These papers stem from the ISOTT Meeting held at Churchill College, Cambridge, from July 27th to 30th, 1986. Although the sun did not shine so brightly as during the Cambridge meeting in 1977, the communications and discussions were as lively and informative and some heat, as well as light, was generated in the presentation of differing views. The meeting was conducted in a generally informal way which allowed maximum time for discussion but the relatively unstructured nature of the debates made them unsuitable for publication. The amount of editing necessary meant that the printed version of the exchanges would bear little resemblance to the original, hence their omission. All the papers presented here have been scrutinized and retyped in a standard format. However, the diverse interests of ISOTT's members, reflected in the wide spectrum of the material submitted, made total editorial uniformity an unrealistic goal. Complete consistency in the use of symbols, abbreviations and units seemed less important than speed of publication.