338 " VCXTIULTION OF MINES OR HOSPITALS. 



the night, means for working the machine may be provided 

 by pnraping tip a quantity of water into a reservoir of suffi- 

 cieat height to admit of its flowing out during the night in 

 a small stream, with sufficient fall, so as to give motion to 

 the engine; or by winding up a weight of sufficient size; 

 or by nsany other means, which are easily devised. 



If, for instance, a room in which fifty persons slept was 

 eighty feet long, twenty wide, and ten high, it would con* 

 tain 16000 cubic (eet of air; and if this was to be removed 

 twice in eight hours, it would require a cylinder of thirty 

 inches diameter, working with a four-foot stroke four times 

 in a minute, to do it; or nearly that. Such a cylinder 

 , could be worked by the descent of ten gallons of water ten 

 feet in a minute; or, for the whole time, by eighty hogs- 

 heads falling the same height. 



But this is a vast deal more than could be required, as the 

 fifty people would, in eight hours, only vitiate three thousand 

 gallons of air, which could be removed by one hundred 

 and fifty strokes of a cylinder, twelve inches diameter, with 

 a four-feet stroke, which would ^ot require an expenditure 

 of more than one thousand five hundred gallons of water 

 properly applied, or about twenty-eight hogsheads. 



JOHN TAYLOR. 



Holwell, near Tavistock, 

 . Feb. 7, 1810. 



Certificate. 

 Te^imony of An extract from the Report of the Committee of Manage- 

 itsefficsicy* tnent of the Tavistock Canal, to the General Meeting of 

 Proprietors, held in August 1808, stating, that great im- 

 pediments had arisen from the want of good air in the tun- 

 nel when distant from a shaft, then adds — " For the purpose 

 of rendering the ventilation in the tunnel completely good, 

 and of doing it in a manner that maybe applied to very 

 considerable lengths in driving, the engineer has erected 

 machines, acting upon the simplest principle, and without 

 friction, which exhaust from the very place in which the 

 men are working a continued volume of vitiated air; the 

 place of which, of course, is as constantly supplied with 

 fresh air, by the pressure of the atmosphere, and thus all 

 difficulty oa this head completely ceases."^ 



V. On 



