GEODESY. 



r.EOGRAPHT. 



Colonel Everest, in hi* 'Account of the Measurement of Two 

 Btf*t"i>* of the Meridional Arc of India, fto.,' ha* deduced the elements 

 of the earth's figure from a discussion of twelve arcs of the meridian. 

 Hi* final results are 



0=80,920,902 feet 

 = 20,858,642 



J 



<= * 311-04 " 



In the ' Account of the Principal Triangulation, Ac.,' relating to the 

 Ordnance Surrey of the British Isles, Captain Clarke has inves- 

 tigated the elements of the spheroid which most nearly represents the 

 surface of Great Britain. The following are the final results obtained 

 by him: 



0=20,927,005 feet, 

 = 20,852,372 

 1 



* = 280-4 " 



From these elements Captain Clarke has deduced the following 

 results : 



1. Radius of curvature of the meridian 



= 20,889,705-111,949 cos 2A + 250 cos4A. 



2. Radius of curvature perpendicular to the meridian 



= 20,964,404-3745-0 cos 2A + 50 cos 4A. 



8. Radius of parallel 



= 20,945,679 cos A-18,700 cos 3A + 25 cos 5A. 



4. Length of a meridian arc whose amplitude is <f> and mean 

 latitude A 



= 20,889,705 0111,949 sin^ cos2A+125 sin2^>cos4A. 



5. Length of a degree of the meridian 



= 364,594-1-1953-8 cos 2A + 4'4 cos 4A. 



6. Length of a degree of longitude 



= 365,571-0 cosA 326-4 cos 3A + 0-4 cos 6A. 



These formulte are, of course, applicable only to the surface of Great 

 Britain. 



In the work above cited, Captain Clarke has also investigated the 

 elements of the earth's figure by a discussion of the totality of trust- 

 worthy arcs of the meridian hitherto measured on the earth's surface 

 (with the exception of Mr. Maclear's arc). The following are the final 

 results: 



0=20,926,348 feet 



6=20,855,233 

 1 



f - 294-26 " 



These elements give for the radius of curvature of the meridian the 

 following expression : 



P= 20,890,805-106,678 cos 2A + 227 cos 4A. 



And for the length of a meridian arc whose amplitude is <p and mean 

 latitude A, the following value : 



8=20,890,805, 106,678 cos 2A sin <f> + 113-5 cos 4A sin 2<f>. 



From the same elements the value of a mean degree of the meridian 

 U found to be 



= 364,613-33 8-0 feet, 



whence the length of the ideal metre 



= 39-378401 -000324 inches. 



Captain Clarke has subsequently shown ('Monthly Notices of the 

 Royal Astronomical Society,' vol. xix., page 36) that the introduction 

 of Mr. Maclear's value of the Cape arc into the investigation does no 

 sensibly modify the final results. 



The most recent investigation of the figure of the earth i* due to 

 General Schubert. (' K*sai d'une Determination de la veritable Figure 

 de U Terre, Mem. de 1'Acad. Imper. de St. Petorsbourg,' vii. serie 

 tome I, No. 8 ; ' Monthly Notice* of the Royal Astronomical Society, 

 vol. xx.. page 104.) His investigation is based upon eight arcs of thi 

 meridian, in which the longitudes are measured eastwan 



Combining these arc* two and two, General Schubert obtain* 

 renty-eight different sets of element* exhibiting great discordance*. 



le i* thereby led to luspeot that the earth U not a solid of revolution. 



f thi* surmise be correct, then all comparisons of arc* of meridian 

 under different longitude* are inadmissible. Assuming the terrestrial 



nrridiam to be ellipse* and the minor axis to be constant for all 

 meridians, he proceed* to determine the value of the minor axi* by a 



oraparison of two different sections of the same arc. Treating the 



tuswan arc and the Indian are in thi* way, he obtains two different 

 values of the minor axis agreeing nearly with each other. The mean 

 of the two results gives 3,261,468 for the number of toises contained 



n the polar scmi-axi*. 



With this value of the minor axis General Schubert investigates the 

 major axes of the meridians of the Peruvian, Russian, and Indian arc*. 



The following are the results obtained by him : 



Longitude. Tolae*. 



Major aris of Peruvian meridian . 298'' 44' 8,272,383 



Russian . . 44 18 8,272,650 



,, Indian . 95 20 3,172,581 



Assuming the terrestrial equator to be an ellipse, General Schubert 

 calculates its elements from the foregoing three radii vectore*, and 

 thus finds. 



Major semi-axis 8,171,671 ; Its longitude 58' 44' or 188 44' 

 Minor semi-axi* 3,272,505 ; tta longitude 148' 44' or 328' 44'. 



imaginary meridian 20 west of Paris. 



Latitude. 



Rnudan are . 

 Indian an . . 

 French are . 

 Cap* arc 

 Pern<Un an . 

 Pruwtan arc . 

 KnglUh an 

 PenniTlranlan arc 



45 20' to 70 40* 



8 10 19 31 



51 1 



54 21 



,. -3 



55 41 



60 50 



39 56 



38 40 



-19 44 



3 



54 13 



37 



88 17 



aitwardly from an 



Longitude. 



44" 23' 



95 20 



10 



36 9 

 S98 44 



88 10 



17 40 

 300 10 



The combination of these with the polar meridian gives ,5,, and 

 .he values of the eliipticity of the two principal meridians. 



With these elements General Schubert computes the radii of the 

 equatorial ellipse corresponding to the different arc*. These radii are 

 of course the major axes of the respective meridian*. With the arc* 

 computed from these elements, and the astronomical differences of 

 utitude, the geodetic measures are compared. The residual difference! 

 are as follows : 



Geodetic amplitude. Aitronomlcal Amplitude. 



Arc of Meridian. 



Peruvian arc . 

 Pennsylvania!! 

 English 



French . . 

 Capo of Good Hope 

 Prussian . . 

 Russian . . 

 [ndlaa . 



+ 0"-077 

 6 -687 

 , +0 -736 

 , 1 -C07 

 . -442 

 , +1 -287 

 , 1 -289 

 , +1 -019 



The Pennsylvaninn arc was measured entirely with rods ; it is not 

 entitled to any confidence. In the Indian arc no account is taken of 

 the disturbing influence produced by the attraction of mountains. 



For the values of the terrestrial eliipticity deduced from oscillations 

 of the pendulum in different latitudes, and from the theory of the 

 moon's motion, see the articles PENDULUM and MOON. 



GE9GRAPHY (a term derived from the Greek >wypo^fo, geo- 

 grdphia) is a science the general object of which is to describe the 

 surface of our globe. Its more vpecial object is to ascertain and 

 describe such physical peculiarities in each country as tend to promote 

 or retard the increase of population and the arts of civilised life. 



The political condition of a nation and the changes to which it is 

 subject are in a great degree dependent on the character of the country 

 which it inhabiU, or of those countries which surround it. The difference 

 in civilisation observed in nations living near one another may also in a 

 great degree be ascribed to the same cause. Accordingly we find that 

 as soon as men began to apply themselves to the explanation of such 

 changes and differences, they were obliged to look to the particular 

 character of the countries inhabited by those nations whose history it 

 was their object to investigate. Geography is coeval with history. It 

 is as impossible to form a just idea of the events which have been 

 most decisive in the history of a nation without a knowledge of their 

 country, as it is to understand the movements of two armies on a field 

 of battle without knowing the nature of the ground which i* the scene 

 of their operation*. 



The first traces of anything like a geographical system, in the litera- 

 ture of the western world, occur in the Homeric poems. According 

 to the Rev. Mr. Bevan, the learned author of the department of 

 Am i' lit Geography in the ' Manual of Geographical Science,' we 

 should be warranted in saying, that these represent the state of geo- 

 graphical knowledge down to the commencement of the 9th century, 

 B.C. " Not that there is any methodical exposition of the view* of the 

 age on this subject," says Mr. Bevau ; " the nature and matter of the 

 poems would not admit, nor lead us to expect, as much ; but the inci- 

 dental notices are numerous enough to enable us to picture to ourselves 

 the world as Homer conceived of it, and have therefore obtained for 



him the reputation of being the first geographer HOUUT, like 



many of his successors, was totally ignorant of the ipherical form of 

 tin- world ; be conceived it to be a flat circular body, the upper face of 

 which was the habitation of men, while the lower was the region of 

 Tartarus^the abode of the punished godt. Over tlie earth ti 

 the vault of heaven, and round it flowed incessantly the sti< 

 ocean. The heaven rested in its extremities on the surface of the 

 earth." The ocean which surrounded the earth like the rim of a 



