The invitation to read this, the Ninth Barnwell Memorial Lecture, gives me the opportunity of acknowledging publicly the friendship and encouragement I used to receive from that great and kind gentleman. For several years before his death, he accorded me the privilege of a weekly meeting, and although I was in every way very junior, he invariably treated me as a friend as well as a colleague, thereby adding affection to the deep respect I felt for him.

I do not recall any details of our discussions of gas turbines, although I am certain we did review their possible advent on more than one occasion. Had he lived to see them, I am sure our efforts would have received his encouragement and support.