Treaties and other international acts series. 4585. Weather stations, cooperative program at Antofagasta, Quintro and Puerto Montt, agreement between United States and Chile, extending agreement of Mar. 1, 1957, as extended, effected by exchange of notes signed Santiago July 21 and Sept. 7, 1960: [entered into force Sept. 7, 1960, operative retroactively Jan. 1, 1960].