three Degrees of the Meridian.. 97 



power than any others to gratify ; I mean hy making new 

 measurements in the southern hemisphere. Those which 

 -have been made hitherto in the northern hemisphere are 

 extremely sansfactory by their agreement, and give us great 

 reason to presume that the general level ot the earth's sur- 

 face is elliptical, and very regularly so; and hence we 

 might expect the opposite hemisphere to be equally so, 

 and to be a portion ot" the same curve. Nevertheless the 

 degree measured at the Cape of Good Hope by Lacaille, 

 in latitude 33^ 18', appears to indicate an ellipse of less 

 eccentricity, or of greater axis ; for the linear extent of 

 57037 toises corresponds to the measure of a degree in 

 latitude 47^ 47' in the northern hemisphere. If now we 

 calculate the arc as before, with an oblateness of g-i-^, 

 and with the sides of Lacaillc's triangles reduced to the 

 meridian, we find it greater by lo" than it was found to 

 be by observations of the stars. An error of ten seconds, 

 by an astronomer so skilful and scrupulous as Lacaille, is 

 too extraordinary to be admitted as probable, ^t is true, 

 that there was a greater error well ascertained to have oc- 

 curred in the measurement in Lapland, amounting to thir 

 teen seconds; but the academicians engaged in this under- 

 taking were by no means equally conversant with observa- 

 tions as Lacaille. 



There remains therefore but one method of removing all 

 doubt on this subject, and this is to repeat and verify the 

 measurement at the Cape, and, if possible, tu extend it still 

 further to the north. The same Major Lambton who has 

 succeeded so well in Asia, and is in possession of such per- 

 fect instruments for the purpose, would be singularly quali- 

 fied for a sinnlar undertaking in Africa, and would furnish 

 us with a measurement in the other hemisphere, as much 

 to be relied upon as the former. He would have the glory 

 of deciding two important questions bv his own observa- 

 tions : first, the similarity and magnitude of the two hemi- 

 spheres ; and, secondly, the degree of reliance lo be placed 

 on the elliptic hypolliesis, 



Jt micrht be still further desirable, if other measurements 

 could also be uudiriaken, either in New Elolland, or in 

 Brazil; for thoutih neither of these countries differs much 

 in latitude from the Cape of Good Hope, they are so re- 

 mote in longitude, that a corrcspordcnce of measures so 

 taken would nearly establish the similarity of all meridians. 



Note. 

 ' T shall now explain the fornudce employed in deducing 

 Vol. 41. No. 178. y-e^. 1813. G the 



