Wireless Telegraphy Theory

WIRELESS TELEGRAPHY THEORY

How a Message is Sent Without the Use of Wires

VERY RAPID PROGRESS IS BEING MADE

Message Radiates in all Directions and to Different Points

Receiving Stations Must be Same Distance From the Ground-New Machinery is Expected Shortly  in Ann Arbor to Telegraph to Detroit and Near by Towns

"When the Daily Argus, exclusively, announced April 8, that the experiment of wireless telegraphy in the university physical laboratory was a success, we were unable to give a full explanation of it, and until now some of the purely physical problems have never been delineated for the public. Just as the world is old so are really all matters of science, only as we are nearing our accomplishinent we go faster until the end.

Wireless telegraphy is not new, only in name. Physicologicly it is analogous to light. The magnetic waves are the same with the exeption of certain physical changes. Of course in seeing you do not get the further point of light, which is really infinite, but this is on account of the ocular incapabilities, and the second place the curvatura of the earth.

A representative of tbe Daily Argus yesterday had an opportunity to see the apparatus for wireless telegraphy and its workings. The matter was explained by Prof. Augustus Torwbridge, and from the explanation no layman ought to misunderstand the workings of it any more than of telegraphy by wire.

The one explanation which treats the subject from a physical standpoint has not been published in any paper, either in Chicago, New York or Ann Arbor, and it is of this that we will treat in part.

In the first place it is not sound that travels, but the effect of the electro-magnetic wave which produces the sound - the instrument clicker. The electro-magnetic wave is produced in this way. At the sending station there is an inductive coil. There is a slight current produced which produces a current of high pressure, this in turn produces an oscillation between two poles which is the electro-magnetic wave which travels ad infinetum. As said before this is a wave analogous to the waves of light and when it reaches the receiving station its connection there produces a light current which produces the sound on the clicker.

Dr. Trowbridge stated to the Daily Argus that although it is plain that it is the ether in the astmosheric space that allows these waves to prevail, yet it is possible that it may yet be found that it also passes through the earth as well. In that case the curvature of the earth would not hinder it.

There is a peculiar thing about this space-telegraphy. Although it matters not at what altitude the receiving station is, whether higher or lower than the sending station, it must only be at the same altitude from the surface of the earth as the other instrument is from the surface of the earth. Another peculiarity is that in sending a message ifc starts from the center (the sending apparatus) and travels in every direction in a radii as for instance from a buggy wheel. In this case were we to telegraph to Detroit it could be heard in Jackson, providing they have a receiving station. However, the matter may be made quite secret by using parabolic mirrors.

The Daily Argus is indebted to the Michigan Alumnus for the cuts used in this connection, also for certain explanations of them by Prof. H. S. Carhart. To give a better idea of this, seemingly simple display of physical science the drawings will be explained.

At the sending station only simple means are employed. The wires a and b in Fig. 1 come from the secondary of an induction coil capable of giving a spark eight or ten inches long; c and d are two balls about an inch in diameter. One of these is connected to earth as shown, and the other to a vertical wire f. The height of this wire must be about 20 feet for sending a message a distance of a mile ; one twice as high will suffice for four miles, etc. This vertical wire is one of the distinctive features of the Marconi system. When the primary circuit of the induction coil is closed by a telegraph key, a spark, or more properly, an osculatory discharge passes between the two balls, c, d. This causes an electrical charge to surge up and down the vertical conductor, which now becomes the source of the electro-magnetic radiations in the other. They are propagated in all directions in the same manner as light and with the same speed. When they encounter the vertical conductor at the receiving station, they in turn give rise to electrical surging in it. To utilize them the vertical receiving wire is connected to one end of a coherer, the other end of which is joined to the earth. The coherer is then subjected to an electric discharge which affects its resistance.

In Fig. 2, f is the vertical conductor, c the coherer, and e the earth connection. If now the coherer is at the same time "made part of a local circuit, containing a battery B and a relay R, then the relay may be so adjusted that its armature will not be drawn down by the very small current travering the coherer till the electric surging, due to an incoming ether or Hertz wave, causes its particles to cohere. lts reduced resistance then allows a larger current from the local battery to pass through the relay sufficient to operate its armature. The relay in turn looses another local circuit by which a bell may be rung, a taper operated, an electric lamp lighted, a motor started, or an ordinary Morse recording instrument may be worked and the does and dashes recorded on a trip of paper.

The sensitiveness of the coherer is a very remarkable fact. One of those recently made by Dr. Trowbridge and Prof. H. S. Carhart had a resistance after tapping of a million and a half ohms; but when the induction coil was worked some 30 feet away.its resistance fell instantly to 12 ohms. A slight tap restored its original high resistance. This is one of the most remarkable facts within the whole range of electrical phenomena.

In speaking of telegraphy it might be said that wireless telegraphy is making more rapid strides than did telegraphy by wire. It was some time before it was successfully operated between Washington and Philadelphia, but it took only a few days for Marconi to successfully telegraph across the English channel, 32 miles. The university will soon be equipped with better apparatus and in a few weeks will make a test to Ypsilanti or Dexter.