On the Attraction of the Himalaya Mountains and of the elevated Regions beyond them, upon the Plumb-line in India
1855; Oxford University Press; Volume: 16; Issue: 2 Linguagem: Inglês
10.1093/mnras/16.2.36
ISSN1365-2966
Autores Tópico(s)Geological and Geophysical Studies
Resumo1. IT is noW well known that the attraction of the Himalaya Mountains, and 0f the elevated regions lying beyond them, has asensible influence upon the plumb-line in North India.This circumstance has been brought to light during the progress of the great trigonometrical survey of that country.It has been found by triangulation that the difference of latitude between the two extreme stations of the northern division of the are, that is, between Kalianpur and Kaliana, is 5°23' 42"'294, Whereas astronomical observations show a difference of 5°23" 37"'058, Which is 5"'236* less than the fOrmer.2. That the geodetic operations are not in fault appears from this; thattwo bases, about seven miles long, at the extremities of the are having been measured With the utmost care, and also the length of the northern base having been computed from the measured length of the southern one, through a chain of triangles stretching ' along the Whole'arc, about 370 miles in extent, the difference between the measured and the computed lengths of the northern base was only 0'6 of a foot, an error Which would produce, even if Whollylying in the meridian, a difference of latitude no greater than 0"'0()6.3. The difference 5"'236 must therefore be attributed to some other cause than errorin the geodetic operations.A very probable cause is the attraction of the superficial matter Which lies in such abundance on the north of the Indian are.This disturbing cause acts in the right direction ; for the tendency of the mountain mass must be to draw the lead of the plumb-line at the nOrthern extremity of the are more to.the north than at the southern extremity, which is further removed from the attracting mass.Hence the effect of the attraction will be to lessen the difference of latitude, Which is the effect observed.Whether this cause will account for the error inthe difference of latitude in quantity, as well as in direction, remains to be considered, and is the question I propose to discuss in the present paper;. 4. But if mountain attraction have any sensible influence at the stations on the are, how is it-that the geodetic operations are not affected by it?How isit that such a remarkable degree of exactness between the measured and computed lengths of the * This is the dificerence as stated by COIOIIBI'EVEREST in his work on the Measurement of the «Meridional Ãrc of India, published in 1847.See p. clxxviii.MDCCCLV.I
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