THE INTERIOR OF THE EARTH. 291 



has an important bearing on any hypothesis of the internal constitution 

 of our planet. Geodesy, that science that may be called surveying on 

 a grand scale, and which takes for its bases of measurement at once 

 the earth and the heavens, has not yet completed its work. Since the 

 labors of the Abbot Picard, to whom we owe the first measurement of a 

 meridional degree, and the celebrated voyages of Bouguer and La Con- 

 damine to Peru, and of Maupertuis to Lapland, which confirmed the 

 supposition of the flattening of the earth, there have been many other 

 immense labors of a similar kind all over the world. The Societe 

 Geodetique Internationale, organized some years ago, is occupied in 

 compiling and perfecting the results of these researches, and in deduc- 

 ing therefrom a provisionally definite result. We know with certainty 

 that the form of the earth is not greatly different from that of a per- 

 fect sphere, for the flattening ascertained by geodetic measurements is, 

 in round numbers, equal to y^-, from which it follows that the equa- 

 torial radius does not exceed the polar by more than twenty-two kilo- 

 metres* (a little less than fourteen miles). This number, which repre- 

 sents the amount of the equatorial swelling, is equal to four and a half 

 times the height of Mont Blanc, but, on a ball thirteen metres in diam- 

 eter, the twenty-two kilometres in question would make an inequality 

 of only two centimetres (about three fourths of an inch), and this would 

 be totally imperceptible to the eye. The natural inequalities of the 

 earth's surface are comparatively insignificant ; the Alps and Hima- 

 layas, on a ball thirteen metres in diameter, would be represented by 

 projections of a few millimetres only, and the greatest ocean-depths 

 would not exceed one centimetre. 



The question of the true figure of the earth is one of the most dif- 

 ficult of problems. From the time of Newton it had been held that 

 the earth was a revolving ellipsoid in other words, that the meridians 

 were ellipses, and the equator and all the parallels true circles ; and it 

 only remained to determine the ellipticity of these meridians, all being 

 supposed alike. It is now twenty years since Captain Clark's calcula- 

 tions, based on the uniformity of the great triangulations made up 

 to that period in various parts of the world, led to the conclusion that 

 the equator itself has an elliptic form, and that, consequently, the 

 meridians are ellipses unequally flattened. According to Clark, the 

 equatorial flattening is 3^-0, or about one tenth of the average flatten- 

 ing of the meridians. This depression, amounting to two kilometres, 

 occurs under the meridian passing, in the east, through the Sun da 

 Archipelago, and in the west through the Isthmus of Panama, while 

 the enlargement occurs under the meridian of Vienna, crossing central 

 Europe and Africa. Thus, according to the calculations, the world is 

 an ellipsoid with three unequal axes. This supposition can be made 

 to harmonize with the hypothesis of the primitive fluidity of the earth, 

 the form in question being one of those assumed by free liquids in 

 * The length of a kilometre is about five eighths of a mile. 



