HAMPDEN AND THE FLAT EARTH 



385 



Mr. Coulcher signed them as being correct, and both are re- 

 produced here. 



For those who do not understand the use of a level, it 

 may be necessary to explain that the cross-hair in the optical 

 axis of the telescope marks the true level of any object at a 

 distance with regard to the telescope. Any point that is 

 seen above the cross-hair is above the level, any point seen 

 below the cross-hair is below the level, and in the latter case 

 the line from the telescope to it slopes downwards. To show 

 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 regards 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 



