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