Royal Astronomical Society. 325 



have been produced by one simultaneous and momentary effort of 

 the elevatory force. It is not, however, to be regarded as a neces- 

 sary consequence of this conclusion, that the whole elevation of the 

 district was thus produced at once ; it might be in some degree pro* 

 duced by previous, and in a considerable degree by subsequent 

 movements ; but it would seem at least highly probable, that that 

 general movement which produced the dislocations of the elevated 

 mass, and impressed upon it its present distinctive characters, should 

 have been the most energetic of those repeated movements to which 

 the whole elevation has probably been due. 



ROYAL ASTRONOMICAL SOCIETY. 



[Continued from p. 245.] 



Dec. 11, 1840. {Continued.) — Description of a Method of dividing 

 one Circle, B, by copying from another, A, previously divided. By 

 Lieut. -Col. Everest, Director of the Trigonometrical Survey of India. 



In Col. Everest's 'Account of the Measurement of an Arc of the 

 Meridian in India,' published in 1830, it was stated that, with a view 

 to avoid the effects of the errors of catalogues and the periodical ir- 

 regularities to which all stars are more or less liable, it had been 

 resolved to substitute two astronomical instruments, each with a 

 vertical circle of three feet and an azimuth circle of two feet dia- 

 meter, for the zenith-sector of Ilamsden, formerly used in determi- 

 ning the amplitudes by his predecessor and himself ; the intention 

 being, that all celestial amplitudes should be determined by obser- 

 vations taken simultaneously at both extremities of the arc. Ac- 

 cordingly, two new altitude and azimuth instruments were ordered 

 in London and forwarded to India, where they arrived in 1832; but 

 an opportunity of giving them a fair trial did not occur until 1837, 

 when a small observatory was constructed at Kaliana, the northern 

 limit of one of the sections of the great arc of the meridian. The 

 instruments proved, on trial, to be of too feeble construction for the 

 purpose for which they were intended, and Colonel Everest found 

 that, in order to render them serviceable, it would be necessary to 

 construct for each a pair of stronger columns, new outriggers and 

 friction-rollers, a new axis for the azimuth motion, a new table for 

 supporting the columns, and a new azimuth circle ; in short, to 

 construct two entirely new instruments, with the exception of the 

 vertical circles. To any other than a professed artist, an operation of 

 this kind, even under the most favourable circumstances, would prove 

 an arduous and formidable undertaking ; but, in a half-barbarous 

 country like Upper India, where no artificer was to be found who had 

 ever tried his hand at dividing, or even seen a cutting-tool, it could 

 not be otherwise than extremely embarrassing. Before Col. Everest 

 undertook the alterations, he had obtained, indeed, the assistance 

 of a mathematical instrument-maker in the service of the Company, 

 at Calcutta ; but, owing to some disagreement, this person left him 

 before the most difficult part of the operation, that of dividing the 



