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Annex (pages 4.10, and 6-6)
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Reduced interval between two tide waves in the lagoon of Venice.
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Introduction.
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In this annex, I will show an example of how a semi-diurnal basin (two tide waves per day), apparently transforms itself into a diurnal basin (one tide wave per day).
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The cause of this transformation is the effect of the declination of the Moon, on the times of the tide generation.
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Warning: the same topic will be treated, in a text partly different, on page 7.3. In that case, it will be given as an example of tide wave during a quadrature day.
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The effects of the Moon and Sun declinations on the times of tide generation.
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| .1 |
Let's consider a tide generating celestial body (either Moon, or Sun), in a semi-diurnal basin, in the northern hemisphere, when it is above the meridian (curve A). If it presents a north declination, it acts early. If it has a south declination, it acts late.
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| .2 |
Consider the generating body above the opposite meridian (curve B). If it presents a north declination, it acts late. If it has a south declination, it acts early.
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Ordinates: values of declination (degrees).
Abscisses: values of the times (minutes).
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Formation of couples of tide waves.
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| .3 |
The effect of the declinations of the celestial bodies, on the times of the tide generation, modifies the intervals between successive tide waves, making one interval shorter, and the following one longer, thus forming a series of couples of tide waves.
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Odd number wave, even number wave.
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| .4 |
The first tide wave of each couple is late (with regard to the normal time, in case the declination was zero). It is an odd number tide wave.
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| .5 |
The second tide wave of each couple is early (with regard to the normal time, in case the declination was zero). It is an even number tide wave.
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Slow outflow.
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| .6 |
In the lagoon of Venice, the interval between the two tide waves, forming a couple, is even shorter, because of the slow outflow of the odd number tide wave, out of the lagoon.
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| .7 |
If the odd number tide wave is very late, the even number one is very early too, for the same reason, the declination. The result is a sort of traffic jam.
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| .8 |
That's due to the almost automatic alternance of the lags and leads of successive tide waves, in agreement with the two curves, A and B, of the effects of the celestial bodies declinations.
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