do not generally extend for a greater depth below the trough of
the wave than the crest is above it, but as they may affect the
movement of the floating particles of sewage to a considerable
extent it is necessary to record the direction and strength of
the wind.

The strength of the wind is sometimes indicated wind at the
time of making any tidal observations. By reference to the
Beaufort Scale, which is a graduated classification adopted by
Admiral Beaufort about the year 1805. The following table gives
the general description, velocity, and pressure of the wind
corresponding to the tabular numbers on the scale:--

[Illustration: PLATE III

PERIOD OF SIX MONTHS.

To face page 20]

The figures indicating the pressure of the wind in the
foregoing table are low compared with those given by other
authorities. From Mutton's formula, the pressure against a
plane surface normal to the wind would be 0.97 lb per sq. foot,
with an average velocity of 15 miles per hour (22 ft per sec.),
compared with o.67 lb given by Admiral Beaufort, and for a
velocity of 50 miles per hour (73.3 ft per sec.) 10.75 lb,
compared with 7.7lb Semitone's formula, which is frequently
used, gives the pressure as 0.005V^2 (miles per hour), so that
for 15 miles per hour velocity the pressure would be 1.125 lb,
and for 50 miles it would be l2.5 lb It must not be forgotten,