34 
which happen near the time of first or last quarter are called “neap” 
tides. The information that has just been obtained from the curve 
clearly discloses the relationship existing between the spring and 
neap tides and the phases of the moon. 
Still another point must be noted: the tides of the 10th, roughly 
a day before “First Quarter/’ are higher than those on the 25th, 
a day before “Last Quarter”; whereas, conditions being the same, 
tides of the same height would have been expected. The reason for 
the discrepancy is not hard to find : on the 10th the moon was in 
perigee or at its nearest distance to the earth, while on the 25th it 
was in apogee or further from the earth than at any other time 
during the month, and hence the moon’s attraction on the 25th would 
be less than on the 10th and consequently the tides would be lower. 
Summarising what has been so far discovered from an examina- 
tion of these June curves, the connection between the moon and the 
tides has been demonstrated beyond doubt. It has been clearly shown 
that the height or range of the tides depends chiefly upon the phase 
of the moon and in a minor degree upon the distance of the moon 
from the earth. The highest tides of all would therefore be expected 
when these two causes act together, namely when new or full moon 
occurs at a time when the moon is also nearest to the earth or in 
perigee. To verify this, it will be necessary to run through the 
whole year’s records and pick out the readings on the days when 
the above coincidences take place. The following dates, picked out 
at random, must suffice: — On September 1st the moon was “New” 
and nearest to the earth, the high water was 26ft. 9in. and the low 
water 3ft. llin. ; while on the 15th, when the moon was “Full,” the 
tide only rose to 25ft. and fell to 5ft. lin., but on this date the moon 
was in apogee. Again, on February 7, new moon occurred at apogee 
and the tides were 24ft. lin. and 6ft. 3in. high and low water respec- 
tively. With which contrast the 21st, the moon being “Full” and in 
perigee, when there is a high tide of 27ft. and a low of 4ft. 7in. 
according to the tide trace. It should be remarked that owing -to the 
tide gauge being about 9ft. above the datum line, this quantity must 
be taken from the readings given to obtain the exact height of the 
water level. 
The relationship between the tides and the phases of the moon 
would at once prove that the sun, even if the fact were not already 
known, plays a very important part in tidal phenomena, and an 
examination of the constants for Port Hedland at the end of this 
paper shows that the mean solar is responsible for a tide about one- 
third that of the mean lunar. And this is exactly what we would 
expect from theoretical reasoning. It can be understood in a general 
way when it is realised that the tide-generating force varies directly 
as the mass and inversely as the cube of the distance of the tide- 
gen erating body. Thus, although the sun is enormously larger than 
the moon, its tide-lifting force is only one-third that of the moon. 
It is quite easy to demonstrate this from the known distances and 
