in the Cornish Pumping Engines. 49 



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 connect- 

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

 respectively of nine and sixteen inches in diameter. 



The lowest lifts at Huel Towan and East Crinnis were 

 lifting 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 

 diu'ing the retm'n-strokes of the engines by the weight of the 

 rods.* 



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

 feet, the connecting rods were foiu'teen inches square ; and 

 from that place do^ATiward they extended about 300 feet, and 

 were twelve inches square. They were kept in then- places 

 by thirteen sets of guides, which exposed a surface of about 

 53.5 square feet.t 



From the sm-face to 396 feet deep in Binner Downs, the 

 rods were fourteen inclifes square ; and from thence down- 

 ward, there were about 258 feet of twelve-inch rods ; these 

 were also retained by thirteen sets of stays, having an area of 

 about 35.6 feet. 



The rods, from the surface to 470 feet deep in East Crinnis, 

 were fifteen inches square, and thence about 200 feet deeper 

 they were twelve inches : eleven sets of stays retained them 

 in their places, and exposed a surface of about 38.8 feet. 



Where the rods touch the stays, they are protected by thin 



tained in the water. At Huel Towan I fouud, by evaporation, that about 

 3C0 grains 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. 



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

 a counterpoise is applied to balance some part of their weight : such was 

 the case in all the engines here mentioned. 



t The lengths of the lifts and of the rods do not coincide, because the for- 

 mer overlap each other in every case, in order that the higher pumps may 

 draw out of the same cisterns into which the lower empty ; and because the 

 rods which take the different Uj'tn are also doubled at the Mtf-aff. 



VOL XXVII. NO. LIII. JVLY 1831*. D 



