INVENTORS
Copy of a G.E.C. report sent under cover of their letter dated 27 March 1917
Mr C A. Coates. General Electric Company Limited said that previous to the letter referred to from Sir Richard Redmayne this was a subject which had engaged the attention of electoral engineers. In particular the General Electric Company, Limited, introduced a new form of relay called the Davies~Railing patent relay, which not only reduced the spark to the safe limit mentioned in Dr. Wheeler's Report, but entirely eliminated all visible sparking on the bare signalling wires when contact was made. In this way a condition of absolute security was afforded. No attention was required to the existing bare'wire signalling system other than connecting up the relay in the line circuit, so the sum involved in the installation was practically
the cost of the relay only. Further, as only two or three cells were required over the longest line likely to be used, the cost of upkeep was extremely low. There were at present over 100 of these relays in use in SOUTH WALES, and orders for considerably more than this number were in hand. At one colliery alone over seventy were in use, while another colliery company had recently ordered sixty for use in their pits. Mr. Coates, after giving a demonstration with the Davies -Railing patent relay, went on to remark that it would be conceded to be quite simple in its operation and construction, and that there was little danger of it getting out of order. The principle on which the relay worked was the inductive rise which caused sparking on the line wires with ordinary bells or relays. This damping was accomplished by means of a combination of a patented special winding of the coils and a comparatively slow moving rotary armature, which closed the circuit in a mercury cup. The whole mechanism was contained in an explosion- proof box, so that any spark at the moment of contact in the mercury was rendered innocuous. Exhaustive tests taken in a colliery gas- testing station had shown that besides no visible spark being produced, the explosive mixtures of gas could not be ignited. The characteristics of the system might be summarized as follows,.
(a)The adoption of the Davies-Railing signalling gear involved no changes in the existing installation beyond the insertion of the relay in the bell circuit and a reduction in the battery power used. (b) No alteration in the mode of signalling was made. The man would only know of the change by the absence of the spark at the moment of contact. (c) There was no limit to the