In 1870 Delaunay was appointed as Director of the Paris Observatory to replace Le Verrier . Tisserand showed remarkable abilities in his work at the Observatory and it was clear that he would soon achieve an elevated position in the world of astronomy.
Sa 1870 Delaunay ay hinirang bilang Director ng Paris obserbatoryo sa palitan Le Verrier. Tisserand ay nagpakita pambihira kakayahan sa kanyang trabaho sa obserbatoryo at ito ay malinaw na siya ay makamit sa lalong madaling panahon ng matataas na posisyon sa mundo ng astronomy.