484 THE POPULAR SCIENCE MONTHLY 



sure of a substance connotes the intensity with which it tends to expand, 

 its temperature the intensity with which it tends to part with heat, 

 while the potential of a given chemical component represents (in Max- 

 well's acute interpretation) the intensity with which it tends to expel 

 itself from the mass or compound containing it."* Mathematically 

 the Gibbsian potential, which Maxwell thought " likely to become very 

 important in the history of chemistry," has been identified by Larmor 

 with the marginal available energy per unit mass of substance at con- 

 stant temperature,"^ depending upon the percentage composition of 

 the substance rather than its actual quantity. The chemical poten- 

 tials may be regarded, not unlike the potentialities of an individual, 

 as definite intensities which set things going, and as such their close 

 relationship to the surface energies and surface tensions of biological 

 science is obvious. As to the ultimate nature of the forces bound up 

 with these potentials, whether due in the last analysis to electronic 

 stresses or rotational stresses in the ether simply, we know little or 

 nothing. Thermodynamic (or "energetic") doctrine rests upon the 

 simple idea that mechanical, thermal, chemical and electric forces are 

 different modes of energy, continually changing and passing into one 

 another in an apparently elusive way, and is more concerned with 

 their dynamic effects than with their actual nature. 



{To he continued) 



" See the report of Maxwell's lecture in Am. J. 8c., 1877, 3. s., XIII., 380, 

 which is fuller than the one given in his collected writings. 

 «"Encycl. Britan.," 10th ed., XXVIII., 168. 



