WORK UNDER PRESSURE AND IN GREAT HEAT 395 



occur in hot air until the skin temperature reaches a certain 

 point. If the skin is cold to begin with it may be half an 

 hour or more before sweating breaks out in a very warm room, 

 whereas there will be profuse sweating within a minute if the 

 skin is warm to start with. 



I found that the Cornish miners were frequently employed 

 in places where the wet-bulb temperature was from 30° to 38 . 

 It might be supposed that, under such circumstances, cases of 

 heat-apoplexy would be common ; but I never could hear of any 

 such cases, nor did I find, even in the hottest places, that the 

 men allowed their temperatures to rise more than very slightly. 

 What they did was simply to come out and rest in a cool place 

 as soon as they felt that they were getting too hot. In fact, 

 they seemed to be nearly always resting in this way. At a 

 wet-bulb temperature of about 27 the amount of work done by 

 a miner begins to fall off, and as the wet-bulb temperature rises 

 further the work done gradually diminishes to a vanishing point. 

 It may be that a miner's health sometimes suffers from the heat ; 

 but I could not find any clear evidence of this, and the men 

 working in hot mines seem to be usually quite healthy. What 

 undoubtedly suffers very heavily is the pocket of the mine- 

 owner. 



On the other hand, mine-horses often die of heat-apoplexy; 

 and so fatal is the heat to horses that their employment is 

 avoided in some of the hotter mines. They are liable to be 

 worked too hard in a warm mine, just as soldiers are liable to 

 be overmarched in hot weather ; whereas the miners, who are 

 perfectly free to follow the promptings of nature — for instance, 

 to take off their clothes, stop working, or go into a cool place, 

 or even into cool water, when they are too hot — escape without 

 harm. 



It seems clear that, for the economical working of a mine, 

 the wet-bulb temperature should not in general be allowed to rise 

 beyond about 27 — unless, perhaps, where there is a good air- 

 current. To maintain this limit in the ordinary working places 

 does not seem to be very difficult, provided the right measures 

 are taken in laying out the ventilation. This matter will soon 

 have to be studied much more closely by mining engineers than 

 has been the case hitherto. 



I should like, in conclusion, to point a moral, if I may, 

 in connection with the hygienic regulation of engineering and 



