1915- ^^o- 5- ROALD Amundsen's antarctic expedition : meteorology. 47 



This error of the altitudes may be due to the combined effect ot" dif- 

 ferent errors, such as error in the determination of the index error, made 

 by the visible snow-horizon, error in the levelling of the artificial horizon, 

 repeated before each observation, curvature of the horizon, prismatic form 

 of the coloured glasses belonging to the sextant, effect of irradiation ren- 

 dering the observed semi-diameter of the Sun greater than that taken from 

 the Nautical Almanac, eccentricity of the sextant, and abnormal refraction. 



The direct observations show that noon at the Station should be about 

 10 p.m. Fr. T. on the 17'^*. The longitude of Framheim is about i3^F.Gr. 

 Hence the approximate longitude of the Station should be about 3^E.Gr. 



The observations taken on the 16^^ December were made by Capt. 

 Amundsen with sextant Xo. i, and by Mr. Helmer Hanssen with sex- 

 tant No. 2. 



Index error — i', Refraction, Sun's Semidiameter, and Parallax to- 

 gether + 1 4'. 5, correction for Sextant No. i ^ 2'. 3 



Sextant No. i Sextant No. 2. 



Dobble alt. — i' 46» i3'.o 46^ i4'.o 



Single » 23 6 .5 23 7 .0 



Red. - 16.8 - 14.5 



Red. Alt. 23 23 .3 23 21 .5 



Zenith Dist. 66 36 .7 66 38 .5 



Sun's Déclin. 23 16 .4 23 16 .4 



Latitude 89053'.! 890 54'.9 E 



Mean 89° 54'° 



The 16 observations give the mean difference Sextant No. 2 minus 

 Sextant No. i = + i'. mean deviation ± i'.3. Applying the correction 

 + 2'.3 to No. I we get No. i minus No. 2 ^ + i'.3. 



From watch No. 3, and his observed altitudes, Capt, Amundsen judged 

 that noon occurred between 5^ and 5^30™ Framheim Time. The compass- 

 bearing of the Sun was SE to SE \ S. Mean SE | S. Compass-course 

 to the Pole NW|N. 



This course was strictly followed on the 1 7^^ , and the measured dis- 

 tance by sledge-meter was 5'. 5. 



As the observations made on the 17^^^ and 18'^ show, the Pole-point 

 was not quite reached. The course steered fell to the right of the meri- 

 dian. The noon on the 16'^'^ had been taken one hour too early. The 

 azimuth and the hour-angle are almost identical. 



The most reliable data that we now have for finding the longitudes 

 are the sides in the triangle between the Pole and the two stations: cola- 



