Kathleen Lonsdale (28 January 1903 – 1 April 1971) was an Irish-born British crystallographer. She was was born in County Kildare, Ireland, the youngest of ten children.
Lonsdale excelled in mathematics and science, and went to attend classes at the boys’ Grammar School because they were not offered at the girls’ school. She was only 16 when she entered Bedford College, University of London, and in 1922 she took her degree in physics, achieving the highest marks of any student for ten years. Professor William Henry Bragg then invited her to join his team researching X-ray diffraction at University College London. In 1927, she married engineer Thomas Lonsdale, and moved with him to Leeds, where as part of the chemistry department she conclusively demonstrated the crystal structure of benzene.
Though it may appear as if Kathleen’s career was destined to take a back seat to her husband’s, Thomas valued and enthusiastically supported Kathleen’s. He had not married, he said, to get a free housekeeper. They went shopping together, once a week, for supplies and Kathleen specialized in meals that took thirty minutes to prepare. Thomas set up some apparatus of his own design at home, with which to measure the torsional properties of annealed metal wires for his Ph.D. degree; while he experimented in the evenings, Kathleen did calculations. In 1929 their first child, a daughter (Jane), was born. Soon afterwards, the family returned to London where Thomas obtained a post at the Road Research Laboratory. Their second daughter, Nancy, was born in 1931, and their son, Stephen, in 1934. 
In fact, when Kathleen thought about the conditions which lead to her success, she noted:
“For a woman, and especially a married woman with children, to become a first class scientist, she must first of all choose, or have chosen, the right husband. He must recognize her problems and be willing to share them. If he is really domesticated, so much the better. Then she must really be a good organizer and be pretty ruthless in keeping to her schedule, no matter if the heavens fall. She must be able to do with very little sleep, because her working week will be twice as long as the average trades unionist’s. She must go against all her early training and not care if she is regarded as a little peculiar. She must be willing to accept additional responsibility, even if she feels she has more than enough. But above all, she must learn to concentrate in any available moment and not require ideal conditions in which to do so.“ 
In 1931, she returned to work with Bragg at the Royal Institute, staying there for 15 years. She was awarded a DSc in 1936, and in 1945, along with microbiologist, Marjory Stephenson, she became one of the first women Fellows of the Royal Society. She was Professor of Chemistry and Head of the Department of Crystallography, University College, London, from 1949 to 1968. She was the first tenured woman professor at that college, a position she held until 1968 when she was named Professor Emeritus.
During WWII, Lonsdale sheltered refugees, and in 1943, she spent a month in jail for refusing to register for civil defence duties or to pay the consequent fine of £2. After WWII, she became an anti-nuclear campaigner.
In the Arthur Stanley Eddington Memorial lecture (1964), Kathleen Lonsdale said:
If we knew all the answers there would be no point in carrying out scientific research. Because we do not, it is stimulating, exciting, challenging. So too is the Christian life, lived experimentally. If we knew all the answers it would not be nearly such fun.
In 1966, lonsdaleite, a rare form of meteoric diamond, was named after her. Wryly, she wrote to Clifford Frondel at Harvard University, who suggested the name:
“Certainly the name seems appropriate since the mineral only occurs in very small quantities (perhaps rare would be too flattering) and is generally rather mixed up!”
Lonsdale died in 1971 of cancer, possibly caused by her prolonged exposure to X-rays.
Quakers in the world: Kathleen Lonsdale (1903-1971)
Kylie Miller and Stephen M. Contakes: Crystallographer, Quaker, Pacifist, & Trailblazing Woman of Science: Kathleen Lonsdale’s Christian Life “Lived Experimentally” in God and Nature, Summer 2014
 Hodgkin, Dorothy M.C. “Kathleen Lonsdale, 28 January 1903 – 1 April 1971” Biographical Memoirs of Fellows of the Royal Society 21 (1975) Hodgkin, Dorothy M.C. “Kathleen Lonsdale, 28 January 1903 – 1 April 1971” Biographical Memoirs of Fellows of the Royal Society 21 (1975)
 Lonsdale, Kathleen “Women in Science – why so few? Laboratory Equipment Digest February 1971, pg. 85, as quoted in Hodgkin, Dorothy M.C. “Kathleen Lonsdale, 28 January 1903 – 1 April 1971” Biographical Memoirs of Fellows of the Royal Society 21 (1975), pg. 474.