TREES AS ELECTRIC AGENTS. 173. 



causes two pith-balls, suspended by threads, when similar- 

 ly electrified, to repel each other at certain distances. All 

 those clouds that show a definite and organized arrange- 

 ment, and resemble feathers or lace, are charged with 

 electricity. As they accumulate they lose their symmet- 

 rical arrangement, but do not mix, until some object, 

 charged with opposite electricity, comes near them and 

 draws from the mass its electric fluid, when the- vaporous 

 particles, losing their mutual repulsion, immediately co- 

 alesce and descend in rain. 



To illustrate the action of trees in producing showers, 

 we will suppose a dense electric cloud to be passing over 

 a dry plain containing only a few trees. Not meeting 

 with any conducting objects of appreciable force on its 

 journey, it remains suspended in the heavens until it 

 reaches either a large collection of water, or encounters a 

 forest, over which, as over a lake, there rests always, in 

 calm weather, a stratum of invisible moisture, which is a 

 powerful conducting agent. The trees, with their numer- 

 ous vegetable points, and the vapor that overspreads them, 

 combine their force in drawing down the electric fluid 

 from the cloud passing over, causing the whole mass to 

 descend in showers. The damp stratum of air which, in 

 still weather, rests upon the surface of every large sheet 

 of water, being a powerful conductor, serves to explain a 

 phenomenon often observed in a dry season near the 

 coast. A dense electric cloud is seen to pass over our 

 heads, without shedding a drop of rain, until it reaches 

 the ocean, when the humid air above the waves, acting as 

 a conductor, causes the cloud to part with its electric fluid 

 and to fall in copious showers at the same moment. 



Occasionally a similar cloud, after rising in the west 

 about thirty degrees, will be turned from its direct course, 

 and repelled by the dry, heated atmosphere resting on the 

 plain, and, attracted by the invisible cloud of moisture that 



