i873«l Limits of our Coal Supply. 351 



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 labour, and that at 

 short periods, was practicable ; and further, that human 

 labour daily and at ordinary periods, is limited by ioo° 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 

 labour at a temperature exceeding 90V 



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

 sions of a physician on such a subject, but I do so never- 

 theless, especially 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 sus- 

 pended 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, sus- 

 pended 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 making 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 position of the men. In one of the 

 Bessemer pits the thermometer reached 140 , and men 

 worked there at a kind of labour demanding great muscular 

 effort. It is true that during this same week the puddlers 

 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 giving 

 a theoretical rock temperature of 212°, and aided by the 

 coal-cutting 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 ioo°, 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 



