Ottoman engineer Mehmed Said Efendi and his treatise on vertical sundial

Atilla Bir & Mustafa Kaçar

At the beginning of the 18th century, the Ottoman Empire witnessed a movement of change and innovation. This transformation was first observed in the military field with the foundation of the Bombardier Corps (Ulufeli Humbaracılar Ocağı) in 1735 to train engineers. The present study aims to introduce Mehmet Said Efendi, professor of geometry at the Bombardier Corps, and his treatise on the construction and setting vertical sundials.

Son of the Mufti of Beyşehir and a member of the ulema class, Said Efendi wrote various treatises on geometry, astronomy, time measuring, geodesy and Earth's shape. Said Efendi Mecmuası (Süleymaniye Library, Esad Efendi Nr.3704) comprises a treatise dealing with the determination of the deviation of vertical sundials from the east-west direction and an appendix on the projections of Sun's orbit. In 1735, Said Efendi heard about the setting of the vertical sundial from his colleague Abdullah Efendi el-Muzafferi el-Bosnavî, an instructor at the Bombardier Corps, and wrote a detailed technical account on 1737.

In the Islamic world, the setting of sundials on the walls of the mosques were of special importance since religious duties required precise time keeping. In the construction of sundials, the deviation of the meridian plane, perpendicular to the horizon, has to be determined correctly. Said Efendi, in his treatise presented a method to measure the correct deviation degree from the east-west direction relative to the meridian of the sundial and gavecalculations of the orbit projections of the Sun. This sundial differed from the sundials normally used by the Ottomans, where the drawing starts from 1 and ends at 6; Said Efendi's drawing starts from 6 o'clock in the morning and ends at 12 o'clock as in European clocks. At the same time his work contains basic information about the construction of sundials and the ways of marking them on a wall, which has now probably been forgotten.