210 



visible masses to their smallest particles; while in steam- 

 engines the internal motion of the heated gaseous particles 

 is transferred to the piston of the machine, accumulated in 

 it, and combined in a resultant whole. 



But what is the nature of this internal motion can only 

 be asserted with any degree of probability in the case of 

 gases. Their particles probably cross one another in rec- 

 tilinear paths in all directions, until, striking another par- 

 ticle, or against the side of the vessel, they are reflected in 

 another direction. A gas would thus be analogous to a 

 swarm of gnats, consisting, however, of particles infinitely 

 small and infinitely more closely packed. This hypothesis, 

 which has been developed by Kronig, Clausius, and Max- 

 well, very well accounts for all the phenomena of gases. 



What appeared to the earlier physicists to be the constant 

 quantity of heat is nothing more than the whole motive 

 power of the motion of heat, which remains constant so 

 long as it is not transformed into other forms of work, or 

 results afresh from them. 



We turn now to another kind of natural forces which 

 can produce work I mean the chemical. We have to-day 

 already come across them. They are the ultimate cause of 

 the work which gunpowder and the steam-engine produce; 

 for the heat which is consumed in the latter, for example, 

 originates in the combustion of carbon that is to say, in a 

 chemical process. The burning of coal is the chemical union 

 of carbon with the oxygen of the air, taking place under 

 the influence of the chemical affinity of the two substances. 



We may regard this force as an attractive force between 

 the two, which, however, only acts through them with extra- 

 ordinary power, if the smallest particles of the two sub- 

 stances are in closest proximity to each other. In combus- 

 tion this force acts; the carbon and oxygen atoms strike 

 Egainst each other and adhere firmly, inasmuch as they form 

 a new compound carbonic acid a gas known to all of you 

 as that which ascends from all fermenting and fermented 

 liquids from beer and champagne. Now this attraction 

 between the atoms of carbon and of oxygen performs work 

 just as much as that which the earth in the form of gravity 

 exerts upon a raised weight. When the weight falls to the 



