THE NEW SCIENCE OF METEOROLOGY 



served that the air is cooler where dew is forming than 

 the air a few feet higher, and they inferred that the dew 

 in forming had taken up heat, in apparent violation of 

 established physical principles. 



It remained for Wells, in his memorable paper of 

 1816, to show that these observers had simply placed 

 the cart before the horse. He made it clear that the 

 air is not cooler because the dew is formed, but that the 

 dew is formed because the air is cooler having become 

 so through radiation of heat from the solids on which 

 the dew .forms. The dew itself, in forming, gives out 

 its latent heat, and so tends to equalize the tempera- 

 ture. 



Wells' s paper is so admirable an illustration of the 

 lucid presentation of clearly conceived experiments 

 and logical conclusions that we should do it injustice 

 not to present it entire. The author's mention of the 

 observations of Six and Wilson gives added value to his 

 own presentation. 



Dr. Wells's Essay on Dew 



" I was led in the autumn of 1784, by the event of a 

 rude experiment, to think it probable that the forma- 

 tion of dew is attended with the production of cold. 

 In 1788, a paper on hoar-frost, by Mr. Patrick Wilson, 

 of Glasgow, was published in the first volume of the 

 Transactions of the Royal Society of Edinburgh, by 

 which it appeared that this opinion had been enter- 

 tained by that gentleman before it had occurred to 

 myself. In the course of the same year, Mr. Six, of 

 Canterbury, mentioned in a paper communicated to 

 the Royal Society that on clear and dewy nights he 



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