INTENSITY AND DIRECTION OF THE FORCE OF GRAVITY IN INDIA. 299 



In Tables III. and IV., given hereafter, the deflections are shown in terms of the 

 Everest, the Clarke, and the Clarke-Bessel spheroids. 



If we compare the deflections of the plumb-line as referred respectively to the 

 Everest and Clarke spheroids, we find that the values are almost identical at all 

 stations. The agreement between the two series, though very remarkable, is a mere 

 coincidence ; the influence of CLARKE'S increased ellipticity happens always in India 

 to neutralise the influence of his increased major axis. 



If we employ the Clarke-Bessel spheroid, the deduced deflections of gravity are 

 appreciably modified. 



(4.) The Regional Classification of Deflections. 



It was in 1900 that the suggestion was first made that the deflections of gravity 

 in India, which had hitherto been attributed to accidental and local attractions, could 

 be broadly classified by regions. This new theory had as a working hypothesis an 

 advantage over the old in that it could be tested by further investigation in the field. 

 From the classification of results of regions it was predicted that a southerly 

 deflection of gravity would be found to exist throughout a great zone enclosing the 

 main valley of the Ganges and running parallel to the Himalayas for 1000 miles; 

 but that both north and south of this zone northerly deflections would be met with 

 (vide Plate 15). 



With the object of testing the correctness of these predictions, Lieutenant COWIE, 

 R.E., proceeded in 1901 to observe several latitudes between Calcutta and Phallut, 

 working across the zone of southerly deflection and up to the Himalayas (vide 

 Plate 15). The results which he obtained were as follows: In the country 

 immediately south of the zone northerly deflections of 3" and 4" were found ; at 

 Calcutta the inclination of gravity was slightly southerly. In the 200 miles 

 immediately north of Calcutta, COWIE found southerly deflections at four successive 

 stations ; the inclination of gravity then changed to northerly, at Jalpaiguri it was 

 6" northerly, at Siliguri 23", at Kurseong 51", and at Phallut 37". 



In 1902-03, Lieutenant COWIE was directed to work again northwards across the 

 zone and to follow the meridian of 79. The results which he obtained were as 

 follows : In latitude 23 30' the direction of gravity was inclined 5" towards the 

 north ; in the next 200 miles Lieutenant COWIE found a southerly deflection at seven 

 successive stations ; in latitude 27 47' the inclination of gravity began to be slightly 

 northerly; in 29 16' its inclination was 12" northwards. At Birond, in the hills, 

 Lieutenant COWIE found a deflection of 44" north. 



It can, therefore, now be prophesied with tolerable certainty that on all Himalayan 

 meridians the direction of gravity will be found to follow one general law ; in the 

 neighbourhood of the tropic, as we move northwards, its direction will change from 

 northerly to southerly; it will then remain deflected towards the south for some 



2 Q 2 



