Among other women astronomers of the eighteenth century who deserve mention are Mme. du Pierry, the Duchesse Louise of Saxe-Gotha, and Mme. Hortense Lepaute.
According to Lalande, Mme. du Pierry was the first woman professor of astronomy in Paris. He dedicated to her his Astronomie des Dames, and incorporated in his own works many of her memoirs on astronomical subjects. She devoted much time to calculating eclipses with a view to accurately determining the motion of the moon, and was, besides, the author of numerous astronomical tables which exhibit patient research and unquestioned skill.
The Duchesse Louise had a great reputation as a rapid and accurate computer, and was celebrated for the number and variety of her computations. Her modesty, however, prevented her from publishing anything or even having her work quoted.
Considering, however, the amount and character of her work, the most eminent woman astronomer that France has yet produced was, without doubt, Mme. Hortense Lepaute, the wife of the royal clockmaker of France. She first distinguished herself by her investigations on the oscillations of pendulums of different lengths, an account of which is to be found in her husband's valuable work, Traité d'Horlogerie, published in 1755.
In 1759 Lalande, who was then the Director of the Paris Observatory, engaged Mme. Lepaute and the celebrated mathematician, Clairaut, to determine the amount of the attraction of Jupiter and Saturn on Halley's comet, whose return was expected in that year. So difficult was this problem, and so numerous were the complications involved, that Lalande frankly confesses that he would not have dared to undertake its solution without Mme. Lepaute's assistance. For it necessitated calculating for every degree, and for one hundred and fifty years the distances and forces of each of the planets with reference to the comet. "It would be difficult," declares Lalande, "to realize the courage which this enterprise required, if one did not know that for more than six months we calculated from morning until night, sometimes even at meals, and that at the end of this enforced labor I was stricken by a malady which affected me during the rest of my life." Clairaut was so impressed by Mme. Lepaute's energy and skill during this time that he declared "her ardor was surprising," and he did not hesitate to call her La savante calculatrice—the learned computer.[143]
The eclipse of 1762 also engaged Mme. Lepaute's attention, as did also the annular eclipse of 1764. The latter was a curious phenomenon for France, as it had never before been observed. Mme. Lepaute calculated it for the whole of Europe and published a chart showing its path for every quarter of an hour. She also published another chart for Paris, in which were exhibited the different phases of the eclipse.
On the occasion of the different eclipses which she had calculated, Mme. Lepaute recognized the advantage of having a table of parallactic angles. She accordingly prepared a very extended table of this kind which was published by the French government. Besides this table, she was the author of numerous memoirs on astronomical subjects. Among them was one embracing calculations based on all the observations which had been made on the transit of Venus in 1761.
"In 1759," again writes Lalande, "I was given charge of the Connaissance des Temps, a work which the Academy of Sciences published every year for the use of astronomers and navigators, the calculations for which gave occupation to several persons. I had the good fortune to find in Mme. Lepaute a co-worker without whom I should not have been able to undertake the labor required. She continued in this occupation until 1774, when another Academician assumed this laborious task. But she thereupon began work on the Ephemeris, of which the seventh volume in quarto, which appeared in 1774, goes to 1784, and of which the eighth, published in 1783, extends to the year 1792. In this latter volume she made, unaided, all the computations for the sun, the moon and all the planets.
"This long series of calculations finally enfeebled her eyesight, which had been excellent, and she was in the last years of her life obliged to discontinue them."[144]
In view of her extraordinary and long-continued work in her chosen specialty, M. Lalande was quite warranted in stating that "Mme. Lepaute is the only woman in France who has acquired veritable knowledge in astronomy; and she is now replaced only by Mme. du Pierry, who has published divers astronomical calculations, and who has deserved to have dedicated to her L'Astronomie des Dames, which appeared in 1786."