i6 



SCIENTIFIC RESULTS OF ZIEGLER POLAR EXPEDITION 



reckoned from midnight, and the deduced azimuth of the mark are given in the following 

 tabulation in deriving which the value for latitude used was 8i" 47. '5 N : 



The angle at pier M between this astronomic meridian mark and azimuth mark No. 2, 

 measured with the circle of the magnetometer, was 121° 49'. 3 ; whence the azimuth of mark 

 No. 2 is 124° 03. '2, a determination with the small instrument which agrees within one minute 

 of the Repsold circle determination. 



By differentiating the spherical triangle and substituting values of the latitude, declina- 

 tions and altitudes, and azimuths for the first observations of June 3 and June 6, A. m., there 



will result 



dA 



^=.7.5 and 7.0 



in which dA and dh are the mutually dependent changes in the azimuth and altitude, respect- 

 ively ; from which we might expect an error in the azimuths about seven times greater than 

 an assumed error in the altitudes. Presumably the altitude could not be measured with these 

 instruments closer than one-half minute of are so that the above results are within the limits 

 to be expected from this uncertainty. 



Pier M and Its Twist 



The ihagnetometer was mounted on the pine pier M which is, as stated, sunk 0.8 meter 

 among large boulders and gravel. It was noticed while sinking the holes for the piers that the 

 whole morainic mass of boulders and gravel was frozen together. The pier is not in contact 

 with the floor and is quite firmly imbedded. 



The horizontal circle of magnetometer No. IIII is rigidly connected with the base which 

 receives the footscrews and, therefore, has no independent motion. As the instrument was 

 left mounted and undisturbed after each day's observations, the various pointings on the 

 azimuth mark taken from time to time should presumably have given the same circle readings. 

 Very soon after the beginning of the winter's work it was noticed that these readings began 

 to vary. The striding level, as well as the stationary level, was carefully examined at each 

 pointing of the mark. When the circle readings were about their maximum and minimum 

 the telescope was reversed in its Y's without disclosing any appreciable coUimation error. 

 Readings were taken when the temperature of the hut, practically the same as the outside, 

 had reached its lowest point, to see if any of the effect was due to the passage of the line of 

 sight from the warmer air of the hut to the colder air outside. 



