136 ANNUAL OF SCIENTIFIC DISCOVERY. 



plant ; and I was thus led to study the electrical effects produced at the 

 contact of the soil with a fall or stream of water, of which I then understood 

 all the importance. This question leads us to one of the principal sources of 

 atmospheric electricity a question of a most complicated nature, from the 

 numerous causes which conduce to the general effect. The apparatus 

 employed in these researches consists of 1. Diaphragms of porous porcelain, 

 or little bags of sail-cloth, each containing a depolarized plate of gold or 

 platinum, surrounded by charcoal of sugar-candy, with a view to render 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 to collect the electricity of vapors formed above 

 the soil or water ; and various accessories, such as copper wires, gold and 

 platinum covered with gutta percha, &c. The electrical effects produced by 

 the contact of the soil and water are complex, for they vary in direction and 

 intensity 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 hi the course of a month the electrical effects are 

 seen to change hi 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 permanent observations to foUow ah 1 the variations to 

 which the actions of contact are subject, and to guard against the effects of 

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

 moments. Very commonly polarization is destroyed in the course of 24 hours, 

 and the effects of which we are in search may then be observed. In some 

 exceptional cases the electrical 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 carry 

 off with it an excess of electricity of the same nature possessed by the one or 

 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 vapors are of contrary signs ; the 

 effects are complex. From the foregoing it will be understood why storms 

 generally take place in summer, at that period of the year when the decom- 

 position of organic matters and evaporation are at their maximum, and also 

 why they are so frequent and so violent under the tropics at the period when 

 the sun approaches 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. The phenomena to which I have referred are so varied 



