-1859] WRITINGS OF JOSEPH HENRY. 863 



If by the action of an elevated horizontal current of air 

 the upper part of a thunder-cloud be separated from the lower, 

 we shall have a mass of vapor charged entirely with negative 

 electricity, and from such a mass floating high in the atmos- 

 phere a new evaporation may take place by the heat absorbed 

 directly from the sun. (Shown at d, Fig. 19.) The column 

 of invisible vapor thus produced being a partial conductor 

 elongated upward, the attraction of the earth will draw down 

 a new portion of its natural electricity into the cloud from 

 which the vapor was produced, and thus diminish its negative 

 intensity. If now the upper end of this transparent column 

 be condensed by the cold of the greater altitude into visible 

 vapor, it will form a cloud of the second order of negative 

 intensity. We shall thus have according to Peltier lower 

 clouds intensely excited with positive electricity, clouds of 

 medium elevation either neutral or slightly negative, and 

 the highest cirrus clouds, which are formed by the secondary 

 evaporation we have mentioned, strongly excited with nega- 

 tive electricity. 



Since particles of ponderable matter similarly electrified 

 repel each other, it is evident that the electrical state of the 

 cloud must in some degree counteract the tendency to con- 

 densation which would result from the cold of the upper 

 regions ; and also the same action in the lower clouds will 

 tend to prevent precipitation in the form of rain, even 

 though the atoms of vapor are in a condition to coalesce into 

 drops of water. It is evident also since the earth is nega- 

 tively electrified, that the particles of vapor in the same 

 state will be repelled farther from the surface, and those 

 which are positively electrified will be drawn down. Hence, 

 the negative clouds will tend to retain their elevated posi- 

 tion, although they may be pressed downward by descend- 

 ing currents. 



Negative clouds may also be formed near the surface of 

 the earth by a detached portion of cloudy matter under a 

 cloud more highly charged with positive electricity, which 

 will cause the former by induction to discharge its positive 

 electricity into the earth as well as a portion of its natural 



