S32 VENTILATIOV OF MINES OR HOSPITALS^ 



several hundred pounds; or in sinking a shaft it maybe 



necessary, at an expense not much less, to drive a IctcI to 



it from some other for this purpose alone. 



Attempts to To avoid this, recourse has been had to dividing the 



avoid this by a ^>iaft-or level into two distinct parts, communicating near 

 doubleshaft: „ . . v , , .. , , . , 



the part intended to be ventilated, so that a current may be 



produced in opposite directions on each side the partition ; 



and this, where room is to be spared for it, is often eflectual 



to a certain extent. It is found however to have its limits 



at;novery great distance, and the current at best is but a 



feeble one, from the nearly equal states of heat in the air on 



or by forcing each side. l^»e only scheme beside these, that I know of, 



tlown iiir. j^^^ hitherto been to force down a volume of purer air, 



through a system of pipes placed for the purpoie, and a 



•variety of contrivances have been devised for effecting this ; 



most of them arc so old that they may be found described 



Common me- in Agricola's work De Re metallica. The most common 



thod of doing areby bellows worked -by hand;, by boxes or cylinders of 



various forms placed on the surface with a large opening 



against the wind, and a smaller one coram uniciiting with tho 



air-pipes by a c^-lindcr and piston working in it, which, 



when driven by a sufficient force, has great power; but the 



Cheaper and cheapest and most efjcctuai scheme for this purpose, where 



moreefficaeious . ^^^^gjjj^j,^3 will admit o{ its being applied, is one which I 



unethod. . , . /. t rn . 1 1 



adopted some time since in the tunnel of the 1 avistock canal. 



^ It is by applying the full of a stream of water for this pur- 



pose, 'and it has been long known that a blast of consider- 

 able strength may be obtained in this manner, which has 

 the advantage of being constant and self-acting. The stream 

 bring turned down a perpendicular column of pipes, and 

 clashing in at a vessel so contrived as to let off the water 

 one way, with an opening at another part for the air, M'hich 

 being presse 1 into it by t\\c falling water, may be conveyed 

 in any direction, and will pass through air,pipes with a 

 strong cwrrent, which will be found eflicacious in ventilating 

 mines in many instances, as it has likewise, in some cases, 

 been sufficient for urging the intensity of fires for the pur- 

 poses of the forge. It is easily procured where a sufficient 

 fall is to be had, and the perpendicular column can be so 

 ^xed, as that the ^yatcr.from. the bottom may pass off, 



while 



