The dial is only the second English example known, the other being in the Horniman Museum, London. It is unsigned; however, the circular map of England on one leaf is from a copper plate that can confidently be ascribed to Charles Whitwell (d. 1611) and it is probably an example of work from his early period, the last decade of the sixteenth century.

The instrument is octagonal in form and measures 84 x 62 x 19mm. It is made from ivory, with hinge, catches, and ring all of silver. The lower leaf holds a magnetic compass, and the underside of the upper leaf is embellished with the map of England, 52mm in diameter and displaying the counties with their boundaries outlined in colour. Inside, both leaves are decorated in a simple manner with small punches, the indentations being coloured in red, green or yellow. On the outside the ivory is entirely without decoration.

The compass on the lower leaf has a compass rose of paper, printed with sixteen triangular pointers, and a blued-iron needle, marked 'N' and 'S' in a gold-coloured medium. Around the compass well are the hour lines marked with roman numerals and divided to quarter-hours.

When closed, the two leaves are held firmly together by a pair of silver catches and pegs. The use of silver for these fittings is quite contrary to continental practice for this type of dial.

To use the dial, the leaves would have been opened with the face containing the map positioned vertically and held in place at 90° to the lower leaf by a catch at the back of the hinge. Between the leaves a string gnomon, now missing, would once have been attached, and it is this that would have cast a shadow over the hour lines on the lower face, indicating the correct time once the dial had been oriented north-south by means of the compass.

Where the gnomon met the upper and lower leaves the number '52' is punched, indicating the latitude at which the dial could be used. A small dial such as this made for a latitude of 52° would serve for Oxford, London and Cambridge.

Like the Oxford instrument, the dial in the Horniman collection is also made from ivory, is octagonal in shape and is quite plain on the outside. It is only slightly smaller than the Oxford dial and it too carries a map of England and has a printed compass card, but in neither respect is it identical to the Oxford dial.

The Horniman dial has a silver hour ring and in contrast to the Oxford example its map and compass card are not coloured and the magnetic needle is shaped like an arrow, pointed at North and feathered at South. Also, unlike the Oxford example, it bears a set of initials - 'R × G' - which could be those of the dial's maker or of an owner.

The Oxford and Horniman dials do have a decorative feature in common: surrounding both the compass and the map are two concentric circles which are themselves embraced north and south by circular arcs. A point of difference is that the lines are single on the Horniman dial, but doubled on the Oxford dial.

In trying to assign the Oxford dial a date, maker and place of manufacture, several of its features are of particular interest: the printing of the compass card, the shape of the magnetic needle, the appearance of the map and the characteristics of its engraving.

The compass card or wind-rose on the Oxford dial is printed with sixteen triangular points, between which are a further sixteen divisions at the outer rim showing the thirty-two winds, or points of the compass. The North point is shown by a fleur-de-lis, and on the rim at the East point is a small cross. There is no other decoration or any colouring or numbering.

Remarkably, there is a second wind-rose underneath the first which can be made visible by shining a light through the translucent ivory of the bottom of the dial. Like the first it has sixteen points. The magnetic north is marked by a similar fleur-de-lis, but it is placed in the compass box one point (i.e.11¼°) east of the dial's meridian line. Unlike the upper wind-rose, the triangular points seem to be coloured, in white, black, red, and green.

The magnetic declination at London in 1580 was 11° 15´ east. It then moved gradually west becoming zero in 1657. Late Elizabethan dials and magnetic compasses in compendia have the magnetic north marked on them at one point to the east, so the evidence given by the concealed card points to an Elizabethan date for this diptych dial. A person using the dial in around 1660 presumably placed a new, and plainer, card over the original one.

As far as the maker of the compass card is concerned, cards used by Humfrey Cole (d. 1591) in his astronomical compendia are much more elaborate than either found in the Oxford dial, having thirty-two ribbon pointers in a variety of colours, many bearing the name of a wind. The same pattern is found cut by Augustine Ryther (fl. 1576-1594) on a plane chart dated 1592 that he produced for Thomas Hood.

A plainer and larger compass card but of similar design to the Oxford cards can be found on a compendium by Whitwell (who was apprenticed to Ryther) in the National Maritime Museum. However, on two compendia dated 1602 and 1606, Whitwell used a version of the elaborate card of Cole and Ryther. He was not alone in using different types of card, however, as Elias Allen (d.1653), who was apprenticed to Whitwell, is also known to have used both patterns of card.

While the compass cards on the Oxford diptych dial are smaller than those on the Cole compendia, in their conception they resemble those found on Whitwell and Allen compendia. The Horniman dial, likewise, has a card of the same size which closely resembles both cards on the Oxford dial.

The magnetic needle on the 1606 compendium by Whitwell is of the same style as that on the Oxford dial, each arm being an elongated lozenge bearing the letters 'N' and 'S'. The Oxford needle is, however, at 37 mm in length, some 13mm shorter than that on the compass of the Whitwell compendium.

It is possible that the Oxford needle was a replacement provided at the time the new compass card was fitted in the 1660s. This would, of course, suggest that the Whitwell compass needle is also a replacement. The needles on the other compasses mentioned above resemble arrows, and different patterns of needle, made in blued iron, are to be found on other dials of the period between 1590 to 1610. All that can be said with confidence is that the Oxford dial has a needle that is not a modern replacement.

Both the Oxford dial and the one in the Horniman Museum have circular maps of England. Both also show the eastern side of Ireland and a portion of Scotland, are labelled the same way, have a scale in the Bristol Channel, and have a compass rose above Norfolk. On the Oxford map the arms of the three kingdoms are also shown.

The high quality of the engraving of the map on the Oxford dial is also very apparent. On the Horniman dial the counties are outlined crudely and are marked with an initial only; on the Oxford map the counties are better delineated and the lettering is finer, and their names are abbreviated or even, in a few cases, given in full.

An example of a map of England within a circle is to be found in Arthur Hopton's Speculum topographicum: or The Topographicall Glasse which was published in London in 1611. The map is reproduced on pages two and eighty-six of the book as well as on the title page, but it is larger than those on the dials, having a diameter of 83 mm.

The copper-plate cut for the Oxford map could have been produced some years before the dial was made. The quality of the engraving points to an engraver with the skill of Ryther, Whitwell or Allen. It is conceivable that the map was modelled on a map of England and Wales engraved by Ryther that was published by Christopher Saxton in 1579. This was the first printed atlas of the country, and the first uniform national atlas for any country. Both Ryther's map and that on the diptych dial have the sea stippled by the point of a burin, and Ireland, Scotland and the three seas are all named in the same way.

Ryther is known for engraving playing cards as well as maps and instruments. His cards, datable to 1574, each have an outline of a county with a few features and initials of towns. The top and bottom of each card has information on the size of the county and its products. There are brief comments, for example:
'SVFFOLKE a ritch & plesaunt coutrey Aboundinge in cheese, & butter, & store of cloth', and 'NORFOLKE large, welthy, & very populous. Full of corne, sheepe, & worsted commod ities'. Such observations seem to anticipate the motto found circumscribing the map of England on the Oxford dial: 'OF THESE THINGES FOLLOWINGE, THIS FAMOVSE ILE IS FVEL, MOVNTAYNES FOVNTAYNES BRIDGES CHVRCHES WOMEN & WOLL +'.

The map is the part of the diptych dial that has the most information suggesting a probable maker and date for the instrument. Many instruments can be dated by the numbers punched into them, but while the latitude number '52' on this instrument is punched, it is not easy to trace because punches were not generally used by Elizabethan engravers and scarcely at all by their successors in the seventeenth century (the occasional exception being their use for the figure zero). Punches are suitable for ivory and wood, but the use of ivory during the relevant period is rare and the earliest dated wooden instrument to survive is a nocturnal of 1637 in a private collection.

However, the map engraver's hand shows certain features, and some of these can be picked out on the Oxford instrument. The only numbers on the map are with the scale, but they are under one millimetre in height, and therefore have no diagnostic value. Amongst the uppercase letters the 'S' tips over towards the right, and the bottom bar of the 'E' is extended. In the lower case letters, the 'p' has a gap at the top between the risers, and the 'r' has its upper curl distant from the riser. These, and other characteristics, are all found on examples of the work of Whitwell, including, for example, on a vertical sundial already in the Museum's collection (Inventory no. 52,101).

At the present time, thirty instruments have been identified as having been made by Whitwell. In addition, he is known to have engraved maps of Jerusalem, France, Surrey and Kent, as well as illustrations for books such as William Barlow's The Navigators Supply (London, 1597) and Thomas Hood's 1598 work on the making and use of the sector.

In many of his products, Whitwell had to engrave very small letters and numbers, and from the variety of instruments surviving, as well as from the level of the patronage he received, it is clear that he was the leading engraver of mathematical instruments between 1590, when he completed his apprenticeship with Ryther, and 1611, the year in which he died.

The round map is a small commission, and was probably done in his earlier period, 1590-1600. Of course, the plate could have produced copies for many years more, so the date of the manufacture of the dial remains somewhat inexact. The Horniman dial also has to be included in a dating estimate because its form suggests that both ivory dials came from the same maker.

The production of diptych dials with magnetic compasses was a trade particularly associated with Nuremberg during the sixteenth and seventeenth centuries. Nuremberg dials were made in ivory, boxwood and, after 1608, pearwood. Ivory examples from the 1550s are preserved, but most extant Nuremberg ivory dials date from the seventeenth century.

Nearly all ivory diptych dials from Nuremberg are rectangular, with a few oval in form, although the Harvard University collection of ivory diptych dials contains three from Nuremberg that are octagonal in form, one dated c. 1620, the other two c.1650. Similar to the dials from Nuremberg are French ivory magnetic azimuth diptych dials which were made in Dieppe during the second half of the seventeenth century. Only a very few are octagonal, however, most being square or rectangular.

Harvard's collection of diptych dials, which numbers eighty-two in total, does not include an English example, neither does the collection of fifty in the Whipple Museum, Cambridge. Until now, Oxford's collection of over a hundred and twenty diptych dials contained no English example either.

Gerard L'E. Turner

Further reading: Penelope Gouk, The Ivory Sundials of Nuremberg, 1500-1750 (Cambridge, 1988) and Steven A. Lloyd, Ivory Diptych Sundials, 1570-1750 (Cambridge, Mass., 1992).