Page 108, last line of text, for P/P″ read P′/P″.
Page 120, last line, for δ v read δ y .
Page 123, line 10, for 4Nn read 4Nu.
Page 125, line 1, for q read q.
Page 126, line 12, for q read q.
Page 135, line 5 from bottom, for y4Nsq read e4Nsq.
Page 141, lines 8