3lO OF THE EXTERNAL SENSES.

fuggeft, not only some conception, but the moftdiftinft conviftion of its own external and inde-pendent existence.

It may be otherwise, perhaps, when those sen-sations are either of them excited by the tempera-ture of the external air. In a calm day whenthere is no wind, we scarcely perceive the ex-ternal air as a solid body; and the sensations 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 rauftbe allowed, I imagine, that those sensations, evenwhen excited in this manner, mull fuggeft somevague notion of some external thing or substancewhich excites them. A new-born animal, whichhad the power of self-motion, and which felt itsbody, either agreeably or disagreeably, more heat-ed or more cooled on the one fide than on theother, would, I imagine, infthuftively, and ante-cedently to all observation and experience, endea-vour to move towards the fide in which it feltthe agreeable, and to withdraw from that inwhich it felt the disagreeable sensation. But thevery defire of motion supposes some notion orpreconception of externality; and the defire tomove towards the fide of the agreeable, or fromthat of the disagreeable sensation, supposes atleaft some vague notion of some external thingor place which is the cause of those respectivesensations.