The Chemist Who Built the Apparatus

Crookes's scientific credentials were not marginal. He identified thallium in 1861 from a green line in a spectrum, built the radiometer whose vanes still spin in shop windows, developed the high-vacuum tube that bears his name and that led directly to the discovery of the electron and of X-rays, and was elected to the Royal Society at thirty-one and eventually to its presidency. When he turned to Spiritualism in 1870 he did so in the manner of an instrument builder, announcing that the question could be settled by measurement and constructing the equipment to do it.

For the sittings with Daniel Dunglas Home he suspended a mahogany board with one end resting on a fulcrum and the other on a spring balance, so that any downward force could be read off a scale, and he reported deflections while Home's fingers rested lightly at the fulcrum end where they could exert no leverage. For the accordion he built a wire cage under the table, placed the instrument inside it, and reported that it played while Home held it by the end away from the keys. The apparatus was good. Whether the protocol around it was is the whole question. A balance reads whatever force is applied to it, and it cannot report who applied the force or by what route, which is the gap the whole controversy occupies.