XIX.] FIGURE OF THE EARTH. 319 



After the hull has passed out of sight, the lower sails, in like 

 manner, are lost to view ; then, the upper sails appear to dip 

 beneath the water ; and, at last, only the tops of the masts 

 are to be seen peeping above sea-level (Fig. 98 1). A telescope 

 may make so much as is to be seen of the ship more 

 distinct ; but, it will not bring the lower part again into 

 view, after it has once been lost. There seems to be no 

 way of explaining this giadual disappearance of a vessel 

 beneath the surface of the sea, on the supposition that the 

 earth is a flat plane ; but the explanation becomes easy 

 enough, if it be admitted that the surface is slightly convex. 

 Fig. 99 may be taken to represent a section of the sea, show- 

 ing the successive positions of a ship as she rides over the 



Fig. 9p. — Ship approaching shcre. Curvature of sea. 



curved surface. If the observer is stationed on the tower, on 

 the left of the figure, his line of vision might be represented 

 by the straight line which runs across the diagram. When 

 a ship is at a distant point on the right hand of this figure, 

 the observer sees only the top of the masts ; because the 

 surface of the water rises, like a flat dome, which comes in 

 the way of his seeing the lower parts of the vessel. But, as 

 the ship approaches the shore, the upper sails come into 

 view ; then the lower sails are seen ; and, last of all, the 

 hull itself. 



To the sailor who is approaching land, similar appearances 



^ Figs. 98 to 100 are taken, by Mr. Bentley's permission, from M. 

 Guillemin's work entitled The Heavens. 



