598 



Tailing through extensive parts of the earth's mass, is found, with a 

 view to determine whether any compensating cause can possibly exist 

 below to counteract the large amount of deflection caused by the 

 superficial mass lying above the sea-level. A survey of the causes 

 of disturbance of the plumb-line cannot be complete without taking 

 into consideration the influence of the ocean. To approximate to 

 this is the object of the present paper. 



The author first adverts to the peculiar geographical position of 

 Hindostan. The highest mountain-ground in the world lies to the 

 north of it ; and an unbroken expanse of ocean extends from its 

 shores down to the neighbourhood of the South Pole. The excess 

 of matter presented by the first causes a deflection of the plumb- 

 line towards the north, decreasing in amount as we travel southwards. 

 The deficiency of matter arising from the second causes a deflection 

 of the plumb-line also towards the north, but decreasing in amount 

 as we travel northwards. The consequence is, that while these two 

 causes conspire to increase the deflection at the different stations, the 

 action of the second tends to reduce in amount the errors which the 

 mountain- attraction causes in the amplitudes. 



But the attraction of the mountains northwards, and the deficiency 

 of attraction of the ocean southwards which last is, in fact, equiva- 

 lent to a repulsive force northwards combine to produce another 

 effect upon the measures of the survey besides the deflection of the 

 plumb-line. They have a sensible influence in changing the sea- 

 level, so as to make the level at Karachi, near the mouth of the 

 Indus to which a great longitudinal chain of triangles is brought 

 down from Kalianpur, in the centre of India many feet higher than 

 the level at Punnae near Cape Comorin, the south extremity of 

 the great arc. In other words, the level at Karachi is many feet 

 higher than it would be at that place, if, while the level at Punnse 

 remained unchanged, the disturbing attractions were removed. 



The author then proceeds with the details of the calculation, which 

 is conducted by the method of his former papers. In our ignorance 

 of the form of the bed of the ocean, especially in a part of the world 

 where bat few soundings have been taken, it is of course necessary 

 to make some assumption respecting the depth of the ocean and 

 the form of its bed. The author assumes a law as to the variation 

 of depth, which, while it is probably a pretty fair representation of 



