M7 



OEODEST. 



OBODBST. 



those of the (tattoo* at the extremities of e*eh side. Th 

 pp< tiled to each station urn to indicate whether the s 

 situate in EngUod (K.), Wale* (W.i. Scotland (8.), Ireland (I. 



Length In Ml!c. 



FUrre rtooird. I. Sci Fell, E ..... Ill-; 



Bllrn Dosuud, 1 Snowilon, W ..... 108-0 



PrwUr. W. Kippure, I ...... J07-S 



Merrick, 8. B*n More, Mull, 8. .... 107-4 



tee Don.rd, I. Criffcl. S ...... 108-1 



Jam, 8. Bn More, s. rial, S ...... 106-0 



South Berulr, I. M. Goat rrU, S ..... 104-1 



Mieve Donard, I. Goal Fell, S ....... 104-1 



Snowdon, \V. Ingleboraugb, K ..... 1' 2-fi 



Snowdon, W. Sea Fell, E ...... 103-2 



CnllMih, I. Keeper, 1 ...... 101-9 



Keeper, I. Sephln, 1 ....... 88-J 



Uerrlck, 8. Bra Lawen, 8. ..... 97-7 



Frteelly. W. Mount Leiniter, 1 ..... 98-9 



Bnowdon, W. Ballycreen, 1 ...... 96-1 



Kippurr, I. South Bf rule, 1. M. . . . 95-8 



Klppnre, I. Gullymorr, 1 ...... 95-7 



Baurtrcgaum, I. Knockanaffrln, I. ... 92-5 



KnocUayJ, I. Ben Lomond, S ...... 95-3 



Preeelly, W. Ballycreen, 1 ...... 9J-1 



Klppure, I. Snowdon, W. ..... 94-1 



Cuileagh, I. Klppnre, 1 ...... 93-5 



Frecc-lly, W._Hlgh Wilhay*, F ..... 98-J 



Snowdon, V. Tan, 1 ....... 91*1 



Ben Macdul, S Barn Law, 8 ...... 3-0 



Ben More, 8. fist, 8. Ben Nevis, S. 92-9 

 South Bcriilr, I. M Ingleborougb, E. ... 



Snowdon, W. Pcndlohill, K ...... 91-9 



Ben Corr, I. Brandon, 1 ....... 90'0 



The length of the entire arc of the meridian included between 

 Dunnoee and Sazarord was found to be 8,729,334-07 feet. The 

 distances between the parallels of Dtmnoae, Arbury, Clifton, Ka^ini;- 

 ton, and tSaxsvord were separately computed. The following are the 



DunnoM to Arbury" 

 Arbury to Clifton 

 Clifton to Eaein.Bton 

 EMingtou to Saxarord 



Feet. 



686,356-38 



450,225-16 



404.32.V22 



2,288,427-33 



8,729,SS4-C7 



The distance between the parallels of Eosington and Saxavord, which 

 lie very nearly upon the same meridian, was computed by two different 

 ysterns of triangles. The results were : 



2,288,427'29 feet, by the one (system of triangles. 

 2,288,427-38 feet, by the other 



Mean 2,288,427-83. 



By the first calculation, the distance of Saxarord from the assumed 

 meridian at Easinpton was 222'56 feet ; by the second calculation it 

 was 221 '94 feet. The difference of the two results amounts to only 

 0-62 feet. 



The operations connected with the great Trigonometrical Survey of 

 India hare resulted in the measurement of an arc of the meridian which 

 in extent is second only to the RuRo-Scandinavian Arc, to be presently 

 alluded to. This important undertaking was commenced in the year 

 1801, under the superintendence of Colonel Lambton. A base was 

 measured in the neighbourhood of Madras, which served as the ground- 

 work for the measurement of an arc of the meridian of about a degree 

 and a half in amplitude. By a course of triangulation, Colonel Lambton 

 subsequently advanced westward to a place called Dodagonntah, about 

 170 miles distant from Madras, where he measured a second base. He 

 now directed his operations southwards, forming a chain of triangles 

 which ultimately reached Punnso (Lat. 8" 9' 85") near Cape Comorin. 

 Bines of verification were measured both at the middle of the arc and 

 at the southern extremity. The arc was subsequently prolonged 

 northwards by Colonel Lambton as far as Damargida, in lat. 18 3' 15". 

 Near this station, at Beder, another base of verification was measured 

 in the year 1815. 



The amplitude of the Indian arc, extending from Punnjo to 

 Damargida, it will be wen, now amounted to 9 53' 40". Witli the 

 view of prolonging it still further north. Colonel Lambton measured a 

 base near Takal Khera, which he intended to be the limit of the next 

 section of the arc. Upon the death of that officer in 1823, Colonel 

 (then Captain) Everest was appointed bis successor, by whom the 

 triangulation was continued from Damargida to Kalianpur, in lat. 24* 

 V 11-8" near which, in the plain of Seronj, another base of verification 

 was measured. 



The base lines determined by Colonel Lambton and Colonel Everest 

 in the course of the operations to which allusion has jutt been made, 

 were measured with a steel chain a hundred feet long, as in the case of 

 the earlier measurements of a similar kind connected with the survey 

 of the British Isle*. The terrestrial angles were measured with a 

 theodolite, 8 feet ID diameter, constructed by Cary, and the latitude* 



were ascertained with a zenith-sector 'of 5 feet radius, by Ramsden. 

 It would appear, according to the candid exposition of Colonel Everest, 

 that the results of Colonel Lambton's operations, and of those hitherto 

 ted by himself, are not entitled to so high a degree of reliance 

 as the present advanced state of geodesy demand*. The azimuths! 

 circle of the great theodolite had received an accidental blow, and 

 although Colonel Lambton had, to a great extent, succeeded in 

 obviating the effects of the injury, still the subsequent use of the 

 instrument, even with the utmost precaution, could not be regarded as 

 altogether unexceptionable. Again, it was found that previous to the 

 measurement of the base at Takal Khera, the joints of tin- chain were 

 found to be thickly covered with rust, the removal of which could 

 scarcely have failed to affect the length of the chain. In the measure- 

 ment of the base, the chain was not supported on coffers, or stretched 

 by a constant weight. The process employed was to lay it 

 ground and stretch it by means of a hand-capstan. The length of the 

 Beder base when computed through the series of triangles from the 

 base at Takalkbera was found to differ from its measured length 

 by 78'72 inches. It was clear therefore that the results did not possess 

 all the precision desirable in such important operations. Great allow- 

 ance must, however, be made for the difficulties arising from the 

 climate and other unfavourable circumstances. (Lambton, ' Asiatic 

 Researches,' vols. viii., x., xii., xiii. ; 'Phil Trans,' 1818; Everest, 

 4 Account of the Measurement of nn Arc of the Meridian betwe 

 Parallels of 18" 8', and 24 7', &c.', 1830.) 



Colonel Everest, who had been compelled by ill-health to proceed to 

 England, returned to India in 1830, with the view of resuming hi 

 geodetical labours. For this purpose the East India Company had 

 provided him with an ample supply of instruments of tho very first 

 quality. He commenced his operations with the measurement of a 

 base at Dhera Dun, near Kaliana, in lat. 29 30' 48*, about 70 miles 

 from the foot of the Himalayas. On this occasion the m 

 was effected with bars provided with Colby's compensation apparatus. 

 From Kaliana the triangulation was extended southwards until at 

 length in 1837 it reached Kalianpur, the northern extremity of the 

 great arc. Upon computing the length of the Seronj ba. 

 been measured in MI tho recently measured baw at Dhera 



Dun, it was found that the measured and computed results din", 

 the extent of 3J feet. In consequence of this discordance, ( 

 Everest measured the Seronj base anew. This important op. 

 was brought to a close in the early part of 1 838. It <m the 



result that an error of nearly 3 feet had been committed in the 

 measurement of 1824. 



In order to remove all suspicion from the measurement of the arc 

 included between Damargida and Kalianpur, Colonel Everest, taking 

 advantage of an interruption of his labours, occasioned by the neces- 

 sity of modifying the instruments for determining the c. 

 amplitudes, resolved to determine afresh the whole terrestrial d : 

 between those two stations. The triangulation was effected by t 

 Waugh and Captain Renny. In 1840 a new base was measured by 

 Captain Waugh in the vicinity of Damargida, It was found impos- 

 sible to identify the nito of the old Beder base measured by Colonel 

 Lambton in 115. The results of the new base measurements were 

 found to be extremely satisfactory. The length of tha Dhera Dun 

 base, when computed from the Seronj base, was 89183-273 f. ct. The 

 measured length was 89183-878 feet. The difference consequently 

 amounted to only 0'600 feet, or rather more than 7 inches, while the 

 distance between the two bases was about 430 miles. The result of a 

 comparison of the measured length of the Beder base and its length as 

 computed from the Seronj base was equally satisfactory. In this 

 case, although the distance between the two bases amounted to 426 

 miles, the difference between the measured and computed results was 

 only a little more than 4 inches. 



For ascertaining the amplitudes of the two sactional arcs, Kaliana- 

 Kalianpur, and Kalianpur-Damargida, Colonel Everest employed the 

 method founded on simultaneous observations, at the extremities of 

 each arc, of the zenith distances of certain stars selected beforehand 

 for the purpose. The observations were made with two vertical circles, 

 8 feet in diameter. The amplitude of the northern section was deter- 

 mined by observations of thirty-nix stars, one half to the north and 

 the other half to the south of the zeniths of hot The obser- 



vations at Kaliana, which were made by Colonel Everest and Captain 

 Kenny, were nearly, but not quite, simultaneous with those made at 

 Kalianpur by Captain Waugh. For the determination of the ampli- 

 tude of the southern section of tho arc, extending from Kalianpur to 

 Damargida, thirty-two stars were simultaneously observed. The 

 result* gave 6" 28' 87"-051 for the amplitude of the arc between K 

 and Kalianpur, and 3' 65" 1 !7S for the ampli' 

 Kalianpur and Damargida. The amplitude of the < n 

 by Colonel Everest consequently amounts to 11* 27' 88"'024. If to 

 this we add 9 63' 40", the amplitude of the arc measured by Colonel 

 n, we obtain 21" 21' l.T-024 for the entire length of the great 

 meridional arc of India. ('Account of the Measurement of Two 

 Sections of the Meridional Arc of India, Bounded by the Parallels of 

 18" S 15"; 24* 7' 11"; and 29* 30' 48".' By Lieutenant-Colonel 

 Everest. London, 1847.) 



The great I arc of Russia originated in the operations 



connected with the trigonometrical survey of the Russian empire. 



