in the Trigonometrical Survey of Great Britain. 141 



titude of Arbury station, from the latitude of Blenheim, as 

 determined by previous observation, independent of any as- 

 tronomical observation made at Arbury, and find it 5 seconds 

 less than shown by the zenith sector ; giving countenance to 

 the probability of local attraction by the high land to the south 

 of the station, which will appear by the following calculation ; 

 in Trigonometrical Survey, vol. ii. p. 137, the latitude of 

 Blenheim by observation is stated as 51° 50' 24" , 9, or nearly 

 51° .50' 25". 



The measured distance, on the meridian, from Blenheim 

 to Arbury, is 139822, deduced from vol. ii. part 2, p. 107; 

 dividing this distance by 60881*7, according to a table in vol. i. 

 part 1, p. 168, corresponding to the middle latitude between 

 Blenheim and Arbury, and multiplying the quotient by 10', 



we obtain the difference of latitude = ° 22' 58"' 



this quantity added to 51 50 25 



gives for the latitude of Arbury 52 13 23 



being 5" less than by the zenith sector. It is true that Colo- 

 nel Mudge corrected the latitude of Blenheim, from the Tri- 

 gonometrical Survey, to 51° 50' 28", and in this case the com- 

 puted latitude of Arbury would come out near 3 seconds less 

 than found by the zenith sector. In vol. ii. part 1, page 118, 

 the latitude of Arbury, as derived from Dunnose meridian, is 

 given .... 52° 13' 26"'6 

 afterwards . .52 13 28 '2 from observation* 



1 '6 or 1^ second south of the observed 

 latitude; all concurring to prove that the observed latitude by 

 zenith sector falls to the north of the calculated, or that the 

 deflection of the plumb-line was to the south. Taking, there- 

 fore, the table above referred to in vol. i. part 1, p. 168, and 

 considering the latitudes of the following stations to be as 

 below : 



Dunnose . . . . 51° 37' 7" 

 Greenwich . . . . 51 28 39^ 

 Blenheim . . . . 51 50 28i 

 Arbury . . . . 52 13 26^ 



Clifton 53 27 20f 



and calculating the length of a degree, in their respective 

 middle points, they will be found to correspond with the said 

 table, and maintain a regular increase to the northwards agree- 

 ing with the assumed general figure of the earth: the above 

 assumption indicates an error of 10|" at Clifton, and If at 



' Vol ii. part 2, [). 10!), Dunnose is slated to be . . 50° .'57' 6" "2 



p. 107» from Duanose to Arbury is . 1 'AG I t) '9 8 



.7„> 13 28-18 



Arbury, 



