SECT, i.] THE STEAM ENGINE. 23 



were cast into a loose ring capable of being taken out, and replaced when occasion 

 required. On the large scale also, Smeaton's boilers were admirably adapted for 

 generating steam, little inferior to any that have since been contrived. 



In a report to the London bridge water works, in 1771, Smeaton proposed to 

 regulate the power of the engine by the injection, whereby the engine-keeper 

 would be enabled, while the engine was working, to vary the quantity in propor- 

 tion to the column to be lifted, and avoid the ill effects arising from a variation of 

 the column, and save fuel. 



Smeaton's first effective introduction of the improvements resulting from his expe- 

 riments on the engine seems to have been in the early part of 1774 ; l and by these 

 improvements he appears to have reduced the expenditure of fuel about one-third. 

 In 1775, he designed the Chase Water Engine, the cylinder of which was seventy- 

 two inches in diameter, and the stroke nine feet. Its power was equivalent to the 

 exertion of 108 horses, and its consumption of fuel was estimated at 1136 Ibs. of 

 Newcastle coal per hour. At its full power it was proposed to make nine strokes 

 per minute, but to be regulated by the cataract to four strokes and a half per 

 minute. The construction of the beam, and other parts of the engine, are 

 sufficiently curious to entitle it to the strict attention of the student. 2 



There seemed to be few practical circumstances that escaped Smeaton's inquiry 

 respecting the atmospheric engine ; and he drew up for his own use a table of the 

 proportions of the parts for different sized engines, which still exists in the col- 

 lection of his papers, purchased by Sir Joseph Banks. But the most important of 

 his researches relate to the load upon the piston, on which he remarks he had 

 found engines calculated to carry a load, varying from under five pounds to 

 upwards of ten pounds to the square inch, those lightly loaded being expected to 

 go with the greatest velocity, so that an engine carrying five pounds to the inch 

 must go with double the velocity of one loaded to ten pounds, the cylinders being 

 of equal area, in order that the effects of the power might be equal. He further adds, 

 that in engines, however, as in other machines, there is a maximum, which, with- 

 out new principles of power, cannot be exceeded : bad proportions of the parts, and 

 bad workmanship, may make an engine fall short, in any degree, of what it should 

 do, but its maximum cannot be exceeded by the most accomplished artists. 



Experience had, however, suggested the idea of a mean burden. The 

 original patentees (Newcomen and Co.), from some of their first performances, laid 

 it down as a rule to load the piston, so as but little to exceed eight pounds to the 

 inch ; but, on more experience, they diminished that load, and amongst the best 

 engines previous to Smeaton's time the load was made about seven pounds to 

 the square inch. 



1 Reports, vol. ii. p. 337. 2 Smeaton's Reports, vol. ii. p. 350. 



