1 8 DETERMINING ONE'S POSITION. 



reality, are simply the prolonged extremities of the axis of 

 terrestrial rotation is always above the horizon, while the 

 other remains below. And this phenomenon would lead to 

 the geometrical conception of an axis of rotation of the celes- 

 tial sphere. Thus we may explain, with perfect ease, why the 

 Bear and the neighbouring constellations should describe 

 perfect circles, and the other and more distant constellations 

 only arcs of circles, of a greater or lesser diameter; finally, 

 without even looking at the sky, we can understand that some 

 stars there are which show themselves on the horizon, only to 

 disappear immediately, and others which remain completely 

 invisible to the inhabitants of our climates. By a singularly 

 fortunate coincidence, the pole, that geometrical point around 

 which revolve those circumpolar constellations that are con- 

 tinually above our horizon, is occupied by a star " well known 

 to fame," and hence, on the faith of its renown, supposed by 

 many people to be a star of peculiar brilliancy.* It is named 

 the Polar Star (a in Ursa Minor), and is between the second 

 and third magnitude. 



Now if, with arms extended, we so place ourselves that our 

 back shall be turned to Polaris, we shall have opposite to us 

 the point of the arc occupied by the sun at noon; on our left 

 the east, and on our right the west. It is thus we may easily 

 learn our position in the absence of the orb of day. 



The discovery of this simple mode of guidance was, never- 

 theless, an epoch in history. From thence the mariner grew 



* The pole-star, however, is not the true polar point, but distant from 

 it about i 32', which, in A.D. 2100, will be decreased to 26' 30". 



