352 



LECTURE XXX. 



ON THE HISTORY OF HYDRAULICS AND PNEUMATICS. 



Notwithstanding a few observations and experiments made by 

 Aristotle and his predecessors, the properties of fluids had scarcely been the 

 subjects of much .accurate investigation before the time of Archimedes. The 

 progress, which the science of hydrostatics in particular made under this 

 eminent mathematician, does the highest honour to his genius and penetra- 

 tion. His treatise on floating bodies, although the theorems which it con- 

 tains are not so general as they have been rendered since the late improse- 

 ments in the methods of calculation, still affords us instances of very in- 

 genious determinations of the equilibrium of floating bodies of different 

 forms, grounded on the true principles of the opposition of the general direc- 

 tions of the weight of the body and of the pressure of the fluid ; and in this man- 

 ner he has shown in what cases the equilibrium of conical and conoidal solids 

 will be stable, and in what cases unstable. Archimedes was the inventor of 

 the mode of measuring the bulk of a solid by immersing it in a fluid: to us, 

 indeed, there appears to have been little difficulty in the discovery, but the 

 ancients thought otherwise. Vitruvius observes that this invention indicates 

 a degree of ingenuity almost incredible. The philosopher himself is said to 

 have valued it is so highly, that when it first occurred to him, in a public 

 bath, he hastened home in an ecstasy, without recollecting to clothe him- 

 self, in order to apply it to the determination of the specific gravity of 

 Hiero's crown, and to the detection of the fraud of the maker, who had re- 

 turned the crown equal in weight to the gold that was given him, but had 

 adulterated it with silver, and imagined, that on account of the complicated 

 form of the work, Avhich rendered it almost impossible to determine its bulk 

 by calculation, he must infallibly escape conviction. The hydrometer, 

 which has sometimes been attributed to Hypatia, a learned Greek lady of 



