AGENCY OF ELECTRICITY. 107 



night, and turn their faces as if eager to catch the first rays 

 of the morning ! 



VI. Electricity. Electricity is a much more subtle 

 agent than any which have been named ; and although the 

 mode in which it produces its effects is not so easily discov- 

 ered, yet from some experiments it is rendered probable, that 

 its action is nmch more direct and efficient upon the vital 

 functions of plants, than has been commonly supposed. It 

 seems to be widely disseminated throughout the atmosphere, 

 the water, and the soil. 



Electricity is developed by friction, and by chemical ac- 

 tion. The former is called common^ the latter Voltaic elec- 

 tricity, or Galvanism. Change of temperature and of form 

 develope it, the condensation of vapor, the variations of 

 temperature in the atmosphere, and the chemical changes, 

 which take place in the soil, are constant sources. The na- 

 ture of the electric fluid is unknown. 



Theory. It is supposed to consist of two fluids pervading 

 all matter ; the one is called positive or vitreous ; the other, 

 negative or resinous. Each repels itself, and attracts the op- 

 posite.* Acids are generally negative, and alkalies positive; 

 hence, the electric state of the soil may generally be known 

 by its composition. 



If a soil is wholly negative, as is the case with pure 

 silica or sand ; or wholly positive, as is the case with alumi- 

 na, lime, magnesia, iron and the alkalies, it is always wholly 

 barren ; or when one ingredient greatly predominates, it is 

 unfavorable to vegetation ; and the object of amendments is 

 to bring the soil to a neutral state.f The animal and vege- 

 table substances in the soil produce acids and alkalies, which 

 develope by their affinities electrical currents. The soil, be- 

 ing composed of different minerals, and saturated with mois- 

 ture,constitutes a galvanic battery, which is constantly acting 

 upon the functions of vegetables, and upon the rocks. 



* See Gray's Chemistry, p. 74. t See ' Soils,' chap. 5th. 



