This paper analyses the fraught relationship between physics and the ‘occult sciences’ in the decades around 1900. For some, there was no relationship at all; for others there was a relationship but they did not agree on what it looked like. Many physicists converged with spiritualists, theosophists, and others in interpreting X-rays, the electrical theory of matter, and other aspects of the ‘new’ physics as powerful ways of rendering psychic and occult effects scientifically more understandable. However, they were opposed by (...) commentators on physics who agreed that there was a relationship between the ‘new’ physics and psychical research but that these were two manifestations of a worrying drift of physics into metaphysics and religion. More redoubtable critics were the psychologists who denied that physicists had the experience or experimental skill to cope reliably with the psycho-physical phenomena encountered in psychical research. This paper shows that physicist–psychical researchers were content to ally the ‘new’ physics with religion because it helped vanquish awkward associations with materialism. They also tried to justify the value of their experimental skills by appealing to their expertise in investigating subtle physical effects and ability to create tests that respected the delicate conditions of séances.Keywords: Physics; Psychical research; Ether; Occult; Psychology; Fin-de-siècle. (shrink)