Wood County reporter. [volume] (Grand Rapids [i.e. Wisconsin Rapids], Wis.) 1857-1923, 1873-01-23

Now, let the reader carefully bear in
mind that these little arrows represent
the total effect of the wind upon the sail.
There is no other effect upon it worth
considering here. In Fig. 2 all the
wind is effective upon the sail; in Fig. 3,
part of the winds force is lost by slipping
past the sail, so to speak; in Fig. 4, more
of its force is lost in this way, but there
is still a considerable pressure eXerted
against The sail; but in Fig, 5, nearly all
the force, and in Fig. l, quite ali the force,
is lost. But what we wish to impress is
that the sail in Fig. 4, for example, is
acted upon just as if a lighter wind than
that actually blowing across the page
were blowing in the direction of the ar
row; and similarly in all cases, and under
all circumstances, a wind blowing IN
one direction will act upon sail which
is inclined to it, just as lighter wind
blowing directly against it would act.
Let us now hoist our little sail upon a
light railway truck, and place this truck
upon railway lying diagorally across
the winds path, as shown in Fig. 6. Here
the sail is set in the same position as it is
in Fig. 2, and the effect Of the wind upon
it will obviously be to propel the tru-k
down the railway in the direction of the
small arrow. 1t is also clear that if we
set the sail in the truck in the position
shown in Fig. 3, the effect of the wind
would still be to drive the truck in the
same direction down the rails, but it
would go more slowly, because, as we
have seen, the force acting on the sail in
Fig. is less than that acting in Fig. 3.
But supposing we now set the sail on the
truck SO that the sail stands along the
truck, parallel to the line of rails, as in
Fig. Z, we shall get no motion of the
truck, because the pressure Of the wind
upon the sail will now be exactly across
the railway, and the sail will be pressing
the truck in that direction. The truck
will not be forced either up the rails or
down the rails, but across them only, and
therefore no motion will ensue. Let US
now turn the sail still more away from the
wind, and set it upon the truck in the
position shown in Fig. 5. The wind, as we
have seen, will press upon the sail, but
with very reduced force. This case is
represented in Fig. s. Now we here see Gig.
8 that although the wind is still blow
ing across the page, the effect of it is to
press the sail almost directly up the page,
and it is easy to see that the effect of the
sail will be to propel the truck up the
railway in the direction of the small ar
row. Here, then, We have a railway
truck literally sailing up to windward,
because while the wind is blowing in the
direction of the one arrow the truck is
moving in the direction of the other; see
Fig. 8.
Now this railway truck illustrates very
fairly the case of ship, with this excep-
tiou, namely, that the truck can make no
leeway the rails prevent this. But a
ship can and does makeleeway, and there
fore cannot sail so near to The wind as the
truck It is obvious, however, that the
same general principles apply to the ship
as to the truck. For example, let us take
the case Of the sail shown in Fig. 3, and
and set it upon a ship, as in Fig. 10 it is
clear that the ship will sail away easilv
enough in the direction of the small ar
row, which is at right angles, or square,
to the direction of the wind, which we
still suppose to blow across the page, but
which takes effect upon the sail in the di-
rectiOn Of the other arrow. Or, let US
take the case of the sail set as in Fig. 4,
and set it similarly upon our little ship,
the wind taking effect as in Fig. II. Is
1t not obvious that, just in the same way,
and for the same reason, as the railway
truck in Fig. was driven up the line, so
in the present case, Fig. II, the ship will
be driven in the direction of the small
arrow, which is manifestly to windward
The only difference between this and the
railway truck is that, while the ship Is
driven ahead, it will also be driven some
what to leeward, which the truck was
not; but this consideration only Affects
the amount of the ships progress 70
windWard. -NagM Science,