COMET OF 18S9-1896-1903 239 



C. Comparison of Observed Places of the Cornet ivith the 



EpJieineris. 



17. An ephemeris for the times of visibility during the three 

 appearances, 1889 to 1903, was computed with Elements III. 

 This ephemeris was obtained in the following manner. A daily 

 ephemeris for the years 1889 to 1897 had previously been com- 

 puted with Elements II. In the direct computations of this a 

 four-day interval had been used, the values for the intermediate 

 dates were found by interpolation using second order differences. 

 This ephemeris gave the true right ascensions and declinations 

 of the comet for Greenwich mean midnight, referred to the 

 apparent equator and equinox of date. The corrections for 

 aberration were not applied. With Elements III were now 

 computed a number of places of the comet, at intervals of from 

 8 to 24 days, and the differences between these places and the 

 ephemeris places, as computed with Elements II, found. These 

 differences formed a smooth curve, from which were found by 

 interpolation the daily corrections which it was necessary to 

 apply to the ephemeris place, computed with Elements II, in 

 order to find the corresponding place for Elements III. 



In computing this ephemeris for the different appearances, 

 the perturbations from the respective osculating epochs to the 

 various dates of computation were not applied. So that, during 

 the years 1889, 1890 and 1891, the ephemeris positions of the 

 comet still had to be corrected by the amount of the perturba- 

 tions from 1889, Sept. 30.5, to date; in the years 1896 and 

 1897, from 1896, Oct. 23.5, to date, and in 1903 from 1903, 

 Sept. 18.5, to date. 



18. The observed right ascensions and declinations of the 

 comet were corrected by applying the corrections for parallax. 

 The observations were freed from aberration bv subtracting the 

 aberration time from the times as given by the observers. These 

 times were then reduced to Greenwich mean time and expressed 

 in decimals of a day. 



1 9. WeigJit of Observations. — The observations made b}' 

 the various observers are of varying values ; the series of obser- 

 vations obtained by one observer agreeing remarkably well 



