When a historian reaches the end of a book he becomes acutely aware of omissions. What there has not been room for, what he has not researched and what he has not prioritised. All this is a necessary part of the craft of selection and organisation, but with this book I am particularly aware of a disparity between the ephemeral nature of my theatrical examples and the enormity of the changes taking place in politics and society. In my introduction I used the metaphor of a hot-air balloon, and I also referred to the spume on a wave. In both cases what is seen is a manifestation of something invisible — the buoyant air or the swell of the sea. The balloon makes a nice comparison because it is a man-made construction apparently entirely free from contact with the earth — just like some of the inconsequential entertainments I have described. However, sea spume is more obviously the product of the violent action of the waves — and in contrast to the driving force of Revolutionary events theatrical entertainment certainly seems a light and frothy concoction. But spume is neither constructed nor controlled, whereas many people were involved in making theatre. It was their livelihood as well others' relaxation.

And spume is not just the white plume on a rolling breaker, it is the froth that remains once the wave, and even the tide, withdraws. It can be a sad looking splodge left on the sand, turning greyish, containing bits of weed and debris.