Mr. G. Rainey on the Cause ofEndosmose and Exosmose. 179 



visible for an hour and a half. On the 23rd the sky was very 

 clear, the air calm, the meteor less brilliant than the evening 

 before ; it was seen suddenly on the horizon at a quarter past 

 seven, and did not disappear till thirty-five minutes past eight. 

 Lastly, on the 28th, the Bise was strong, and fleecy clouds 

 were perceived around the luminous band, which lasted until 

 forty-two minutes past eight. It appears certain that it was 

 always seen single, vertical, and with parallel edges. 

 Lausanne, June 30, 1846. 



XXXII. On the Cause of Endosmose and Exosmose. 

 By George Rainey, M.R.C.S.* 



THE phaenomena of endosmose and exosmose were attri- 

 buted by Dutrochet to the passage of currents of elec- 

 tricity of unequal intensity through a membrane situated be- 

 tween two fluids of different densities, these currents being 

 supposed to carry with them unequal quantities of fluid. Al- 

 though the facts of endosmose and exosmose, as described by 

 this philosopher, are admitted by all to be correct, yet his ex- 

 planation of them has not been generally received ; nor am I 

 aware that they have ever been explained in a manner gene- 

 rally satisfactory, and therefore I shall be obliged if you will 

 insert in your valuable journal the following explanation. 



It is a fact which probably no one will question, that when 

 two fluids of unequal density are brought into contact in mi- 

 nute quantities, without any membrane being interposed, they 

 will intermix by diffusion, the rarer fluid intermingling itself 

 with the denser one, and the denser fluid diffusing itself 

 through the rarer one, until the one becoming gradually more 

 dense, and the other less so, the whole mass acquires one uni- 

 form consistency. However, should this fact be doubted, it 

 can be well illustrated by introducing between two surfaces of 

 glass, placed almost in contact, some thick mucilage, and a 

 little thin coloured fluid of any kind, for instance common 

 writing-ink, and observing with the microscope the part where 

 they become united, when the two fluids will be seen gradually 

 to intermix, and to become so blended together, that their 

 line of union will become lost. 



The same fact can be shown by introducing some mucilage 

 into a piece of thermometer tube, and after it, at the same end, 

 some writing-ink. The coloured fluid will at first pass only 

 in a small column through the mucilage, along the centre of 

 the tube, leaving the mucilage in contact with its parietes, 

 but afterwards they will become gradually blended together. 

 * Communicated by the Author. 



