180 ELEMENTS OF STATIC ELECTRICITY. 



communicated with an electroscope at its lower extrem- 

 ity. As the arrow rose, the electroscope showed a 

 steadily increasing difference of potential, till the 

 indications equaled the full capacity of the instrument. 



The arrow was then shot horizontally, at an eleva- 

 tion of about three feet, but no change of potential was 

 indicated ; proving that the indications resulted from a 

 difference of potential existing in the atmosphere, and 

 were not due to the friction of the arrow in passing 

 through the air. 



The difference of potential, in this experiment, was 

 between the earth and atmosphere : but the following 

 experiment was entirely independent of the earth. 

 During a balloon ascent, a conductor, 170 feet in length, 

 was lowered into the air ; a ball being attached to its 

 lower end, and its upper end connected with an elec- 

 troscope. The indications showed a marked difference 

 of potential between the upper and lower strata. 



As the balloon moved with the wind, the friction 

 between the ball and the air could not have been suf- 

 ficient to affect the electroscope perceptibly ; so that, 

 in this instance, as in the former, the indications of the 

 instrument must be attributed to a difference of po- 

 tential existing in the atmosphere. 



The series of observations already referred to, and 

 numerous others of a similar character, prove that the 

 potential of the atmosphere is almost invariably positive 

 with reference to that of the earth. 



THE ATMOSPHERE AS A LEYDEN JAE. It is evi- 

 dent that we have, in the atmosphere and on the earth's 

 surface, the same conditions which exist in the Ley den 

 j ar tvvo conducting surfaces insulated by a dielectric ; 

 the stratum of least resistance forming the upper con- 



