With Charles Darwin and Thomas Huxley his name is inseparably connected with the battle which began in the middle of the 19th century for making the new standpoint of modern science part of the accepted philosophy in general life. For many years, indeed, he came to represent to ordinary Englishmen the typical or ideal professor of physics.

His strong, picturesque mode of seizing and expressing things gave him an immense living influence both in speech and writing, and disseminated a popular knowledge of physical science such as had not previously existed. But besides being a true educator, and perhaps the greatest popular teacher of natural philosophy in his generation, he was an earnest and original observer and explorer of nature.

Tyndall was to a large extent a self-made man; he had no early advantages, but with indomitable earnestness devoted himself to study, to which he was stimulated by the writings of Carlyle. He passed from a national school in Co. Carlow to a minor post (1839) in the Irish ordnance survey, thence (1842) to the English survey, attending mechanics' institute lectures at Preston in Lancashire.

He then became for a time (1844) a railway engineer, and in 1847 a teacher at Queenwood College, Hants. Thence with much spirit, and in face of many difficulties, he betook himself, with his colleague Edward Frankland, to the university of Marburg (1848-1851), where, by intense application, he obtained his doctorate in two years. His inaugural dissertation was an essay on screw-surfaces.

Tyndall's first original work in physical science was in his experiments with regard to magnetism and diamagnetic polarity, on which he was chiefly occupied from 1850 to 1855. While he was still lecturing on natural philosophy at Queenwood College, his magnetic investigations made him known in the higher circles of the scientific world, and through the initiative of Sir E Sabine, treasurer of the Royal Society, he was elected F.R.S. in June 1852. In 1850 he had made Michael Faraday's acquaintance, and shortly before the Ipswich meeting of the British Association in 1851 he began a lasting friendship with Thomas Huxley.

The two young men stood for chairs of physics and natural history respectively, first at Toronto, next at Sydney, but they were in each case unsuccessful. On February 11, 1853, however, Tyndall gave, by invitation, a Friday evening lecture (on "The Influence of Material Aggregation upon the Manifestations of Force") at the Royal Institution, and his public reputation was at once established. He then joined Huxley in running the science section of the Westminster Review and helped to form a group of evolutionists who paved the way for Charles Darwin's 1859 publication of The Origin of Species.

In May 1854 Tyndall was chosen professor of natural philosophy at the Royal Institution, a post which exactly suited his striking gifts and made him a colleague of Faraday, whom in 1866 he succeeded as scientific adviser to the Trinity House and Board of Trade, and in 1867 as superintendent of the Royal Institution. His reverent attachment to Faraday is beautifully manifested in his memorial volume called Faraday as a Discoverer (1868).

His inquiries into glacier motion were notable for his association with Switzerland and for prolonged controversy with other men of science on the subject. In 1854; after the meeting of the British Association in Liverpool, a memorable visit occurred to the Penrhyn slate quarries, where the question of slaty cleavage arose in his mind, and ultimately led him, with Huxley, to Switzerland to study the phenomena of glaciers.

Here the mountains seized him, and he became a constant visitor and one of the most intrepid and most resolute of explorers; among other feats of climbing he was the first to ascend the Weisshorn (1861). Tyndall climbed to within a few hundred feet of the top of the Matterhorn in 1864, the year before Edward Whymper succeeded. The strong, vigorous, healthfulness and enjoyment which permeate the record of his Alpine work are magnificent, and traces of his influence remain in Switzerland to this day. The problem of the flow of glaciers occupied his attention for years, and his views brought him into acute conflict with others, particularly James Forbes and James Thomson.

Every one knew that glaciers moved, but the questions were how they moved, for what reason and by what mechanism. Some thought they slid like solids; others that they flowed like liquids; others that they crawled by alternate expansion and contraction, or by alternate freezing and melting; others, again, that they broke and mended. Thus there arose a chaos of controversy, illuminated by definite measurements and observations. Tyndall's own summary of the course of research on the subject was as follows:

The idea of semi-fluid motion belongs entirely to Rendu; the proof of the quicker central flow belongs in part to Rendu, but almost wholly to 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.

But while Forbes asserted that ice was viscous, Tyndall denied it, and insisted, as the result of his observations, on the flow being due to fracture and regelation. All agreed that ice flowed as if it were a viscous fluid; and of this apparent viscosity James Thomson offered an independent explanation by the application of pure thermodynamical theory, which Tyndall considered inefficient to account for the facts he observed.

It is unnecessary here to rake among the ashes of this prolonged dispute, but it may be noted that Helmholtz, who, in his lecture on "Ice and Glaciers," adopted Thomson's theory, afterwards added in an appendix that he had come to the conclusion that Tyndall had "assigned the essential and principal cause of glacier motion in referring it to fracture and regelation" (1865).

Tyndall's investigations of the transparency and opacity of gases and vapours for radiant heat, which occupied him during many years (1859-1871), are frequently considered his chief scientific work. But his activities were essentially many-sided. He definitely established the absorptive power of clear aqueous vapour--a point of great meteorological significance. He made brilliant experiments elucidating the blue of the sky, and discovered the precipitation of organic vapours by means of light.

He called attention to curious phenomena occurring in the track of a luminous beam. He examined the opacity of the air for sound in connection with lighthouse and siren work, and he finally clinched the proof of what had been already substantially demonstrated by several others, viz. that germ-free air did not initiate putrefaction, and that accordingly "spontaneous generation" as ordinarily understood was a chimera (1875-1876).

One practical outcome of these researches is the method now always adopted of sterilizing by a succession of gentle warmings, sufficient to kill the developed microorganisms, instead of by one fierce heating attempting to attack the more refractory undeveloped germs of the same. This method of intermittent sterilization originated with Tyndall, and it was an important contribution to biological science and industrial practice.

For the substantial publication of these researches reference must be made to the Transactions of the Royal Society; but an account of many of them was incorporated in his best-known books, namely, the famous Heat as a Mode of Motion (1863; and later editions to 1880), the first popular exposition of the mechanical theory of heat, which in 1862 had not reached the textbooks; The Forms of Water, &c. (1872); Lectures on Light (1873); Essays on the floating-matter of the air in relation to putrefaction and infection (1881); On Sound (1867; revised 1875, 1883, 1803).

The original memoirs themselves on radiant heat and on magnetism were collected and issued as two large volumes under the following titles: Diamagnetism and Magne-crystallic Action (1870); Contributions to Molecular Physics in the Domain of Radiant Heat (1872). In 1875 Tyndall reported to the Royal Society in London that a species of Penicillium had caused some of his bacteria to burst. This discovery of antibiotic properties of penicillium predated Ernest Duchesne by 20 years and Alexander Fleming by over 50 years.

It was on the whole the personality, however, rather than the discoverer, that was greatest in Tyndall. In the pursuit of pure science for its own sake, undisturbed by sordid considerations, he shone as a beacon light to younger men--an exemplar of simple tastes, robust nature and lofty aspirations. His elevation above the common run of men was conspicuous in his treatment of the money which came to him in connexion with his successful lecturing tour in America (1872-1873). It amounted to several thousands of pounds, but he would touch none of it; he placed it in the hands of trustees for the benefit of American science--an act of lavishness which bespeaks a noble nature.

Though not so prominent as Huxley in detailed controversy over theological problems, he played an important part in educating the public mind in the attitude which the development of natural philosophy entailed towards dogma and religious authority. His famous Belfast address (1874), delivered as president of the British Association, made a great stir among those who were then busy with the supposed conflict between science and religion; and in his occasional writings--Fragments of Science, as he called them, "for unscientific people"--he touched on current conceptions of prayer, miracles, etc., with characteristic straightforwardness and vigour.

As a public speaker he had an inborn Irish readiness and vehemence of expression; and, though a thorough Liberal, he split from Mr Gladstone on Irish home rule, and took an active part in politics in opposing it.

In 1876 Tyndall married Louisa, daughter of Lord Claud Hamilton. He built in 1877 a cottage on Bel Alp above the Rhone valley, and in 1885 a house on Hindhead, near Haslemere. At the latter place he spent most of his later years; his health was, however, no longer as vigorous as his brain, and he suffered frequently from sleeplessness. On December 4, 1893, having been accidentally given an overdose of chloral hydrate, he died at Hindhead.

A crater on Mars is named in his honor.