184 LECTURE XX. 



the centre of gravity ; for the discovery of the laws of hydrostatics, and 

 of the modes of determining the specific gravities of bodies ; for the con- 

 struction of the first cranes and of the first planetarium ; and for those 

 improvements of the methods of mathematical investigation which have 

 been the basis of every modern refinement in analytical calculation ; for 

 all these additions to our knowledge and our powers, we are indebted to 

 Archimedes. On a character so conspicuous, we can with pleasure dwell 

 long enough to attend to some particulars of his history, which are related 

 by Plutarch in his account of the siege of Syracuse ; omitting, however, 

 such details as are evidently fabulous. "Archimedes," says Plutarch, 

 " armed with his own inventions only, made light of the splendour of the 

 Roman preparations, and of the glory of the name of Marcellus. And 

 these were inventions that he even considered as of subordinate value, as 

 geometrical playthings, which had been the amusements of his leisure hours. 

 It was king Hiero that first induced him to transfer a portion of his science 

 from intellectual to material objects, and to condescend in some degree to the 

 comprehension of the multitude, by giving a sensible form to those truths 

 which in their abstract state are discoverable only to the reasoning faculty. 

 Archimedes, who was a friend and a relation of Hiero, had asserted that 

 any weight whatever might be moved by any given power : and depending 

 on the validity of his arguments, had given scope to his imagination, and 

 boasted that if he had another earth to which he could step over, he would 

 draw the whole of the present globe out of its place. Hiero, surprised at 

 the boldness of his assertion, requested him to give some substantial proof 

 of its truth, by moving a great weight with a small power ; upon this 

 Archimedes procured a ship, which was with great labour drawn up on the 

 shore, and having completely manned and freighted her, he seated himself 

 at a distance, and by lightly touching the first movement of a machine, he 

 drew her along as smoothly and as safely as if she had been sailing in the 

 deepest water. Hiero, full of astonishment, and admiring the powers of 

 mechanical art, prevailed on Archimedes to construct such engines both of 

 defence and of offence, as might be of use to him in case of a siege : for 

 these, however, Hiero, who lived a life of peace and prosperity, was not so 

 unfortunate as to have occasion ; but they now became highly valuable to 

 the Syracusans, and they were of the more advantage, as their inventor 

 was present to direct their use. And in fact the whole people of Syracuse 

 constituted but a part of Archimedes's corporeal machinery, and he was 

 the soul that moved and governed the whole. All other arms were deserted, 

 and they employed his engines alone, both for their own defence, and for the 

 annoyance of the enemy. In short the Romans soon became so terrified, 

 that if they saw a stick or a rope upon the walls, they cried out that it was 

 some machine of Archimedes, and immediately fled ; so that Marcellus 

 at last determined to desist from attempting to take the place by assault, 

 and resolved to blockade it only. 



" Archimedes, however, had such depth of intellect, and such sublimity 

 of mind, that notwithstanding he had obtained by these inventions, the 

 credit and glory of an intelligence rather divine than human, he thought it 

 unworthy of him to leave any written treatise on the subject, considering 



