284 Catalogue of Works on Gardenings fyc. 



attended with electromotive action. In all probability, the electricity is of the 

 negative or resinous kind, and will thus neutralise a small quantity of the -f- 

 electricity rising at the same time 



" In the processes of animal life there are numerous changes, in which elec- 

 tricity is necessarily extricated ; but the amount thrown into the atmosphere in 

 this way is thought to be but trifling. Volcanoes and earthquakes are sources 

 of atmospheric electricity, but this department of the subject has not yet been 

 investigated. 



" If the surface be covered with water, humid soil, or vegetation, the evapo- 

 ration and consequent electricity will be increased in proportion to the velocity 

 of the wind ; but when ground is so parched that the moisture is entirely 

 exhaled, the air' above it partakes of the drought, and both bodies, by their 

 nonconducting qualities, retain the electricity developed, either by the air 

 moving on the surface, or by that which ascends among the dry and heated 

 particles of sand. 



" Having thus pointed out the various sources, we may remark that, though 

 each of them must be had regard to in particular cases, yet that the electricity 

 which is constantly present in the atmosphere can be derived only from the 

 process of evaporation, than which there is no other sufficiently copious or 

 prevalent, and corresponding in its fluctuations. Even the electricity of 

 vegetation is subordinate to that, as assimilation in plants is vigorous according 

 to the rapidity of evaporation ; and the electricity, on being communicated to 

 the atmosphere, leaves the oxygen or the carbonic acid, for the vapour 

 nascent at the same time, as the better conductor. The electrical effects of 

 the other causes which have been mentioned may be compared, in their 

 amount, with the influence of animal heat and artificial fires, perceptible 

 enough in a small compass, but not interfering with the general distribution of 

 temperature." 



It is assumed, therefore, as a general principle, that the electricity of the 

 atmosphere follows the course of the aqueous vapour. It is continually 

 received from the earth into the atmosphere, and as continually returned to 

 it ; its distribution never being equable, but disturbed by the formation of 

 clouds, ''in which it is detained, and by the mingling of different strata by the 

 winds, which, bringing successive portions of the air into contact with the 

 earth, the electricity is again absorbed. As might be expected from the 

 nature of the exciting causes, the quantity is extremely variable, according to 

 the climate, the season, and the time of day. In hot climates, not deficient 

 in humidity, it is more abundant than where the air is cold and dry." In 

 Equinoctial America the intensity of the electricity is much greater than in 

 Europe ; and in the polar regions it can scarcely be detected. Change of 

 season is attended with the same variation in electricity, as is produced by 

 difference of climate. Electricity undergoes a succession of changes during 

 every twenty-four hours. " It is first perceptible soon after sunrise. The rise 

 at sunset must be owing to the formation of dew, by which the electricity 

 attached to the vapour is contracted into less space, and its intensity pro- 

 portionably increased. The oscillation evidently follows the course of the 

 vapour, but it must be understood that its regular outline can be traced only 

 in calm and serene weather, being disturbed by whatever affects the temper- 

 ature and vapour. By the influence of condensing vapour there is an inver- 

 sion of the distribution, which ensues in a homogeneous atmosphere. The 

 electricity which has been concentrated in the planes of aqueous precipitation 

 gradually communicates itself to the surrounding air, its intensity becoming 

 weaker as it recedes from the plane. The change is, therefore, stronger as we 

 ascend above the earth. In connexion with this part of the subject, we may 

 mention the periodicity of thunder storms. When the temperature begins to 

 decline, clouds which have formed become more dense, in consequence of 

 receiving additional vapour without a corresponding supply of heat. They 

 may again evaporate, if the neighbouring air be not nearly saturated ; but 

 often they are precipitated in showers, after which the weather again clears. 



