ON WATER-PRESSURE ENGINES. 15 
_ referring to the “great pressure-engine in Derbyshire.” In one of these, 
_ dated January 10th, 1804, he says, “ It has been at work about three months 
and neyer missed one stroke, except when they let a tub swim down the 
_ descending column.” 
_ This it appears damaged the cylinder cover, which was speedily repaired 
and the engine again set in motion ; for in a subsequent letter he complains 
f non-payment for his foreman’s attendance and travelling expenses and for 
the wages of the men he sent, adding, “If they found fault with the engine 
there would be some reason for not paying, but they say it is the best in the 
world.” 
The cylinder of Mr, Trevitheck’s engine is, I believe, thirty inches in 
iameter. 
In 1841, our respected Treasurer, Mr. John Taylor, advised the application 
of another and more powerful engine at the Alport mines, which was made 
“under my direction at the Butterley Works. This was the most powerful 
"engine that had been made: the cylinder is 50 inches in diameter and the 
‘stroke 10 feet. It is worked by a column of water 132 feet high, acting 
below the piston and lifting by direct action a weighted plunger pole 42 
‘inches in diameter, which raises the water from the mine to a height of 132 
feet, so that the proportion of power to effect is as the area of the piston to . 
that of the plunger, namely, 1963 to 1385, or full 70 per cent. (see the three 
figures, Plate I.). 
I received a letter a short time ago from Mr. Darlington, who has the care 
of the machinery at the mines, and who fixed this engine, in which he says 
_the engine has never cost them £12 a-year since it was erected. 
_ The usual speed is about five strokes per minute, but it will work at the 
“rate of seven strokes without any concussion in the descending column ; the 
duty actually done being then equal to 168 horses’ power, of 33,000 lbs. 
da foot high in a minute. Thus, the area of the plunger, 3 feet 6 inches 
nh diameter, is 9°621 square feet x 10 feet, the length of stroke, x’7 strokes 
ber minute —673°47 cubic feet of water raised 132 feet high in a minute; 
and 673°47 cubic feet of water x62:5lbs., the weight per foot, x 132 feet in 
height =5,556,127, which, divided by 33,000, gives 1683, say 168 horses’ 
wer. The pressure upon the piston from a column of water 132 feet 
gh, reckoning 27 inches of water equal to a pound, is about 58 pounds on 
e square inch, or rather more than 50 tons pressure on the area of the piston. 
Thus, the area of the piston, 50 inches in diameter, is 1963 square inches 
' 58lbs.=113,854, and this divided by 2240, the number of pounds in a 
ton, gives 50°8, say 50 tons.. 
_ This engine was erected early in 1842, and has been at work without 
intermission for more than six years. On one occasion, when I made inquiry 
about it, I was told that it had been constantly going for the last seventeen 
weeks, and nobody had seen it during the time. 
_ An excellent model of this engine will be found in the museum of Econo- 
mic Geology, made by Mr. Jordan, since so well known by his invention for 
earving wood by machinery. . 
It will be observed that after the large valves are closed, the pressure is 
continued upon the piston to complete the stroke. This was at first done by 
aeans of cocks at the sides, but as the friction of these caused some little 
ouble, Mr. Darlington substituted some small pistons to shut off the water 
| at the termination of the stroke, and at the same time made the openings a 
‘little larger. 
| Mr. Taylor has since, I believe, had another engine of the same size made 
for a lead mine in Wales, and the result has been equally satisfactory. 
hs 
