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120 honors of the Jardin des Plantes, and Gay-Lussac and Larrey entertain her with chat.... At Geneva she met Mrs. Marcet, whose 'Conversations on Chemistry' were said by Faraday to have first opened his mind to the wonders of that science. There, too, were Sismondi and De la Rive. A letter from De Candolle, whose acquaintance she had made there, gives shortly afterward some excellent hints for the prosecution of the botanical studies in which she had already made much progress. The interest which she takes in the most diverse branches of knowledge makes every one forward to bring her the first intelligence of anything new or of significance. Dr. Young is eager to submit an Egyptian horoscope he has that evening deciphered from a papyrus of the age of the Ptolemies; Wollaston hurries to Hanover Square to show, by means of a small prism in a darkened room, the seven dark lines he had discovered crossing the solar spectrum, the germ of the most important series of modern discoveries in solar physics; Babbage discourses over his analytical engine; Sir J. Herschel exhibits nebulæ and binary stars in the field of his great reflector; Ada, Byron's daughter, afterward Lady Lovelace, compares difficulties with Mary Somerville in mathematics. Among her most intimate and valued friends was Maria Edgeworth, to which number were later added Joanna Baillie and her sister. Year by year her acquaintance and correspondence grew, until they included well-nigh every name of distinction in literature or science."

This activity continued till the last day of her life. She spent many years in Italy, having removed there for the benefit of the health of her husband, who died at Florence in 1861 at the age of ninety-one, and continuing to reside there till her death. In her eighty-ninth year she revised some of her earlier mathematical manuscripts, which had been forgotten for many years, and was surprised at the facility she still retained for the calculus. One of her latest writings was the acknowledgment of the receipt from Mr. Spottiswoode of a parcel of recent advanced books upon the higher algebra, including quaternions. In her ninety-second year, when she had written of the "Blue Peter having long been flying at her foremast," and of her soon expecting the signal for sailing, she was interesting herself in the phenomena of volcanic eruptions, and speculating on their effects, and was following with unabated interest the progress of scientific discovery and keeping up with the record of events. She died in sleep. The list of scientific societies of which Mrs. Somerville was a member, and of honors she received, is a long one, and includes a number of American societies. She also had among her personal friends many men of chief distinction in American science and letters.

During her later years Mrs. Somerville noted down some recollections of her life, and they, edited and supplemented by her daughter, Martha Somerville, were published in 1873, under the title of "Personal Recollections, from Early Life to Old Age, of Mary Somerville."