THE CONQUEST OF NATURE 



precisely similar to the apparatus employed by Hero of 

 Alexandria in various of his fountains, as regards the 

 principle of expanding gas to propel water. An im- 

 portant difference, however, consists in the fact that the 

 scheme of della Porta and of de Caus embodied the 

 idea of generating pressure with the aid of steam, 

 whereas Hero had depended merely on the expansive 

 property of air compressed by the water itself. 



While these mechanisms contained the germ of an 

 idea of vast importance, the mechanisms themselves 

 were of trivial utility. It is not even clear whether 

 their projectors had an idea of the properties of the con- 

 densation of vapor, upon which the working of the 

 practical steam engine so largely depends. This idea, 

 however, was probably grasped about half a century 

 later by an Englishman, Edward Somerset, the cele- 

 brated Marquis of Worcester, who in 1663 described in 

 his Century oj Inventions an apparatus for raising water 

 by the expansive force of steam. His own account of 

 his invention is as follows: 



"An admirable and most forcible way to drive up 

 water by fire; not by drawing or sucking it upwards, 

 for that must be as the philosopher calleth it, intra 

 sphceram activitatis, which is but at such a distance. 

 But this way hath no bounder, if the vessel be strong 

 enough: for I have taken a piece of whole cannon, 

 whereof the end was burst, and filled it three-quarters 

 full of water, stopping and screwing up the broken end, 

 as also the touch-hole; and making a constant fire 

 under it, within twenty-four hours it burst and made a 

 great crack; so that having a way to make my vessels 



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