300 NATURAL HISTORY 
LETTER LI. 
Oct. 10, 1781. 
Dear Sir,-—I ruinx I have observed before that 
much the most considerable part of the house-mar- 
tins withdraw from hence about the first week in 
October ; but that some, the latter broods, I am 
now convinced, linger on till towards the middle of 
that mouth; and that at times, once perhaps in two 
or three years, a flight, for one day only, has 
shown itself in the first week in November. 
Having taken notice, in October, 1780, that the 
last flight was numerous, amounting perhaps to one 
hundred and fifty, and that the season was soft and 
still, I was resolved to pay uncommon attention to 
these late birds, to find, if possible, where they 
roosted, and to determine the precise time of their 
retreat. ‘The mode of life of these latter hirundines 
is very favourable to such a design, for they spend 
the whole day in the sheltered district between me 
and the Hanger, sailing about in a placid, easy 
manner, and feasting on those insects which love 
to haunt a spot so secure from ruffling winds. 
As my principal object was to discover the place 
of their roosting, I took care to wait on them be. 
fore they retired to rest, and was much pleased to 
find that, for several evenings together, just at a 
quarter past five in the afternoon, they all scudded 
away in great haste towards the southeast, and 
darted down among the low shrubs above the cot- 
tages at the end of the hill. ‘This spot in many re- 
spects seems to be well calculated for their winter 
residence, for in many parts it is as steep as the 
