Complex sentence: Whilst at the museum, Maclagan wrote many articles and catalogues, he also wrote an essay entitled'The Bayeux Tapestry' published (as a King Penguin) in 1943 which became a minor best seller.
Split into simpler sentences: Whilst at the museum, Maclagan wrote many articles and catalogues. He also wrote an essay entitled'The Bayeux Tapestry', published (as a King Penguin) in 1943, which became a minor best seller.