280 Mr. Christie on the Aurora Borealis. 



greater certainty, whether decided changes in the direction of 

 the needle were simultaneous with the occurrence of distant 

 aurorse. 

 Royal Military Academy, 27th September, 1831. 



ON THE PHYSICAL CAUSE OF ENDOSMOSIS. 



By M. DUTROCHET. 

 Read to the Academic des Sciences, 25th July, 1831*. 



TX7HEN two liquids, differing in capillary ascension, are 

 separated by a thin and permeable partition, two cur- 

 rents, flowing in opposite directions through this partition, are 

 produced ; the strong current is that of the liquid which would 

 rise highest, directing itself towards that which would rise the 

 least, and the weak current is that of the liquid which would 

 rise the least, directing itself towards that which would rise 

 the most. The progressive augmentation of the volume of 

 the liquid, which would rise the least, is the result of this double 

 phenomenon. This augmentation is in proportion to the dif- 

 ference, which exists between the force of the two opposite cur- 

 jrents : it results from the excess of the strong current as 

 compared with the weak current. This excess manifests itself 

 by a simple dynamic effect, for the two opposite currents are 

 in equilibrium, or in a state of compensation to the extent of 

 their equal parts. The force resulting from this excess is that 

 of the endosmosis. 



When I first discovered this phenomenon, I was led to con- 

 sider it as the result of an electric impulsion ; and, in fact, 

 the curious electric phenomenon discovered by M. Porret 

 appears susceptible of being referred to endosmosis, may even 

 be said not in any manner to differ from it. In this pheno- 

 menon two portions of pure water are separated by a mem- 

 brane and electrified, the one positively, and the other nega- 

 tively, by the two poles of a voltaic pile. The water electrified 



* The Committee have succeeded, by means of their foreign correspondent, in 

 establishing arrangements by which they may obtain original communications 

 from abroad for publication in this Journal. The present paper by M Dutrochet, 

 on the important subject of endosmosis, is a paper of this kind, 



