John Tyndall's crucial work on magnetism has been all but written out of the history books. Roland Jackson puts the record straight.
The physicist John Tyndall (1820-1893), so closely associated with the Royal Institution, is best known for his work establishing the physical basis for the atmospheric warming effect of carbon dioxide and water vapour, for explaining why the sky is blue and for his work on the germ theory and spontaneous generation. But he has been all but written out of the history of magnetism, in which he actually played a significant role. In a previous blogpost I described the story of why he turned down the prestigious Royal Medal for his initial work on diamagnetism. This is the story of his substantive contribution to the field (if I may be permitted a pun) and an attempt at a little rewriting of history.
Michael Faraday’s discovery in 1845 of diamagnetism, the weak repulsion of substances by a magnetic pole, stimulated efforts across Europe to understand this new magnetic phenomenon and to link it to wider ideas about electricity and magnetism. Effectively it became a test piece between Faraday’s emerging ‘field theory’ and ideas based on the attraction and repulsion of magnetic poles acting at a distance.
Faraday developed his thinking in terms of a force field filling space, with physically real lines of force having certain properties such that magnetic materials, rather than being ‘attracted’ or ‘repelled’, tended to move from stronger to weaker places of force, or vice versa. But Faraday did not clearly specify the underlying mechanisms. Tyndall once described this as Faraday’s ‘mistiness,’ since his own focus was firmly on clear physical explanations.
William Thomson, later knighted by Queen Victoria for his contribution to the electric telegraph, and then ennobled as Lord Kelvin (hence the derivation of the standard unit for temperature), was able to put Faraday’s ideas into mathematical form. These were built on in the 1860s and beyond by James Clerk Maxwell, architect of the classical theory of electromagnetism, culminating in his great publication of 1873, A Treatise on Electricity and Magnetism.
But Tyndall was having none of this. Starting his experiments in Marburg in 1849 just before he finished his PhD, he built up over sustained periods of work from 1849-1852 and 1854-1856 a meticulously constructed body of experimental evidence and theoretical interpretation. He challenged Faraday’s theory with a model of diamagnetic polarity and magnetic forces acting in couples, based on a firm vision of the importance of the underlying structure of materials in defining their properties. In doing so, this thrusting young philosopher took on the might of Faraday, Thomson and the German mathematician turned physicist Julius Plücker, often in public at British Association meetings, or at the Royal Institution and Royal Society, and occasionally to excess – his relationship with Plücker only became friendly in 1858. But he also had many allies, including Wilhelm Weber on the Continent and others in Britain, who were equally confused by Faraday’s notions. Unfortunately there was no mathematician, like Thomson, who could express Tyndall’s concepts mathematically, which Tyndall himself was unable to do. That had to wait for the later development of vector theory. When it came, in the late 19th Century, it very much vindicated Tyndall’s approach as a valid and consistent way of interpreting the phenomena.
At the time, the quality of Tyndall’s work was thoroughly appreciated, and he remained on excellent terms with Faraday throughout. He published his six major papers on diamagnetism and much additional material in a collection in 1870 entitled ‘Researches on Diamagnetism and Magnecrystallic Action’, and it makes a compelling read. Yet Maxwell’s development of Faraday’s field theory had prevailed. Tyndall’s work was largely forgotten although he had made a major contribution to the experimental definition of the actual phenomena and to one means of explaining them, which retains its validity today even if his model was superseded at the time.
Roland Jackson is a Visiting Fellow at the Royal Institution and Honorary Research Associate at UCL, studying the work of John Tyndall, and has recently published an academic paper on Tyndall’s contribution to our understanding of magnetism (open access) , and a previous one on the Royal Medal episode (£).
As his time at the Ri comes to an end, and he prepares to return to his PhD research, Matt Greenwell reflects on his experience as the Ri's Digital Intern.
Posted to Behind the scenes on1st February 2019