An improvement that should reduce the cost of converting leather into shoes would, by the sale of the shoes, call for more leather, more cattle, more appliances, more tanning, and larger buildings for shoe factories, furnished with more shoemaking machinery and greater motive power, even though the particular machines which were improved by the invention had become so much more efficient that no more of them were needed. This depends on the extent to which a certain reduction of cost of a product enlarges the market for it. _Principles Governing the Enlargement of the Effectual Demand for One Commodity._--In determining how much a reduction of the price of a single article will at once enlarge the market for it, there are two things to be considered, namely, the elasticity of the want itself to which the article caters, and the extent to which an article catering to a particular want may be substituted for other articles designed to satisfy the same one. The desire for jewels and other articles of personal adornment is very expansive, and a fall in the price of any one article of this kind causes a relatively large increase in the consumption of it. Since the want to which a costly ornament caters is thus elastic, the cheapening of all articles that cater to this want would enlarge the consumption of all of them. The cheapening of a particular one of these articles, if there were in the market many others of the same general kind, would cause that one to be extensively used in preference to the others. By an enlargement of the total amount of decorative articles used and by a relative favoring of a particular one of them at the cost of others, the sale of that one would be doubly increased. Cheaper diamonds might mean an increased use of them without any large reduction in the use of other gems; but if many other gems happened to be available for the purposes subserved by the diamonds the use of these others would be curtailed and that of diamonds would be disproportionately increased.