BOOK REVIEW The final masterpiece of John Harrison Sleeping in Oblivion, John ‘Longitude’ Harrison’s Forgotten Masterpiece, by David Heskin. Second edition, published 2008 by Soptera Publications, Loughborough, Leicestershire, (email@example.com <mailto:firstname.lastname@example.org>); hardback, 201 pages, 20x27 cm; ISBN 978-0-9555875-2-8 (hand bound hard back) and 978-0-9555875-1-1 (comb bound paperback), 95 figures (b&w photographs) and 8 section frontispieces (white on grey design studies). (Text in English). Index, Terminology (Glossary) and Abbreviation List. Available from Soptera Publications. (Text in English). Index, Terminology (Glossary) and Abbreviation List. Available from Soptera publishers Current prices at http://soptera.blogspot.com., or consult at the Library & Research Center at the National Watch & Clock Museum. (The author has restricted the lending of the copy for fear the lender will make photocopies) Even the casual timekeeping enthusiast will be familiar with John Harrison’s great achievement in winning the Longitude prize by increasing the sustained performance of seagoing clocks sufficently to allow accurate longitudinal navigation at sea. Far fewer realize that Harrison’s success was due to meticulous, systematic and scholarly work on various issues affecting the accuracy of timekeepers, work he continued for many years after building his prizewinning marine chronometer H4 around 1757. But hardly anybody knows that, in the final phases of his life, John Harrison published in 1775 - a year before his death –a manuscript called “Concerning Such Mechanisms as will Afford a Nice, or True Measurement of Time, …” summarizing the work of and horological insights gathered over an entire lifetime. The text repeatedly refers to a precision longcase regulator Harrison was building at the time, and which would incorporate all of Harrison’s ideas, and which he expected to be accurate to better than one second in 100 days. Sadly that clock was never completed by Harrison. Its final Harrisonian state was never fully documented, and the clock was only completed in the 1920s by Rupert Gould. That clock is known as the Royal Astronomical Society Clock (after its owner). Both the 1775 text and the RAS clock have since then been mostly ‘sleeping in oblivion’, a term used by Harrison himself when writing about what he hoped to avoid for the future of his discoveries. The author of the book under review, David Heskin, is convinced that a thorough study of – and experimentation with the design of – the RAS clock, combined with a careful reading of the Harrison text will provide new knowledge of Harrison’s understanding of precision horology. As a step in that process he set out on the arduous journey to build a functional replica of the RAS clock. That task was greatly complicated by the fact that the RAS clock has never been fully documented, and Heskin was never allowed to physically examine or handle it, let alone disassemble the movement. The movement was on display in a glass show case in Greenwich, and the author -starting in 2002-painstakingly recorded it through pencil and paper sketches as photography was not allowed. The book is a detailed description and documentation of the ‘functional replica’ of the RAS clock as built by Heskin at the beginning of the 21st century. The author, of course, realizes that his publication, due to the handicaps imposed by the way it came into being, falls far short of the desired ideal outcome, a detailed and dimensioned technical documentation of the actual, historic RAS clock movement (as completed by Gould). But Heskin is convinced that his approach is a viable first step in the process of rescuing Harrisons horological insights imbedded into the RAS movement from being forever lost ‘in oblivion’. He expresses the hope that other clock builders will use his data to build other functional replicas of Harrisons ‘Final Regulator’. The book itself makes for fascinating reading for the small target audience of technically inclined Harrison fans. While the ultimate purpose presumably is to describe in great detail how the RAS movement and its grasshopper escapement works, in practicality it reads more like a step by step, ‘how to’ guide for building and assembling a replica movement. The core of the book, its largest section, labeled ‘Detailed Pictorial’, consists of 83 pages, each made up of one or several detailed black and white photographs of parts, components and subassemblies and the complete movements. Many of these are like de-facto dimensioned drawings and manufacturing instructions of the various parts, but also a series of a dozen close-up photos showing the operating sequence of Harrisons design for the grasshopper escapement of the RAS clock. Heskin had to make many choices along the way to define his concept of a ‘functional equivalent’ replica. While he meticulously maintained the overall geometry of Harrison’s design, and used pairs of large anti-friction wheels for the pivots in the gear train and self lubricating lignum vitae components in some places, he used mostly modern standard metric screws and industrial ball bearings for the great arbor and the weight pulleys, arguing that Harrison would have used these components had they been available in his time. The resulting movement is a curious hybrid of traditional and modern elements, and this reviewer found it hard to judge definitively how closely the performance of the resulting mechanism would match Harrison’s original ideas. Since the time that Heskin started building his ‘functional replica’ and wrote his book, the owners of the original Harrison clock have allowed a scholar to actually disassemble and measure the clock and it appears that the dimensions that Heskins had determined based on his sketches and observations, as well as from various published sources, are amazingly close to correct. Rumor has it that currently there are two other parties in the early phases of building replicas of the RAS clock. So we may soon find out if Harrison’s performance claims of ‘one second in 100days’ are factual. (The Heskin book was written before the author had any long term performance data from his clock). Other sections of this book cover: ‘Principles of Precision’, talking about concepts such as the gridiron compensating pendulum or the escapement action; ‘Construction’; ‘Assembly’; ‘Operations’, outlining some practical issues about running the resulting timekeeper. While reading –even in great detail- about an important clock movement can never fully replicate the experience of handling, ‘playing-with’ and experimenting with an unusual or historically significant clock movement, this reviewer found the process of studying the RAS movement in this text and image format surprisingly satisfying, and an obvious alternative for learning quite a lot about an artifact whose custodians would never let us examine it physically. Despite the obvious limitations of his ‘functional replica’ approach to truly replicate any original, Heskin deserves the gratitude of Harrison scholars around the world for doing his share of rescuing key facets of Harrison’s longcase precision movement design knowhow out of oblivion by not only building his replica, but for making its construction details accessible through this book to a wider audience. Fortunat Mueller-Maerki Sussex, New Jersey February 22, 2009 .