DEW. 



THERE are few phenomena of common occurrence which 

 have proved more perplexing to philosophers than those 

 which attend the deposition of dew. Every one is familiar 

 with these phenomena, and in very early times observant 

 men had noticed them ; yet it is but quite recently that the 

 true theory of dew has been put forward and established. 

 This theory affords a striking evidence of the value of care- 

 ful and systematic observation applied even to the simplest 

 phenomena of nature. 



It was observed, in very early times, that dew is only 

 formed on clear nights, when, therefore, the stars are shining. 

 It was natural, perhaps, though hardly philosophical, to con- 

 clude that dew is directly shed down upon the earth from 

 the stars ; accordingly, we find the reference of dew to stellar 

 influences among the earliest theories propounded in ex- 

 planation of the phenomenon. 



A theory somewhat less fanciful, but still depending on 

 supposed stellar influences, was shortly put forward. It 

 was observed that dew is only formed when the atmosphere 

 is at a low temperature ; or, more correctly, when the air 

 is at a much lower temperature than has prevailed during 

 the daytime. Combining this peculiarity with the former 

 ancient philosophers reasoned in the following manner : 

 Cold generates dew, and dew appears only when the skies 

 are clear that is, when the stars are shining; hence it 

 follows that the stars generate cold, and thus lead indirectly 



