DENSITY OF THE EARTH. 21 



divides itself in its application into two : viz. the measure- 

 ment of degrees of latitude on an arc of the meridian, and 

 the measurement of degrees of longitude on different 

 parallels. Although seven years have now elapsed since I 

 included in my " General Representation of Nature" the re- 

 sults of Bessel's important memoir on the dimensions of the 

 Earth, yet his investigation cannot even now be replaced by 

 a more comprehensive one, based on later measurements of 

 degrees. There are, indeed, to be soon expected, one 

 important addition, and one more perfect revision, the 

 publication of the nearly completed Russian Arc, extending 

 almost from the North Cape to the Black Sea; and the 

 careful comparison of the standard employed in the Indian 

 Arc, whereby the results of the latter will be more assured. 

 By the determinations published by Bessel in 1841, the 

 mean dimensions of our planet, according to the most exact 

 investigation ( 7 ) of ten measured arcs, are as follows : the 

 semi-major axis of the spheroid of rotation, which approxi- 

 mates most nearly to the irregular figure of the Earth, is 

 3272077,14 toises; the semi-minor axis, 3261139^33 ; the 

 length of a quadrant of the Earth, 5131179 t ,81 ; the length 

 of a mean degree of latitude, 57013 t ,109; the length of a 

 degree of longitude, on the equator, 57108^520, and in 

 latitude 45, 40449 t ,371; the ellipticity, or flattening at 

 the poles, 29 -~r 2 ; and the length of a German geographical 

 mile of 15 to an equatorial degree, 3807 fc ,23. The following 

 Table shows the increase of the length of a degree of the 

 meridian from the equator to the poles, as found by ob- 

 servation, modified, therefore, by local disturbances of 

 attraction : 



