Lonsdale, Dame Kathleen Yardley

(b. Newbridge, Ireland, 28 January 1903;d. London, England, 1 April 1971)

crystallography, chemistry, physics.

Kathleen Lonsdale was the tenth and youngest child of Harry Frederick Yardley and Jessie Cameron. Her father was postmaster at Newbridge, but the family later moved to England and Kathleen won scholarships which took her to the County High School for girls at Ilford and later to Bedford College for Women, which she entered at the age of sixteen. There she studied mathematics and physics and received a B.Sc. with highest honors at the age of nineteen. She took first place in the University of London list and one of her examiners, W.H. Bragg, was so impressed that he offered her a post in his research team to work on the crystal structure of organic compounds by X-ray analysis. Thus her scientific career began in 1922, first at University College and then at the Royal Institution in London. It continued throughout her life, with only brief interruptions following her marriage to Thomas Lonsdale in 1927, when she moved to Leeds for three years before returning once more to the Royal Institution.

In 1945 she became the first woman to be admitted as a Fellow of the Royal Society. In 1946 she was appointed reader in crystallography at University College, London, and professor of chemistry in 1949. She was appointed Dame Commander of the British Empire in 1956, received the Davy Medal of the Royal Society in 1957 and was its vice-president from 1960–1961. In 1966 she was president of the International Union of Crystallography and president of the British Association from 1967 to 1968. During her long and intensely active scientific career Kathleen Lonsdale raised two daughters and one son, had many outside interests, and traveled widely in most countries of the world. She was a member of the Society of Friends, and worked hard for peace and for prison reforms. But her many and varied interests were always closely integrated with her scientific work.

X-ray crystallography is primarily concerned with deducing the positions of atoms in space from a study of the diffraction patterns obtained when a beam of X rays is passed through a crystal. Kathleen Lonsdale began her work in 1922, ten years after the original discovery of the diffraction effect by Laue. In that time considerable advances in the theory and practice of the method had been made, and the structure of many simple and some quite complex inorganic substances had been deduced. But little was known about the dimensions and exact metrical structure of organic molecules.

As a physicist and mathematician by training, Kathleen Lonsdale’s first major contribution to this subject was a profound and systematic study of the theory of space groups, methods for their determination, and the possibilities of molecular symmetry that are involved. This work was published with W. T, Astbury in 1924. To some extent it duplicated the work of Wyckoff and Niggli (of which Astbury) and Kathleen Lonsdale were ignorant), but it further and was much more useful for those whose work was concerned with organic molecular crystals. A later continuation and extension of this work consisted of the structure factor tables published in 1936 in photo-litho-printed form from the handwritten manuscript, and the many volumes of the International Tables for X-Ray Crystallography published from 1952 onwards. These volumes, of which Kathleen Lonsdale was principal editor, are in crystal structure determination.

Kathleen Lonsdale’s main task at the Royal Institution was to try to solve the problem of organic crystal structures. Although she confessed that she “knew no organic chemistry and very little of any other kind,” she was destined to make one of the most outstanding advances in that subject for many decades. Her work on hexamethylbenzene, published in 1929, and hexachlorobenzene demonstrated for the first time that the benzene ring was hexagonal and planar, and she gave its precise dimensions. Of this result C, K. Ingold wrote, “one paper like this brings more of activity by us professionals.”

Her later work, however, was more concerned with the physics of crystals than with chemistry. She made an intensive study of the magnetic anisotropy of crystals, and by measuring the diamagnetic susceptibilities in and perpendicular to the planes of a number of aromatic molecules, she was able to show that, while the σ electronic orbits were of atomic dimensions the π orbits were of molecular dimensions. The far-reaching importance of this result was that it established the reality of the concept of molecular orbitals.

Later she was responsible for the development of divergent-beam X-ray photography of crystals, a technique which gives information about the texture and perfection of the crystal, and can also be used to make precise measurements of lattice constants or wavelength. By this means she was able to measure the C-C distance in individual diamonds to seven significant figures. She had a special interest in the structure of diamonds and made many other important contributions to their study.

Another important field in which she made outstanding contributions was the study of diffuse X-ray reflection by single crystals. She showed that this diffuse scattering is directly related to the elastic constants of the crystal. It is also dependent on the crystal structure and can be used to determine molecular orientation. In general, the thermal motion of atoms and molecules in crystals was one of her special interests.

In her later work she returned again to more chemical interests, as in her study of the solid-state transformation of anthracene to anthraquinone and Enthrone, and to medical problems concerned with the mode of action of drugs and the composition of endemic bladder stones.

Kathleen Lonsdale had a profound influence on the development of X-ray crystallography and related fields in chemistry and physics. Very few have made so many important advances in so many different directions.

BIBLIOGRAPHY

Among Lonsdale’s more important works are “Tabulated Data for the Examination of the 230 Space-groups by Homogeneous X-Rays,” in Philosophical Transactions of the Royal Society,224A (1924), 221–257, written with W. T. Astbury; “The Structure of the Benzene Ring in” in Proceedings of the Royal Society,123A (1929), 494–515; “An X-Ray Analysis of the Structure of Hexachlorobenzene, Using the Fourier Method,” ibid., (1931), 536–552; Simplified Structure Factor and Mathematical Crystallography (London, 1936), and “Magnetic Anisotropy and Electronic Structure of Aromatic Molecules,” in Proceedings of the Royal Society,159 A (1937), 149–161.

With H. Smith, she wrote “An Experimental Study of Diffuse X-Ray Reflection by Single Crystals,” ibid., 179A (1941), 8–50. Also see “Extra Reflections From the Two Types of Diamond,” in Proceedings of the Royal Society,179 A (1942), 315–320; “X-Ray Study of Crystal Dynamics: An Historical and Critical.Survey of Experiment and Theory,“in Proceedings of the Physical Society,54 (1942), 314–353; “Divergent Beam X-ray Photography of Crystals,“in Philosophical Transactions of the Royal Society,240A (1947), 219–250; Crystals and X-rays (London, 1948); “Geiger Counter Measurements of Bragg and Diffuse Scattering of X-rays by Single Crystals,“in Acta crystallographica,1 (1948), 12–20; and “Vibration Amplitudes of Atoms in Cubic Crystals,’ ibid., 1 (1948), 142–149

J. M. Robertson