I’m working on a scene in my next Martha book. In 1700s Edinburgh, there was no such thing as a sewage system. James Buchan, in his fascinating book Crowded with Genius: The Scottish Enlightenment: Edinburgh’s Moment of the Mind, writes of servants flinging open the shutters at ten o’clock every evening, calling out “Gardy loo!”—a heads-up for passersby—and emptying the household chamberpots onto the street below.

I am suddenly feeling very fond of my toilets.