LETTER LI.

DEAR SIR,

Oct. 10, 1781.

I THINK I have observed before, that much the most considerable part of the house-martins 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 month: 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 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 secure from

the annoyances of water; and it is moreover clothed with beechen shrubs, which being stunted and bitten by sheep, make the thickest covert imaginable, and are so entangled as to be impervious to the smallest spaniel; besides, it is the nature of underwood beech never to cast its leaf all the winter, so that, with the leaves on the ground and those on the twigs, no shelter can be more complete. I watched them on the 13th and 14th of October, and found that their evening retreat was exact and uniform; but after this they made no regular appearance. Now and then a straggler was seen; and on the 22d of October, I observed two, in the morning, over the village, and with them my remarks for the season ended.

From all these circumstances put together, it is more than probable that this lingering flight, at so late a season of the year, never departed from the island. Had they indulged me that autumn with a November visit, as I much desired, I presume that, with proper assistants, I should have settled the matter past all doubt; but though the 3d of November was a sweet day, and in appearance exactly suited to my wishes, yet not a martin was to be seen, and so I was forced, reluctantly, to give up the pursuit.

I have only to add, that were the bushes, which cover some acres, and are not my own property, to be grubbed and carefully examined, probably those late broods, and perhaps the whole aggregate body of the house martins of this district, might be found there in different secret dormitories; and that, so far from withdrawing into warmer climes, it would appear that they never depart three hundred yards from the village.

LETTER LII.

THEY who write on natural history cannot too frequently advert to instinct, that wonderful limited faculty which, in some instances, raises the brute creation, as it were, above reason, and in others. leaves them so far below it. Philosophers have defined instinct to be that secret influence by which every species is impelled naturally to pursue, at all times, the same way, or track, without any teaching or example; whereas reason, without instruction, would often vary, and do that by many methods which instinct effects by one alone. Now this maxim must be taken in a qualified sense, for there are instances in which instinct does vary and conform to the circumstances of place and convenience.

It has been remarked, that every species of bird has a mode of nidification peculiar to itself, so that a schoolboy would at once pronounce on the sort of nest before him. This is the case among fields, and woods, and wilds; but, in the villages round London, where mosses and gossamer and cotton from vegetables are hardly to be found, the nest of the chaffinch has not that elegant finished appearance, nor is it so beautifully studded with lichens, as in a more rural district; and the wren is obliged to construct its house with straws and dry grasses, which do not give it that rotundity and compactness so remarkable in the edifices of that little architect. Again, the regular nest of the house-martin is hemispheric; but where a rafter, or a joist, or a cornice, may happen to

stand in the way, the nest is so contrived as to conform to the obstruction, and becomes flat, or oval, or compressed.

In the following instances, instinct is perfectly uniform and consistent. There are three creatures, the SQUIRREL, the field mouse, and the bird called the nut-hatch (sitta Europaea), which live much on hazel

nuts, and yet they open them each in a different way. The first, after rasping off the small end, splits the shell into two with his long fore teeth, as a man does with his knife; the second nibbles a hole with his teeth, so regular as if drilled with a wimble, and yet so small that one would wonder how the kernel can be extracted through it; while the last picks an irregular ragged hole with its bill; but as this artist

has no paws to hold the nut firm while he pierces it, like an adroit workman, he fixes it as it were in a vice, in some cleft of a tree, or in some crevice, when, standing over it, he perforates the stubborn shell. We have often placed nuts in the chink of a gate-post, where nut-hatches have been known to haunt, and have always found that those birds have readily penetrated them. While at work, they make a rapping noise, that may be heard at a considerable distance.

You that understand both the theory and practical part of music, may best inform us why harmony or melody should so strangely affect some men, as it were by recollection, for days after a concert is over. What I mean, the following passage will most readily explain :

"Præhabebat porrò vocibus humanis, instrumentisque harmonicis, musicam illam avium: non quod aliâ quoque non delectaretur; sed quod ex musicâ humanâ relinqueretur in animo continens quædam, attentionemque et somnum conturbans agitatio: dum ascensus, exscensus, tenores, ac mutationes illæ sonorum et consonantiarum, euntque, redeuntque per phantasiam :-cum nihil tale relinqui possit ex modulationibus avium, quæ, quod non sunt perinde a nobis imitabiles, non possunt perinde internam facultatem commovere.”—GASSENDUS, in Vitá Peireskii1

1 But to vocal and instrumental music he preferred that of birds; not from being incapable of finding delight in the other also, but because human music leaves in the mind a continual agitation, which disturbs both attention and sleep, owing to those risings, fallings, tenors, and variations of sounds and harmony, passing and repassing continually through the imagination; whereas no such effect can be left from the modulations of birds, because these modulations, not