The day is a unique temporal category in being, most of the time and in most parts of the world, clearly bounded at beginning and end – by night – and always recurring in a regular rhythm. Close to the poles days can become exceptionally long or exceptionally short, but they will still wax and wane in a predictable annual pattern. Thus, unlike the relatively artificial divisions of the hour or the week, the day presents a naturally occurring, observable temporal unit, one that technology and human innovation cannot change; as Heidegger would concede, it is ‘the “most natural” measure of time’. Even now, at the beginning of the twenty-first century, the fact of there being a pattern of darkness and light that gives rise to something called ‘a day’ cannot ultimately be questioned, undermined, deconstructed we might say; along with death, it is the only thing in life of which we can be sure.

A century ago, during the period when the artistic movement we call modernism was gathering pace, technology was becoming increasingly able to modify and regulate the rhythms of life.