1 6 COSMOS. 



the irregular figure of our earth, was 3272077.14 toises, or 

 20,924,774 feet ; the semi-axis minor, 3261139.33 toises, 

 or 20,854.821 feet; the length of the earth's quadrant, 

 5131179.81 toises, or 32.811,799 feet ; the length of a mean 

 meridian degree, 57013.109 toises, or 364,596 feet ; the 

 length of a parallel degree at latitude, and consequently 

 that of an equatorial degree, 57108.52 toises, or 365,186 

 feet ; the length of a parallel degree at 45, 40449.371 toises, 

 or 258,657 feet ; the ellipticity of the earth, ?-$-$, TTT \ an( ^ 

 the length of a geographical mile, of which sixty go to an 

 equatorial degree, 951.8 toises, or 6086.5 feet. 



The table (page 17) shows the increase of the length of the 

 meridian degree from the equator to the pole, as it has been 

 found from observations, and therefore modified by the local 

 disturbances of attraction 



The determination of the figure of the earth by the mea- 

 surement of degrees of longitude on different parallels re- 

 quires very great accuracy in fixing the longitudes of different 

 places. Cassini de Thury and Lacaille employed, in 1740, 

 powder signals to determine a perpendicular line at the 

 meridian of Paris. In more recent times, the great trigono- 

 metrical survey of England has determined, by the help of 

 far better instruments and with greater accuracy, the lengths 

 of the arcs of parallels and the differences of the meridians 

 between Beachy Head and Dunnose, as well as between 

 Dover and Falmouth. These determinations were, however, 

 only made for differences of longitude of 1 26' and 6 C 22' . 8 

 By far the most considerable of these surveys is the one that 

 was carried on between the meridians of Marennes, on the 

 western coast of France, and JFiume. It extends over the 

 western chain of the Alps, and the plains of Milan and Padua, 

 in a direct distance of 15 32' 27", and was executed under 

 the direction of Brousseaud and Largeteau, Plana and Car- 



epeaking, 1.84. According to the earliest determinations, the length of 

 the metre was determined at 0.5130740 of a toise, while according to 

 Bessel's last determination it ought to be 0.5131180 of a toise. The 

 difference for the length of the metre is, therefore, 0.038 of a French 

 line. The metre has, therefore, been established by Bessel as equal 

 to 443.334 French lines, instead of 443.296, which is its present legal 

 value (Compare also, on this so-called natural standard, Faye, Lemons <U 

 Cosmographie, 1852, p. 93). 



8 Airy, Figure of the Earth in the Encycl. Metrop. 1849, pp. 214216. 



