ST JOHNS CHURCH in Hampstead’s Church Row lies 0.1811 degrees west of the Greenwich Meridian. Its longitude is 0.1811 W. This fact is unimportant to most people living in the area because Hampstead is high above sea level. However, an accurate measurement of longitude (and latitude) is extremely important to seafarers.
I am no expert in navigation, so please excuse me if the following explanation seems oversimplified. Latitude can be assessed measuring the positions of fixed astronomical objects such as the sun and the North Star and relating them to the horizon. Longitude proved far harder to measure because it involves relating the local time to the time at a reference position, now at the commonly accepted Greenwich Meridian. The difference in the time at a position in the sea and that at Greenwich is the way that the calculation of longitude is made. Local time can be measured by means such as observing where the sun appears in the sky. Until the 18th century, no clocks existed that could reliably record the time at the reference position whilst at sea. The uncertainty involved in assessing longitude resulted in many unfortunate disasters at sea. In 1714, the British Parliament passed the Longitude Act of 1714, which offered prizes for a simple and practical method of assessing longitude out at sea.
To solve the problem, a clock that accurately recorded the time at Greenwich was required. This clock had to remain accurate despite the many changes that it would encounter as it moved across the seas. It had to record Greenwich Mean Time accurately and reliably despite changes in temperature, humidity, air pressure, motion of the vessel, and so on. Major advances in the solution of this demanding technical problem were made by a carpenter and clockmaker John Harrison (1693-1776), who was born near Wakefield in Yorkshire. For over 40 years, he worked on the problem, producing ever more reliable chronometers, which were tested at sea. Eventually, his H4 design became the prototype for what was best suited to the job. With the help of his son William Harrison (1728-1815), Harrison was rewarded with much of the financial reward offered in the wording of the Act passed in 1714.
When he died, John Harrison was living at his home in Red Lion Square in Holborn, whose longitude is 0.1186 W. He is buried in the same churchyard as the great artist John Constable: in the cemetery next to St Johns Church in Church Row, Hampstead. His tomb, which close to the south wall of the church, is of Portland stone and decorated with pilasters in the style of the architect Robert Adam. The north side of this shoebox shaped monument has an inscription that gives a brief biography of John Harrison. His wife, Elizabeth, who died in 1777, aged 72, is also commemorated on this tomb. The south side gives a short biography of his son William, who is also buried here. In addition to helping his father test his chronometer, he was also a Governor of the Foundling Hospital in London and High Sheriff of Monmouthshire (in 1791).
According to Christopher Wade in his “Buried in Hampstead”, several persons, who were not resident in Hampstead were interred in the churchyard of St John. The Harrisons figure amongst these. Wade states that there is no evidence that John Harrison and his family had any connection with Hampstead. He speculates that they obtained a burial plot there because they were “… affected by the charm of this particular graveyard.”
The graveyard still retains its charm. It contains the resting places of many people, who have achieved fame in diverse fields of activity. Some of them are mentioned in my new book about Hampstead, which is available as a paperback from Amazon (https://www.amazon.co.uk/dp/B09R2WRK92) and as a Kindle e-book.