440 Summarij RevieXc of the late Lwcstigations 



discharged by the pumps from many of the Cornish mines is 

 very considerable : thus Huel Abraham discharges, fiom the 

 depth of UiO feet, about 2,092,320 gallons every 24 hours; 

 Dolcoath, from nearly the same depth, 535,173 gallons in 

 the same time; and Huel Vor, from the depth of 950 feet, 

 1,692,660 gallons." 



" 4. In giving an account of the ventilation of mines, it is 

 necessary to anticipate, in some degree, the result of our in- 

 vestigations respecting temperature, and to notice the degree 

 of heat that is found in the air, water, and earth, at the bot- 

 tom of mines. The precise degree of this temperature will 

 be hereafter stated ; it will suffice here to mention that it ex- 

 ceeds 80° 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 (however produced) will, of itself, necessarily 

 occasion a constant circulation 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 communication 

 between the different galleries, and also on the state of the 

 wind at the surface. The cooling effect of high winds is very 

 perceptible even at the bottom of shallow mmes, and it appears 

 that the currents of air in the very deepest mines are consi- 

 derably influenced by the force and direction of these." 



" For the following observations on this subject, relative to 

 the magnificent mine of Dolcoath, I am indebted to Mr. John 

 Rule jun., one of the superintendants. ' I have made some 

 experiments to ascertain the direction of the currents of air in 

 this mine, and find that in 25 of our principal shafts (the whole 

 of those open on the main lode) 1 3 have a strong current of 

 air downwards, and 12 about the same degree of current up- 

 wards ; they differ however with respect to the strength of the 

 currents, some being very strong, others less so. I never 

 made any experiments to ascertain the currents of air before ; 

 but from common observation, I am enabled to state that 



" that all the water of the deepest level finds its way to the sump. The 

 water from the upper levels is received into cisterns placed in different 

 parts of the shaft, at the termination of each tier of pumps, from whence 

 It is drawn to the adit." 



they 



