L. T. KNIGHT

A question frequently propounded by beginners in wireless experiment work is that of how far wireless signals may be transmitted by a given spark. It is to be presumed that the writer contemplates purchasing an induction "coil of one or more inches spark length, and wishes to use it for communication with a station several miles distant, but foreseeing numerous expenditures for appartus, seeks advice as to the advisability of proceeding with such a limited source of energy. In attempting to answer the above question it is well to state that there seems to be a very general misunderstanding regarding the principles of wireless signaling, especially in regard to the receiving apparatus, and the functions performed by the latter.

In order to follow intelligently the advances of wireless telegraphy it is necessary to have a general idea of the modern scientist's view regarding the nature of electrical phenomena.

All space must be regarded as something styled the "luminiferous ether. " Not only does this ether permeate all space, but it also permeates all solids. Further, its nature is such that the movement of solids is not restrained by such permeation, the closest analogy being that of a wire sieve, representing the solid, being moved about in the water, which represents the ether.

This ether is the sea, not only of all electrical phenomena, but also of all the phenomena of heat and light. Heat, light and electricity are but the result of vibrations or waves in the ether, the apparent differences being due to the differences in length and frequency, just as one musical note differs from another in the same particulars, only that sound waves are air waves, not ether waves.

It is claimed that in wireless telegraphy that currents are vibrations of the ether along the path of the wire. That is, the wire acts merely as a guide for the ether waves.

In wireless telegraphy ether vibrations are also set up at the transmitting end, but these waves have no conducting guide, and so radiate in all directions through space. and a small percentage of them arrive at the receiving end where they are caught on the aerial wire and caused to record themselves upon a coherer or similar device.

The first receiving device studied by the amateur is the coherer, the earliest successful collector of Hertzian waves. The coherer is an insulated container, usually a tube of glass. Sealed between two metal plugs in this tube may be found fillings of iron. antimony, silver or nickel, in quantitities and proportions calculated by the designer to give the most satisfactory results under certain conditions or distance. Each coher of a collection has some especial qualification, determined by tests after manufacture ; some are suited for long distance and some for short, all vary in sensitivity after repeated use.

When inserted in the relay circuit a coherer must be susceptible to waves entering on the aerial wire, and cohere or, rather, the filings inclosed in the tube must cohere or "stick" electrically more closely together, causing a sudden fall in resistance to a point where the battery in the relay circuit may pass through both coherer and relay, and thus operate a sounder and other recording devices.

Often the first of a chain of waves will somewhat lessen the coherer resistence, but not sufficiently to operate the relay. In this case more waves must perform their duty upon the coherer before the first dot or dash can be recorded. While waves come to the coherer at a rapid rate, this delay in cohering counts considerably, both in accuracy and in the time it takes to send a given message. Hence the necessity of having the coherer as sensitive as possible.

Connected in one branch of the receiving circuit is the decoherer, a device operated electrically like a vi brating door bell, which taps the coherer near the fi ings chamber with the purpose of restoring or deco hering the filings to that state of inactivity where no current can pass through the relay until one or more waves have again reached the aerial wire. Oft times the tapper, instead of completely performing its function, simply partially decoheres thefilings, causing er rors in recording. Frequently the tapping throws the filings into a state of higher resistance than formerly, and makes readjustment of the relay circuit necessary, for it must be remembered that in setting up the relay and battery circuit a variable resistance was included, by which the current was kept at a point where it would not force through the coherer normally but would press through instantly when the resistance of the coherer was lowered by incoming waves. Such is the theory of the coherer, and to date no amount of tinkering with vacuum or filings, or distance between electrodes will greatly alter the situation. Atmospheric disturbances will store electrical charges upon aerial wires, and the coherer operates at random moments.

The writer recalls, while visiting quite recently a coherer receiving station, the illegible records made on the tapes by the impulses that followed along with and after the regular message. These marks were explained by the operator to be atmospheric disturbances which were caught because the coherer and relay circuit were adjusted to a most sensitive degree, owing to the extreme distance between stations.

To the coherer must be given the credit, however, of opening up the field of investigation more effectively, because of these very short comings. Many wireless experts dropped the coherer principle after a few trials and took up the study of electrolytic, thermostatic and magnetic detectors, many of which, like the coherer, at times have their failings.

The problem of recording, by means of a relay and recording device, waves which decrease in direct propor-tson to the distance between stations, is a task calcu-ated to cause many a clever man much loss of sleep. How to take an accurate, decipherable record of an impulse transmitted from a point a thousand miles away, possessing less than one thousandth of the energy it had when wafted from its sending aerial, is a problem, the final solution of which should mean a comfortable fortune for the inventor, and a wide development of wireless telegraphy.