242 M. Arago's Biographical Memoir of James Watt- 

 is produced a moving power almost indefinite, by means sim- 

 ply of a fagot and match, will always maintain a distinguished 

 place in the history of the steam-engine.* 



It is exceedingly doubtful whether either Solomon de 

 Caus or Worcester ever constructed the apparatus they pro- 

 posed. This honour belongs to an Englishman, to Captain 

 Savery. I have no hesitation in associating the machine 

 which this engmeer constructed in the year 1698, with those 

 of his two predecessors, although it must be added he intro- 

 duced some important modifications ; and among others, that 

 of generating the steam in a separate vessel. If it signify 

 little as to principle, whether the motive steam be produced 

 from the water which is to be raised, and in the interior of 

 the same boiler in which it is abdut to act, or, whether it be 

 produced in a distinct vessel, whence it is at will to be con- 

 veyed by means of a communicating pipe and a stopcock, to 

 the surface of the liquid proposed to be raised, it is very differ- 

 ent in a practical point of view. Another and a still more 

 important change introduced by Captain Savery, will more 

 appropriately find a place in the remarks we shall presently 

 devote to the labours of Papin and Newcomen. 



* It has been published to the world, that J. B. Porta in the year 1606, in 

 his Spiritali, nine or ten years before the publication of Solomon do Caus's 

 work, gave a description of a machine, the operation of which was intended 

 to elevate water by means of the elastic power of steam. I have elsewhere 

 demonstrated that the learned Neapolitan did not speak, either directly or indi- 

 rectly, of any machiite in the passage aUuded to ; that his object — his only object 

 — was to determine experimentally the relative volumes of water and steam ; 

 that La the small apparatus he employed for this purpose, the steam could 

 not elevate the liquid, according to the author's own account, above a few 

 inches ; and that in the whole description of the experiment, there is not a 

 single word that conveys the idea that Porta was aware of the power of 

 this agent, or of the possibility of applying it to the production of a useful 

 working machine. 



Again, are there those who think that I ought to have named Porta on 

 account simply of his researches concerning the transformation of water in- 

 to steam ? I answer, that the phenomena had been previously studied with 

 attention by Professor Besson of Orleans, about the middle of the sixteenth 

 century, and that one of the works of this mechanician contains, in 1569, 

 an essay expressly upon the determination of the relative volumes of steam 

 and water. 



