The University of Manchester has announced plans to digitize the holdings of the Cardinal Newman archive. Among the roughly 200,000 items of handwritten and other unpublished materials are 171 files of letters to (and from) “particular individual correspondents.”
One such correspondent of particular interest is Lord Acton. A selection of Acton’s correspondence with Newman is available digitally courtesy of the Online Library of Liberty. Lord Acton’s periodical, The Rambler, is also the subject of seven separate files of Newman’s correspondence “concerned with various specific issues,” according to the checklist available from the national archives (PDF).
For more on liberalism and the Catholic Church in the nineteenth century, see The Acton-Newman Relations: The Dilemma of Christian Liberalism, by Hugh A. MacDougall (Fordham University Press, 1962).