From Roger Luckhurst's excellent book The invention of telepathy, 1870-1901 (2002):
The connections between scientific and occult inter-phenomena sometimes make demarcations difficult. Heinrich Hertz's experiments with 'spark-gaps' in 1889, his detection of 'sympathetic' sparks produced at a distance in secondary circuits, produced a succession of new inter-phenomena in the 1890s. Wireless telegraphy and X-rays astonished and bewildered many. When the leading British experimenter in wireless telegraphy came to the Royal Institution to honour and remember Hertz, he traced the route from Hertz's spark-gap to Guglielmo Marconi's ongoing trials with 'wireless' technology from ship to shore in the English Channel. This lecture began with the sympathetic vibrations of tuning forks, and demonstrated how a discharge of electricity in one circuit could produce a spark at a distance in a secondary circuit, provided they were in sympathy or 'syntony'. The lecturer was Oliver Lodge, a physicicist present at early thought-reading experiments in Liverpool in 1884, and who had proposed in the pages of the PSPR that 'just as the energy of an electric charge, though apparently on the conductor, is not on the conductor, but in all the space around it . . . so it may be that the sensory consciousness of a person, though apparently located in the brain, may also be conceived of as also existing like a faint echo in space, or in other brains'. Telepathy had been coined by Frederic Myers and syntony by Arthur Myers, Frederic's brother.
Roentgen's demonstration of X-rays in 1898 could also be traced back to foundational experiments on anomalous inter-phenomena investigated in vacuum tubes by William Crookes. In 1879, Crookes rehabilitated himself with his lecture 'On Radiant Matter' to the British Association. It was termed 'exquisite' and 'unique' by Nature, and was reprinted in full. Crookes's lecture was replete with evidence of some form of contact made between distant electrical poles in high vacua, whether demonstrated by producing a vividly phosphorescing diamond, by a paddle-wheel being pushed along a track, or by forming shadows by interrupting the path of phosphorescing radiant matter. These ingenious apparatuses rendered visible what Crookes called 'matter in a fourth state of condition'. 'In studying this fourth state of matter,' he suggested, 'we seem at length to have within our grasp and obedient to our control the little invisible particles which with good warrant are supposed to constitute the physical basis of our universe.' His speech steered close to his previous enquiries into psychic force and his vacuum tubes mischievously abutted onto the same terrain: 'We have actually touched the bornerland where matter and force seem to merge into one another, the shadowy realm between the Known and the Unknown which for me has always had peculiar temptations.' Crookes was wrong about the nature of the particles at work; J. J. Thomson's work at the Cavendish laboratory later reconceived these inter-phenomena as streams of electron particles. Yet Thomson, too, became involved with his Cambridge colleagues in psychical research, insisting in his memoirs in the 1930s that 'the investigation of short-range thought transference is of the highest importance' and that such experiments would support the view of his colleague Lord Rayleigh that 'telepathy with the dead would present apparently little difficulty when it is admitted as regards the living'.