84 REPORT— 1882. 



remarkable consistency between observations at various points, gives 1° in 

 68 feet. 



Radstock Collieries, near Bath (XIV.), witb a depth of 1,000 feet, give 

 a doubtful average of 1° in between 60 and 70 feet, the results in different 

 parts being irregular. We have adopted 1° in 62 feet. 



Fowlee's Collieet, Ponttpeidd, with a depth of 8-55 feet, gave, by one 

 observation at the bottom compared vpith the known surface-temperature, 

 a rate of 1° in 76 feet. 



Professor Phillips' observations in Monkwearmouth Colliery, published 

 in ' Phil. Mag.' for December 1834, showed a temperature of 71°2 in a hole 

 bored in the floor of a recently exposed part at the depth of 1,584 feet. 

 The surface of the ground is 87 feet above high water, and the mean 

 temperature of the air is assumed by Professor Phillips to be 47°'6. If, as 

 usual, we add 1" to get the soil temperature, instead of assuming, as 

 Professor Phillips does, that the temperature 100 feet deep is identical 

 ■with the air temperature at the surface, we obtain a rate of increase of 

 1° in 70 feet. 



3. The following are the most trustworthy results from wells and 

 borings : — 



The Sperenberg bore, near Berlin (IX. 204), in rock salt, with a depth 

 of 3,492 English feet, to the deepest reliable observation, gave an average 

 of 1° in 51'5 feet. This result is entitled to special weight, not only on 

 account of the great depth, but also on account of the powerful means 

 employed to exclude convection. 



Rock salt, according to Professor Herschel, has the very high conduc- 

 tivity -0113. 



Three artesian wells in the chalk of the Paris Basix gave the following- 

 results (IV. 24) :— 



St. Andri3, depth of observation . 8.S0 ft. . rate 1° in .564 ft. 



Grenelle l,iU2 „ . „ 1° in 56 9 „ 



Military School .... 568 „ . „ 1° in 56-2 „ 



The great well of La Chapelle, in the same basin, is not yet finished, 

 and a very great change in its indications may be expected when it 

 strikes the strong springs which it is intended to bring to the surface. 

 Up to the present time the deepest observation has been at 2,165 feet, 

 and this, by comparison with the known temperature in the artificial caves 

 under the Paris Observatory, gives a rate of 1° in 90-5 feet, which is 

 probably much slower than the truth, by reason of convection. The 

 temperature at 328 feet compared with that at 2,1 65 feet, gives 1° in 

 111 feet, this result being affected by convection at both ends. 



An artesian well at St. Petersburg (IV. 22), in the Lower Silurian 

 strata, with a depth of 656 feet, gives about 1° in 44 feet. 



A -well sunk at Takoutsk, in Siberia (IV. 22), to the depth of 540 feet, 

 disclosed the fact that the ground -was permanently frozen to this depth, 

 and probably to the depth of 700 feet. The rate of increase of tempera- 

 ture -was 1° in 52 feet. 



Of the English wells in which observations have been taken, the most 

 important is that at Kentish Town (II., III., IV.), in which Mr. G. J. 

 Symons, F.R.S., has taken observations to the depth of 1,100 feet. The 

 temperatures at different depths form a smooth series, and have been con- 

 fii'med by observations repeated at long intervals. The only question that 

 can arise as to the accuracy of the results is the possibility of their being 

 affected by convection. 



