the singular one lately exhibited at Javelle, on the Seine below
Paris, where a clumsy boat was moved across that river in three
minutes by rowing, not in the water, but in the air, that is, by
whirling round a set of windmill vanes fixed to a horizontal axis,
parallel to the keel, and placed at the head of the boat. The axis
was bent into an elbow at the end, by the help of which it was turned
by one man at a time. I saw the operation at a distance. The four
vanes appeared to be about five feet long, and perhaps two and a
half wide. The weather was calm. The labour appeared to be great
for one man, as the two several times relieved each other. But the
action upon the air by the oblique surfaces of the vanes must have
been considerable, as the motion of the boat appeared tolerably quick
going and returning; and she returned to the same place from whence
she first set out, notwithstanding the current. This machine is since
applied to the moving of air-balloons: an instrument similar may be
contrived to move a boat by turning under water.
Several mechanical projectors have at different times proposed
to give motion to boats, and even to ships, by means of circular
rowing, or paddles placed on the circumference of wheels to be turned
constantly on each side of the vessel; but this method, though
frequently tried, has never been found so effectual as to encourage
a continuance of the practice. I do not know that the reason has
hitherto been given. Perhaps it may be this, that great part of the
force employed contributes little to the motion. For instance, (fig.
12) of the four paddles a, b, c, d, all under water, and turning to
move a boat from X to Y, c has the most power, b nearly though not
quite as much, their motion being nearly horizontal; but the force
employed in moving a, is consumed in pressing almost downright upon
the water till it comes to the place of b; and the force employed
in moving d is consumed in lifting the water till d arrives at the
surface; by which means much of the labour is lost. It is true, that
by placing the wheels higher out of the water, this waste labour
will be diminished in a calm, but where a sea runs, the wheels must
unavoidably be often dipt deep in the waves, and the turning of them
thereby rendered very laborious to little purpose.
Among the various means of giving motion to a boat, that of M.
Bernoulli appears one of the most singular, which was to have fixed
in the boat a tube in the form of an L, the upright part to have a
funnel-kind of opening at top, convenient for filling the tube with
water; which, descending and passing through the lower horizontal
part, and issuing in the middle of the stern, but under the surface
of the river, should push the boat forward. There is no doubt that
the force of the descending water would have a considerable effect,
greater in proportion to the height from which it descended; but
then it is to be considered, that every bucket-full pumped or dipped
up into the boat, from its side or through its bottom, must have
its _vis inertiæ_ overcome so as to receive the motion of the boat,
before it can come to give motion by its descent; and that will be a
deduction from the moving power. To remedy this, I would propose the
addition of another such L pipe, and that they should stand back to
back in the boat thus, figure 13, the forward one being worked as a
pump, and sucking in the water at the head of the boat, would draw it
forward while pushed in the same direction by the force at the stern.
And after all it should be calculated whether the labour of pumping
would be less than that of rowing. A fire-engine might possibly in
some cases be applied in this operation with advantage.
Perhaps this labour of raising water might be spared, and the whole
force of a man applied to the moving of a boat by the use of air
instead of water; suppose the boat constructed in this form, figure
14. A, a tube round or square of two feet diameter, in which a piston
may move up and down. The piston to have valves in it, opening
inwards to admit air when the piston rises; and shutting, when it
is forced down by means of the lever B turning on the centre C. The
tube to have a valve D, to open when the piston is forced down, and
let the air pass out at E, which striking forcibly against the water
abaft must push the boat forward. If there is added an air-vessel
F properly valved and placed, the force would continue to act while
a fresh stroke is taken with the lever. The boat-man might stand
with his back to the stern, and putting his hands behind him, work
the motion by taking hold of the cross bar at B, while another
should steer; or if he had two such pumps, one on each side of the
stern, with a lever for each hand, he might steer himself by working
occasionally more or harder with either hand, as watermen now do
with a pair of sculls. There is no position in which the body of a
man can exert more strength than in pulling right upwards. To obtain
more swiftness, greasing the bottom of a vessel is sometimes used,
and with good effect. I do not know that any writer has hitherto
attempted to explain this. At first sight one would imagine, that
though the friction of a hard body, sliding on another hard body,
and the resistance occasioned by that friction, might be diminished
by putting grease between them, yet that a body sliding on a fluid,
such as water, should have no need of, nor receive any advantage
from such greasing. But the fact is not disputed. And the reason
perhaps may be this--The particles of water have a mutual attraction,
called the attraction of adhesion. Water also adheres to wood, and
to many other substances, but not to grease: on the contrary they
have a mutual repulsion, so that it is a question whether when oil
is poured on water, they ever actually touch each other; for a drop
of oil upon water, instead of sticking to the spot where it falls,
as it would if it fell on a looking-glass, spreads instantly to an
immense distance in a film extremely thin, which it could not easily
do if it touched and rubbed or adhered even in a small degree to the
surface of the water. Now the adhesive force of water to itself, and
to other substances, may be estimated from the weight of it necessary
to separate a drop, which adheres, while growing, till it has weight
enough to force the separation and break the drop off. Let us suppose
the drop to be the size of a pea, then there will be as many of these
adhesions as there are drops of that size touching the bottom of a
vessel, and these must be broken by the moving power, every step
of her motion that amounts to a drop's breadth: and there being no
such adhesions to break between the water and a greased bottom, may
occasion the difference.
So much respecting the motion of vessels. But we have sometimes
occasion to stop their motion; and if a bottom is near enough we can
cast anchor: where there are no soundings, we have as yet no means
to prevent driving in a storm, but by lying-to, which still permits
driving at the rate of about two miles an hour; so that in a storm
continuing fifty hours, which is not an uncommon case, the ship may
drive one hundred miles out of her course; and should she in that
distance meet with a lee shore, she may be lost.
To prevent this driving to leeward in deep water, a swimming anchor
is wanting, which ought to have these properties.
1. It should have a surface so large as, being at the end of a hauser
in the water, and placed perpendicularly, should hold so much of it,
as to bring the ship's head to the wind, in which situation the wind
has least power to drive her.
2. It should be able by its resistance to prevent the ship's
receiving way.
3. It should be capable of being situated below the heave of the sea,
but not below the undertow.
4. It should not take up much room in the ship.
5. It should be easily thrown out, and put into its proper situation.
6. It should be easy to take in again, and stow away.
An ingenious old mariner, whom I formerly knew, proposed, as a
swimming anchor for a large ship, to have a stem of wood twenty-five
feet long and four inches square, with four boards of 18, 16, 14, and
12, feet long, and one foot wide, the boards to have their substance
thickened several inches in the middle by additional wood, and to
have each a four inch square hole through its middle, to permit its
being slipt on occasionally upon the stem, and at right angles with
it; where all being placed and fixed at four feet distance from
each other, it would have the appearance of the old mathematical
instrument called a forestaff. This thrown into the sea, and held by
a hauser veered out to some length, he conceived would bring a vessel
up, and prevent her driving, and when taken in might be stowed away
by separating the boards from the stem. Figure 15. Probably such a
swimming anchor would have some good effect, but it is subject to
this objection, that lying on the surface of the sea, it is liable to
be hove forward by every wave, and thereby give so much leave for the
ship to drive.
Two machines for this purpose have occurred to me, which, though not
so simple as the above, I imagine would be more effectual, and more
easily manageable. I will endeavour to describe them, that they may
be submitted to your judgment, whether either would be serviceable;
and if they would, to which we should give the preference.
The first is to be formed, and to be used in the water on almost the
same principles with those of a paper kite used in the air. Only as
the paper kite rises in the air, this is to descend in the water. Its
dimensions will be different for ships of different size.
To make one of suppose fifteen feet high; take a small spar of that
length for the back-bone, AB, figure 16, a smaller of half that
length CD, for the cross piece. Let these be united by a bolt at E,
yet so as that by turning on the bolt they may be laid parallel to
each other. Then make a sail of strong canvas, in the shape of figure
17. To form this, without waste of sail-cloth, sew together pieces of
the proper length, and for half the breadth, as in figure 18, then
cut the whole in the diagonal lines a, b, c, and turn the piece F so
as to place its broad part opposite to that of the piece G, and the
piece H in like manner opposite to I, which when all sewed together
will appear as in fig. 17. This sail is to be extended on the cross
of figure 16, the top and bottom points well secured to the ends of
the long spar; the two side points d, e, fastened to the ends of
two cords, which coming from the angle of the loop (which must be
similar to the loop of a kite) pass through two rings at the ends of
the short spar, so as that on pulling upon the loop the sail will be
drawn to its extent. The whole may, when aboard, be furled up, as in
figure 19, having a rope from its broad end, to which is tied a bag
of ballast for keeping that end downwards when in the water, and at
the other end another rope with an empty keg at its end to float on
the surface; this rope long enough to permit the kite's descending
into the undertow, or if you please lower into still water. It should
be held by a hauser. To get it home easily, a small loose rope may be
veered out with it, fixed to the keg. Hauling on that rope will bring
the kite home with small force, the resistance being small as it will
then come end ways.
It seems probable that such a kite at the end of a long hauser would
keep a ship with her head to the wind, and, resisting every tug,
would prevent her driving so fast as when her side is exposed to it,
and nothing to hold her back. If only half the driving is prevented,
so as that she moves but fifty miles instead of the hundred during a
storm, it may be some advantage, both in holding so much distance as
is saved, and in keeping from a lee-shore. If single canvas should
not be found strong enough to bear the tug without splitting, it may
be doubled, or strengthened by a netting behind it, represented by
figure 20.
The other machine for the same purpose, is to be made more in the
form of an umbrella, as represented, figure 21. The stem of the
umbrella a square spar of proper length, with four moveable arms, of
which two are represented C, C, figure 22. These arms to be fixed in
four joint cleats, as D, D, &c. one on each side of the spar, but so
as that the four arms may open by turning on a pin in the joint. When
open they form a cross, on which a four-square canvas sail is to be
extended, its corners fastened to the ends of the four arms. Those
ends are also to be stayed by ropes fastened to the stem or spar, so
as to keep them short of being at right angles with it: and to the
end of one of the arms should be hung the small bag of ballast, and
to the end of the opposite arm the empty keg. This, on being thrown
into the sea, would immediately open; and when it had performed its
function, and the storm over, a small rope from its other end being
pulled on, would turn it, close it, and draw it easily home to the
ship. This machine seems more simple in its operation, and more
easily manageable than the first, and perhaps may be as effectual[32].
Vessels are sometimes retarded, and sometimes forwarded in their
voyages, by currents at sea, which are often not perceived. About
the year 1769 or 70, there was an application made by the board
of customs at Boston, to the lords of the treasury in London,
complaining that the packets between Falmouth and New-York, were
generally a fortnight longer in their passages, than merchant-ships
from London to Rhode-Island, and proposing that for the future
they should be ordered to Rhode-Island instead of New-York. Being
then concerned in the management of the American post-office, I
happened to be consulted on the occasion; and it appearing strange
to me that there should be such a difference between two places,
scarce a day's run asunder, especially when the merchant-ships are
generally deeper laden, and more weakly manned than the packets, and
had from London the whole length of the river and channel to run
before they left the land of England, while the packets had only to
go from Falmouth, I could not but think the fact misunderstood or
misrepresented. There happened then to be in London a Nantucket
sea-captain of my acquaintance, to whom I communicated the affair. He
told me he believed the fact might be true; but the difference was
owing to this, that the Rhode-Island captains were acquainted with
the gulf-stream, which those of the English packets were not. We are
well acquainted with that stream, says he, because in our pursuit
of whales, which keep near the sides of it, but are not to be met
with in it, we run down along the sides, and frequently cross it to
change our side: and in crossing it have sometimes met and spoke with
those packets, who were in the middle of it, and stemming it. We have
informed them that they were stemming a current, that was against
them to the value of three miles an hour; and advised them to cross
it and get out of it; but they were too wise to be counselled by
simple American fishermen. When the winds are but light, he added,
they are carried back by the current more than they are forwarded
by the wind: and if the wind be good, the subtraction of 70 miles
a day from their course is of some importance. I then observed it
was a pity no notice was taken of this current upon the charts,
and requested him to mark it out for me, which he readily complied
with, adding directions for avoiding it in sailing from Europe to
North-America. I procured it to be engraved by order from the general
post-office, on the old chart of the Atlantic, at Mount and Page's,
Tower-hill; and copies were sent down to Falmouth for the captains
of the packets, who slighted it however; but it is since printed in
France, of which edition I hereto annex a copy.
This stream is probably generated by the great accumulation of
water on the eastern coast of America between the tropics, by the
trade-winds which constantly blow there. It is known that a large
piece of water ten miles broad and generally only three feet deep,
has by a strong wind had its waters driven to one side and sustained
so as to become six feet deep, while the windward side was laid dry.
This may give some idea of the quantity heaped up on the American
coast, and the reason of its running down in a strong current through
the islands into the bay of Mexico, and from thence issuing through
the gulph of Florida, and proceeding along the coast to the banks of
Newfoundland, where it turns off towards and runs down through the
Western Islands. Having since crossed this stream several times in
passing between America and Europe, I have been attentive to sundry
circumstances relating to it, by which to know when one is in it; and
besides the gulph weed with which it is interspersed, I find that it
is always warmer than the sea on each side of it, and that it does
not sparkle in the night: I annex hereto the observations made with
the thermometer in two voyages, and possibly may add a third. It will
appear from them, that the thermometer may be an useful instrument to
a navigator, since currents coming from the northward into southern
seas, will probably be found colder than the water of those seas,
as the currents from southern seas into northern are found warmer.
And it is not to be wondered that so vast a body of deep warm water,
several leagues wide, coming from between the tropics and issuing
out of the gulph into the northern seas, should retain its warmth
longer than the twenty or thirty days required to its passing the
banks of Newfoundland. The quantity is too great, and it is too
deep to be suddenly cooled by passing under a cooler air. The air
immediately over it, however, may receive so much warmth from it as
to be rarefied and rise, being rendered lighter than the air on each
side of the stream; hence those airs must flow in to supply the place
of the rising warm air, and, meeting with each other, form those
tornados and water-spouts frequently met with, and seen near and over
the stream; and as the vapour from a cup of tea in a warm room, and
the breath of an animal in the same room, are hardly visible, but
become sensible immediately when out in the cold air, so the vapour
from the gulph stream, in warm latitudes is scarcely visible, but
when it comes into the cool air from Newfoundland, it is condensed
into the fogs, for which those parts are so remarkable.
The power of wind to raise water above its common level in the sea
is known to us in America, by the high tides occasioned in all our
sea-ports when a strong north-easter blows against the gulph stream.
The conclusion from these remarks is, that a vessel from Europe to
North-America may shorten her passage by avoiding to stem the stream,
in which the thermometer will be very useful; and a vessel from
America to Europe may do the same by the same means of keeping in
it. It may have often happened accidentally, that voyages have been
shortened by these circumstances. It is well to have the command of
them.
But may there not be another cause, independent of winds and
currents, why passages are generally shorter from America to Europe
than from Europe to America? This question I formerly considered in
the following short paper.
On board the Pennsylvania Packet, Capt. Osborne.
_At Sea_, _April 5, 1775._
"Suppose a ship to make a voyage eastward from a place in lat. 40°
north, to a place in lat. 50° north, distance in longitude 75 degrees.
"In sailing from 40 to 50, she goes from a place where a degree of
longitude is about eight miles greater than in the place she is going
to. A degree is equal to four minutes of time; consequently the ship
in the harbour she leaves, partaking of the diurnal motion of the
earth, moves two miles in a minute faster, than when in the port she
is going to; which is 120 miles in an hour.
"This motion in a ship and cargo is of great force; and if she could
be lifted up suddenly from the harbour in which she lay quiet, and
set down instantly in the latitude of the port she was bound to,
though in a calm, that force contained in her would make her run a
great way at a prodigious rate. This force must be lost gradually in
her voyage, by gradual impulse against the water, and probably thence
shorten the voyage. Query, In returning does the contrary happen, and
is her voyage thereby retarded and lengthened?"[33]
Would it not be a more secure method of planking ships, if, instead
of thick single planks laid horizontally, we were to use planks of
half the thickness, and lay them double and across each other as
in figure 23? To me it seems that the difference of expence would
not be considerable, and that the ship would be both tighter and
stronger.
The securing of the ship is not the only necessary thing; securing
the health of the sailors, a brave and valuable order of men,
is likewise of great importance. With this view the methods so
successfully practised by Captain Cook in his long voyages cannot be
too closely studied or carefully imitated. A full account of those
methods is found in Sir John Pringle's speech, when the medal of the
Royal Society was given to that illustrious navigator. I am glad to
see in his last voyage that he found the means effectual which I had
proposed for preserving flour, bread, &c. from moisture and damage.
They were found dry and good after being at sea four years. The
method is described in my printed works, page 452, fifth edition[34].
In the same, page 469, 470[35], is proposed a means of allaying
thirst in case of want of fresh water. This has since been practised
in two instances with success. Happy if their hunger, when the other
provisions are consumed, could be relieved as commodiously; and
perhaps in time this may be found not impossible. An addition might
be made to their present vegetable provision, by drying various roots
in slices by the means of an oven. The sweet potatoe of America and
Spain is excellent for this purpose. Other potatoes, with carrots,
parsnips and turnips, might be prepared and preserved in the same
manner.
With regard to make-shifts in cases of necessity, seamen are
generally very ingenious themselves. They will excuse however the
mention of two or three. If they happen in any circumstance, such
as after shipwreck, taking to their boat, or the like, to want a
compass, a fine sewing-needle laid on clear water in a cup will
generally point to the north, most of them being a little magnetical,
or may be made so by being strongly rubbed or hammered, lying in a
north and south direction. If their needle is too heavy to float by
itself, it may be supported by little pieces of cork or wood. A man
who can swim, may be aided in a long traverse by his handkerchief
formed into a kite, by two cross sticks extending to the four
corners; which, being raised in the air when the wind is fair and
fresh, will tow him along while lying on his back. Where force is
wanted to move a heavy body, and there are but few hands and no
machines, a long and strong rope may make a powerful instrument.
Suppose a boat is to be drawn up on a beach, that she may be out of
the surf; a stake drove into the beach where you would have the boat
drawn, and another to fasten the end of the rope to, which comes
from the boat, and then applying what force you have to pull upon
the middle of the rope at right angles with it, the power will be
augmented in proportion to the length of rope between the posts. The
rope being fastened to the stake A, and drawn upon in the direction
C D, will slide over the stake B; and when the rope is bent to the
angle A D B, represented by the pricked line in figure 24, the boat
will be at B.
Some sailors may think the writer has given himself unnecessary
trouble in pretending to advise them; for they have a little
repugnance to the advice of landmen, whom they esteem ignorant and
incapable of giving any worth notice; though it is certain that most
of their instruments were the invention of landmen. At least the
first vessel ever made to go on the water was certainly such. I will
therefore add only a few words more, and they shall be addressed to
passengers.
When you intend a long voyage, you may do well to keep your intention
as much as possible a secret, or at least the time of your departure;
otherwise you will be continually interrupted in your preparations
by the visits of friends and acquaintance, who will not only rob
you of the time you want, but put things out of your mind, so that
when you come to sea, you have the mortification to recollect points
of business that ought to have been done, accounts you intended to
settle, and conveniencies you had proposed to bring with you, &c. &c.
all which have been omitted through the effect of these officious
friendly visits. Would it not be well if this custom could be
changed; if the voyager after having, without interruption, made all
his preparations, should use some of the time he has left, in going
himself to take leave of his friends at their own houses, and let
them come to congratulate him on his happy return.