John C. Briggs and Rotary Pendulum Clocks. 27 page booklet, written by Charles Terwilliger. Originally published as a bulletin of the National Association of Watch and Clock Collectors in April, 1978. 

This booklet is a fascinating study of the history of the American rotary pendulum clock, with patent information, pictures and stories of the original Welsh model I and II rotary clocks, many other notable rotary clocks, conical pendulum clocks, and the Horolovar reproduction of the Briggs Rotary Pendulum Clock.