Seven Dials Covent Garden is a unique quarter of London whose star-shaped layout remains as constructed in the early 1690s. It was brought back to life largely through the dedication of the Seven Dials Trust, working in partnership with the local authorities and landowners for nearly forty years.

The Trust appointed Gordon E. Taylor (formerly of the Royal Greenwich Observatory) as its astronomical consultant. The base of the Sundial Pillar had to be aligned in a North-South direction, but how does one determine direction accurately in a crowded, built-up area such as Seven Dials? Certainly nothing as crude as a magnetic compass can be used. Helpfully, John Strype's 1723 map illustrated both the final layout of Seven Dials and the base of the Sundial pillar with a degree of accuracy confirmed in John Rocque's map of 1745. The latter also illustrates the early street names - the Monmouth Street on the top left is now Shaftesbury Avenue.

The direction ('azimuth' in astrological terminology) of the Sun was noted at certain times by marking the shadow line cast by a vertical rod onto the ground. These times were recorded using a digital watch which displayed GMT to an accuracy of one second. These times, together with the longitude and latitude of Seven Dials, were fed into a computer. A specially-written programme was used to call up a data file containing an ephemeris (a set of positions) of the sun in astronomical coordinates, and its position in the sky as seen from Seven Dials at the observed times was calculated. From this a true North-South line was derived.

The mathematical knowledge necessary to construct accurate sundials, whether trigonometrical or the geometry of projection, was part of Renaissance Europe's rediscovery of ancient mathematics and discoveries pioneered in the Arab world. In the mid ninth century, Muhammed Ibn Jafir Al-Battani first solved a spherical triangle, given two sides and the included angle. At the beginning of the thirteenth century, Ali Ibn Omar Abul-Hassan al-Marrakushi introduced the idea of making all the hours of equal length. Astronomy flourished throughout the Muslim world from the ninth through to the sixteenth century, from Arab states, through Persia into Central Asia.

This illustration by Persian astronomer Al-Biruni (973-1048) depicts the phases of the moon.

In Europe, these discoveries coincided with an upsurge of interest in recreational mathematics and an everyday need for reliable public timepieces. So sundials were erected in public places to regulate the growing number of clocks which, though popular, were still unreliable and inaccurate, amusingly illustrated in the contemporary quotation from the Athenian Mercury (1692/3).

The position of the base of the Sundial Pillar can be clearly seen on two contemporary maps: John Rocque's Map of London (left) published in 1746 and a Map of the Parish of St. Giles-in-the Fields (right) published c. 1720. On both these maps the position of the base is identical and one face is opposite Queen Street (now Short's Gardens).

Astronomer Gordon E. Taylor's conversion tables.

Gordon E. Taylor's chart to convert Apparent Solar Time to Greenwich Meantime.

The Time Plaque sponsored by musician Dave Stewart raised £12,800 for The Trust.

For more detail, read below: Gnomonics – The Construction of Sundials written by Frances Massison, Curator Museum of the History of Science, University of Oxford:

Seven Dials was laid out by Thomas Neale MP in the early 1690s. Neale commissioned England's leading stonemason, Edward Pierce, to design and construct the Sundial Pillar in 1693/4 as the centrepiece of his development. It was regarded as one of London's 'great public ornaments' and the layout and identity of the area revolved around it. On October 5th 1694, the diarist John Evelyn went "to see the building beginning near St Giles, where seaven streetes made a starr from a Doric Pillar placid in the middle of a Circular area."

The Seven Dials Sundial Pillar that you see today is a meticulous reconstruction of that designed and built by Pierce.

Every book on London, including the official Survey of London, refers to the story that the Pillar was pulled down in 1773 by the Mob looking for buried gold. However, research by Trust Chairman David Bieda revealed that the Pillar was removed by order of the Paving Commissioners in 1773 in an attempt to rid the area of 'undesirables' who congregated around it.

“The removal of that great public ornament the Seven Dials, (or as the French refugees of that quarter used to call it, La Pyramide) and the discontent it has occasioned will, it's thought, make the commissioners, or their deputies, more cautious how they take such liberties again, either from false œconomy, secret avarice, or partial complaint. It is certain the nuisance complained of is not thereby removed: the centre where the column stood, being a rendez-vous for blackguards, &c. as much as ever; but, alas! The elegant object, seen from seven different avenues, is and will be no more, unless it rises again in some or one of the commissioners' or surveyor's gardens, or sinks into some body's pocket, while a wide, dreary, and naked prospect of the blackguards, &c. only remains.” — Morning Chronicle and London Advertiser,  June & July 1773.

The remains of the Sundial Pillar were later purchased by the architect James Paine and taken to his home at Sayes Court, Addlestone, but were not re-erected there. In 1820, the remains of the Pillar and the very worn dialstone were purchased via public subscription and re-erected on Weybridge Green as a memorial to the Duchess of York.  Various attempts were made by the London County Council, the Greater London Council and Camden Council to have the Pillar returned to its original site in Seven Dials, but Weybridge Council refused. In 1984 the intricate and fascinating project to reconstruct the Pillar began.

Even though clocks existed in the 1670s, public sundials were an important part of everyday life in London and throughout Europe. This story from the Athenian Mercury of 1692/3 (iv, No. 4), the year before the erection of the original Sundial Pillar, provides a graphic illustration of the need for sundials:

"I was walking in Covent Garden where the clock struck two, when I came to Somerset-House by that it wanted a quarter of two, when I came to St. Clement Danes it was half past two, when I came to St. Dunstans it wanted a quarter to two, by Mr. Knib's Dyal in Fleet-street it was just two, when I came to Ludgate it was half an hour past one, when I came to Bow Church it wanted a quarter of two, by the Dyal near the Stocks Market it was a quarter past two, and when I came to the Royal Exchange it wanted a quarter of two. Thus I averr for a Truth, and desire to know how long I was walking from Covent Garden to the Royal Exchange?"

The following extracts are from The Seven Dials by founder trustee, the late Sir John Summerson.

Book  THE SEVEN DIALS - Erected 1694, Removed 1773, Reconstructed 1988-9.
Published by  The Trust in 1989.