politician. He was appointed professor of rational mechanics at the Faculty of Science of the University of Bucharest. The next year (1879), Haret became a correspondent member of the Romanian Academy, receiving full membership in 1892. He kept the professorship at the Faculty of Science until his retirement in 1910, when he was followed as professor of mechanics by Dimitrie Pompeiu. From 1882 he was also a professor of analytical geometry at the School of Bridges and Roads in Bucharest. After retirement, Haret occasionally lectured at the informal People's University. Haret was the Minister of Public Education in three liberal governments, between 1897 and 1899, 1901–1904, and 1907–1910. As Minister of Education he ran a complete reform, basically building the modern Romanian education system. In January 1883, he married in Buzău a local, Ana Popescu, 15 years his junior. The two had a son, Ion, who died at age 1, and later adopted a child, Mihai. Haret died in Bucharest in 1912 of cancer, and was buried in the city's Bellu Cemetery; Ana Haret died in 1941, aged 74. Scientific activity Haret's major scientific contribution was made in 1878, in his Ph.D. thesis Sur l’invariabilité des grandes axes des orbites planétaires. At the time it was known that planets disturb each other's orbits, thus deviating from the elliptic motion described by Johannes Kepler’s First Law. Pierre Laplace (in 1773) and Joseph Louis Lagrange (in 1776) had already studied the problem, both of them showing that the major axes of the orbits are stable, by using a first degree approximation of the perturbing forces. In 1808 Siméon Denis Poisson had proved that the stability also holds when using second degree approximations. In his thesis, Haret proved by using third degree approximations that the axes are not stable as previously believed, but instead feature a time variability, which he called secular perturbations. This result implies that planetary motion is not absolutely stable. Henri Poincaré considered this result a great surprise and continued Haret’s research, which eventually led him to the creation of chaos theory. Haret established the instability of the model of the n-body problem assuming frequencies to be incommensurable; Poincaré also into account commensurabilities, and using generalized Fourier series (which generate quasi-periodic solutions), he proved the divergence of these series (which means instability), thus confirming Haret’s result. Félix Tisserand recommended the extension of Haret's method to other astronomic problems and, much