HOW COULD AN EXPLORER FIND THE POLE 97 



A compass is of great value to keep one's course between observa- 

 tions on the sun; and an aneroid barometer and a thermometer make 

 possible a more accurate correction for refraction. A pedometer, also, 

 or some other form of distance meter, would be useful to estimate the 

 distance traveled. 



Although the methods of determining one's geographical position 

 would be the same near either pole, there are slight differences in their 

 applications; for instance, the solid land of the Antarctic continent 

 precludes drift, and therefore this disturbance is absent. Moreover, 

 when Lieutenant Shackleton reached his farthest south in the begin- 

 ning of January, 1909, the sun was about 25 degrees above the horizon; 

 at this altitude the refraction is not large and its value is well enough 

 known not to introduce any great error. Near Lieutenant Shackleton's 

 base camp, at the foot of Mount Erebus, the north pole of the compass 

 needle pointed about 30 degrees east of south. Along the most south- 

 erly part of his route, on his dash toward the pole, the north end of the 

 needle pointed very nearly to the south pole. 



On the return trip Lieutenant Shackleton could have been guided 

 by his compass, by the mountain range which ran very nearly parallel 

 with his route, or by other landmarks, and, perhaps, to some extent, by 

 his tracks ; so that he found it unnecessary to make many astronomical 

 observations. Commander Peary was guided, to a great extent, on his 

 return by his tracks and those of his supporting parties ; and Dr. Cook 

 seems to have relied entirely on his astronomical observations. 



Note. — For the sake of simplicity the sun has been generally taken, 

 in this article, as the heavenly body on which observations are made. 

 But the stars could serve equally well, and, for some observations, 

 better. If the pole should be approached when the stars were visible, 

 the altitudes of two stars lying on meridians about 90 degrees apart 

 would determine one's position without delay; moreover, stars could be 

 selected whose altitudes were sufficiently great to exclude errors due to 

 refraction ; or this correction could be determined by observations on a 

 pair of stars having about the same altitude and lying on opposite sides 

 of the zenith. 



The sun's apparent motion around the earth is not uniform, and 

 therefore a correction, known as the equation of time, must be applied 

 to all observations on the sun; but this correction is accurately known 

 and leads to no error. 



VOL. LXXVI.- — I. 



