Significant dials

This is one of a series of articles written for "Clocks" magazine by the late Noel Ta'bois, and reproduced with permission here as a memorial to him.

In this article, which appeared in 1985, Noel C Ta'bois reviews in question and answer form a selection of sundials which have unique features or a place in horological history.

Probably it was Egyptian dating from the 15th century BC and, as the photograph shows, was shaped like a letter 'T' with the cross-piece raised so that it cast a shadow on to the limb. This lay horizontally and was inscribed to indicate the time. Accounts of its method of use differ: some say that the cross piece was faced towards the east before noon and towards the west after noon, so that the instrument functioned something like a modern polar sundial, others that it was faced directly towards the sun at all times, so that the instrument functioned by the sun's altitude as does, say, a pillar dial.

Is there any evidence of sundials in Biblical times?

Yes. In II Kings 20, 9-11 and Isaiah 38, 7-8 reference is made to the dial of Ahaz but the form of the dial will probably always be conjectural. Also mentioned is the retrograde motion of the sun's shadow, an enigma which is yet to be scientifically explained. A puzzle of a similar nature is found in Joshua 10, 12-14, which reports a unique occasion when the sun stood still.

Which is the earliest dial whose design and method of use are not in doubt?

The hemispherium, a stone block hollowed out and fitted with a central vertical gnomon, the concave surface being marked with other hour and delination lines. It is attributed to Berosus, a Chaldean astronomer who lived in the fourth century BC , and it indicated time, not by the angle of the shadow as we are more accustomed to today, but by the position of the tip of the shadow. Because this tip always lay within a band bounded by the summer and winter solstice lines, part of the concave surface of the bowl served no purpose. Its removal led to the hemicycle which in turn points the way to the development of Greek and Roman sundials which also function by the position of the tip of the shadow.

Where in Britain, apart from in museums, can a Roman sundial be seen?

In the Rose Garden at Hever Castle in Kent where there is a marble hemicycle which is probably unique in that it shows equal hours. Other dials of this type show unequal hours, unequal because they divide the daylight from dawn to dusk into 12 parts which vary in length as the length of daylight changes with the seasons. Before taking the photograph I wedged an ice cream stick (it was a hot day!) in a crack at the top to show how a gnomon would cast a shadow on to the concave surface. The shadow tip falls just to the right of the third hour after noon and close to the summer solstice line indicating a few minutes after three on a midsummer day. This time will not be correct because the dial was designed for a latitude of 37 degrees and my gnomon should have had a downward tilt, but it would not hold in that position.

Incidentally, not far away in the same garden is an Italian 17th century polyhedral sundial with 21 individual dials on its various faces, all now sadly without styles and rather the worse for weathering.

Where is there a functioning polyhedral sundial with the greatest number of individual dials?

I do not know of one with more than 25, the number on an excellent example to be found in the gardens of Penshurst Place, also in Kent. In the same garden in a similar specimen but this was only nine individual dials.

Which is the earliest sundial in Britain

The Saxon dial on the south side of the churchyard cross at Bewcastle in Cumbria, 15 miles north-east of Carlisle. Its date is c675 AD. The vertical noon line and two lines at 45 degrees to it have short cross marks near their ends, marks which are characteristic of Saxon sundials and of the octaval system of time measurement. These crossed lines divide the daylight into four parts known as tides, whence are derived such words as noontide and eventide. Two hour lines between each of the tide lines divide the day in 12 hours, the duodecimal system, and are therefore possibly later additions.

Where in Britain is the best example of a Saxon sundial?

On a large stone slab over the south door of St Gregory Minster in Kirkdale, N Yorkshire. Its significance is that the inscriptions on the stone enable it to be dated to within the ten years 1056 to 1066. Saxon sundials gave way to rather crude mediaeval time indicators known as scratch dials or mass clocks which are to be found on many British churches.

Where are the largest and smallest scratch dials

The largest I have found is on the south side of the church of St Mary and St Bartholomew, Hampton in Arden, Warwickshire, and the smallest at the church of St Margaret, Tintinhull, Somerset. The former measures 23in across and the latter a mere 2in in height.

Where are the largest and smallest sundials?

If one rejects the doubtful possibility that the pyramids were intended to be sundials as well as burial chambers then the largest must surely be at an old and most remarkable astronomical observatory in India, 50 miles south-west of Delhi, at Jaipur where there are many giant instruments the largest of which, the Samrat yantra - the 'supreme instrument' - is an equinoctial sundial with a gnomon rising to a height of 90ft. The style lies parallel with the earth's axis, or to put it another way, it is set at an elevation of 27 degrees, the latitude of Jaipur, and points to the north celestial Pole.

The smallest sundial of which I have knowledge consists of a tiny gnomon hinging on a n equally tiny dial plate in the centre of which is a miniature magnetic compass, all neatly mounted on a finger ring. Unfortunately I cannot now recall where I read about it.

Where are the most interesting public sundials?

To my mind, in the University towns of Oxford and Cambridge. The front quadrangle of Corpus Christi College, Oxford, is enhanced by a tall central stone column exhibiting in brilliant colours several types of sundials as well as legends, shields, carvings, and calendar, planetary and moon tables. It is known as the Pelican or Turnbull dial and it was skilfully and delightfully restored in 1976.

On the north wall of the Old Court at Queens' College, Cambridge is the famous so-called Newton's Dial although there is no evidence that Sir Isaac Newton had anything to do with it. It has much dial furniture in colour giving a wealth of information, and below it are three rows of figures to enable it also to be used for finding the time by moonlight.

Both these dials have had publications devoted solely to them; there cannot be many dials so honoured!

Where can one find sundials made by famous people?

Above the front door of George Stephenson's cottage in Paradise Row, Killingworth, Northumberland, is a vertical sundial made by the famous railway engineer himself. It is in a good state of preservation but the gnomon appears to be bent towards the east.

In the church of St John the Baptist, Colsterworth, Lincolnshire, tucked away behind the organ and difficult to photograph, is a stone dial plate cut with a penknife by Isaac Newton at the age of nine. The stone - it has no gnomon - is mounted (upside down1) below a carved wooden effigy of the scientist.

Where can one see a stained glass sundial in a church window?

At Ledbury, Hereford, at the church of St Michael and All Angels. The sundial is not in its original position for it is designed to face south and is now in the west window. This dial too has no gnomon and has been mounted upside down. To the glazier it probably looked like a clock face so it was natural to put the 12 at the top!

Which is the most delightful modern horizontal sundial?

This is very much a matter of taste, but for me it is the Meadow Brown Butterfly dial made by Brookbrae.

Where in England during 1984 did Brookbrae exhibit a large analemmatic dial?

In the garden of the George Wimpey Homes at the Liverpool International Garden Festival the central attraction was a sundial designed by Christopher St J H Daniel. It was laid out on the ground and measured 15ft across. The visitor stood at the appropriate point astride a line marked with the mouths. His shadow (if he had been lucky enough to pick a sunny day!) fell across an ellipse of hour stones to indicate the time. Now that the Festival has closed, negotiations are taking place to try to find a permanent home in Merseyside for this intriguing sundial. There is now no public analemmatic sundial in this country, but they do exist abroad.

Which is the first commercial sundial to have its dial plate made by computer?

The Sun-Vial designed by larry Bohlayer the President of Celestial Products Inc of Middleburg, Virginia, USA, who manufacture it. When an order is placed for the Sun-Vial, the latitude and longitude of the place where it is to be set up are fed into the computer which then draws two groups of S-shaped curves labelled with times and dates, on a piece of translucent plastic. This is then housed in a glass cylinder, and a spot of light produced by a sunbeam passing through a small hole in the brass cap falls on to the curves to indicate clock time with an error of less than half a minute. As each group of curves is valid for only six months they are changed over at the solstices.

Which is the most interesting sundial in the USA?

My travels in that country are very limited! However, I commend the memorial to Dr Lyman James Briggs, a past director of the National Bureau of Standards. The Bureau and the dial were originally in Washington but both have been moved some 15 miles north-west to Gaithersburg Maryland. On the sloping front of the memorial are three polar dials, the centre one showing sun time and the two others clock time for six months each. Above these is a sunburst with a central hole which throws a spot of light on to an arc at the back. On this arc are an analemma indicating mean time moon and the date, and scales showing the sun's declination and altitude at noon.

Are there any sundials which function other than by a shadow or a spot of light?

Yes, the Optical Sundial invented by Gordon Benoy at his home near Newark. It is an equinoctial dial with a central glass cylindrical lens which casts a diacaustic curve on to a white dial plate calibrated in summer time. Its advantages are that it functions well in weak or hazy sunlight, and the moon gives quite a good image even when nowhere near full, but to translate that reading into clock time is another story! Its disadvantage is that it will not function between the equinoxes when the sun is below the celestial equator. Unfortunately this exquisite sundial is no longer in production but a specimen is in the Science Museum in London.

Where in Britain can one see a modern mean time sundial?

On the south side of the National Maritime Museum at Greenwich where stands the Silver Jubilee Sundial designed by Christopher St J H Daniel and modelled in bronze by Edwin Russell. Two dolphins on the crest of a wave hold the equinoctial dial plate in their mouths and on this the sunlight passing through the tiny gap between the tail fins indicates clock time. There are two dial plates which are interchanged every six months.

The earliest sundial has been mentioned. Which is one of the most modern?

Here may I be forgiven for blowing my own trumpet! The managing director of Brookbrae, having seen my Concorde Mystery clock and concluding that I might know something about the famous aircraft, asked me if I would make a sundial with a model of Concorde as the gnomon, for a customer in Oxfordshire who wanted to present it to her husband, a Concorde fanatic, as a retirement present. To design it I made a jig to study, in a matter of minutes, the shadows that this particular aeroplane would cast throughout the day and throughout the year.

In this review I may well have raised more questions in readers' minds than I have answered. If so, and if it provokes further reading, that is all to the good. I have tried to give correct answers but some could be contested, particularly where matters of opinion are concerned. If any readers know better, it is hoped they will write to the editor to say so!