# Navigating the Ship; A Series of Lessons in Elementary Navigation Based Upon a Course of Lectures, Now in Use at the Officers' Material School, Naval Auxiliary Reserve

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1919 edition. Excerpt: ...case of the sun. The semi.diameter of a heavenly body is half the angle subtended by the diameter of the visible disk at the eye of the observer. For the same body, the SD varies with the distance. Thus, the difference of the sun's SD at different times of the year is due to the change of the earth's distance from the sun. The SD is to be added to the observed altitude in case the lower limb is brought in contact with the horizon, and subtracted if the upper limb is used. Probably most of the sights you take will be of the sun's lower limb, i.e., when the lower limb is brought in contact with the horizon, so all you need to remember is that in that event the SD is additive. Put in your note book: Dip is--Table 14 Bowditch Refraction is--Table 20A Bowditch Parallax is + Table 16 Bowditch S.D. is + Nautical Almanac Observed altitude of Sun's lower limb is expressed.Q.. True altitude is expressed--S--. In order to become familiar with these corrections you should first apply each of them separately to an observed altitude in order to get the corresponding true altitude After that, and for future work, you should use Table 46, Bowditch, which combines all the corrections into one and, at the head of each column for the sun and a star, respectively, tells you whether this combined correction is + or--. Remember that before an observation is at all accurate it must be corrected to make it a true altitude. Remember also that the Index Error must be applied, in addition to these other corrections, in order to make the observed altitude a true altitude. So there are really five corrections to make instead of four, providing, of course, your sextant has an Index Error. CHAPTER IV NAVIGAT ION LESSON 18.--THE LINE OF POSITION...