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



portance ; in fact, it is a true steam-engine. It is scarcely, 

 however, necessary to add, that it has no real resemblance, 

 either as regards form, or the mode of action of the moving 

 force, to the machines which are now in use. Were, how- 

 ever, the reaction of a cuiTsnt of steam ever to become prac- 

 tically useful, it would unquestionably be right to trace the 

 idea back as far as Hero ; at the present day, the rotatory 

 Eolipyle can be introduced here, only as wood-engraving is 

 mentioned in the history of printing.* 



In the steam-engines of our manufactories, our steam- 

 vessels, and railroads, the motion is the immediate result of 

 the elasticity of the steam. Hence we must inquire where 

 and how the idea of this power took its origin. 



The Greeks and Romans were not ignorant that steam 

 might acquire a prodigious mechanical power ; for they ex- 

 plained, with the help of the sudden vaporization of a certain 

 quantity of water, those frightful earthquakes which in a few 

 moments force the ocean from its wonted bed, overturn to 

 their foundations the most solid monuments of human indus- 

 try, suddenly produce considerable islands in the midst of 

 deep seas, and uplift high mountains in the centre of con- 

 tinents. 



Though the contrary has been asserted, it does not appeal* 

 that this theory of earthquakes presupposes that those who 

 were its authors had engaged in any calculations, experiments, 

 or exact measurements. Every one at the present day, knows 

 the fact, that if at the moment a boiling metal enters into the 

 earthy or plaster moulds of the founder, but a few drops of 

 liquid be enclosed in the moulds, the most dangerous explosions 

 follow. Notwithstanding the progress of science, founders even 



• These remarks apply likewise to the project whicli Branca, an Italian 

 architect, published at Rome in the year 1629, in a work entitled The Ma- 

 chine, and which consisted in producing a movement of rotation by directing 

 tlie steam issuing from an eolipyle, under the form of a blast or wind, upon 

 tlie winglets of a wheel. If, contrary to all probability, steam should ever 

 be employed in the form of a direct blast, Branca, or the now unknown 

 author from whom he borrowed this idea, would take the first place in the 

 history of this new kind of machines. As it respects those at present in 

 use, the claims of Branca are absolutely null. 



