Synopsis
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1900 Excerpt: ...Noon at Ship, and hence the Longitude. If however, the ship has made Northing or Southing, a correction must be applied. It is found in this way: Sin £ Diff. Lat. x Sec Lat. x Cot Az. = Sin Correction; or Log. Sin £ Diff. Lat. + Log. Sec Lat. + Log. Cot Az. = Log. Sin Correction. This correction turned into time must be subtracted from the time by Chronometer if the ship has approached the Sun in the interval; but must be added to it if she has gone away from that luminary. Latitude by a change of Altitude.--You can find your Latitude without reference to the Nautical Almanac by observing the change in Altitude of any Heavenly Body in a given time when such Body is on or near the Prime Vertical. Divide the number of seconds in the change of Altitude by 15 times the number of seconds in the interval of time, and you have the Cosine of the Latitude. Thus, for an example, suppose that during an interval of 2 m. 50 s. the Altitude of a Body near the Prime Vertical changes 32'. 32' = 1920" 2" 50' = 170o x 15 = 2550' Cos. Lat. = 9-?®, or Log. Cos Lat. = Log. 1920-Log. 2550 1920 Log. 3-283301 2550 Log. 3-406540 1W6761 = Log. Cos Lat. 41 9' 35" and Lat. is 41 9' 15" If you are observing the Sun it is, perhaps, simplest to note the time in which he rises or falls his own diameter. 167 CHAPTER XXIV ADDITIONAL CHART PROBLEMS The following problems, though not given in the Board of Trade Examination, are very useful, in coasting especially, and may, I think, be profitably studied here. They depend upon the fact that any chord of any circle subtends the same angle from any point., r Fio. 102 on the circumference of the circle on one side or the other of the chord. Thus in the diagram Hedc is a circle, and the chord A B subtends equal a...
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