Mr Henwood 07i the temperature of Mines. 239 



temperature at considerable depths, &c. In Fig 8. Plate II. 

 which refers to Dolcoath mine*, A is the bottom of the engine 

 shaft, 235 fathoms deep ; B,C the deepest galleries or levels 

 on the course of the vein at 230 fathoms deep ; D E galleries 

 220 fathoms deep on the same vein. A great portion of the 

 water finds its way to A, whence it is pumped by a steam-en- 

 gine, the quantity discharged at the pump head in 24 hours 

 being estimated at 500,000 gallons. At «, a stream at the 

 temperature of 82° issued, and at e, a smaller one at 78°, the 

 air near A being at 80°. These results were obtained at inter- 

 vals of some years. A hole, three feet in depth, was made at 

 o in the deepest level, 15 fathoms from the engine shaft. It 

 was usually quite dry, and for some years no men had been 

 employed nearer to it than at A. In this hole was inserted 

 the bulb of a thermometer, four feet in length, the space 

 round the lower extremity of the instrument being carefully 

 filled with clay. The persons employed below DE were usu- 

 ally two, and occasionally three at a time, on an average say 

 2J constantly. In DE there were four or five at a time. 



In the galleries, 10 fathoms higher up, 10 men at a time, 

 ^ " Do. 10 do. 14 do. 



Do. 10 do. 14 do. 



The total number of men was 360, but as each worked only 

 six- hours at a time, say, equal to about 100 constantly in the 

 mine. 



The thermometer, which was placed at o in January 1821, 

 being taken up in September 1822, did not seem to be affected 

 by the seasons ; but the influx of water into the gallery, which, 

 in consequence of the stoppage of the machinery, sometimes 

 took place, caused the mercury to rise a little, to the extent of 

 1° or l.°5, the observations being made as soon as the station 

 became again accessible. At other times the temperature was 

 75° to 75.''5. A thermometer, buried eight inches in the rock, 

 at different stations, in many of the superior galleries of this 

 mine, that nearest to the surface being 100 fathoms deep, in- 

 dicated temperatures varying, according to the depth, from 



* The experiments here detailed were made before the shaft was sunk 

 so deep as 240 fathoms, mentioned in the preceding tables. 



