Mr. Ivory on the Figure of the Earth. 205 



principles. The problem then to be solved, is that of distri- 

 buting with all possible accuracy, according to those principles, 

 and relatively to the circumstances under which any population 

 or select class is acknowledged to exist, the comparative total 

 of such population (supposed stationary) or class as arising 

 from a stated quantity of annual births. 



5, Hercules' Buildings, Lambeth. 7th Nov. 18.38. 



XXXII. Some Argumetits fefidhig to prove that the Earth is a 

 Solid of Revolution. By James Ivory, Esq. M.A. F.R.S.<$'c.* 



TN the investigation of the figure of the earth, the first point 

 -*■ that engages attention, is to determine the nature of the 

 meridians. Are these all equal and similar curves ? or are 

 they variable or irregular in their form? It can hardly be 

 expected that these questions can be answered with the strictest 

 mathematical precision. There will occur, it is likely, discre- 

 pancies caused both by local circumstances and by the want 

 of perfect exactness in the data of observation. But at the 

 same time that, in every particular measurement, the greatest 

 care must be taken to insure the utmost degree of accuracy 

 compatible with experimental operations, we must likewise 

 endeavour to deduce some general conclusion from a com- 

 parison of the whole series of individual results, and to form 

 a general notion of the figure of the earth, overlooking local 

 and casual irregularities. Unless we thus attempt to genera- 

 lize the knowledge we obtain, the inquiry, it is evident, would 

 lose much of its interest and utility. The most probable in- 

 ference that we can at present draw from the best measure- 

 ments that have been made, is that the meridians are equal 

 and similar ellipses, the difference of the two semi-axes being 

 about 'OOSSt of the equatorial semi-diameter. 



But if the meridians be equal and similar ellipses, the earth 

 must necessarily be an oblate spheroid of revolution. And 

 there are not wanting arguments that very forcibly confirm 

 this inference. In all times, past and present, it has been 

 assumed that a terrestrial meridian is a plane containing the 

 earth's axis; and likewise that a j)lumb-line, or a perj)endi- 

 cular to the earth's surface, lies wholly in one plane with the 

 same axis. AH astronomy is built on these supjiositions, and 

 no grounds have ever occurred that make their accuiacy (jues- 

 tionablc. Now the pi-operties we have mentioned belong ex- 



• Coinimmitatctl hy tUc Autiior. 



dubivfly 



