THE LIMITS OF OUR COAL SUPPLY. 201 



duty of the poor wretches who are doomed to this work. 

 It is hard to believe that human beings could be got to 

 labor under such conditions, yet such persons are to be 

 found. The work of stoking or feeding the fires is usually 

 done by Arabs, while the work of bringing the coal from 

 the bunkers is done by sidi-wallahs or negroes. At times 

 some of the more intelligent of these are promoted to the 

 stoking. The negroes who do this kind of work come 

 from Zanzibar. They are generally short men, with strong 

 limbs, round bullet heads, and the very best of good nature 

 in their dispositions. Some of them will work half an 

 hour in such a place as the stoke-hole without a drop of 

 perspiration on their dark skins. Others, particularly the 

 Arabs, when it is so hot as it often is in the Eed Sea, have 

 to be carried up in a fainting condition, and are restored 

 to animation by dashing buckets of water over them as 

 they lie on deck." 



It must be remembered that the theoretical temperature 

 of 116 at 4000 feet, the 133 at 5000 feet, or the 150 at 

 6000 feet, are the temperatures of the undisturbed rock ; 

 that this rock is a bad conductor of heat, whose surface may 

 be considerably cooled by radiation and convection; and 

 therefore we are by no means to regard the rock tempera- 

 ture as that of the air of the roads and workings of the 

 deep coal-pits of the future.* It is true that the Eoyal 

 Commissioners have collected many facts showing that the 

 actual difference between the face of the rocks of certain 

 pits and the air passing through them is but small; but 

 these data are not directly applicable to the question under 

 consideration for the three following reasons: 



First. The comparisons are made between the tempera- 

 ture of the air and the actual temperature of the opened 



*In a paper on the Comstock mines, read at the Pittsburg meet- 

 ing of the American Institute of Mining Engineers in 1879, by Mr. 

 John A. Church, tiie hot mine waters are described as reaching 158 

 Fahr. (so hot that men have been scalded to death by falling into 

 them). Tlie highest recorded air temperature there is 128. These 

 are silver mines, and vigorously worked in spite of this tempera- 

 ture and great humidity. A much higher temperature is endurable 

 in dry air. 



