236 PHYSICAL SCIENCE IX THE MIDDLE AGES. 



and theorems. Thus, "gravity is a motive quality, arising from cold_ 

 density, and bulk, by which the elements are carried downwards." 

 " Water is the lower, intermediate element, cold and moist." The first 

 theorem concerning water is, " The moistness of the water is controlled 



o * 



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 concluding specimen of this kind, mention those propositions 

 or maxims concerning fluids, which were so firmly established, that, 

 wLen 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 gravitate 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 na- 

 ture abhors a vacuum ; that some bodies have a positive levity in 

 others, as oil in water ; and the like. 



4. Authority of Aristotle among the Schoolmen. The authority of 

 Aristotle, and the practice of making him the text and basis of the- 

 system, especially as it regarded physics, prevailed during the period 

 of which we speak. This authority was not, however, without its fluc- 

 tuations. Launoy has traced one part of its history in a book On the 

 various Fortune of Aristotle in the University of Paris. The most 

 material turns of this fortune depend on the bearing which the works 

 of Aristotle were supposed to have upon theology. Several of Aris- 

 totle's works, and more especially his metaphysical writings, had been 

 translated into Latin, and were explained in the schools of the Univer- 

 sity of Paris, as early as the beginning of the thirteenth century. 21 At 

 a council held at Paris in 1209, they were prohibited, as having given 

 occasion to the heresy of Almeric (or Amauri), and because " they 

 mio-ht a'ive occasion to other heresies not vet invented." The Logic 



O D * -* 



of Aristotle recovered its credit some years after this, and was publicly 

 taught in the University of Paris in the year 1215 ; but the Natural 

 Philosophy and Metaphysics were prohibited by a decree of Gregory 

 the Ninth, in 1231. The Emperor Frederic the Second employed a 

 number of learned men to translate into Latin, from the Greek and 



21 Moslieim, iii. 157. 





