Now two other kinds of things are bought and sold besides physical and tangible things, namely, personal services and commercial credits; and it is very plain, that Value cannot be a quality of any one personal service rendered, as looked at by itself, such as the service of a physician towards a fever patient, because the service in and of itself might be the same whether rendered to his own child or the child of one of his patrons, while in the former case there would be no value, and in the latter there would be; and so too the very name "commercial credit" implies an exchange of two Renderings, out of which Value always emerges, and not at all an attribute of one credit considered by itself. Value is no more a characteristic of single intangible services and claims than it is of single intangible commodities rendered. And what makes all this still more certain is, that Value even in physical things, and perhaps still more in services and claims, is all the while changing under demand and supply, now rising and then falling, while the physical properties of things, that make them what they are, are fixed and unchangeable. A gold eagle, for example, has certain primary qualities as gold, without which it would not be gold; it is hard and heavy and colored: gold is gold the world over and in all ages: Value is not one of these primary qualities, nor even a secondary quality, nor any quality at all, of gold as such; because circumstances are readily conceived and have often occurred, in which gold has no Value even in exchange; for instance, among a crew abandoned at sea, a bag of gold belonging to one of the sailors might not buy even a biscuit belonging to another; all the natural qualities of the gold are present,--it is still yellow and weighty and solid,--but its Value has escaped altogether. Gold is always 19 times heavier than water: specific gravity is a _quality_ and is constant in all physical things: Value is not a quality in this sense at all, inasmuch as it is something that is constantly changing, rising or falling, and not infrequently disappearing altogether, leaving no sign.