Motion of the Solar Si/slem in Space. 



a view of attaining the necessary degree of accuracy, a catalogue of 

 2066 stars has since been observed, and the observations of a former 

 catalogue of 2881 stars, have Hkewise been brought to bear upon the 

 same subject ; whereby I am now enabled to encounter the enquiry 

 with something like appropriate means. To render this subject more 

 clear to the general reader, it may be as well here to notice, that 

 the term " proper motion" has long since been employed by astro- 

 nomers to designate the effect resulting from an actual change in the 

 situation of the stars in space. I have adopted the term " true" 

 proper motion to represent that species of motion which obviously from 

 its magnitude pertains to motion in the star itself; and have applied 

 the term " apparent," to proper motions which would be exhibited from 

 a change of place of the solar system. It necessarily happens, however, 

 that, in consequence of the errors incidental to observers and instru- 

 ments, many stars will appear to have a true proper motion, which 

 really have none, and the contrary: hence, to enable us to avoid as 

 many as possible of the true proper motions, it becomes necessary to 

 lay down some limits, without which the errors of observation do not 

 reach ; thus, for the Madras and Palermo results, I have supposed the 

 limit of error for A. R. to be 0.52.?.* for each ; and for the declination, 

 the limits of 4'' for the former, and 4,5" for the latter : or, the error 

 of observation may give rise to an error in the proper motion, for the 

 year 1832, for instance, compared with 1800 to the amount 



,5 2 + ,52 ^ ^Q325 for the right ascension, 

 32 



4'/ + 4" 5 



— .-= 0,266'' for the declination : 



o2 



hence we are safe in assuming, that all the stars of the Madras ca- 

 talogue for 1832, which, on comparison with Piazzi's catalogue fof 

 1800, exhibit a proper motion exceeding the above limits, are bond fide 

 true proper motion stars ; thus, in the three catalogues to which 

 allusion is made above (containing about 7600 stars), there are 309 starSi 

 6r 1 in 25, which exhibit a true proper motion in A. R. ; and 388 stars, 

 or 1 in 20, which exhibit true proper motion in declination. Amongst 

 these, we find that the + proper motions occur as often as those of 

 opposite tendency, and indifferently at one part of the heavens as well 

 as at another : hence, taking the sum of the true proper motions of a, 



' * This being the extreme difference I have yet met with between any two determina- 

 tions of the place of the same star, 



