Page:The wealth of nations, volume 3.djvu/94

 expected that any individual or small number of individuals should erect or maintain. The performance of this duty requires two very different degrees of expense in the different periods of society.

After the public institutions and public works necessary for the defence of the society, and for the administration of justice, both of which have already been mentioned, the other works and institutions of this kind are chiefly those for facilitating the commerce of the society, and those for promoting the instruction of the people. The institutions for instruction are of two kinds; those for the education of the youth, and those for the instruction of people of all ages. The consideration of the manner in which the expense of those different sorts of public works and institutions may be most properly defrayed, will divide this third part of the present chapter into three different articles.

the erection and maintenance of the public works which facilitate the commerce of any country, such as good roads, bridges, navigable canals, harbors, etc., must require very different degrees of expense in the different periods of society, is evident without any proof. The expense of making and maintaining the public roads of any country must evidently increase with the annual produce of the land and labor of that country, or with the quantity and weight of the goods which it becomes necessary to fetch and carry upon those roads. The strength of a bridge must be suited