46 



III. — On the Formation of Dew. By Thomas Hopkins, 



Esq. 



Read February 22, 1848. 



The nature of Dew and the mode of its formation have 

 long engaged the attention of enquirers, and many specu- 

 lations and opinions have been advanced respecting it. It 

 is common to speak of the rising of the dew — some parties 

 maintaining that it rises from the earth. Others have con- 

 tended that it falls from the sky ; and this latter view is 

 countenanced by the common way of speaking of falling 

 dew, A paragrapli lately appeared in the public newspapers, 

 stating that " a French savant has recently pubhshed two 

 letters to prove that dew does not arise from the earth, or 

 fall from the sky, but is formed by the elastic and invisible 

 vapour diffused throughout space, which surrounds bodies." 



The labours of Dr. Dalton, Wells, and others, have 

 thrown much light on the nature of dew; but the attention 

 recently bestowed on meteorology, and the large mass of 

 facts accumulated relating to it, may possibly enable us to 

 obtain a more full view of the phenomena attending the 

 formation of dew than had been previously presented. 



Those who were of opinion that dew rose from the earth, 

 did not maintain that it came thence in the form of globules 

 of water, as it is seen by us, but that the aeriform material 

 of which it is constituted was supplied directly from the 

 earth. And those who asserted that the dew fell, assumed that 

 it was formed from vapour at some height in the atmosphere, 

 whence it descended to the surface of the earth. Thus the 

 idea, that dew is formed from "the elastic and invisible 



