XXXIX] HAMPDEN AND THE FLAT EARTH 369 



this "true level" is the whole purpose of the instrument 

 called a surveyor's level, and it does show it with wonderful 

 accuracy. The mere fact, therefore, that the top disc on the 

 pole was apparently more below the cross-hair than the two 

 discs were apart, proved that the surface of the water was not 

 flat, or continuously extended in a straight line. And again 

 the fact that the distant signal was again about the same 

 distance, apparently below the middle one, as that was below 

 the telescope of the level, shows that the surface of the water 

 did not merely slope down in a straight line, but was curved 

 downwards with regard to its surface at the starting-point. 

 The following diagram will illustrate this : — 



The lower curved line represents the supposed curved 

 surface of the water. The points ABC are three points 

 equi-distant above that surface. The top line from A is the 

 level line shown by the cross-hair in the level-telescope. If 

 the water surface had been truly level, the two points B and 

 C must have been cut by the cross-hair. But even if the 

 cross-hair did not show the true level, but pointed upwards, 

 and the water was truly level, then the distant mark, being 

 the same height above the water as the top disc at half the 

 distance and the telescope, these two objects must have 

 appeared in a straight line, the nearer one covering the more 

 distant. It should appear on the straight line drawn from 

 the eye at A through B, whereas it appears a long way below 

 it, thus proving curvature, the essential point to be shown. 



Thus the view in the large telescope and in the level- 

 telescope both told exactly the same thing, and, moreover, 

 proved that the curvature was very nearly of the amount 



VOL. II. 2 B 



