222 REPORT— 1844. 



being a difference in excess of the rock over the air of "IDS, or nearly '2 of 

 a degree, and of the lode over the rock of -546. 



Taking the temperature of the rock thus determined as tlie general average, 

 it siiows an increase of 7°'34'3 Fahr. for a depth of 774 feet, or deducting 

 100 feet for the line of no variation, we have 7°*343 for 674 feet, or 1° for 

 91-82 feet. 



This is a much lower rate of increase than has been noticed in general 

 hitherto. It was found necessary in the present case to fix the instruments 

 not far from being perpendicularly under the sea, the shaft of the mine being 

 nearly on the edge of the cliff, which is here 70 to 75 feet high. If there- 

 fore we should allow- for this difference, and consider the sea level as the 

 surface, we shall iiave a depth of 600 feet corresponding to 7°'343 Fahr., or 

 1°=81°"74 feet, still, after making every allowance, a slower rate of increase 

 than usually observed. 



Another important circumstance which seems to be fully established by 

 these observations, is the fact that there was a gradual though slight dimi- 

 nution of the temperature as the observations proceeded. Thus, if we take 

 the average of the first half of the observations for the tliermometer in air 

 at the bottom, and compare it with the average of the last half, we find the 

 result thus : 



First half, from August to January . . . 57'613 

 Last half, from January to July .... 56*697 



Difference '916 



the diminution being nearly one degree. 



Similarly, the thermometer in the rock gives as an average for the first 

 half 57-718 ; for tlie last half 57*044 ; the difference being -674. 

 The thermometer in the lode gives, — 



First half 58*000 



Last half 57-675 



Difference . . . -325 



a smaller difference than in the last cases ; but this instrument, it should be 

 remembered, was not fixed for four months after the others. 



That this diminution was a gradually increasing one would become evident 

 from comparing the results more in detail ; but the general fact seems abun- 

 dantly established, that so far from the operations of mining, the men em- 

 ployed, the lights, blasting, &c., having the result of increasing the tempera- 

 ture below, this temperature constantly and gradually decreased as these opera- 

 tions became more extensive. 



It may be mentioned, in connection with the observations here given, that 

 it is also the impression of the miners employed in these mines, many of 

 whom have also worked in Cornwall, America, &c., tliat it is the coolest copper- 

 mine they ever wrought in. 



In addition to these observations, arrangements have been made for a 

 similar series in other mines, where the rocks are of a different character, 

 but as yet no results have been obtained sufficient to report to the Associa- 

 tion. 



Of the £10 granted at the last meeting of the Association for these expe- 

 riments, £5 has been expended for the repairs of instruments, carriage, &c. 



T. Oldham. 



[To this Report was appended a register of all observations from August 

 7, 1843, to July 13, 1844.] 



