44 HABIT AND INTELLIGENCE. [cHAP, 



separately, but of both jointly. And the potential energy 



due to oxygen and carbon that are ready to burn together, 



is a function of neither separately, but of both jointly. 



No distinc- It follows from this last remark, that the common dis- 



^^^^gj^^^jj^_ tinction between combustible substances and those which 



bustibles support combustiou has no foundation in the nature of 



porters of things. We can burn a jet of oxygen in an atmosphere of 



combus- hydrogen, just as we can burn a jet of hydrogen in an 



atmosphere of oxygen. The definition of combustion is 



the rapid comhination of two substances (of which oxygen is 



generally, but not always, one) with great production of 



heat ; and the one burns as truly as the other. 



Forces be- Another result of the highest importance is, that matter 



original ° ^^ endowed with active forces, as a part of its original 



constitu- constitution. 



matter. The laws of the conservation of momentum, the con- 



servation of rotation, and the conservation of energy, have 

 nothing to do with the nature of the force, or w^ith the 

 source of the energy ; they are equally true, whether the 

 forces that we have to consider in any case are primary 

 forces, like gravity, or acquired ones, like magnetism : and 

 they are equally true, whether the energy is the result of 

 the mutual actions of the bodies under consideration, as 

 for instance in a steam-engine at work ; or whether it is 

 the result of some force that has acted from without, as 

 Theory of when we spin a gyroscope. It was, I believe, the opinion 

 of Descartes, and regarded as probable by Locke, that 

 matter had no dynamical properties except the merely 

 passive capacity of being acted on by force, and of trans- 

 mitting the action on to other matter : that it was by its 

 original constitution without active forces, and was set in 

 motion by the same supernatural Power that created it. 

 I do not see how this theory was ever reconcilable with 

 the most obvious of all dynamical facts, that of weight ; 

 and all that modern research has taught of dynamics and 

 disproved, chemistry proves the theory to be entirely wrong ; it shows 

 that matter possesses, as part of its original constitution, 

 not only passive properties, but the active forces of gravity, 

 capillarity, and affinity. In other w^ords, matter possesses. 



