444 Intelligence and Miscellaneous Articles. 



and zinc, according to which calculation it must be more than 

 3 X 10 - 7 millim. With this agree F. Kohlrausch's experiments on 

 the capacity of galvanically polarized platinum surfaces for very- 

 weak charges, from which the distance comes out equal to the 

 2475000th part of a millimetre, if the potential-difference be as- 

 sumed to be equally divided between the two plates. 



The author showed that the laws of the flow of water through 

 capillary tubes and porous diaphragms occasioned by electric cur- 

 rents, as ascertained by Gr. Wiedemann and Quincke, and the laws 

 of the electric tension excited by the flowing of water, between the 

 beginning and the end of the course of the stream, discovered by 

 the latter observer, can all be deduced from the hypothesis that a 

 difference of electrical potential exists between the sides of the 

 vessel and the liquid (which M. Quincke also assumed, and sup- 

 ported by many experiments), and that it is the part of the double 

 layer falling in the water that both yields to the electric attractive 

 forces on the tube being traversed by an electric current, and is also 

 taken along by the introduced motion of the water. The boundary 

 layer of the liquid must be assumed to be at rest against the sides 

 of the tube, as in Poisseuille's theory of the flow of liquids in capil- 

 lary tubes. In a series of cases the data supplied suffice for the 

 calculation of the electric moment of the part of the double layer 

 that falls in the liquid (in which calculation the opposite electricities 

 must be assumed to be combined in the bounding surface). The 

 values then obtained do not exceed those with which we are ac- 

 quainted from the galvanic tensions between metals. 



Thus M. Wiedemann's experiments on the electric conveyance of 

 sulphate-of -copper solution through clay diaphragms give the mo- 

 ment of the electrical layer in the liquid as equal to 2-4 Daniells. 

 M. Quincke's experiments on the height to which water, conveyed 

 by electricity, ascends in glass tubes give 3-9 Daniell's • and his 

 experiments on the electric tensions which arise when very dilute 

 salt-solutions are driven through clay diaphragms give 1*9-2-7 

 Daniells. As the electromotive force between potassium and pla- 

 tinum amounts to about 3*4 Daniells, all the above-mentioned 

 numbers lie within or but little beyond the limits of the observed 

 differences of potential between metals. 



The assumption that the extreme boundary layer of the liquid 

 adheres immovable to the sides of the vessel was founded upon the 

 determinations made by M. Quincke of the heights of ascent of 

 electrically carried liquid in cylindrical glass tubes, according to 

 which they are inversely proportional to the square of the radius. 

 This results from the theory only on the assumption that no sliding 

 of the boundary layer occurs. The calculation was accomplished 

 even for those cases in which a cylindrical thread is placed in a cy- 

 lindrical tube ; and it showed tolerable accordance with the obser- 

 vations, so far as could be expected with experiments so subtile and 

 so disturbed by manifold influences. — Monatsbericht der Icon.joreuss. 

 JJcademie zu Berlin, Feb. 1879, pp. 98-200. 



