704 THE POPULAR SCIENCE MONTHLY. 



nize another reason for believing that Nature will never attain abso- 

 lute equilibrium, from the variety of forces ever abiding together 

 within her sphere. 



Fourthly, our present inability to obtain the movement of masses 

 from, the motion of molecules or small masses that is, the derivation 

 of work from uniformly heated matter does not decide that such con- 

 version is impossible in Nature, or even to science in the future. 

 While it is perfectly right to reason from what we know, it is of 

 yet higher importance to constantly bear in mind how little we know. 

 It would require infinite knowledge to say that the motion of uniform 

 heat may not be transformable into phases of energy quite as diverse 

 as high and low temperatures. 



Such a change would not contravene the truth of the uncreatability 

 or indestructibility of force, but would simply be an enlargement of 

 the known, which every one feels to be indefinitely small as compared 

 with the knowable. The possibility here suggested may be conceiv- 

 able as depending on the definiteness in size of atoms ; or, on the va- 

 riety of motions to which the differences between atoms, as chemical 

 elements, may give rise differences in size and form ; or, on the va- 

 riety of motions implied by the checks offered to steady accessions of 

 temperature, already explained in this paper. 



One of the first principles to which the mind clings as fundamental 

 is, that every truth has its converse. Although this may seem an 

 axiom, yet its demonstration may be often very difficult, and, at 

 times, even impossible. A knife-blade held over a gas-flame for a 

 moment shows that hydrogen and oxygen combine to form watery 

 vapor; yet the proof of the converse the decomposition of water 

 into its elements demands extensive and powerful apparatus. Oer- 

 sted, in a happy hour, noticed that an electric wire moved a magnetic 

 needle ; but years of experiment had to elapse before the electro-mag- 

 net and the magneto-electric machine established the complementary 

 principles in a practical form. The analysis of compounds, chemi- 

 cally, is vastly easier than the building them up from their elements. 

 We know the exact percentages of carbon, hydrogen, and oxygen, 

 that go to make up sugar, and can express to a nicety the dynamical 

 relations of the compound to its elements ; but how to bring about 

 the changes desired, with economy, is what puzzles us. 



When we see high and low temperatures coming to an equality, 

 it is certainly permissible to entertain faith in the possibility of the 

 converse ; in a change equivalent to a mass becoming, in its several 

 parts, hotter and colder. To have recourse to such a supposition is 

 less straining to the mind than the alternatives usually proposed by 

 the theory under consideration. 



If that theory be true, the question suggests itself, "Why has not 

 the universe come to death by this time, for limits cannot be imagined 

 to past duration ? " 



