The Earth. 335 



Having obtained this terrestrial distance to a 

 great degree of accuracy, he had only to find the 

 celestial arc which corresponded with it. This 

 he did by observing the meridian distances of the 

 same star, both from the zenith of Sourdon and 

 Malvoisine, and taking their difference ; and as 

 this difference, which he found to be one de- 

 gree, eleven minutes, and fifty-seven seconds, 

 answered to a distance of sixty eight thousand 

 four hundred and thirty fathoms upon the earth, 

 he concluded, by the rule of proportion, that the 

 length of a degree, in that latitude, must be fifty 

 seven thousand and sixty-four fathoms. But 

 having connected Amiens to his series of triangles, 

 and finding from this new measure that a degree 

 would be fifty-seven thousand and fifty-seven 

 fathoms, he took a mean between the two, and 

 fixed his degree at fifty-seven thousand and sixty, 

 or about sixty-nine and a "half English miles. 



The surveys were all taken upon a supposition 

 that the earth was a perfect sphere ; but the 

 truth of this doctrine was soon called in question 

 as the science advanced. Newton and Huyghens 

 had shown, from the known laws of gravitation, 

 that the true figure of the earth must be that of 

 an oblate spheroid, flattened at the poles, and 

 protuberant at the equator. Dominique Cassini, 

 on the other hand, depending more upon the 

 accuracy of his measures, than upon deductions 

 drawn from theoretical reasoning, asserted it to 

 be that of a prolate spheroid, flattened- at the 



