194 NATURAL HISTORY 
late as November the 3d and 6th, after they were 
supposed to have gone for more than a fortnight. 
They therefore withdraw from us the latest of any 
species. Unless these birds are very short-lived 
indeed, or unless they do not return to the district 
where they are bred, they must undergo vast de- 
vastations somehow and somewhere; for the birds 
that return yearly bear no manner of proportion 
to the birds that retire. 
House-martins are distinguished from their con- 
geners by having their legs covered with soft downy 
feathers down to their toes. ‘They are no song- 
sters, but twitter in a pretty, inward, soft manner in 
their nests. During the time of hatching they are 
often greatly molested with fleas. 
LETTER XVII. 
Ringmer, near Lewes, Dec. 9, 1773. 
Dear Sir,—I ReEcEIvVED your last favour just as 
I was setting out for this place, and am pleased to 
find that my monography met with your approba. 
tion. My remarks are the result of many years’ 
observation, and are, I trust, true in the whole, 
though I do not pretend to say that they are per- 
fectly void of mistake, or that a more nice observer 
might not make many additions, since subjects of 
this kind are inexhaustible. ie; 
If you think my letter worthy the notice of your 
respectable society, you are at liberty to la 
fore them; and they will consider it, I ho 
ie 
was intended, as an humble attempt to pron 
