ON COAL-CUTTING MACHINERY. 179 



that the object excited much contiauous interest, and that amongst so many 

 miscarriages our mechanics were still hopeful. 



Amongst these devices may be enumerated the " Saw," " Catapult," 

 " Battering-Earn," " Plough," " Rotary Wheel," " Endless Chain," " Planing 

 Machine," and many others. 



There had been no suitable power made known for diivrng the machines ; 

 and it was to that cause, in my opinion, that so many failures and disap- 

 pointments were attributable. The steam engine, even since it attained to 

 its most perfect form, is in itself insufficient for the purpose, because steam 

 cannot be produced near to the place where the work has to be done, nor can 

 it be carried long distances in effective condition, by reason of its rapid con- 

 densation. Moreover an escape of exhaust-steam could not be permitted in 

 the coal-mine, because of its tendency to soften and bring down the roof, the 

 difficulty of maintaining which is already the most serious and troublesome 

 part of the coal-mining operations. 



Hydraulic power might in certain cases be, and has been recently tried ; 

 but its unfavourable conditions exceed its advantages for the purpose of 

 cutting coal in mines, and may be put aside from present consideration. 



But in compressed air, so far as the moving power is concerned, every 

 requirement is found, and from the date of the experiments at West Ardsley, 

 in 1862, the question was undoubtedly settled. 



The elastic property of air under compression is an old and well-known 

 power ; but until these experiments had been completed, its value was but im- 

 perfectly understood, and its future beneiicial influence, being dormant, was 

 imappreciated. 



The engine for compressing the air is generally placed on the surface, near 

 to the top of the shaft ; a receiver is fixed in close proximity thereto ; and the 

 air is taken from the compressor to the receiver, which is 30 feet in length 

 and 4 feet in diameter. 



The pressure is generally of about three atmospheres. 



Iron pipes of sufficient area are laid on from the receiver to the bottom of 

 the shaft, and there, being spht into smaller sizes, are led in every needed 

 direction through the roads and passages .of the mine, exactly as the gas and 

 water services are laid on in our towns. 



At the entrance into the working places, a screw joint and stopcock are 

 fixed to the iron air-pipe, at which point an india-rubber hose, fifty or sixty 

 yards in length (as the length of the " bank " may require), is screwed on ; 

 the other end of the hose is attached to the cutting machine ; and when aU is 

 in readiness, the tap at the receiver is turned on, and the air rushes down, 

 and throughout the whole service of pipes. 



The air does not require to be forced from the receiver, for by its own 

 elasticity it is carried forward at a velocity depending on its own pressure. 



Apparently it loses none of its power by distance, excepting the frictional 

 retardation ; and machines are working nearly two miles distant from the 

 air-engine without any material loss of force. 



I have no doubt that if the compressor were stationed in Bradford the 

 air would travel, and the machines work by it at Ardsley (ten miles; as 

 satisfactorily as they now do by the engines on the spot. 



In calculating the cost of compressed air, I am satisfied that, although 

 it is admittedlj' not a cheap power relatively to steam, yet there is no 

 other available power so cheap or so good for the purpose of cutting coal in 

 mines ; and I invite attention to the figures on this head which follow, viz. :— 



With well-constructed machineiy, 45 to .50 per cent, of the steam power 



N 2 



