232 WRITINGS OF JOSEPH HENRY. [1855- 



mained for several years undisturbed in this condition with- 

 out the least perceptible diminution in the amount of the 

 liquid. In another experiment a pane of glass was removed 

 from an external window of a room and the place of the 

 glass supplied by a board, through the middle of which a 

 hole of about an inch in diameter was made, and in this 

 opening a tube was placed horizontally, one end being in 

 the room and the other in the outer air. To each end of 

 this tube a glass bulb was attached, air tight, the one within 

 the room containing about an ounce of water, while the tube 

 and the bulb on the outside were occupied with air. The 

 temperature of the air within the room was on an average 

 about 70°, while that of the air without was on an average 

 nearly 32°, and although the experiment was continued for 

 several months during winter not one drop of water was 

 distilled over into the outer bulb. When however the latter 

 was surrounded by a freezing mixture a small quantity of 

 vapor did pass over and was condensed into water ; and also 

 when the vapor in the outer bulb was absorbed by introduc- 

 ing a quantity of strong sulphuric acid into this bulb the 

 water in the other bulb gradually diminished in weight. 



From these experiments it would appear that there is more 

 than a mechanical obstruction to the transfusion of vapor 

 through air, and that if the difference of tension of vapor in 

 two vessels only amounts to a certain quantity no transfusion 

 from one will take place to the other, or in other words for 

 each inch or foot of thickness of a stratum of air a certain 

 amount of unbalanced repulsive energy is required for trans- 

 fusion. The rapid mingling of vapor with air is due in a 

 considerable degree to the currents produced by the mixture 

 itself and by variations of temperature. 



From an application of the principle relative to the co- 

 existence of vapor and air, above given, we are able by means 

 of tables A and B to immediately ascertain by inspection 

 the amount of vapor which exists at any time and in any 

 place in a foot of air perfectly saturated with moisture and its 

 tension; that is, which contains as much vapor as it can 

 hold at the given temperature. If for example the tem- 



