In what year was the first book detailing the language 'Esperanto' published?

My grandfather learnt Esperanto after the First World War, which he survived but suffered from his war wounds all his life. He learnt this Universal language with the hope it could unite the world and war would no longer be necessary. Sadly the language died out and we are where we are in our world today... but it seems that English has pretty much taken over as a language franca so we can hope!