U OLDHAM: THE STRUCTURE OF THE HIMALAYAS, ETC. 



which must be attributed to some other cause, one of which might 

 be a variation in the depth of the trough. There are in fact too 

 many corrections of unknown amount to justify a detailed dis- 

 cussion of the inconclusive results, from which only one conclusion 

 could be drawn, that neither the course of the main boundary, nor 

 that of the outer boundary between hill and plain, coincided in 

 detail with the limit of the compensation of the range. 



We have seen that from the outer edge of the hills inwards, 

 there is an excess of gravity, or a defect of compensation, which 

 increases continuously as far as the observations extend, and that 

 these show no indication of the progressive increase coming to an 

 end. Yet it cannot go on for ever,' and sooner or later the excess 

 of gravity must diminish and ultimately disappear, and the prin- 

 ciple of general isostasy requires that the excess of gravity, which 

 has been established, should be balanced by a corresponding defect 

 on one or both sides, of the under supported tract. To the south- 

 wards we can get no direct evidence, owing to the preponderating 

 effect of the defect of density in the alluvial trough, the amount 

 of which cannot be estimated with accuracy. To the northwards 

 we shall have precise information when the observations made 

 by Dr. F. de Filippi's expedition are published, but in the mean- 

 while we have a good indication of what the nature of these 

 results is likely to be in Capt. Basevi's determination of the force 

 of gravity at' More. The results obtained by this observer, after 

 having been discredited, have been reinstated and, the cause of 

 the discrepancies between his values and those of later observers 

 having been detected, it is once more possible to make use of his 

 results. Every correction which has to be applied was used by 

 Basevi, with the exception of that for flexure of the stand, the 

 necessity for which had not been recognised, nor means devised 

 for measuring its amount. Had he followed the usual practice 

 of having pillars built at each station it would have been impossi- 

 ble to allow for this correction, but instead he used a strongly 

 braced wooden stand, which was transported from station to 

 station, and later observations, at stations where this stand was 

 used, have so far indicated a fairly constant flexure correction 

 of about -04 dyne, with variations up to -01 dyne on either side of 

 the average. Had this stand been used at More we should be able 

 to determine the force of gravity, within a limit of -01 dyne, but 



[ 258 ] 



