1. a Dept. of Mechanical Engineering , University of Bristol , Bristol , BS8 1TR
2. b U. K. Ministry of Defence , Waltham Abbey , Essex , EN9 1AX
3. c Malaysian Rubber Producers' Research Association , Brickendonbury , Hertford , SG13 8NL
4. d Ministry of Defence, Waltham Abbey, now Dept. of Mechanical Engineering , Imperial College , London , SW7 2BX , England