ii. 2. 25 



and that they are moreover the causes of sleep and waking, of 

 maturity and old age, of health and disease ; while no similar 

 influence belongs to roughness and smoothness, to heaviness and 

 lightness, nor in short to any other such properties of matter. That 

 this should be so is but in accordance with rational expectation. 

 For hot and cold, solid and fluid, as was stated in a former 

 treatise," are the foundations of the physical elements. 



Is then the term hot used in one sense or in many ? To answer 

 this we must ascertain what special effect is attributed to a hotter 

 substance, and if there be several such, how many these may be. 

 A body then is in one sense said to be hotter than another, if 

 it impart a greater amount of heat to an object in contact with 

 it. In a second sense, that is said to be hotter which causes the 

 keener sensation when touched, and especially if the sensation be 

 attended with pain. This criterion however would seem some- 

 times to be a false one ; . for occasionally it is the idiosyncracy 

 of the individual that causes the sensation to be painful.^^ Again, 

 of two masses of one and the same substance, the larger is said 

 to have more heat than the smaller. Again, of two things, that 

 is the hotter, which the more readily melts a fusible substance, 

 or sets on fire an inflammable one. Again, of two bodies, that is 

 said to be the hotter which takes the longer time in cooling, as 

 also we call that which is rapidly heated hotter than that which 

 is long about it ; as though the rapidity implied proximity and 

 this again similarity of nature, while the want of rapidity implied 

 distance and this again dissimilarity of nature. The term hotter 

 is used then in all the various senses that have been mentioned, 

 and perhaps in still more. Now it is impossible for one body 

 to be hotter than another in all these different fashions. Boiling 

 water for instance, though it is more scalding than flame, 

 yet has no power of burning or melting combustible or fusible 

 matter, while flame has. So again this boiling water is hotter 

 than a small fire, and yet gets cold much more rapidly and 

 completely. For in fact fire never becomes cold ; whereas water 

 invariably does so. Boiling water again is hotter to the touch 

 than oil ; yet it gets cold and coagulates more rapidly than this 

 other fluid.'^ Blood again is hotter to the touch than either 

 water or oil, and yet coagulates before them. Iron again and 

 stones and other similar bodies are much longer in getting heated 

 than water, but when once heated burn other substances with 

 648 b. 



