Description
Britain holds at least forty sundials made in China during the eighteenth and nineteenth centuries, most of which are direction dials. Unlike horizontal dials that measure the Sun’s altitude above the horizon, direction dials measure the Sun’s azimuth along the celestial equator to determine time. This factor explains why many of these dials incorporate magnetic compasses, which help users align the sundial along the celestial meridian. Among the surviving Chinese sundials in Britain, more than half are diptych dials, followed by inclining, horizontal, and equinoctial dials.  

Sundials have been a part of China’s horological tradition for centuries. The earliest surviving Chinese mathematical texts detail the use of calendrical gnomons, which helped imperial astronomers determine solstices and equinoxes. Over time, Chinese timekeeping was influenced by other cultures, particularly during the Song and Yuan dynasties (10th–14th centuries CE), when Islamic astronomers introduced new instruments, and an Islamic calendar was issued alongside the Chinese one every year by the Imperial Astronomical Bureau. The Jesuits further impacted Chinese timekeeping in the seventeenth century, bringing diptych sundials from places like Nuremberg as gifts for the emperor and the scholar-literati.  

The portable Chinese sundials in British collections can be classified by their materials, which also indicate their different places of origin. Diptych and inclining dials made from boxwood with Chinese inscriptions were produced in Xin-An, a mountainous region in modern-day Anhui Province. These dials, though reminiscent of the popular diptych dials made in Nuremberg, are adjusted according to jieqi (one of the twenty-four solar terms in the Chinese lunisolar calendar) rather than latitude. Meanwhile, diptych dials made from ivory, and horizontal and equinoctial dials in brass, were crafted in the maritime trading regions of Quanzhou in Fujian and Canton (Guangdong). These regions also produced ‘hybrid’ sundials, with a more explicit aim to appeal to both Western and Chinese tastes. The same sundial might be admired as an exotic object in Beijing for its brass and gemstone decoration, and in Britain for its use of Chinese numerals and craftsmanship.
25/09/2024
Created by: Zhiyu Chen on 25/09/2024

Description
The Diptych dial is a common form of portable multi-function sundial. Diptych dials were made popular by the instrument makers in Nuremberg during the sixteenth and seventeenth centuries. They are usually made of ivory with brass fittings, and are often elaborately decorated. The name of the device derives from the Greek diptychos for a pair of folding writing tablets, which the instrument resembles.

Diptych dials consist of two leaves hinged together, with a string ‘gnomon’ stretched between the inner surfaces of the leaves for casting a shadow. To use the device as a sundial the lower leaf must be placed parallel to the horizon and the upper leaf must be at a right angle vertically to it. The gnomon must then be aligned with the meridian of the place where it is being used by using the inbuilt magnetic compass. Time can then be read from the horizontal or vertical dial by the location of the shadow cast by the string gnomon.

In addition to the horizontal and vertical dials, diptych dials normally carry a number of other features, such as equinoctial dials, windroses, tables of latitude for adjusting the string gnomon for different locations, epact tables, lunar volvelles for telling time at night by the moon, and various pin-gnomon dials for telling the time according to Babylonian or Italian hours, or for calculating the position of the Sun in the zodiac.
27/05/2009
Created by: Joshua Nall on 27/05/2009