Clocks logo
  Reader's letter | September 2008 | Clocks Magazine

Shortt answers

Re Bill Brading’s letter (‘Shortt regulator’, Clocks, July 2008) the ‘cylindrical object’ next to the Synchronome is the reason for the price reached by this clock. The cylinder contains the Shortt free pendulum, which works under reduced pressure, hence the copper cylinder. Shortt clocks were capable of extremely stable rates and were only superseded by the more refined quartz clocks. It is a master-slave system, in which the Synchronome does all the work to maintain oscillation of the master pendulum which then corrects the rate of the Synchronome. The system is explained in Frank Hope-Jones’ book Electrical Time-Keeping and there is a CD with animations of electric clock movements available from A Google search would also probably reveal some information.

I have no idea whether there are any Shortt clocks in New Zealand, but if Bill should visit England I would be happy to show him two in operation at the bhi.

Colin Fergusson, UK

I refer to my previous letter which related to the recent sale at Christie’s of an example of the Shortt Synchronome clock which you published in the July issue of your excellent magazine.

I now have to admit that this letter was written without my having the remotest idea of what a Shortt clock was, a situation that has now been happily corrected thanks to a fellow engineer directing me to a most informative website. The website is that of the Department of History and Science at Harvard University.

The master in the possession of Harvard University is numbered 17 and was set up in the University’s Institute of Geographical Exploration. It comprises two main components, namely a master having a pendulum kept as free as possible by being enclosed in an evacuated and temperature controlled chamber. The latter is the wall-mounted copper cylinder shown in the photograph of the one sold at Christie’s, and the more conventional slave Synchronome. It is still not clear how the two were kept in synchronism as there are no electrical interconnections. This may well have been magnetic. The system was claimed to be accurate to one second per year (one second in 30 million).

It appears that the description available on the website is very recent, having been provided by Richard Ketchen, horologist, in February 2008.

Extensive references are given.

Bill Brading, New Zealand

© 1977 to 2014 Clocks Magazine & Splat Publishing Ltd