The 19th-century "free love" movement was not particularly focused on the idea of multiple partners, but did agree with Wollstonecraft that state-sanctioned marriage was "legal prostitution" and monopolistic in character. It has somewhat more in common with early feminist movements (particularly with regard to the writings of Mary Wollstonecraft, whom Blake admired). Blake was critical of the marriage laws of his day, and generally railed against traditional Christian notions of chastity as a virtue. At a time of tremendous strain in his marriage, in part due to Catherine's apparent inability to bear children, he directly advocated bringing a second wife into the house. His poetry suggests that external demands for marital fidelity reduce love to mere duty rather than authentic affection, and decries jealousy and egotism as a motive for marriage laws. Poems such as "Why should I be bound to thee, O my lovely Myrtle-tree?" and "Earth's Answer" seem to advocate multiple sexual partners. In his poem "London" he speaks of "the Marriage-Hearse" plagued by "the youthful Harlot's curse", the result alternately of false Prudence and/or Harlotry. Visions of the Daughters of Albion is widely (though not universally) read as a tribute to free love since the relationship between Bromion and Oothoon is held together only by laws and not by love. For Blake, law and love are opposed, and he castigates the "frozen marriage-bed". In Visions, Blake writes: Till she who burns with youth, and knows no fixed lot, is bound In spells of law to one she loathes? and must she drag the chain Of life in weary lust? (5.21-3, E49) In the 19th century, poet and free love advocate Algernon Charles Swinburne wrote a book on Blake drawing attention to the above motifs in which Blake praises "sacred natural love" that is not bound by another's possessive jealousy, the latter characterised by Blake as a "creeping skeleton". Swinburne notes how Blake's Marriage of Heaven and Hell condemns the hypocrisy of the "pale religious letchery" of advocates of traditional norms. Another 19th-century free love advocate, Edward Carpenter (1844–1929), was influenced by Blake's mystical emphasis on energy free from external restrictions. In the early 20th century, Pierre Berger described how Blake's views echo Mary Wollstonecraft's celebration of joyful authentic love rather than love born of duty, the former being the true measure of purity. Irene Langridge notes that "in Blake's mysterious and unorthodox creed the doctrine of free