318 ATMOSPHERIC ELECTRICITY. 



carbon, as observed by M. Pouillet,* we obtain signs of electricity only 

 while the carbon, held perpendicularly, burns at its upper surface ; if 

 it be held nearly horizontally so that the carbonic acid which is formed 

 cannot rise except by ascending along the base of the carbon, the con- 

 denser no longer becomes cliarged, the two electricities having had 

 time to recombine. Now it is known that the combination of oxygen 

 with the carbon of the plant does not take place outside of the paren- 

 chyma, but in the interior; therefore before the carbonic acid formed and 

 remaining in contact with the carbon in excess is disengaged, the elec- 

 tricities that are developed ought to reunite and every sign of free elec- 

 tricity disappear. On the other hand it may be asked how it is that the 

 electrical effects obtained by M. Pouillet were the same night and day. 

 Ought they not to be different, since in the day there is the decompo- 

 sition of the acid absorbed, while during the night a portion of the 

 oxygen is transformed into acid ? Further, may not these same 

 electrical effects proceed from the remains of organic bodies which are 

 found in the vegetable earth of the capsules, and which, decomposing 

 by contact of air, generate carbonic acid, or rather may they not ho 

 attributed to the electro-cliemical action which the same earth would 

 naturally exercise on the conducting wires with which they may come in 

 contact? 



Vegetation is, without doubt, the result of a multitude of chemical 

 reactions which necessarily disturb the equilibrium of the two elec- 

 tricities and thereby set free a portion of each ; but it is very difficult 

 to see in this the cause of the uniformly positive electricity, which 

 manifests its presence in the atmosphere whenever the sky is clear. If, 

 with M. Pouillet, we attribute the production of atmospheric elec- 

 tricity to evaporation and vegetation, the usual electrical state of 

 the atmosphere must vary in different regions, as this philosopherf 

 himself observes ; in one place we ought to find positive electricity 

 predominant, and in another negative. But experience is opposed to 

 this conclusion. We do not find any notice of observations of nega- 

 tive electricity in clear weather, except in the report of M. Arago,J 

 on a memoir containing the researches and observations made by 

 Marshal Mormont, duke of Ragusa, during his voyage to the East. 

 " I perceived in this memoir," says M. Arago, ''three observations of 

 negative atmospheric electricity, made at Constantinople in clear 

 weather; three observations of the same kind at Alexandria, and three 

 entirely similar ones made near Cairo. We do not think," adds he, 

 'Hhat in France, England, or Germany, any observer has ever found 

 negative atmospheric electricity in clear weather." But if we recollect 

 that these experiments were made by means of a conductor, which 

 was moved slowly downward from above and upward from helow until 

 an electric effect was produced in the electroscope with which it was 

 in communication, we see from what has been said (1 part chap. II) 

 of the electric phenomena which the electrometers present when they 



* Annales de Chimio et de Physique, torn. XXXV, page 405. 



t Elements de Physique Expe'iiaieutale et de Mdte'orolog'c, torn. II, page 827, Paris, 1829. 



t Coiuptes llendus, torn. II, pnge 212, 1836. 



