Lectures in Navigation Part 17

in Time which turns into degrees, minutes and seconds by Table 7. If G.A.T. is greater than L.A.T. longitude is West; if G.A.T. is less than L.A.T. longitude is East. Example:

August 26th, 1919, A.M. CT 26d 2h 29m 03s A.M. CC 16m 08s slow. (_) 44 57' 00". IE--1' 30". HE 32 ft. D.R. Lat. 4 55' 32" N. Required longitude in at time of observation.

26d--2h--29m--03s A.M.

- 12 ------------------ CT 25d--14h--29m--03s --90 00' 00"

CC+ +16 --08 Dec. 10 49 48 ------------------ -------------- G.M.T. 25d 14h 45m--11s P.D. 79 10' 12"

Eq. T. -2 --05 ------------------ G.A.T. 25d 14h--43m--06s - 1' 30"

+ 9 27 (_) 44 57' 00" --------- Corr. + 7 57 Corr. + 7' 57"

----------- -(-)- 45 04' 57"

Lat. 4 55 32 N sec. .00160 P.D. 79 10 12 cosec. .00781 ------------ 2) 129 10' 41"

------------ 1/2 S 64 35' 20" cos. 9.63266 - 9 -(-)- 45 04 57 ------------ Diff. 19 30' 23" sin. 9.5235O--14 ------------- 9.16557 + 5 + 5 ------------- log. hav. S.H.A. (L.A.T.) 9.16562

S.H.A. (L.A.T.) 25d--21h--00m--01s G.A.T. 25 --14 --43 --06 ----------------- Lo. in T. 6h--16m--55s E

Lo. (Table 7) 94 13' 45" E

I wish to caution you about confusing this method with the one Bowditch uses, and still another which Henderson uses in his book "Elements of Navigation." It is not exactly like either one. It requires one operation less than either, however, and it also requires the use of fewer parts of the various tables involved. For that reason it is given you.

a.s.sign for work in cla.s.s room and also for work at night examples similar to the following:

1. Oct. 1st, 1919. A.M. (_) 17 15' 00". G.M.T. 1d 11h 30m 00s A.M.

D.R. Lat. 40 30' N. IE--2' 20". HE 25 ft. Required longitude in.

2. Oct. 10th, 1919. P.M. (_) 25 14' 30". CT 1h 15m 20s. CC 4m 39s slow. IE--3' 10". HE 26 ft. D.R. Lat. 41 29' 00" S. Required longitude in.

3. May 27, 1919. P.M. Lat. by D.R. 40 55' N. (_) 34 4' 00". IE + 1' 10". HE 10 ft. CT 8h 55m 42s. CC 2m 02s fast. Required longitude in.

4. May 18th, 1919. A.M. (_) 29 41' 15". WT 7h 20m 45s. C-W 2h 17m 06s. CC 4m 59s slow. Lat.i.tude by D.R. 41 33' N. IE--1' 30". HE 23 ft. Required longitude in.

5. August 24th, 1919. A.M. (_) 23 32' 10". IE--2'00". HE 16 ft.

In lat.i.tude 39 04' N. CT 24d 2h 47m 28s A.M. CC + 4m 28s. Required longitude in.

6. June 26th, 1919. P.M. (_) 44 08' 20". IE--2' 20". HE 37 ft.

CT 8h 18m 45s. CC 3m 20s fast. Lat.i.tude by D.R. 6 43' S. Required longitude in.

7. July 29th, 1919. A.M. CT 29d 11h 14m 39s A.M. CC 2m 18s slow.

(_) 28 08' 30". IE + 0' 30". HE 38 ft. Lat.i.tude by D.R. 39 48' N.

Required longitude in.

8. May 22nd, 1919. P.M. CT 9h 14m 38s. CC 5m 28s slow. (_) 21 07' 40". In lat.i.tude 41 26' N. IE + 3' 10". HE 40 ft. Required longitude in.

WEEK VI--NAVIGATION

TUESDAY LECTURE

LONGITUDE BY CHRONOMETER SIGHT OF A STAR

In getting your longitude by a time sight of a star, you proceed somewhat differently from the method used when observing the sun. What you wish to get first is G.S.T., i.e., the distance in time Greenwich is from the First Point of Aries. If you can then get the distance the ship is from the First Point of Aries, the difference between the two will be the longitude in, marked East or West according as to which is greater.

By looking at the diagram furnished you when we were talking of Sidereal Time, all this becomes perfectly clear. The full rule for finding longitude by a star is as follows, which put in your Note-Book:

Correct your CT to get your G.M.T. From the G.M.T. get the G.S.T. From the observed alt.i.tude of the star, obtain the star's H.A. at the ship in the same way L.A.T. is secured in case of the sun. To or from the R.A.

of the star add, if West of your meridian, subtract if East of your meridian, the star's H.A. at the ship, just obtained. The result is the R.A. of the ship's meridian or L.S.T.

Find the difference between G.S.T. and L.S.T. and the result is the longitude, marked East or West according as to whether G.S.T. is less or greater than L.S.T. Note: Always take the star's H.A. from the top of the page of Table 45.

Dec. 2, 1919. A.M. Observed alt.i.tude Star Sirius 2O 05' 20", West of meridian. CT 11h--45m--29s P.M. CC 1m--28s slow. IE--1' 20". HE 21 ft.

Lat.i.tude by D. R. 38 57' N. Required longitude in.

CT 11h--45m--29s CC + 1 --28 ------------------- G.M.T. 11h--46m--57s (.)RA 16 --37 --10.3 (+)CP 1 --56.1 ------------------- G.S.T. 28h--26m--03.4s IE -1' 20"

--24 HE -7 08 ------------------- ------- G.S.T. 4h--26m--03.4s Corr. -8' 28"

Obs. Alt. 20 05' 20 Corr. -8 28 ---------- T.C.A. 19 56' 52"

Lat. 38 57 sec. .10919 P.D. 106 36 24 cosec. .01849 + 1

2 ) 165 30' 16"

------------- 1/2 S 82 45' 08" cos. 9.10106 - 13 T.C.A. 19 56 52 ------------- Diff. 62 48' 16" sin. 9.94911 + 2 --------- 9.17785 - 11 --------- log. hav. Star's H.A. at ship 9.17774

Star's H.A. 3h--02m--40s Star's R.A. 6 --41 --39 -------------- L.S.T. 9h--44m--19s G.S.T. 4 --27 --01 -------------- Lo. in T. 5h--17m--18s E

Longitude in 79 19' 30" E

a.s.sign for Night Work or work in the cla.s.s room examples similar to the following:

1. April 16, 1919, in Lat.i.tude 11 47' S. Observed alt.i.tude of the Star Aldebaran, West of the meridian 23 13' 20". CT 6h 58m 29s. CC 2m 27s fast. IE--2' 00". HE 26 ft. Required longitude in.

2. Dec. 10th, 1919. Observed alt.i.tude of Star Sirius 20 05' 40" West of meridian. CT 11h 45m 29s. CC 1m 28s slow. IE--1' 20". HE 21 ft. D.R.

lat.i.tude 38 57' N. Required longitude in.

Note to Instructor: If any time in the period is left or for Night Work a.s.sign examples to be worked by Marc St. Hilaire Method, changing slightly the D.R. Lat. and Longitude just obtained by the Time Sight Method.

WEDNESDAY LECTURE

EXAMPLES ON LONGITUDE BY CHRONOMETER SIGHT OF A STAR

1. Dec. 9th, 1919. In lat.i.tude 36 48' N. Observed alt.i.tude Star Capella, East of meridian 46 18' 30". IE 2' 50" off arc. HE 33 ft. CT 10d 3h 05m 05s A.M. CC 1m 18s slow. Declination of star is 45" 55' N.

Required longitude in.

2. October 26th, 1919. In lat.i.tude 39 54' S. Observed alt.i.tude Star Rigel, West of meridian 42 18' 40". CT 27d 10h 32m 55s A.M. CC 2m 18s fast. IE 4' 20" off arc. HE 42 ft. Required longitude in.