 While in prison, he sent a brief address (written in the Prison of Belle-Ile-en-Mer, 10 February 1851) to a committee of social democrats in London.The text of the address was noted and introduced by Karl Marx.In 1865, while serving a further term of imprisonment under the Empire, he escaped, and continued his propaganda campaign against the government from abroad, until the general amnesty of 1869 enabled him to return to France.