TRANSACTIONS OF SECTION G. 751 



boilers, whilst the various engines are now being constructed on the most modern 

 and improved principle. 



Compressed air has for many years been used extensively in our coal mines as 

 a motive power. Electricity also has made rapid strides in the same direction ; 

 and I have no doubt that, in conjunction with a better type of machinery for the 

 compression and use of air, will eventually become the principal agent in under- 

 ground mechanical operations. 



Many large electrical installations have already been in use for a considerable 

 period. Notably amongst the number I may mention that at Messrs. Locke 

 & Co.'s St. John's Colliery, Normanton, where both hauling on the endless-rope 

 system and pumping are very largely adopted, and it has been proved that a useful 

 effect equal to 60 per cent, can be obtained. This high rate of efficiency is un- 

 doubtedly very satisfactory. I am, however, of opinion that there is still great 

 room for improvement in electrical plant before it will be adopted in preference to 

 other machinery now in general use, especially in gaseous mines, and these im- 

 provements must embrace a certain means of rendering sparking absolutely harmless 

 under all conditions, for it involves not only the question of the increased effi- 

 ciency of one class of machinery over another, but also the protection of human life. 



There must also be devised a ready means of reversing the power, so that the 

 system of haulage known as the main-and-tail-rope system can be applied with 

 equal safety and readiness in any part, as compared with absolute safety in the use 

 of compressed air. 



An electrical hauling plant to be worked on this system (which I am sure will 

 be watched with very great interest) is now erected at one of the Plymouth 

 collieries in this district, by an eminent firm of electricians, as a trial and demon- 

 stration of what can be done in this direction. This will comprise, when fully com- 

 plete, a generating plant at the top of the pit, and two electrically-driven hauling- 

 engines underground, connected by a suitable cable carried down the shaft and along 

 the roadway for some 1,200 yards. 



The generating plant and one hauling-engine are now erected, and the other 

 hauling-engine will shortly be ready. 



The generating plant consists of a 40 horse-power compound engine working at 

 110 revolutions per minute ; this engine drives by belt a specially constructed 

 dynamo, which is of a horizontal pattern, built on a wrought-iron girder bed plate. 

 It is compound wound, and capable of giving off 160 amperes with 500 volts 

 pressure, running at 500 revolutions per minute. 



The cable, which is 3,200 yards in length, is made of 37 strands of No. 14 

 high conductivity copper-wire, highly insulated with vulcanised bitumen, double- 

 taped, and surrounded wtli two layers of jute yarn compounded between each, 

 and is protected by a double sheath of No. 8 steel-wire. It is of sufficient size to 

 carry the necessary current, and in case of falls of roof it has been constructed so 

 that it will stand a shearing strain of 10 tons per square inch. 



The hauling-engine consists of two drums, each fitted with a clutch and foot- 

 brake. The drum-shaft is driven from a counter-shaft by spur gearing, and this 

 counter-shaft is driven from the motor by six ropes 1 inch in diameter. 



The motor is a shunt-wound machine, built to run at 600 revolutions per 

 minute, and works with 80 amperes at 450 volts, and is able to take 160 amperes 

 without harm at starting. The whole engine is mounted on a wrought-iron bed- 

 frame. The motor will be reversed by a specially-designed switch, the efficiency 

 of which has yet to be proved. The useful effect of this plant, when working at 

 full power, is expected to be from 60 to 65 per cent. 



Possibly the leather-belting and ropes used for transmitting the power from the 

 motor to the hauling-drums or pumps, might with advantage be replaced by some- 

 thing less liable to be damaged by the rough usage and other contingencies usually 

 met with undergroimd. 



As I have previously mentioned, compressed air is another motive power very 

 largely used in coal-mining, it being not only absolutely safe in explosive atmospheres, 

 but tends to reduce any danger which might exist from sudden outbursts of gas 

 by assisting the ventilation. This may be considered as rather an expensive 



