M. Arago's Biographical Memoir of James Watt. 263 



wheels, constitute the secret, the true secret, of the astonish- 

 ing perfection of the manufactures of our epoch. It is this 

 which now-a-days confers on the steam-engine a working move- 

 ment which is wholly free from irregularity ; hence it can as 

 easily embroider muslin as forge anchors, — can weave the most 

 delicate fabrics, as well as communicate a rapid movement to 

 the ponderous stones of a flour-mill. This also explains how 

 Mr Watt said, without fearing the reproach of exaggeration, 

 that to avoid the intrusion of domestics, we might employ 

 steam, and in cases of sickness could supply medicines through 

 its silent agency. I am not ignorant that in popular estima- 

 tion this gentleness of movement is supposed to be obtained 

 at the expense of power. But this is an error, and a gross 

 one ; and the apophthegm " Much noise and little work," is 

 not only true in the moral world, — it is also an axiom in me- 

 chanics. 



A few words more, and we reach the termination of these 

 technical details. Within these few years great advantage 

 has been derived from not allowing a free communication 

 between the boiler and cylinder, throughout the whole con- 

 tinuance of each stroke of the machine. This communication 

 is accordingly interrupted when the piston has traversed, we 

 shall say, a third of its course. The two remaining thirds of 

 the stroke are thus accomplished in virtue of the pre-acquired 

 velocity, and especially by the expansion of the steam. Now, 

 Mr Watt had already indicated this procedure.* Excel- 

 lent judges place it, in point of economical importance, on a 

 level with the condenser. It appears certain that since its 

 adoption the Cornish machines have yielded unlooked-for re- 

 sults ; and that, with a bushel of coal, they realize the work 

 of twenty men working for ten hours. Let us remember that 

 in the coal districts a bushel of coal often does not cost nine- 

 pence, and it will be seen that Watt has established, that 



* The principle of the expansion of steam, clearly indicated in a letter of 

 Mr Watt'n to Dr Small, dated in May 1769 (see the letter in Favey's Steam- 

 Engine, vol. i. p. 339), was put in practice in the year XTTii at Solio, and in 

 1778 at the Shadicell WuU-r- Works, from economical considerations. The in- 

 vention, and tin- advantages which were expected from it, are fully described 

 in the patent of 1782. 



