12 BEPORT— 1884. 



ance of the principle of dissipation iu relation to their science, pointing 

 out the error of the usual assumption that a general criterion is to be 

 found in 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 therefore 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 achievement. The foundations laid by Thomson 

 now bear an edifice of no mean proportions, thanks to the labours of 

 several physicists, 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 pro- 

 portion to the affinities 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 recom- 

 mendation, it would be in favour of a more minute study of the simpler 

 chemical phenomena. 



Under the head of scientific mechanics it is principally in relation to 

 fluid motion that advances may be looked for. In speaking upon this 

 subject I must limit myself almost entirely to experimental work. Theo- 

 retical hydro-dynamics, however important and interesting to the mathe- 

 matician, are eminently unsuited to oral exposition. All I can do to 

 attenuate an injustice, to which theorists are pretty well accustomed, is 

 to refer you to the admirable reports of Mr. W. M. Hicks, published under 

 the auspices of this Association. 



The important and highly practical work of the late Mr. Froude in 

 relation to the propulsion of ships is doubtless known to most of you. 

 Recognising the fallacy of views then widely held as to the nature of the 

 resistance to be overcome, he showed to demonstration that, in the case 

 of fair-shaped bodies, we have to deal almost entirely with resistance 

 dependent upon skin friction, and at high speeds upon the generation of 



