ON THE HISTORY OF HYDEAULICS AND PNEUMATICS. 353 



Constantinople, is mentioned by Fannius, an early writer on weights and 

 measures, and is ascribed by him to Archimedes. 



The forcing pump, or rather the fire engine, was the invention of Ctesibiusof 

 Alexandria, the greatest mechanic of antiquity after Archimedes. He is 

 also said to have invented the clepsydra, for the hydraulic measurement of 

 time, and Philo informs us that he constructed an air gun, for propelling 

 a stone, or rather a ball, by means of air, previously condensed by a syringe. 

 The ball was not immediately exposed to the action of the air, but was im- 

 pelled by the longer end of a lever, while the air acted on the shorter. 

 Ctesibius is said to have been the son of a barber, and to have had his at- 

 tention turned to mechanics and pneumatics, by being employed to fit a 

 shutter, with a counterpoise sliding in a wooden pipe, for his father's shop 

 Avindow. 



Hero was a cotemporary, and a scholar of Ctesibius; he describes, in his 

 treatise on pneumatics, a number of very ingenious inventions, a few of 

 which are calculated for utility, but the greater part for amusement only; 

 they are principally siphons variously concealed and combined, fountains, 

 and water organs, besides the syringe and the fire engine. The description 

 of this engine agrees precisely with the construction which is at this day 

 the most usual ; it consists of two barrels, discharging the water alternately 

 into an air vessel; and it appears from Vitruvius, that this was the 

 original form in which Ctesibius invented the pump. Hero supposes the 

 possibility of a vacuum in the intervals of the particles of bodies, ob- 

 serving that without it no body could be compressible; but he imagines that 

 a vacuum cannot exist throughout a perceptible space, and thence derives the 

 principle of suction. The air contained in a given cavity may be rarefied, 

 he says, by sucking out a part of it, and he describes a cupping instrument, 

 Avhich approaches very nearly to the nature of an imperfect air pump. 

 (Plate XXIV. Fig. 324.) 



After the time of Ctesibius and Hero, the science of hydraulics made 

 little further progress, until the revival of lette;rs. The Romans had water 

 mills in the time of Juhus Caesar, which are described by Vitruvius; and 

 it appears that their ac[ueducts were well built, and their waterpipes well 



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