remarkable advance of electro-physics during the past few years. Prof. H. T. Simon ascertained that an ordinary arc-light could be made to reproduce articulate speech more clearly and distinctly than any phonograph, by superimposing a feeble alternating current upon a heavy direct current. The diagram, Fig. 2, illustrates one form of the method by which this may be accomplished.
    An ordinary telephone transmitter 1 and battery 2 are connected in series with the primary of a small induction coil 3; the secondary coil 4 leads through the condensers 5 5, to the opposite carbons 6 6 forming the electrodes for the arc-light 7; the latter is produced by a direct 50-volt current from a generator or--which is still better--a storage battery. When the speaking arc or "arcophone" is operated, the voice causes the air waves to vary the resistance of the transmitter 1 in the usual manner; the current from the battery 2, thus varied, energizes the primary coil 3, setting up alternating currents in the secondary coil 4. The condensers 5 5 produce no appreciable effect on the wave form of the current, which is superimposed upon the current from the generator flowing through the circuit formed of the carbons 6 6, the arc-light 7, and the generator 8. The object of the condensers, however, is to prevent the direct current from backing up into the transmitter and burning it out. The superimposed current, however feeble, varies the resistance of the arc, and this produces a change in its temperature, which gives rise in turn to sound waves. Figure 2
    Another important function of the speaking arc is connected with the fact that there is also a variation of the intensity of the light which it emits. It is this by-product, as it were, of the speaking arc, that Ruhmer employs in his photo-electric telephone--a device which in all other respects is based upon the original Bell photophone. In Ruhmer's system, the speaking arc is placed in the focus of a parabolic reflector, whence its rays are directed to the distant receiver. When the two are in perfect alignment, a voice into the one will be distinctly audible in the other. The arrangement then takes the form shown diagrammatically in Fig. 3. With the description already given of the speaking arc and the selenium cell, the details of operation will be readily understood.
Figure 3
Ruhmer System on Lake
The  Collins  System
Collins
Figure 4 + 5
    The writer, in endeavoring to bring about the advent of a commercial wireless telephone which would not be interfered with by fogs or other atmospheric conditions and which would not require either alignment or a direct visual line, investigated the several schemes of dispersion, inductivity, and electro-magnetic wave methods. The last-mentioned method is the most interesting, since it partakes of the nature of the wireless telegraph as well as of the wire telephone, yet it will do that which is not possible with either of the latter--namely, it will transmit articulate speech wirelessly.
    In the beginning of this article, it was pointed out that electric waves, when emitted by a high-frequency and high-potential oscillation equalized through a spark-gap, were periodic, as indicated in the diagram, Fig. 4, the current strength decreasing in geometrical progression like the vibrations of a straight steel spring. In wireless telephony an undulatory oscillation is required, and this may be obtained by loading the radiating circuit with large inductances and capacities whose coefficients possess the properties of slowing down each oscillation until a more or less perfect sine wave results, as indicated in Fig. 5. Collins Telephone
    When this point is reached, the striking effect of the oscillatory discharge on the ether is greatly weakened, but at short distances the telephone will respond audibly without the usual coherer intervening. Some of the most recent work by the writer, however, has shown that a liquid detector made by immersing a platinum point and a platinum plate in an alkaline solution increases the volume of sound to an appreciable extent.
    The first series of tests with this type of apparatus was made at Rockland Lake, N. Y., a distance of a mile; while, under very favorable conditions, articulate speech has been transmitted and received over a distance of three miles and a-half. Successful tests have also been carried out between the ferryboats John C. McCullough and Ridgewood plying between New York and Jersey City. John G. McCullough
    The equipment of vessels with wireless telephone apparatus will tend to obviate the danger from collisions in harbors; while telephone communication between docks and vessels will facilitate transportation, thus saving time and money as well as insuring the safety of passengers and crews. The development of this latest phase of applied electrical science is another onward step in the march of human progress.
Ridgewood