AGENCY OF ELECTRICITY. 109 



d. The force thus exerted by the membrane is equal to the 

 weight of the atmosphere, as it vvouJd, in time, raise the col- 

 umn of water thirty-two feet in height. If now P, the posi- 

 tive wire of a galvanic battery, is immersed in the water, and 

 n, the negative wire communicate with the interior through 

 the cork e, the effect will be greatly increased ; and, if the 

 wires are reversed, the liquid in the receiver may be made to 

 flow out into the vessel of water. 



According to the experiments of Dutrochet, the ascensional 

 force in this instrument is about equal to the pressure of the 

 atmosphere ; and Mirbel found the ascensional power of the 

 sap in a grape-vine to be the same as in this instrument. By 

 cutting off a grape-vine, and adapting to it a glass tube filled 

 with mercury, the outpouring of the sap will raise the mercury 

 twenty-eight inches in the tube. 



If now we examine the spongioles of vegetables, we shall 

 find, that each has a bladder which stands out to absorb the 

 nutritious particles ; and that the tubes are filled with mem- 

 branes, in which the endosmometric action is produced. The 

 fluids constituting the sap are generally denser than water, a 

 circumstance which is esssential to the action. If we sup- 

 pose currents of electricity, developed in the soil, to be passing 

 through the tubes of the vegetable, we have perhaps the most 

 satisfactory theory of the ascent of the sap* which can be 

 furnished. Hence it appears that one prominent object of 

 the agriculturist is to balance the electrical forces in his soil, 

 in order that the highest effect of this power may be produced 

 upon his crops. There appears also to be an opposite move- 



* As the ascent of the sap may thus be accounted for on mechanical 

 and electrical principles, it may be thought that this example is op- 

 posed to the views respecting the vital principle^ which were present- 

 ed in the first chapter. But it should be remembered, that the effect 

 here depends upon the tissue or membrane which is a product of vital- 

 ity. How can chemical laws construct the spongelets, and the mem- 

 branes, which must be placed across the tubes in which the sap cir- 

 culates .'' 



