Johan Carl-Erik Stèn and Per Pippin Aspaas
Anders Johan Lexell (1740-1784) was a mathematician who gained considerable recognition for his scientific achievements during the century of Enlightenment. Born and educated in Åbo/Turku in the Finnish part of the Swedish Realm, he was invited as an assistant and collaborator of Leonhard Euler at the Imperial Academy of Sciences in Saint Petersburg in 1768. After Euler's death in 1783 he inherited his mentor's chair and became professor of mathematics at the Petersburg Academy of Sciences, but survived only a year in this office. One of Lexell's first tasks in Saint Petersburg was to assist in the calculations involved in the Venus transit project of 1769. Under Euler's supervision, Lexell formulated a system of modeling equations involving the whole bulk of observation data obtained from all over the world. Thus, by searching (manually) the best estimate of the parallax with respect to all available measurements made of the Venus transit simultaneously, he anticipated later statistical modeling methods. The usual method at the time consisted of juxtaposing a pair of measurements at a time and taking a mean value of all the parallax values obtained in this way. What had started as an innocent, purely academic attempt to establish the solar parallax, soon escalated into a heated controversy of international dimensions. The roles played by Jérôme de Lalande in Paris and Maximilian Hell in Vienna in this controversy are well known; Lexell's role less so. Our analysis has two aims. First, we elucidate Lexell's place in the international solar parallax controversy by making use of his published works as well as surviving parts of his correspondence. Second, we present the method used by Lexell and analyze his way of calculating the solar parallax.
Manuscript: jad19_1g.pdf