2B< THE NATURAL HISTORY [LETT. 



way they become whimsical and unnatural, and liable to the 

 objection due to him "who loves to vary every single thing 

 prodigiously " 



" Qui variare cupit rem prodigialitfer unam." 



(HoR. Ars. Poet. 29.) 



LETTER XCIX. 



TO THE HONOURABLE DAINES BARRINGTON. 



I THINK I have observed before, that much the most consider- 

 able part of the house-martins withdraw from hence about the 

 first weekin October ; but that some, the latter broods I am 

 now convinced, linger on till towards the middle of that month : 

 and that at times, once perhaps in two or three years, a flight, 

 for one day only, has sho.wn 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 uncom- 

 mon attention to those 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 before 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 

 south-east, and darted down among the low shrubs above the 

 cottages at the end of the hill. This spot in many respects 

 seems to be well calculated for their winter residence : for in 

 many parts it is as steep as the roof of any house, and therefore 



