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force is used,) will cause as good a ventilation as 46 cwt. will 

 do when consumed at a furnace. I take the above 200 

 yards as the average depth of mines generally. 



" I might here observe, that where a fire is used in the 

 bottom of a shaft, the temperature in the upcast decreas es 

 as the square of the distance from the fire. Therefore, I 

 should not say that a deep mine is more difficult to ventilate 

 than one of 60 or 70 yards. Suppose a furnace consumes 

 18 cwt. of coal in 24 hours, and exhausts 212 cubic yards 

 of air per minute, if I wish to ascertain how much fuel it 

 would require to exhaust double the quantity of air in the 

 same given time ? The following rule will give the answer : — 

 The required quantity being 424, it must be cubed and 

 multiplied by 18, the quantity of fuel known for 212 cubic 

 yards. The product of the larger number must be divided 

 by the lesser, which gives a quotient of 144; when divided 

 by 2, the square of the increased quantity equals 72 cwt. 

 for 24 hours. If we are desirous of knowing how much air 

 80 cwt. of good coal will cause to pass through a mine per 

 minute, half the square root of 80 gives the answer, allowing 

 the two first decimals in the root to be primes ; the quotient 

 is 447 cubic yards of air per minute. This question may 

 also be answered thus : — Suppose air travels at the rate 

 of five miles per hour through the workings of a mine, every 

 object this air comes in contact with, it strikes with a given 

 force equal to 0.123 of a pound on the square foot; but if 

 caused to travel ten miles per hour, it will strike with four 

 times the force, viz., 0.492 of a pound on the square foot. 

 Therefore, if wind is required to travel at double the velocity 

 through mines, there must be four times the quantity of fuel 

 used to produce the force above specified. Allowing these 

 observations to be correct, many evils would arise from the 

 use of such extensive fires, such as destruction of the sides 

 of the upcast shafts ropes ^ guide rods, and, indeed, all sub- 

 stances that come within the limits of its power. 



