by K. J. Binns and P. J. Lawrenson. by A. G. Martin and F. W. Stephenson. by I. F. Henderson and W. D. Henderson. by H. J. Emeleus and J. S. Anderson. by L. G. Berry and R. M. Thompson. by A. Yariv and J. E. Pearson. by F. A. Benson and D. Harrison. by W. G. McLean and E. W. Nelson. by J. R. Green and D. Margerison. by J.R. Lucas and P.E. Hodgson.