THE CONQUEST OF THE ZONES 



reflected one. The angle thus measured will represent 

 twice the angular elevation of the body in question 

 above the horizon, — this being, as we have seen, the 

 infonnation which the user of the sextant desires. 



Of course the explorer makes his "dash for the pole" 

 in a season when the sun is perpetually above the hori- 

 zon. As he approaches the pole the course of the sun 

 becomes apparently more and more nearly circular, 

 departing less and less from the same altitude. Hence 

 it becomes increasingly difficult to determine by ob- 

 servation the exact time when the sun is at its highest 

 point. But it becomes less and less important to do so 

 as the actual proximity of the pole is approached; and 

 as viewed from the pole itself the sun, circling a prac- 

 tically uniform course, varies its height in the course of 

 twenty-four hours only by the trifling amount which 

 represents its climb toward the summer solstice. Such 

 being the case, an altitude observation of the sun may 

 be made by an observer at the pole at any hour of the 

 day with equal facility, and it is only necessary for him 

 to know from his chronometer the day of the month in 

 order that he may determine from the Nautical Al- 

 manac whether the observation really places him at 

 ninety degrees of latitude. Nor indeed is it necessary 

 that he should know the exact day provided he can 

 make a series of observations at intervals of an hour or 

 two. For if these successive observations reveal the 

 sun at the same altitude, it requires no Almanac and 

 absolutely no calculation of any kind to tell him that 

 his location is that of the pole. 



The observation might indeed be made with a fair 



tsi] 



