488 Mr. Henwood on the Cornish Ptimping-Engines. 



unable to state. From the 2nd of March to the 5th of August, 1836, the 

 duty was about 65 millions of pounds lifted one foot, by 100 lbs. of coal, 

 and the evaporation by the same quantity of fuel for the same period was 

 15-4 cubic feet. This is a sufficient approximation to the result which I had 

 five years previously obtained at Huel Towan. 



The stroke in the cylinder of Loam's engine is estimated at 10 feet ; an 

 apparatus is fixed on it for registering the actual space passed over, and the 

 mean for five months was 9-913 feet. 



Table III. — (Constants.) 

 Dimensions of the Pttmps. 



The whole loads of the three engines of which it was in- 

 tended to ascertain the duty were raised perpendicularly, ex- 

 cept the deepest lift of Wilson's engine at Huel Towan; and 

 this was inclined to the horizon about 70°, and was connected 

 to the engine-rod by a chain passing over two small wheels 

 respectively of 9 and 16 inches in diameter. 



The lowest lifts at Huel Towan and East Crinnis were lift- 

 ing pumps, and their loads were raised by the working strokes 

 of their respective engines. All the other pumps were forcing 

 pumps (plungers), and their columns were lifted during the 

 return strokes of the engines, by the weight of the rods§. 



At Huel Towan, from the surface to a depth of about 534 

 feet, the connecting rods were 14 inches square; and from 



* No correction has been applied for temperature, nor for impurities 

 contained in tlie water. At Huel Towan I found, by evaporation, that 

 about 360 trains were contained in a cubic foot. The temperature is 

 higher as we descend ; which adds to the already abundant evidence of the 

 great heat prevailing in the interior of the earth. 



t The stroke in this punij) is but 5-5 feet. 



* This lift took its supply from the hot-well. 



§ The rods are usually very much heavier than the column of water, 

 and a counterpoise is applied to balance some part of their weiglit: such 

 was the case in all the engines here mentioned. 



