70 



dually increased in depth until it stood at four feet all over 

 the floor. "When at this depth, with the fans making 100 

 revolutions per minute, the flow of air was quite sensible to 

 the hand placed on the surface of the coffee, and was ren- 

 dered apparent by the smoke from a match following the 

 direction of the air ; at the same time the rarefaction of the 

 air within the enclosed space was so very slight as barely to be 

 appreciable by a very delicate mountain barometer, though it 

 had the effect of causing the door to shut with a slam ; thus 

 showing that a slight rarefaction of the air is sufficient to 

 disturb the balance of atmospheric pressure, even when act- 

 ing through a medium of coffee of considerable depth. The 

 current of air thus established continued to flow without in- 

 terruption until the fans were stopped. 



A cold glass tumbler taken into the store in a warm clay, 

 when the fans were not in motion, became instantly dimmed 

 and wet by the precipitation of moisture from the internal 

 air. "When another glass was taken into the store, one 

 minute after the fans were put in motion, it [remained clear, 

 without a trace of moisture. 



A very satisfactory result soon showed itself, viz. that 

 whilst the temperature of the air as it entered the moist 

 coffee was 80 in a warm day, the temperature of the coffee 

 itself, as indicated by an immersed thermometer, was only 

 58 ; the wet coffee being invariably coldest when the air 

 that was made to pass through it was warmest. This para- 

 dox admitted of easy explanation, when it was considered 

 that each bean of undried coffee was under similar circum- 

 stances to evaporating vessels of water placed in a draught of 

 warm air for the purpose of cooling the water. The cold thus 

 produced was, therefore, the necessary concomitant of the 

 evaporation that was going on, and the difference between 

 these temperatures afforded a measure of the drying power 

 in different states of the weather. The circumstance of the 



