COMPARATIVE LITERATURE: Dieter Riefler Riefler Präzisions-Pendeluhren von 1890-1965, Callwey, Munich, 1981.
The serial number on this pendulum indicates that it was the original pendulum for Riefler clock No.20, made for the Royal Geodetic Institute, Potsdam and sold these rooms 13 December 2000, lot 79.
Riefler's H-type pendulum was patented in 1891 and was a great improvement on Harrison's gridiron and Graham's mercury pendulums. The present H1 version was for use in airtight tanks where aerodynamic styling of the bob was not necessary. 235 of these H type pendulums were produced, the last being delivered in 1902.