SECT, ix.] OF THE APPLICATION OF STEAM ENGINES. 279 



The engineers' names are given who plan the construction and superintend the 

 execution and erection of the engines, for which they are paid in proportion to the 

 power ; they also attend to them afterwards, and direct such renewals or repairs 

 as may be necessary, at fixed salaries. The principal manufacturers of engines 

 for the Cornish mines are Messrs. Trevenan, Carne, and Wood ; Messrs. Harvey 

 and Co. ; Messrs. Fox and Co. ; and Messrs. Price and Co. 



577. The depth of the pump shaft of a mine is divided into lifts of not more 

 than twenty-five or thirty fathoms, if it can be avoided, with a cistern at each lift, 

 consequently the water is raised from cistern to cistern. The size of the pumps 

 is seldom greater than sixteen inches in diameter, and it will always be found 

 better to make an additional set than to exceed this size. 



578. The engines most adapted for economy of fuel are described in art. 411 

 and 419 ; those which are most simple, in art. 393 and 400 ; and as it frequently 

 happens that engines have to be removed from place to place, an engine supported 

 by frames of cast iron is shown in Plate xi. 



579. For drawing ores and coals, a double engine of from twenty to thirty 

 horse power is used ; the size of the cylinder should be such, that the power shall 

 be equal to the resistance when the stress is the greatest ; hence, engines for this 

 purpose require more fuel to raise the same quantity of matter a given height, and 

 there is also much loss of effect through stoppages, changes of motion, &c. When 

 1 Ib. of coal raises 70,000 Ibs. of ore, it is about the maximum quantity in irregular 

 work of this kind. The weight of matter drawn at once is from 3 to 7 cwt. 

 The weight of a rope is about -27 c* Ibs. per fathom ; when c is the circum- 

 ference in inches: the greatest stress on a rope should not be more than 700 

 times the weight of a fathom of the rope ; and the stress on the engine should be 

 equalized by the rope winding on to a spiral drum, * like the fusee of a watch, 

 by which the expense of the engine, and the expenditure of fuel would be reduced. 

 The engine should work expansively, (art. 419.) and be equalized by a fly wheel, 

 (art. 540.) and regulated by a governor, (art. 550.) 



When an inclined plane is necessary under ground, a small high pressure engine 

 is sometimes used to draw the coals to the principal shaft, of the kind described 

 in art. 371. 



580. Engines are also employed to break ores by means of stampers, a 

 process which seems capable of much improvement. Double engines are em- 

 ployed to raise the stampers by means of cams ; and as the power of the engine 

 is nearly uniform, the space through which the stamper is raised, should increase 



1 See Encycl. Metho. Diet, de Chimie et Metallurgie, Seconde Partie, Planche 20 ; or Gilpiri's 

 Method, Transactions of the Society of Arts, vol. xxv. p. 76. 



