342 Mr. William Galhraith on some 



Method of W. Galbraith. 



e — o = 



'/ __ (g -— o) a 



- 16-5 ' 



— 16-5 X ir^-51 



20 



= — 9 '-496 = 



the correction of the level with its proper sign. 



This last method is very easy when the divisions of the 

 level read from a central zero, but cannot he so well prac- 

 tised by a scale having two zeros. 



The preceding is the commencement of a series of obser- 

 vations on the obliquity of the ecliptic, which it is intended 

 to be continued for some time, to ascertain the accuracy of 

 a circle of very moderate dimensions. By the facility of 

 repeating the observations, and the general stability of the 

 instrument from the nature of its construction, much more 

 accurate results may be obtained than is generally supposed. 

 It is well known that the latitudes of different points in the 

 trigonometrical survey were determined by a zenith sector 

 of eight /6fe^ radius, while those of the French arc of the 

 meridian were observed with one of Borda's repeating 

 circles of about eight inches radius, and it is at least 

 doubtful, which of the two is, on the whole, the more 

 correct, the accuracy arising from the facility of repeating 

 the observations in the latter case being nearly equivalent 

 to that derived from the greater dimensions of the instru- 

 ments in the former. 



