with astronomy after the death of their mother, and made the calculations, for the Academy of Sciences of Berlin, of the "Ephemeris" and the "Almanac" which were sources of revenue to that learned body. In the same period a number of French and Italian astronomers had female collaborators in their own families. Celsius, the celebrated professor at Upsala, and a pupil of Kirch the son, was entertained, while passing through Paris to Bologna, by De l'Isle, whose sister was devoting herself to astronomy. Reaching Italy, he found likewise that his new master, Manfredi, had two learned sisters, engaged, like their brother, in the study of the stars. This caused Celsius to say, in a letter to Kirch: "I begin to believe that it is fated for all the astronomers whom I have had the honor of becoming acquainted with during my journey to have learned sisters; I have a sister, too, but not a very learned lady. To keep up the coincidence, we must make an astronomer of her."
Other women, whose names are less well known, wrote on astronomy during the seventeenth century. We may cite Maria Cunitz, daughter of a Silesian doctor, who published astronomical tables in 1650; Jeanne Dumé, who in 1650 wrote a book defending the Copernican system against "scientific" attacks upon it. Of more modern date was Madame Gabrielle Emilie de Breteuil, Marquise du Châtelet, who was for fifteen years the constant friend of Voltaire, and in her retreat at Cirey devoted her whole life to the sciences. She it was who first made known to France, then devoted to scientific Cartesianism and the doctrine of elementary vortices, the masterly work of Newton. This was a title to glory which might have made the fortune of more than one scientific man, and it fell upon a woman. Mademoiselle de Breteuil had received a very careful education, but her natural taste for study and serious occupations did not prevent her from shining brilliantly in the society of the courts of the Regency for some years after her marriage with M. du Châtelet. One of the best evidences of her genius that we have is in the bearing toward her of Voltaire, who had no respect for any but mental gifts. He had returned from Great Britain full of enthusiasm for English science and philosophy, and occupied with the dream of making Newton known to his countrymen and dethroning Descartes at the Academy. It may appear singular that he selected Madame du Châtelet for this work; but the choice was not extraordinary after all. She had already made some progress in mathematical studies under the direction of Maupertuis and Clairaut, and Voltaire was looking for the assistance he needed to some one outside of the official scientific circle. The translation of Newton's "Principia" would be the best means of making known in France the great English geometrician and the admirable simplicity which his theory of attraction lent to the study of the movements of the stars. This work Madame du Châtelet did well. But she did more than make a simple translation. The algebraic com-
