Feb. 14, 1884] 



NA 1 URE 



361 



special attention of photographers and engravers. An 

 appendix, separately paged, of 120 pages, completes the 

 volume, and consists of extracts from the narrative report 

 of the executive officers in charge of the survey parties 

 and operations. 



This report is distinguished from previous ones by 

 announcing the completion of the great triangulation on 

 the lines originally marked out in 1830 by Col. Everest, 

 which affords the Surveyor-General, in his introductory 

 statement, an opportunity of giving a brief but interesting 

 history of this great undertaking from its commencement 

 in the vear 1800, in Southern India, by Major Lambton, 

 on the recommendation of the Hon. Col. Wellesley, after- 

 wards the Duke of Wellington. The object of this 

 so-called " Mathematical and Geographical Survey " was 

 then stated to be "to determine the exact positions of all 

 the great objects best calculated to become permanent 

 geographical marks to be hereafter guiJes for facilitating 

 a general survey of the peninsula," and further, that in 

 the interests of general science it would have to be 

 executed with the utmost possible precision, and be 

 supplemented by astronomical determinations of po?ition, 

 with a view to the requirements of geodesy. 



The operations between the years iSooand 1825 may 

 be briefly described as consisting of a network of tri- 

 angulation over Southern India, and through the middle 

 of which a principal chain of triangles was carried in a 

 meridional direction from Cape Comorin up to Sironj in 

 Central India. This chain forms that which is now 

 known as Lambton and Everest's Great Arc. Col. 

 Lambton died in 1823, and was succeeded by Col. 

 Everest, who, two years afterwards, proceeded to Europe, 

 spending four years in supervising the construction of 

 new instruments — great theodolites, astronomical circles, 

 standards of length, and compensation bars for base-line 

 measurements, for employment in extending and revising 

 the Great Arc, the importance of which was recognised 

 by all men of science in Europe. 



Returning to India in 1830, Col. Everest recommended 

 the abandonment of the network system of triangulation 

 and the substitution instead of what he called the "grid- 

 iron " system, consisting of meridional chains of triangles 

 tied together at their upper and lower extremities by 

 longitudinal chains. The meridional chains were to be 

 constructed at intervals of about one degree apart, while 

 longitudinal chains would follow the parallels of Calcutta, 

 Bombay, and Madras, and thus run at intervals of from five 

 to six degrees apart. The external chains of the gridiron 

 would of course follow the British frontier lines and the 

 coast lines, and all grounded on ten base lines measured 

 with the Colby apparatus of compensation bars and micro- 

 scopes. This programme of operations was approved by 

 the Government of India and Court of Directors, and 

 has furnished the guiding lines on which the principal 

 triangulation has been executed during the period of 

 almost exactly fifty years which has since elapsed. For 

 geodetic purposes, the amount of principal triangulation 

 is now ample. Outside the limits of India proper, the 

 recently completed chain of principal triangles, called the 

 eastern frontier series, is a valuable contribution to 

 geodesy and geography. 



Thus the great work of the principal triangulation of 

 Fndia is now an accomplished fact. Commenced in iSoo, 

 under the auspices of the Madras Government, it was 

 carried on, almost alone, by Major Lambton, until 1S18, 

 when the Marquis of Hastings, then Governor-General, 

 placed it under the control of the supreme Government, 

 and Capt. Everest was appointed assistant to Major 

 Lambton. In 1832 additional officers were appointed, 

 and by the year 1S40, when the northern section of the 

 Great Arc was completed, the personnel sufficed for the 

 equipment of six triangulation survey parties, which 

 number has been uniformly maintained from that time 

 onwards until gradually diminished on the completion of 



the successive chains of triangles. The operations have 

 been uniformly and consistently supported by successive 

 Governments of India with equal liberality and con- 

 stancy, and to whom it must be a source of much satisfac- 

 tion to know that this great work of permanent peaceful 

 usefulness will assuredly take the highest rank as a work 

 of scientific labour and skill. 



It is stated that there are 3472 principal s'ations. On 

 the plains they are constructed in the form of towers, 

 rising from 20 to 40 and even 60 feet above the ground, 

 and usually about 16 feet square at base, with an isolated 

 central pillar for the instruments to rest on. On hills and 

 mounds and other eminences the central pillar, always of. 

 masonry, is raised 2 to 4 feet above the ground level, and 

 is surrounded with a platform of earth and stones. Mark- 

 stones, engraved with circle and central dot to define 

 precisely the station point of observation, are inserted at 

 the surface and at the base of the pillar. The stations, 

 scattered over 338 Briii-h districts and native states, are 

 placed under the protection of local officials, each of 

 whom is required to send annual reports of the condition 

 of the stations within his district. Repairs are effected 

 when necessary, and if so maintained by [future genera- 

 tions of officials, the duration of the stations should be 

 coeval "with the hills and plains on which they stand, 

 and be of lasting utility. 



The field operations of measurements of base-lines and 

 angles of the principal triangulation being completed, the 

 simultaneous reduction of the vast number of such facts, 

 acquired over all India, by many individuals and during 

 a period of many years, to a harmonious whole, was 

 obviously impossible. Thus it became necessary to divide 

 the triangulation of India proper into five sections ; and 

 even then the simultaneous reduction of the numerous 

 facts of observation collected together in each group was 

 a work of enormous labour, necessitating, as stated by 

 the most eminent living authority (Col. Clarke, C. B., 

 Geodesy, p. 257), " the most elaborate calculations that 

 have ever been undertaken for the reduction of triangula- 

 tion by the method of least squares." The final results 

 of the first section are given in vols, ii., iii , and 

 iv. of the '■ Account of the Operations of the Great 

 Trigonometrical Survey of India," published in 1S79 

 (vol. i. is devoted to base-lines, and vol. v. to pendulum 

 operations) ; those of the second section in vol. vi., pub- 

 lished in 18S0, and those of the third in vols. vii. and 

 viii. will be shortly published. The simultaneous reduc- 

 tion of the fourth section is now com[.leted. The final 

 reduction of the last section has not yet commenced, nor 

 has the recently completed eastern frontier series. 



The requirements of geodesy necessitate a:tronomical 

 observations for the determination of latitude and azimuth 

 and electro-telegraphic observations for the determination 

 ofdiffereiicesoflongitude at several stations of the principal 

 triangulation. These have already been completed to a 

 considerable extent ; and further operations of this nature 

 are in progress by two small astronomical parties attached 

 to the geodetic branch of the department, and by whom 

 all the operations subservient to geodetic science should 

 be completed in the course of a few years. .An extensive 

 series of pendulum observations for investigations of 

 gravity and the figure of the earth, tiken chiefly at 

 stations of the principal triangulation, has been completed 

 and connected with the groups of corresponding observa- 

 tions in other parts of the globe. Long lines of spirit 

 levels have been, and are still being carried on in connec- 

 tion with the principal triangulation, from the sea to the 

 base-lines in the interior, and from sea to sea across the 

 peninsula ; they rest on determinations of the mean sea 

 level, which have been and are being made at tidal 

 stations on the coasts, and which promise to furnish most 

 in portant data by means of which our knowledge of the 

 constitution of the earth's mass may be extended. 



Reference can only be here made to the report for most 



