ATMOSPHERIC ELECTRICITY. 317 



this instrument as he was able to seize the instant when the electrici- 

 ties were set free, when the disengagement ceased, and to follow step 

 Ly step the phases of the phenomena, he could thus distinguish what 

 was owing to chemical action, produced by the high temperature, from 

 that which was due to simple evaporation. 



M. Pouillet* pointed out another source of atmospheric electricity in 

 the act of vegetation. He had established, by a series of previous 

 experiments, that gases give off electricity when they combine either 

 together or with solid or liquid bodies ; that in these combinations, 

 oxygen disengages positive electricity, and the combustible body, what- 

 ever it may be, negative electricity ; and that reciprocally, when a com- 

 pound is decomposed, tach of the elements then wanting the electricity, 

 which it has disengaged, is found in an opposite electrical state. Thus 

 when oxygen combines with carbon, the carbonic acid which is formed 

 is positively electrified, while the carbon remaining becomes negatively 

 electrified. We may verify this phenomenon by j)lacing a cylinder of 

 charcoal perpendicularly, at about a foot below a metallic plate, con- 

 nected Avith the upper disk of a condenser with plates of gold, and 

 having placed its lower portion in connexion with the ground, then 

 igniting the upi3er part of it, a column of carbonic acid gas imme- 

 diately rises, and transmits to the upper plate an excess of positive 

 electricity. 



But we know that different parts of plants act on atmospheric air ; 

 that sometimes they form, at the expense of the oxygen_, quite a large 

 quantity of carbonic acid, Avhich escapes insensibly, and that sometimes 

 they exhale pure oxygen, arising from some combination in the in- 

 terior of the plant. JNow, if it be true, says M. Pouillet, that carbonic 

 acid is positively electrified at the moment of its formation, it follows 

 that plants ought to yield to the air, by the exhalation of that acid, 

 a greater or less quantity of positive electricity. This scientist at- 

 tempted to verify his conclusion directly by experiment. If the hypo- 

 thesis be true, the plant ought to take the negative electricity, and M. 

 Pouillet obtained, in fact, in the day as well as at night, signs of nega- 

 tative electricity, by germinating grains in glass capsules, varnished 

 on the outside, which were connected together by metallic wires and 

 at the same time with the lower plate of a condenser, while the upper 

 plate was in communication with the ground. Thus he thought he 

 might conclude from liis experiments that on a surface, in full vegeta- 

 tion of one hundred metres square, there was eliminated in one day 

 more positive electricity than was necessary to charge the strongest 

 battery. 



Many philosophers have believed that the effect obtained by M. 

 Pouillet cannot be attributed to the combination of the oxygen of the 

 air witli the carbon of tlie plant, since this phenomenon being analagous 

 to combustion, the plant will set free the negative electricity, and the 

 carbonic acid, the opposite electricity, which will immediately enter 

 into combination with the Ibrmer, if ever so little gas remains in contact 

 with the excess of carbon. This is so far true that in the combustion of 



* Annales de Chimio et de Physinue, torn. XXXV, p. 405. 1827. 



