44 Dr. Woods on the Heat of Chemical Combination. 



they come exactly to the same condition with respect to the 

 distance between their particles; but we shall also see that the 

 cube which contracted lost more space than was gained by the 

 other. The coefficient of expansion increasing - with the tempe- 

 rature, there must be more space lost from 1000° to 500° than 

 gained from 0° to 500°. 



If, instead of the colder cube of iron we substitute a cube 

 of ice, we find that the ice expands until it reaches its melting- 

 point ; it then becomes fluid, and ultimately is converted into 

 vapour; its expansion in the last case being enormously greater 

 than the contraction of the iron which occasions it. 



(14.) Now what do we learn from this experiment ? 



1. That if two bodies unequally heated be placed together, 

 contraction occurs in one, expansion in the other, until their par- 

 ticles are at a common distance, proving that heat cannot con- 

 sist in motion abstractedly considered; for the particles of the 

 cooling body move as well as those of the body becoming heated, 

 but in an opposite direction ; therefore it would be as correct to 

 say that heat is absorbed, as to say it is produced by motion. 



2. That tbe theory of heat being a subtle fluid gives no ex- 

 planation of expansion ; for we see that this fluid should itself 

 expand, as when converting the water into steam it occupies a 

 much greater space than it did in the iron ; therefore, although 

 it might be said that heat expands bodies, we should still inquire, 

 what expands the heat ? 



3. That the nearer the particles of bodies are to each other, 

 the less they require to move to produce a given expansion or 

 contraction in those of another body. 



(15.) As far as either of these two bodies, taken by itself, is 

 concerned, all we see is, that for every temperature it has a cer- 

 tain volume, a constant volume for a constant temperature ; and 

 as far as our experiments enable us to judge, any body taken by 

 itself, that is, uninfluenced by others, would always remain at 

 the same temperature, with the same degree of expansion among 

 its particles ; for instance, a body will not expand or become 

 hotter without some other body more heated than itself being 

 present ; and as far as our experimental knowledge goes, a body 

 cannot cool without some colder one taking up the heat. I say, 

 as far as our experimental knowledge goes, for theoretically a 

 body is said to give off its heat independent of the presence of 

 other bodies, and it is taken for granted that heat can be radiated 

 into space and exist uncombined with matter ; but we have no 

 proof 'of it. As far then as our experience, our positive knowledge 

 allows us to go, we must admit that the particles of bodies are 

 placed at certain distances from each other ; that they have no 

 power to move themselves, inasmuch as the presence of a second 



