METHODS OF OCEANOGRAPHIGAL RESEARCH 2 59
salinity its course can be roughly traced as it m0ves north—»
wards.
The physical state of the water and its chemical
composition have an extremely important bearing_on the
life contained therein, and the temperature, density and
saltness of the water are being kept continually under
observation by those engaged in marine biological research
in different regions.
'
The chief instrument for studying the temperature ”of
the sea is the thermometer.
The study is a fairly simple
matter when it is only necessary to nd the temperature
of the water at the Sea surface.
Water is merely dipped up
in a wooden bucket and anaœurate thermometer placed
in it for two or three minutes ;
it is important to use a
wooden bucket rather than a metal one, because metal is
such a good conductor of heat that in a short time it may
materially affect the temperature of the water contained
in the bucket and so lead to
-
But it is quite another matter When we wish to know
the temperature at fty, 100 or even 1,000 fathoms. The
water down to a certain depth becomes cooleraS one goes
deeper, andthe rst difculty to be :overcomé=therefore is
that if a thermometer is loWered, say to fty fathonis,
it will pass through_Warmer and warfner water as it is
hauled to the surface, and by the time it is examined it
will be registering quite a different“ temperature from that
actually occurring at fty fathoms.
_
This difculty is
_
overcome
by using specially designed bottles that are
—
-
thoroughly insulated. Ï In addition, by means of a weight
known as a “
messenger
”
which
be sent down the
‘
bottle, which is loWered Open at b0th ends, can
_.
-
be closed (Plate '92).
on its downward journey the Water '
'
mérely ows through it, so that when it is closed it takesa
—
sample of water from that depth at which closing‘ took
place.
Owing to the insu1ation the water sample Sthus
.