§2. To encourage and promote domestic navigation, an act was passed by the first congress conferring special privileges upon vessels built and owned by citizens of the United States. This was done by laying _duties on tunnage_. _Tunnage_ means the content of a ship, or the burden that it will carry, which is ascertained by measurement, 42 cubic feet being allowed to a tun. This act imposed a duty of fifty cents a tun on foreign vessels, and upon our own a duty of only six cents a tun. As such a law discriminates, or makes a distinction or difference between domestic and foreign vessels, these duties are also called _discriminating_ duties. §3. By the aid of these protective duties, slightly changed from time to time, our shipping interest acquired great strength. But the necessity of discriminating duties no longer exists. By the stipulations of existing treaties between the principal commercial nations, each is to admit into her ports the vessels of the others on equal terms with her own. Our government having become a party to this agreement, discriminating tunnage duties have been abolished. §4. The registry, however, of vessels of the United States, and other regulations concerning them, are for the most part continued. A vessel is measured by a surveyor to ascertain her tunnage, and the collector records or registers in a book her name, the port to which she belongs, her burden or tunnage, and the name of the place in which she was built, and gives to the owner or commander a certificate of such registry. §5. The master of a vessel departing from the United States, bound to a foreign port, must deliver to the collector of the district, a _manifest_, which is an invoice, or account of the particulars of a cargo of goods, and of their prices or value. This statement is subscribed by the master, and sworn by him to be true. The collector then grants a _clearance_, for the vessel, which is a certificate stating that the commander has cleared his vessel according to law. §6. Vessels of the United States going to foreign countries, are, at the request of the masters, furnished with passports. A _passport_ is a writing from the proper authority of a state or kingdom, granting permission to pass from place to place, or to navigate some sea without hinderance or molestation. It contains the name of the vessel and that of her master, her tunnage, and the number of her crew, certifying that she belongs to the subjects of a particular state, and requiring all persons at peace with that state, to suffer her to proceed on her voyage without interruption. In this country the form of a passport is prepared by the secretary of state, and approved by the president.