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Fray Pedro Font and the Astrolabe Quadrant, 1775

Astrolabe Quadrant

    Fray Pedro Font, a member of Captain Juan Bautista de Anza’s historical 1775-76 expedition beginning in Mexico, passing through Arizona, and ultimately ending at the San Francisco Bay, was charged with making scientific observations and calculations along the way, which he recorded in his journal.
     He documents the use of a relatively simple instrument known as the Islamic quadrant, or astrolabe quadrant, the roots of which can be traced back to 1288 and, having evolved to include moving parts, was popular in the Ottoman Empire during the 17th century and into the early 20th century. Few examples of this instrument have survived, but from these and from descriptions, it is known to be in the shape of a quarter circle. The curved edge is numbered from zero to 90 degrees and the apex is at a right angle. Two upright pieces with holes are mounted along one of the straight edges, and are used for sighting. The quadrant is held vertically so the straight edge can be aligned with the sun or a star. A weighted plumb line falls across the scale of marked degrees and the angle of elevation can be read. There are various types of quadrants and they can be used in various ways, such as determining the altitude of heavenly bodies and solving astronomical problems, finding the time, or solving problems in trigonometry.
     This particular instrument was sent by the viceroy to Fr Font for his use, but was kept in the possession of Capt. Anza, who took it from its box only when it was necessary for Fr Font to make an observation.  This may have been due to a bit of envy on the part of Capt. Anza who, not possessing Fr Font’s abilities, wished to be seen as having complete control over the expedition and its assets.
     We have a long history of astronomy in the Santa Cruz Valley, which, remarkably enough, seems to have been foreshadowed by Fr Font’s use of the astrolabe quadrant during his journey so many years ago.
     A more complete version of this article by Shaw Kinsley appeared previously in The Villager, Tubac, Arizona. To see an accurate depiction of an astrolabe quadrant and other interesting instruments, visit  The Astrolabe.   See our Astrolabe Quadrant Postcard, pictured to the left, here.  Be sure to visit the Tubac Presidio Park Shop, where your purchase preserves history.


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