The main purpose of Cambridge's system of proportional representation is to give minorities a vote in city government. In the 22 years it has been in use, PR has proved complicated, slow, and all but impractical; as last week's City Council election demonstrated, however, PR does what it was designed to do. Two minority groups-the academic and Negro communities-gained their first spokesmen on the Council in many years, and the new Councillors are welcome, both because of their own qualifications and because of the importance of the groups they represent.

Unless an impending recount invalidates his election, one of the two new Councillors will be Thomas H.D. Mahoney, an M.I.T. professor who, as a School Committeeman for three terms, established the Committee's "university chair." Mahoney may be able to start a similar precedent on the Council, but even if he does not, he should serve as a highly valuable liaison between Cambridge and the universities. Harvard and M.I.T. have much to offer Cambridge in the way of talent and theoretical knowledge, and the City can do much to aid the universities in matters concerning revenues and land.

The other new City Councillor is Thomas Coates, who will be the first Negro to serve on the Council since 1923. His election is all the more encouraging for coming at a time when the break-down of communication between races threatens to have explosive political results. It is risky comparing the politics of Cambridge to those of Boston, if only because of the great differences of size between the cities. One cannot help nothing, however, that Coates was elected on the same day that 128,000 Bostonians cast their votes for Mrs. Louise Day Hicks.

Both new Councillors were endorsed by the Cambridge Civic Association, and since the CCA also backed the two retiring Councillors, it will retain possession of the four Council seats it has held for a decade. Despite its shortcomings, the CCA is Cambridge's most effective influence for good government. The result of last week's election insures that it will continue to play an important role.