92
THE SEAS
SHAPE
'
To the average person the word sh summons up in the
imagination a silvery, wriggling, slipp‘ery animal of a certain
denite torpedo shape.
»
'
,
This characteristic spindle or torpedo shape is admirably
suited to the habits of most shes.
If we take, for example,
a sh like the mackerel, we realize that not only is it beautiful and elegant, but that it is efcient ; the sh is made to
.
_
swim and nature has made no mistake.
just as —man has
.
learnt many lessons from the forms of birds to aid him in the - ‘
_.
.
designing of the most
'
A
B
C
.
'
efc1ent aeroplanes, so
_
HH
UU
HU
can
much
be
learned
.{ d u\
( //\\
{{ \\ from themackerel about
'
H
\\ thebestshapesf0rrapid\//, +’,/ \\/1 “u 11
motion
through
the "
_
\ 0 °
vb
water.
Its
shape is
\\°;/j
\\”H
\\
1/
“
.
ht
\\31'1
\\ //
stream—lmed , t a
_
,
i
_
\
is,
it
15
adapted
so
_
,
11“
l‘”
that m its-progression
FIG. I4.——A, B, andC, are diagrains showing
through thé water the
ÏËÎÊÏÊËÎÊÏÆÈ?ËËË2Ëä%°îäâäîËîäâäêäîä least possible friction is
_
.
caused by eddiesf
set up and it can cleave
_'
its way without hindrance.
If a square block of wood
placed in a owing stream there will be considerable
resistance on the front surface and at the same time many
eddies will be created just behind it, which act as a _suction
..
and impede its passage through the water (Fig. 14).
If
_
now the front surface be rounded off the water becomes
'
:
parted with a minimum of resistance ; the water can now be
_
seen to _ow round the block in two streams which meet
_
—
again some little way behind. Between the back surface
of the. block, the two
divided stream, and
‘
'