Essay on the Indian Summer. 143 



perincumbenl columns of air are soon saturated with vapor, the pro- 

 duction of which is accompanied by a great accumulation of elec- 

 tricity in the higher regions of the air; at length an intermixture of 

 the strata begins to take place, produced chiefly, it would appear, by 

 electrical explosions ; the precipitation of the condensed vapor 

 commences, and proceeds (especially during the day) with scarce- 

 ly any intermission. The rain now descends in vast sheets; the 

 rivers, raised above their ordinary level, can no longer be confined 

 within their banks ; and the supply they receive from the clouds ex- 

 ceeding the discharge by their channels, they spread far and wide 

 over the adjacent fields, and exhibit on every hand a dreary expanse 

 of muddy and discolored waters. This state of things undergoes 

 litde alteration until the sun returns to the signs of the other hemis- 

 phere ; at that period the aerial currents from the homonymous pole 

 are renewed, and the air which flows from it being very far from the 

 point of saturation, the rains cease, and the sky resumes its former 

 clearness and serenity." 



From this detail of facts, it appears to us highly probable that elec- 

 trical causes are negatively concerned in the production of the Indian 

 summer; for instance, as during the warmer months, they act vigor- 

 ously by producing an intermixture of the different currents or strata 

 of air ; so, on the contrary, at the approach of winter, they act with 

 diminished energy, and hence suffer portions of air, differing greatly 

 in their temperature and humidity, to remain for a length of time 

 without flowing into each other. We might mention evaporation as 

 one of the causes concerned in the production of haze or clouds, but 

 as it is dependant on, and influenced by, existing temperatures, we 

 shall, in summing up our arguments, shew how far the mean hygro- 

 metric condition of the air is affected by the annual change of tempe- 

 rature, as also by particular winds, and by the local conformation and 

 geographical position of the adjacent country. Having now noticed 

 the more prominent causes concerned in the production of the phe- 

 nomena of the Indian summer, we proceed to explain, as far as pos- 

 sible, their mode and extent of operation. 



The first important conclusion that we draw from the above de- 

 tails is, that the formation of haze or clouds, viewing the subject in 

 its most general outline, must depend essentially on a reduction of 

 atmospherical temperature, which brings the water contained in the 

 air to a visible sub-vaporous state, constituting haze, or to an actual 

 liquid condition, (minutely divided,) forming clouds. We believe 



