Page:On the economy of machinery and manufactures - Babbage - 1846.djvu/317

Rh

(340.) time during which a machine will continue to perform its work effectually, will depend chiefly upon the perfection with which it was originally constructed,upon the care taken to keep it in proper repair, particularly to correct every shake or looseness in the axes,and upon the smallness of the mass and of the velocity of its moving parts. Every thing approaching to a blow, all sudden change of direction, is injurious. Engines for producing power, such as wind-mills, water-mills, and steam-engines, usually last a long time.

(341.) Many of the improvements which have taken place in steam-engines, have arisen from an improved construction of the boiler or the fire-place. The following table of the work done by steam-engines in Cornwall, whilst it proves the importance of constantly measuring the effects of machinery, shows also the gradual advance which has been made in the art of constructing and managing those engines.