264 M. Arago's Biographical Memoir of James IFatl. 



over a great part of England, a man's hard day's work — ten 

 work hours to the day — may be done for less than a half- 

 penny.* 



Such numerical valuations so strikingly prove the importance 

 of the inventions of our learned associate, that I cannot resist 

 the temptation of giving two other illustrations, both of which 

 I borrow from Sir John Herschel, one of the most distin- 

 guished correspondents of the Academy. The ascent of Mont 

 Blanc, starting from the valley of Chamouni, is very justly 

 considered as one of the hardest tasks which it is possible 

 for a man to execute in the course of two days. Thus the 

 maxinmm of the labour which we are capable of undergoing in 

 twice twenty-four hours, may be measured by the transport of 



* At a time when so luany people are occupied with projects of rotatory 

 steani-eugines, it would be unpardonable were I not to state that Watt liad 

 not only thought of them (of which we find proof in his patents), but had 

 actually constructed them. Mr Watt subsequently abandoned them, not 

 because they did not work, but because they appeared to him decidedly in- 

 ferior in an economical point of view to machines of double powers and 

 rectilineal oscillations. 



There are, in fact, few inventions, great or small, among those so admi- 

 rably combined in our present steam-engines, which are not the develop- 

 ment of some of the original ideas of Watt. Examine his labours, and, in 

 addition to the principal points minutely enumerated in the text, you will 

 iind he proposed machines without condensation, in which, after having 

 acted, the steam is dispersed in the air, and which were intended for loca- 

 lities where large quantities of cold water could not readily be procured. 

 Tlic operation of the iirinciple of expansion in machines with several cylin- 

 ders was also one of the projects of the Soho engineer. He suggested the 

 idea of pistons, which should be perfectly steam-tight, although composed 

 exclusively of metal. It was Watt also who first had recourse to mercurial 

 manometers for measuring the elasticity of the steam in the boiler and the 

 condenser, who conceived the idea of a simple and peiinanent gage by 

 whose assistance might always be ascertained, with a glance of the eye, the 

 level of the water in the boiler, and who, to prevent this level ever varying 

 injuriously, connected the movements of the feeding pump with those of a 

 float; and wlio, -when required, placed in an opening in the cover of 

 the principal cylinder of the machine the indicator, a small apparatus so 

 constructed that it accurately exhibits the state of the steam, in relation to 

 the position of the piston, &c. &c. Did time permit, I could shew that Watt 

 was not less skilful and happy in his attempts to improve the boilers, to di- 

 minish the loss of heat, and to consume those torrents of black smoke which 

 issue from common chimneys, however elevated they may be. 



