308 Royal Astronomical Society. 



or we may use the mean errors as the errors for the mean times, and 

 make our whole calculation one of errors." 



By grouping the observations for each month, in the manner 

 above described, Professor Airy deduces from the comparison of 

 the errors which are given, that his observations (his own catalogue 

 of stars included) give the sun north of the ecliptic assumed in the 

 tables, by 



- 1"-061 cos long. - 0"-427 sin long. -J- 0"-487. 



The correction required by the first term is equivalent to a re- 

 duction of s * 18 in the right ascensions of the stars employed, being 

 the excess above Bessel's right ascensions which Professor Airy's 

 catalogue assumes ; showing that Bessel's place of the equinox is 

 precisely that deducible from the Cambridge Observations. " This 

 accuracy of coincidence," Professor Airy remarks, " is to a certain 

 degree accidental ; but I do not think that accident would extend 

 so far as to the difference between Mr. Pond and Bessel." 



The second term implies that the obliquity is less than that of 

 the Berliner Jahrbuch by 0"*427. 



The third term would imply that the sun moves in a small circle 

 of latitude 0"*487, which increases the apparent obliquity in summer 

 and diminishes it in winter. This result, similar to that obtained 

 from other circles, is made the occasion of introducing the following 

 remarks. 



It is found that the difference of N.P.D. of a northern and 

 southern star observed directly is always less than the same by 

 reflected observation. At Cambridge a mean zenith point has been 

 obtained from northern, zenithal, and southern stars, and subse- 

 quent single observations are corrected by comparing the zenith 

 points deduced with the mean zenith point. All stars are thus 

 corrected, and, by graphical interpolation, the sun and planets 

 also ; and the result is confirmatory of the method, since without it 

 the discordance of obliquities would have amounted to five seconds. 

 On the actual discrepancy in question, Professor Airy observes, 

 1st, that an error of less than 0"*25 in the correction of the circum- 

 polar stars and the sun would entirely remove it; 2nd, that we are 

 not justified in positively asserting the mean of direct and reflected 

 observations to be the true difference of N.P.D. of two stars. He 

 is disposed to attribute it to a small defect in the tables of refrac- 

 tion, where a trifling error in the law, the constant, or the thermo- 

 meter readings, would remove it entirely. In this case the summer 

 observations would be the more correct. But these would only 

 require an increase of 7, 06 in the Berlin obliquity — a quantity 

 much too small to be answered for. 



IV. On the transit instrument of the Royal Observatory of 

 St. Fernando, and the manner of using it. By Don Jose Sanchez 

 Cerquero. An abstract of this paper is given in the Monthly No- 

 tices. 



V. On the Mural Circle of the Observatory at the Cape of Good 

 Hope. By Mr. Henderson. 



