bringing any burden upon the general revenue of the society.

A highway, a bridge, a navigable canal, for example, may in most cases be both made and maintained by a small toll upon the carriages which make use of them: a harbour, by a moderate port-duty upon the tonnage of the shipping which load or unload in it. The coinage, another institution for facilitating commerce, in many countries, not only defrays its own expense, but affords a small revenue or seignorage to the sovereign. The post-office, another institution for the same purpose, over and above defraying its own expense, affords in almost all countries a very considerable revenue to the sovereign.

When the carriages which pass over a highway or a bridge, and the lighters which sail upon a navigable canal, pay toll in proportion