in which the Electricity passed from the Earth. 85 



it has frequently appeared to irie like the motion of a sky-rocket 

 rising with extraordinary rapidity, commonly inclined when 

 first rising from the earth, and becoming more horizontal when, 

 it reaches the cloud, where it often divides into two ; sometimes 

 it describes a curved line with zig-zags. The thunder seems to 

 proceed first from the quarter where the ball of fire appears to 

 have risen, and terminates in a distant roll amongst the clouds. 

 The cause of the negative state of clouds may perhaps be ex- 

 plained in the following manner : — The capacity of water for 

 electricity is increased when it assumes the state of vesicular 

 vapour, as may be shown by the experiment of throwing water 

 on hot coals. The rising vapour immediately takes the shape 

 of that kind of cloud denominated the cumulus, and is positively 

 electrified, as may be proved by the electroscope. But in the 

 slower process of natural evaporation by the sun and wind, the 

 intensity of the electricity of the rising vapour is not sufficient 

 to be shown in the same way. However, there is reason to think 

 the fact is otherwise ; and Dr Franklin*'s ingenious experiment 

 of the electrified can and chain throws considerable light on 

 the subject. In this experiment, by raising the chain from 

 the can, the connecting electrometer proves that the capaci- 

 ty of the chain for electricity is increased by its increase 

 of surface exposed to the air, as the electrometer indicates 

 a weak intensity. But on again returning the chain into 

 the can, the original intensity is manifested. So each particle 

 of rising vapour as it leaves the earth's surface, combines with 

 caloric, and partakes of the electricity of the common reservoir, 

 the earth. It remains in mixture with the air, but in a state of 

 very minute division ; for we observe, whether raised by the sun's 

 heat from moist soil, or from water artificially heated, the parti- 

 cles of vapour or steam disappear, and do not disturb the tran- 

 sparency of dry air, till they rise into a stratum of air, where 

 the cold occasions it to be again condensed into vesicular va- 

 pour or clouds. This, in an ordinary summer's day, takes place 

 at different heights in the atmosphere, according to the heat 

 and dryness. It is probably the dew point of that stratum of air 

 where the fleecy clouds begin to form in a clear sunny morning ; 

 and, as compared with the known height of mountains, these 

 clouds are first seen at from 1500 to 3000 feet. These small 

 fleecy clouds sometimes rc-evaporatc soon after they begin to 



