TRANSACTIONS OF THE SECTIONS. 3 



tions, the superintendence of which had also fallen on himself, had been commenced 

 more lately : and this he characterized as by far the most important astronomical 

 work which had been for many years undertaken. The observations were reduced 

 by means of Bessel's tables. The places of the moon deduced from the observa- 

 tions were compared with places computed from Plana's theory, modified by 

 certain corrections introduced by Sir J. W. Lubbock and M. de Pontecoulant. For 

 this theoretical computation, Damoiseau's tables had been used as basis, and small 

 supplementary tables had been computed for the difference between Damoiseau's 

 theory and Plana's corrected theory. Thus the observations, reduced by a uniform 

 system of sidereal tables, would be compared with the best lunar theory in existence. 

 In Damoiseau's tables (edition 1824) the centesimal division of the circle is intro- 

 duced, which affords much facility in the calculations. A few months would now 

 complete the calculations ; but the printing had not yet commenced. Fourteen com- 

 puters were usually engaged upon them ; and by certain improvements which he had 

 introduced into the methods of computing, such as discarding the use of the negative 

 sign altogether, by increasing the quantities from which they could result by a con- 

 stant number, he had been able, in many instances, to avail himself of the assistance 

 of boys as computers, and thus saved the heavy expense of the more experienced 

 persons. The lunar observations reduced amounted to about 9000 ; and the compu- 

 tations were made in duplicate, for the purpose of detecting errors. 



On the Geodetical Operations of India. 

 By Lieut.-Col. Everest, F.R.S., S^c, late Surveyor-General of India. 



A series of triangulations on the most magnificent scale has for many years been 

 conducted in India, by Colonel Larabton up to the year 1823, and after his death by 

 Colonel Everest (who had for some years previous been his chief assistant) up to the 

 close of 1843, when this officer resigned the charge to Captain Waugh of the Bengal 

 Engineers, who had been trained by him in the habits of exact observation. As the 

 Court of Directors of the East India Company have, with their characteristic libera- 

 lity, directed the publication of Colonel Everest's labours, it is unnecessary to enter 

 into the details of the account of them which he laid before the Section, further than 

 to notice a few facts^ -which may give some notion of their probable accuracy, and 

 the immense exertion reqoic^d to obtain it in such a climate. 



Colonel Everest published in 1830 an account of his work from Damargida, the 

 northern extremit)^ of Lambton's arc, lat. 18° 3' 16", to Kalianpur, lat. 24° 7' 12"; 

 but as he then was furnished with new instruments by Troughton and Simms, supe- 

 rior to those which he previously possessed, he repeated all this, and extended it aa 

 far as Kaliana, lat. 29° 30' 49", where his celestial arc terminates. The terrestrial is 

 carried further to Banog, lat. 30° 28' 30'^but as this station is in the Himalaya, the 

 attraction of this mighty mountain chain requires to have the zenith distances of stars 

 observed there. \ 



The lengths of these arcs depend on three bases, which were measured with com- 

 pensation bars similar to those used by Colonel Colby in the triangulation of Ireland ; 

 but, on account of the extreme heat of Inpia, applied with even more minute atten- 

 tion than in that instance. The whole operation was conducted under tents, and every 

 thermometer used in the survey was verified by comparison with two standards. 

 The scales employed, two iron of ten feet, and two brass of six inches, have been com- 

 pared by 101 comparisons, and one of each has been left in India, while the others 

 are deposited in the military store of the Hon. East India Company in Leadenhall 

 Street. The most northern of these buses is near 



/ o I II feet. 



DehraDun, in lat. ..../. 30 18 18 of 39183-873 



The next at Seronj .../ 24 6 50 of 38413-367 



The third near Beder /. 17 54 32 of 41578-536 



This last replaces Lambton's base of 1815, the marks of which have been irrecover- 

 ably lost. Remeasuring the Dehra Ibase there was found a difference of 2-40 inches, 

 or 0-3 per mile, an extraordinary coincidence considering the wide range of tempe- 

 rature during the process ; but it is confirmed by the agreement between the mea- 

 sured and triangulated lengths of two parts of it deduced from the third. When 



b2 



