222 I. P. Косн. 
of the discrepancies in the altitudes computed (95.8 m and 183.6 m) 
viz. that the telescope had been directed at two different hilltops. 
This incident shows how careful one must be, and how necessary 
it is to control the observations. As the observation journal contains 
no remarks implying uncertainty, I have consequently in the course 
of the survey entertained no doubt whatsoever, that from the two 
stations I have measured at the same point. 
The position of the point was determined during the following 
year, and here it appeared with full certainty that one of the two 
sights from 1906 had been directed towards quite a different hilltop. 
The including of the Observatory in the triangulation 
network. 
In the course of the triangulation of the base net the Observatory 
had constantly been comprised as “Cairn” from all stations, with 
the exception of IV. The material collected in this manner for the 
determination of the position of the Observatory must, however, be 
considered less valuable, because it had not been possible to point 
the granite pillar itself, seeing that it did not reach above the side 
walls of the Observatory. In stead of the pillar I generally pointed 
the roof of the Observatory; but from the stations I and II I had 
succeeded in pointing the iron table, which had been cast with the 
pillar. The black roof was, however, as a rule, difficult to point, 
and it is also possible that it was not well centred above the axis 
of the instrument. The errors of centration could, however, easily 
have been found, but before the computation began, I had made 
up my mind to condemn all sights at the Observatory (with the 
exception of sight I—O and II—Q), and so the elements of centration 
of the roof were not measured at all. 
Instead of that I determined, by means of two trigonometric 
station pointings, to connect the Observatory with the base network, 
as well as directly with the cairns V, VIII and X. The object of 
the latter station pointing was partly to get a convenient and sure 
connection of azimuth at the sides of the outer triangles, and partly to 
facilitate the subsequent computation of the geographical coordinates 
of the triangulation points. 
The trigonometric station pointing is a well-known problem’). 
Its principles will, however, be treated briefly in this place, partly 
out of regard to the establishment of a practical computation table, 
1) The below treatment of the problem of the trigonometric station pointing with 
the computing table belonging to it is a compendium of a guide, published by 
the General Staff to be used for survey work in Iceland. 
