74 PHENOMENA OF HEAT AND SOUND. 



said to be hotter than another if it gives up to a body in 

 contact with it a greater quantity of heat, and in another 

 sense if it causes a sharper sensation when touched by any- 

 one. This second test is not rehable, because the intensity 

 of the sensation varies with the individual. Again, a body 

 which causes a fusible body to melt more quickly, or more 

 readily ignites an inflammable substance, is said to be 

 hotter. A larger body is said to have more heat than a 

 smaller one of the same material, and, if a body takes 

 longer to cool than another, it is said to be hotter, and so 

 also if the body can be heated more quickly than the other. 

 The term " hotter " is used in all these and probably in still 

 more senses, but it is impossible for a body to be hotter than 

 another in all these senses. Boiling water scalds more than 

 flame, yet it does not melt or ignite bodies like flame does, 

 and boiling water is hotter than a dull fire but becomes cold 

 more quickly than the fire, for fire never becomes cold, 

 whereas water does. 



It is obvious from all this that Aristotle had no means 

 of determining temperatures, even approximately, and that 

 he was well aware that such rough methods as were 

 available were quite unreliable. His discussion of the 

 meaning of the term "hotter" shows, however, that he had 

 attempted to make some relevant observations or experi- 

 ments. If he had had even an approximately reliable 

 means for measuring temperatures, he would at once have 

 found that a dull fire or a flame, say of oil or wood, was much 

 hotter than boiling water. The statement he makes about 

 the fire keeping hot longer than boiling water shows that 

 the generation of heat by combustion was not known to 

 him. The phenomena of combustion were not correctly 

 described, in fact, until long after Aristotle's time by 

 Lavoisier. Just as Aristotle believed that some bodies were 

 essentially cold, so he believed that others were essentially 

 hot, and that this was the reason why some bodies cooled 

 faster than others, although they were hotter to the touch. 

 He decided that, in bodies which are not inherently hot but 

 become hot by being heated externally, cold is not a mere 

 privation of heat, but an actual existence.* 



Animal heat is discussed by Aristotle in many scattered 

 passages in his Parts of Animals, Generation of Animals, 

 History of Animals, and the Parva Naturalia. He believed 



* P. A. ii. c. 2, 649a. 



