THK STAR VAULT. 9 



amplitude of east or west 90° north is seen constantly to . 

 diminish, until the Tropic is reached. 



And thus, as the Torrid Zone has already been discussed, 

 the whole hemisphere is accounted for. 



When, now, the same has been said, with the proper 

 change of data, concerning the southern hemisphere, it will 

 appear, as stated, that the sun can be seen in every point of 

 the horizon by proper adjustment of season and latitude. 



Our conclusions thus far have beeii reasonably practical ; 

 though fancy has aided us to devise the problem which science 

 was to solve. We may look a little farther in the same direction 

 and, if we gain no other advantage from so doing, we shall, 

 at least, have had a wholesome exercise for the imagination. 



If one start from the e^iua^or and move constantly north- 

 east, his course will be a curve of double curvature, and he 

 will of necessity strike the north pole. For he moves on the 

 surface of a sphere, at an angle of 45 degrees, with a constant 

 series of meridians which converge to the pole. And when 

 the very pole is reached there is but one way to move or look, 

 and that is southward. This fact has been mentioned before, 

 but not the proof of it. We look, namely, east or west along 

 our parallel ; and one must leave the pole some short distance 

 liehind in order to have a parallel. 



It will be understood, with but little effort of memory or 

 imagination, that if one could be instanth^ transported, say, 

 90 degrees eastward on his parallel, he would find the time by 

 the clock six hours later than at his starting point ; but if the 

 same movement had been made westward he would have 

 found the time b}^ the clock six hours earlier than at his start- 

 ing point. This state of things is virtually realized by the 

 telegraph. A message leaves London at noon and arrives at 

 Philadelphia, longitude 75° west of Greenwich, so quickly 

 that the time of transit may be wholly neglected. But when 

 it is noon at London it is seven o'clock in the morning here ; 

 so that, although starting and arriving at the same moment of 

 absolute time, the message may be said to reach its destina- 



