Time Quadrant At Equal Time. Blois Region , Sundial, Shadow Square

TIME QUADRANT Unsigned, [France, Blois?], 17th century, 53.5 x 54 x H. 59 mm; thickness: between 22 and 25 mm, mercury-gilded and engraved brass Small square sundial which could be related to the hourly quadrant (quarter circle at 90°), however its square shape differs from classic hourly quadrants*. We have not, for the moment, found any other similar model, the piece was perhaps inserted in another larger one as is the case of a quadrant preserved at the British Museum (inventory no. 1897,0112.1 visible in line in the "online collection"). The quadrant is one of the oldest instruments of astronomy and celestial navigation, it made it possible to measure the height of the sun and the stars, and to determine the time. The instrument engraved on one side only has two sighting pins placed on one of the sides and an orifice, pierced at one of the corners, which allowed the insertion of a plumb line fitted with a sliding bead (element which is not present on this model and which made it possible to determine the time). The engraved side offers: A scale of the months located between the two pinnules; a shadow square with the words in curved letters: "Right Shadow" [umbra recta] and "Verted Shadow" [umbra versa] graduated from 1 to 12, on both sides, placed below the arc of degrees (graduated from 5 to 90° with a division of 5 into 5); the graduated time lines “5-12-7”; an equal hours plot for latitude 47° 30' indicated at the top of the dial by the words: "47DetDemy" which corresponds to the following French cities: Angers, Auxerre, Bayonne, Blois, Dijon, La Flèche, and Tours. Beautiful finely engraved instrument, atypical model in its shape, unique and curious piece which probably has its place of origin in the city of Blois. *Documentation on the time quadrants: - Ackermann, Silke et al, EPACT: Scientific instruments of medieval and renaissance Europe, online, http://www.mhs.ox.ac.uk/epact/index.php, 1998 - Ester Higton , Sundials at Greenwich, Oxford, 2002, pp. 337-358: Horary Quadrants
Quadrants at equal times In the West, in the 14th century, the rise of the mechanical clock probably favored the adaptation to equal hours of the time instruments of the time. This transformation was necessary to set this new time keeper. Among these instruments, some of which were used since Antiquity, the quadrants derived from the ancient quadrant occupy an important place. These new quadrants cannot be universal, the complexity and confusion between time lines making this representation impossible. They will then be drawn simply for a given latitude and different models will emerge over the following centuries. Probably originally made of wood, the few existing examples are made of brass and dedicated to rich personalities.