The Mountains and their Roots

Abstract

As an officer of the Survey of India, employed for many years in determining deflections of the plumbline and variations in the intensity of gravity, I was interested to find in the article which appeared under this heading in NATURE (No. 2261, vol. xc., February (27) reference to the hypothesis suggested in I 1904 by the Rev. O. Fisher as to the nature of mountain compensation, and the statement that this hypothesis goes far to explain the deflections of the plumb-line observed at the foot of the Himalayas and in the Gangetic plain. The article states that, according to Mr. Fisher's hypothesis, “the crust is of uniform density, the isostatic compensation being obtained by a variation in thickness,” and that, on this hypothesis, Mr. Fisher “finds that the attraction of the visible range combined with the negative attraction of the downward protuberance should give a northerly deflection of about 24″ at the foot of the hills, of about 2″ at sixty miles away, and a southerly deflection of about 2″ at the farther edge of the plains. These results appear to be in very fair accord with the observations....”