It may, however, be asked, How does it happen that the sum of two commodities so exchanged has a greater value after the exchange than before? or in other words, Whence has the profit arisen?—is there any third party at whose expense it has been acquired? The answer is—that there is another source which almost always either directly or indirectly contributes towards this profit. The advantage is most frequently won by industry and knowledge from nature herself. § The following illustration, which happens also to be a tolerable approach to truth, will explain this principle more clearly:— It is found by experience that the upper-leather of Boots made in France, is better and more durable than the upper-leather manufactured in England. On the other hand, it is found that the leather prepared in England for the soles of boots is less permeable by water, and more durable than that made in France. Let us suppose that in each country a pair of boots will endure twelve months’ continual wear; after which time they are thrown aside. In England the destruction of the boots will arise from that of the upper-leather, whilst in France it will be caused by that of the sole. Let us also suppose that the upper-leather of France will wear three months longer than the French soles, and reciprocally that the soles of England will wear three months longer than the English upper-leather. Under these circumstances, it is clear that if the inhabitants of each country insist on making their boots _entirely_ with the produce of _their own_ tanneries, the average duration of a pair of boots both in France and in England will be twelve months. Let us assume, for the sake of simplicity, that in each country the upper-leather and the soles have the same value. Then it is equally clear, if England were to give to France a million pair of soles in exchange for a million pair of French upper-leathers, that one million of the inhabitants of each nation would find their boots last during fifteen instead of twelve months. This prolonged duration of their boots would not have been acquired by any sacrifice on either side: the exchange is here for the common and great advantage of both. This probably arises from the joint action of many causes. The animals which in each country supply the hides, may either from breed, from food, or from climate be best adapted to produce that kind of leather in which each country excels. The water, the bark, or the climate peculiar to each country, may then contribute its share to the same effect. Again, the industry, the skill, and the knowledge of the people employed, as well as the character of the population and the distribution of its capital, may also have its influence on these results. If we pursue this illustration one stage further, it will appear that it is our interest not only that we should make these exchanges with France, but that she should also make exchanges with other countries than our own.