Why, Philip Ball asks, are we so fascinated by invisibility? What would we do if we happened upon the Ring of Gyges – or of Frodo Baggins? ‘The chances are,’ Ball thinks, ‘it will have something to do with power, wealth or sex. Perhaps all three, given the opportunity.’ Power, wealth and sex would constitute a pretty potent publishing trifecta as far as snagging readers’ attention is concerned. Imagine if the pop-sci book that tapped those three phenomena actually existed. Imagine if it were more than a mirage, flickering on the edge of sight.

Invisible does its best to catch some of that glamour; but there’s a problem right away. The most obvious drawback of invisibility is blindness, because an invisible retina stops no photons. The real question, therefore, is not what would you do with Frodo’s ring, but would you even want to