ly extracting the foul Air from them. 125 



seen from its furthest end. After blowing up the rock, the 

 miners could instantly rtturn to the place where they were 

 employed, unimpeded by the smoke, of which no appear- 

 ance would remain underground in a very few minutes, 

 ■while it might be seen to be discharged in gust^, from the 

 valve at the top. of the shaft. Tiie constant current into 

 the pipe, at the same time effectually prevented the accumu- 

 lation of air unfit for respiration. The influx of air, from 

 the level into the mouth of the pipe, rushes with such force 

 as instantly to extinouish the flame of a large candle; and 

 any substance applied, so as to stop the orifice, is hekl tight 

 by the outward pressure. 



It is now more than two years since the machine was 

 erected, and it has been uninteriuptedly at work ever since, 

 and without repair. The length of the tunnel has been 

 nearly doubled, and the pipes of course in the same propor- 

 tion, and no want of ventilation is yet perceptible. 



Two similar engines have been since constructed for other ' 

 parts of the same tunnel, and have in every respect answered 

 the purpose for which they were designed. 



The original one is worked by the small stream of water 

 before mentioned, by means of a light overshot-wheel twelve 

 feet in diameter, and about six inches in breast. — The two 

 others are attached to the great overshot-wheel which pumps 

 the water from the shafts which are sinking upon the line ; 

 and as their friction is comparatively nothmg, this may be 

 done in any case, with so little waste of power for this pur- 

 pose as not to be an object of consideration, even if the 

 power be derived from more expensive means. 



The size of the exhauster may always be proportioned to 

 the demand for air; and by a due consideration of this cir- 

 cumstance, this engine may be effectually adapted not only 

 to mines and collieries, but also to manufactories, \vork- 

 houses, hospitals, prisons, ships, and so on. 



Thus, if it were required to ventilate a shaft of a mine, 

 or a single level, which is most frequently the case, where 

 three men are at work at one time, and we allow that tho«e 

 three men vitiate each twenty-seven and a half cubic inches 

 ot air per minute, (as determined by the cxperinients of 

 Messrs. Allen and Pepvs,) and allownig furtlier that their 

 candles vitiate as nuieh as I he men, there will be six times 

 twenty-seven and a half cubic inches of air to be drawn out 

 in a ujinute, equal to one hundred and sixtv-five. 



Now a cylinder five inches in dianielcr, working with a 

 stroke at nine inches, will eflect this by one stroke m a mi- 

 nute ; 



