gradually acquired by successive
agreeable sensations, as in learning a favourite song or dance; others by
disagreeable sensations, as in coughing or nictitation; these become
associated by frequent repetition, and afterwards compose parts of greater
circles of action like those above mentioned.

Other catenations of motions are gradually acquired by frequent voluntary
repetitions; as when we deliberately learn to march, read, fence, or any
mechanic art, the motions of many of our muscles become gradually linked
together in trains, tribes, or circles of action. Thus when any one at
first begins to use the tools in turning wood or metals in a lathe, he
wills the motions of his hand or fingers, till at length these actions
become so connected with the effect, that he seems only to will the point
of the chisel. These are caused by volition, connected by association like
those above described, and afterwards become parts of our diurnal trains or
circles of action.

3. All these catenations of animal motions, are liable to proceed some time
after they are excited, unless they are disturbed or impeded by other
irritations, sensations, or volitions; and in many instances in spite of
our endeavours to stop them; and this property of animal motions is
probably the cause of their catenation. Thus when a child revolves some
minute on one foot, the spectra of the ambient objects appear to circulate
round him some time after he falls upon the ground. Thus the palpitation of
the heart continues some time after the object of fear, which occasioned
it, is removed. The blush of shame, which is an excess of sensation, and
the glow of anger, which is an excess of volition, continue some time,
though the affected person finds, that those emotions were caused by
mistaken facts, and endeavours to extinguish their appearance. See Sect.
XII. 1. 5.

4. When a circle of motions becomes connected, by frequent repetitions as
above, we can exert our attention strongly on other objects, and the
concatenated circle of motions will nevertheless proceed in due order; as
whilst you are thinking on this subject, you use variety of muscles in
walking about your parlour, or in sitting at your writing-table.

5. Innumerable catenations of motions may proceed at the same time, without
incommoding each other. Of these are the motions of the heart and arteries;
those of digestion and glandular secretion; of the ideas, or sensual
motions; those of progressi