CHAPTER III.
CURRENT OBSERVATIONS.
There is considerable diversity in the design of floats
employed in current observations, dependant to some extent upon
whether it is desired to ascertain the direction of the surface
drift or of a deep current, it does not by any means follow
that they run in simultaneous directions. There is also
sometimes considerable difference in the velocity of the
current at different depths--the surface current being more
susceptible to influence of wind. A good form of deep float is
seen in Fig. 8. It consists of a rod 2 in by 2 in, or 4 sq in
The lower end of which a hollow wooden box about 6 in by 6 in
is fixed, into which pebbles are placed to overcome the
buoyancy of the float and cause it to take and maintain an
upright position in the water with a length of 9in of the rod
exposed above the surface. A small hole is formed in the top of
the box for the insertion the pebbles, which is stopped up with
a cork when the float is adjusted. The length of the rod will
vary according to the depth of water, but it will generally be
found convenient to employ a float about 10 ft and to have a
spare one about 6 ft deep, but otherwise it is similar in all
respects, for use in shallow water. A cheap float for gauging
the surface drift can be made from an empty champagne bottle
weighted with stones and partly filled with water.
Pages:
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41