MAGNETIC OBSERVATIONS 



DECLINATION 



AZIMUTH MARKS 



Azimuth Mark No. i was the anemometer staff permanently fixed to the northwest corner 

 of the astronomic observatory. It was used at first because of its early availability during 

 daylight of October, 1903. Afterwards a hole 3 inches in diameter was cut through the east 

 wall of this observatory. A cross radiating from this hole was painted on the wall to be used 

 in daylight and a bull's eye lantern seen through the hole was used at night. The center of 

 the hole was on the line of sight from the magnetometer telescope to the telescope of the Rep- 

 sold circle in the astronomic observatory when these two were directed towards each other 

 and it is designated Azimuth Mark No. 2. The distance is approximately 288 meters. It 

 should be noted that a distant mark is seldom available at Teplitz Bay on account of darkness 

 or thick weather. 



The azimuth of the magnetometer at the Repsold circle was first determined by measuring 

 the angle between the magnetometer and the south pointing of the vertical thread as deter- 

 mined from star transit on December 2 and December 18, 1903, and January 27, 1904. It was 

 again determined by measuring the same angle as determined from a combination of the transits 

 of 17 Cephei at lower culmination and i H. Draconis at upper culmination on March 17, 1904. 

 Filially the angle between the astronomic meridian mark (6440 meters distant) and the 

 magnetometer was measured July i, 1904, at the end of the season's work. It was measured 

 on April n, 1905, without any sensible difference jn the results. 



These observations by Mr. R. W. Porter are given in the astronomic notes ; the result of 

 of four days' observations are tabulated below : 



Date 



December 2, 1903 

 December 18, 1903 

 January 27, 1904 



February 12, 1904 



Method 



Star transits for time 

 Star transits for time 

 Star transits for time 

 f Combining circumpolar 

 1 stars at U. C. and L. C 



Mean 



This with distance to the magnetometer, 287.82 



meters, gives additive 



Hence the reverse azimuth 



Resulting azimuth 

 of vertical thread 

 Repsold circle 



304 01 20 

 40 

 44 



32 



304 01 34 



108 oo 53 

 124 02.5 



This is the value adopted and used in the final reduction of the magnetic declination 

 observations. 



For a rough check and to test the four-inch Berger & Sons' theodolities under existing 

 unfavorable trigonometric and meteorologic conditions, some azimuths were obtained from 

 solar altitudes with one of these instruments by Mr. W. J. Peters. 



The four-inch theodolite in these observations was placed about 36 meters south of the 

 magnetometer and exactly on a line connecting the magnetometer with the astronomic meridian 

 mark (approximately 6430 meters distant). Both circles were graduated to read by two verniers 

 to single minutes. 



The instrument was reversed and opposite limbs of the sun were symmetrically observed. 

 The means of each set of four pointings with the corresponding approximate local civil times, 



