320 



Mr. Hinds on Climate in connexion 



to suffer evaporation from the surface as in ordinary circum- 

 stances. A register was kept of the quantity ^Yhich made its 

 way through the soil into the bottles ; and a rain-gauge of 

 equal surface was placed close by for the sake of comparison." 

 The results obtained by this instrument are given in the fol- 

 lowing table. 



The figures express the quantities in inches and hundredths; 

 in the first three columns the amount of the water found in 

 the bottles attached to the cylinder is expressed ; deducting 

 this from the rain found in the gauge, the remainder becomes 

 the quantity evaporated. The next three columns contain 

 means which are interesting sources of comparison ; for the 

 same reason the last column is also valuable, as enabling us 

 to compare a surface of water unprotected by covering with 

 the condition of the water in the experiment. 



Raised from the earth by evaporation, the aqueous vapour 

 mixes with the atmosphere and becomes henceforth a consti- 

 tuent portion ; its existence here is entirely dependent on the 

 presence of a certain temperature, and the higher this is, the 

 greater will be the quantity of moisture found suspended : 

 hence occurs, irom the equator to the poles, a progressive de- 

 crease of the aqueous vapour. The circumstance observed 

 here on a large scale also happens with the progression of 

 the seasons : as the temperature fluctuates the atmosphere 

 holds in solution a greater or less quantity of vapour ; changes 

 occurring rapidly in short periods of time are not what affect 

 it so much as the general mean of the season, of the month. 



