.
METHODS OF OCEAN OGRAPHICAL RESEARCH
2‘61.
,
on
the amount of salt contained, on the alkalinitÿ or
acidity, and on the presence of minute‘organic substances
in solution.
,
,
A further physical observation that has to be made is
the penetration of light into the sea.
It is interesting to
know the strength and colour of the light at different
_
depths. A rough “and ready Way Of noting;the transparence ' of the water from place“ to place is- to lower a
circular, white disc to the depth at which it" disappears;
This method of course gives little information beyond a
mere rough Comparison of—the _transparencÿwof
'
regions.
Special cameras have been used which can be
'
exposed for a'denite time at any required depth, but they
'
have
yielded little information (beyond recording. the
actual presence and Colour of the light.“
Recently the light
‘
has been measured electrically by means'of photo—electric
‘
cells and it isto be hoped that by thisymeansan advancef
Will soon be made in our* knowledge of the light under the
sea.
'
‘
«
.
This completes a
the methods used in
studÿing the actual
and
chemical
conditions
,
in*tlîe sea_——the.depth, theCurrents, the temperature
and so
"on.
It yet remains to he said how knowledge is obtained
living world .preSent ' therein;
‘VariOus
animals and plants thatlive eithe’r creeping on‘thebottom;
'
orçswiniming; or
the water above rthebottoni,; -
"have to be captured‘
the
‘
catching haveto
thought out because not
animals
_
in,Ordefg
_
__
'
buÏt
be
..
'
_
…-from“seaäoîi°
'
instruments to:—be
;.
ammalsfrom the sea bottom