THE METROPOLITAN COLLIERY. 155 



between tliem, cut-throughs are made about every 44 yards 

 apart ; between each pair of heading's is a pillar 100 yards 

 wide. This method requires narrow-work, but the expense of 

 supporting- the roof is less, and the pillar between each pair of 

 headings is double the width of that left by the old melbhod, 

 so they do not have to be put in so often, also there are no 

 small holes to be made through the goaf in the bords as with 

 the old method. The pillars are worked out 011 the same prin- 

 ciple as before ; the wider they are taken out the less trouble 

 they cause. From two to four roadways are turned off from 

 the end of a heading on either side of a pillar, depending on 

 the width of the pillar strip to be extracted at one time ; these 

 are extended as work proceeds, and when one strip is com- 

 pleted, the rails are taken up and used for the next strip. The 

 coal requires little or no holing, so is unsuitable for coal cut- 

 ting machinery. All the filling into the skips is done by fork. 

 There is practically no water in the mine, so the workings are 

 very dusty. 



Four hundred thousand cubic feet of air at five inches 

 water gauge pressure pass through the mine per minute, and 

 the return air contains 1J per cent, of fire-damp. There are two 

 Walker-Schiele fans, each driven from, horizontal engines by 

 fifteen manilla ropes, but only one fan is worked at a time. 

 The bigger fan, 24 feet in diameter, by 8 feet wide, revolves 

 106 times per minute, and is driven by a compound engine 

 having 23in. and 36iu. diameter cylinders with a three foot 

 stroke. The other fan is 20 feet by 7 feet wide, has 180 re- 

 with a 36in. diameter cylinder. Being driven at such 

 a high speed, the bearings of these fans have to be kept cool b w y 

 streams of water playing on them. The air drifts are so 

 arranged that they can be put into communication with either 

 fan by means of doors. A large iron framework is built across 

 the drift on each side of the fan, and in this are three pairs of 

 iron doors, one above the other, that open towards the fan. 

 These are of such a size that they can be easily manipulated, 

 and as they move in the direction of the air current, they re- 

 quire no special fastening. Underground the fresh air from 

 the down-cast shaft passes along the intake headings, and re- 

 turns partly along the return headings, and partly along the 

 disused or partly disused workings. The aggregate amount of 

 air circulated by the two fans is not only the largest in Aus- 

 tralia, but is probably greater than that produced in any one 

 mine elsewhere. 



The upcast shaft is housed in with brick walls, provided 

 with windows, and roofed with galvanised iron, so in case of 

 an explosion this would give way readily, and save the fans 

 from being disabled. The pit-head frame is of timber, the 

 sills of which are mounted 011 brick walls. An emergency 

 winding engine is located at this shaft, and single skip cages 



