When you take a class with the Harvard University art historian Jennifer Roberts, your first task is always to choose a work of art, then go and look at it, wherever it’s displayed, for three full hours. Three hours! If that notion doesn’t horrify you at least a little, I suspect you’re atypical: in our impatient, accelerated age, the mere thought of it is sufficient to trigger an irritable jumpiness. (Stick me in front of a painting for three hours and I’d soon be swiping my thumb on it downwards, to see if there had been any updates.) Roberts knows this: the whole point, she writes, is that it’s “a painfully long time”. She doesn’t expect her students to spend it all in rapt attention; rather, the goal is to experience that jumpiness, tolerate it, and get through it – whereupon they see things in the artwork they’d never have imagined were there.