Museo Galileo
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Virtual Museum
Section of Room V
 The Problem of Longitude

The quest for longitude was the most crucial problem in the art of navigation, often determining the success of voyages and the survival of seamen. In 1530 the cosmographer Reiner Gemma Frisius (1508-1555) proposed a method based on the difference between the time at the port of departure, retained aboard ships by mechanical clocks, and the local time measured with astronomical instruments. Each hour of difference equalled fifteen degrees of longitude, and each degree of longitude was equivalent to a continuously varying distance from the Pole to the Equator.

Objects
Astrolabe

Astrolabe

Inv. 1103
Gualterus Arsenius, Louvain, 1572

Astrolabe

Astrolabe

Inv. 1097
Johann Richter (Praetorius), Altdorf, 1591

Astrolabe

Astrolabe

Inv. 1098
Gerard Mercator [attr.], Duisburg, ca. 1570

Astrolabe

Astrolabe

Inv. 1094
Gualterus Arsenius [attr.], Flemish, ca. 1570

Astrolabe

Astrolabe

Inv. 1100
Maker unknown, English?, late 16th cent.

Astrolabe

Astrolabe

Inv. 1093
Thomas Gemini, English, 1550-1559

Bust of Amerigo Vespucci

Bust of Amerigo Vespucci

Inv. 3903
Giovan Battista Foggini, 17th cent.

Hourglass

Hourglass

Inv. 138
Maker unknown, 17th cent.

Model of the application of the pendulum to the clock

Model of the application of the pendulum to the clock

Inv. 3450
Eustachio Porcellotti, 1860

Nautical hemisphere

Nautical hemisphere

Inv. 1099, 1122
Charles Whitwell, English, late 16th cent.

Single-handed dividers

Single-handed dividers

Inv. 1479
Maker unknown, 17th cent.

Single-handed dividers

Single-handed dividers

Inv. 1478
Maker unknown, 17th cent.

Spring-driven clock movement and dial

Spring-driven clock movement and dial

Inv. 3557
Johann Philipp Treffler, Florence, ca. 1659

Table-clock movement

Table-clock movement

Inv. 3821
Maker unknown, Italy, 16th cent.