Page 204 - (DK) Smithsinian - Military History: The Definitive Visual Guide to the Objects of Warfare

202 NAVIGATION AND Suspension ring

ONET 1680–1815 COMMUNICATION AT SEA

Specialized tools were used at sea to communicate signals, calculate
position, and plot navigational routes. Aside from the magnetic compass,
the navigator’s principal tools were instruments such as the astrolabe and
sextant, used for measuring the altitude of the Pole Star or the sun at noon.

latitude (how far north or south of the equator it was). Until the mid-18th
century, longitude (a ship’s east–west position) was calculated by “dead
Y In conjunction with astronomical almanacs, these readings indicated the ship’s
reckoning,” using the ship’s direction of travel and its speed. However, the
AND BA marine chronometer of 1730–35, and his H4 timepiece of 1759, made
invention of timepieces of unprecedented accuracy, such as John Harrison’s
precise calculations of longitude possible. The difference between the
time on the clock—set to the time at Greenwich in London, England—
and noon—as observed from the sun’s position—indicated how many
FLINTLOCK degrees the ship had sailed east or west of Greenwich.

Animals represent
constellations or specific stars
Gnomon hinged for folding
down when traveling

▲ ASTROLABE
▲ BUTTERFIELD DIAL A Butterfield dial was a small portable
Date Late 17th century sundial with an incorporated Date 1690
compass. The dials took their name Origin Austria
Origin France
from their inventor, Michael
Material Silver, glass Butterfield (1635–1724), an English Material Brass Movable elements set to
instrument-maker who worked in The astrolabe was used by medieval display date and time
Paris. The gnomon (the raised blade astronomers to observe the stars.
that casts the shadow) was adjusted A simplified version was adopted
according to the latitude. North point by mariners from c.1450 onward.
marked with
a fleur-de-lys
Hand-colored card

Retractable eyepiece

▶ NAVIGATIONAL Wooden
COMPASS surround
Date c.1719
Origin Italy Pillar stand
Material Wood, card
▶ GREGORIAN The Gregorian telescope, named
Developed in China, the navigational TELESCOPE after its 17th-century Scottish
compass came to be used in Europe inventor James Gregory, used two
by the 12th century. On this Date 1752 concave mirrors. This one, made
mariner’s compass, a quadrantal Origin England by James Short of London, is 3 ⁄4in
1
degree scale runs around the outer Material Brass (8.5cm) in diameter and 20 ⁄2in
1
edge of the face. The cardinal and (52.5cm) long with its eyepiece
intercardinal points are identified extended. Its inclination could be
by the initial letter of the Italian Arrow labeled “S” for adjusted and it could be moved
name for the wind that blows the south-easterly easily from side to side.
from that direction. North is sirocco wind
the exception, being marked
by a fleur-de-lys. Three folding legs