Sensitive flames and invisible worlds

'Psychical' science or physical phenomena? Philip Ball investigates William Barrett's sensitive flames that lit a fire of controversy in the 1800s.

  • Dancing flames

    Credit: Oscar - CC BY-SA 3.0

It was while he was assisting John Tyndall at the Royal Institution in 1865 that William Barrett became fascinated by flames. Barrett was helping Tyndall – the Professor of Natural Philosophy at the Ri and a lecturer with much of Michael Faraday’s flair and charisma – prepare for the Christmas lecture for children, which included demonstrations of acoustics. He noticed that high-pitched sounds seemed to have a peculiar effect on gas flames. “At the sound of any shrill note”, Barrett wrote in an 1867 paper on “sensitive flames”, “the flame shrank down several inches, at the same time spreading out sideways into a flat flame” [see picture from Barrett’s paper below]. It made Barrett think of “a sensitive nervous person uneasily starting and twitching at every little noise.”

  • Illustrative photograph of sensitive flame from 1867

    From W. F. Barrett, “Note on ‘sensitive flames’”, Philosophical magazine, xxxiii (1867), 216–22, p. 218.

  • Diagram of sensitive flames

    Credit: Popular Science Monthly Volume 36 (1889)

Tyndall was intrigued too, and he incorporated the “sensitive flame” into his spectacular lectures on sound and heat. In fact, although he at first acknowledged Barrett’s role in discovering the effect, soon it seemed to his young assistant that Tyndall was appropriating the phenomenon. This worsened the growing tension between the two, which led Barrett to hand in his resignation in July 1866. It had been less than three years earlier that Barrett’s enthusiastic response to Tyndall lectures had moved the professor to offer the young man the post. Tyndall had set out to train his protégé as “a competent experimenter”, but he was a hard taskmaster who would tolerate no “neglect of duty” and issued sharp reprimands for any mishaps.

It’s quite possible, however, that beyond Barrett’s displeasure at the harsh way Tyndall treated his assistants – there are shades of Humphry Davy’s curt manner with Faraday – the relationship between the two might have also been troubled by their different views on strange effects like the sensitive flame. Both agreed that there was a physical explanation connected to the way the sonic vibrations in air affected the flame. But for Tyndall, that was where the matter ended. He was utterly dismissive of the growing vogue at that time for spiritualism – the claims of mediums to be able to contact dead souls and demonstrate paranormal phenomena such as levitation and telekinesis. He was a thorough materialist, impatient with anything that smacked of the mystical: in 1864 he and Thomas Henry Huxley convened the dining society called the X Club, which opposed clerical or theological influences on science.

Barrett was different. Although he sympathized with Tyndall’s desire to use science to dispel superstition, he was a devout Christian who regarded the “scientific investigator as a high priest of God”. He allowed the possibility that some “psychic” effects were genuine, even if many others were fraudulent. And in the “sensitive flame” he saw an intimation of how some kind of resonant phenomena could enable the transmission of mental states, for example to permit such things as telepathy.

Perhaps, Barrett suggested, some people were like sensitive flames, especially attuned to picking up vibrations that others couldn’t perceive. Barrett went on from the Ri to establish a highly successful career in Ireland, becoming Professor of Physics at the Royal College of Science in Dublin in 1873. By 1881 his status was grand enough that he could publish in Nature a paper on experiments in thought transference. Here he described how the children of a Derbyshire clergyman were able to transmit information mentally with a failure rate of not more than one trial in ten.

Unsurprisingly, a controversy erupted, for this was just the moment at which passions were running high on the issue of whether or not alleged psychic phenomena were a proper subject for scientific enquiry. Barrett was so dismayed by what he regarded as the closed-mindedness of his critics that in 1882 he formed the Society for Psychical Research (SPR) in collaboration with Edmund Dawson Rogers, vice president of the Central Association of Spiritualists. The SPR was dedicated to investigating paranormal claims using the methods of science, and it included sceptics alongside committed spiritualists. Several leading scientists joined in the early years, among them William Crookes (one of the leading advocates of a “psychical” science in the Victorian age), Lord Rayleigh and J. J. Thomson. Other prominent members included two prime ministers, William Gladstone and Arthur Balfour, as well as Lewis Carroll, William James, Alfred Tennyson and John Ruskin. The society still exists, and continues to attract scientists – the president for 2000-2004 was the distinguished astrophysicist Bernard Carr.

Barrett maintained the belief throughout his life that some psychical phenomena drew on invisible forces and might be mediated by unseen spirit beings within the ether, their existence halfway between the physical and spiritual planes. He insisted that these explanations were not in fact supernatural – that term applied only to God – but were “supernormal” in that they worked outside of known physical laws but nevertheless were natural effects that followed “the laws of the spiritual kingdom.”

Barrett laid out this vision in his 1917 book On the Threshold of the Unseen – in retrospect a kind of swansong for the late-nineteenth-century intersection of science and spirit that hinged on the possibility of invisible, ethereal realms of existence populated with intelligent entities. What’s striking about these ideas is that science, far from challenging them, seemed at that time to be supporting them. As the historian Richard Noakes has said, “it was Tyndall’s experimental culture of sensitive flames and sympathetic vibrations that informed Barrett’s strongest arguments for the connections between physics, psychology, and ultimately spirituality.” Which should perhaps prompt us to wonder: what supernormal dreams is today’s science fostering?


Philip Ball is a freelance science writer. He writes regularly for Nature and has contributed to publications ranging from New Scientists to the New York Times¸ the Guardian and New Statesman. His latest book, Invisible: The Dangerous Allure of the Unseen is out now. INVISIBLE is a fascinating history of our obsession with invisibility, taking in cathode rays and nineteenth-century science, electromagnetism, H.G. Wells, the microscopic world, military camouflage, prestidigitation and twenty-first century nanoscience. Ball argues that achieving invisibility is not a technical challenge but a mythical idea with moral implications.

Further reading

P. Ball (2014), Invisible: the Dangerous Allure of the Unseen (Bodley Head).

R. Noakes (2004), “The ‘bridge which is between physical and psychical research’: William Fletcher Barrett, sensitive flames, and spiritualism”, History of Science 17, 419-464.

W. F. Barrett (1917), On the Threshold of the Unseen (Kegan Paul, Teench, Trubner & Co.).

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