08 MEMOIR OF ARISTOTLE. 



pher. His sentiments on this subject are fully stated 

 in his book on the Soul ; and in several smaller trea- 

 tises on the Parts and Motives of Animals, on Per- 

 ception, on the Duration of Life, Youth and Old 

 Age, Life and Death, Respiration, Memory, 

 Sleep, Waking and Dreaming ; and to these may 

 he added his book on Physiognomy, and his Trea- 

 tise on Animals, which, though properly a work of 

 Natural History, is also illustrative of the nature of 

 the soul, considered as the living principle in all ani- 

 mated beings. 



In Mathematics, little comparatively has been left 

 of what Aristotle must have written. The only 

 treatises under this head, are the Mechanical Ques- 

 tions, and a book on Indivisible Lines. But as he 

 had been trained in the school of Plato, whose 

 threshold was impassable to those who had not drunk 

 deeply at the fountain of geometry, and attained a 

 perfect skill in the methods of mathematical investi- 

 gation then known, we may infer that his studies in 

 this department were as minute and extensive as 

 in others in which more of his writings have been 

 preserved. Of this, indeed, we require no better 

 proof, than may be gathered from passages in his 

 physics, in which We find him often establishing con- 

 clusions by steps of mathematical demonstration. 

 To this class may be referred his treatise called the 

 Problems, containing queries chiefly on subjects be- 

 longing to Natural Philosophy, with brief answers ; 

 and a curious tract against the doctrines of Xeno- 



