Mr Galbraith on the English Arc of the Meridian. 267 



Trigonometrical Survey, vol. ii., Arc of the Meridian, page 

 53, No. XX. Here tlie error is — 1".21, from an erroneous 

 calculation. The diflferences in any other case are hardly 

 worth pointmg out. 



In preparing the triangles for calculation, according to Le- 

 gendre's method, by the mean angles, I have taken a fair mean 

 of all the angles, whether by simple observation or by combi- 

 nation mth others, without any arbitrary or empirical mode of 

 proceeding according to any judgment formed of then- relative 

 accuracy in the opinion of the observers, as adopted m the 

 Survey, being convinced, from experience, that such a method 

 of procedure is often fallacious. 



II. Trigonometrical Results. 



With the bases and angles thus prepared, I found, from the 

 bases, as measured on Hounslow Heath, the distance between 

 Bagshot and Hindhead, forming one of the sides of the series 

 of triangles constituting the arc of the meridian between Dun- 

 nose and Clifton. From the base on Salisbury Plain, I found 

 the distance between Deanhill and Highclere, another of the 

 sides of one of the triangles of the same series. Lastly, I found 

 from the base measured on INIisterton Carr, the distance of 

 Clifton from Gringley, one of the sides of these series also. 

 Whence I had the means of computing the sides of the whole 

 series from four different bases, two values of that on Hounslow 

 Heath, one on Salisbury Plain, and one on Misterton Carr— 

 all prepared for calculation with the greatest care. I had also 

 the choice of three methods of computing the length of the 

 whole, two by paraUels to the meridian, one on the east, one 

 on the west, and a third by the intersections of the arc with 

 the sides of the triangles. 



From the base on Salisbury Plaui I obtained 

 By the eastern series from Dunnose to Clifton, . 1036406.62 ft. 

 By the western series from Clifton to Dunnose, . 1036406.13 

 By intersections from Dunnose to Clifton, . • 1036405.58 



,T ... 1036405.78 



Mean, ..•••••• a. 'ic\(\ 



Correction for position of Zenith sector, . • 1~ '^"" 



Final results from Salisbury Plain base, . . 1036408.78 



