164 ' COSMOS. 



compression at the poles and the equatorial diameter ; m or- 

 der, however, to obtain a perfect representation of its form it 

 is necessary to have measurements in two directions, perpen- 

 dicular to one another. 



Eleven measurements of degrees (or determinations of the 

 curvature of the Earth's surface in diflerent 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."* If these measurements 

 do not always accord in the curvatures of different meridians 

 under the same degree of latitude, this very circumstance 

 speaks in favor 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 increase of forces of attraction (in the direction from 

 the equator to the poles) with respect to the figure of a planet 

 is dependent on the distribution of density in its interior. 

 Newton, from theoretical principles, and perhaps likewise 

 prompted by Cassini's discovery, previously to 1666, of the 

 compression of Jupiter,! determined, in his immortal work, 

 PhiLoso2:)hice Naturalis Principia, that the compression of the 

 Earth, as a homogeneous mass, was -^^-^Xh.. Actual meas- 



* Plin., ii., 68. Seneca, Nat. Qucest., Prcef., c. ii. " El mundo as 

 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 philosophic views of the aforesaid Romans, but because it appeared 

 advantageous to him to maintain that the journey from Spain w^as not 

 long, if, as he observes, " we seek the east from the west." Compare 

 my Examen Crit. de VHist. de la Geogr. dn 15me Siecle, t. i., p. 83, and 

 t. ii., p. 327, where I have shown that the opinion maintained by De- 

 lisle, Fr6ret, and Gosselin, that the excessive differences in the state- 

 ments regarding the Earth's circumference, found in the writings of 

 the Greeks, are only apparent, and dependent on different values being 

 attached to the stadia, was put forward as early as 1495 by Jaime Fer- 

 rer, in a proposition regai'ding the determination of the line of demark- 

 ation of the papal dominions. 



t Brewster, Life of Sir Isaac Newton, 1831, p. 162. " The discovery 

 of the spheroidal form of Jupiter by Cassini had probably directed the 

 attention of Newton to the determination of its cause, and, consequent- 

 ly, to the investigation of the true figure of the Earth." Although Cas- 

 sini did not announce the amount of the compression of Jupiter (—jth) 

 till 1691 (Anciens MSmoires de V Acad, des Sciences, t. ii., p. 108), yet 

 we know from Lalande (Astron., 3me ed., t. iii., p. 335) that Moraldi 

 possessed some printed sheets of a Latin work, " On the Spots of the 

 Planets," commenced by Cassini, from which it was obvious that he 

 was aware of the compression of Jupiter before the year 1666, and 

 therefore at least twenty-one yeai's before the publication of Newton's 

 Principia. 



