Complex sentence: Tamsen was an expert in the stamps of Transvaal, about which he researched and wrote, and he was one of the founders in 1894 of the Johannesburg Philatelic Society.
Split into simpler sentences: Tamsen was an expert in the stamps of Transvaal, about which he researched and wrote. He was one of the founders in 1894 of the Johannesburg Philatelic Society.