DOMESTIC VEXTILATIOJST. G< 



ing, and then th long wall itself becomes the cross communi- 

 cation, 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 coalpit in full work- 

 ing 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 sub- 

 terranean 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 completely the most diffi- 

 cult problems of ventilation may be solved when ignorance and 

 prejudice are not permitted to bar the progress of the practi- 

 cal 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 prohibited, on 

 account of serious accidents that have been caused by the fract- 

 ure 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 sim- 

 ilar to that of canal locks. Valve-doors or " stoppings" arc 

 arranged in pairs, and when the " hurrier" arrives with his 

 curve, or pit carriage, one door is opened, the other remain- 

 ing shut ; then the corve is hurried into the space between 

 the doors, and the entry-door is closed ; now the exit- 

 door is opened, and thus no continuous opening is ever per- 

 mitted. - 



Only one such opening would derange the ventilation of the 

 whole pit, or of that portion fed by the split thus allowed to 



