ELECTRIC CULTIVATION IN RELATION TO HORTICULTURE. 405 



condensation effects. The electrical potential of this storage is dis- 

 tributed to the soil and the roots and leafy surfaces of plants.* 



Obviously, therefore, the electrical potential of the atmosphere is 

 a function of the amount of water suspended or flowing through the air. 



During the time rain falls, bringing down the electrical energy from 

 higher altitudes, it will be found that the electric potential near the 

 earth's surface is increased from, say, 30 volts normal to COO volts and 

 higher. This electric environment will constitute a highly stimulating 

 influence on vegetation. Volta, over a century ago, discovered with 

 some degree of exactitude that the proportions of the ordinates of the 

 curve or gradient of electric potential increased as the distance from 

 the earth increases, and, more recently, Engel has provided data to 

 calculate the increase. It appears that the electric density increases 

 38 volts with each metre of altitude above the earth, or, in feet 

 equivalents, 1*19 volts per foot of altitude (fig. 64). 



This- fact is emphasised, because in future developments of one of the 

 methods of securing the services of electricity for the stimulation of plant 

 growth, it may be desirable to locate the electro-static collecting apparatus 

 at a comparatively high altitude — a principle the author has already 

 adopted in other applications of static electricity. 



Even at a height of only 64 feet, the output of a given collector 

 should be twenty times greater than if it were located at the ground 

 level. 



It may be mentioned that the late illustrious savant, Berthelot, made 

 certain experiments at Meudon to determine the electric potential on the 

 summit of a tower of 28 metres high. In fine weather the electric potential 

 of the air oscillated between 600 and 800 volts. The least fall of rain 

 raised the potential to no less than 12,000 to 15,000 volts.f As will 

 be shown further on, in the historical notes (p. 408), as early as 1783 the 

 Abbe Berthelon suggested the collection of electric energy by raising 

 a conductor with metallic heads and points high into the air. 



Referring again to the role that water plays in the physiology of 

 vegetable and animal life, we recognise that water serves as a carrier 

 of electrical potential. It assists in the process of assimilation of carbon, 

 and constitutes the source of the hydrogen in the carbo-hydrate forma- 

 tion. It attracts the atmospheric electricity. It also constitutes the great 

 storage element for receiving the flow of electricity through the soil, and 

 it returns the electricity to the surface of the earth and to the plants 

 upon it. Doubtless it serves in some equivalent capacity for animal 

 life ; it is certainly one of the elements of exchange between plant and 

 animal life. 



Even when the water is evaporated, the electric energy is deposited, 

 hence probably the origin of the radio-activity of many minerals. 



The electrical energy supplied by the sun is stored under characteristic 

 excess of normal requirements in the water above and beneath the 

 earth's surface. The vastness of the proportions of the stored electrical 

 energy is immeasurably beyond our conception. 



* Elster and Geitel say that the source of radio-activity is the soil, 

 f Vide Comptes Rendus, November 12, 1900, page 976. 



