208 Mr. J. Aitken on Dew. 



with equal clearness gives under eight heads what he calls 

 Mr. Aitken's theory of dew. If he had entitled these last as 

 eight points contended for in my contribution to the theory of 

 dew, no fault could be found with this part of his paper, as 

 he states the points with clearness and precision. But unfor- 

 tunately he still looks on these eight points as rivals to the 

 previous six of Dr. Wells, and so continues hostile to them. 

 " 8uch," he says, "is the new theory of dew, which, if ac- 

 cepted, must go far to render nugatory the results obtained 

 by some of the most celebrated observers." After reading 

 Mr. Tomlinson's paper, however, I do not find that he adduces 

 any results of previous observers that are in any way ren- 

 dered nugatory by the results set forth in my paper. It has 

 already been stated that the " new theory " is not in opposition 

 nor are the results contrary to the teaching of Dr. Wells ; 

 nor are they, so far as I know, contrary to those of any of the 

 " celebrated observers." 



In continuation, my critic then, in place of sustaining his 

 accusation by giving examples in which my teaching is at 

 variance with recognized authorities, gives an example in 

 which my observations agree with recognized authority. At 

 the foot of p. 486 he objects to the statement in my paper 

 that " the ground at a short distance below the surface is 

 always hotter than the air over it," because it is not a new 

 observation, Pictetin 1779 having previously observed the fact. 

 I am, however, puzzled to understand what bearing this has on 

 the subject, or what conclusion he wishes to be deduced from 

 this statement. To compare small things with great : more 

 than one person had seen an apple fall to the ground before 

 Newton made such good use of the observation. Pictet, when 

 he made this observation, was working at another subject, and 

 did not draw any conclusion which would be rendered nuga- 

 tory by the acceptance of my conclusions. 



Mr. Tomlinson proceeds to say, " that dew rose out of the 

 ground is a very old notion." I was well aware that the idea 

 was an old one, and it is distinctly stated in my paper. It is 

 difficult to understand what impression my critic wishes to 

 convey by this remark. If it is that the idea does not possess 

 the merit of novelty, having been already expressed, my reply 

 is that it has been already said that dew was caused by the 

 moon-beams, that it descended from the stars, &c. ; and each 

 and all of these ideas were supported by about the same 

 amount of evidence, namely the ipse dixit of the theorist. 



The same answer applies to the footnote, p. 486, regarding 

 the exudation of moisture by plants. Though " Muschen- 

 broeck regarded dew as a real perspiration of plants," yet 



