SCIENCE IK SHOUT CHAPTERS. 



with tlie 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 thermome- 

 ter 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 dis- 

 cussing this question, tells iis 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 fiom 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 J 

 to 140 only a very small amount of labor, and that at short periods, 

 was practicable ; and further, that human labor daily, and at ordi- 

 nary periods, is limited by 100 of temperature, as a iixed point, and 

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

 endure ordinary labor at a temperature exceeding 90." 



It may be presumptuous on my part to dispute the conclusions of 

 a physician on such a subject, but I do so nevertheless, as the data 

 required are simple practical facts such as are better obtained by 

 furnace-working than by sick-room experience. 



During the hottest days of the summer of 1868 I was engaged in 

 making some experiments in the re-heating furnaces at Sir John 

 Brown and Co. 's works, Sheffield, and carried a thermometer about 

 with me which I suspended in various places where the men were 

 working. At the place where I was chiefly engaged (a corner between 

 two sets of furnaces), the thermometer, suspended in a position 

 where it was not affected by direct radiations from the open furnaces, 

 stood at 120 while the furnace doors were shut. The radiant heat to 

 which the men themselves were exposed while mkiang their greatest 

 efforts in placing and removing the piles was far higher than this, 

 but I cannot state it, not having placed the thermometer in the posi- 

 tion of the men. In one of the Bessemer pits the thermometer 

 reached 140, and men worked there at a kind of labor demanding 

 great muscular effort. It is true that during this same week the pud- 

 dlers were compelled to leave their work ; but the tremendous 

 amount of concentrated exertion demanded of the puddler in front 

 of a furnace, which, during the time of removing the balls, radiates a 

 degree of heat quite sufficient to roast a sirloin of beef, if placed in 

 the position of the puddler's hands, is beyond comparison with that 

 which would be demanded of a collier working even at a depth giv- 

 ing a theoretical rock temperature of 212, and aided by the coal-cut- 

 ting and other machinery that sufficiently high prices would readily 

 command. In some of the operations of glass-making, the ordinary 

 summer working temperature is considerably above 100, and the 

 radiant heat to which the workmen are subjected far exceeds 212. 

 This is the case during a " pot setting," and in the ordinary work of 

 flashing crown glass. 



As regards the mere endurance of a high temperature, the well- 

 known experiments of Blagden, Sir Joseph Banks, and others have 

 shown that the human body can endure for short periods a tempera- 

 ture of 260 F., and upward. My own experience of furnace-work, 

 and of Turkish baths, quite satisfies me that I could do a fair day's 



