4

31 O OF THE EXTERNAL SENSES.

fnggeft, not only fome conception, but the moftdiflinfl conviction of its own external and inde- 'pendent exiftence.

It may be otherwife, perhaps, when thofe fen-fations are either of them excited by the tempera-ture of the external air. In a calm day whenthere is no wind, we fcarcely perceive the ex-ternal air as a folid body; and the fenfations ofHeat and Cold, it may be thought, are then feltmerely as affeftions of our own body, withoutany reference to any thing external. Several ca-fes , however, may be conceived, in which it nraftbe allowed, I imagine, that thofe fenfations, evenwhen excited in this manner, mult fuggeft fomevague notion of fome external thing or fubftance•which excites them. A new-born animal, whichhad the power of felf-motion, and which felt itsbody, either agreeably or difagreeably, more heat-ed or mote cooled on the one fide than on theother, would, I imagine, inftinctively, and ante-cedently to all obfervation and experience, endea-vour to move towards the fide in which it feltthe agreeable, and to withdraw from that in•which it felt the difagreeable fenfation. But thevery defife of motion fuppofes fome notion orpreconception of externality; and the defire tomove towards the fide of the agreeable, or fromthat of the difagreeable fenfation, fuppofes atleaf! fome vague notion of fome external thingor place which is the caufe of thofe respectivefenfations.