28 



Prof. J. Prestwich. 



crepancies in the rate of temperature with depth observed in the 

 Talargoch Mine (No. 158, 160) ; for although the temperature of the 

 air is not there given, we know that it will vary with the distance from 

 the shaft, of which particulars are given in the Brit. Assoc. Reports : — 



Rate of 







Distance 



Temp. 



increase with 



Station. 



Depth. 



from shaft. 



of rock. 



depth. 



III. . . . 



660 feet 



120 yards S. 



54° P. 



132 feet 



v.... 



555 „ 



170 „ S.E. 



52-9 



140 „ 



IV.... 



465 „ 



190 „ S.W. 



534 



116 „ 



I.... 



1041 „ 



190 „ KB. 



60-8 



88 „ 



VI. . . . 



636 „ 



840 „ S.W. 



58-8 



64 „ 



VII. . . . 



660 „ 



1240 „ S.S.W. 



62 



51 n 



The two partial exceptions (IV, V) are in both cases at stations of 

 lesser depths, and, being still near the shaft, are possibly more 

 exposed to the influence of the outer air. 



The effects of ventilation are also shown in another way. Some of 

 the early experiments of Dr. Porbes were made in the water in sumps 

 and pools, which necessarily would be much exposed to the cooling 

 effects of the circulating air. His tables, which give the results of 

 observations in six mines (No. 18), show a rate of increase of tempera- 

 ture relatively less with increased depth. The observations are so 

 much at variance with those subsequently made by Mr. Pox and 

 Mr. Henwood, that I can only attribute the discrepancy to the cause 

 I have here named, viz., a relatively greater cooling of the water, due 

 to increased ventilation at increased depths. It is not necessary to 

 give the whole series : the following instances bring out the fact : — 



Temperature Rate of increase 



Depth. of the water. per 1° F. 



500 to 550 feet .... 65° .... 35 feet* 



900 „ 950 „ .... 71 .... 44 „ 



1350 „ 1400 „ .... *79 .... 47i„ 



The early observations of Mr. Pox, which were made in the same 

 way in the water in fifty-three mines, gave also a diminished rate of 

 temperature with increase of depth : — 



Rate of increase 

 Mean depth. per 1° F. 



354 feet 1° in 35*4 feet 



448 „ 1 „ 43-8 „ 



648 „ 1 „ 64-2 „ 



* The rapid rate constantly observed near the surface is probably in great part 

 owing to chemical decomposition in the lodes which is most active near the surface, 

 and also to a less active ventilation. 



