O the casual observer it would seem that it is only a question of months until the wireless telephone will supplant the present systems of telephony as a means of communication. In fact, scarcely a month passes in which important steps are not taken toward the goal of practical wireless telephony. But the difficulties to be overcome are enormous. Some idea of these difficulties and the methods by which they are being surmounted may be gained from recent developments along this line.

Some investigations of considerable importance in the field of wireless telephony were commenced a few years ago by Mr. E. Ruhmer of Berlin, who developed a rather promising system in which the light waves given out from an arc lamp projector were used as a medium in transmitting the human voice from one station to another. At the starting point was installed a very sensitive telephone transmitter in circuit with a battery and the primary terminals of an induction coil, whose secondary terminals were connected through condensers to the terminals of an arc lamp supplied from a direct current generator. When words were spoken into the transmitter varying currents were induced in the secondary of the coil, changing the current on the lamp, and thus varying the intensity of its light. This also produced sounds of vary

ing intensity and pitch, and constituted what is known as a "speaking" or "singing" arc. As the arc light was situated in the focus of a powerful projector these changes in illumination were projected as far as the receiving station, where a similar projector was installed containing in its focus a selenium resistance or selenium cell, as it is called. Selenium is a substance possessing the very remarkable property of varying its electrical conductivity under the action of light. When this cell is in a circuit through which a current is passing the variations in resistance of the selenium cell due to the actions of the rays of light will cause changes in current intensity in the circuit. As the latter in the present case contained a telephone, it will be readily understood that similar fluctuations in current intensity to those taking place in the transmitting circuit were pro

duced at the receiving station, giving in the telephone a distinct reproduction of the words spoken at the other end. Now this system is obviously practicable within only a rather limited range, the foremost condition being that the two stations be situated in sight of one another. In the case of distances exceeding even a mile or so the stations communicating with each other-or at least one of them-should therefore always be placed on some elevated spot, which is not always feasible.

Endeavors were therefore made by various experimenters to use electric. waves-in a way similar to that in wireless telegraphy-in the place of light waves, for transmitting the human voice to a distance, without any material connection between the transmitting and receiving stations. As, however, electric waves generated by spark discharges rapidly decrease in amplitude no practical results were obtained in this line.

Now, some pioneers in the field of wireless telegraphy have quite recently succeeded in increasing the frequency of what is called a "singing" or "speaking" electric arc, by placing the latter in an atmosphere of hydrogen-as suggested by Poulsen-or cooling the electrodes of the arcs as achieved by the Telefunken Co. of Germany-and thus advancing into the range of electric oscillations or waves. A practical solution of the problem of electric wave telephony has thus become possible. In fact if such undamped electric vibrations are influenced in some manner corresponding to the talk to be transmitted, the latter will be reproduced

at the receiving station, a telephone being actuated by the electric waves sent out from the starting point with the characteristic modulations corresponding to the sound waves.

The above principle thus is identical with the principle used in optical wireless telephony, but for the substitution of the far more rapid light waves as carriers of language.

The sending apparatus used in wireless telephony is based on a vibratory circuit permanently crossed by free electric waves, and which, for giving out electric waves, is coupled in exactly the same way as in wireless telegraphy, with a tuned open vibratory system in the shape of a steel wire aërial.

Now there are two possibilities of acting on electric vibrations through the agency of the human voice according as either their intensity is influenced in a manner corresponding to language -without any variation in frequency-or else the characteristic vibration of the closed or open vibratory system is altered. In both cases electric waves undulating in accurate agreement with the sound waves will be produced, their frequency being either constant or variable.

sult in a corresponding alteration in the effect exerted on the receiver, while with variable wave lengths a variable number of waves will, during the same time act on the receiver, the effect on which thus depends on the number of arriving waves of constant intensity.

Mr. E. Ruhmer of Berlin has just succeeded in obtaining a first practical solution of the above problem, an account of which he communicated to the International Conference on Wireless Telegraphy which was recently held at Berlin.

A sending apparatus arranged according to Poulsen was used, comprising a "singing" arc lamp arranged in a hydrogen atmosphere and being fed with direct currents at 220 volts. The vibratory circuit was constituted by a capacity consisting of seven Leyden jars-of about .002 microfarads-an adjustable self-induction coil and the primary coil of a Tesla transformer. In the case of a convenient tuning a high tension flaming arc, several centimeters in length could be maintained quietly burning between the secondary terminals of the Tesla transformer.

On examining this electric arc it was. found to show the appearance of a continuous-current arc, its frequency-about 300,000 per second-being far too high to decompose it into individual spark discharges. This observation induced Mr. Ruhmer to alter the generation of waves in the same way as the "speaking" arc lamp. The choking coil so far inserted in the feeding circuit of the arc, and which was intended to prevent any reaction of the rapid oscillations on the direct current circuit, was replaced by an induction coil the secondary winding of which was connected to a transmitter and battery (fig. 1). This experiment proves successful, as on talking into the transmitter the oscillograph tube-an instrument for measuring the shape of the wave-distinctly showed a glowing band of variable luminous intensity with notches corresponding to the sound waves, showing the intensity of the high frequency currents in the secondary coil of the Tesla transformer to be influenced in a manner corresponding to the spoken words. While being unable to decide which of the two processes above referred to has been realized in the present case, Mr.

process with the aid of electric waves. The arrangement used to this effect is represented in figures 2 and 3.

After first using a transmitter contact as wave detector, Ruhmer eventually replaced this by an electrolytic cell, which proved more efficient.

Experiments so far made, while being confined to the inventor's laboratory, gave surprisingly favorable results, spoken words being transmitted, with the aid of an aerial one and one-half meters in length, to the available distance of thirty meters.

Mr. Ruhmer is actively engaged in continuing these interesting experiments and confidently hopes by this method to bridge distances of several kilometers, provided aerials of sufficient length be employed. The most advantageous feature of this method seems to be the

fact that a most accurate tuning can be obtained such as that required for two stations to communicate with each other without any risk of interference on the part of a third party.

The utility of the wireless telephone will probably be first seen in its applica

tion to vessels as a means of lessening the danger of collisions. This is a field already taken by space telegraphy but involves the presence of a skilled operator constantly at the side of the officer in charge-an objection which will not apply to wireless telephony.

F a voice from Bedlam like a triple blast of a monster siren, rendering dumb all the little noises, yelps, toots, and whines of smaller mechanical throats, should suddenly pierce a traveler's ears, it is very likely he would quickly cover them and wonder what had broken loose. A hundred chances to one, when the roaring blast had ceased, he would seek the cause of the uproar to register his denunciation of the giant whistle trust, a noise combine, that has throttled all the smaller whistles in a radius of twenty miles.

But if he sought a resident of East St. Louis-the busy St. Louis suburb across the Mississippi-and necessarily a victim of the nerve-racking and discordant blasts proceeding from the manufactories, he would be told that the seemingly terrible, three-mouthed monster is a blessing in disguise to the 100,000 people living within the range of its deep, penetrating blasts.

East St. Louis probably had more independent whistles than any other city of like size in the country, and exercised them more. Each factory possessed its special whistle, actuated in accordance with its particular clock; and scarcely two time-pieces being exactly synchronized, the din produced by the various sirens, each of which had a distinctive tone, was a discordant jamboree.

Whistles blew at all kinds of timetramp, local, and standard, also in variations. The iron and steel foundry's

whistle sounded at seven o'clock by its clock time, and the aluminum works' whistle sounded at 7:05 by the foundry's clock, but at seven by its own. Whistles on the glass works, elevators, flour mills, gas works and a hundred others in various lines were let loose before and after the correct time, and for ten minutes or more residents throughout the city were in despair. In some factories there was a rivalry to see whose whistle would get the air first; and in this way many minutes were lost at night, but made up in the morning. All this whistling meant extravagance, and discord, and danger to the ear drums.

In order to reclaim the city from this whistling babel a practical way was devised by L. C. Haynes, general manager of a suburban electric railroad. The company communicated with various industrial concerns in the city, proposing to establish one powerful steam whistle in a central location, to serve all the manufactories. The plan was adopted, and it was generally agreed that the new siren should have a loud and penetrating tone capable of being heard at least ten miles, but that its voice was not to be objectionably shrill.

After careful designing, an immense siren, the greatest whistle in the world, was made and installed on the power house of the railroad company. great modern siren comprises three whistles. The largest is almost six feet in height and nearly as large in diameter as a man's body. On each side of the main whistle there is a smaller one. The

central whistle unit is loud and shrill and penetrating, the two associate whistles voice throaty tones, while the combination of the three chimes makes a pleasant sound, devoid of ear-splitting quality. The deep, thunderous sound seems to spread out and fill the sky from the earth to the smoky dome above.

The great siren has never given voice to a full, round blast, and what the tone would be if the railroad company turned full pressure into the whistle, nobody knows. The pressure now used on the whistle is about 150 pounds of steam through a three-inch pipe only half open, for thirty seconds.

To 20,000 men, women, and children, on work-day mornings, this whistle sounds forth the command, "Go to work." At noon it announces the lunch hour, a time of rest, and at one o'clock its call is, "Back to your tasks." But its six o'clock blast in three whole notes, welcome to the tired workers, means "Home, Sweet Home." For two minutes every day all East St. Louis is bewildered in a fog of noise, while the siren's tones are heard over the territory eastward as far as the towns of Belleville and Collinsville, and the entire city. of St. Louis to the west.

All the independent whistles are now silent, squelched by the dominating tone of the big whistler, the devil of noise. Since the giant whistle trust can make so much more noise in a half minute than all the small sirens could make in an hour, the profane have nothing to say. They could not be heard. Even the boats on the Mississippi withhold the steam from their deep-toned sirens until the great annihilator of peace has sounded its calls to duty.

But the economy of the greatest whistle in the world and its relief to the nerves and tempers of the residents of East St. Louis, are not its only features. It has the desirable trait of always sounding on time, at the exact second. This is because it is

connected with an electrical clock which is regulated by the government standard time sent out from Washington at exactly noon each day. The electrical clock is guaranteed not to vary five seconds in time a year; and thus the siren's voice indicating the exact time every day, is one of its notable features.

The giant trust siren is also a valued factor in the noise-making celebrations, and on these occasions it, of course, holds a monopoly. It drowns all other noises, so that cannons are not fired, nor bells rung while it sends forth its full swirl of sound, straight heavenward, without an echo. On election night the siren shouts the returns to the towns, villages, and hamlets within ten miles in every direction.