THE CONQUEST OF TIME AND SPACE 



secured, he would depend thereafter on the familiar 

 method of triangulation, in which angles are measured 

 very accurately, and from such measurement the length 

 of the sides of the successive triangles determined by 

 simple calculation. In the end he would thus have 

 made the most accurate determination of the distance 

 involved, without having actually measured any por- 

 tion thereof except the original base line. Notwith- 

 standing the crudity of Norman's method, however, his 

 estimate of the actual length of a degree of the earth's 

 surface was correct, as more recent measurements have 

 demonstrated, within twelve yards — a really remark- 

 able result when it is recalled that the total length of 

 the degree is about sixty nautical miles. 



Inasmuch as the earth is not precisely spherical, but 

 is slightly flattened at the poles, successive degrees of 

 latitude are not absolutely uniform all along a meridian, 

 but decrease slightly as the poles are approached. The 

 deviation is so slight, however, that for practical pur- 

 poses the degree of latitude may be considered as an 

 unvarying unit. But obviously such is not the case 

 with a degree of longitude. The most casual glance at 

 a globe on which the meridian lines are drawn, shows 

 that these lines intersect at the poles, and that the dis- 

 tance between them is, in the nature of the case, differ- 

 ent at each successive point between poles and equator. 

 It is only at the equator itself that a degree of longi- 

 tude represents t5t of the earth's circumference. 

 Everywhere else the parallels of latitude cut the merid- 

 ians in what are termed small circles — that is to say, 

 circles that do not represent circumference lines in the 



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