394 I. Р. Косн. 
distance threads of the telescope, in the case of the Danmark-Eks- 
pedition was performed with a special distance measurer, the stereo- 
telemeter constructed and manufactured by Zeiss in Jena. In the 
course of the survey itself the stadia were not used, and so two 
rodmen per topographer could be dispensed with. The stadia, which 
as far as the plane table survey was concerned were only used in 
the verification of the universal diopters, were not at all brought 
into requisition in the field. 
The Zeiss stereo-telemeter is a binocle, the stereoscopic effect of 
which is strengthened thereby that the objectives are placed within 
a distance of each other of 0.5 п. This half metre is the base of 
the distance measurer.') By means of prisms the rays of light are 
refracted twice in their passage from the objectives to the oculars. 
In the two fields of the telescope the two stereoscopic images of a 
zigzag scale are inserted. When using the telescope one gets in this 
manner the impression that a scale flashes across the landscape. In 
order to measure the distance at a definite point, all that is required 
is to give the telescope such a direction that the scale is made to 
pass over this point, and then the direction is read off direct on 
the scale. 
The divisions of the scale run from 200 to 5000 metres. On the 
Danmark-Ekspedition we have, with great certainty, been able to 
measure distances with the stereo-telemeter of up to 1000 metres, 
and even within 2000 metres the uncertainty of the measuring of 
the distance generally did not play any part. For distances exceeding 
2000 metres we could only use the stereo-telemeter, when the con- 
ditions were very favourable. If the distance exceeded 2500 metres, 
we could not rely on the measuring, even in the most favourable 
conditions. 
The use of the stereo-telemeter requires some practice; according 
to experiments made in the Danish Army it even seems as if there 
are people who cannot learn to use it at all. On the Danmark-Eks- 
pedition, however, the training in the use of this instrument did not 
cause us any trouble worth speaking of. 
As regards the exactitude of the measuring of distances the relief, 
as was to be expected, played a certain part. Projecting object points, 
such as large stones, rocky knolls, crests &c are easy measuring 
objects; on the other hand it might cause trouble to measure at less 
projecting points in more even planes. 
As advantages of the stereo-telemeter I have mentioned that it 
1) Zeiss has manufactured two other stereoscopic distance measurers, a small one 
to be used at quite short distances, and a large one, which requires to be 
placed on a tripod, for the measuring of distances of several kilometres. 
