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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,
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.
The action of a spark, FUNDAMENTAL EXPERIMENT, SHOWING PRINCIPLE OF
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 by cept this action. The distance through Dr. Branly, of Paris.
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
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
DISTRIBUTING Axle, OPERATED CLOCK a tape of telegraph paper, the whole ap
theatres, in order to control by the action tion in question has been really produced of electric sparks many spectacular ef- at the distant station. This is effected fects.
by an ingenious outfit designed by Dr. If a number of electric circuits, each Branly and of which a short description controlling a given mechanical effect, are is given in the following: installed beforehand at the receiving sta- At the receiving station, where the tion, each circuit having a special coherer, various effects to be produced have been a single spark would simultaneously arranged beforehand and where the complete all the circuits thus producing services of no operator are required, all the effects at the same time. More there is installed a receiving apparatus complicated effects can however be pro- which under the action of sparks given duced by so arranging the several cir- off at convenient intervals from the startcuits as to have a single spark from the ing station, will control not simultanestarting station control a first effect, this ously but successively, either a series of first effect controlling another, and so phenomena, being independent of one anforth. Now as most effects produced in other or phenomena depending on each the circuit of the coherer itself, require other. In the first case, Dr. Branly's apa strong current, which would be apt to paratus affords a means of producing the damage the coherer, it will in most cases several effects in any desired order, while be preferable to produce the action in in the latter, they may be produced in a neighboring circuit, actuated by a relay their proper order and discontinued in an disengaged by
inverted order. the coherer.
At the starting For all these
station there is inmechanical ef
stalled an operator fects realized
acting on a transwithout the
mitting apparatus agency of inter
by means of which mediate wires,
sparks are given distances of 100,
off. Being some200 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
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
substituted for the clock mechanism
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
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 each 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