Conversation so far:
What is the Second Select Committee in relation to Charles Bradlaugh?
The Select Committee began deliberating when it considered a paper put in by Sir Thomas Erskine May found several precedents for Members disabled to sit for refusing to take Oath
What was Charles Bradlaugh involvement in the Second Select Committee?
Erskine May and Bradlaugh himself were questioned by the Committee.
What were Erskine May and Charles Bradlaugh questioned about?
Bradlaugh arguing that, should the Committee decide he had no right to affirm, he would take the oath and regard it as binding on his conscience.

Question: What oath did they refuse to take?
Self-contained rewrite: What oath did Erskine May and Charles Bradlaugh refuse to take?