250 WIEDEMANN OX THE MOTION OF LIQUIDS 



the difficulty of covering exactly a certain fraction of the surface 

 with shell-lac. 



The result expressed in this section also agrees with the law 

 before established, according to which the intensity of the galvanic 

 current being the same, the quantities of liquid transported were 

 independent of the magnitude of permeable surface presented 

 by the clay cylinder. For if we assume that the capillary 

 apertures of the clay cylinder are equally distributed over its 

 surface, then the quantity of liquid driven through a given 

 fraction of that surface by means of a certain hydrostatic pres- 

 sure will be directly proportional, first to the magnitude of sur- 

 face, and secondly to the pressure itself. But the quantity 

 of liquid transported by a galvanic current of constant intensity 

 through a surface, for example, ten times smaller, is exactly 

 the same as that through the whole undiminished surface. In 

 order, however, that the same amount of liquid may be pressed 

 through two surfaces, one ten times smaller than the other, by 

 hydrostatic pressure, the pressure on the former case must be 

 ten times greater than on the latter. Hence to equilibrate the 

 action of the galvanic current, the hydrostatic pressure must 

 increase in the same proportion as the permeable surface of the 

 clay cylinder decreases. 



Exactly similar considerations apply to the case where clay 

 plates of different thicknesses are used. With capillary tubes 

 of different lengths, and doubtless also with clay plates of dif- 

 ferent thicknesses, the quantities of liquid forced through are 

 inversely proportional to the lengths of the capillary tubes or 

 the thicknesses of the clay partitions. In order therefore that 

 the action of a galvanic current, which with constant intensity 

 transports equal quantities of liquid in equal times through clay 

 partitions of different thicknesses, may be always equilibrated 

 by hydrostatic pressure, the latter must increase in direct pro- 

 portion to the thickness of the partitions. Hence the heights to 

 which liquids ascend under the influence of the same galvanic 

 current are^ under otherwise equal circumstances, directly pro- 

 portional to the thicknesses of the clay partitions. 



This law, which follows necessarily from the foregoing, the 

 author also sought to corroborate by experiment. As it was 

 difficult however to obtain clay partitions of different thick- 



