of touch, are combined with its solidity, weight, or vis intertiæ; whereas
those, that are perceived by this organ, depend alone on its elasticity.
But though the vibration of the air is the immediate object of the sense of
hearing, yet the ideas, we receive by this sense, like those received from
light, are only as a language, which by acquired associations acquaints us
with those motions of tangible bodies, which depend on their elasticity;
and which we had before learned by our sense of touch.

V. _Of Smell and of Taste._

The objects of smell are dissolved in the fluid atmosphere, and those of
taste in the saliva, or other aqueous fluid, for the better diffusing them
on their respective organs, which seem to be stimulated into animal motion
perhaps by the chemical affinities of these particles, which constitute the
sapidity and odorosity of bodies with the nerves of sense, which perceive
them.

Mr. Volta has lately observed a curious circumstance relative to our sense
of taste. If a bit of clean lead and a bit of clean silver be separately
applied to the tongue and palate no taste is perceived; but by applying
them in contact in respect to the parts out of the mouth, and nearly so in
respect to the parts, which are immediately applied to the tongue and
palate, a saline or acidulous taste is perceived, as of a fluid like a
stream of electricity passing from one of them to the other. This new
application of the sense of taste deserves further investigation, as it may
acquaint us with new properties of matter.

From the experiments above mentioned of Galvani, Volta, Fowler, and others,
it appears, that a plate of zinc and a plate of silver have greater effect
than lead and silver. If one edge of a plate of silver about the size of