Kerr, John

(b. Ardrossan, Ayrshire, Scotland, 17 December 1824; d. Glasgow, Scotland, 18 August 1907)

physics.

The second son of Thomas Kerr, a fish dealer, Kerr received part of his early education at a village school on Skye. He attended the University of Glasgow, beginning in 1841, and received his M.A. with “highest distinction in Physical Science” in 1849. He studied natural philosophy under David Thomson He was a member of the first group to work with the latter in the laboratory that was converted from a wine cellar and was known among the students as the “coal hole.”

A divinity student, Kerr completed the courses in theology at the Free Church College in Glasgow but did not take up clerical duties. In 1857 he was appointed lecturer in mathematics at the Free Church Normal Training College for Teachers in Glasgow, remaining in this post for forty-four years. The facilities for research at this institution were limited, as was the time that Kerr could devote to it. Therefore the paucity of his publications is not surprising; their quality, however, is high.

Kerr is remembered primarily for two discoveries. The first, which he announced in 1875, was the birefringence developed in glass in an intense electric field. He bored holes into the ends of a piece of glass two inches thick until they were about a quarter of an inch apart. An intense electric field was applied to electrodes placed in these holes. The effect on a beam of polarized light shining perpendicular to the electric field was to give it elliptical polarization. The effect was strongest when the plane of polarization was at an angle of 45° to the field and zero when it was parallel or perpendicular to the field. In subsequent papers Kerr extended his findings to other materials, including a large number of organic liquids. He also found that the size of the effect was proportional to the square of the electric force.

Kerr’s second discovery, which bears his name, was announced at the meeting of the British Association in Glasgow in 1876, and an account was published the following year. The Kerr effect is detected when abeam of plane polarized light is reflected from the pole of an electromagnet. When the magnet is activated, the beam becomes elliptically polarized, with the major axis rotated from the direction of the original plane. Extended by Kerr and others, these experiments were first treated theoretically by George F. Fitzgerald in “On the Electromagnetic Theory of the Reflection and Refraction of Light” (Philosophical Transactions of the Royal Society, 171 [1880], 691-711) and in more general terms by Joseph Larmor in “The Action of Magnetism on Light” (Report of the British Association. . . [1893], 335-372).

Kerr received an hohorary LL.D. degree form the University of Glasgow in 1868, in recognition of his achievements in teaching, and was elected to the Royal Society in 1890. He was married to Marion Balfour and had three sons and four daughters.

BIBLIOGRAPHY

I. Original Works. Kerr’s book include The Metric System; Its Prospects in This Country (London, 1863); An Elementary Treatise on Rational Mechanics(London,1867); Memories Grave and Gay; forty years of school Inspection (Edinburgh-London, 1902); and Scottish Education, School and University, From Early Times to 1908 (Cambridge, 1910). His articles are listed in the Royal Society Catalogue of Scientific Papers; most of them appeared in Philosophical Magazine. The two discoveries cited above were announced in “On a New Relation Between Electricity and Light: Dielectrified Media Birefringent,” in Philosophical Magazine, 50 (1857), 337-348, 446-458;and “On the Rotation of the Plane of Polarization by Reflection From the Pole of a Magnet.” ibid., n.s. 3 (1877), 321-343. Some of Kerr’s original apparatus is preserved at the University of Glasgow.

II. Secondary Literature. Short biographical accounts include those by C. G. Knott, in Nature, 76 (1907), 575-576; by Andrew Gray, in Proceedings of the Royal Society, 82A (1909), i-v; and, by Robert Steele, in Dictionary of National Biography, supp. II , 394.

Bernard S. Finn