=Shipping Board.=--With a view to building up the American merchant marine, which in recent years had greatly declined, Congress in 1916 provided for the appointment by the President of a federal shipping board composed of five commissioners with power to construct or purchase merchant vessels suitable as naval auxiliaries and for the carriage of American commerce. The board is also to supervise common carriers engaged in transportation by water. As a war measure, the extent of its building operations was greatly increased in 1917. =International Postal Union.=--In this connection it may be noted that practically all the countries of the world have joined in forming what is known as the International Postal Union, for the reciprocal exchange of mails between the post offices of all countries belonging to the Union. The rates are fixed by a congress which represents the member states and which meets, in normal times, every five years. A letter may therefore be sent from one country to any other in the Union at a uniform rate, which, with some exceptions, is five cents. By special arrangement the rate on letters between the United States and the British Isles has been reduced to two cents. Likewise the rate between the United States and Canada or Mexico or most of the West Indies is by special arrangement two cents. =Classes of Post Offices.=--Post offices are grouped in four classes on the basis of their gross annual receipts. First-class offices are those whose gross receipts exceed $40,000 a year.[48] They are usually located in buildings owned by the government, and in the larger cities there are branch offices or sub-stations in different parts of the city. Fourth-class offices are those whose annual receipts are below $1,000. [48] The receipts of the New York post office are about $45,000,000 a year. Salaries of postmasters of the offices of the first three classes are determined mainly on the basis of the receipts of the office. Fourth-class postmasters receive no fixed salary, but instead are paid a percentage of the value of the stamps cancelled. In the larger post offices there are in addition to the postmaster one or more assistant postmasters and a force of clerks and carriers, the number depending on the amount of business and the size of the city. All postmasters are appointed after examinations under the civil service rules. Postmasters of the fourth class are appointed by the postmaster-general; those of the other three classes are appointed by the President.