182 Mr. Pond uu the Changes in the 



of declination, and two of the stars, « Herculis, and « Pegasi*, 

 being within half a degree of each other. In this group 

 « Pegasi is at least 3" south of its predicted place, whereas the 

 other two stars have not deviated much more than 0"-5 to the 

 south. 



4-. ciOrionis, x Scrpcntis, and Procifon^ fuinish an example 

 equally striking, they being within less than 2° of declination 

 from each otlier; a. Serpentis is exactly in its ])redicted place, 

 while a. Orionis and Procyon are each of them at least 2" to 

 the south. 



5. Rigel, Spica Virginis, and Sirins, are not contained within 

 so short an arc as the former groups, nor are their places so 

 well determined, on account of their proximity to the horizon ; 

 but they afford another instance of the inequality ol" southern 

 deviation in stars having nearly the same polar distance, but 

 opposite right ascensions. 



But leaving the considerations suggested by these groups 

 of stars, let us examine more minutely the diflerent hypotheses 

 that may be formed on the supposition, that th.e whole of these 

 deviations depends on error of observation caused by some 

 defect in the instruments employed : this investigation becomes 

 the more necessary, as it does not a]i}^car that Dr. Brinkley, 

 with his instrument at Dublin, has met with similar discord- 

 ances. Admitting the accuracy of the observations of Bradley 

 to form the gjound-work of this inquiry, there are then two 

 distinct hypotheses, that may be formed by those who ai'e in- 

 clined to maintain, that the proper motions of the stars are 

 uniform ; and that the discordances in question have their 

 source, not in any astronomical cause, but in some erroneous 

 system of observation. Of the observations from which the 

 catalogues of 1813 and of the present year have been com- 

 puted, we may suppose the one or the other to be erroneous. 

 Let us consider the consequences of each hypothesis. 



Let us first suppose the error to be in the observations of 

 1813. Then the observations of 1756 and 1822 being sup- 

 posed perfect, a catalogue for the year 1813 may be computed 

 by interpolation ; such a catalogue is annexed, and this (as- 

 siuued to be correct) compared with the observed catalogue 

 of 1813, will show the errors of observations at that period. 

 On this assumption the Greenwich circle must, in 1813, have 

 been in a very defective state ; and admitting the instrument 

 to be now perfect, this can be only attributed to the insuffi- 

 ciency of the braces which then connected the telescope to the 

 circle ; for this is the only difference between the instrument 



* The lunar mitafioii of « Pegasi was Jieaily a miniiuiiiii at each period. 



in 



