302 ATMOSPHERIC ELECTRICITY. 



nameof the electric column and atmospheric electroscope, consisting of 

 a dry pile, composed of 1,600 disks of zinc and gilded paper, which 

 appeared to him adapted to determine the electrical variations of the 

 air and of the surface of the earth. A small pendulum set in motion 

 by the electricity of the column alternately struck against two metal- 

 lic balls, one in constant communication with the positive pole, the 

 other with the negative pole or with the ground. The vibrations of 

 this pendulum would, according to De Luc, indicate by their fre- 

 quency the electrical variations of the surroundicg medium or those of 

 the surface of the ground."^ But it is now known that the irregularity 

 of the vibrations of the pendulum cannot be regarded as an indication 

 of the influence of the surrounding electricity; that it is the character 

 of the dry pile to permit only a very gentle circulation of electricity, 

 and not to become recharged, except very moderately, after having 

 lost its electricity by the communication of its poles ; consequently, 

 that more or less time must pass before sufficient electricity is accumu- 

 lated at the two poles of such a battery to renew and continue the 

 movements of the pendulum. Besides, Schiiblerf examined this ques- 

 tion, and concluded, from a great number of observations, made under 

 very different circumstances, that the action of De Luc's dry pile was 

 subject to the influence of moisture, and not to that of atmospheric 

 electricity. 



CHAPTER II. 



OF THE USE OF ELECTRO-ATMOSPHERIC APPARATUS. 



When we examine the opinions which have been advanced as to the 

 phenomena of atmospheric electricity^ we are struck with their want 

 of harmony. The mode of action of this agent on the instruments 

 has been variously interpreted by scientists ; and while some consider 

 these instruments as having been electrified by the contact of the sur- 

 rounding air, whoie electricity is positive, others see in the electrical 

 signs which are manifested only the effect of electricity of induction. 

 In speaking of the electrical phenomena of the atmosphere M. BiotJ 

 says : 



" The experiments on atmospheric electricity present the only case 

 of an indefinite medium, such as the air, all the molecules of which 

 are individually charged with an excess of electricity of the same kind 

 adhering to their surface; so that the whole mass of the medium be- 

 comes pervaded with it in proportion to the heights. The difterent 

 particles of this medium cannot be in repose except from the mutual 

 compensation of their repulsive forces, combined with their weight ; 

 and the same condition applies to the conducting bodies which are 

 immersed in it. Thus, in all bodies in the air, the electrical equilibrium 

 cannot take place when their natural electricities are merely neu- 



« Bibli<;th. Biitann. Sc. et Arts, tom. XLVII, p. 213. 1811. 



I Jourii. (le Schweigger, torn. XV, p. 130. 



j Traitc de Pbys. Expciiiu. ct ilatliom., torn. II, p. 457. 



