BY WM. FRYAR, INSPECTOR OP" JUNES, yUEENSLAXD. 27 



premium for attention to underyvound ventilation ; and yet com- 

 paratively few of the managers of mines miderstand the 

 principles which govern the motions of the atmosphere,"' and 

 fm'ther, " In districts where ventilation is not miderstood it is 

 •commonly asserted by miners and others that the deeper the 

 mine the more dilKcult the ventilation, when as will presently be 

 shown the contrary should be the case, many parts of the deep 

 metalliferous mines are altogether abandoned in consequence o^ 

 the poor air and high temperature; this is neither due to the heat 

 communicated by the rock, however deep the shaft, nor to the 

 thousands of yards which it may be indispensible for the air to 

 travel before it reaches the surface." An example is then given 

 in which the air increased 5^ degs. in descending according to the 

 usual rule of 1 degree increase of temperature for every 300 feet 

 •of descent, due to the increased pressure of the air ; which it 

 again lost on returning to the surface where it exhibited a tem- 

 perature of 4G degrees. No notice is here taken of the internal 

 heat of the earth, but the air at the surface was below the 

 average temperature, and therefore, the heat at the invariable 

 plane of temperature might in part account for the oh degrees 

 difference, the pressure owing to depth being lost by friction in 

 the shaft, and the drawing effect of furnace or other artificial 

 ventilation, as the example is taken from a coal mine. 



Andre, in his " Mining Engineering," refers to it as a well- 

 known fact that the temperature increases at the rate of about 

 1 deg. Fahrenheit for every (30 feet in depth, but gives no proof. 

 Gallon says, — "It is well known that at a little depth below the 

 surface we arrive at a point where the temperature is invariable 

 throughout the year; this is the case all over the globe, and the 

 invariable temperature referred to is the mean temperature of 

 the year at the surface at the place of observation. In sinking 

 below this point again, we find an increase of temperature which 

 varies according to circumstances, still imperfectbi imdemtoud ; but 

 amongst them may be reckoned the peculiar conductivity of the 

 rock, which is an important factor. This increase amounts to 

 1 deg. Fahrenheit for every 45 to 50 feet of vertical depth sunk 

 through." In the " History of Fossil Fuel " the writer says. — 

 " The long agitated question as to whether the temperature of our 

 planet increases towards the centre or not has received little 



