298 LIGHTNING AND RAIN. 



would appear, that the under surface of dense 

 clouds in the north of England, does not exceed 

 1300 yards during winter, nor 2000 yards in 

 summer.* 



To pursue this subject through all the compli- 

 cated phenomena of meteorology, would far ex- 

 ceed the scope of the present inquiry, the prin- 

 cipal object of which is to trace the origin and 

 history of atmospheric electricity. 



The cardinal facts which connect the pheno- 

 mena of lightning with the theory of rain, may 

 be reduced to the following propositions : 



1. In the torrid zone, where evaporation and 

 rain are most copious, the amount of lightning 

 is greatest. There is also far more during sum- 

 mer than winter in the middle latitudes, and 

 scarcely any in the polar regions. 



2. In those parts of the world where there is 

 no rain, there is no lightning, as at Lima in 

 Peru ; nor is there any in Egypt, Palestine, and 

 other parts of the world during the prevalence of 

 dry weather. It therefore follows, 



3. That where there is no condensation of 

 aqueous vapour, there is no lightning. 



The most superficial observers of nature have 

 been impressed with the immediate connexion 

 between lightning, intense heat, and rapid preci- 

 pitations of rain. By a careful analysis of the 

 phenomena it becomes self-evident, that if caloric 



* Dalton's Meteorological Essays, p. 136. 



