On page IV of the Nautical Almanac, January 19th, the moon's meridian passage is 18h 52m, which shows that the moon passes the meridian of Greenwich on the 20th (civil time) at 6h 52m A.M. Then the astronomical date and time would be 19d 18h 52m, to which is added the correction 10m for longitude 5 hours west, which gives the moon's upper transit at Boston, to which is added the high water interval, 11h 27m, and the result will be the astronomical date and time of high water, which is 20d 6h 29m, and being less than 12 hours is also civil time P.M. To the moon's upper transit at Boston, 19d 19h 02m, add the low water interval, 5h 17m, which gives the astronomical date and EXPLANATION OF EXAMPLE 5. On page IV of the Nautical Almanac, January 9th, the moon's meridian passage at Greenwich is 10h 00m. If either the high or low water intervals are added to it, it is clear that the resulting times of tides will be on the 10th, but they are not wanted for that date. On the 8th the moon's meridian passage is 9h 4m, which would be expressed as 8d 09h 04m, to which is added the correction 10m for longitude 5 hours west, which gives the moon's upper transit at Savannah. To this add the high water interval, 8h 13m, and the result will be the astronomical date and time of high water, 8d 17h 27m. To this add 1 day and subtract 12 hours to convert the astronomical time into civil time the 9th, 5h 27m A.M. To the moon's upper transit at Savannah, 8d 21h 42m, add the low water interval, 3h 7m, and the result will be the astronomical date and time of low water, 8d 12h 21m. To this add 1 day and subtract 12 hours to convert the astronomical time into civil time the 9th, Oh 21m A.M. The lower transit is found by adding together the moon's meridian passages for the 8th and the 9th, taking care to include the days dividing by 2, which gives the moon's lower transit at Greenwich, to which is added the correction 10m for longitude 5 hours west, which gives the moon's lower transit at Savannah. To this add the high water interval, 8h 13m, and the result will be the astronomical date and time of high water, 9d 05h 55m, and being less than 12 hours is also civil time P.M. To the moon's lower transit at Savannah, 8d 21h 42m, add the low water interval, 3h 07m, which gives the astronomical date and time of low water, 9d 00h 49m, and being less than 12 hours is also civil time P.M. |