210 Mr. J, Aitken on Dew. 



off by the earth. This supply is quite sufficient under all 

 conditions, so far as I have observed, to maintain the soil and 

 the thermometer over it at a temperature much above that at 

 the top of the grass ; and while the thermometer at the top 

 of the grass falls quickly at night and falls a good deal, the 

 one u buried in the grass " falls comparatively little, the upper 

 one remaining much the colder throughout the night. It is 

 not till day arrives and the temperature rises that the upper 

 thermometer gets heated and rises to the temperature of the 

 lower one. 



With regard to the remarks about dew in " Persia " and 

 " the African desert," I have nothing to say, as they do not 

 bear on my paper, it being distinctly stated there that my 

 remarks apply only to this climate. I may, however, add 

 here that I wait -for further information before forming any 

 opinion as to what takes place in other and unknown con- 

 ditions. 



At page 493, Mr. Tomlinson says, " There is such a vast 

 consensus of scientific opinion in favour of the received theory 

 of dew, that any attempt to set it aside in favour of another 

 must be supported by the strongest experimental evidence." 

 Now, as I have already said, I have never made any attempt 

 to set aside Wells's theory; and as all my work has tended to 

 confirm and extend his, I hope Mr. Tomlinson will, on recon- 

 sideration, give my contribution to this subject a more favour- 

 able reception ; and might I also ask a more careful consider- 

 ation of that part referred to by him in this same paragraph, 

 where he says, " Mr. Aitken exposes a turf six inches square 

 to the air in a scale-pan" ! ! This misconception of the essen- 

 tial conditions of the experiment has given rise in his mind 

 to the objection to the conclusion I have drawn from the 

 experiment, and has also given rise to the confusion Mr. Tom- 

 linson has made in comparing my experiment with other 

 previous ones. 



If Mr. Tomlinson had delayed till he had seen the complete 

 paper, he probably would not have found the difficulty he has 

 experienced in reconciling the two sets of observations referred 

 to in the first paragraph, page 494, of his paper. The paper 

 containing the account of my experiments, on which Mr. 

 Tomlinson founds his criticism, being in abstract was made as 

 short as possible, and does not contain sufficient information 

 to make the conditions of the experiments clear to Mr. 

 Tomlinson. The edges of the trays were, as he supposes, in 

 contact with the ground; one slate and one weight were 

 also in contact with the ground. But, in referring to the 

 latter, they were simply described as they appeared without 



