Complex sentence: The Institute's predecessor organisation the Birmingham Philosophical Institution had held music classes since its foundation in 1800, and the Institute itself conducted informal musical instruction in its early years, but it was in 1859 that music was first formally established as part of the curriculum.
Split into simpler sentences: The institute's predecessor organisation, the Birmingham Philosophical Institution, had held music classes since its foundation in 1800. The institute conducted informal musical instruction in its early years, but it was in 1859 that music was established as part of the curriculum.