Hydraulics. 53 



a mill, and the greater part of the winter is desti- 

 tute of water. This probably communicates by 

 a syphon with some cavity in the earth, which is 

 filled by the melting of the snow to a certain 

 height, and after that it will continue to be drawn 

 off by the brook, so as to furnish a stream till the 

 reservoir is entirely emptied. 



It is by the pressure of the atmosphere that 

 the common or sucking pump is enabled to act. 

 It is said to have been invented by a mathemati- 

 cian of the name of Ctesebes, about one hundred 

 and twenty years before Christ ; but the principle 

 on which it acted was unknown till the 17th cen- 

 tury. Mankind, perfectly ignorant that the air 

 had weight, attempted to account for these effects 

 by a maxim not only unfounded, but even desti- 

 tute of meaning. This was, " that Nature ab- 

 horred a vacuum." What they meant by Nature 

 is as little to be understood as when the same 

 word is used by those ignorant sciolists who affect 

 to deny the existence of a God. Absurd, how- 

 ever, as this maxim was, it remained uncontra- 

 dicted till within one hundred and sixty years, 

 when it met with a practical refutation. About 

 that time some workmen were employed by the 

 duke of Florence, to raise water by a common 

 sucking pump to the height of fifty or sixty feet. 

 A pump was accordingly constructed for that 

 purpose; but, after all their efforts, they were 

 unable to raise it above the height of thirty-two 

 feet. It was then found either that Nature had 



