Climate of London and Philadelphia. 1 1 



Is not evaporation, therefore, a more accurate test 

 of the moisture or dryness of the atmosphere, than 

 the quantity of rain ? 



Though the quantity of rain and of evaporation 

 varies at different seasons, according to the wind? 

 and temperature which prevail, yet, on an average of 

 four years, it has been found that the evaporation very 

 nearly equals the rain. 



The evaporation from the surface of water is also 

 found about six times greater than from a surface of 

 earthy 



When the wind sweeps over warmer latitudes, it 

 envelops a vast portion of moisture exhaling from the 

 ocean, and retains it till it reaches the colder climate 

 of England, where it remains suspended in clouds, 

 or precipitated in rain, according to the state of the 

 atmosphere. Hence the south or south-west winds 

 are so often accompanied with rain. The surplus of 

 the rain, not raised by evaporation, tends to refresh 

 the ground, and to supply springs and rivers, and is 

 thence perpetually returning to the ocean, the grand 

 reservoir, from whence it came. " All rivers (says 

 the inspired preacher, in the true spirit of philosophy) 

 run into the sea, yet the sea is not full ; unto the 

 place froni whence the rivers came, thither they again 

 return." 



It has long been generally allowed, that water may 

 ^xist in air in three different states. 1st, In a state 



