258
,
THE SÈAS
directionsprinted on it in ve different languages instructing the nder to place it in the nearest letter box after
having lled in the place and date of “recovery.
Some
of these bottles travel for enormous distances, and recently
one 'WhîÇh was liberated in' the middle of the English
Channel was picked up away on the Coast of Norway having
'
journeyed a distance of 1,440 miles in 190days.
-
Currents can also be directly measured by means of
special recording instruments. - Several instruments
been invented, but thereis one in general use to-day the
principle of Which isas folloWs.' The machine is lo'weied
to’a*given depth in the Waterand to it is xed a-vane which
at"
the instrument facing in the direction of the
current.
The current then acts on a small propeller which
it rotates.
Fixed to the instrumentunderneath is a small‘
"
circular tray- -dividèd into a number of* compartméntsf
-
corresponding to.the divisions on a compass.
every—so many revolutions
the propeller a little lead
shot is releaSed' which falls ;on=—to the centre of a grooved
magnetic needle, runs down it, falls off its North point
into-the compartment of the tray that lies immediatelv
beneath it, according to the direction of the current.
After" a certain time “the instrument is hauled up ‘on
board, and by 'counting the number'of shot in the differ—
ent compartments of the tray the number of ‘
revolutions of the prope'er can at once be; calculated, and
-
from this the speed, of the current ;. also at the same time,
_
by noting the
number of shot in each separate compart_
_,ment,
the direction in_which the current has been
"is at once given.
g
‘
.
The indirect methods of attack depend upon the_£act
that the physical
chemical characters of the water
vary from place to place. For instance the Gulf Stream
.water is notably saline,‘ and by an examination of the
,
THE SÈAS
directionsprinted on it in ve different languages instructing the nder to place it in the nearest letter box after
having lled in the place and date of “recovery.
Some
of these bottles travel for enormous distances, and recently
one 'WhîÇh was liberated in' the middle of the English
Channel was picked up away on the Coast of Norway having
'
journeyed a distance of 1,440 miles in 190days.
-
Currents can also be directly measured by means of
special recording instruments. - Several instruments
been invented, but thereis one in general use to-day the
principle of Which isas folloWs.' The machine is lo'weied
to’a*given depth in the Waterand to it is xed a-vane which
at"
the instrument facing in the direction of the
current.
The current then acts on a small propeller which
it rotates.
Fixed to the instrumentunderneath is a small‘
"
circular tray- -dividèd into a number of* compartméntsf
-
corresponding to.the divisions on a compass.
every—so many revolutions
the propeller a little lead
shot is releaSed' which falls ;on=—to the centre of a grooved
magnetic needle, runs down it, falls off its North point
into-the compartment of the tray that lies immediatelv
beneath it, according to the direction of the current.
After" a certain time “the instrument is hauled up ‘on
board, and by 'counting the number'of shot in the differ—
ent compartments of the tray the number of ‘
revolutions of the prope'er can at once be; calculated, and
-
from this the speed, of the current ;. also at the same time,
_
by noting the
number of shot in each separate compart_
_,ment,
the direction in_which the current has been
"is at once given.
g
‘
.
The indirect methods of attack depend upon the_£act
that the physical
chemical characters of the water
vary from place to place. For instance the Gulf Stream
.water is notably saline,‘ and by an examination of the