ccxlvi 



EQUATIONS OF CONDITION. 



FORMATION OF EQUATIONS OF CONDITION. 



VENUS II. 



Meridian, Cracow. 

 (OBSERVED CENTER.) 



10.-WEIGHTS AND MEAN ERR011S. 



It is manifest that, whatever efforts may be directed to the investigation of the relative value 

 of the several classes of observations, and to the relative precision of measurements made with 

 different instruments and by different observers, the ultimate combination of these observations 

 must be in a great degree empirical, and, if not directly, yet certainly implicitly dependent 

 upon the judgment and discretion of the investigator. Under no circumstances can this fact be 

 better illustratedjthan the present. 



We are to endeavor to deduce a correction for the adopted parallax from the materials furnished 

 by observations of two different planets, the one superior, the other inferior, and each of them 

 during two oppositions or conjunctions. A measure of relative value for these four diverse 

 cases seems unattainable, and the course of this discussion is directed to the attainment, from 

 each of these four series, of the best independent value which they can be made to yield. 



But in each planet- series the case is analogous. We have different classes of observations, 

 some absolute, and some relative ; different instruments, some powerful and some but mediocre ; 

 different stations, some favorable for comparison with the others, and some the reverse; different 

 climates, some offering a cloudless and transparent sky, and some seldom permitting the 

 planet's disc to be distinctly seen ; while the so-called observation itself is in some cases deduced 

 from forty or fifty single comparisons which have occupied a period of several hours, and in 

 others simply the result of a single pointing. To establish a unit of weight common to all, 

 and to determine with correctness the proportionate value of each observation, is purely 

 impossible. 



