M. Arago's Biographical Memoir of James Watt. 26 1 



repair it, and under the able hand of the artist all the defects 

 of its construction disappeared, and from that time the ap- 

 paratus annually performed its task in the class-room, to the 

 astonishment of the admiring pupils. With this degree of suc- 

 cess most men would have been satisfied. Not so Watt ; who, 

 according to custom, here beheld an occasion for the gravest 

 study. His researches were successively directed to all the 

 points which seemed capable of explaining the theory of the 

 machine. He determined the extent to which the water dilated 

 in passing from its liquid state into that of steam ; he calcu- 

 lated the quantity of water which a given weight of coal could 

 vaporize, — the quantity of steam, in weight, which each stroke 

 of one of Newcomen's machine of known dimensions expended, 

 — the quantity of cold wat.er which required to be injected into 

 the cylinder to give the descending stroke of the piston a cer- 

 tain force ; and finally, the elasticity of steam at diff'erent 

 temperatures. All these investigations would have occupied 

 the lifetime of a laborious philosopher, whilst Watt brought 

 all his numerous and difficult researches to a conclusion, with- 

 out allowing them to interfere with the labours of his work- 

 shop. Dr Cleland wishing, not long ago, to shew me the 

 house, near Port-Glasgow, whither our associate retired, after 

 quitting the shop, to follow out his experiments, we found it 

 pulled down. Our disappointment was great, but happily of 

 short continuance, for, within the site on which it had stood, 

 we found ten or a dozen vigorous workmen, who seemed oc- 

 cupied in doing all honour to the cradle of modern steam-en- 

 gines ; they were at work on boilers whose united dimensions 

 certainly equalled those of the humble dwelling which then 

 stood no more. In such a spot, and in such circimistances, 

 the most elegant mansion, the most superb monument, or the 

 most pei'fect statue could not have so much awakened the 

 most interesting associations as these colossal caldrons ! 



If the properties of steam be still present in your recollec- 

 tion, you will at once perceive that the economical play of 

 Newcomen's machine seemed to require two irreconcilable 

 conditions. When the piston descends, the cylinder must be 

 cold ; if this be not the case, it encounters steam still highly 

 elastic, which much retards its progress, and diminishes the 



