633 
that has not been tested, simply because an enlarged area and 
increased furnace arrangements have always produced a cor- 
respondingly greater quantity of air ; and I am of opinion 
that the furnace on the dip side of the up-cast shaft not only 
secures its safety in all contingencies, but also gives it greater 
power as a ventilating agent. I would further arrange 
that the furnace be supplied with fresh air from the down- 
cast shaft direct, and take the return current into the dumb 
drifts from the furnace. I propose to convey the return air 
by over-throws, and construct them on such a principle as to 
resist any force that could be brought to act upon them. 
It will be seen that I propose, for working a large coal- 
field, to have only four main currents or divisions, two north 
and two south ; more may be a matter of arrangement. 
I propose further that these divisions for the ingoing air 
shall take place at the bottom of the down-cast shaft, and 
shall be regulated in the return at an over-throw on each 
side, north and south ; and as there will be two currents of 
unequal length on each side, the regulators must govern them. 
I think it possible to ventilate successfully any mine with 
four main divisions ; there may be more at the discretion of 
the viewers, but I should require six when the coal is 
worked on the dip side of the shaft. I propose, further, 
that the up-cast shaft should not be less than twelve feet 
diameter, that would give an area of 113; the same in the 
down-cast ; and as shafts are a great expense to open, and 
subject to the influx of water, it would be wise in all deep 
mines to have them large enough. To commence with an area 
of 1 13, would give in four equal divisions, twenty-eight feet to 
each, and would require six tons of coal in twenty-four hours 
to produce a column of air through the up-cast shaft of 1 12,000 
feet per minute; and assuming the data on which these 
results are based to be correct, this would also give to each 
division in the working 28,000 feet, at a velocity of 560 
