198 MR. JOSEPH BAXENDELL ON 



the removal of the Munich refractor to make room for a 

 still larger instrument^ a fine equatorially-mounted achro- 

 matic of thirteen feet focal length and nine inches aperture^ 

 by Cooke^ of York. 



Keverting to the results of my own observations, the 

 periods of spots B, C, E and ¥, compared with that of A, 

 give the following differences and probable errors : 



Ti-jr, Probable 



Difference. -,-, 

 ^ Jbrror. 



A and B i'265± 0-719 



C 6-846+ 1-477 



E 8-274+o-76o 



F 6-228 + 1*477 



As some of these differences considerably exceed their 

 probable errors, the conclusion which has been drawn from 

 former observations, that different spots have different 

 periods of rotation, is thus fully confirmed. 



The following table shows the observed distance between 

 the spots A and B on eleven different nights : 



1858. m. 1859. m. 1 859' ■w». 



Dec. 20 51-8 Jan. 22 55*3 Feb. 7 52*4 



23 54'2 23 55-8 II 54-1 



21 52*8 

 1859. 



Jan. I 56-5 Feb. 2 50-3 Mar. 10 58-0 



18 60-4 



The probable error of a single distance is 2"/ m., and we 

 may therefore fairly conclude that the changes indicated 

 by the numbers in the table were real, and that the dis- 

 tance between the spots was greater on the I'^th January 

 and 10th of March than on the 20th December and znd 

 of February. We have already seen that the probable 

 error of the mean period of B, as derived both from my 

 own and Sir William Keith Murray's observations, is 

 greater than that of A, and it may therefore be reasonably 

 inferred that the changes in the distance between the spots 

 were principally due to irregularities in the motion of B. 

 The few observations which were made of spot F show 

 that its motion also was not uniform. On the 2'jth of 



