*74 D>*. Maskelyne’s Obfervations on the Latitude 
anfwer, that the very ingenious method which he ufed of get* 
ting his refractions from the comparifon of the fum of the 
apparent altitudes of the poles at Paris and the Cape with the fum 
of the apparent zenith diflances of flars palling the meridian be- 
tween the two places, has fortunately, without his being aware 
of it, given him the refractions affeCted with the error of the 
arc of the inftrument, and confequently proper for correcting his 
obfervations ; for, if the inftrument be fuppofed ill divided, 
any error in the divifions will naturally be thrown upon the refrac- 
tions ; and, if the total'arc is too large for the radius, the flars 
will appear to approach the zenith by the error of the divifions 
as well as the refraCtions, and the refraCtions in the table will 
come out too large, but flill fuitable to the inftrument, becaufe 
a correction is neceflary to be added to the obferved zenith 
di-ftance, on account of the error of the inftrument, as well as 
of the true refraCtions, and the table deduced from the inftrument 
gives the fum of the two corrections together, without deter- 
mining them feparately. 
Hence his table of refraCtions, though well adapted to his 
inftrument, may be very unfit to be applied to any other. His 
latitudes of his obfervatories and his declinations of the flars 
will not lofe any of their certainty, at leaft within the limits of 
the zenith diftances meafured by his feClor, viz. 6o°* And this 
accounts for a circumftance, at firft fight rather extraordinary, 
that his declinations of flars fhould agree fo nearly (generally 
within 5" of Dr. Bradley’s, as Dr. Bradley himfelf re- 
marked) though his refraClioiis made ufe of were fo very 
different. 
Having now {hewn, that the Abbe de la Caille’s refrac- 
tions are too great, and only fit to be applied to his own inftru- 
ment, it will be eafy, by a juft calculation, to reconcile the 
before 
