高緯度における位置の線(日本航海学会第15回講演会)

抄録

The line of position of heavenly body plotted on Mercator's chart deviates from the true circle of position as follows: (i) the length of intercept is not exactly correct because of the scale of meridional parts, (ii) the position of the terminal of intercept plotted as a loxodrome deviates from that of intercept plotted as a great circle, (iii) the azimuth of the line of position is not equal to that at the estimated (or assumed) position owing to the convergency of the meridians, and (iv) the line of position is plotted as a loxodrome whereas the true line of position is a kind of a plane curve of transcendental equation on the chart. Moreover, if the correction for run is reckoned: (v) the tangent to the locus of the probable transferred position does not coincide with the transferred line of position obtained by the parallel displacement. Investigating these esrors in turn, we get the correction formulae and their nomograms for high latitndes. For their effects to the line of position, the component for latitude and longitude due to (ii) cancels each other, and it is sufficient to account only for (i) and (iii). (The effect of (iv) is, as is well known, neglegible unless the altitude of the heavenly body is greater than 60°, and its corrections are found in many nautical tables.) Adopting the probable maximum values, the ultmate errors of the ship's position obtained at the chart can sufficiently be negligible for the latitude of 70°, and we may use the ordinary method of Sumner's line in the coming antarctic operations of SOYA to the Prince Harald Coast (lat. 70°S) without any anxiety on Mercator's position plotting sheets.