748 THE POPULAR SCIENCE MONTHLY. 



formation 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 

 dissipation 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 down-hill transformation. It in- 

 volves 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 ray recommendation, with an emphasis 

 justified by actual acliievement. The foundations laid by Thomson 

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

 several physicists, among whom must be especially mentioned Wil- 

 lard Gibbs and Helmholtz. The former has elaborated a theory of 

 the equilibrium of heterogeneous substances, wide in its principles, 

 and we can not 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 gal- 

 vanic cell. He points out that the mere tendency to solution bears in 

 some cases no small proportion to the afiinities more usually reckoned 

 chemical, and contributes largely to the total electro-motive force. 

 Also in our own country Dr. Alder "Wright has published some valu- 

 able ex} eriments relating to the subject. 



From the further study of electrolysis we may expect to gain im- 

 proved 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 toward a first love may blind me, but I can not 

 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. 



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. 

 Theoretical hydro-dynamics, however important and interesting to the 

 mathematician, are eminently unsuited to oral exposition. All I can 

 do to attenuate an injustice, to which theorists are pretty well accus- 

 tomed, is to refer you to the admirable reports of Mr. 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. Recognizing the fallacy of views then widely held as to the na- 

 ture of the resistance to be overcome, he showed to demonstration that, 



