Number of senators
As already noted, under the Constitution each original state is represented by a minimum of six senators. This number has been twice increased, in 1948 (taking effect at the 1949 elections) to 10, and in 1983 (taking effect in the election of 1984) to 12. The Senate's size also increased after 1975 following election of two senators each by the Australian Capital Territory and the Northern Territory. The size of the Senate was 36 from 1901 until 1949; 60 from 1950 to 1975; 64 from 1976 to 1984; and 76 since 1985. The places of half of the senators for each state are open to election each three years, under the system of rotation. Electoral arrangements for territory senators are described below.