SAVING LIFE BY WIRELESS

Evening Star, Issue 19020, 15 August 1925, Page 9

SAVING LIFE BY WIRELESS

APPAIUTIIS FOB MINES. There is'good reason to hope that it will not he very long before some method of using wireless for life saving in mines will ho developed on really practical lines (states a correspondent in the London ‘Times’). In mining accidents it generally happens that or the total number of deaths only a comparatively small number are caused, directly by the accident itself, the majority being due to suffocation, gassing, or starvation following the mishap. It follows, therefore, that every second saved in rescue work is of the utmost value, and an hour spent in exploring a wrong level, or in clearing what proves to be an unoccupied shaft, is priceless time wasted. Tims, any reliaole method of locating the positions of entombed men may easily mean tho.saving of many lives. Tho chief difficulty in the way of investigators so far has been to discover a method of applying wireless to rescue work in mines iviiich shall be efficient in the conditions which usually attend mine disasters. The solution <ff the entire mine communication problem is dependent mainly upon the working out of a practical, portable apparatus of sufficient sensitivity in reception and power in transmission to have an effective range over the area of the average mine.

The ideal system would he one _in which voice transmission and reception were possible. Failing that a simple system in which prearranged signals were used on the lines of the graphic code might be well worth while. The apparatus must bo robust and simple in operation, easily maintained in good working order, and so designed that it might he enclosed in a watertight bos ' strong enough to withstand shocks and jars. No apparatus on the market, except possibly wireless operated fog-signalling devices, fulfils these conditions. In practically all methods of underground communication high absorption of transmitted current has to 'b« reckoned with. This depends largely upon the amount of water present, its sheet distribution, and tho type oi ore or mineral present:. Jn practically every deep mine test it has been noticed that reception is much better in one place than another, and the effect of conduction and absorption lias therefore to bo considered in each case. In mines having electric light and power circuits such conductors will carry signals down from tho surface often with inappreciable or only slight diminution in intensity, but the extent to which such conductors act ns carriers for high-frequency currents depends upon their electrical characteristics and the frequency used. Serious investigations have been carried out iu this counfry at the Hlnojohn Mine, Castlcton, Derbyshire; Pricstners Colliery, Wigan; lieslord Colliery, Leicester; Dykehead Mine, Glasgow; Ashington Colliery. Northumberland, and Woodpark Colliery, Cheshire; but tho most exhaustive tests as yet undertaken have been those ol _ the United States Bureau of alines in coal pits near Pittsburg. The conclusions arrived at bear out those of tho Lnglish investigations, and go beyond anything done in this country, so they may be taken as .summarising the position to-day and as forming the ton Adaption for all future experiments along these lines.

The power buzzer, or ground conduction method, in which the earth is used as the conducting medium, has been found to be reliable, but it. does not provide, a general solution of the problem, because it is limited to the telegraphic code, and tho requirements of ground terminals for communication over useful distances are not easy to arrange in tho mine workings. With regard to pure radio, relatively highpowered equipment, is required because of the high earth conductivity and resultant attenuation of high-frequency radio waves in penetrating to low levels. This means bulk and weight. Such equipment is now believed to be impracticable for general mine communication or for rescue purposes. Another method, and one that appears to hold out the greatest promise at the moment, is the system known as wired wireless, or communication by means of radio-frequency currents which travel along electrical conductors such as telephone or power lines, trolley wires, or hoisting cables. Tho value of this system is that it can bo operated over'-buried wires, which are most likely to escape destruction in the majority of mine disasters. With wired wireless a range of a five-watt transmitter has .been found to be several thousand feet. A groat deal of investigation is still necessary, however, before tho problem can be regarded as solved and before any particular apparatus can be recommended for general adoption*