OF SELBORNE. 195 



prevalent in bottoms ? or rather have not those elevated pools 

 some unnoticed recruits, which in the night time counter- 

 balance the waste of the day ; without which the cattle alone 

 must soon exhaust them ? And here it will be necessary to 

 enter more minutely into the cause. Dr. Hales, in his Vege- 

 table Statics, advances, from experiment, that " the moister 

 " the earth is the more dew falls on it in a night : and more 

 " than a double quantity of dew falls on a surface of water 

 " than there does on an equal surface of moist earth." Hence 

 we see that water, by it's coolness, is enabled to assimilate to 

 itself a large quantity of moisture nightly by condensation ; 

 and that the air, when loaded with fogs and vapours, and even 

 with copious dews, can alone advance a considerable and 

 never-failing resource. Persons that are much abroad, and 

 travel early and late ; such as shepherds, fishermen, &c. can 

 tell what prodigious fogs prevail in the night on elevated 

 downs, even in the hottest parts of summer ; and how much 

 the surfaces of things are drenched by those swimming vapours, 

 though, to the senses, all the while, little moisture seems to fall. 



I am, &c. 



LETTER XXX. 



TO THE SAME. 



Selborne, April 3, 1776. 



DEAR SIR, 



MONSIEUR HERISSANT, a French anatomist, seems persuaded 

 that he has discovered the reason why cuckoos do not hatch 

 their own eggs ; the impediment, he supposes, arises from 

 the internal structure of their parts, which incapacitates them 

 for incubation. According to this gentleman, the crop or 

 craw of a cuckoo does not lie before the sternum at the 

 bottom of the neck, as in the gallium, columbce, &c. but imme- 

 diately behind it, on and over the bowels, so as to make a 

 large protuberance in the belly. 



Histoire de V Academic Royak, 1752. 



o2 



