Global Positioning System Reference
In-Depth Information
CHAPTER SEVEN
The Age of Sail and Steam
The seventeenth through nineteenth centuries saw the emergence of new
colonial empires—the Dutch, the French, and especially the British—and new
maritime navigational techniques to assist the flow of trade goods from colo-
nies to home countries. In this chapter we see how the sextant was employed
by maritime navigators and how the longitude problem was solved. Land-
based exploration and navigation also increased, as continents were ex-
plored and mapped for the first time.
Bearing Up
Vernier introduced his scale; magnetic variation was discovered and
mapped;
1
galleons gave way to barks, brigs, and sloops. All of these de-
velopments were important, but most important for us during this period
was the introduction of the sextant for surveying and navigating. This
instrument permitted estimation of azimuth (horizontal) angle as well as
elevation angle, unlike earlier devices such as the mariner's astrolabe, and
could therefore be used to provide a bearing. Mariners used increasingly
refined sextants for centuries, not only to estimate their positions at sea but
also to survey the world's coastlines. Sextants are still part of a navigator's
toolkit, if only as a backup for satellite navigation.
Here I provide some examples of sextant use in coastal navigation that
show the increasing sophistication and accuracy of position-estimating
techniques in general, and in particular of the techniques for estimating
1. Edmund Halley mapped magnetic declination, and Henry Gellibrand published
yearly accounts of the changes, both in the seventeenth century. See Wikipedia's entry
''Earth's Magnetic Field Declination'' for an interesting animation of the change in declina-
tion over the last four centuries.
