72 



ill the column G. The quantity in G is to be applied to the 

 fourth column to give the north polar distances by the 

 Greenwich mural circle. 



The 30 stars marked * are those which Mr. Pond uses 

 as standard stars ; the north polar distances of which he 

 has determined by a great number of observations in 1812 

 and 1813. (vid. Phil. Tran. 1813, part 2.) Now among 

 these 30 stars there arc 24 in which the results do not differ 

 by 1", four in which the differences exceed 1", but do not 

 amount to 2", and two in which the differences exceed 2", 

 but do not amount to 2"i. This is highly creditable to the 

 divisions of our circle. In the Greenwich circle the errors 

 of divisions, if any, will entirely disappear in a mean of a 

 great number of observations, in consequence of the teles- 

 cope being moveable. And in fact in this way Mr. Pond 

 has ascertained that the errors of division of the Greenwich 

 circle are too small to be noticed. (Phil. Tran. 1813, p. 281.) 

 In our instrument the effect of the errors of division in the 

 mean of the six readings of the microscopes, cannot be made 

 to disappear. The above comparison shews satisfactorily 

 that no material error can arise from thence. 



For the stars not marked * the comparison has been 

 made with the north polar distances given in the Phil. Tran. 

 1813, part 1. The differences as to these low stars are 

 greater, and may probably be attributed partly to the uncer- 

 tainty of refraction, and partly to the use of Bradley's tables. 

 . In Dr. Bradley's formula for refraction the effect of the 



