152 



ATMOSPHERIC ELECTRICITY. 



necting links between its assumed chemical origin and its ultimate conversion 

 into the lightning flash. « 



As the friction of watery particles is a discovery only just matured, the idea 

 has not yet occurred of including it in the investigation of atmospheric electri- 

 city. Though the present state of our knowledge does not justify us to haz- 

 ard an answer, yet Ave are called on to propose the question — Do the watery 

 particles with which the atmosphere is charged acquire positive electricity as 

 they are rubbed by the wind against the earth, and all it sustains, as hills, 

 rocks, trees, &c, in the same manner as the stream of steam and water be- 

 comes positive by rubbing against the jet 1 If so, what connexion may not be 

 traced between the hurricane winds of the tropics and the prevailing lightning- 

 storms with which those regions abound f Does the friction together of two 

 currents of air, charged to different degrees with moisture, develop the two 

 electrical states 1 



Throwing out these hints, we come to consider the actual conditions pre- 

 sented by the atmosphere. The first fact which presents itself is the extreme 

 irregularity in the distribution of the electricity ; and this would necessarily 

 ensue from either theory, for local variation is an essential element in any view 

 which we may be induced to adopt. Each theory includes evaporation, either 

 as producing the electricity, or as providing the rubbing particles ; so that, in 

 the sequel, we may safely adopt the current language, without pledging our- 

 selves against conviction to either theory, in the present undecided state of the 

 question. 



If the evaporation or other processes by which positive electricity is sup- 

 plied to the atmosphere were uniform over the surface of the globe, the spher- 

 ical shell of air by which the globe is enclosed would be uniformly charged 

 with positive electricity, and, being a nonconductor, it would be related to the 

 crust of the globe on which it rests in the same manner as the cake of an elec- 

 trophorus is related to the metallic disk in contact with it. The positive elec- 

 tricity of the atmosphere will then act by induction on the natural electricities 

 of the superior parts of the earth ; and if we suppose them to possess conduct- 

 ing power in the same degree throughout the surface, the positive fluid result- 

 ing from the decomposition would be driven downward, while the negative fluid 

 would be drawn toward the surface, and would augment the intensity of the 

 negative fluid already collected there from other causes. 



Thus the atmosphere over different parts of the surface of the earth will re- 

 ceive different quantities of electricity, and, since air is a nonconductor, the 

 inequality of the electric state thus produced will continue, except so far as it 

 may be modified by the effects of atmospheric currents. 



DIURNAL VARIATION OF THE ELECTRICITY. 



The electric state of the air depending, then, on the results of the evapora- 

 tion of water on the surface, that state may naturally be expected to be subject 

 to periodical changes corresponding in some definite manner to the changes 

 incidental to the process of general evaporation ; and, as these latter changes 

 must be related to the influence of the sun on the atmosphere, a series of vicis- 

 situdes in the electricity of the air may be looked for, having some correspond- 

 ence with the rising and setting of the sun and the epochs of noon and mid- 

 night. Observation, accordingly, sanctions this anticipation. 



If the electricity of the air be examined by proper eiectroscopic instruments 

 at and immediately after midnight, its intensity will be found to be gradually 

 decreasing, and this decrease will continue till a little before sunrise, when the 

 intensity, becoming stationary for a short time, will afterward begin to increase 



