Relating to the FIGURE of the EARtH. 23 



27. It may be fliewn, too, nearly in the fame manner, that 

 if a degree of the perpendicular to the meridian were meafured 

 in Siberia, as far north as the latitude of 70°, fuppofing tl^t to 

 be poilible, and compared with a degree in latitude 45", or even 

 confiderably farther fouth, it would not give a refult fo exa(fl as 

 the degree of the meridian and perpendicular meafured in the 

 fouth of England. This fhews, that the method of afcertain- 

 ing the figure of the earth, propofed by the authors of the Tri- 

 gonometrical Survey, {Phil. Tranf. ibid. p. 529.), as a fubjedl of 

 future inquiry, is Iqfs exadl than that which is founded on their 

 own obfervations. 



28. We may alfo afcertain, by the fame means, the relative 

 accuracy of the method of finding the figure of the earth, from 

 the comparlfon of a degree of the meridian with a degree of the 

 perpendicular in the fame latitude, and of the method of refol- 

 ving the fame problem by the comparifon of two degrees of the 

 meridian in different latitudes. 



If, then, D be a degree of the meridian, and D' of the per- 

 pendicular, in latitude (p, and if A be a degree of the meridian in 

 a different latitude <f\ it is required to find whether the moft ac- 

 curate value of ^ will be found, by comparing D and D', or D 

 and A. 



Since we have, by what has been already ftated, § 4. 

 TtiD — a — 2c + 3c fin ^(p, and 

 mt>. — a — ic ■\- y fin Y', we have alfo 



^= 1 + f (fin '(p — fin '<p') and therefore, 



c D — A 



a ~ 3A (fin ^? — fin ^? ')' 



Now, it has been already fiiewn, that, by comparing D and 

 D' we have - = zD'^f.^ - Suppofing, therefore, equal errors 



to 



