On the other hand diamonds, though much valued, are used for few purposes; they make beautiful ornaments and they serve to cut glass or to bore rocks. Their high value chiefly arises from the fact that they are scarce. Of course scarcity alone will not create value. There are many scarce metals, or minerals, of which only a few little bits have ever yet been seen; but such substances are not valuable, unless some special use has been found for them. The metal iridium is sold at a very high price because it is wanted for making the tips of gold pens, and can be got only in small quantities. #8. Wealth is useful.# In the third place, we can easily see that everything which forms a part of wealth must be #useful#, or have #utility#, that is, it must serve some purpose, or be agreeable and desirable in some way or other. Senior said correctly that #useful things are those which directly or indirectly produce pleasure or prevent pain#. A well tuned and well played musical instrument produces pleasure; a dose of medicine prevents pain to one who is in need of it But it is often impossible to decide whether things give more pleasure or prevent more pain; dinner saves us from the pain of hunger and gives us the pleasure of eating good things. There is utility so far as pleasure is increased and pain decreased; nor does it matter, as far as political economy is concerned, what is the nature of the pleasure. Then, again, we need not be particular as to whether things #directly produce pleasure#, like the clothes we wear, or whether they #indirectly# do so, as in the cases of the machines employed to make the clothes. Things are indirectly useful when, like tools, machines, materials, &c., they are only wanted to make other things, which shall be actually consumed and enjoyed by some person. The carriage in which a person takes a pleasant drive is directly useful; the baker's cart which brings him food is indirectly useful. But sometimes we can hardly distinguish. Shall we say that the meat put into the mouth is directly, but the fork which puts it in is indirectly, useful? #9. Commodity.# We now know exactly what is wealth; but instead of speaking continually of wealth, it will often be convenient to speak of commodities, or goods. #A commodity is any portion of wealth#--anything, therefore, which is useful, and transferable, and limited in supply. Wool, cotton, iron, tea, books, boots, pianos, &c., are all commodities in certain circumstances, but not in all circumstances. Wool on a stray sheep lost in the mountains is not a commodity, nor iron in a mine which cannot be worked. #A commodity, in short, is anything which is really useful and wanted, so that people will buy or sell it.# But, instead of the long word commodity, I shall often use the shorter word goods, and the reader should remember that #goods = commodities = portion of wealth#. CHAPTER II. UTILITY.