In around 1920, the Astronomer Royal, Frank Dyson asked the clockmaker Edwin Cottingham to make a copy of a Riefler Regulator for use as a new sidereal standard at Greenwich. Delivered in February 1921, it was adopted as the Sidereal Standard in place of Dent 1906 in October 1922.
The Reports of the Astronomer Royal indicate that two later clocks of the Riefler pattern destined for other observatories were tested at the Observatory before being despatched. The following excerpts are taken from the 1924 and 1925 Reports:
1924: ‘A precision clock of Riefler pattern, in air-tight case, and a clock with Graham Escapement, also in an air-tight case, were under test from 1923 February to 1924 March. These clocks, required for the Time Service at Mauritius, were tested at the request of the Crown Agents for the Colonies.’
1925: ‘A precision clock of Riefler pattern, in air-tight case, was under test from 1924 June to 1924 September. This clock, required for the Time Service at Hong Kong, was tested at the request of the Crown Agents for the Colonies. The clock gave a satisfactory performance, and has been despatched for shipment to Hong-Kong.’
It is understood that the clocks were the same as the Cottingham at Greenwich (with modifications?) and that the first was made by Cottingham and the second by Thomas Mercer Ltd., of St. Albans on his behalf under a contract signed on 19 October 1923 (Tony Mercer, 2003). In an obituary written by F. Mercer, the clocks are described as having a simplified Riefler escapement. Further research is required to establish the precise differences between the original Rieflers, the Greenwich Cottingham and the various Mercer versions. According to the obituary written by Eddington, Cottingham made just two Riefler copies in total (Greenwich and Mauritius) and Mercer made three, the one sent to Hong Kong, one which he kept himself and one which was kept by Cottingham and is now at the Science Museum. The dial of the latter carries the names of both Cottingham and Mercer on the dial. Click here for an image of the complete clock (with perspex replacement dome). It would appear however that Mercer also made at least one other copy signed with his name only. Click here to view.