M. Arago's Biographical Memoir of James Watt. 239 



Upon this last-named fact, enlightened minds will not dwell 

 with foreboding melancholy. They know well that mechani- 

 cal powers, like hmnan passions, will become useful or hurt- 

 ful according as they are directed right or wrong. In the 

 case of steam, it in fact requires only a very simple con- 

 trivance, to make available to productive labour, the for- 

 midable elastic power which, according to all appearance, 

 shakes the earth to its centre, surrounds the art of the sta- 

 tuary with imminent danger, and breaks into a thousand 

 pieces the strongest bombshell. 



In what state do we find this projectile previous to its ex- 

 plosion ? The lower part contains water at a very high tem- 

 perature, hut still liquid, and its remaining portion is filled 

 with steam. This, according to the characteristic law of all 

 gases, exercises its power equally in all directions ; it presses 

 with equal intensity upon the water, and the metallic sides 

 which contain it. Let us now place a stopcock at the lower 

 part of these sides, — on opening it, the water, forced by the 

 steam, will issue forth with extreme velocity. If the stopcock 

 was placed upon a tube, which, after taking a bend round the 

 outside of the bomb, were then directed vertically from below 

 upwards, the water would ascend in the tube in the ratio of 

 the elasticity of the steam ; or rather, for it is the same thing 

 in other words, the water would rise according to the degree 

 of temperature ; and this ascending movement would find its 

 limits only in the strength of the apparatus. 



For this bomb let us now substitute a strong close boiler of 

 large dimensions, and then there is nothing to prevent our 

 forcing great masses of liquid to indefinite heights by the sole 



Alberti, who ^v^ote in 1411, he should inform us that, in the beginning of 

 the fifteenth century, lime-burners were much alarmed both for themselves 

 and tlieir kilns, on account of the explosions which were produced when the 

 pieces of limestone had a cavity in their interior, I answer, that Alberti 

 himself was ignorant of the real cause of these terrible explosions ; that he 

 attributed them to the transformation by flame of the air they contained 

 into steam. To this I add, that the explosion of a piece of limestone thus 

 accidentally hollow, supplied no means of that numerical calculation, of 

 which the experiment of Uivault was evidently susceptible. 



