Intelligence and Miscellaneous Articles. 299 



when the circuit is closed, is most remarkable. In twenty-four hours 

 the electromotive force only loses 0'02 of its original intensity, and 

 then the couple becomes perceptibly constant for several days. Ter- 

 restrial couples with a constant current are likewise obtained with 

 iron and lead. 



The composite terrestrial couple was formed of a plate of amal- 

 gamated zinc with an area of 1 decimetre square, placed in a good 

 vegetable mould at 1 decimetre from the surface, and of a plate of 

 manganized coke, immersed in an earthen cylinder open at both ends, 

 with one end buried in the earth and surrounded with clay to a height 

 of 1 decimetre ; then filled with salt water marking 3°. The zinc 

 was 2 metres from the coke. 



The resistance of this terrestrial couple is 5"34 greater than that 

 of the nitric acid couple ; but this resistance is variable, and depends 

 on the nature of the soil, its hygroscopic state, and the distance 

 between the elements. 



Fourth Part. On Storms. — Amongst the natural sources which 

 furnish electricity continually to the air, we must distinguish the 

 following : — 



1. The exhalation of oxygen and carbonic acid gas by the leaves 

 of plants, which furnishes positive electricity to the air. 



2. The contact of soils and fresh and salt waters ; the former 

 acquire an excess of positive, and the latter of negative electricity. 



Living vegetables behave in the same way in relation to the earth, 

 that is to say, the parenchymatous tissues are negative, and the earth 

 positive ; the two electricities are transmitted to the air by the me- 

 diation of vapours. 



3. The decomposition of animal and vegetable matters at the sur- 

 face of the earth and in the water, which gives rise to complex effects. 



4. The contact of cold and warm waters circulating on the sur- 

 face of the seas ; the cold waters are positive, and the warm nega- 

 tive. The tension of the electricity, considering the extent of the 

 surfaces, must certainly be exceedingly weak ; for the evolution of 

 electricity only takes place by contact where there is a mixture of 

 cold and warm waters. 



It has been asked whether, in evaporation in the present and 

 similar cases, that is to say, in a voltaic couple of which the circuit 

 is not closed, each element can furnish electricity to the vapour 

 which escapes from it. We know very well that when one of the 

 elements of a couple is put in communication with the earth, we may 

 give a charge to a condenser by placing one of the plates in com- 

 munication witli ilie other element; ought the case to be similar in 

 this same couj^le when vapour escapes from each element ? There 

 is nothing to opjjose this, seeing that the vapour continually carries 

 off the excess of electricity proper to each element, as might be done 

 by a conducting body which would complete the circuit. It is pre- 

 cisely what takes i)lace when the two plates of a condenser are put 

 in communication with the two elements of a couple. 



We see therefore that a great number of facts tend to prove that 

 electricity, sometimes positive, sometimes negative, is evolved in the 



