THE SUPPORT OF THE HIMALAYAS. Ill 



it was replaced at this station by a lighter tripod, whose flexure 

 would be different, and greater in amount than in the case of the 

 standard stations ; fortunately, however, the same stand was used 

 at Mian Mir, and a later observation by Col. Lenox Conyngham 

 showed that Basevi's determination was in defect by -109 dyne at 

 that station, a difference which may be attributed to the flexure of 

 the stand used at that station and at More\ 



The published discussion of Capt. Basevi's observation indicates 

 a defect of gravity, or negative anomaly, amounting to 24 11 swings 

 of a pendulum which would beat seconds at the equator, after 

 allowing for the effect of latitude, altitude and attraction of the 

 visible masses above sea level. 1 Converted into modern standards 

 the anomaly becomes -545 dyne, to which the correction found at 

 Mian Mir may be applied, making the actual anomaly about 



— -434 dyne. As the formulae on which this result is based have been 

 superseded by others, believed to be more accurate, it will be safer 

 to use the more modern value published in the Report of the 1009 

 meeting of the International Geodetic Association, where the 

 anomaly is given as — -433 dyne, an allowance of -107 dyne being 

 made for the flexure of the stand. 2 The two values of the anomaly 

 differ by only "01 dyne and we may take it that the deficiency at 

 More is not far from '43 dyne, omitting the third decimal figure 

 as meaningless in the circumstances of the case. 



This deficiency of gravity represents the effect not only of the 

 compensation of the range but also that of the distant topographv. 

 The exact amount of this last has not been calculated in detail, 

 but some estimate can be based on the fact that at Dehra Dun the 

 effect of topography beyond a radius of 104 miles from the station 

 amounts to — "055 dyne on the Hayford hypothesis, and will not 

 be materially different on any other admissible hypothesis of com- 

 pensation. At More the effect of distant topography would cer- 

 tainly be greater than at Dehra Dun, but is not likely to be 

 twice as much ; if it should be as much as — -100 dyne it would leave 



— -33 dyne for the effect of the compensation of the range, a value 

 which is not materially different from the effect of compensation 

 within 100 miles of a station situated 150 miles from the edge of 

 the Imaginary Range, namely about — '33 dyne if the Hayford 



1 Account of the Operations of the Great Trigonometrical Survey of India, V, p. 147, 

 1879. 



2 Comptes Bend us de la seizieme conference, generate dc V Association geodtsit/iu In- 

 ternationale. Vol. Ill, pp. 222 & 236 (1911). 



[ 259 j 



l2 



