Analysis of the Mechanisms for Compensation in Clock B

This chapter assesses the design requirements of the grasshopper escapement, the pendulum and suspension spring to provide compensation for changing density and viscosity of the air surrounding the pendulum and changing escapement torque. It assesses the key components of the Harrison system: a pendulum bob of modest mass; a pendulum operating at a large running arc; and the grasshopper escapement’s increased torque delivery, ability to run without lubrication, its composers that allow fine adjustment to the torques delivered before and after the escaping arcs are reached and the importance of the thickness of the suspension spring that runs within circular cheeks. It also compares the system to the traditional pendulum clock design that traditionally employs a pendulum with a large mass and high-quality factor—high Q. Furthermore, it discusses Harrison’s stipulation that the pendulum needed to slightly reduce its length when warm.

The Origins of John Harrison’s ‘Pendulum-Clock’ Technology

Working in Lincolnshire in the 1720s, John Harrison (1693–1776) established a unique approach to making accurate pendulum clocks that was born from his experiences in the family business that served country estates in Yorkshire and Lincolnshire. The chapter charts Harrison’s early clock-making practice, inspired by local traditional clocks, and his unique interpretation. He used wood for the frames and most of the wheelwork before key elements of his precision timekeeping crystallised in the making of an estate clock for Brocklesby Park in Lincolnshire. Notably, the elimination of requirement for lubrication formed a solid bedrock for his life’s work in precision in this field. It examines Harrison’s early influences and progression of thinking through documentary evidence and artefacts to introduce the beginnings of his unique approach to precision pendulum clock making.

Decoding the Physical Theory of Harrison’s Timekeepers

Harrison worked in an extraordinary time and was privileged to rub shoulders with many of London’s prominent figures in the history of science. Importantly his first sponsor and mentor, George Graham FRS, was undoubtedly a great source of inspiration and a connection to the resources of the Royal Society. This paper presents Harrison’s own writing, drawing resonance and parallels with contemporary popularisers of Newtonian science, such as Nicholas Saunderson and Venteri Mandey. It also examines connections to later scientific work and oscillator theory and that Harrison’s often-cryptic expression demonstrated an advanced understanding of the physics of pendulums swinging in free air.

Completing Clock B

Charles Frodsham & Co. completed the work on Clock B that finalised its aesthetic and enabled it to run effectively in a sealed case with minimal human interaction for very long periods. This chapter documents their work on the clock and discusses their choices for implementing modern materials, such as Polyetheretherketone (PEEK) as bushing for gold pivots in the grasshopper escapement. It presents the reasoning for changing Burgess’s original method of driving the clock, which is found on Clock A (also known as the Gurney Clock). Instead of using a weight on a Huygens endless chain with motorised rewind, the team elected to use an unobtrusive weighted arm with electrical rewind to drive the clock.

Reflections on Making Clocks Harrison’s Way

Martin Burgess reflects on his experiences in making Clocks A and B and outlines some vital guidelines to anyone considering making a regulator clock that follows Harrison’s principals. For example, the pendulums on Clocks A and B are both made from Invar, an alloy developed in the early twentieth century that has a very low coefficient of thermal expansion. In keeping with standard practice, the pendulums are compensated for temperature change by inclusion of a small brass block that supports the pendulum bob. Any downward expansion of the rod is counteracted by an upward expansion of the brass—the dimensions of the brass block is easily calculable. Burgess later understood that the modern form of pendulum, though easier to construct, lacked the frictional properties of the gridiron, which come to play in compensating for changes in barometric pressure.

Introducing Martin Burgess, Clockmaker

In 1775, two years after receiving the second half of the Longitude Prize, John Harrison (1693–1776) published a book, which, among other things, described a pendulum clock that could keep time to one second in 100 days. His claim of such unprecedented accuracy for a clock with a pendulum swinging in free air (i.e. not in a vacuum) was met with ridicule both at the time of its publication and for the next two centuries. This chapter describes the early life of Martin Burgess, the clockmaker who proved that Harrison’s claim was indeed true. Like Harrison, Martin was a self-taught clockmaker. From his training in the arts and crafts, he saw the mechanics of clockwork as sculpture in its own right, each element contributing to the overall design. Martin’s upbringing, his education, and his unusual lifestyle and approach were all crucial to his quest to prove that John Harrison was right.

Rescuing Martin Burgess’s Clock B

Intrigued by a forlorn and dilapidated yet compellingly unusual clock in a repair shop above an antique furniture dealer’s nineteenth-century mid-town New York building, Saff’s journey began. This clock was originally commissioned by rock music impresario, Simon Napier-Bell, who requested that it be suitably mesmerising that it might preoccupy clients with whom he was negotiating. A small presentation plate on the clock led the author to Burgess’s work on Harrison’s approach to horology, which defied the commonly accepted view that precision timekeeping is only achievable by high-Q pendulum systems. The chapter identifies a parallel between Harrison’s late regulator and Burgess’s Clock B—both of which were never finally adjusted to their makers’ satisfaction—and outlines the author’s quest to prevent further ‘scandalous neglect’.

Crunching the Numbers

This chapter offers an in-depth analysis and examination of measurement data for Clock B, trialled from 2012 to 2016 at the Royal Observatory, Greenwich. It evaluates the merits and shortcomings of barometric and temperature compensation, based on data gathered after adjustments made to the clock in 2014. The clock clearly met John Harrison’s claim of accuracy to within one second in 100 days in the 2015 peer-reviewed trial; however, Harrison did not outline the conditions of measuring accuracy. This paper explores potential methods for quantifying clock accuracy and lays bare details of the electronic measurement system. The raw data yielded some apparent anomalous values, which are unpicked and explained.

Adjusting and Testing Clock B at the Royal Observatory, Greenwich

This paper provides a narrative of the trials and adjustments of Burgess Clock B at the Royal Observatory, Greenwich from 2012 up until 2015, first briefly contrasting this author’s experiences in rating and adjusting conventional regulator technology. Secondly, this paper explains in simple, practical terms how Harrison’s whole precision pendulum system works and comments on the extraordinarily successful results of the trials.

Introducing the Precision Pendulum Clock

This chapter provides historical context to the development of the precision pendulum clock. It primarily looks at the historical astronomical clocks at the Royal Observatory, Greenwich; their use, acquisition, and modification to demonstrate that there was continual desire for better timekeeping in the Observatory. It argues that the core theoretical principals in clock making began with Robert Hooke’s demonstration to the Royal Society in 1669 and remained largely unchanged through to the obsolescence of pendulum time standards in the mid-1900s. By studying historical experiments into the effects of weather variation on pendulum clocks, it will familiarise the reader with the physical effects on pendulum clocks that are critical to the study of Martin Burgess’s Clock B.