188 HYDRODYNAMICS. 



en crown of the ancient king of Syracuse. He first 

 weighed it, and then found that it displaced more wa- 

 ter when plunged in a vessel just filled, than a piece of 

 pure gold, and also that it displaced less than silver, 

 whence he inferred the mixture of these two metals. 



When the specific gravity of a substance hghter than 

 water is to be ascertained, it is loaded down by a 

 weight, so as to sink in water, for which allowance is 

 made in the calculation. A very simple way to deter- 

 mine this in different kinds of wood is to form them 

 into rods or sticks of uniform size throughout, and then 

 to observe what portion of them sink when placed end- 

 wise in water. 



A knowledge of the specific gravities of various sub- 

 stances becomes useful in many ways, among which 

 is ascertaining the weight of any structure, machine, 

 or implement, according to the material used in its 

 manufacture ; determining the cost, by the pound, of 

 such material ; or knowing the bulk or size of any load 

 for a team. The latter may often become of great use 

 in ordinary practice, by enabling the teamster to cal- 

 culate beforehand the amount of load to give his horses, 

 whether in timber, plank, brick, lime, sand, or hon, 

 without first subjecting them to overstraining exer- 

 tions in consequence of error in random guessing. 



Tables of specific gravities, for this purpose, and 

 weights of a cubic foot of different substances, are giv- 

 en in the Appendix. 



