14 SPECIAL RESULTS OF OBSERVATION IN THE DOMAIN 



motions. Thus we even findinthe book "De Anima" ( 18 ) 

 the germ of the undulatory theory of light. The sensation 

 of seeing follows from a movement or vibration of the medium 

 between the sight and the object seen, not from effluxes either 

 from the object or from the eye. Hearing is compared 

 with seeing, as sound is also a consequence of concussion of 

 the air. 



In inculcating the exercise of thoughtful reason in the 

 search after that which is general or universal amidst the 

 particular facts perceived by the senses, Aristotle always com- 

 prehends the whole of Nature, and the internal connection 

 not only of forces but also of organic forms. In the book 

 which treats of the parts (organs,) of animals, he clearly 

 enounces his belief in the gradual chain of beings ascending 

 from lower to higher forms. Nature proceeds in uninter- 

 rupted progressive development from the inanimate (ele- 

 mentary,) through plants to animals : advancing first to 

 " what indeed is not properly an animal, but so nearly allied 

 thereto that it is on the whole but little distinguished from 

 one."" ( 19 ) In the transition of forms " the intermediate 

 steps are almost insensible/'' ( 20 ) The unity of Nature is to 

 the Stagirite the great problem of the Cosmos. He says, 

 with singular vivacity of expression, "In Nature nothing 

 is isolated; there is no want of connection as in a bad 

 tragedy." ( 21 ) 



In all the physical writings of this profound, sage, and 

 accurate observer of nature, we cannot fail to recognise 

 the philosophical tendency to subordinate all the pheno- 

 mena of the one Cosmos to a single principle of expla- 

 nation ; but the defective state of knowledge, and ignorance 

 of the method of experimenting, (i. e. } of calling forth 

 phenomena under definite conditions), prevented even small 



