The changes in appearances of an object which are due to changes in the intervening medium
will not affect, or will affect only very slightly, the appearances from places close to the object.
For as there are persons who, by conscious art or mere habit, imitate and represent various objects through the medium
of colour and form, or again by the voice; so in the arts above mentioned, taken as a whole, the imitation is produced by rhythm, language, or 'harmony,' either singly or combined.
Money then being established as the necessary medium
of exchange, another species of money-getting spon took place, namely, by buying and selling, at probably first in a simple manner, afterwards with more skill and experience, where and how the greatest profits might be made.