Among the buildings he designed were three churches in Clapham, South London, Mark Masons' Hall, London (later the Thatched House Club), Lord Tennyson's house at Aldworth, the Leicester Square garden (as restored at the expense of Albert Grant), Albert Mansions, Victoria Street in Westminster,[2] and an 1882 enlargement of the Royal Sea Bathing Hospital at Margate in Kent.
This resulted in a close friendship, Knowles assisting Tennyson with business matters, and among other things helping to design scenery for the play The Cup, when Henry Irving produced it in 1880.
[4] Knowles corresponded with a number of the most interesting men of the day, and in 1869, with Tennyson's cooperation, he initiated the Metaphysical Society, the object of which was to attempt some intellectual rapprochement between religion and science by inviting major representatives of faith and unfaith to meet and exchange opinions.
[4] Members included Tennyson, Gladstone, W. K. Clifford, W. G. Ward, John Morley, Cardinal Manning, Archbishop Thomson, T. H. Huxley, Arthur Balfour, Leslie Stephen, and Sir William Gull.
In 1870 he succeeded Dean Alford as editor of the Contemporary Review, but quit it in 1877 owing to the objection of the proprietors to the inclusion of articles (by W. K. Clifford notably) attacking Theism, and he initiated the Nineteenth Century (to the title of which, in 1901, were added the words And After).