Deborah Warner, "Compasses and Coils: The Instrument Business of Edward S. Ritchie," Rittenhouse, 9 (1994): 1-24.
Copies of a series of patents from the 1860s pertaining to marine compass inventions of Edward S. Ritchie can be found in the file of a CHSI inv. 5330a,b:
PAT. 36.422
PAT. 105.492
PAT. 77.763
PAT. 38.125
PAT. 38.126