July 30, 2012

Flemish Psalter

This Flemish Psalter from the library of the Irish College in Paris was made in Bruges (present-day Belgium) around 1500. The manuscript is written in Latin on vellum, and it has a 19th-century binding. Psalters are religious books, especially popular in the Middle Ages, containing the psalms (poems that are sung) from the Bible, often with other devotional texts. Richly decorated, the Psalter includes a fully illuminated page depicting the Tree of Jesse and a miniature of King David, the main author of the psalms. Twelve illuminations, each composed of two panels, depict the months of the year and the signs of the zodiac. Nine sheets have borders ornamented with flowers, birds, and butterflies. The last illumination introduces the text of the Office of the Dead. The manuscript was commissioned by an unknown ecclesiastic whose coat of arms, consisting of azure-colored lion rampant on a silver background, is painted nine times in the volume.

July 31, 2012

The Book of the Sundials

This 19th-century manuscript is a treatise on gnomonics, the mathematical discipline concerning the calculation of the projection of shadows for timekeeping purposes. The relatively recent date of the work attests to the great and lasting importance attributed in the Islamic world to the reckoning of time through the observation of shadow lengths. The use of gnomonics and the construction of sundials were perceived as the most religiously correct way to calculate the right times of prayers, since religious texts already define the midday (zuhr) and afternoon (‘asr) prayers in terms of shadow lengths. This treatise is devoted to one particular kind of sundial only, the munharifa (literally "inclined") or vertical sundial, but Islamic tradition records a vast number of treatises that also describe the so-called horizontal sundial (known as ruhāma or basīta). The tradition of treatises about sundials began in the ninth century with the set of tables for the production of sundials created by the famous mathematician and astronomer Muḥammad ibn Musá al-Khuwarizmi (active 813–46). The work presented here begins with a general description of the shape and features of vertical sundials, which is followed by tables for the appropriate construction and positioning of sundials. The tables are outlined in black and red ink and can be seen on some of the early folios. In some cases these tables occupy a complete manuscript page.

Treatise for Observers on Constructing the Circle of Projection

This work is a treatise on the important subject of timekeeping. It is a work of technical astronomy, in 19 folios, that begins by emphasizing the religious significance of knowledge of time. It is divided into an introduction, two chapters, and a conclusion. Comprehensive procedures for the construction of tables and their use are provided. The work was completed in 1473 (878 A.H.).

Compendium on Using the Device Known as the Almucantar Quarter

This work, by a timekeeper at the Al-Azhar Mosque in Cairo, is an important and comprehensive textbook on timekeeping. It introduces the useful device of dividing a quarter of a circle of projection into sections known as almucantars (muqanṭarāt). The work, comprising 100 folio pages, contains 30 chapters and a conclusion. The work was composed in 1440-1 (844 A.H.) and was copied in 1757 (1170 A.H.).

The Travelers Guide on Drawing the Circle of Projection

This is a work on timekeeping and the determination of the direction of prayer (qibla), particularly intended for people who travel. The author, Abu al-‛Abbās Shihāb al-Dīn Ahmad b. Zayn al-Dīn Rajab b. Tubayghā al-Atābakī, known as al-Majdī or Ibn al-Majdī (1366-1447 [767-850 A.H.]), was descended from a powerful family with ties to Mamlūk rulers and was a renowned and prominent mathematician, geometrician, and astronomer. He served as the timekeeper of the Al-Azhar Mosque. This work is an abridgment of his other major book, Irshād al-ḥā’ir ilā ma‘rifat waḍ‘ khuṭūṭ faḍl al-dā’ir (Guide to the perplexed on drawing the circle of projection), but it also contains material not in the other book. The present manuscript, completed sometime before 1637-38 (1047 A.H.) by Ḥasan ibn abī al-Bajṭīṭī, once belonged to ‘Abd-Allāh al-Ṭūlūnī and then, from 1644 (1054 A.H.), to ‘Alī ibn Ḥājj Yūsuf al-Labūdī. The work is composed in three chapters: drawing the circle of projection (faḍl al-dā’ir) on a plane parallel to the horizon, which is called a simple plane (basīṭa); drawing it on a perpendicular place, known as a deviant plane (munḥarifa); and drawing it in parallel to other planes. The conclusion addresses issues such as locating the center of the circle, measurement of latitude, and other topics. The work contains extensive tables.

Maximum Benefit from the Knowledge of Circles of Projection on the 30 Degree Northern Latitude

This work, a treatise on practical astronomy, deals with such issues as timekeeping and determining the proper direction of prayer. The work begins with a brief introduction, but the bulk of the manuscript contains tables used to determine time. The introductory section contains illustrative examples on how to use the tables.