92 THE POPULAR SCIENCE MONTHLY 



The North Star, so closely associated in our minds with the pole, 

 would be of no use to the explorer, for it is about a degree and a 

 quarter from the pole, and, like the other stars, it would circle around 

 the observer, and at times even be directly south of him. To deter- 

 mine its direction the explorer would have to know his own latitude 

 and local time; moreover, it would be invisible if the sun were above 

 the horizon. 



By means of his chronometer, keeping Greenwich mean time, the 

 explorer could determine the direction of any meridian, for the sun 

 would be on the meridian of Greenwich at Greenwich noon, and would 

 move 15 degrees in longitude for every hour thereafter; this knowledge 

 would be very valuable to enable him to lay out his return course from 

 the pole to his base of supplies, but it would not, in ignorance of his 

 meridian, help him to find the pole; for the direction of the pole in 

 relation to the direction of the sun, or of the compass needle, does not 

 depend upon the general direction of the meridians, but upon the par- 

 ticular meridian on which he happens to be. 



We have thus the apparent anomaly that the same observations 

 would enable a person to set a satisfactory course away from the pole, 

 but not toward it. But the anomaly is only apparent; for, suppose 

 the base of supplies were on the 70th meridian and in latitude 83° ; 

 and suppose the explorer were near the pole and twenty miles from the 

 70th meridian, on one side or the other; he could lay a course parallel 

 with the 70th meridian and this direction would only differ by about a 

 third of a degree from the most direct line to his base of supplies ; but 

 if he kept this course accurately, he would miss his base by twenty 

 miles. This, however, would be less important than missing the pole 

 by the same distance. 



The very simple method of determining latitude by the altitude of 

 the sun when on the meridian would not be available to the explorer, 

 for his meridian would not be known; and it would require a set of 

 observations extending over several hours to learn when the sun was 

 on his meridian. On the sixth of April the sun would circle around 

 the horizon, at an average altitude of about 6| degrees, and would only 

 be two degrees higher at midday than at midnight, as seen by an ex- 

 plorer one degree from the north pole, provided its declination were 

 constant; this, however, is not so; but on the date mentioned we should 

 find, superposed on the variation in altitude due to the rotation of 

 the earth, a steady increase in altitude amounting to a little more 

 than a third of a degree in a day. On April 21 the sun's altitude 

 would be about llf degrees above the horizon, and the variations 

 in altitude during the day would be almost the same as on the earlier 

 date. 



To determine his position, and the direction of the pole, the ex- 



