BY JOHN TEBBUTT, JUX. 151 



are measured are known with certainty. For the accomplish- 

 ment of this great work, we must, in a great measure, look to 

 our observatory : a valuable instalment of it has already been 

 presented to the scientific world in the three volumes of 

 observations for 1859, 1860, and 18(51. 



The following table contains the results of my observations, 

 with the exception of those where the stars of comparison could 

 not be found in the catalogues of the British Association, 

 Brisbane, and Lacaille. The later observations will prove useful 

 in the event of the comet not being more accurately observed 

 elsewhere. The positions are uncorrected for parallax, and referred 

 to the mean equinox and mean equator of January 1st, 

 18G2. The last two columns of the table exhibit a comparison 

 of some of the places derived from observation with the 

 corresponding positions deduced from the parabola. In 

 order to this comparison, the comet's places have been 

 corrected for parallax. C and O denote respectively the 

 calculated and observed places of the comet, and A a, ATT, the 

 differences of right ascension and north polar distance. The 

 October comparisons indicate the necessity of a further slight 

 correction of the elements, but it would be a waste of time to 

 attempt extreme accuracy, considering the probable amount of 

 the errors of the catalogues, and of the comparison obser- 

 vations themselves. The positions of the loth October, are the 

 latest that can be depended on for a comparison ; the comet's 

 distances from the sun and earth, were then respectively, one 

 hundred and twenty-five and one hundred and forty -six millions 

 of miles. I succeeded in making some observations on the 

 evening of the 21st, but the results, owing to the excessive faint- 

 ness of the comet, are liable to errors of upwards of a minute of 

 arc ; they are, therefore, not sufficiently accurate for a correction 

 of the orbit. 



Having now given you as much information as I can under 

 the circumstances, I must take leave of the subject. The members 

 of the Society will, doubtless, find much to interest them in the 

 intelligence which will be received respecting the comet by t-ho 

 English mail, now due, and that of December next. 



