ATMOSPHERIC ELECTRICITY. 



323 



Gothard, 6,200 feet above the level of the ocean, was only -{- 10 de- 

 grees of Volta's electrometer, but the instrumeat rapidly passed to 50 

 and even to 60 degrees when it was placed on a granite rock 30 feet 

 high, which was found near tlie place where the observation was made. 

 The same instrument ordinarily indicated only 4 or 5 degrees at the 

 same time of the year, and at the same hour of the day, in the low 

 part of the same country. 



Though Schiibler could not discover any direct relation between the 

 intensity of atmospheric electricity and the height of the place above 

 the level of the sea, yet he thought that this relation existed, but that 

 it was influenced by a multitude of causes. He believed he could not 

 be mistaken in general as to an increase of electricity with the height, 

 as is manifest in the following table, which contains the result of 

 his experiments made under a clear sky on the inclinations of an Alpine 

 mountain : 



De Saussuref found, on the contrary, atmospheric electricity weaker 

 on mountains than in the plains. Thus, according to him, it is rather 

 the relative height of the place of observation than its absolute height, 

 which exercises an influence on the indications of the instruments. 



The mode of action of atmos})heric electricity on the electrometer, 

 and the negative electricity which terrestrial bodies possess, explain 

 the influence which local causes exert on that instrument. Though 

 in general the electrometer gave no indication in places which were 

 sheltered, we ought, however, to remark, that it might give indica- 

 tions under trees or near buihlings which are in the neighborhood 

 of uncovered places, but then these indications are negative. This 

 happened when, after having brought the instrument to an equi- 



- We shall hereafter see the cause of this negative electricity. 



t Voyages dans les Alpes, torn. IV, sec. 200S, p. 197, and sec. 2055, p. 257. 



