be found to come under the same or closely analogous heads.
I need hardly premise that movements or changes in any part of the body,--
as the wagging of a dog's tail, the drawing back of a horse's ears,
the shrugging of a man's shoulders, or the dilatation of the capillary
vessels of the skin,--may all equally well serve for expression.
The three Principles are as follows.

[1] Mr. Herbert Spencer (`Essays,' Second Series, 1863, p.
138) has drawn a clear distinction between emotions and sensations,
the latter being "generated in our corporeal framework."
He classes as Feelings both emotions and-sensations.

I. _The principle of serviceable associated Habits_.--Certain complex
actions are of direct or indirect service under certain states of the mind,
in order to relieve or gratify certain sensations, desires, &c.; and whenever
the same state of mind is induced, however feebly, there is a tendency through
the force of habit and association for the same movements to be performed,
though they may not then be of the least use. Some actions ordinarily
associated through habit with certain states of the mind may be partially
repressed through the will, and in such cases the muscles which are least
under the separate control of the will are the most liable still to act,
causing movements which we recognize as expressive. In certain other cases
the checking of one habitual movement requires other slight movements;
and these are likewise expressive.

II. _The principle of Antithesis_.--Certain states of the mind lead to certain
habitual actions, which are of service, as under our first principle.
Now when a directly opposite state of mind is induced, there is a strong
and involuntary tendency to the performance of movements of a directly
opposite nature, though these are of no use; and such movements are in some