Complex sentence: In 1826, out of the 120 members of the Edinburgh society an estimated one third were from a medical background, and by the 1840s there were over twenty-eight phrenological societies in London with over 1000 members.
Split into simpler sentences: In 1826, out of the 120 members of the Edinburgh society an estimated one third were from a medical background. By the 1840s there were more than 28 phrenological societies in London with over 1000 members.