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February 1924 Find. ‘ Shs Position by New Method A new and shorter method for find- ing a ship’s position is given in hydro- graphic office publication No. 203, carrying the title of “The Summer Line of Position, furnished ready to lay down upon the chart by means oi Tables of Simultaneous Hour—Angle and Azimuth of Celestial Bodies.” It is desirable that navigators should be informed of the delivery by the government printing office of this vol- ume, in which the hydrographic office has provided the means for the prac- tice of a new method of finding po- sition in navigation from the obser- vation of the altitude of the sun or other celestial body. The chronometer time of the ob- servation of an altitude indicates the longitude from Greenwich of the meridian on which the observed celes- tial body is. located. The tables of this publication give the hour-angle, er longitude counted from the merid- ian of the observed body of the in- tersection of the observer’s position- line with a designated parallel of lati- tude so that the longitude from Greenwich of this point of lat- itude of the observer’s position- line is immediately found by algebrai- cally adding together the longitude of the observed celestial body indicated by the chronometer and the longitude of the’. observer from “the. Ob- served body, taken from the tables, and hence, since the azimuth of the observed celestial body is tabulated by the side of the hour-angle, the position line may be at once drawn through the point thus found in a direction at right angles to the bear- ing of the observed body, as indi- cated by the azimuth. Divested, as it is, of the use of logarithms and, indeed, of all compu- tation within the usual meaning of that term, and requiring reference to only a single page of the table, the solution is of unusual simplicity and brevity among navigational methods which yield results suffering no de- traction from theoretical accuracy, and renders the course of procedure the same, whatever the situation of the observed body in the heavens may- be, provided only that the conditions admit of the accurate measurement of the altitude at a known instant of time. The limits of the tables in H. O. No. 203 are latitude 60 degrees N., to 60 degrees S., declination 27 degrees N. to 27 degrees S. The statutory price of this volume of 869 pages has been fixed at $2.25 MARINE REVIEW Position by New Method, H. O. No. 203 April 5, 1918, p. m., latitude by D. R. 20° 38’ S., longitude by D. R. 90° 10’ E., or 6 00™ 40° E., observed simultaneous altitudes of stars a Tauri (Aldebaran) bearing northward and westward, and 8 Leonis (Denebola) bearing northward and eastward. Sextant altitude of a Tauri 26° 00’ 40”, of B Leonis 25° 17’ 00” I. C—1’ 00”; height of eye 19 feet; W. T. of observer 7" 16" 44*; C.—W. 5 55™ 24°. Chronometer fast of G. M. T. 1™ 38". Required the ship’s position. Xx Data for a Tauri (Aldebaran). Data for 8 Leonis (Denebola). h. ms. on oo ee W.T. 716 44 Alt. by sextant % 0 #0 Alt. by sextant % 17 00 c.—W. 5 55 % Correction -7 15 Correction —7 19 ee 1 3 by True altitude 3B 8 True altitude 2 OO Al ae = Table 1 -6 15 | Tablet 6 19 Q@.M. T. 1 10 30 I.c. —1 00 I.c. —1 R.A. M. 8. 0 Sl 546 __o : mmr Oho Cor. for G. M. T. 11.6 Correction a —7 15 Correction —7 19 . mm. 8s, h. m. 3. @.8.T 2 02 36.2 R.A. from Nautical Almanac 4 31 14.0} R.A. from Nautical Almanac 11 44 55.8 Dec. from Nautical Almanac 16° 20.7’ N | Dec. from Nautical Almanac 15° 01.5’ N h. m. s. h. m. s. Q.3.T. 2 02 %.2 QG.8. T. 202 %.2 R. A. @ Tauri 4 31 140 R. A. B Leonis ll 44 55.8 G.H.A. 228 37.8 E.'G, H.A. 9 42 19.6E. From the tables of simultaneous hour angles and azimuths for latitude 21° S., which is the whole degree of latitude next to the D. R. latitude, and altitude 26°, which is the nearest tabu- lated altitude to the corrected measured altitude, we obtain the hour angle and the azimuth for a Tauri (Aldebaran) thus: Corresponding to declination 16° of the contrary name to the latitude, h. m. s. ° 8. he - H. A. 3 32 56 Diff. for i’dec. 2.8] Azimuth S$. 121.1 W. Diff. for 1’ dec. 0,022 Cor. for 20’.7 dec. 58 20,7 | Cor. for 20.7’ dec. 0.5 20.7 Local H. A. 3 31 58 W. 196 | Local azimuth S. 121.6 W. 154 G.H.A. 2 @ 37.8E. % ww Longitude 8 E. 57.96 0, 4554 6 00 35. or 90° 08’ 57” E. And likewise for the hour angle and azimuth of 8 Leonis (Denebola), by entering the tables with latitude 21° and altitude 25°, we obtain: Corresponding to declination 15° of contrary name to the latitude, h.m. 8s s. bd i H.A. 3 40 35 = Diff. for 1’ dec. 2.7} Azimuth S.119.0E. Diff. for 1’ dec. 0.022 Cor, for 1.5’ dec, 4 1.5 | Cor. for 1.5’ dec. 0 L5 Local H. A. 3 40 31E. 135 | Local azimuth S. 119.0 E, 110 G.H.A. 9 42 19.6E. 7 22 Longitude Ol 48.6 E. 4.05 +0330 uF 90° 27’ 00’ E. The preliminary Sumner line from the observation of a Tauri (Aldebaran) is therefore drawn through a geographical position in 21° S. and 90° 08’ 57’’ E. in a direction 211.°6—that is, at right angles to the direction S. 121°.6 W.—and then transferred parallel to itself for a dis- tance of 6.6’ away from the bearing of « Tauri (Aldebaran), since the corrected measured altitude is 25° 53’ 25’’, which is 6.6’ less than the altitude 26° employed in entering the tables, And, in like manner, the preliminary Sumner line from 6 Leonis (Denebola) is drawn through a geograph- ical position in 21° S. and 90° 27’ 09’ E. in a direction 151°—that is, at right angles to the direc- tion S. 119° E.—and then transferred parallel to itself for a distance of 9.7’ toward the bearing of 8 Leonis (Denebola), since the corrected measured altitude is 25° 09’ 41’’, which is 9.7’ higher than the altitude 25° employed in entering the tables. These Sumner lines are plotted in the accompanying figure, and the intersection of the required lines shows the ship’s position at the time of the observations to have been in latitude 20° 423’ S. and longitude 90° 284’ K. Although the method of plotting—which is the most convenient course to pursue when the necessary chart or plotting sheet is supplied—has been prescribed as the means of finding the Sumner line and finding the intersection, it will not escape attention that the procedure by computation, out- lined in Articles 372 and 376 to 390 of the American Praétical Navigator, is fully available. LATITUDE 21°. ATITUDE—Continued. 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