36 
figures from other ports on the coast were available, it would 
probably be found that this interval between the moon’s meridian 
passage and the time of high water varied widely — so widely that 
it would seem impossible to reconcile the equilibrium theory with 
the discordant results. However, the four factors just mentioned 
would be quite sufficient to account for all the different intervals 
that may exist, and hence it is not fair to say that the theory breaks 
down because the crest of the wave does not occur approximately 
under the sun and moon at all places about the time of new and full 
moon. In connection with wave transmission it is worth remember- 
ing that a wave travels faster in deep water than in . shallow, and 
hence the lag of the tide-wave behind the moon must vary directly 
with the different depths of the ocean along the coast. At some 
future time, when the importance of tidal work has been recognised 
in Western Australia and observations taken at all the ports, a com- 
plete discussion it is hoped will be undertaken. 
The time that elapses between the moon’s meridian passage and 
high water is termed the Lnni-tidal Interval, and if these intervals 
are plotted, using the moon’s meridian passage as an argument, a 
curve results which is known technically as ‘‘The True Establishment 
of the Port.” Plate XII., Fig. 1 shows the Establishment for Port 
Hedland. To make use of the diagram the time of the moon’s transit, 
taken from the Nautical Almanac, is noted on the top or bottom line, 
and then the point on the curve vertically above or below. From 
this point the horizontal line is followed to the time scale on either 
side, giving the luni-tidal interval, which, added to the time of moon’s 
transit, gives approximately the time of high water. To obtain a 
more accurate result corrections for the sun’s position, the moon’s 
declination, and the time of the year must be added. 
It stands to reason that this rough and ready method is only 
applicable at places where the tides are fairly regular; it would 
break down in cases where the tides are irregular or do not depend 
in the main upon the moon. Thus at Fremantle, as will be found 
later on in this paper, it would be impossible to determine any 
definite curve. 
Just as a rough rule for finding the time of high water can be 
made out, so in the same way curves can be drawn, having the moon’s 
meridian passage as argument, from which the approximate heights 
may be estimated. Thus Plate XII., Fig. 2 provides a means of find- 
ing the height of high and low water and consequently the range of 
the tide at Port Hedland. 
The Fremantle Tides. 
Turning now to the Fremantle tides it will be found that the 
matter becomes very much more complicated and not nearly so easy 
of elucidation. As mentioned above it is impossible to make a curve 
of the luni-tidal intervals; nor is it possible to show on a diagram 
the height or range of the tide depending upon some determinable 
