Our President, Sir Alwyn Williams, asked me to act for him in this last element of our Symposium and he stressed that I should tell you how unhappy he was to be absent today.

I found myself reflecting on some possible reasons for the invitation to me to deputise. The most obvious is perhaps my seniority as a Fellow of the Royal Society of Edinburgh. I have been a Fellow for almost forty years. In addition, and more pertinent to my immediate task, for over fifty years I have been involved in research, or close to research, in nuclear science and particularly concerned with research on penetrating radiation. I trust this qualifies me to discuss some important trends.