He is paying the silversmith so to exert his muscles that an ounce or a pound of silver may be wrought into a specific form.

If he pays a toy-maker to make him a dancing-doll, he is virtually paying him to dance in his own person.

He is paying him to go through a series of prescribed muscular movements.

Similarly when he pays a large number of men to construct a productive machine instead of a doll or an ornament, he is paying for the muscular movements from which the machine results.

Here we come back to one of the main economic truths to the elucidation of which our earlier chapters were devoted.