 Soon he became a member of the socialist "Circle of Artillerists-Chernyshevs" that included such future prominent revolutionaries as Peter Kropotkin and Pyotr Lavrov.Jacobi retired from the Army and studied at the University of Heidelberg.In 1863-1864 he participated in the January Uprising in Poland planning to organize "Russian Republican Legion" fighting for the freedom of Poland from the Russian Empire.