236 
THE NATURAL HISTORY 
[LETT. 
LETTER C. 
TO THE HONOURABLE DAINES BARRINGTON. 
They who write on natural Iiistory cannot too frequently advert 
to instinct, that wonderful, but 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 naturalJy to pursue, at all times, the same way or track, 
without any teaching or example ; whereas reason, without in- 
struction, would lead them to 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. I'his 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 con- 
trived 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 Eioropma), which 
