It has been pointed out to me by Professor A. M. Macbeath that the proof of Theorem 2 which is given in (2) is incorrect, in that it relies on Proposition 3·1 of (2), which is false, the mistake in its proof being the assumption that in an arbitrary compact topological space, every sequence has a convergent subsequence. However, we can still prove Theorem 2 of (2), simply by replacing section 3 of (2) by the corrected section 3 below, and replacing the proof of Proposition 4·2 of (2) by the corrected proof of Proposition 4·2 given below.