10 Mr. J. Napier on Electrical Endosnwse. 



We may divide the causes which we might conceive con- 

 cerned in the production of aberration into three: — (1), the 

 motion of the earth ; (2), the velocity of light ; (3), the change 

 in the direction of the light coming to the earth. Professor 

 Challis has shown that a certain apparent displacement of a 

 star would result from the first two causes; and as this hap- 

 petis to be the whole displacement observed (neglecting a 

 quantity which may be considered insensible), so that there is 

 none left to be attributed to the third cause, he says that he 

 has explained aberration, assuming merely the first two 

 causes. It is evident that the two senses attached to the 

 words, to explain a phenomenon, are quite different. Ac- 

 cording to the sense in which I used the words, the explana- 

 tion of the absence of any change in the final direction of the 

 light would have to be included in any theory which professed 

 to explain aberration by means of the first two causes only. 

 In the present communication I have used the words in my 

 own sense, for I believe that there is no impropriety in it; but 

 Prof. Challis may, if he pleases, consider the object of my 

 July paper to have been the explanation, not of aberration, 

 but of the absence of any change in the final direction of the 

 light. Whichever of these results be arrived at, the other 

 readily follows. 



III. On Electrical Endosmose. By Mr. James Napier*. 



THx\T two dissimilar solutions, separated by a porous par- 

 tition, will pass the one into the other, is a phaenomenon 

 long observed, the only necessary condition being that the 

 liquids have a strong tendency to combine, and that the one 

 is more capable of entering into or wetting the porous par- 

 tition than the other. The liquids eminently fitted to effect 

 this are alcohol and water, and saturated solutions of some 

 salts and pure water. But the phaenomenon of endosmose 

 takes place also when an electric current passes through liquids 

 separated by a porous partition. When all the above con- 

 ditions are absent, and even when these conditions are pre- 

 sent, the endosmotic current will follow the electric, although 

 in a contrary direction to that which would take place were 

 there no electric current passing, showing that, under these 

 circumstances, it has its origin in the passage of the electric 

 force. This fact was first made known by Mr. Porrett in the 

 Annals of Philosophy for 1816. 



* Communicated bv the Chemical Society; having been read December 

 15, 1845. 



