32 On the VtuLilalion of Mines. 



during the operations, before the communication for the venti- 

 lating current can be effected, and before the mine and roof could 

 be subjected to the plans of Ryan or Menzies. 



Even where the works are complete, a change in the tem- 

 perature of the atmasphere may occasion a change in the di- 

 rection of the current, -so that what was the upcast shaft may be- 

 come the doivncast shaft*. Against this case, I think, Mr. Men- 

 zies' plan makes no provision. 



A stream of water falling down through one of the shafts is 

 frequently used as a means of ventilation. This expedient is 

 suited, I think, to the case where only carbonic acid gas is pre- 

 sent ; and besides, as the water must be lifted afterwards, this 

 mode of ventilation is too expensive to be practicable, except 

 on extraordinary occasions. 



It appears then that a mode of vevtilation ly mechanical 

 TTieanSy and completely under control, would be highly eligible 

 in a great variety of cases. 



Veutilation by mechanical means must be effected by a blowing 

 apparatus of some sort. This apparatus nuist be applied, either 

 Xo force a quantity of air into the mine, by which the foul gases 

 may be displaced, or to extract these gases out of the mine, 

 while common air will replace them spontaneously. In either 

 case, a tube should extend from the blowing apj)aratus to that 

 part of the mine in which ventilation will be chiefly required and 

 most useful. The mode of ventilation by extracliun seems most 

 eligible, for two reasons : 1st, The extracting tubes can be di- 

 rected to any spot in the roof or floor of the mine where the foul 

 gas is lodged, and this gas only needs to be removed ; but by 

 blow ing into the part, a quantity of harmless or salutary air must 

 also be forced away. 2dly, By the mode of extraction by a tube, 

 the foul gas is kept in a state of se))aration in its progress throngh 

 the mine and up the shaft ; but it it were to be discharged by 

 blowing inward, it might come in contact with the lights in its 

 progress, and explode, or prove otherwise dangerous or dis- 

 agreeable. 



The extracting or blowing tube would be the most expensive 

 part of this apparatus. It should be flexible, or otherwise fitted 

 to apply to and feed from either the roof or floor at pleasure ; but 

 it might be formed of the cheapest materials : and in works in 

 which there is a spare shaft, this shaft may be employed to 

 form so much of the ventilating tube. 



The best sort of blowing apparatus for ventilating mines is 



* Tliis, if we rightly understand Ryan's system, can never happen where 

 it is employed. IJis npcast anil downcast shafts are, \vc believej never 

 fcufTered to alternate. — EJ)ir. 



evidently 



