80

COAL MINES OF

the current of air passing from the downcastshaft through the mine to the upcast shaftwhere it ascends.

a the downcast pit, b the upcast pit, a A theeast mothergate, B a the west mothergatefrom the downcast pit a. By tracing thedarts it will be seen that the current of airfrom the bottom of the downcast pit a, firstpasses along the east mothergate a A, andthe adjoining south board M B, to which ithas free access through the holings or walls,1 2 3 4: it then passes through the holing 5,called the air-wall, into the boards (workings)C D , having free communication between themby the holings 6 7 8 and 9.

After passing the boards CD it enters thehead-ways E E, in going along which it ven-tilates the boards F G by being forced intothem by the brattices X X X X, when thecurrent of air sweeps the boards by two andtwo as above described: this is called doublecoursing; but when it is thrown down oneboard and up another, as it is from H to H,it is called single coursing.

The remaining part of the ventilation backto the east mothergate a A is in double courses.The current of air is at last discharged out ofthe first board L, north of the east mother-