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12. Example: January 22, 1917. Find the times of high waters and low waters at Tacoma, Washington.

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I High water, 22nd
2 Low water, 22nd
3 High water, 22nd
4 Low water, 22nd

3h 38m A. M. 9 51 A. M. 4 09 P. M. IO 22 P. M.

BY UPPER TRANSIT.

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Moon's upper transit 21st N. A.
Cor. for long. 8h W.
Moon's upper transit Tacoma
High water interval
High water (civil time)
14 lunar day
Low water (civil time)
1/2 lunar day
Low water (ast. time)
Add 1 day and sub. 12 hours
Low water (civil time)
14 lunar day
High water (civil time)

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i High water, 22nd 2 Low water, 22nd 3 High water, 22nd 4 Low water, 22nd

3h 43m A. M. 9 56

A. M. 4 09 P. M. IO 22 P. M.

EXPLANATION OF EXAMPLE 13.

On page 118 of the Nautical Almanac, January 8th, the moon's upper transit at Greenwich is 12h 39m, which shows that the moon passes the meridian of Greenwich on the 9th (civil time) Oh 39m A.M. Then the astronomical date would be expressed as 7d 11h 51m, from which subtract the correction 18m for longitude 9 hours east, and gives the moon's upper transit at Port Darwin. To this add the high water interval, 4h 57m, and the result will be the astronomical date and time of high water, 7d 16h 30m. To this add 1 day and subtract 12 hours to convert the astronomical time into civil time the 8th, 4h 30m A.M.

To the moon's upper transit at Port Darwin, 7d 11h 33m, add the low water interval, 11h 18m, which gives the astronomical date and time of low water, 7d 22h 51m. To this add 1 day and subtract 12 hours to convert the astronomical time into civil time the 8th, 10h 51m A.M.

From the same page of the Almanac take the moon's lower transit for the 7th, 7d 23h 27m, from which subtract the correction 18m for longitude 9 hours east, which gives the moon's lower transit at Port Darwin, to which add the high water interval, 4h 57m, and the result will be the astronomical date and time of high water, 8d 04h 06m, and being less than 12 hours is also civil time P.M.

To the moon's lower transit at Port Darwin, 7d 23h 09m, add the low water interval, 11h 18m, and the result will be the astronomical date and time of high water, 8d 10h 27m, and being less than 12 hours is also civil time P.M.

13. Example: January 8, 1917. Find the times of high waters and low waters at Port Darwin, Australia.

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High water (ast. time)
12 lunar day
High water (civil time)
14 lunar day
Low water (civil time)

7d 16h 30m

12 26 8

04 56 P.M.

+

6 13 8 II

09 P.M.

1 High water,

8th 2 Low water, 8th 3 High water, 8th 4 Low water, 8th

4h 30m A. M.
1Ο 43 A. M.
4 56

P. M.
II
09

P. M.

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