45^ ^f ^'^^ Propagation of Heat 



peared in the experiment (No. 4) with raw silk, above- 

 mentioned. 



If air and water conducted Heat in the same manner^ 

 it is more than probable that their conducting powers 

 might be impaired by the same means ; but when I 

 made the experiment with water, by filling the glass 

 globe, in the center of which the bulb of the thermom- 

 eter was suspended, with that fluid, and afterwards varied 

 the experiment by adding 16 grains of raw silk to the 

 water, I did not find that the conducting power of 

 the water was sensibly impaired by the presence of the 

 silk.* 



But we have just seen that the same silk, mixed with 

 an equal volume of air, diminished its conducting power 

 in a very remarkable degree; consequently, there is great 

 reason to conclude that water and air conduct Heat in a 

 different maimer. 



But the following experiment, I think, puts the matter 

 beyond all doubt. 



It is well known that the power which air possesses 

 of .holding water in solution is augmented by Heat, 

 and diminished by cold, and that, if hot air is saturated 

 with water, and if this air is afterwards cooled, a part of 

 its water is necessarily deposed. 



I took a cylindrical bottle of very clear transparent 

 glass, about 8 inches in diameter, and 12 inches high, 

 with a short and narrow neck, and, suspending a small 

 piece of linen rag, moderately wet, in the middle of it, 

 I plunged it into a large vessel of water, warmed to 

 about 100° of Fahrenheit's thermometer, where I suf- 



*,The experiment here mentioned was made in the year 1787 ; but the result of a 

 more careful investigation of the subject has since shown that Heat is not propagated 

 in water in the manner here supposed. (See Essay VII, Edition of 1798.) 



