EARLIEST MEASURES OF THE EARTH 75 



was asked to explain why it was so evident, and it is recorded 

 that it often cost the great mathematician half a day to work 

 back through his calculations to make the fact clear. Much 

 depends on the point of view. Eratosthenes lived at the apex 

 of a civilisation inferior in but little to our own. To reach the 

 point where his ingenious mind might divine the method I have 

 described above was a long travail. Perchance a hundred 

 thousand years stood between cave- dwelling man and the 

 theorems of Euclid, which enabled the Alexandrian astronomer 

 to take the earth in his hands as a vase and say : This is so 

 many inches around. 



Was Eratosthenes the first ? Probably not by many cen- 

 turies. Aristotle, in the work which has come down to us 

 under the title De Ccello, has a line about the geometers who 

 had fixed the circumference of the earth at 400,000 stadia. He 

 did not have the exact and measuring sort of a mind, and he 

 is so little curious of the matter that he gives no hint of how 

 it was done. It is not impossible that he did not know ; that, 

 as Bailly conjectures, the figures had been sent him by Callis- 

 thenes from Babylonia, when the latter journeyed thither with 

 the silver shields of the Macedonian. It is Bailly's idea that 

 the measure may have been even of Chaldean origin, and hence 

 very old. 



There was a curious tradition, preserved by Achilles Tatius, 

 that the Chaldeans had measured the earth in terms of a day's 

 march. They said if a man were able to walk steadily, and at 

 good pace, he would encompass the earth in one year. They 

 counted that he would do 30 stadia (about 3 miles) an hour, 

 and so computed the great circle of the globe at 263,000 stadia, 

 which was very close to the estimate made by Eratosthenes. 

 Whether they employed the same scheme in their measure- 

 ments as he did, we do not know. But there were others as 

 simple and direct as the Alexandrian's. For example, the 

 foundation which bears up the weight of the Great Pyramid 

 was levelled with an astonishing accuracy ; and we have already 

 noted that the axis of the long tunnel leading from the subter- 

 ranean chambers beneath it was directed toward the polar star. 

 The lines of this remarkable passage-way and the foundation of 

 the pyramid naturally form a certain angle, as the figure below 

 will disclose. (See Fig. 5.) 



As the foundation is the plane of the horizon, the angle 



