what Miss Hill has done . . . the worst districts of London
Note from the Letter Baron's Gate by John Ruskin

The reference is to Octavia Hill, the social reformer. Ruskin met her when in her late teens she studied drawing under him. In 1864 she and Ruskin embarked on a project to improve housing conditions for the poor in London. They began with six dwellings in Marylebone, which Ruskin had inherited from his father. The experiment met with some success; as W. G. Collingwood puts it,

'They showed what a wise and kind landlord could do by caring for tenants, by giving them inhabitable dwellings, recreation ground, and fixity of tenure, and requiring in return a reasonable and moderate rent' [ The Life and Work of John Ruskin ].