Above: Byrhtferth’s Diagram; Computus Diagrams (detail), from the Thorney Computus, Cambridgeshire, England, ca. 1102–10, Saint John’s College, Oxford, MS 17.
I have long been fascinated by medieval diagrams. Even before this exhibition provided the opportunity to unpack their often arcane content, I appreciated their elegant geometry. Although the systems of thought and basic formats of these diagrams often come from antiquity, I like to think their aesthetic potential was only fully realized by medieval thinkers and draftsmen.
We attribute the form of the magnificent diagram from a twelfth-century manuscript known as the Thorney Computus (shown above) to Byrhtferth, a monk and scholar who lived at Ramsey Abbey in England around the year 1000. Like all effective graphs and charts, whether modern or medieval, the diagram seeks to convey a maximum amount of information in a clear, concise, and aesthetically pleasing manner. Byrhtferth’s diagram coordinates the many quaternities—or four-part schemes—used by ancient and medieval thinkers to organize and explain natural phenomena. Thus at a single glance we can see how the four elements, the four directions, the four ages of man, the four winds, the four seasons, the twelve signs of the zodiac (divisible into four), among other pieces of information, could be mapped one on top of the other. With its multiple sets of neat correlations, the diagram also gave visual affirmation to the medieval idea that the cosmos is a splendid system, organized according to the divine geometry of God. (These systems of fours appear again in a wind diagram that is also on view in the exhibition.)
As mentioned above, Byrhtferth’s Diagram is found in a computus book, replete with some one hundred other fascinating diagrams. (Computus refers to the measurement of time, particularly as it concerns the complex calculations required to determine the dating of Easter and its associated feasts.) I can’t begin to tell you how most of these diagrams work, but I can admire their beauty. Many of the diagrams in this manuscript are framed by architectural elements, and as I first turned the pages, I felt I was on an extraordinary architectural tour. The care with which these diagrams were rendered, the lively use of color, the quality of the parchment, and the relatively large size of the book gives a sense of how much the monks at Thorney Abbey, where this book was housed, valued its content. McGill University has created a digitized version of the manuscript (see http://digital.library.mcgill.ca/ms-17/index.htm) that allows visitors to see each of its pages, along with helpful commentary written by Prof. Faith Wallis, the leading expert on the Thorney Computus.
The most geometrically perfect diagram in the entire exhibition may be the Consanguinity Chart (Bayerische Staatsbibliothek, Munich, Clm. 13031), which was found within a copy of a medieval encyclopedia. It is a meticulously symmetrical composition made up of rigid straight lines, perfect circles, tidy triangles, and neatly detailed inscriptions that adhere to the chart’s overall geometric aesthetic. The purpose of the chart is to determine degrees of kinship—important in matters of marriage or inheritance.
Studying medieval diagrams has made me all the more appreciative of well-designed graphs and charts of any era, and in that regard, I’ve learned the most from Prof. Edward Tufte, who has been called “the Leonardo da Vinci of data.” Prof. Tufte has graciously agreed to speak about medieval diagrams at the Metropolitan Museum on Sunday, July 19, at 3:00 p.m. I hope many of you can join us for what will surely be an enlightening program.