70 PHENOMENA OF HEAT AND SOUND. 



iris, •x/xf'OTiQy to the darker shades of blue or grey, and y>MUK6v 

 to the hghter shades of these colours. That yXaw^oV refers to 

 the lighter shades is shown by a passage in the Problems, 

 xiv. 14, where it is stated that the colour of the iris in 

 those living in the northern parts of the ancient World 

 was 7^a«xoV, and that this colour was nearly white. 



The words xapoTro'v and yXat/xoV were used, at first, with- 

 out any reference to mere colour, the former meaning glad- 

 eyed, and the latter clear or bright. Aristotle advanced far 

 beyond this stage in the formulation of ideas, and was 

 evidently dealing with colours and even shades of colours. 

 In various parts of his works, especially in those parts re- 

 lating to birds, he uses many words to denote colours, but, 

 in some cases, it is impossible to determine what these were 

 intended to be, simply because the objects to which he is 

 referring cannot be identified. His colour vocabulary, if it 

 could be completed, would be a long one. 



Aristotle's observations on heat phenomena are not alto- 

 gether unimportant, and some of them are very interesting. 

 They relate chiefly to the effects of heat, the essentially hot 

 or cold nature of bodies, including the determination of what 

 came to be called by Aristotelians the Primum Frigidum, the 

 production of heat by friction, the modes of determining 

 roughly the temperatures of different bodies, the consideration 

 of the question whether cold is nothing more than privation 

 of heat, and some questions connected with animal heat. 



Of the four Aristotelian elements or forces, heat and cold 

 are active, and the moist and the dry or solid are passive.* 

 By acting on matter in such a way as to overcome it, 

 heat and cold produce therefrom fully matured products.! 

 Aristotle's statements about the effects of heat were based 

 on ordinary observations of everyday operations in the home 

 and workshop. In Meteorol. iv. cc. 2-6, he shows that the 

 result of the action of heat is a cooking effect, including 

 under this phrase not only boiling and roasting, but also the 

 ripening of fruits. He also refers to the drying effects of 

 heat, the hardening of clay by baking, and the fusion of 

 metals and other substances. 



Aristotle expresses an opinion that heat brings together 

 bodies of the same kind, but separates those which are not 

 allied to each other, t This opinion was accepted by the 



* Meteorol. iv. c. 1, s. 1. f Ibid. iv. c. 1, s. 6. 



I De Gener. et Corr. ii. c. 2, 3296. 



