482 



when it is no longer necessary to discuss the claim of 

 either of the methods to have its result accepted in 

 preference to that of the other, since they are now found 

 to unite in a conclusion which, if not absolutely identical, 

 is so nearly so as to leave scarcely anything more to be 

 desired. The calculations of the Russian arc, extending 

 from the North Cape to the Black Sea, and the revision 

 ' of the Indian arc with the comparison of its standard 

 scale with that of the Russian arc, which are referred to 

 in the text (p. 21) as having been in progress when that 

 part of the volume was written, have since been com- 

 pleted ; and although the details are not yet published, 

 it has for some time past been known, on the authority 

 of M. Struve, that the result of this combination is to 

 manifest a much greater compression than had pre- 

 viously been deduced by Airy and Bessel in 1830, 1837, 

 and 1841 from all the arcs then at their command. It 

 is now known that the ellipticity derived from the 

 Russian and Indian arcs is between ^Y and -^j ; and 

 from the magnitude of those arcs (the Russian exceed- 

 ing 25, and the Indian exceeding 21) and the great 

 meridional extent embraced between them, it is not 

 likely that this conclusion will be disturbed by exten- 

 sions which yet remain to be completed of arcs of less 

 magnitude, which, being also in intermediate latitudes, 

 are of less importance in regard to the ellipticity. 



It may be worth while to cast a retrospective glance 

 on the progressive assimilation of the ellipticity deduced 

 from the measurement of degrees, as these measures have 

 increased in number and magnitude and have brought 

 i-nto- comparison more distant portions of the meridian, 

 to the ellipticity derived from the pendulum. Without 



