in the Cornish Pumping Engines. 51 



III. The work accomplished for a certain expense.^The 

 foregoing details supply all that is requisite for this inquiry, 

 except the prices of the materials consumed ; these were coal, 

 at the rate of forty-one shiUings for 72 measured bushels ;* 

 grease, forty-five sliillings and sixpence per 112 lb. ; and oil, 

 foiu' shillings and twopence per gallon ; at which rates the 

 results were by 



Huel Towan, Wilson'^s engine, 1085 tons ; 



Binner Downs, Swan's engine, 1006 tons ; 



East Crinnis, Hudson's engine, 870 tons ; 

 lifted one foot high for the expense of one farthing. 



As supplementary to the general object of the first part of 

 this inquiry, it may be useful to compare the maxima of pres- 

 sures which obtain in the cylinders, with known elasticities in 

 the boilers ; the loads of the engines remaining unchanged. 



TABLE VI. — Load of Engines, and relative pressures of Steam in the 

 Boilers and Cylinders. 



Many subjects which are yet undetermined have pressed 

 on my attention during these experiments ; among which, the 

 steam-case and air-pump are not the least important. 



If any condensation take place in the case, when protected 

 from the influence of the external air, it must be by radiation 

 to the rarer steam witliin the cylinder. Now, such influence, 

 if exerted during at least two-thirds of every stroke, J would 



' The bushel measure with a heaped head is the same which was used 

 in Mr "Watt's time, varying only as prescribed by law. 



t AH the pressures mentioned throughout this paper are absolute, and 

 as if acting against a vacuum. 



X See Table IV. 



