38 
just as much in evidence. The use of the words “peculiar irregu- 
larities” in connection with them is, perhaps, inaccurate, and is only 
justified by comparison with the tides of the North Atlantic, which 
are really exceptional in their simplicity. There are probably many 
other ports in the world where the tides are just as uncertain. 
Although the luni-tidal interval, namely, the lime that elapses 
between the moon’s meridian | assage and the following high tide, 
is subject to every possible variation, to such an extent that no 
reliance can be placed upon Ibis method of predicting the time of 
high or low water, still an examination of the Fremantle tides bring 
some interesting features to light. 
Thus when the moon is in Perigee the tides are invariably 
higher and the range greater than in Apogee. This is only to be 
expected, for its attractive force is then at a maximum. So in this 
respect, at all events, the Fremantle tides conform to the generally 
recognised law. On the other hand, we might expect to find some 
regular sequence of change existing between the tides and the phases 
of the moon, but a comparison between the times and heights of 
high and low water with the age of the moon fails to disclose any 
existing connection, in fact, il only still further serves to emphasise 
the complications present in the tide-governing forces, and to 
demonstrate the difficulties likely to be met with in an attempt to 
accurately explain them. For the greatest and least ranges occur 
both at the change and full of the moon alike. 
It should be noted in this comparison that at about the time 
of first quarter and again at last quarter the diurnal tide, namely 
one high and one low during the day, is almost invariably in evidence. 
Jt also may be taken as a general rule that the highest tides and 
greatest range occur about the time of moon’s first quarter, although 
t his sometimes breaks down. At the time of full or new moon the 
semi-diurnal tides often make their appearance, marked by small 
range and great irregularity. But it sometimes happens, as men- 
tioned above, that the highest tides and the greatest range take place 
at these times, with the almost certain prevalence of a diurnal tide. 
A comparison, however, with the moon’s position in declination 
shows that when the moon is on the Equator, the least range occurs, 
the variation in water-level being about one foot, and also great 
irregularity in the times of high and low water is apparent. Very 
little reliance can be placed upon the tidal predictions at this period. 
Often for quite a considerable length of time the water remains 
unchanged in level. The semi-diurnal tides, namely, two highs and 
two lows during the twenty-four hours are also in evidence, but 
the secondaries are sometimes barely perceptible, the difference 
between I he heights of this inferior high and low water being only 
a few inches. 
As the moon moves North or South of the Equator, the range 
gradually increases and the tidal curve becomes regularly diurnal 
