. Tables of calculated hour-angles and altitude azimuth table 30N. to 30S. : ex-meridian tables 60N. to 60S. and calculated reductions ans azimuths of bright stars from 1 hour to 3 hours from Meridian / c by Blackburne . Green. 19 d. 22 h. 30 m. the true altitude of suns centre was 52° 9; and again, on sameday, when chronometer indicated 20 d. o h. 16 m. the true altitude of suns centre was 65° 18, the ship havingmade 23 miles on a true N. 24° E. course during the interval between the observations. Required the lineof position and true bearing of the sun at time of ist Observation, a
. Tables of calculated hour-angles and altitude azimuth table 30N. to 30S. : ex-meridian tables 60N. to 60S. and calculated reductions ans azimuths of bright stars from 1 hour to 3 hours from Meridian / c by Blackburne . Green. 19 d. 22 h. 30 m. the true altitude of suns centre was 52° 9; and again, on sameday, when chronometer indicated 20 d. o h. 16 m. the true altitude of suns centre was 65° 18, the ship havingmade 23 miles on a true N. 24° E. course during the interval between the observations. Required the lineof position and true bearing of the sun at time of ist Observation, and the position of the ship when2Qd Observation was taken, assuming latitudes 46° N. and 47° N. 1ST Observation. 2ND Observation. D. H. M. Green. 19 22 30 oEq. of Time — i 16-7 Green. 19 22 28 43-3 D. H. M. o 16 o-I 17-7 Green. 20 o 14 42-3 Decl. 23 27 o 66 33 Lat. 46 o N. Long. A. 15 031 W.,, 47 o ,, ,, B. 14 20 54 W. Long. C. 16 18 51 W.,, D. 12 57 52 W. Run between Observations N. 24° E. 23 miles was on line of first Position-Line. Line of position N. 24 J bearing S. 65J E. Position at 2nd Obsn. Lat. 46 27 N. True Posn. Lat. 46 30 20 14 43 VV. Long. 14 41 o With the desire to show the superiority of the method advocated in these pages for accuracy andbrevity over the method still employed in the Board of Trade examinations of masters and mates, for the Sumner problem, the above example is given and plotted on the chart by both methods. For thesake of better illustrating the possible error due to the old method, a wider range of latitude has been takenthan is usually given in the examination papers, though, considering the high speed of some of the present-day steamers, the range is not excessive, as the run in interval itself might often amount to over 1° of the tropics, with a much smaller range of latitudes, the error resulting from considering the line of positionof the higher altitude as a straight l
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