ALEXANDRIAN SCIENCE. 



the screw of Archimedes, and of which one form is represented in 

 Fig. 13. It commonly Consists of a pipe wound like the thread of 

 a screw round a cylinder. The cylinder~bemg placed in a sloping 

 position with its lower extremity immersed in a reservoir of water, the 

 effect of turning it round is to cause the water to ascend the pipe, 

 from the upper orifice of which it is discharged, and thus the water is 

 transferred from the lower to the higher level. It may be that this 

 apparatus was not invented by Archimedes, but only adapted by him 

 from Egypt, where it is still in use. 



FIG. 13. 



The story of Hiero's crown has often been told. The King had 

 given to an artificer aTquaStity of gold which was to be fashioned into 

 a crown. When the work was completed, the King found that its 

 weight corresponded with that of the metal which had been delivered 

 to the goldsmith ; but he suspected that some of the precious metal 

 had been kept back, and its weight made up by baser materials al- 

 loyed with the gold in the crown. He sent the crown to Archimedes 

 to pronounce on the true state of the case. How to do this was for 

 some time a puzzle to the philosopher ; but while thinking over the 

 matter, a slight incident suggested the solution of the problem. He 

 was one day entering his bath, which happened to be quite filled, and 

 noticing that the water overflowed its edge in proportion as he im- 

 mersed his body in the liquid, it struck him that the quantity of water 

 which thus ran out constituted an exact measure of the bulk of the 

 immersed body which displaced it. He immediately perceived if the 

 crown were of pure gold, it would, when immersed in a vessel quite 

 full of water, cause the same quantity of the liquid to run over the brim 

 as would a lump of gold of the same weight as the crown ; whereas the 



