Introduction

From the 14th century to the early 19th century in Europe, chequered scales like , and later , are sometimes found on clocks, astrolabes and other measuring instruments, globes and armillary spheres, in book illustrations and also on maps - where the practice still survives. This article, in a preliminary and tentative way, presents some of the evidence I have found and suggests a reason for the phenomenon.

The evidence

I have a list of around 300 items, about half of which have chequered scales. It should be stressed that my material is not a statistical survey, but simply what I have been able to find.

c.1140 Adelard of Bath's astrolabe.

1288-1301 A new quadrant of Profacius.

I know of 27 other non-chequered instruments of the 14th century.
The following lists give the earliest and some of the latest examples of chequering.

c.1306-33 A portolan chart has an unlabelled scale patterned something like . The alternation, which is an incipient chequering, could be for ease of reading. (Portolan charts were navigational aids combining charts with general information. The scales show miles.)

14th cent. The scale on another is partly like and partly alternates the group of six lines with a blank space.

1311 & 1313 The borders of two charts were decorated with a chequer pattern (this might not be a scale).

1320There is an early example of dots in circles in an atlas. The scale has seven blank stretches of five miles before defining each of the five miles with a circle and dot: .

1325 A more typical and decorative example is .

1375A portolan atlas has chequered circles.

c.1380The Lund cathedral clock has the quarters of each hour chequered in three colours, blue-red-yellow-blue.

c.1390-95. The first treatise on the magnet has a circular scale has ten-degree divisions coloured alternately red-black.

1424 An early example of the use of a black-white chequered scale is a volvelle. The circular centre is also decorated with the 2-dimensional chequerboard pattern .

c.1430The next example is a pendant sundial with calendar, quadrants and lunar volvelle. Only one of its scales is chequered. The inscription 'Roger Brechte 1527' is thought to have been put on it by an owner, although Gunther [Vol.II] took 1527 to be its date of origin.

1492 The oldest extant terrestrial globe has two circles chequered.

late 15th cent.There is an astrolabe with a chequered scale - thought to be of the late 15th century because the year 1492 is mentioned on an attached sheet.

1566 Chart scales were often highly decorated: .

c.1600 A double chequered scale is found on an astrolabe: .

1611 Even triple chequered scales occur: .

Two-dimensional chequering and other similar decoration is used here and there. One volvelle has .

Chequered scales are frequent in the 16th and 17th centuries and seemingly fewer in the 18th century. Non-European items are usually non-chequered, although there is an exception in the 1647 astrolabe of Shah Abbas II.

1805 Chequered scales on an Italian armillary sphere.

1811 A book contains a map of the world in two circular parts, the outer scale of degrees being chequered.

Contemporary Chequered scales of distance are still used on maps today.

There is an architectural use of chequering, especially the two-dimensional chequerboard pattern, which may have some relevance. Such decoration is found in both East and West, and I am not sure of its early history.

Interpretation

The opinion of Derek J. de Solla Price, in response to a letter from the author, was that chequered scales may derive from MS drawings and blocks in printed books rather than from instrument making. He had not come across any cross-hatched chequers on scales of metal instruments before a large number appeared in South Germany in the mid-sixteenth century, but in MSS they were found at least from the later middle ages. He considered that the blocking in alternate degrees was a quite natural thing when working in ink, and decidedly advantageous when cutting wood blocks, but that cross-hatching engravings of brass was laborious and not at all an obvious thing to do, perhaps even detracting from clarity of reading. (Letter to the author, dated 28 May 1956)
It seems to me that the time and place are significant. Chequered scales appear in Europe during the period when measurement was becoming an important way of looking at the natural world. There were always items which did not use chequering. It does not appear on nautical astrolabes, as far as I know, and I have never seen it on an astrolabe made by Georg Hartmann (1489 - 1564), for instance. It seems to have been a psychological matter - a process in which a new view of nature came into consciousness.

References

Authors' names, etc., refer to the list of sources.
c.1140: Gunther, Cambridge. (back to c.1140) || 1288-1301: Gunther, Oxford, Vol.II (back to 1288-1301) || Other: mostly Gunther. (back to other) || 1306-33: Kamal, Plate 21. Florence: R. Archivo di Stato, carte naut. No.2. (back to 1306-33) || 14th C: Kamal, Plate 22. Atlante Luxoro. (back to 14th C) || 1311 & 1313: Kamal, Plates 27-30. Florence: R. Archivo di Stato, carte naut. No.1, Paris, Bib. Nat., Rés. Ge. DD687. (back to 1311 & 1313) || 1320: Kamal, Plate 31. Vatican Library, Codex Palat. Lat.1362. (back to 1320) || 1325: Kamal, Plate 37. By Angelino de Dalorto. Florence, colln. of H.H. the Prince Corsini. (back to 1325) || 1375: Gernez. Paris, Bib. Nat., MS Espagnol 30. (back to 1375) || c.1380: Skåne. (back to c.1380) || c.1390-95: Quaritch. (back to c.1390-95) || 1424: Bodleian Library, MS Ashmole 370 f.25r. (back to 1424) || c.1430: Mus. of Hist. of Sci., Oxford; cf. Gunther, Oxford, vol.II. (back to c.1430) || 1492: Stevenson, Globes (back to 1492) || late 15th C: Mus. of Hist. of Sci., Oxford. (back to late 15th C) || 1566: Stevenson, Charts, item 17. (back to 1566) || c.1600: Gunther, World (by A.Danfrie) (back to c.1600) || 1611: Humphreys (by Speed) (back to 1611) || 1647: Gunther, World. (back to 1647) || 1805: Item 2891 (either at Rome or Florence). (back to 1805) || 1811: Brewster (back to 1811)

General references

J. Huizinga, The Waning of the Middle Ages (1924), Penguin Books, 1955.
Lynn Thorndike, A History of Magic and Experimental Science, Vol.V, Columbia University Press, 1941.
Abbott Payson Usher, A History of Mechanical Inventions, Harvard University Press, revised ed. 1954.

Last updated: 8 March 2008