Rayleigh's Address to the British Association. 99 



or can take place in Nature does so at the cost of a certain 

 amount of available energy. If, therefore, we wish to enquire 

 whether or not a proposed transformation can take place, the 

 question to be considered is whether its occurrence would involve 

 dissipation of energy. If not, the transformation is (under the 

 circumstances of the case) absolutely excluded. Some years ago, 

 in a lecture at the Royal Institution, I endeavored to draw the 

 attention of chemists to the importance of the principle of dissipa- 

 tion in relation to their science, pointing out the error of 

 the usual assumption that a general criterion is to be found 

 in respect of the development of heat. For example, the solution 

 of a salt in water is, if I may be allowed the phrase, a downhill 

 transformation. It involves dissipation of energy, and can there- 

 fore go forward ; but in many cases it is associated with the 

 absorption rather than with the development of heat. I am glad 

 to take advantage of the present opportunity in order to repeat 

 my recommendation, with an emphasis justified by actual achieve- 

 ment. The foundations laid by Thomson now bear an edifice 

 of no mean proportions, thanks to the labors of several physi- 

 cists, among whom must be especially mentioned Willard Gibbs 

 and Helmholtz. The former has elaborated a theory of the 

 equilibrium of heterogeneous substances, wide in its principles, 

 and, we cannot doubt, far-reaching in its consequences. In a series 

 of masterly papers Helmholtz has developed the conception of 

 free energy with very important applications to the theory of the 

 galvanic cell. He points out that the mere tendency to solution 

 bears in some cases no small proportion to the amnities more 

 usually reckoned chemical, and contributes largely to the total 

 electro-motive force. Also in our own country Dr. Alder Wright 

 has published some valuable experiments relating to the subject. 



From the further study of electrolysis we may expect to gain 

 improved views as to the nature of the chemical reactions, and of 

 the forces concerned in bringing them about. I am not qualified 

 — I wish I were — to speak to you on recent progress in general 

 chemistry. Perhaps my feelings towards a first love may blind 

 me, but I cannot help thinking that the next great advance, of 

 which we have already some foreshadowing, will come on this 

 side. And if I might without presumption venture a word of 

 recommendation it would be in favor of a more minute study of 

 the simpler chemical phenomena. 



