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Wireless Control of Mechanisms

By Dr. Alfred Gradenwitz

Berlin Correspondent TECHNICAL WORLD MAGAZINE

VER since the dis- of a tube containing metal filings, which,
covery of wireless when inserted in an electric circuit, will
telegraphy, which enable the presence of electric waves
in so short a career, flowing through the space to be detected
has assumed such without any material connection with
universal impor- their starting point.
tance, it has been The tube used by Branly was a tube of
the dream of invent- some insulating material-usually glass-

ors to transmit, traversed by two conductive rods between without the agency of any conductive which metal filings were inserted without wire, not only telegraphic messages, but any noticeable pressure. (See Fig. 1.) any kind of mechanical effects, govern- This tube was found to become conducting, from a distance, all sorts of mechan- ive for electricity, like any metallic conisms. For instance, ability to control the ductor, as soon as, at some distant point, motors propelling a vessel or an air-ship, an electric spark was made to pass beor the engines of a power station from tween two metal balls, and to lose this some distant point, would be an invalu- conductivity under the action of a shock. able power. In order fully to understand Whenever such a tube is inserted in the

circuit of an electric battery, the current will be arrested, until a spark is produced in the neighborhood. The current is then allowed to pass until the temporary conductivity of the tube is destroyed by a shock imparted to the tube, These phenomena are the starting points of

wireless telegraphy. Fig. 1. FUNDAMENTAL EXPERIMENT, SHOWING PRINCIPLE OF WIRELESS

The action of a spark, as shown by this “co

herer" tube, spreads. this problem, it will be well to recall the round the spark gap in all directions at fundamental principle underlying wire- the speed of light, traversing air as well less telegraphy.

. as insulating bodies, pure water, partiWhile we are indebted to Marconi for tions and walls. Metal covers, metallic its first practical realization, wireless solutions and salt water, however, intertelegraphy was invented in principle bycept this action. The distance through Dr. Branly, of Paris. Several years which the action of the spark can be before Marconi's successful work—in noted is some hundreds of feet, but it can fact, as far back as 1890—Dr. Branly be extended considerably by fitting a discovered the remarkable properties metal rod called "antenna” to the spark

[graphic]

TELEGRAPHY.

gap. The action is due to the electric vi- paratus will constitute a Morse receiver, brations originated by the spark simul- which registers messages in ordinary teletaneously with its characteristic light and graph codes. If at the sending station, sound effects. While the latter are per- a spark be produced between the two ceived by the organs of our senses, we balls of the induction coil, the coherer do not possess any organ capable of de- becoming conductive at the receiving statecting electric vibrations and must re tion, the electro-magnet will be energized

and the plate, being attracted, a dot will be marked on the tape. The shock of the plate against a stop will be sufficient to discontinue the conductivity of the radioconductor. Between the starting point, where the spark is produced, and the receiving station where the circuit of the radio-conductor is closed, there is no intermediary conductive wire..

From the above it will be readily understood why a radio-conductor should be able to produce at the distant station, without the intermediary of a wire, not only a deflection of a galvanometer or energizing of an electro-magnet but any ef

fects of the electric current: incandesFig. 2. SENDING OPERATOR.

cence of metal wires for electric lamps,

lighting of electric arcs, illumination of sort to artificial means, such as the co Geissler tubes, production of X-rays, igherer tube or radio-conductor above de- nition of combustible bodies, explosion of scribed. This plays the same rôle, then, mines, etc. It would also make possible in regard to electric vibrations, as does production of the many mechanical efthe eye in regard to light waves, and fects at a distance: drilling of metal has been fitly termed the "Electric Eye." pieces, lifting of loads, etc.

An improved type of radio-conductor Devices allowing these effects to be is the tripod disc, designed by Branly produced are actually employed in some and which consists of a brass plate having three feet, the lower points of which, (of polished steel), rest on a polished steel disc. When this is inserted in an electric circuit the current is interrupted by the imperfect contact between the points and the disc. The obstacle due to this contact is, however, overcome by the battery current as soon as a spark is produced by the induction coil of the sending station and the current continues to pass until its temporary conductivity is discontinued by a shock imparted to the disc.

The presence of the battery current is shown by the deflection of a galvanometer-needle. If now the galvanometer is replaced by an electro-magnet this will be energized as soon as the electric current is allowed to pass, thus attracting a soft iron plate. If this plate, pivoted upon a fixed axis, be so arranged as to mark by its swinging motion a dot on a tape of telegraph paper, the whole ap

[graphic]
[graphic]

TIG. 3. DISTRIBUTING AXLE, OPERATED BY CLOCK

• WORK

theatres, in order to control by the action of electric sparks many spectacular effects.

If a number of electric circuits, each controlling a given mechanical effect, are installed beforehand at the receiving station, each circuit having a special coherer, a single spark would simultaneously complete all the circuits thus producing all the effects at the same time. More complicated effects can however be produced by so arranging the several circuits as to have a single spark from the starting station control a first effect, this first effect controlling another, and so forth. Now as most effects produced in the circuit of the coherer itself, require a strong current, which would be apt to damage the coherer, it will in most cases be preferable to produce the action in a neighboring circuit, actuated by a relay disengaged by the coherer.

For all these mechanical effects realized without the agency of intermediate wires, distances of 100, 200 and more miles, as in wireless telegraphy, can be traversed.

The above apparatus will, . however, not be fully reliable unless there be some means of ascertaining whether the ac

tion in question has been really produced at the distant station. This is effected by an ingenious outfit designed by Dr. Branly and of which a short description is given in the following:

At the receiving station, where the various effects to be produced have been arranged beforehand and where the services of no operator are required, there is installed a receiving apparatus which under the action of sparks given off at convenient intervals from the starting station, will control not simultaneously but successively, either a series of phenomena, being independent of one another or phenomena depending on each other. In the first case, Dr. Branly's apparatus affords a means of producing the several effects in any desired order, while in the latter, they may be produced in their proper order and discontinued in an

inverted order.

At the starting. station there is installed an operator acting on a transmitting apparatus by means of which sparks are given off. Being some

[graphic]

FIG. 4. DISTRIBUTING AXLE, OPERATED BY ELECTRO-MOTOR, AND DISENGAGING RELAYS.

times as far distant from the receiving will produce or discontinue the effect in station as 200 miles, he is obviously not question. The sectors of the several able to see the latter, but, controlling at discs successively press against their rewill the phenomena to be produced at the spective contact rods. This will be illusreceiving station, he is thereby kept trated by the following example: posted, being able to check the effects Consider a disc controlling a lampproduced by them as though they took lighting circuit. This disc will, by means place under his eyes.

of its thickened sector, press against its The apparatus at the receiving station contact rod during a given number of is to this effect provided with a horizon- seconds, completing during this interval tal cylindrical steel axle rotating slowly. of time a first circuit which includes an In the first model constructed by Dr. electric cell, a radio-conductor and a Branly and which

striking electro-magis represented in

net, destroying by a figure 3, the axle

shock the conductivwas driven by

ity of the latter. If, clock work, while

during this interval in the second ap

of time, a spark be paratus, which is

produced at the startbetter fitted for

ing station, it will, by industrial use, a

closing the circuit of small electric

the radio-conductor, motor has been

actuate the relay con

[graphic]

FIG. 5. COMPLETE RECEIVING STATION WITH SELF-ACTING TELEGRAPH.

substituted for the clock 'mechanism trolling another circuit, which contains (Fig. 4,) which can be set moving or the lamps in question, thus lighting these. arrested at any moment from the start- After another revolution or any number ing station. The rotating axle,—which, of revolutions of the distributing axle the on account of its functions, is termed operator is in a position to put out the “distributing axle” – carries metal burning lamps by means of a spark from discs insulated from each other and the starting station at the moment when each controlling the closing and opening the thickened sector of the same disc, by of a given circuit corresponding to a pressing on its contact rod, once more given effect. In order to be able allows a current to traverse the circuit of to play this double part, the circumfer- the radio-conductor. Each of the discs ence of each disc has been thick- thus constitutes a current interrupter conened on a sector which during each revo trolling one of the effects to be produced. lution of the axle presses against a rod, If there are four such discs it will be establishing by this pressure, during possible to produce four different effects. some fraction of a revolution, a contacť These effects may be independent of each able to close the corresponding circuit. other, being, for instance, the firing of a By a convenient mechanism this contact revolver, operation and stopping of a exerted during a fraction of a revolution ventilating fan, lighting and extinction of

[graphic]

FIG. 7. ELECTRIC FAN MOTOR AND INCANDESCENT LAMPS OPERATED BY WIRELESS

ACTION.

tod

incandescent lamps, energizing of an the telegraph tape at the starting staelectro-magnet able to lift an iron ball tion, each interval left between two conand to release it as soon as the mag- secutive sets corresponding to a length of netization ceases. While the above phe- 4 inches through which the paper tape nomena have been chosen for demonstra- unwinds in the meantime. A sample of tion, their choice evidently is entirely two such wireless messages received at arbitrary. The various functions of a the starting station during a complete complicated working machine could, for revolution of the axis is represented instance, be controlled by the spark. below in figure 6. The Marconigram in

During the fraction of a revolution of question is as simple as possible, comthe axle while a given effect is being prising only five sets of one, two, three, produced, none of the remaining effects four and five sparks respectively, which can take place, all the remaining circuits sparks in eachi set are very close to each being interrupted.

other. The interval between the first The operator at the starting station is spark, which is simple, and the second, enabled to ascertain whether the effect double, is called interval 1-2; let this be in question has been actually produced set apart for the firing of a revolver. The at the given moment, by means of an interval 2-3 between the double and triple automatic wireless telegram starting sparks will correspond to the starting of from the receiving station and which is the ventilating fan; the interval 3-4 to recorded automatically on a Morse re- the lighting of the incandescent lamps, ceiver, the tape of which unwinds under and the interval 4-5 to the energizing of the eyes of the operator at the starting the electro-magnet lifting the iron ball. station. The signals thus recorded are In these intervals take place, one after all due to sparks automatically produced the other, the effective contacts of the by an induction coil at the receiving sta- thickened sectors with their contact rods, tion, and this automatic wireless telegra- closing the circuits for the various efphy is controlled by a special disc mount- fects, all of which circuits are open dured on the distributing axle, and which is ing the sparking intervals, that is during provided at its circumference with five the short fraction of a revolution when sets of projecting teeth, the contacts of the sparks are produced. During the which, with convenient springs at each contact intervals, the operator, while complete revolution of the axle, produce keeping his eyes fixed on the unwinding five sets of sparks separated by prac- paper tape, will, by means of a key, cause tically equal intervals of time. (Com- the sparks to pass in the induction coil. plete apparatus shown in Fig. 5.) The The interval 5 to 1 corresponds to the five sets of sparks record themselves on electro-motor substituted for the clock

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