John Tyndall FRS (2 August 1820 – 4 December 1893) was a prominent 19th century physicist. His initial scientific fame arose in the 1850s from his study of diamagnetism. Later he studied thermal radiation, and produced a number of discoveries about processes in the atmosphere. Tyndall published seventeen books, which brought state-of-the-art 19th century experimental physics to a wider audience. From 1853 to 1887 he was professor of physics at the Royal Institution of Great Britain, where he became the successor to positions held by Michael Faraday. He spent his later years living at the village of Hindhead, near Haslemere, approximately 45 miles south-west of London Tyndall was born in Leighlinbridge, County Carlow, Ireland. His father was a local police constable and small landowner, descended from Gloucestershire emigrants who settled in southeast Ireland around 1670. Tyndall attended the local schools in County Carlow until his late teens, and was probably an assistant teacher near the end of his time there. Subjects learned at school notably included technical drawing and mathematics with some applications of those subjects to land surveying. He was hired as a draftsman by the government's land surveying & mapping agency in Ireland in his late teens in 1839, and moved to work for the same agency in England in 1842. In the decade of the 1840s, a railroad-building boom was in progress, and Tyndall's land surveying experience was valuable and in demand by the railroad companies. Between 1844 and 1847, he was lucratively employed in railroad construction planning.[1][2] In 1847 Tyndall opted to become a mathematics teacher at a boarding school in Hampshire. Recalling this decision later, he wrote: "the desire to grow intellectually did not forsake me; and, when railway work slackened, I accepted in 1847 a post as master in Queenwood College."[3][4] Another recently-arrived young teacher at Queenwood was Edward Frankland, who had previously worked as a chemical laboratory assistant for the British Geological Survey. Frankland and Tyndall became good friends. On the strength of Frankland's prior knowledge, they decided to go to Germany to further their education in science. (Among other things, Frankland knew that certain German universities were ahead of any in Britain in experimental chemistry and physics. British universities were still focused on classics and mathematics and not laboratory science.) The pair moved to Germany in summer 1848 and enrolled at the University of Marburg, where Robert Bunsen was an influential teacher. Tyndall studied under Bunsen for two years.[5] Probably more influential for Tyndall at Marburg was Professor Hermann Knoblauch, with whom Tyndall maintained communications by letter for many years afterwards. Tyndall's Marburg dissertation was a mathematical analysis of screw surfaces in 1850 (under Friedrich Ludwig Stegmann). He stayed at Marburg for a further year doing research on magnetism with Knoblauch, including some months' visit at the laboratory of Knoblauch's main teacher, Gustav Magnus in Berlin. It is clear today that Bunsen and Magnus were among the very best experimental science instructors of the era. Thus, when Tyndall returned to live in England in summer 1851, he probably had as good an education in experimental science as anyone in England. Tyndall's early original work in physics was his experiments on magnetism and diamagnetic polarity, on which he worked from 1850 to 1856. His two most influential reports were the first two, co-authored with Knoblauch. One of them was entitled "The magneto-optic properties of crystals, and the relation of magnetism and diamagnetism to molecular arrangement", dated May 1850. The two described an inspired experiment, with an inspired interpretation. These and other magnetic investigations very soon made Tyndall known among the leading scientists of the day.[6] He was elected a Fellow of the Royal Society in 1852. In his search for a suitable research appointment, he was able to ask the longtime editor of the leading German physics journal (Poggendorff) and other prominent men to write testimonials on his behalf. In 1853, he attained the prestigious appointment of Professor of Natural Philosophy (Physics) at the Royal Institution in London, due in no small part to the esteem his work had garnered from Michael Faraday, then the leader of magnetic investigations at the Royal Institution.[7] Beginning in the late 1850s, Tyndall studied the action of radiant energy on the constituents of air, and it led him onto several lines of inquiry, and his original research results included the following:[8] As an indicator of his lifetime research output, an index of 19th century scientific research journals has John Tyndall as the author of more than 147 papers, with practically all of them dated between 1850 and 1884, which is an average of more than four papers a year over that 35-year period.[21] Tyndall was an experimenter and laboratory apparatus builder, not an abstract model builder. But he did attempt to extend his studies on the heat-absorptive power of gases and vapors into a research program about molecules. That is one of the underlying agendas of his 1872 book Contributions to Molecular Physics in the Domain of Radiant Heat. It is also evident in the spirit of his widely read 1863 book Heat Considered as a Mode of Motion. Besides heat, he also saw phenomena of magnetism and sound propagation as reducible to molecular behaviors. Invisible molecular behaviors were the ultimate substrate of all physical activity. With this mindset, and his experiments, he outlined an account whereby differing types of molecules have differing absorptions of infrared (or other) radiation because their molecular structures give them differing oscillating resonances. He'd gotten into the oscillating resonances idea because he'd seen that any one type of molecule has differing absorptions at differing radiant frequencies and he was entirely persuaded that the only difference between one frequency and another is the frequency.[22] He'd also seen that the absorption behavior of molecules is quite different from that of the atoms composing the molecules -- for example the gas nitric oxide absorbed more than a thousand times more infrared radiation than either nitrogen or oxygen.[23] In several kinds of experiments he showed that no matter whether a gas or vapor is a weak absorber of broad-spectrum radiant heat, it will strongly absorb the radiant heat coming from a separate body of the same type of gas or vapor.[24] That demonstrated a kinship between the molecular mechanisms of absorption and emission. Such a kinship was also in evidence in experiments by Balfour Stewart and others, cited and extended by Tyndall, that showed with respect to broad-spectrum radiant heat that molecules that are weak absorbers are weak emitters and strong aborbers are strong emitters.[25] (For example rock-salt is an exceptionally poor absorber of heat via radiation, and a good absorber of heat via conduction. When a plate of rock-salt is heated via conduction and let stand, it takes an exceptionally long time to cool down; i.e., it's a poor emitter of infrared.) The kinship between absorption and emission was also consistent with some generic (or abstract) features of resonators.[26] The photochemical effect convinced Tyndall that the resonator could not be the molecule as a whole unit; it had to be some substructure, because otherwise the photochemical effect would be impossible.[27] But he was without testable ideas as to the form of this substructure, and did not partake in speculation in print. His promotion of the molecular mindset, and his efforts to experimentally expose what molecules are, has been discussed by one historian under the title "John Tyndall, The Rhetorician Of Molecularity".[28] In his lectures at the Royal Institution Tyndall put a great value on -- and was talented at producing -- lively, visible demonstrations of physics concepts.[29] In one lecture, published later in one of his books, Tyndall demonstrated the propagation of light down through a stream of falling water via total internal reflection of the light. It was referred to as the "light fountain". It is historically significant today because it demonstrates the scientific foundation for modern fiber optic technology. During second half of the 20th century Tyndall was usually credited with being the first to make this demonstration. However, Jean-Daniel Colladon published a report of it in Comptes Rendus in 1842, and there's some suggestive evidence that Tyndall's knowledge of it came ultimately from Colladon and no evidence that Tyndall claimed to have originated it himself.[30] Tyndall was a pioneering mountain climber and distinguished member of the London-based Alpine Club. He visited the Alps almost every summer from 1856 onward, was a member of the very first mountaineering team to reach the top of the Weisshorn (1861), and led one of the early teams to reach the top of the Matterhorn (1868). He summited Mont Blanc and Monte Rosa several times.[31] In the Alps, Tyndall studied glaciers, and especially glacier motion. His views on glacial flow brought him into dispute with others, particularly James David Forbes and James Thomson. It was known that glaciers moved, but the mechanism for this action was uncertain. Some thought they slid like solids, others that they flowed like viscous liquids, others that they crawled by alternate thermal expansion and contraction, or by fracture and regelation. Tyndall believed that regelation, discovered by Michael Faraday, played a key role. Forbes didn't see regelation in the same way. Complicating the debate, a disagreement arose publicly over who deserved to get investigator credit for what. Articulate friends of Forbes (as well as Forbes himself) thought that Forbes should get the credit for most of the good science, whereas Tyndall thought the credit should be distributed more widely. Tyndall commented: "The idea of semi-fluid motion belongs entirely to Louis Rendu; the proof of the quicker central flow belongs in part to Rendu, but almost wholly to Louis Agassiz and Forbes; the proof of the retardation of the bed belongs to Forbes alone; while the discovery of the locus of the point of maximum motion belongs, I suppose, to me."[32] When Forbes and Tyndall were in the grave, their disagreement was continued by their respective official biographers. Everyone tried to be reasonable, but agreement wasn't attained. More disappointingly, aspects of glacier motion remained not understood or not proved.