The general principles are that no franchise can be given but for a limited time, that it must be bought at public auction, that the earnings beyond a certain percentage on investment must revert to the city, and that there must be a referendum to popular vote in the locality interested.

Appended to his "Opera Omnia," published in 1707, there is a very needful "Clavis ad obscuriorum sensum referendum," in which the following passage occurs.