LIGHTNING AND LIGHTNING CONDUCTORS. 3 



56. The principles of electric action enable us to under- 

 stand that the presence of a highly charged cloud will disturb 

 the previous electric condition of the vicinal air, as well as 

 that of other clouds of lower intensity. In the latter case, 

 the disturbed cloud becomes prepared for the reception of a 

 discharge from that which disturbed it: hence one cause at 

 least why flashes of lightning more frequently occur amongst 

 the clouds themselves than between them and the earth. This 

 tendency to aerial lightning is also enhanced by the abundance 

 of aqueous vapour condensing in the region of the clouds, 

 which affords a conducting medium more easily transpierced 

 than the interposing dry air which separates clouds from the 

 ground, and consequently it is but seldom that lightning 

 strikes terrestrial objects previously to the intervening aerial 

 resistance being in a great measure removed by copious 

 showers of rain. 



57. But, notwithstanding the facilities afforded by falling 

 rain, terrestrial objects require a predisposition to receive 

 lightning before it can assail them. This disposition is 

 enforced by the presence of the cloud, which disturbs the 

 normal electric state of the air beneath it, by a repellency 

 of its fluid into the ground, which will allow of its intro- 

 mission in proportion as its surface is prepared for its recep- 

 tion. Now, allowing a plot of ground, or even an extensive 

 tract of country, to be of an uniform conducting quality 

 throughout, its reception for the electric fluid from the air 

 would depend upon the character of its surface; if barren 

 of vegetation, it could not receive the electric fluid with the 

 same degree of facility as when luxuriously clothed with grass, 

 corn, trees, &c, which would present myriads of conducting 

 points and sharp edges in the best possible direction for the 

 electric ingress, and the multitude of roots ramifying into 

 the soil would facilitate its intromission and disposition below 

 the surface. 



58. But the electric force of a cloud capable of repelling 



