The main hypnosis discoveries came in 1842 when Braid started to learn more about its effects. He did not think that 'mesmerism' was the cause of hypnosis, and in the end he thought that trances were only a 'nervous sleep'. In 1843 he wrote a book about this with the title "Neurypnology". In this book Braid described hypnotism as a state of physical relaxation accompanied and induced by mental concentration ("abstraction").