ll fitted to transmit its vibrations; the
nostrils, while they afford a passage to the air in its way to the
lungs, intercept any odorous particles which it contains, and the
tongue is provided with spongy papillae to imbibe the sapid
liquors which are the objects of taste.

It is by these organs that we become acquainted with what passes
around us; by these we know that a material world exists. We may
however observe, that the nervous system, besides making us
acquainted with external things, gives us notice of many changes
that take place within our own body. Internal pain warns us of the
presence of disease; and the disagreeable sensations of hunger,
thirst, and fatigue, are signs of the body standing in need of
refreshment or repose.

Concerning the manner in which we become acquainted with external
things, by means of the senses, we know nothing. Many hypotheses
have been offered to explain this: none of them however are the
result of experiment and observation. Many philosophers have
supposed the universe to be filled with an extremely subtile
fluid, which they have termed ethereal; and this hypothesis has
been sanctioned by the illustrious authority of Newton. He however
merely offered it in the modest form of a query, for the attention
of other philosophers; little thinking that it would be made use
of to explain phenomena which they did not understand. His query
about a subtile elastic fluid pervading the universe, and giving
motion and activity to inert masses of matter, and thereby causing
the phenomena of attraction, gravitation, and many other
appearances in nature, was immediately laid hold of by his
followers, as a fact sufficiently supported, because it seemed to
have the sanction of so great an authority.

This hypothesis was made use of to explain a great number of
phenomena, and the physiologists, whose theories were generally
influenced by the prevailing philosophy, eagerly laid hold of it
to explain the phenomena of sensation, and muscular motion. When
an impression was made upon any part of the external surface of
the body, whether it was occasioned by heat, or mechanical
impulse, they supposed, that the ether in the extremities of the
nerves was set in motion. This motion, from the energy of the
ether, is communicated along the nerves to the brain, and there
produces such a change as occasions a consciousness of the
original impression, and a reference in the mind to the place
where it was m