GALILEO AND THE NEW PHYSICS 



and remains there. Now to make it return to the 

 surface by virtue of the air which before sustained it, 

 thrust into the water a glass with the mouth down- 

 ward, which will carry with it the air it contains, and 

 move this down towards the ball until you see, by the 

 transparency of the glass, that the air has reached the 

 top of it; then gently draw the glass upward, and you 

 will see the ball rise, and afterwards stay on the top of 

 the water, if you carefully part the glass and water 

 without too much disturbing it." 3 



It will be seen that Galileo, while holding in the main 

 to a correct thesis, yet mingles with it some false ideas. 

 At the very outset, of course, it is not true that water 

 has no resistance to penetration; it is true, however, 

 in the sense in which Galileo uses the term that is to 

 say, the resistance of the water to penetration is not 

 the determining factor ordinarily in deciding whether 

 a body sinks or floats. Yet in the case of the flat 

 body it is not altogether inappropriate to say that 

 the water resists penetration and thus supports the 

 body. The modern physicist explains the phenom- 

 enon as due to surface-tension of the fluid. Of course, 

 Galileo's disquisition on the mixing of air with the 

 floating body is utterly fanciful. His experiments 

 were beautifully exact; his theorizing from them was, 

 in this instance, altogether fallacious. Thus, as al- 

 ready intimated, his paper is admirably adapted to 

 convey a double lesson to the student of science. 



WILLIAM GILBERT AND THE STUDY OF MAGNETISM 



It will be observed that the studies of Galileo and 

 Stevinus were chiefly concerned with the force of 



in 



