CORRESPONDENCE WITH HIS FAMILY. 115 



himself to such a murmur, but takes his cue from some hasty 

 and inaccurate correspondent. 



I beg you would take two pieces of sponge of equal size, 

 weight, and softness, and hang them by strings over an upland 

 pond, in foggy w r eather, the one as near the surface as possible 

 the other several feet above the \vater; then I desire you would 

 squeeze the spunges in a morning and see 'which produces the 

 most water. Then if the lower spunge should prove from 

 repeated trials to be the moistest, I should hope the fact would 

 in some measure corroborate my suspicions that ponds and 

 pools do by condensation from the coolness of their surfaces, 

 assimilate to themselves fogs and vapours by contact, and that 

 is one reason why many very little upland ponds, tho' subject 

 to a continual waste by cattle &c., yet never fail in the 

 severest droughts, while larger ponds in bottoms frequently 

 become dry. But as your father and you may probably hit 

 upon a better experiment, I desire you would try such as you 

 think most to the purpose *. 



Moreover I desire that both of you would send me every 

 hint in Nat. Hist, that occurs to your minds after your recent 

 visit to these parts. My swallow monographies are printed 

 off by the R. S. in vol. 69, p. 258 : but the corrector of the 

 press has made sad w r ork with my unfortunate letters ; for in 

 one place he makes me say that "swallows eat grass," and in 

 another uses caves instead of eaves ; moreover he has trans- 

 posed my letters so as to misplace them, though I numbered 

 them most exactly, and by that means has made a jumble of 

 dates, besides putting two whens in one sentence and many 

 more inaccuracies too numerous to mention ! fie ! for so 

 young a man to use glasses that magnify 2<K) times, when 

 Linmeus planned and perfected his whole sexual system 



I wish you joy that Jupiter is restored to his liberty and 



* [This subject is discussed in a very interesting manner in the XXIXth 

 letter to Baines Barringtou, Vol. I. pp. 192 to 195. It is probable that 

 the experiments suggested above were carried out, as the more elaborate 

 observations addressed to Barrington are dated three months later than 

 this letter to his nephew, T. B.] 



12 



