EXTRAORDINARY TIDES.
[TO THE EDITOR OF THE "SPECTATOR:1
Sru,—In the Spectator of the 7th November, 1874, I wrote : —tt Extraordinary tides are, I maintain, almost as easily foretold as ordinary ones. Since 1850 there have been four—one in 1862, two in 1869, and one in March, 1874—and for the next three years, two more are possible, one on the 25th of this month, the other in November, 1875." I found afterwards that I had made a thoughtless mistake in regard to the November tide in 1874; the spring tide which happens at the second full or new moon (full moon is taken, if perigee coincides with it ; if not, new moon), after the autumnal equinox, is the one which may be extraordinary. In the ease in question, it would be the spring tide at the end of October, but this would give no extraordinary tide. I was
working with the spring tide at the end of November, which followed the third full moon from the equinox, and of course my calculation was falsified by the result. This was, however, so far a proof of the correctness of my theory—the exception which proved the rule.
The tide which I predicted for November, 1875, is that which would, and did, follow the second full moon after the equinox, and coincided with perigee. As a matter of fact, the tide ought to have been somewhat less than that of March, 1874. The swollen state of the river through rains helped to increase it, and so did the N.-W. gale, which confirms Captain Bursted's belief in the superior augmenting power of a N.W. wind.
When I informed you, Sir, of my mistake, the cares of the world entered in, and drove the subject from my mind completely for about a year, and it was only on Tuesday evening last that I accidentally heard of the disaster, when what I had written in -the Spectator flashed across my mind.
It may be some comfort to some of your readers to know that no extraordinary tide can occur this side of January, 1878. What may occur within the next twenty-five years I cannot now ray, but it would not be very difficult to discover.—I am, Sir, &c., B. G. JENKINS.
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