Relation to the Constitution of the Earth's Crust. 9 



The first six columns of the foregoing table involve no 

 hypothesis beyond that the curve, which represents the Indian 

 meridian, does not sensibly depart from that which best repre- 

 sents the Earth as a whoie, which Colonel Clarke considers 

 may be assumed*; and that the sea-level is not affected by 

 local attraction. The fifth column is consequently the simple 

 statement of the fact that local attraction at each station must 

 be such as to account for so many swings of the pendulum 

 per diem relative to the number at Punnse reduced to sea- 

 level, and must bear the ratio to the attraction of the sphere 

 which is expressed in the sixth column. The seventh and 

 eighth columns, deduced from the account of the pendulum- 

 operations f, involve the further suppositions that the forms 

 and positions of the attracting masses above the sea-level have 

 been correctly estimated relative to the station, and that their 

 density is half the mean density of the earth, the sea-level 

 being supposed not to be disturbed by attraction. It will 

 therefore appear that, although giving further information, 

 they contain more elements of uncertainty than affect the 

 numbers in the former columns. The numbers in the seventh 

 column have been obtained from a tabular statement in the 

 'Account, &c/f by subtracting the vibration-numbers in the 

 column headed "Keduced height and mass" from those in 

 the column headed " The reduced height only." It appears 

 that this ought to give the effect at the station in vibration- 

 numbers of the attraction of the masses elevated above the 

 sea-level. 



When we compare these numbers with those in column 5, 

 it is seen at a glance how much smaller local attraction 

 actually is than it might be expected to be. It is no doubt 

 true that if allowance has to be made for a rise in the sea- 

 level, it would make the heights of the masses above the 

 mean level greater, and consequently diminish the numbers 

 in column 4, and increase those in 5 and 6; but at the 

 same time it would increase the masses referred to in column 

 7; so that the excess of the numbers in that column over those 

 in column 5 would not be thereby explained. But, what is 

 still more remarkable, is that local attraction is in some 

 instances actually negative, where from the size and distri- 

 bution of the masses it might be expected to be large and 

 positive, as shown in column 7. This is notably the case, 

 especially at Dehra, and to a less extent at Nojli ; while at 

 More, the most elevated station (15,408 feet), it is reduced from 

 the amount which ought to be equivalent to cause 23'57 addi- 



* Account &c. p. xxxii. f H>id. p. [146]. 



