56 Arctic and Antarctic Exploration [part i 
Florence, and the edition of Ptolemy published at Ulm in 
1482 — the earliest printed map showing Greenland. 
Most of the names on the Zeno map were supposed 
to be oi'iginal ; due to their discoveries, and not existent 
on any earlier map. The discovery of these earlier 
medieval maps, however, has disposed of that delusion. 
Of the 19 Zeno names on Iceland, 12 are in the Zamoiski 
map, 3 in the Florence map, and the others in that of 
Olaus Magnus. On the Cantino map in 1502 appears 
Frisland, placed due north of Scotland. It is a clerical 
error in copying' Stillanda from the Cosa map. This is 
the way Zeno got hold of the name Frislanda. The whole 
was concocted by Niccolo Zeno and his publisher Mar- 
coloni in 1558, from materials on maps then existing. 
The Zeno imposture was first studied by Professor 
Storm, in the light of the Zamoiski and Olaus Magnus 
maps, and he exposed the falsities of the narrative, and 
the imposture of the map. The whole subject was dis- 
cussed in an exhaustive work by Mr F. W. Lucas, from 
which the above details have been taken 1 . The mischief 
done by the Zeno forgery, while it lasted. was very serious; 
causing confusion in the work of cartographers as well 
as mistakes in the reports of navigators. 
In the period of the beginning of English Arctic ex- 
ploration, the instrument mainly used for finding the lati- 
tude was the astrolabe. The cross-staff had been invented, 
but was not in general use, nor was the quadrant with 
a plumb-line, though it had been used by Columbus. 
The astrolabe was a circular metal ring with inlet 
plates and discs. These plates were fitted to drop into 
an inner depression of the ring, the principal one being 
called the rete. It consisted of a circular plate marked 
with zodiacs sub-divided into degrees, with narrow 
branching limbs having smaller tongues terminating in 
points, each denoting the position of a star. The plates, 
or " tables " as Chaucer calls them, were differently 
marked for places having different latitudes. Within 
all these scales of Umbra recta and Umbra versa there 
is a division into 12 parts for taking and computing 
heights and distances by an approximate method. The 
1 Voyages of the Brothers Zeni, by F. W. Lucas (Stevens, 1897). 
