How do you measure a spirit, or dissect a phantom? For many, ghosts are beyond the frontier of what science can interest itself in, one boundary for the discipline. For others, ghosts, being a phenomenon like any other, are equally open to objective study. Yet most interesting of all, the technologies and machines that define the modern world and would investigate the spectral themselves have seemed prone to being haunted.The process, perhaps, began with the gloomy railways of Charles Dickens’s “The Signalman” or Arnold Ridley’s “The Ghost Train”. But soon it spread to demon-driven cars, to mezzotints, to haunted motorways, ghostly presences in lifts, or confined to a cursed submarine. Most intriguingly, the instruments that ghost hunters themselves would use have seemed spooked: the photograph that freezes a vanishing moment catching the recurring vanishing of a ghost; the tape-recorder left on in an empty room that picks up bodiless voices; the numerous tales of eerie messages on mobile phones or ghostly disturbances within computers. Like our photos, our recordings, our texts and our tweets, the ghost is a trace, linked to technology, detected within it, and somehow inhabiting it. When the familiarities of life are themselves revealed to be haunted and strange – when there are slight deviations from the customs that conceal our relation to death – we are closest to the anxious heart of the ghost story.