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