60 



NATUBE FOR ITS OWN SAKE 



the horizon-ring appear so small, as upon the 

 open sea. The ship upon which we stand is the 

 centre of a watery field, the mainmast points 

 overhead to the centre of the blue firmament, and 

 all around spreads the deep azure glow. Judging 

 from vision alone the world appears very small. 

 The uttermost rim is just beyond us. The ex- 

 panse of the sea and the reach of the atmos- 

 phere about the whole globe are practically un- 

 felt. Even the height overhead seems greater 

 than the sweep before and after us. The limi- 

 tation becomes still more limited when the va- 

 pors lying along the surface of the sea thicken 

 the air and obscure the sight. We cannot as a 

 general rule under favorable conditions see more 

 than fifteen or twenty miles across sea water, 

 and even in calm weather the horizon is often 

 clouded by vapor banks that lie along it like a 

 row of faintly seen hills. All this helps the illu- 

 sion of being circled and shut in by the horizon. 

 Then again the sense of distance by perspective 

 lines is practically annihilated. Occasionally 

 the skeleton masts and black trailing smoke of 

 an ocean steamer, or the tower-like looking 

 sails of a square rigged ship appear, and act as 

 catch-points ; but these are slight, and as for 

 aerial distance we recognize it only by obscurity 



