OBSERVATIONS COMPARED WITH EPHEMERIS. 

 Computation for Santiago Meridian Observations Continued. 



CXCVll 



In the Santiago meridian series for Mars II are a number of observations, which were made 

 with the micrometer in the eye-piece of the meridian-circle, and which, in addition to the 

 measurement of absolute declination, give a measurement of distance from some one of the 

 regular comparison-stars. In such cases we are put in possession of two determinations made 

 at the same time. The meridian observations may, in fact, be classed under three categories. 



1. Mars observed on fixed thread. 



2. Star observed on fixed thread, and Mars shortly after on the movable thread. 



3. Mars observed on fixed thread, and star on the movable thread. 

 The first of these gives in each case one normal meridian observation. 



The second furnishes a determination of the star's place, and also a micrometric comparison 

 of Mars with the star. 



The third affords both an absolute measurement of Mars belonging with the first series, and 

 a micrometric determination like those included in the second division of the second category. 



In strictness, the Jfars-determinations of the second category, being micrometric, ought to be 

 combined in the same series with those of the third ; but since the precise character of these 

 determinations was only comprehended after study of the original manuscripts, at which time 

 these cases had already been incorporated with the absolute determinations of the first category, 

 a repetition of the computation has not appeared sufficiently important to call for a new distribu- 

 tion and discussion. 



Consequently, our series, "MarsII, Santiago meridian," contains the Mws-observations of the 

 first two divisions and the absolute determinations of the third ; the star-observations of the 

 second being already included in our discussion of the comparison-stars, and the micrometric 

 measurements of the third furnishing us the annexed new group. 



