102 OLDHAM: THE STRUCTURE OF THE HIMALAYAS, ETC. 



altered from -f 2" to — 2". This change would also affect the stations 

 further in, whereby the diilerences at Bahak and Bajamara would be 

 altered by — 2", and at Lambatach and Kidarkanta by — 1", but 

 there would still remain a difference of about — 3" as between 

 the outer and the central, and about — 10" as between the outer and 

 the inner, stations of this group. So, too, a change in the estimate 

 of the effect of the range would alter the estimated deflections at all 

 stations, and only change the value of the differences, of the estimated 

 residuals, by a small fraction of their total amount. 



In this group of stations Major Crosth wait's calculation of the 

 effect of the actual complicated topography surrounding two of the 

 stations gives us a good check on the correctness of the conclusions 

 drawn from the method of investigation which has just been out- 

 lined. At Lambatach he found a residual of — 18", using the Bessel- 

 Clarke spheroid, after allowing for the effect of the visible topo- 

 graphy and its compensation, but not for the effect of the trough. 



This latter would account for about 1" of Major Crosth wait's 



residual, leaving — 14" still unaccounted for, as compared with 

 — 12" in table No. 29. At Mussooree the residual was — 18"; the 

 effect of the trough, as estimated in table No. 28, is — 17" in the 

 meridian, leaving a residue unaccounted for of — 1" as against the 

 -f 3" indicated in table 29. Major Crosthwait's figures thus make 

 the northerly residual of deflection at Lambatach greater by 5" 

 than at Mussooree, a difference which is increased by some 10" to 

 12" if the effect of the trough is included, bringing it into fair agree- 

 ment with the difference of — 15" in table 29. We may therefore 

 conclude that the increase in the unexplained residual of northerly 

 deflection is a real one and amounts to about 10" at 40 miles into 

 the hills on this section. 



The two stations in Nepal show an excess of northerly deflection 

 amounting to about 10", at a distance of 30 miles from the main 

 boundary, and the same is noticeable in the more complete section 

 in Sikkim, where the difference between the observed and the cal- 

 culated deflections amounts to — 9" at Phallut and — 10" at Tonglu. 

 At the station of Senchal the difference between calculated and 

 observed deflections is + &", out tnc situation of this station is 

 altogether exceptional, and the observed deflection departs largely 

 from the average of similarly situated stations from purely a local 

 cause. Due north of Senchal the deep-cut valley of the Rangit 

 penetrates the range of the Himalayas, and about N.N.E. of the 



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