362 E. S. Holden — Oii supposed changes in Nebula M. 17. 



duties, and although every endeavor was made to obtain high 

 accuracy, and above all to determine the limits of error, yet his 

 ttparatively inadequate. He esti- 



[ by : 



The 



method chosen by M. Trouvelot and 

 noticed. It may be of interest to remark that the : 

 of Trouvelot referred to Lassell is about 7"'7 in R. A. and 5'''3 

 in N, P. D. The larger residual in R A, is due to imperfect 

 running of the driving clock of the Equatorial. When this 

 clock is in its usual good condition I believe that this error will 

 not exceed 6", a quantity which is not appreciable in any draw- 

 ing of a considerable nebula which can be put upon a quarto 

 page. 



Table I.— Mason's Sta 



Lassell's 



Mason's 



Mason's 



Mason's 



Mason's 



Remarks. 



number. 



number. 



magnitude. 



R. A. 1830-0 



6 1830-0. 



~ir 



1 



U15 



32-9 



-I0^13'4r 



When the identifica- 

 tion of one of Mason's 

 stars with one of Las- 



10 





14 







sell's is at all doubtful a 









34U 



11 45 



question-mark (?) is add- 



15 



\ 



12 





11 50 



ed in the first column. 



11 



10 





















identified but only so 













many are included as 



35 



i' 





It 



13 58-9 



th'" St? S th^nebr- 



28 



15 







13 30 



losity. The same re- 







14-1^5 



10 ii^ 













15 21 













10 57 





























20 



2T 















12 



18 11 2J-3 



-16 W '1 





