82 PHENOMENA OF DEW. 



the leaves of the forest become moist with a fluid of 

 the most translucid nature. Well might the ancients 

 imagine that the dews were actually shed from the stars ; 

 and the alchemists and physicians of the middle ages 

 conceive that this pure distillation of the night possessed 

 subtile and penetrating powers beyond most other 

 things ; and the ladies of those olden times endeavour 

 to preserve their charms in the perfection of their youth- 

 ful beauty through the influences of washes procured 

 from so pure a source.* 



Science has removed the veil of mystery with which 

 superstition had invested the formation of dew ; and, in 

 showing to us that it is a condensation of vapour upon 

 bodies according to a fixed law of radiation, it has also 

 developed so many remarkable facts connected with the 

 characters of material creations, that a much higher 

 order of poetry is opened to the mind than that which., 

 though beautiful, sprang merely from the imagination. 



Upon the radiation of heat depends the formation of 

 dew, and bodies must become colder than the atmos- 

 phere before it will be deposited upon them. At what- 

 ever temperature the air may be, it is charged to 

 saturation with watery vapour, the quantity varying 

 uniformly with the temperature. Supposing the tem- 

 perature of the air to be 70 F., and that a bottle of 

 water at 60 is placed in it, the air around the bottle 



* Ammiamis Marcellinus ascribes the longevity and robust 

 health of mountaineers to their exposure to the dews of night. 

 Dew was employed by the alchemists in their experiments on the 

 solution of gold. The ladies of old collected the " celestial wash, 3/ 

 which they imagined had the virtue of preserving their fine forms, 

 by exposing heaps of wool to the influences of night radiation. It 

 was supposed that the lean features of the grasshopper arose from 

 that insect feeding entirely on dew : " Dumque thyuio pascentur 

 apes, dum rore cicadse," Virgil, Eclog. 



See some curious remarks by Boyle, On the Power of Dew in 

 Working OH Solid Bodies : Works of the Honourable R. Boyle, 

 vol. v. p. 121. 1744. 



