198 SCIENCE IN SHORT CHAPTERS. 



bearing upon the rate of increase of temperature with 

 depth. His conclusions give a greater rate of increase 

 than is generally stated by geologists; but for the present 

 argument I will accept, without prejudice, as the lawyers 

 say, his basis of a range of 1 F. for 60 feet. According 

 to this, the rocks will reach 99. 6, a little above blood-heat, 

 at 3000 feet, and 116.3 at the supposed limit of 4000 feet. 

 It is assumed by Mr. Hull, by the Commissioners, and 

 most other authorities, that this rock temperature of 116 

 will limit the possibilities of coal-mining. At the average 

 prices of the last three years, or the prospective prices of 

 the next three years, this temperature may be, like difficul- 

 ties of the thin seams, an insurmountable barrier; but I 

 contend that at higher prices we may work coal at this, 

 and even far higher, rock temperatures ; that it matters 

 not how high the thermometer rises as we descend, we 

 shall still go lower and still get coal so long as prices rise 

 with the mercury. Given this condition, and I have no 

 doubt that coal may be worked where the rock temperature 

 shall reach or even exceed 212. I do not say that we 

 shall actually work coal at such depths; but if we do not, 

 the reason will be, not that the thermometer is too high, 

 but that prices are too low; in other words, value, not 

 temperature, will determine the working limits. 



Mr. Leifchild, in the last number of the " Edinburgh 

 Review," in discussing this question, tells us that "the 

 normal heat of our blood is 98, and fever heat commences 

 at 100, and the extreme limit of fever heat may be taken 

 at 112. Dr. Thudichum, a physician who has specially 

 investigated this subject, has concluded from experiments 

 on his own body at high temperatures, that at a heat of 

 140 no work whatever could be carried on, and that at a 

 temperature of from 130 to 140 only a very small amount 

 of labor, and that at short periods, was practicable; and 

 further, that human labor daily, and at ordinary periods, 

 is limited by 100 of temperature, as a fixed point, and 

 then the air must be dry, for in moist air he did not think 

 men could endure ordinary labor at a temperature exceed- 

 ing 90." 



It may be presumptuous on my part to dispute the con- 



