Transactions. 5 



loth Noceinher, IS'Jl. 



Mr James Bardour, V.-P., in the chair. 



New Members. — Miss Lennox and Miss Agnes B. Lennox, 

 Edeubank. 



Donations. — Copies of Linn«us's Genera Plantarum and 

 Philosophia Botanica, presented by Mr James Barbour, V.-P. ; 

 Catalogue of Antiquities and Cariosities in possession of Dr 

 Paterson of the Bridge of Allan, by Mr S. S. Brown, of Crieff ; 

 Part I. of the Flora of Dumfriesshire, by Mr G. F. Scott-Elliot ; 

 the Proceedings of the Berwickshire Naturalists' Club. 



Communications. 



I. — Mr Aitkens Theorij of Dew. By the Eev. WiLLIAM 



Andson, V.-P. 

 \\\ former times various ideas prevailed as to the origin 

 of dew — some maintaining that it descended from the heavens, 

 and that the moon and stars had no small influence on its 

 formation ; and others that it ascended from the earth. But it 

 was not until the year 1814, when Dr Wells, a London physician, 

 published his work upon the subject, that it received a really lucid 

 and philosophical explanation. His theory was that dew is simply 

 aqueous vapour condensed out of the air Avhen in contact with the 

 surface of bodies cooled by radiation below the dew-point of the 

 air at the place. His opinion, supported by a series of experi- 

 ments made by Dr Wells, and described in his book, has since that 

 time been generally received as the true one. AVithin the last few 

 years, however, considerable additional light has been thrown 

 upon the subject by the experiments of Mr Aitken of Darrock, an 

 acute and careful observer in meteorology, and published in a 

 paper read by him before the Royal Society of Edinburgh in 

 December, 1885. Mr Aitken does not controvert the opinion 

 expressed by Dr Wells in his essay as to the causes which operate 

 in the formation of dew. The only point in regard to which he 

 suggests a different theory relates to the source of the vapour 

 which is precipitated into dew. Dr Wells thought that most of 

 the moisture deposited as dew at night was taken up from the 

 ground by evaporation during the heat of the day. He admitted, 

 indeed, that some part of it miglit be owing to vapour rising out of 



