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THEORY OF THE DEW. 
"1. Dew is commonly more plentiful in spring and autumn than in summer; 
the reason is, that a greater difference is generally found between the temperatures 
of the day and the night in the former seasons of the year than in the latter. In 
spring this circumstance is often prevented from having a considerable effect by the 
opposite influence of northerly and easterly winds ; but during still and serene 
nights in autumn, Dew is always highly abundant." 
Before we proceed in quotation, and while admitting the abstract truth of the 
above facts, we put the question, why should these things be so ? Why should the 
east and north winds, colder as they usually are than those winds which blow 
between south and west, prevent the deposition of dew ? Doctor Wells deals with 
facts, and refers his phenomena to radiation. He appears to have lost sight of, 
or rather, never to have entertained the slightest notion of electricity — its attractive 
and repulsive agency. The reader is requested to bear this in mind. Causes there 
are, and must be ; and to the study of those we shall hereafter solicit the reader's 
attention. 
"2. Dew is always very copious on those clear and calm nights which are 
followed by misty or foggy mornings : the turbidness of the air in the morning 
shows that it must have contained, during the preceding night, a considerable 
quantity of moisture. 
" 3. I have observed Dew to be unusually plentiful on a clear morning which 
had succeeded a cloudy night. For the air having in the course of the night lost 
little or no moisture, was in the morning more charged with watery vapour than it 
would have been if the night had also been clear. 
"4. Heat of the atmosphere, if other circumstances are favourable, occasions 
a great formation of dew. I always found, when the clearness and stillness of the 
atmosphere were the same, that more Dew was formed between midnight and sunrise 
than between sunset and midnight, though the positive quantity of moisture in the 
air must have been less in the former than in the latter time, in consequence of a 
previous precipitation of part of it. The reason, no doubt, is the cold of the atmos- 
phere being greater in the latter than in the early part of the night. 
" 5. Dew forms in very different quantities on different substances under the same 
circumstances : thus, on metals it is sparingly deposited ; on glass, it forms abund- 
antly, as it does also on straw, grass, cloth, paper, and other similar substances. 
Now, as the metals radiate heat imperfectly, and the other bodies mentioned in a 
much greater degree, they become consequently colder than the metals, and hence 
condense more vapour into Dew." Here, again, a remark is called for. Metals 
reflect and conduct more freely than they radiate, and also far more so than do the 
other substances. The system of points, in which the latter abound, must not be 
overlooked. Vegetable points are among the primest of conductors, and become 
more freely dewed, as also does rough fresh-dug ground. All rough and pointed 
surfaces are covered with dew, when a well-rolled walk and a hard-bound soil 
remain comparatively free from a trace of it. 
