observed by him in 1835. 406 



with Ramsden's moveable vertical circle, in order to deduce 

 corrected observations of the error in the line of collima- 

 tion. These observations were principally on stars, which 

 had peculiar motions, because he thought, that by com- 

 paring them with such as he had made before, much pre- 

 cision and accuracy might be attained. For, although the 

 interval of time between the observations did not exceed 

 45 years at most, and was often 40 or 30 only ; yet, as 

 they were made with the same instrument, by the same 

 methods of observations, calculation, and by the same eye, 

 their differences were not subject to the small inequalities, 

 which might effect observations made with different instru- 

 ments and observers. The nature of the great circle of Rams- 

 den, in his possession, not enabling him to make precise 

 observations on the revolutionary movements of the double 

 and triple stars, he was confined to the investigation of their 

 peculiar motions. According to this method, it is. easy to 

 observe other stars which occasionally accompany, in the 

 field of the eye-glass, the star under examination. Caccia- 

 tore is in the habit of noting the difference in their passage 

 of the vertical wire, and the difference in their zenith dis- 

 tance. When there are several stars in the field, he is in the 

 habit of estimating these differences at sight, and experience 

 has fully shewn, that his estimate is never far from the truth. 

 He had in vain, during several evenings in the month of 

 May, 1836, prepared his instrument for observation, until 

 the 11th, when he began his series of observations. Among 

 the stars, which he observed, was the 503rd of Mayer, 

 which is the 17th of the 12th hour of Piazzi ; it is of the 

 7th or 8th magnitude, and has, according to the catalogue, 

 a peculiar angular motion in right ascension — 0"-33. Near 

 it he saw another star of less lustre, and a little smaller, 

 which followed it at a distance of about two seconds of 

 time to its passage, and which was about 2^ minutes farther 

 . to the south. This constituted the whole of the observa- 

 tion ; the star was noted, and no more was thought of it. 

 Next day the weather was unfavourable, and it was only 

 on the 14th, that the observations were resumed. When 

 his assistant read to him the note which he had made 

 relating to the small star, he was surprized at not finding 

 it — he feared that he had committed an error — he diminished 



