FIGURE OP THE EAETH. 155 



ancient geognostic events, as every attentive reader of the 

 book of .nature can easily discern ; and an analogous fact is 

 presented in the case of the Moon, the perpetual direction 

 of whose axes towards the Earth, that is to say, the increased 

 accumulation of matter on that half of the Moon which is 

 turned towards us, determines the relations of the periods of 

 rotation and revolution, and is probably contemporaneous with 

 the earliest epoch in the formative history of this satellite. 

 The mathematical figure of the Earth is that which it would 

 have were its surface covered entirely by water in a state of 

 rest ; and it is this assumed form to which all geodesical 

 measurements of degrees refer. This mathematical surface is 

 different from that true physical surface which is affected by 

 all the accidents and inequalities of the solid parts.* The 

 whole figure of the Earth is determined when we know the 

 amount of the compression at the poles and the equatorial 

 diameter ; in order, however, to obtain a perfect representa- 

 tion of its form it is necessaiy to have measurements in two 

 directions, perpendicular to one another. 



Eleven measurements of degrees, (or determinations of the 

 curvature of the Earth's surface in different parts,) of which 

 nine only belong to the present century, have made us ac- 

 quainted with the size of our globe, which Pliny named " a 

 point in the immeasurable universe. "f If these measurements 

 do not always accord in the curvatures of different meridians 

 under the same degree of latitude, this very circumstance speaks 

 in favour of the exactness of the instruments and the methods 

 employed, and of the accuracy and the fidelity to nature of 

 these partial results. The conclusion to be drawn from the 



* Bessel, Allgemeine Betrachtungen uler Gradmessungen nach astro - 

 nomisch-geodatischen Arbeiten, at the conclusion of Bessel and Baeyer, 

 Gradmessung in Ostpreussen, s. 427. Regarding the accumulation of 

 matter on the side of the Moon turned towards us, (a subject noticed in 

 an earlier part of the text,) see Laplace, Expos, du Syst. du Monde, 

 p. 308. 



t Plin., ii. 68. Seneca, NaP Quast. Praef., c. ii. " El mundo es poco," 

 (the Earth is small and narrow) writes Columbus from Jamaica, to Queen 

 Isabella, on the 7th of July, 1503 ; not because he entertained the philo- 

 sophic views of the aforesaid Romans, but because it appeared advantageous 

 to him to maintain that the journey from Spain was not long, if, as he 

 observes, " we seek the east from the west." Compare my Examen crit. 

 de VHist. de la Giogr. du 15me Si&le, t. i. p. 83, and t. ii. p. 327; 



