Page 192 - Das Wunder der Migration bei Tieren

Com pass
Sin ce the 12th cen tury, oce an-go ing
exp lo rers ha ve used mag ne tic com pas ses
to de ter mi ne the ir ro ute. The first com pas ses
con sis ted of no mo re than mag ne ti zed ne ed les sus -
pen ded on strings to show the north. La ter, the se
ne ed les we re
fi xed on a pivot at the cen ter of a dial.

Cross-staff
Above left: This inst ru ment, po pu lar with 16th-cen tury na vi - Ast ro la be
ga tors, was used to measure latitude. One end of the staff was Above: Ara bi an ast ro no mers ma de a
held at the na vi ga tor's eye. The cross- pi ece was then slid two-di men si onal mo del of the
for ward or bac k un til its up per he avens. The instrument was sus-
ed ge li ned up with the Sun or po le star and the lo wer ed ge pended from a cord so as to hang per-
with the ho ri zon. The po int whe re the cross-pi ece cut the sca - pendicular to sea level, while the user
le on the staff was no ted, to be converted into degrees accord- co uld sight a star or the Sun thro ugh
ing to a table. two small ho les in the plates on its
moveable vane, and re ad its al ti tu de
from the graduated scale around the
rim.
Sex tant
Right: The Eng lish navy in ven ted the sex tant
in the mid-18th cen tury. It co uld me asu -
re la ti tu de to a
deg ree of ac cu racy of 0.01 by me -
ans of a mir ror ar ran ge ment.
The na vi ga tor views the Sun
through the telescope and reads
its angular distance above the
horizon off the scale. The data is
then used to calculate the ship's posi-
tion.

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