\ 



the Indian Meridian. 407 



Hence the total rise of the ocean from the equator to this point, 

 owing to the attraction, 



= (yjradd= |^cosec| (33°-^) =^(4-620- 3-521) =28 ft., 



taking the limits from the equator to Cape Comorin. This shows 

 that the attraction has a considerable influence, even at that di- 

 stance, upon the ocean. The fact is, that though the force is 

 small it acts horizontally in the nearer and most important parts 

 of the ocean, and, owing to the peculiar property of fluid pres- 

 sure, accumulates the effect*. Had I supposed that the law of 

 the inverse distance had prevailed below C, the result would 

 have been still larger. 



8. An inference I would draw from this calculation is, that 

 the sea-level affords us no real standard from which to measure 

 heights, and thence determine the ellipticity of the earth with 

 extreme precision. Had I calculated the height of the ocean at 

 Karachi, it would have come out much more than 28 feet, so as 

 quite to derange the perfect spheroidal form. The height in 

 the latitude of C would be 105 feet, and at Karachi 225 feet. 

 Moreover, had I integrated from the antipodes instead of from 

 the equator, all these elevations would be larger by about 67 

 feet : but my object has been to refer the change of sea-level to 

 the equator. 



9. In the paper to which I allude, in a previous note I have 

 shown that it is not impossible, nor perhaps improbable, that a 

 cause does exist, which, if not altogether, yet nearly counteracts 

 the effect of the Himalayan Mass. At the same time it will not 

 explain the anomalies of the Indian Arc. There must be some 

 other cause besides Himalayan attraction to account for them — 

 either some local cause in the neighbourhood of one or both of 

 the extreme stations where the astronomical amplitude is ob- 

 served, or in the interior of the earth. Unless these disturbing 

 causes can be detected, and their effects calculated, the errors 

 are sure to be reproduced in the mapping of the country. The 

 measurement of the lengths of arcs has been carried out by the 

 Survey with wonderful jjrccision, as the tests show. It is when 

 the degree of bending (the knowledge of which is essential to 



* The moon's inuxiinuui power to disturb the oceau = , ) - ^,„„^ tli part of 

 (gravity. (Sec llerschel's ' Astrouoiny,' j). 4.'^fi.) The Iliniahiyan momitain- 

 attractioii at the eijuator and at Cape Couioriu equals (aeconhuu; to the 

 above) f^;;^,tli ami i^,;J5,th jjart of {gravity respectively, and is therefore very 

 much greater than the force producing the tides. 



