In the eighteenth century it was often convenient to regard man as a clockwork automaton. In the nineteenth century, with Newtonian physics pretty well assimilated and a lot of work in thermodynamics going on, man was looked on as a heat engine, about 40 per cent efficient. Now in the twentieth century, with nuclear and subatomic physics a going thing, man had become something which absorbs X-rays, gamma rays and neutrons.

Chapter Ten, Part II - V. (1963)