Le Nord : revue internationale des Pays de Nord - 01.06.1944, Blaðsíða 331

REVUE LITTÉRAIRE
291
features of his life have formerly
been known, but extremely little
has been known about the question
how he managed the surveying and
the construction of the maps. N. E.
Norlund’s statement is a perfectly
new and extremely instructive con-
tribution to our understanding of
the geodesy of the 17th century.
The written evidence of his methods
at the solution of the task, gigantic
to a single man, of making maps of
the whole of the Danish kingdom,
is scanty, and Norlund therefore
through detailed and penetrating
analyses of the maps themselves has
had to reconstruct method and basis.
Norlund has solved this problem
with proficiency and elegance and
has reconstructed all essential con-
stituents of his method.
The chief basis of Johannes
Mejer’s cartography is his deter-
mination of geographical latitudes,
which has been carried out with an
accuracy so astonishing that we
come to have a considerable respect
for his skill as an observer. It is
true that there is a permanent sy-
stematic error, his determination of
latitudes being about l-2 minutes
of arc too high, an error that must
be ascribed to the fact that at the
calculation of his nightly observa-
tions of the lower heights of cul-
mination of the stars he had not
sufficient knowledge of the refrac-
tion of the atmosphere.
His determinations of the longi-
tudes are more defective. The di-
rection of the north has been deter-
mined by means of a compass with-
out correction for the variation, and
so his meridians become erroneous.
He became aware of the error him-
self, and in his last maps tried to
correct it. However, we get in this
way, through his non-corrected
maps, a possibility of determining
the variation at Mejer’s time. For
Jutland is amounted to about 3~
East.
It was, however, much more dif-
ficult to determine the units of
length used by Mejer. The scale in
his maps as a rule is divided into
miles or roods, but in order to use
his maps we must of course know
the lengths of these units as ex-
pressed in modern measures.
Through a huge work and much
acuteness Norlund has disentangled
these most delicate problems. His
account and valuation of the geo-
detic technique and theory of the
time are like a search-light on the
research of a remote past and its
effective, though not always vic-
torious fight against the refractory
substance for the recognition of the
truth.
Modern cartographers operate
with exactly fixed units of length,
ell, English foot, etc., but in the
17th century they had not yet at-
tained to such a fixation of units of
measurement, thus when Johannes
Mejer in his maps introduces a scale
in miles, we cannot a priori be sure
what his miles denote, in other