Margaret Todd lived from 1859 to 3 September 1918. She was a pioneering woman doctor and an author, and the woman who coined the word "isotope". The wider picture in Scotland at the time is set out in our Historical Timeline.
Little appears to be known about Margaret Todd's early years: even her date of birth seems to elude the sources we have seen. She is said to have worked as a schoolteacher in Glasgow before, in 1886 at the age of about 27, she moved to Edinburgh to become one of the first students at the Edinburgh School of Medicine for Women, founded in that year by Sophia Jex-Blake. Although she was 19 years younger than Jex-Blake the two formed a close personal relationship that lasted until Jex-Blake's death in 1912.
Margaret took eight years to complete her medical studies, partly because she was also writing the first of a series of novels, which she published under the pseudonym "Graham Travers". She graduated in 1894 before being awarded her M.D. in Brussels. She was then appointed Assistant Medical Officer at Edinburgh Hospital and Dispensary for Women and Children. She retired in 1899 at the same time as Sophia Jex-Blake, and the two moved to live together in Sussex.
Margaret's first novel had been entitled "Mona Maclean, Medical Student". It was negatively reviewed by Punch magazine as "a novel with a purpose, no recommendation for a novel, more especially when the purpose selected is that of demonstrating the indispensability of women-doctors". The book nonetheless proved popular, and she wrote two more novels which were also successful. After Sophia Jex-Blake died in 1912, Todd published a detailed biography as "The Life of Dr Sophia Jex-Blake".
Margaret Todd's other claim to fame results from circumstances that are rather elusive. It seems she was a family friend of the chemist Frederick Soddy. At some point he described to her his work on radioactive elements that have more than one atomic mass, although the chemical properties are identical and they share the same place in the periodic table. He was apparently having trouble coming up with a satisfactory name. It is said that Margaret told him he needed a good Greek term: perhaps, she suggested, he should try "isotope" from the Green for "same place". Frederick Soddy went on to win the Nobel Prize for Chemistry in 1921, and has a (small) crater on the Moon named after him. He would doubtless have achieved these honours using a different name for the subject of his work, but it is good that the long-standing assumption that he coined the work "isotope" has been corrected in recent years.
Margaret Todd died at the age of 58 or 59, possibly as a result of suicide, just three months after her biography of Sophia Jex-Blake had been published.