OI THE EXTERNAL SENS E S. 273

immediate caufeofthe Senfation ofTafte. Certainjuices of the exciting body are fuppofed to enterthe pores of the palate , and to excite, in the ir-ritable and fenfible fibres of that organ, certainmotions or vibrations, which produce there theSenfation ofTafte. But how thofe juices Jhouldexcite fuch motions, or how fuch motions ihouldproduce, either in the organ, or in the princi-ple of perception which feels in the organ, theSenfation of Tafte; or a Senfation, which notonly does not bear the fmalleft refemblance toany motion, but which itfelf feems incapable ofall motion, no philofopher has yet attempted,nor probably ever will attempt to explainto us.

The Senfations of Heat and Cold, of Smelland Sound, are frequently excited by bodies ata diftance, fometimes at a great diftance, fromthe organ which feels them. But it is a very an-cient and well-eftabliihed axiom in metaphyfics,that nothing can aft where it is not; and thisaxiom, it muft, I think, be acknowledged, is atleaft perfectly agreeable to our natural and ufualhabits of thinking.

The Sun, the great fource of both Heat andLight, is at an immenfe diftance from us. Hisrays, however, (traverfing, -with inconceivable ra-pidity, the immenfity of the intervening regions,)as they convey the Senfation of Light to our eyes,fo they convey that of Heat to all the fenfibleparts of our body. They even convey the powerof exciting that Senfation to all the other bodies