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Quadrant
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This type of instrument is called a quadrant because it is shaped like a quarter-circle. It may be regarded as an astrolabe folded back twice on itself. This folding process yields the configuration of the planisphere on the front, and the overlay of the hour lines on the shadow square on the back of the quadrant. The limb, or graduated rim, is reduced to a single 90° arc, while the sights are mounted in a fixed position on one of the straight sides. To the right angle is attached a small plumb line for reading the angular altitude of the stars on the limb. As in the astrolabe, the shadow square was used for terrestrial measurements, while the hour lines enabled the instrument to be used as a sundial. Time reckoning could be confined to a single latitude as in the case of the two-limbed hour quadrant that showed the hours on a second limb and the signs of the zodiac on one of the straight sides. Alternatively, time reckoning could be extended to all latitudes, as in the universal quadrant with cursor, which enabled the user to shift the zodiac band along the graduated arc. Latitude could be easily determined by measuring the altitude of the Sun or North Star; that was the instrument's main application in navigation. The main variants of the quadrant were designed for the same purpose. They included the sextant, which measures the sixth part of a circle; the octant, which measures the eighth part; the sinical quadrant, also known as primum mobile quadrant, for trigonometric calculations; and the Davis quadrant, composed of two complanar graduated arcs that allowed the user to measure solar altitude without having to look at the Sun directly.

Objects
Altazimuth quadrant

Altazimuth quadrant

Inv. 684
Dubois, Paris, 18th cent.

Declinatory

Declinatory

Inv. 3822
Giovanni Battista Giusti [attr.], Florence, second half 16th cent.

Horary quadrant

Horary quadrant

Inv. 239
Girolamo della Volpaia, Florence, 1570

Horary quadrant

Horary quadrant

Inv. 2499
Stefano Buonsignori, Florence, ca. 1580

Horary quadrant

Horary quadrant

Inv. 2524
Giovanni Battista Giusti, Florence, 1565

Horary quadrant

Horary quadrant

Inv. 2520
Giovanni Battista Giusti, Florence, 1568

Horary quadrant

Horary quadrant

Inv. 155, 156 (cavalletto)
Christoph Schissler, Augsburg, 1599

Horary quadrant

Horary quadrant

Inv. 1306
Joseph Pinam, Italian, 17th cent.

Horary quadrant

Horary quadrant

Inv. 2519
Charles Whitwell, English, 1595

Horary quadrant

Horary quadrant

Inv. 2525
Giovanni Battista Giusti, Florence, ca. 1575

Horary quadrant

Horary quadrant

Inv. 3628
Camillo della Volpaia, Florence, mid-16th cent.

Nocturnal and sundial

Nocturnal and sundial

Inv. 1305
Lorenzo della Volpaia, Florence, 1511

Nocturnal and sundial

Nocturnal and sundial

Inv. 3264
Eufrosino della Volpaia, Florence, 1520

Portable quadrant

Portable quadrant

Inv. 2513
Maker unknown, 17th cent.

Portable quadrant

Portable quadrant

Inv. 2513
Maker unknown, 17th cent.

Quadrans vetus

Quadrans vetus

Inv. 662
Maker unknown, German?, late 14th cent. - early 15th cent.

Quadrant

Quadrant

Inv. 1495, 2465
Tobias Volckmer, Braunschweig, 1608

Quadrant

Quadrant

Inv. 2509
Thomas Gemini, English, mid-16th cent.

Quadrant

Quadrant

Inv. 2522
Maker unknown, Naples, 1553

Quadrant

Quadrant

Inv. 2544, 3187
Carlo Renaldini, Italian, 1667

Quadrant

Quadrant

Inv. 3812
Bernardo Facini, Venice, 1701

Quadrant

Quadrant

Inv. 3365
Maker unknown, English, 1597

Quadrant

Quadrant

Inv. 2523
Jean Giamin, Rome, late 16th cent.

Quadrant

Quadrant

Inv. 2521
Giovanni Battista Giusti [attr.], Italian, 1556

Quadrant with Easter scale

Quadrant with Easter scale

Inv. 2518
Josua Habermel [attr.], German, ca. 1600

Trigonometric quadrants

Trigonometric quadrants

Inv. 2529, 2637
Christoph Schissler [attr.], German, late 16th cent.