Intelligence and Miscellaneous Articles. 545 



by the septum, and the liquid B, which attracts it with a force su- 

 perior to that exercised between the molecules of A, there is no reason 

 why the movement should not take place as well in one direction as 

 the other. 



At the moment when the pores of the septum are charged with 

 the liquid A, and if the passage of the liquid threads A towards the 

 liquid B is considered to be more rapid than the passage of B towards 

 the liquid threads A, on account of the smaller mass of A, it follows 

 that when the septum is charged with the liquid B, the threads will 

 be attracted by the mass of A, and the movement will take place in 

 a contrary direction. 



Dutrochet and Mr. Graham have pointed out, in opposition to 

 this theory, that the elevation of liquids in capillary tubes is very 

 slight compared with the height of the columns of liquid supported 

 by endosmose ; but these observers do not appear to have taken 

 into account the circumstance that, in reality, the height of the 

 liquid in ordinary tubes indicates merely the action of the liquid 

 upon itself. This is proved by the circumstance, that the liquid 

 column is always the same height in tubes of equal diameter, and 

 made of any substance that is wetted by the liquid, as if the 

 layer of liquid nearest to the surface of the tube were the seat of the 

 action ; whereas the capillary force essential in endosmose results 

 from the action of the solid substance on the liquid. 



In order that this may produce its greatest effect, the diameter of 

 the tubes must not be more than double the distance at which the 

 attraction is exercised ; and in ordinary capillary tubes the conditions 

 requisite for the production of an appreciable osmotic motion are far 

 from being fulfilled. 



The only weak point of Poisson's theory, so far at least as regards 

 the porous septum, consists in the disregard of the elective action of 

 the solid substance just at the point where its consideration becomes 

 necessary. When the surfaces of the septum are in contact with two 

 liquids which are miscible, one being more strongly attracted by the 

 substance of the septum than the other, there would at the moment of 

 contact between the liquids be an expulsion of one by the other, and 

 a consequent motion which would cease so soon as the liquid was in 

 contact with the septum throughout its entire extent. 



Porous clay vessels have channels whose minuteness is evident 

 from the slowness with which water passes through them, never- 

 theless they are inferior to liquids in the osmotic faculty. There is 

 no doubt but that this is owing to the difference in the distance 

 between the molecules of the latter compared with the mechanical 

 or accidental interstices of the former. Liquids are osmotic agents 

 par excellence. 



When two liquids of different densities are placed in a cylindrical 

 test tube, and separated by a third liquid of intermediate density 

 which dissolves, in appreciable quantity, only one of the other liquids, 

 this one will pass into the other. When, for instance, chloroform is 

 at the bottom, above it a layer of water, and then a layer of eether, 

 the chloroform layer gradually increases in volume ; the aether layer 

 diminishes and at last disappears ; while the water layer is scarcely 

 Phil. Mag. S. 4. No. 62. Suppl. Vol. 9. 2 N 



