Intelligence and Miscellaneous Articles. 485 



cated nature, from the numerous causes which conduce to the general 

 effect. 



The apparatus employed in these researches consists of — 1. dia- 

 phragms of porous jiorcelain, or little bags of sail-cloth, each con- 

 taining a dejjolarized plate of gold or platinum, surrounded by 

 charcoal of sugar-candy, with a view to rendering the electrical 

 effects constant during a few moments in order to measure them ; 

 2. tangent compasses of great delicacy, adapted for experiments of 

 this nature ; 3. atmospheric electrometers destined to the collection 

 of the electricity of vapours formed above the soil or the water ; and 

 4. various accessories, — amongst others conducting wires of copper, 

 gold and platinum covered with gutta percha, &c. 



I have said that the electrical effects produced by the contact of 

 the soil and water are complex, for they vary in direction and inten- 

 sity according to the substances which compose the soil, or which 

 are dissolved in the water ; for the production of electrical effects, it 

 is necessary that there should be a heterogeneity between the water 

 of the river and that by which the soil is moistened. When the 

 waters are slightly alkaline they are negative ; when they are acid, 

 as is the case with the earth of heaths, they are positive. The well- 

 waters of Paris often present effects of this kind, in consequence of 

 the infiltration of drainage waters, which change in nature from time 

 to time ; thus in the course of a month the electrical effects are seen 

 to change in intensity and sign, without any derangement of the 

 apparatus. From this state of things it results that sometimes there 

 are no electrical effects, as is also the case in experimenting with the 

 water of a river and its sandy banks, or the adjacent lands which 

 are washed during inundations. It is necessary to establish per- 

 manent observations to follow all the variations to which the actions 

 of contact are subject, and to be on one's guard against the effects 

 of polarization, which are always to be found in operating only for a 

 few moments. Very commonlj' the polarization is destroyed in the 

 course of twenty-four hours, and the effects of which we are in 

 search may then be observed. In some exceptional cases the elec- 

 trical current has sufficient intensity to cause the action of a needle 

 telegraph at a distance of several kilometres. 



When water evaporates, either from a stream or from the earth, 

 it must necessarily cany off with it an excess of electricity of the 

 same nature possessed by the one or the other, and this becomes 

 diffused in the atmosphere ; this electricity may arise not only from 

 the reaction of the water of the river upon that with which the soil 

 is moistened, but also from the decomposition of organic matter. 

 In the latter case the electricity is always positive, whether it arises 

 from the river or from the soil ; in the former the two vapours are of 

 contrary signs; the effects are comjjlex. 



From the foregoing it will be understood why storms generally 

 take i)lacc in summer, at that period of the year when the decom- 

 position of organic matters and evajjoration are at their maximum, 

 and also why they are so frequent and ho violent under the tropics 

 at the j)eriod when the sun ap])roaches the zenith. This is so true, 

 that in those regions there is always a storm bursting at each instant 

 in a locality suitably placed in relation to the sun. 



