398 POWER OF STEAM ENGINES* 



tates that reduction, is an instance of arrangement so hap- 

 pily suited to the purposes of human industry, that it can 

 hardly be considered as recurring unnecessarily to final 

 causes, if we conceive that this distribution of the rude 

 materials of the earth was determined with a view to the 

 convenience of its inhabitants." 



Let us briefly consider what is the effect of mineral fuel, 

 on the actual condition of mankind. The mechanical power 

 of coals is illustrated in a striking manner, in the following 

 statement in Sir J. F. W. Herschel's admirable Discourse 

 on the study of Natural Philosophy, 1831, p. 59. 



" It is well known to modern engineers that there is virtue 

 in a bushel of coals, properly consumed, to raise seventy 

 millions of pounds weight a foot high. This is actually the 

 average efiect of an engine at this moment working in 

 Cornwall. 



The ascent of Mont Blanc from Chamouni is considered, 

 and with justice, as the most toilsome feat that a strong 

 man can execute in two days. The cumbustion of two 

 pounds of coal would place him on the summit." 



The power which man derives from the use of mineral 

 coal, may be estimated by the duty* done by a pound, or 



* The number of pounds raised, multiplied by the number of feet througli 

 •which they are lifted, and divided by the number of bushels of coal (each 

 weighing eighty-four pounds) burnt in raising them, gives what is termed 

 the duty of a steam engine, and is tlie criterion of its power. (See an im- 

 portant paper on improvements of the steam engine, by Davis Gilbert, Esq. 

 Phil. Trans. 1830, p. 121.) 



It is stated by Mr. J. Taylor, in his paper on the duty of steam engines, 

 published in his valuable Records of Mining, 1829, that the power of the 

 steam engine has within the last few years been so advanced by a series of 

 rapid improvements, that whereas, in early times, the duty of an atmospheric 

 engine was that of 5,000,000 pounds of water, lifted one foot high by a bushel 

 of coal, the duty of an engine lately erected at Wheal Towan in Cornwall, 

 has amounted to 87,000,000 pounds; or, in other words, that a series of 

 improvements has enabled us to extract as much power from one bushel, as 

 originally could be done from seventeen bushels of coal. Thus, through the 

 instrumentality of coal as applied in the steam engine, the power of man 



