Under the Universal Postal Convention of 1874, the Universal Postal Union was established in 1875 and became a specialized agency of the United Nations in 1948. Its permanent headquarters are in Bern, Switzerland. By 1990 it had 169 members. Each member country, under the postal convention, pays transportation charges to members who carry international mail across their borders. In 1863, the U.S. postmaster general, Montgomery Blair, first proposed that representatives of leading countries meet to solve the problems involved in moving mail across international boundaries. The first international postal congress at Bern brought together representatives of 22 countries. This set of eight stamps consists of famous works of art, the subjects of which deal with letter-writing.