178 Mr. Poiitt on the Changes in Ihe 



mination of such small quantities as form tlu^ subjtcl of the 

 present communication. 



Horizontal point of the Circle as found hj different Stars ob- 

 served hi) direct Vision and Refection, from II th to 23d 

 March 1822. 



h Urs. Maj. 123° 30 20-55 



V 28-95 



m 29-75 



ji 29-45 



« 29-50 



o 29-05 



Castor .... 29-8G 



Capella .... 29-55 



Pollux .... 29-95 



(3 AurijTfe . . . 29-35 

 Mean of 10 29-54 



Sirius 29-47 



There being no perceptible difference in the results ob- 

 tained near the zenith and near the horizon, it may be con- 

 cluded that the instrument has no deviation, either from fiexion 

 of the telescope or change of figure. 



Appendix to the preceding Paper. 



The observations which have been made during the last 

 summer, confirm in a very decided manner the results which 

 formed the subject of my last communication ; in which I laid 

 before the Society the nature of the diffei'ences that exist be- 

 tween the computed places of the principal stars of the Green- 

 wich catalogue, and those deduced from actual observation. 

 It is not my present intention to offer any explanation of the 

 cause of these phaenomena, althougli many obvious conjectures 

 present themselves, the value of which it will requiie perhaps 

 many years to determine. It is now my principal object to 

 consider the force of that explanation of the differences in 

 question, which will most readily occur to every astronomer, 

 namely, that the whole may arise either from error connnilted 

 by the observer, or from defect in the instruments of observa- 

 tion : this objection being the more weighty i'rom the circum- 

 stance, that the observations of three distant periods are em- 

 ployed, and that an error in those of either period (but parti- 

 cularly of the two latter) would materially affect the result now 

 under consideration. 



I believe that every person, in proportion to his exjierience 

 in the use of astronomical instruments (even ol' the most \w~ 



exceptional)i(. 



