No. EXAMPLES FOR PRACTICE. In each of the following examples the variation is required: CIVIL DATE. 1. 1865, Jan. 27th, 9. Feb. 17th, March 29th, April 5th, March 5th, May 26th, 6h 55m40s A.M. 35° 42' N. 12° 52′ W. 34 57 N. 25 50 S. 20 20 S. 4I 2 N. 51 22 S. 40 8 E. 127 35 W. 155 30 E. 22 o W. W. S.E. E. 48 o E. E. June 2nd, 8 8 2 P.M. 52 30 N. 27 6 W. 6 50 58 A.M. 28 59 S. III II W. Aug. 27th, Nov. 3rd, Dec. 4th, March 20th, Sept. 22nd, Feb. 26th, 6 34 O P.M. 7 56 48 P.M. 6 O O P.M. 6 O O P.M. 6 O O A.M. 7 49 O A.M. 6 28 12 P.M. 7 40 O P.M. 4 6 O A.M. 6 14 O P.M. 5 49 O A.M. 352 24 22 N. 42 44 S. 56 41 S. 29 20 S. 49 59 S. 55 10 N. 60 I S. 36 19 E. 57 30 W. 175 15 W. 73 15 E. 136 35 E. 160 45 E. 60 32 E. 106 45 W. 10 21 W. E. O P.M. 52 30 S. 24 50 W. ON FINDING THE TIME OF HIGH WATER. IN the Nautical Almanac the mean time of high water at London Bridge is given for every day of the year, on the assumption that the time of high water on the days of full and change, or as it is termed, the ESTABLISHMENT OF THE PORT (see Nautical Almanac for 1865, page 488) is 2h7m. The first high water which occurs after mean noon of each day is inserted in the first column, and the second in the second column. Where a line () is inserted, it indicates that there is only one high water on that day. Thus, on 1865, January 8th, there is only one high water: it occurs January 8th, at 11h 33m (P.M.); but the succeeding high tide does not take place until o1 6m after mean noon January 9th. The time given, it will be observed, is expressed in astronomical time. Again, on February 7th, 1865, there is only one high tide: it occurs at February 74 12 28m astronomical time; i.e., 12h 28m past the noon of the 7th, which is oh 28m past midnight, or expressed in civil time it is February 8d oh 28m A.M. Immediately following the Table just referred to, is another in which is registered the Establishment for nearly one hundred important stations (pages 490 and 491), under the heading "Time of High Water on the Full and Change of the Moon." Hence may be deduced the time of high water for any day at the given place. FIRST METHOD.-By Nautical Almanac. RULE LI. 1o. Take out of Nautical Almanac (page 490, for 1865) the establishment of the port, or the time of high water on the full and change of the moon, at the given place and also at London Bridge. 2o. Take the difference of these two quantities, and mark it + when the establishment of port at the given place is more than that at London Bridge, but mark the difference when the establishment of port at the given place is less than at London Bridge. 3°. Take the times of high water at London Bridge for the given day from the Nautical Almanac (pages 488, 489, for 1865.) The morning tide is found in the second column and opposite the preceding day of the month, the time thus given being diminished by 12h. The afternoon tide is found in the first column, opposite the given day of the month. If a blank occurs in either column, use the tide preceding instead when the difference found by Rule 2o is marked +, but use the tide following the blank when the difference is marked – -. Be sure to annex the letters A.M. or P.M. to the tides so taken out. 4. To the times of high water at London Bridge apply the difference, or constant, adding or subtracting said difference according as it is marked +or; the result in each case, if less than 12h, is the A.M. and P.M. tides respectively. (a) When the sum of the constant and the A.M. London Bridge tide exceeds 12h, deduct 12h; the remainder is P.M. tide at the given place. To obtain the A.M. tide at the place, if any, add the constant to the London Bridge tide preceding, that is, the afternoon tide of the day before; or if the sum is less than 12", it is the P.M. tide of the day before, and there is no A.M. tide that day at the given place; but if the sum exceeds 12", deduct 12, the remainder is A.M. tide sought. but (b) When the constant added to London A.M. tide is less than 12h, when added to London P.M. tide preceding exceeds 12h there is only an A.M. tide at the given place on that day. (c) When the constant is subtractive and exceeds the London A.M. tide, reject this last, and use the P.M. London tide following. If the constant being subtractive exceeds London P.M. tide, 121 must be added to this last before subtraction is made; the remainder will be A.M. tide at given place. For the P.M. tide use the following London tide, that is the morning tide of next day, borrowing 12h if constant exceeds it, the remainder is P.M. tide at given place. (d) If constant being subtractive exceeds the London A.M. tide, but is less than the London P.M. tide, there is only a P.M. tide at the given place on that day. (e) If when constant is subtractive the London P.M. tide has to be increased 12a, but constant is less than the London A.M. tide following: there is only an A.M. tide at the given place that day. EXAMPLES. Ex. 1. 1865, January 11th: required the times of high water at Shields, A.M. and P.M. Establishment of Port at Shields, page 491, N.A. 3h23m London Bridge Time H.W. London Bridge, 1h 55mp.M. Difference +1 16 Time H. W. London Bridge, Jan. 10th, 13h 32m, or 11th, 1h32m A.M. Time H. W. Shields, 11th, 3 II P.M. Time H.W. Shields, 11th .. 2 48 A.M. Ex. 3. 1865, March 6th: find the A.M. and P.M. tides at Liverpool (St. George's Pier). Establishment of Port, Liverpool Dock.... 11h 23m London Bridge. 2 .... Difference +9 16 Ex. 4. 1865, June 21st: find the times of high water at Beaumaris, A.M. and P.M. The second column opposite the preceding date, which is the one usually taken out, being blank, and the difference being marked +, we must use the preceding tide as above. Ex 5. 1865, May 22nd: find the times of high water at Greenock. Ex. 6. 1865, May 8th: find the times of high water at Dunkerque, A.M. and P.M. Ex. 7. 1865, July 20th: find the A.M. and P., tides at Tay Bar. London Bridge 2h 6m Ex. 8. 1865, December 29th: find the times of high water at the Downs Stream, A.M. and P.M. Time H. W. Downs, 29th II 33 A.M. Time H. W. Downs, 29th.. 12 7 P.M. 30th.. O 7 A.M. Whence there is no P.M. tide, as it flows past midnight (12h 7m P.M.) Ex. 9. 1865, November 15th: find the A.M. and P.M. tides at Dunbar. A blank occurring in the second column of the preceding date, and the constant being additive, the tide preceding the blank is employed to find the A.M. tide, but since the sum of constant and London tide does not amount to 12h, it gives the P.M. tide at given place on preceding day, whence it is evident there is only a P.M. tide on that day at the given place, U |