Complex sentence: Since Merro was living in Gloucester, Fallows hypothesized that the partbooks were acquired by Edward F. Rimbault from Martin Smith (father of John Stafford Smith), organist at Gloucester Cathedral from 1739 to 1781.
Split into simpler sentences: Since Merro was living in Gloucester, Fallows hypothesized that the partbooks were probably acquired by Edward F. Rimbault from someone living in that region. He views John Stafford Smith as the likely candidate since his father, Martin Smith, was organist at Gloucester Cathedral from 1739 to 1781.