324 T^HE EXPLORATION OF THE FREE AIR. 



change of relative humidity with altitude, as during cold waves, or 

 with no change of temperature vertically, both the absolute and rela- 

 tive humidity may decrease rapidly with increase of altitude, as is the 

 case in areas of high barometric pressure. At the height of half a 

 mile the diurnal changes of relative humidity are the inverse of those 

 at the ground. In brief, then, during fair weather in the upper air the 

 days are relatively cold and damp, while the nights are warm and dry, 

 as compared with surface conditions. Electricity is usually noticed on 

 the kite wire whenever the altitude of the kites exceed 1,700 feet. At 

 higher altitudes during snowstorms and near thunderstorms the poten- 

 tial increases and is sufficient to cause strong sparking discharges. 

 It therefore appears to be only necessary to tap the great atmospheric 

 reservoir to obtain an inexhaustible supply of electricity, which 

 perhaps may be applied to the service of man. 



