ISO ESSAY 



hereafter remarked, during the formation of 

 dew, must be considered as effects, and not 

 as the cause, of the conversion of the watery 

 vapour of a clear atmosphere into a fluid. 



A remaining argument applies equally to all 

 the theories, which have hitherto been made 

 public on the cause of dew. This is, that none 

 of them include the important fact, that its pro- 

 duction is attended with cold ; since no explana- 

 tion of a natural appearance can be well founded, 

 which has been built without the knowledge of 

 one of its principal circumstances. It may seem 

 strange to many, that neither Mr. Wilson, nor 

 Mr. Six, applied this fact to the improvement 

 of the theory of dew. But according to their 

 view of the subject, no such use could have been 

 made of it by them, as they held the formation 

 of that fluid to be the cause of the cold observed 

 with it. I had many years, as was formerly 

 mentioned, held the same opinion ; but I began 

 to see reason, not long after my regular course 

 of experiments commenced, to doubt its truth, 

 as I found that bodies would sometimes become 

 colder than the air, without being dewed ; and 

 that, when dew was formed, if different times 

 were compared, its quantity, and the degree 

 of cold which appeared with it, were very far 

 from being always in the same proportion to 

 each other. The frequent recurrence of such 



