Pedro II became a member of the Royal Society, the Russian Academy of Sciences, The Royal Academies for Science and the Arts of Belgium and the American Geographical Society. In 1875, he was elected to the French Academy of Sciences, an honor previously granted to only two other heads of state: Peter the Great and Napoleon Bonaparte. He exchanged letters with scientists, philosophers, musicians and other intellectuals. Many of his correspondents became his friends, including Richard Wagner, Louis Pasteur, Louis Agassiz, John Greenleaf Whittier, Michel Eugène Chevreul, Alexander Graham Bell, Henry Wadsworth Longfellow, Arthur de Gobineau, Frédéric Mistral, Alessandro Manzoni, Alexandre Herculano, Camilo Castelo Branco and James Cooley Fletcher. His erudition amazed Friedrich Nietzsche when the two met. Victor Hugo told the Emperor: "Sire, you are a great citizen, you are the grandson of Marcus Aurelius," and Alexandre Herculano called him a "Prince whom the general opinion holds as the foremost of his era because of his gifted mind, and due to the constant application of that gift to the sciences and culture."