124 PHYSICAL SCIENCE 



The explanation of the coagulation of colloidal 

 solutions as an effect on the surface conditions at 

 the junction between colloid and solvent, brought 

 about by the chance conjunctions of dissociated 

 electric ions, is an illustration of a course of 

 history which indeed constantly repeats itself 

 in scientific inquiry. An observation is made, 

 perhaps long series of experiments are carried 

 out, before the general state of knowledge enables 

 a satisfactory explanation of the phenomena to 

 be formed, or a theoretical co-ordination of them 

 with other phenomena to be traced. Even 

 Graham's acute and powerful mind, in the absence 

 of the dissociation theory of electrolytes, and of 

 the knowledge of the surface relations of two 

 phases which we now possess, could frame no 

 explanation of the coagulation effects which he 

 examined with such skill. By experiments on 

 coagulation alone it is probable that an explana- 

 tion could never have been reached. But by the 

 advance of other observers, led by Gibbs on one 

 far-off flank, and by Van't Hoff and Arrhenius 

 on the other, almost out of touch with the 

 original attack, the position of the adversary — 

 ignorance — was turned ; and when, at a later 

 time, a new frontal assault was made, the way 

 lay open to an approximate theory, and probably 

 in the future will lead to a complete explanation. 



For, while the tired waves, vainly breaking, 



Seem here no painful inch to gain. 

 Far back, through creeks and inlets making. 



Comes, silent, flooding in, the main. 



And not by eastern windows only, 



When daylight comes, comes in the light ; 



In front the Sun climbs slow, how slowly ! 

 But westward, look ! the land is bright. 



