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'ation sometimes ventured, in eulogy of a favorite writer, that 

 '■ he has exhausted his subject," means but that he has 

 exhausted his own and the rosoarces of his eulogist. 



In the discussion of electricity few attempt to dogmatize. 

 As the air and the ocean have hitherto defied the efforts of man 

 to convert them into real estate, so electricity but partially 

 subdued by theory, still invites, nay, defies the scientific student 

 to drive again the shuttle through the web of theory. 



In the investigation of this subject, it is necessary to assume 

 the following postulates : — 



1. That electricity exists in all bodies. 



2. That it exists in two conditions, positive and negative. 



3. That each kind repels itself and attracts the other kind. 



4. That the two electricities tend to an equilibrium. 



5. That this tendency produces lightning and other changes 

 in nature. 



Every recorded series of experiments on the air favors the 

 idea that it is usually positive as it rises from the earth, and 

 that the surface of the earth is usually negative, though the 

 conditions of both are sometimes for a short period changed. 



The negative state of growing vegetables appears to result 

 from conditions analogous to those of the galvanic battery in 

 active operation; the earthy mineral, salts in solution, and the 

 vegetable, having their analogy in the copper, the sulphate of 

 copper, and the zinc of the battery. 



Thus the solution of the salts of the earth furnished by a 

 supply of rain is decomposed, the alkali passing to the plant, 

 and the acid selecting the more positive pole the earth. But when 

 free alkali is in excess, it may form a solution for evaporation, 

 according to the observations of Becquerel, giving a more 

 decidedly negative character to the earth's surface, and by the 

 induction of electricity promoting the positive character of the 

 atmosphere at a distance from the earth, the stratum of air 

 between them acting as an electric ; giving us the condition of 

 a Leyden jar, — 'the earth's surface being the outer coating, the 

 air remote, the inner or positive coating, — and the air between, 

 the glass separating the two. 



Thus clouds are repelled to a distance from the earth's 

 surface, till a current of moist air, a mountain height, a tree, 

 or any elevated object, furnishes the medium, when the equil- 

 ibrium is restored by a discharge or lightning flash. 

 As there are however opposite currents of air above us, it is 



