12 



Prof. J. Prestwich. 



that ventilation has a preponderating influence is shown by an experi- 

 ment of Mr. Wynne, who found that in a rise of the Dukinfield 

 Colliery, where owing to defective ventilation the temperature of the 

 air and rock were both 76°, the rate of increase from the surface gave 

 only 55 feet per degree. 



Other causes have also been suggested for the lower temperature of 

 the Dukinfield pit. Mr. Dickinson states that before the shaft was 

 sunk, two of the principal seams of coal in the upper part had been 

 worked away from other pits, and that the lower seams had been 

 worked a long way from the outcrop down towards the Astley pit.* 



The Dukinfield observations, therefore, while they confirm the 

 general law of increase of temperature with the depth, are scarcely 

 admissible in estimates concerning the exact rate of increase of 

 temperature with the depth, and it would be safer to omit them in 

 such calculations. 



I do not mean to imply that good observers have or would select 

 long exposed and cooled surfaces, but others have done so, and my 

 object here is to show that cooling must at once commence, and that 

 it is difficult to escape in any part of the pit, or however early the 

 experiments are made, from the effects of ventilation. It is not a 

 question of weeks or months, but of days, if not hours. 



Effects of Ventilation. — The evidence given before the Committee 

 of the Royal Coal Commission of 1867, " On the Possible Depths of 

 Working," is particularly valuable for the information it affords 

 respecting the effects of ventilation. 



At the Pendleton Colliery (Nos. 104 and 122), near Manchester, 

 the coal in a level 500 yards from the down brow, had a temperature 

 of 70°, and at 1000 yards distant, in the same level, and when just 

 opened, it had a temperature of 83° P. 



At the Rosebridge Colliery, Wigan, the temperature of the Raven 

 coal in the shaft was 78°, whilst at 630 yards distant it had a tem- 

 perature of 88°. The air at the bottom of the down-shaft at a depth 

 of 1800 feet was 60-5°, and, after circulating 1500 yards, 73°. At 

 another time it was 51'5°; after circulating 2400 yards, 67*5° ; and 

 after 3140 yards, 71°. In July, 1858, the strata at the same depth 

 had a temperature of 80° ; in March, 1861, it was reduced to 72°. 



At the Annesley Colliery (No. 106), Nottinghamshire, a fresh cut 

 coal at a depth of 1425 feet had a temperature of 73°, and six months 

 later it had fallen to 64°. In another case, the coal cooled 11° in three 

 months. 



The volume and velocity of the air currents vary greatly. In one 

 place a circulation of 5000 cubic feet per minute is recorded. In 

 another pit the circulation was 100,000 cubic feet per minute, while 



* Coal Commission Eeport, vol. ii, " Depth of Working." 



