DEPARTMENT OF MERIDIAN ASTROMETRY. 



189 



preceding four columns, and the bottom row of the table gives the 

 mean results of 6-hour divisions for the whole period of observation. 

 It can readily be seen that the motion of the mire was slight, and 

 such motion as is indicated does not appear to be seasonal in char- 

 acter. The mean of all the 6-hour groups might indicate a slight 

 diurnal variation, but the probable errors of the means so far exceed 

 the variations that we must conclude that the mire-mark was fixed 

 as far as diurnal changes are concerned. 



Monthly Mean Readings of Mire, San Luis. 



1909. 



April 



May 



June 



July 



August 



September. . 



October 



November. . 

 December... 



1910. 



January 



February. . . , 



March 



April 



May 



June 



July 



August 



September. . 



October 



November . . 

 December.. 



1911. 

 January 



Meana 



Ql'tol 



.876 

 .776 



.797 

 .735 

 .774 

 .704 

 .692 

 .740 



.775 

 .747 

 .766 

 .718 

 .687 

 .733 

 .708 

 .732 



A.M. 



O'' to 6^. 6'' to 12*'. 



.715 

 .730 

 .743 

 .726 

 .720 

 .757 

 .812 

 .795 

 .771 



.763 

 .707 

 .782 

 .727 

 .708 

 .745 

 .705 

 .777 

 .777 



The preliminary clock corrections as given in the last report 

 resulted in a systematic error dependent upon right ascension of 



-0!0084 sin a +0!0087 cos a 



and the effect night minus day for the various observers : 



