6 GUNN. ISACHSEN. [2nd arc. exp. fram 



our best pocket-chronometers. The longitude of the fourth winter haven, 

 1901—02, in Gaase Fjord, was determined in relation to that of the 

 third, by triangulation in the summer of 1902. 



In the autumn of 1899, I was engaged in surveying in Jones' Sound 

 — the region east of Havne Fjord — in very much the same manner 

 as in our first winter quarters. 



My plan in my first work in 1900 was to use, instead of a plane- 

 table, the altazimuth for angles, and the odometer for distances; but 

 there were many hindrances to this method. The employment of the 

 altazimuth for terrestrial purposes presupposes clear weather, of which 

 there was exceedingly little at that time of year. On such expeditions 

 too, the time that can be spared for waiting is limited. We therefore 

 greatly felt the want of a large compass on this expedition; but we had 

 only one, and that was being used by Sverdrup. The tract mapped by 

 him north of Gape Farewell was thus determined by compass, and by 

 the distances traversed by odometer. 



It was also very unfortunate for us that the odometer's coupling 

 with the sledge broke three times over the rough pack-ice, the last time 

 irreparably. 



Surveying operations in 1901 and 1902 were carried on with plane- 

 table, kippregel, and odometer, the last-named having now attained almost 

 "perfection". The points were further verified by astronomical observations 

 with an altazimuth or a pocket sextant. This was necessary, as the 

 recorded traversed distances between two points are of course somewhat 

 greater than they are in reality, on account of the impossibility of going 

 in a perfectly straight line. 



The western part of Jones' Sound, Hell Gate (Helvedsporten), and 

 a iew other tracts, were surveyed without using the odometer, principally 

 on boat-expeditions. 



The island of St. Helena, off Colin Archer Peninsula, was an 

 important point as far as the first of the above districts was concerned. 

 Its position was found from the triangulation of Gaase Fjord, mentioned 

 above and below, in 1902, from azimuths observed from points in Gaase 

 Fjord, that are intersected by the mean of several observations of latitude 

 made on St. Helena. 



Thus, with the assistance of St. Helena, points on the north side 

 of Jones' Sound were connected with points on its south side. 



In order to verify these points, several determinations of longitude 

 were also made by sun and chronometer, and several points were marked 

 by Sumner's lines. 



