Over the last three hundred or more years there are probably hundreds of compass related patents that have been applied for. Those listed below are ones that are relevant to my collecting:
Schmalcalders Patent, 1812 addressed the issue of directly reading a bearing by use of a prism and transit sight. This approach has lasted even to today and was in common use for surveyors, military and marine compasses.
Singers Patent, 11 June 1861 in Great Britain and 31 Dec 1861 in France addressed the issue of reading a compass card in the dark. This was a significant issue at a time when the primary form of illumination at night was a candle.
Hunters Patent, 6 May 1862 in USA, addressed the issue of both reading a compass card in the dark and features such as the transit lock to secure the compass card.
Symons Patent, 20 September 1875 in Great Britain, addressed the issue of how to give a True North reading.
Verners Patents, various patents some of which were not granted in 1887, 1889 (three patents) and 1895, addressed issues, primarily related to military compasses and their use in the field.