242 WKITINGS OF JOSEPH HENRY. [1855- 



can give himself a clothing of grease. The tendency to 

 evaporation from the skin during high winds must be op- 

 posed b}' a substance which will partially close the minute 

 orifices. Warmly clad and protected from the cold of winter 

 the civilized man can enjo}'' the luxury of washing which 

 is denied to the naked savage. 



Among other efifects of evaporation connected with its re- 

 duction of temperature, should be mentioned the advantages 

 derived from draining marshy soil, that the cooling due to 

 the evaporation of the surface water, is thereby diminished. 

 It is said that the mean temperature of certain parts of 

 England has been perceptibly increased by the general 

 introduction of this system of agricultural improvement. 



The moisture of the atmosphere often affects our health 

 and comfort by its deposition on the walls and other parts 

 of our habitations. It is absorbed with great force and in 

 large quantities into the pores of almost every substance, and 

 is given out again when a change in the temperature or dry- 

 ness of the air occurs. Building-stone and brick absorb a 

 large amount, which may be transmitted by capillarity from 

 without through a wall of considerable thickness and evapo- 

 rated at the interior surface. The dampness however of a 

 stone house is not principally due to this cause, but to the 

 deposition of moisture from the air on the cold surface of 

 the wall — precisely analogous to the formation of dew on the 

 surface of a pitcher containing cold water. 



If during a period of cold weather an apartment of a stone 

 house has been closed, and on the recurrence of a warm day 

 the windows are opened to air the room, the deposition we 

 have mentioned takes place in abundance, and the result 

 intended to be guarded against is promoted rather than 

 diminished. If a fire be made in the room previous to open- 

 ing the windows, so that the sides of the apartment may be 

 made warmer than the air, the deposition will not take place. 

 The effects both of the transmission and of the deposition of 

 moisture can in a great measure be obviated by the means 

 now generally adopted of lining the interior of the room 

 with a thin coating of a non-conducting material separated 



