The Development and Use of the Pilkington and Gibbs Heliochronometer and Sol Horometer

Abstract

To meet the continuing requirement for an accurate time standard to calibrate timekeeping instruments, George James Gibbs, later director of the Jeremiah Horrocks Observatory in Preston, invented in 1906 the Pilkington and Gibbs mean time universal Heliochronometer.

Gibbs went into partnership with the businessman William Renard Pilkington who travelled the globe selling Heliochronometers as far as Russia, South America, and Australia, often in regions where the telegraph, and later the radio time signals, were not available.

The Heliochronometer was claimed to provide direct reading mean time within an accuracy of 1 min. To convert solar time to mean time, the instrument used an innovative cam mechanism to apply the equation of time and provided other adjustments for longitude and latitude. The Heliochronometer was produced in six different types, and versions were made for the Northern and Southern Hemispheres. During production, the Heliochronometer underwent several design modifications to improve ease of use and to simplify manufacture.

The partnership entered difficult times and Pilkington developed his own mean time sundial, the Sol Horometer, which looked similar to the Heliochronometer but was sufficiently different to enable a separate patent to be issued in 1911.

Production of both instruments effectively ceased at the outbreak of WWI in 1914. Sales records indicate that only 1000 Heliochronometers were produced, but due to their robust construction, many are known to have survived and are still in use.

The Pilkington and Gibbs Heliochronometer and Sol Horometer are relatively unknown but might be the last sundials in the twentieth century to be used as a practical time standard.

This presentation will explore the purpose, development, and use of these instruments and compare the manufacturing techniques and achievable accuracy. It will place the Pilkington and Gibbs Heliochronometer in its rightful place in the chronological history of timekeeping.