ASTRONOMICAL OBSERVATIONS 



INSTRUMENTS 



The Repsokl Circle used by the Expedition at Teplitz Bay and Alger Island was secured 

 through the courtesy of Professor Geelmuyden, Director of the Christiania Observatory. This 

 instrument (see figure i) is of the alt-azimuth type, with horizontal and vertical circles of 30 

 centimeters and 25 centimeters diameter respectively. The telescope is of the broken type, 

 with the eyepiece at one end of the hollow horizontal axis, the opposite end of the axis pro- 

 viding for the illumination of the threads. The magnifying power of the telescope is about 

 40.4. The horizontal circle is graduated into divisions of four minutes of arc and is provided 

 with four verniers, the least count of each being four seconds of arc. The scale of the ver- 

 tical circle, situated at the opposite end of the horizontal axis from the eyepiece, is similarly 

 divided into four-minute divisions and provided with two micrometers, whose heads are grad- 

 uated into sixty parts, giving a least count of four seconds of arc. The vertical circle is so 

 numbered as to give nadir distances. The weight of the telescope with alidade and clamps 

 attached is 7.7 kilograms. 



The reticule is a piece of glass engraved with seven vertical lines and two horizontal ones, 

 the latter close together. The space between two consecutive vertical lines is crossed by an 

 equatorial star in about twelve seconds of time. 



The values of the divisions of the levels were determined in June, 1905, at Alger Island 

 and found to be as follows : 



Striding level, per division of 2.0 mm 2. "98 



Alidade level, per division of 1.8 mm 2."i6 



Some of the secondary astronomical work was executed with two small lo-centimeter 

 theodolites made by C. L,. Berger and Sons, both vertical and horizontal circles being read to 

 single minutes of arc by two verniers each. These were of the usual type of instrument (see 

 figure 2) made for finer grade field work by this firm, with the addition of several features to 

 render them more convenient for use in extremely low temperatures. All of the tangent and 

 leveling screw milled heads had small ivory buttons set in the outer circumference about 

 3 millimeters in diameter and projecting about the same distance beyond the heads. The 

 compass needle was mounted in a closed tube attached to the under side of the telescope, the 

 glass ends of this tube being engraved with collimating lines. These instruments, with cases, 

 are very light and were found extremely useful and convenient, particularly so in the field 

 work of the Expedition. 



Only two chronometers were carried ; one, a mean time, and the other, a siderial time, 

 both by Negus. 



39 & 



