404 



TRANSACTIONS OF THE 



CHAPTER III. 



The ventilation of mines being the next subject which 

 comes under consideration, and as there are startling 

 facts connected with it, which have of late engaged at- 

 tention, I will take occasion to place them in that light 

 which their importance merits. 



Under this view, it becomes necessary to allude to the 

 temperature and degree of heat which exist at various 

 depths in mines. It would appear, from data entitled to 

 every credit, that a considerable increase takes place, in 

 a certain ratio, as we proceed in depth ; that it exceeds 

 ^0° in the deepest mines; that it amounts to 70° at a less 

 depth than 1000 feet, and that it is 5 or 6° above the 

 mean temperature of the climate, at no greater depth 

 than from 200 to 400 feet. 



The existence of this temperature, at the bottom of 

 mines, will, of itself, necessarily occasion a constant cir- 

 culation of air upwards, through the shafts ; and as what 

 ascends must be replaced by the air above, there will, 

 of course, be a constant current downwards, through the 

 same or other shafts. The extent of ventilation in mines 

 will depend on many circumstances, more especially on 

 their depth, the number of shafts, the degree of commu- 

 nication between the different galleries, and also on the 

 state of the wind at the surface. 



Variations in the wind at the surface would appear to 

 affect considerably the currents of air underneath in the 

 levels as well as in the shafts, and that where at one 

 shaft the current has been upwards, and in another 

 downwards, a change in the wind has placed it vice 

 versa — thus making the current run in opposite direc- 

 tions at different times. The strength also of the cur- 

 rent underground would seem to depend upon the wind 

 at the surface blowing hard or softly. 



In a mine extensively worked, where a communica- 



