Martineau edited a volume of "Letters on the Laws of Man's Nature and Development", published in March 1851. Its epistolary form is based on correspondence between her and the self-styled scientist Henry G. Atkinson. She expounded the doctrine of philosophical atheism, which she thought the tendency of human belief. She did not deny a first cause but declared it unknowable. She and Atkinson thought they affirmed man's moral obligation. Atkinson was a zealous exponent of mesmerism. The prominence given to the topics of mesmerism and clairvoyance heightened the general disapproval of the book. Literary London was outraged by its mesmeric evolutionary atheism, and the book caused a lasting division between Martineau, her beloved brother, James who had become a Unitarian cleric, and some of her friends.