2. At sea, Jan. 20th, 1919. CT 21d 2h 16m 48s A.M. In longitude 56° 29' 46" W. Observed altitude of Star Polaris 48° 44' 30" N. IE + 10' 20". HE 37 ft. Required latitude in.
3. At sea, June 4th, 1919. A.M. at ship. CT 10h 16m 32s. CC 5m 45s fast. Lat. by D.R. 42° 44' N, Longitude 53° 13' 44" E. Observed altitude of Star Altair East of meridian, 52° 19' 30". IE - 14' 00". HE 56 ft. Required line of position by Marc St. Hilaire Method and most probable position of ship.
Etc.
Assign for Night Work the following Articles in Bowditch: 336 through 341, disregarding the formulas.
SATURDAY LECTURE
Longitude by Chronometer Sight of the Sun (Time Sight)
You have now learned, first, how to get your latitude by a meridian altitude of the sun or a star and second, how to get your Line of Position and most probable fix, including both latitude and longitude, by the Marc St. Hilaire Method, using for your calculations either the sun or a star. We are now going to take up a method of getting your longitude only. This method requires as much, if not more, calculation than the Marc St. Hilaire Method. Its results, on the other hand, are far less complete, for while the Marc St. Hilaire Method will give you a fairly accurate idea of both your latitude and longitude, this method will, at best, only give you your longitude. Moreover, you can use it for accurate results only when the sun bears almost due East or West of you, for that is the best time, as you have already learned, to get a line of position running due North and South, which is nothing more than a meridian of longitude. The only reason we explain this method at all is because it is in common practice among merchantmen and may, therefore, be of assistance to you, if you go on a merchant ship. Remember, however, that it belongs to Old Navigation as distinguished from New Navigation, exemplified by the Marc St. Hilaire Method. It is undoubtedly being used less and less among progressive, up-to-date navigators, and will continue to be used less as time goes on. The fact remains, however, that at present many merchantmen practice it, and so it will do you no harm to become familiar with the method, too.
This method is based on securing your longitude by a time sight or longitude by chronometer sight, meaning that at the time the sun bears as near due East or West as possible, you take a sight of it by sextant and at the same instant note the time by chronometer. With this information you proceed to work out your problem and secure your longitude according to the following formula. Put in your Note-Book: