ichaelmas.

As the summer declines the congregating flocks increase in numbers daily
by the constant accession of the second broods, till at last they swarm
in myriads upon myriads round the villages on the Thames, darkening the
face of the sky as they frequent the aits of that river, where they
roost. They retire, the bulk of them, I mean, in vast flocks together
about the beginning of October, but have appeared of late years in a
considerable flight in this neighbourhood, for one day or two, as late as
November 3rd and 6th, after they were supposed to have been gone for more
than a fortnight. They therefore withdraw with us the latest of any
species. Unless these birds are very short-lived indeed, or unless they
do not return to the districts where they are bred, they must undergo
vast devastations 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 congeners by having their legs
covered with soft downy feathers down to their toes. They are no
songsters, but twitter in a pretty inward soft manner in their nests.
During the time of breeding they are often greatly molested with fleas.

I am, etc.

LETTER XVII.

RINGMER, near LEWES, _Dec._ 9_th_, 1773.

Dear Sir,--I received your last favour just as I was setting out for this
place, and am pleased to find that my monography met with your
approbation. 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 perfectly void of mistake, or that a more nice observer might not
make many additions, since subjects of this kind are inexhaustible.

If you think my letter worthy the notice of your respectable society, you
are at liberty to lay it before them, and they will consider it, I hope,
as it was intended, as a humble attempt to promote a more minute inquiry
into natural history, into the life and conversation of animals. Perhaps,
hereafter, I may be induced to take the house-swallow under
consideration, and from that proceed to the rest of the British
hirundines.

Though I have now travelled the Sussex Downs upwards of thirty years, yet
I still investigate that chain of majestic mountains with fresh
admiration year by year, and I think I see new beauties every time I
traverse it. This range, which runs from Chichester eastward as far as
East Bourn, is about sixty miles in l