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how the return air can be successfully conveyed into the 
up-cast shaft, and also what part of a coal field is the most 
proper for the said up-cast shaft ; as, in my judgment, the 
situation is of some moment, not as compared with the main 
question, which is that it be of sufficient capacity wherever 
it may be placed, also of ventilating power adequate to the 
workings in operation, both shafts being of sufficient 
dimensions to admit the required quantity. On this subject 
we are not without data, though very imperfect, as I believe 
I should be right in stating on this question of power that 
one ton of coal consumed in a furnace in twenty-four hours 
would, under ordinary circumstances, produce on an average 
20,000 cubic feet of air per minute, allowing for unequal 
depths of shaft or length of air-courses and other inequalities ; 
as it is proved, I think, beyond a doubt that 190,000 feet of air 
have been passed through one heated shaft in one minute, also 
that air can be passed through a shaft at the rate of twenty 
miles an hour, and along the underground passages at the 
rate of fourteen miles an hour ; and to produce these results 
the temperature does not require to be raised to more than 
from 170 to 200 degrees Fahrenheit. Put such a force as 
this into operation in the Barnsley Thick Coal, and what 
would be the quantity of air forced along ? Why, eight 
years ago, about 31,000 feet of air in one minute was the 
largest quantity found in any mine in Yorkshire, and 40,000 
the largest in Derbyshire. Both these mines were under 
the direction of J. T. Woodhouse, Esq., who appears to 
have been the pioneer of improved ventilation in these 
districts ; and now a few may be found with near 100,000 feet 
of air passing up the up-cast shaft per minute ; but much 
more than this can be effected by the up-cast shaft being 
even in the centre of a coal field and near the down-cast 
shaft, and the furnace on the dip side. Though there is 
no doubt a limit to the furnace, as a creative power, yet 
