98 
MEMOIR OF ARISTOTLE. 
pker. 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 
be 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 hook 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 Btudies 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 he gathered from passages in his 
physics, in which w T e find him often establishing con- 
clusions by Bteps 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- 
