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in the upper air, and comparatively deficient near the earth, 
whereby the balance of tension, or its equilibrium, must 
become more or less disturbed according as evaporation 
varies at the surface. In this way such continuous fluxions 
of heat into the higher regions, and its redundant state 
there, generates and sustains the return currents of the 
element from above towards the lower clouds and the 
earth, which elemental movements constitute the electrical 
currents, such as are shown by electrometers. The 
diurnal variations of these currents arise from the differing 
rates of evaporation in the day and night. The ordinary 
course of these elemental fluxions apply to the common in- 
visible currents, but, in like manner, when the mutations 
are excessive, they will account for the more rapid and 
violent electrical phenomena, constituting the thunder 
storms and lightnings, which so often occur within the 
tropics, and sometimes in our latitudes when evaporation is 
very rapid.* In fine, all of the corruscations, or vivid 
transits of the said element to restore its disturbed equi- 
librium are to be taken as constituting what we call the 
electrical and magnetic currents — as before said. Since we 
find that mechanical forces are exerted, as in telegraphy, 
&c., both by the electrical and magnetic currents, their 
materiality is clearly proved, for such action can only be by 
contact of natural bodies; and by conjoint action they are 
shown to be merely two conditions of one and the same 
element, just as the mingled and alternate action of light 
and heat show them to be but two forms of one element. 
The amounts of latent heat in different bodies may be here 
passed by, but one other case of latent heat in aqueous 
# “The phenomena of aqueous meteors, such as rain, fog, and dew 
depend upon the known relations of heat and water ; electricity appears to 
be a consequent, rather than an agent, in the formation and decomposition 
of clouds, or if a necessary agent, it is equally so in the boiling of water in 
our houses or the drying of piece goods in a stove.” — Dalton : Memoirs 
Literary and Philosophical Society , vol. 2nd series, page 123. 
