-1859] WRITINGS OF JOSEPH HENRY. 31 



cubic foot of air, but the fractional part of the whole amount 

 necessary to produce entire saturation ; thus if saturation is 

 represented by 100, 57 indicates that this number of parts 

 of water is contained in the air, or that it is a little more 

 than half saturated. We are obliged to adopt this method 

 of representation, because the relative moisture and dryness 

 of the air depend upon the temperature, and not on the abso- 

 lute quantity of vapor present. Thus air at 32° F., which 

 contains as much water as it can hold, or in other words is 

 saturated would by heating, become exceedingly dry, though 

 containing absolutely the same amount of water. The rela- 

 tive dryness is indicated by the complement of the numbers 

 in the table, and consequently may be found by subtracting 

 these numbers from 100. The state of our feelings is much 

 more affected by the moisture of the atmosphere than by the 

 temperature, and the sensation called " closeness " is princi- 

 pally due to the great amount of humidity, or in other words, 

 to the diminution of the dryness of the air, which prevents 

 evaporation from the surface of the body, and its attendant 

 cooling etfects. A series of observations on the relative 

 humidity in the regions west of the Mississippi, and the 

 northern portions of the middle part of our continent, 

 in connection with the different winds, would be highly in- 

 teresting in determining the source of the vapor in these 

 regions, as well as settling definitely the fact in regard to 

 their average productiveness. 



Another element intimately connected with the moisture 

 in the air, is the amount of rain and snow, particularly the 

 former. Besides the whole amount which falls during a 

 year, it is necessary to know the relative quantity which 

 falls in different months. A large amount of rain may fall 

 at once, and a greater relative proportion of it will be carried 

 off, before the earth can have time to be fully saturated 

 through the streams of creeks and rivers, and thus do much 

 less in the way of fertilizing the earth, than if the same 

 amount were distributed over a longer period. 



The indications of the rain, as of the other elements, would 

 be more interesting, could they be compared with the average 



