Derby was significant in the eighteenth century for its role in the Enlightenment, a period in which science and philosophy challenged the divine right of kings to rule. The enlightenment has many strands, including the largely philosophical "Scottish enlightenment" centred around the philosopher David Hume, and political changes that culminated in the French revolution, but the English Midlands was an area where many key figures of industry and science came together. The Lunar Society included Erasmus Darwin, Matthew Boulton, Joseph Priestley and Josiah Wedgwood with Benjamin Franklin corresponding from America. Erasmus Darwin, grandfather of Charles Darwin, started the Derby Philosophical Society when he moved to Derby in 1783.