342 PHYSICAL SCIENCE IN THE MIDDLE AGES. 



form of definitions and theorems. Thus, "gravity 

 is a motive quality, arising from cold, density, and 

 bulk, by which the elements are carried down- 

 wards." " Water is the lower intermediate element, 

 cold and moist." The first theorem concerning 

 water is, " The moistness of water is controlled by 

 its coldness, so that it is less than the moistness of 

 the air; though, according to the sense of the 

 vulgar, water appears to moisten more than air." 

 It is obvious that the two properties of fluids, to 

 have their parts easily moved, and to wet other 

 bodies, are here confounded. I may, as a con- 

 cluding specimen of this kind, mention those pro- 

 positions or maxims concerning fluids, which were 

 so firmly established, that, when Boyle propounded 

 the true mechanical principles of fluid action, he 

 was obliged to state his opinions as " hydrostatical 

 paradoxes." These were, that fluids do not gravi- 

 tate in proprio loco; that is, that water has no 

 gravity in or on water, since it is in its own place ; 

 that air has no gravity on water, since it is above 

 water, which is its proper place; that earth in 

 water tends to descend, since its place is below 

 water; that the water rises in a pump or siphon, 

 because nature abhors a vacuum ; that some bo- 

 dies have a positive levity in others, as oil in water ; 

 and the like. 



4. Authority of Aristotle among the School- 

 men. The authority of Aristotle, and the practice 

 of making him the text and basis of the system. 



