ON INSTRUMENTS FROM ITALY. 139 



sought after, it is indeed rare, if some glimmering of the fact be not 

 derived from them, or the falsity of some other contrary supposition 

 discovered by their means." 



Of the three ingenious experiments that were made to compress 

 water viz., by the force of rarefaction, by the pressure of mercury, 

 and by the force of a blow the last has remained the most universally 

 known. It was made with a subtle ball of silver containing the water, 

 which, when the ball was beaten with a hammer, sweated through all 

 the pores of the metal, and looked like quicksilver coming out drop by 

 drop through some skin in which it was squeezed. Here is the ball 

 which was used for this celebrated experiment, and it still contains 

 some water. This other one, which likewise has water in it, was pre- 

 pared by the academicians for a repetition of the experiment, which 

 did not, however, take place. Other most ingenious and conclusive 

 experiments were made by the academicians on the question of posi- 

 tive lightness namely, " whether those things which are commonly 

 called light are so by their own nature, and whether they float upwards 

 of their own accord, or whether their rising be merely the effect of 

 heavier bodies driving them away ; these weightier bodies having 

 more vigour and greater power to descend and place themselves lower, 

 squeeze the lighter ones away (so to speak), and compel them to rise." 

 Nor did they forget the marvellous operations of the magnet, a vast 

 field, in which though much be already discovered, there undoubtedly 

 remains a great deal more to be found out. They clearly showed 

 that iron and steel are essentially magnetic ; that attraction and re- 

 pulsion can take place, even through solids and liquids ; that the poles 

 of the magnetic needle are much enfeebled wlien held in the position 

 of the magnetic equator. With regard to the electrical action, the 

 academicians merely explained which substances possessed such a 

 property, and which not, and concluded that it was common to all 

 transparent stones and not to opaque ones, but that it was more 

 especially a property of amber, which, even attracts smoke. 



With regard to the experiments on sound, we have already spoken 

 of them at sufficient length ; those on projectiles are but experimental 

 proofs of three propositions of Galileo. The first, that a ball dis- 

 charged horizontally from a tower always takes precisely the same 

 time in reaching the earth as it would take had it been let fall freely 



