Latitude by the Lingke and Würdemann instruments—Continued. Initials of observers. Lingke combined instrument. T. A. B. C. McD. T. 21.52 21.50 21.41 19.49 21.73 G. J. F. A 21.93 22.35 20.31 20.72 21.05 18. 62 19.87 20.37 20.94 21.64 20.60 21.57 Latitude by the Lingke and Würdemann instruments-Continued. The following observations with the Russian combined instrument are not comparable in point of precision with those of the other two. The instrument is not so well adapted to reversals, and has other defects as a zenith telescope, and the work with it was done by the observers entirely without assistance, either by calling off settings, noting time, or recording observations. The results should be given no weight in deciding upon the latitude of the place, but they are reported for comparison with other methods. A rigid discussion of the individual results obtained by each officer, with a view to determine from them the most probable latitude of the observatory, has not been attempted this season because of their great number. This was done last year (see General Orders No. 3, series of 1881), giving as the result of 326 observations on 84 pairs the following value: North latitude 40° 47′ 21′′.59 0.082. The grand means of all the observations made this season with the Würdemann and Lingke instruments, throwing out only those rejected by the criterion as applied by each officer to his entire work and giving all pairs and observations equal weight, are the following: Würdemann (197 observations on 57 pairs) latitude 40° 47′ 21′′.55. Lingke (394 observations on 100 pairs) latitude 40° 47′ 21′′.43. Grand mean (591 observations on 104 pairs) latitude 40° 47′ 21′′.47. There is, therefore, an absolute discrepancy of only about 12 feet in the latitude of the observatory, as determined in 1880 and in 1881. The grand mean of the 77 observations made with the Russian transit is 40° 47' 21". 29. Lieutenant Casey, by discussing his own observations by the method of least squares, obtained 40° 47′ 22.78, the value of a turn of the micrometer being 69".152 and of a level division 0.810. With sextant.-The following table exhibits the latitude results submitted by each officer, the corresponding determinations of time having been already reported: The methods in use are the following-occultations by the dark limb of the moon, lunar culminations, eclipses of Jupiter's satellites and (chiefly for practice with the sextat) lunar distances. The delay in the receipt of the equatorial and the frequent occurrence of cloudy nights prevented the observing of any occulations during the past year. Lunar culminations.-The American Ephemeris is used in reducing these observations. The computations receive the same care that would be given to them on a boundary survey. No observation is rejected unless noted as doubtful, or thrown out by Peirce's Criterion. The mode of recording time on each date has already been reported in the general table giving the result of the transit work. |