 Claire Clairmont gave birth to a baby girl on 13 January , at first called Alba , later Allegra . In March of that year , the Chancery Court ruled Percy Shelley morally unfit to assume custody of his children and later placed them with a clergyman 's family . Also in March , the Shelleys moved with Claire and Alba to Albion House at Marlow , Buckinghamshire , a large , damp building on the river Thames . There Mary Shelley gave birth to her third child , Clara , on 2 September . At Marlow , they entertained their new friends Marianne and Leigh Hunt , worked hard at their writing , and often discussed politics . 
