Returning from a lecturing tour at the end of 1855, he was conscious of a great and vital change which had for some time been going on within his mind, and when he attempted to recommence his work at the City Hall in January, 1856, he found it impossible to go on along the old lines. On a certain memorable night, when announced to speak on "Sweden and the Swedes," he could not utter a word. He turned pale as death, and as the audience sat gazing and wondering what could have come to the bold and fluent speaker, whose tongue was ready on every theme, his pent-up feelings at length found vent. He told the people he could lecture on Sweden, but must relieve his conscience, for he could suppress conviction no longer. He then declared that he had been insisting on the duty of morality for years, but there had been this radical defect in his teachings, that he had "neglected to teach the right foundation for morals--the existence of a Divine moral Governor."[69] In the storm which followed he challenged them to bring the best sceptics they could muster in the metropolis, and he would meet them in debate on the being of God and the argument for a future state. He kept his promise, and for four nights maintained his ground against _Robert_ Cooper[70] and others in the City Hall and the John Street Institute. [69] Ibid p. 335. [70] The charges of atheism and atheistic advocacy made against _Thomas_ Cooper have often arisen from confounding _Thomas_ Cooper the _sceptic_ with _Robert_ Cooper the _infidel_. See "Life of Thomas Cooper," p. 357.