200 CONTINUITY. 



no problem in celestial dynamics more deeply interesting than 

 this, and we may be no farther removed from its solution than 

 the predecessors of Newton were from the simple dynamical 

 relation of matter to matter which his potent intellect de- 

 tected and demonstrated. 



Passing from extra-terrestrial theories to the narrower field 

 of molecular physics, we find the doctrine of correlation of 

 forces steadily making its way. In the Bakerian Lecture for 

 1863 Mr. Sorby shows, not perhaps a direct correlation of 

 mechanical and chemical forces, but that when, either by 

 solution or by chemical action, a change in volume of the 

 resulting substance as compared with that of its separate 

 constituents is effected, the action of pressure retards or pro- 

 motes the change, according as the substance formed would 

 occupy a larger or smaller space than that occupied by its 

 separate constituents ; the application of these experiments 

 to geological enquiries as to subterranean changes which 

 may have taken place under great pressure is obvious, and 

 we may expect to form compounds under artificial compres- 

 sion which cannot be found under normal pressure. 



In a practical point of view the power of converting one 

 mode of force into another is of the highest importance ; and 

 with reference to a subject which at present, somewhat pre- 

 maturely, perhaps, occupies men's minds, viz. the prospective 

 exhaustion of our coal-fields, there is every encouragement 

 to be derived from the knowledge that we can at will produce 

 heat by the expenditure of other forces ; but, more than 

 that, we may probably be enabled to absorb or store up, as 

 it were, diffused energy for instance, Berthelot has found 

 that the potential energy, as it is termed, of formate of potash 

 is much greater than that of its proximate constituents, caus- 

 tic potash and carbonic oxide. This change may take place 

 spontaneously and at ordinary temperatures, and by such 

 change carbonic oxide becomes, so to speak, re-invested with 

 the amount of potential energy which its carbon possessed 

 before uniting with oxygen, or, in other words, the carbonic 

 oxide is raised as a force-possessor to the place of carbon by 

 the direct absorption or conversion of heat from surrounding 

 matter. 



