Another range of extensions came in relation to what could be copyrighted. The Statute only referred to books, and being an Act of Parliament, it was necessary to pass further legislation to include various other types of intellectual property. The Engraving Copyright Act 1734 extended copyright to cover engravings, statutes in 1789 and 1792 involved cloth, sculptures were copyrighted in 1814 and the performance of plays and music were covered by copyright in 1833 and 1842 respectively. The length of copyright was also altered; the Copyright Act 1814 set a copyright term of either 28 years, or the natural life of the author if this was longer. Despite these expansions, some still felt copyright was not a strong enough regime. In 1837, Thomas Noon Talfourd introduced a bill into Parliament to expand the scope of copyright. A friend of many men of letters, Talfourd aimed to provide adequate rewards for authors and artists. He campaigned for copyright to exist for the life of the author, with an additional 60 years after that. He also proposed that existing statutes be codified under the bill, so that the case law that had arisen around the Statute of Anne was clarified.