180 Mr. G. Rainey on the Cause of Endosnwse and Exosmose. 



Also by filling a piece of thermometer tube with water, closing 

 its upper extremity, and placing it vertically with its lower one 

 in a solution of gum coloured with logwood, when the latter 

 will gradually ascend and colour the former, showing that the 

 diffusion is independent of gravity, and therefore may be in- 

 ferred to be the result of that attraction which is exerted uni- 

 versally between the particles of matter, varying in the inverse 

 ratio of the squares of their distances, and in the direct ratio of 

 their masses ; the particles in this instance, upon which the dif- 

 ference of density of the two fluids depends, being contained in 

 a medium which allows of their free motion one upon another, 

 cannot therefore come to a state of rest until every one of 

 them is attracted equally on all sides, that is, until all the fluid 

 is of one density. It is also a fact equally unquestionable, 

 that if solutions of the same substance in the same menstruum, 

 but of different densities, be filtered through the same mem- 

 brane, the more rare fluid will pass through it with greater 

 rapidity than the denser one. This is one of the effects of the 

 same principle of attraction, the dense fluid being in this case 

 more strongly attracted by the material of which the mem- 

 brane is composed than the rare one. 



Now, when two fluids of different densities are separated by 

 a porous membrane, the porosities being merely a multitude 

 of capillary tubes, like the space between the pieces of glass, 

 or the tube of the thermometer, will allow of the passage 

 through them of the particles of one solution into the other; 

 and they will become mixed together by diffusion the same 

 as if no regular membrane were present, as in the experiments 

 just detailed; so that electricity may just as well be regarded 

 as the cause of diffusion as of endosmose, these being the 

 same. However, the membrane being traversed by an im- 

 mensity of extremely minute porosities, will extend the sur- 

 face of the two fluids between which it is placed, and in this 

 way, bringing into close proximity a great number of parti- 

 cles, place them under circumstances very favourable for the 

 operation of the force of attraction of one particle for another. 

 But the characteristic feature of endosmose and exosmose is, 

 that the rarer fluid passes through the interposed membrane 

 more rapidly than the denser one ; and therefore that an ac- 

 cumulation takes place on that side of it on which the latter 

 was placed. The reason of this is obvious; for had it been 

 otherwise, or even had these quantities been equal, then the 

 rarer fluid must have repassed through the interposed mem- 

 brane, after its density had been increased by its intermixture 

 with the denser fluid, as rapidly as it passed through it before 

 its density had been thus augmented; or from the commence- 



