" 122 On Veiitilathig Mines or Hospitals, 



cheapest and most oflTectual scheme for this purposCj where 

 circumstances will admit of its being applied, is one which 

 I adopted some time since in the tunnel of the Tavistock 

 canal. It is by applying the fall of a stream of water for 

 this purpose, and it has been long known that a blast of 

 considerable strength may be obtained in this manner, which 

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

 stream being turned down a perpendicular column of pipes, 

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

 one way, with an opening at another part for the air, which 

 being pressed into it by the falling water, may be con- 

 veved in any direction, and will pass through air-pipes 

 with a strong current, which will be found efficacious in 

 ventilating n)ines in many instances, as it has likewise, in 

 some cases, been sufficient for urging the intensity of fires 

 for the purposes of the forge. It is easily procured where 

 a sufficient fail is to be had ; and the perpendicular column 

 can be so tlxed as that the water from the bottom may pass 

 off, while the air is forced into a pipe branching from the 

 air-vessel, and which is to be continued to the part of the 

 mine where the supply of fresh air is recjuired. 



I have found, howtver, that the forcing into vitiated air 

 a mixture of that which is purer, even when the best means 

 are used, though a measure which affords relief, is not in 

 bad cases a complete remedy; and, where the operation de- 

 pends on nianual labour, or any means that are not unre- 

 mitted in their action, it becon)cs (juite ineffectual. The 

 foul air, charged with the smoke of gunjiowder used in 

 blasting, and which it slronglv retains, is certainly amelio- 

 rated by the mixture of pure air, but is not removed. While 

 the blast continues, some of it is driven into the other parts 

 of the muie; but when the influx of pure air ceases, it re- 

 turns again :-or if during the influx of pure air a fresh vo- 

 lume of smoke be produced by explosions which are con- 

 stantly taking place, it is not until some lime afterwards 

 that it becomes sufficiently attenuated for the workmen to 

 resume their stations with comfort. 



A consideration of these circumstances led me to think 

 that the usual operation of all ventilating engines ought to 

 be reversed, toalloid all the advantages that could be desired; 

 that, instead of using tlje machines which serve as con- 

 densers, cxhaesters should be adopted ; and thus, instead 

 of forcmir pure air into thai in a vitiated state, a complete 

 remedy could only be had by pumping out all that was 

 inipure as fast as it becairie so. 

 Many modes of doir.g ibis suggested theipseh«es to me, 



' by 



