DOMESTIC VENTILATION. 345 



we go on until we reach the working, and then the long 

 wall itself becomes the cross communication, and through 

 this working-gallery the air sweeps freely and effectually. 



In the above I have only considered the simplest possible 

 elements of the problem. The practical coal-pit in full 

 working has a multitude of intervening passages and 

 "splits," where the main current from the downcast is 

 divided, in order to proceed through the various streets and 

 lanes of the subterranean town as may be required, and 

 these divided currents are finally reunited ere they reach 

 the upcast shaft which casts them all out into the upper 

 air. 



In a colliery worked on the pillar and stall system i.e., 

 by taking out the coal so as to leave a series of square 

 chambers with pillars of coal in the middle to support the 

 roof the windings of the air between the multitude of 

 passages is curiously complex, and its absolute obedience to 

 the commands of the mining engineer proves how com- 

 pletely the most difficult problems of ventilation may be 

 solved when ignorance and prejudice are not permitted to 

 bar the progress of the practical applications of simple 

 scientific principles. 



Here the necessity of closing all false outlets is strikingly 

 demonstrated by the mechanism and working of the "stop- 

 pings" or partitions that close all unrequired openings. 

 The air in many pits has to travel several miles in order to 

 get from the downcast to the upcast shaft, though they 

 may be but a dozen yards apart. (Formerly the same shaft 

 served both for up and down cast, by making a wooden 

 division (a brattice) down the middle. This is now pro- 

 hibited, on account of serious accidents that have been 

 caused by the fracture of the brattice.) 



But it would not do to carry the coal from the workings 

 to the pit by these sinuous air-courses. What, then, is 

 done ? A direct road is made for the coal, but if it were 

 left open, the air would choose it: this is prevented by an 

 arrangement similar to that of canal locks. Valve-doors or 

 " stoppings" are arranged in pairs, and when the "hurrier" 

 arrives with his corve, or pit carriage, one door is opened, 

 the other remaining shut; then the corve is hurried into 



