"What _is_ the compass?" every philosophical youth of inquiring
disposition will naturally ask. We do not say that all youths will make
this inquiry. Many there are who will at once say, "Oh, I know! It's a
needle with a card on the top of it--sometimes a needle with a card
under it--which always points to the north, and shows sailors how to
steer their ships."
Very well explained indeed, my self-sufficient friend; but you have not
answered the question. You have told us what a compass is like, and one
of the uses to which it is applied; but you have not yet told what it
_is_. A man who had never heard of a compass might exclaim, "What! a
needle! Is it a darning needle, or a knitting needle, or a
drawing-through needle? And which end points to the north--the eye or
the point? And if you lay it on the table the wrong end to the north,
will it turn round of its own accord?"
You laugh, perhaps, and explain; but it would have been better to have
explained correctly at first. Thus:--
The mariner's compass is a small, flat bar of magnetised steel, which,
when balanced on a pivot, turns one of its ends persistently towards the
north pole--the other, of course, towards the south pole; and it does
this in consequence of its being magnetised. A card is fixed above,
sometimes below, this bar of steel (which is called the needle), whereon
are marked the cardinal points--north, south, east, and west--with their
subdivisions or intermediate points, by means of which the true
direction of any point can be ascertained.
"Aha!" you exclaim, "Mr Author, but you yourself have omitted part of
the explanation. _Why_ is it that the magnetising of the needle causes
it to turn to the north?"
I answer humbly, "I cannot tell;" but, further, I assert confidently,
"Neither can anybody else." The fact is known, and we see its result;
but the reason why magnetised steel or iron should have this tendency,
this polarity, is one of the mysteries which man has not yet been able
to penetrate, and probably never will.
Having explained the nature of the compass, as far as explanation is
possible, we present our reader with a picture of one.
It will be seen that there are four large points--N, S, E, and W--the
cardinal points above referred to, and that these are subdivided by
twelve smaller points, with one little black triangular point between
each, and a multitude of smaller points round the outer circle. To give
these points their correct names is called "boxing the compass,"--a
lesson which all seamen can trip off their tongues like A, B, C, and
which most boys could learn in a few hours.
For the sake of those who are anxious to acquire the knowledge, we give
the following explanation: Let us begin with north. The large point
midway between N and E (to the right) is _north-east_. The
corresponding point midway between N and W (to the left) is
_north-west_. A glance will show that the corresponding points towards
the south are respectively _south-east_ and _south-west_ (usually
written S.E. and S.W., as the two former points are written N.E. and
N.W.). Now, to read off the compass with this amount of knowledge is
very simple. Thus: _North_, _north-east_, _east_, _south-east_,
_south_, _south-west_, _west_, _north-west_, _north_. But be it
observed that, in the language of the sea, the _th_ is thrown overboard,
except when the words north and south occur alone. When conjoined with
other points they are pronounced thus: nor'-east, sou'-east; and so on.
To come now to the smaller subdivisions, it will suffice to take a
quarter of the circle. The point midway between N.E. and N. is
"nor'-nor'-east" (N.N.E.), and the corresponding one between N.E. and E.
is "east nor'-east" (E.N.E.). These points are again subdivided by
little black points which are thus named:--The first, next the N., is
"north by east" (N. by E.); the corresponding one next the E. is "east
by north" (E. by N.). The second _black_ point from N. is "nor'-east by
north" (N.E. by N.), and the corresponding one--namely, the second black
point from east--is "nor'-east by east" (N.E. by E.). Thus, in reading
off the compass, we say--beginning at north and proceeding to east--
North: north by east; nor'-nor'-east; nor'-east by north; nor'-east;
nor'-east by east; east nor'-east; east by north; east;--and so on with
the other quarters of the circle.
So much for "boxing the compass." The manner in which it is used on
board ship, and the various instruments employed in connection with it
in the working of a vessel at sea, will be explained shortly; but first
let us glance at the history of the compass.
It is a matter of great uncertainty when, where, and by whom the
mariner's compass was invented. Flavio Gioia, a Neapolitan captain or
pilot, who lived about the beginning of the fourteenth century, was
generally recognised throughout Europe as the inventor of this useful
instrument; but time and research have thrown new light on this subject.
Probably the Neapolitan pilot was the first who brought the compass
into general notice in Europe; but long before 1303 (the year in which
it was said to have been invented) the use of the magnetic needle was
known to the Chinese.
_Loadstone_, that mineral which has the mysterious power of attracting
iron, and also of imparting to iron its own attractive power, was known
to the Chinese before the year 121, in which year a famous Chinese
dictionary was completed, wherein the word _magnet_ is defined as "the
name of a stone which gives direction to a needle." This proves not
only that they knew the attractive properties of the loadstone, and its
power of imparting these properties to metal, but also that they were
aware of the polarity of a magnetised needle. Another Chinese
dictionary, published between the third and fourth centuries, speaks of
ships being guided in their course to the south by means of the magnet;
and in a medical work published in China in 1112, mention is made of the
_variation_ of the needle, showing that the Chinese had not only used
the needle as a guide at sea, but had observed this one of its
well-known peculiarities--namely, the tendency of the needle to point in
a _very slight degree_ away from the true north.
In the thirteenth century, too, we find mention made of the needle by a
poet and by two other writers; so that whatever Flavio Gioia may have
done (and it is probable he did much) in the way of pushing the compass
into notice in Europe, he cannot be said to be the inventor of it. That
honour doubtless belongs to the Chinese. Be this as it may, the compass
was invented; and in the fourteenth century it began that revolution in
maritime affairs to which we have alluded.
The first compasses were curiously formed. The Chinese used a
magnetised needle, which they placed in a bit of rush or pith, which was
floated in a basin of water, and thus allowed to move freely and turn
towards the poles. They also made needles in the form of iron fish. An
Arabian author of the thirteenth century thus writes:--"I heard it said
that the captains in the Indian seas substitute for the needle and reed
a hollow iron fish magnetised, so that, when placed in the water, it
points to the north with its head and to the south with its tail. The
reason that the iron fish does not sink, is that metallic bodies, even
the heaviest, float when hollow and when they displace a quantity of
water greater than their own weight."
The use of the compass at sea is so simple, that, after what has been
said, it scarcely requires explanation. When a ship sets sail for any
port, she knows, first of all, the position of the port from which she
sets sail, as well as that to which she is bound. A straight line drawn
from the one to the other is her true course, supposing that there is
deep, unobstructed water all the way; and if the compass be placed upon
that line, the point of the compass through which it passes is the point
by which she ought to steer. Suppose that her course ran through the
east point of the compass: the ship's head would at once be turned in
that direction, and she would continue her voyage with the needle of the
compass pointing straight _across_ the deck, and the east and west
points straight _along_ it.
But various causes arise in the actual practice of navigation to prevent
a ship keeping her true course. Winds may be contrary, and currents may
drive her either to the one side or the other of it; while land--
promontories, islands, and shallows--compel her to deviate from the
direct line. A vessel also makes what is called "leeway;" which means
that, when the wind blows on her side, she not only advances forward,
but also slides through the water sidewise. Thus, in the course of a
day, she may get a considerable distance off her true course--in sea
parlance, "make a good deal of leeway."
To perform the voyage correctly and safely in the face of these
obstacles and hindrances is the aim and end of navigation; and the
manner of proceeding is as follows:--
The hour is carefully noted on setting sail, and from that moment, night
and day, to the end of the voyage, certain observations are made and
entered in the ship's journal, called the log. Every hour the rate at
which the ship is going is ascertained and carefully noted. The point
of the compass towards which the ship is to be steered is given by the
captain or officer in command to the steersman, who stands at the wheel
with a compass always before him in a box called the "_binnacle_." The
course is never changed except by distinct orders from those in command;
and when it is changed, the hour when the change is made and the new
course to be steered are carefully noted down. Thus, at the end of the
day, or at any other time if desired, the position of the ship can be
ascertained by her course being drawn upon a chart of the ocean over
which she is sailing,--correct charts, or maps, being provided by the
captain before starting.
The estimate thus made is, however, not absolutely correct. It is
called the "_dead-reckoning_," and is only an approximation to the
truth, because allowance has to be made for leeway, which can only be
guessed at. Allowance has also to be made for variations in the rate of
sailing in each hour, for the winds do not always blow with exactly the
same force during any hour of the day. On the contrary, they may vary
several times within an hour, both in force and in direction. Those
variations have to be watched and allowed for; but such allowance may be
erroneous in a greater or less degree. Currents, too, may have exerted
an unseen influence on the ship, thus rendering the calculation still
less correct. Nevertheless, dead-reckoning is often the only guide the
sailor has to depend upon for days at a time, when storms and cloudy
skies prevent him from ascertaining his true position by other means, of
which we shall speak presently.
Of course, in the early days of navigation there were no charts of the
ocean. The navigator knew not whither he was hurrying over the wild
waste of waters; but by observing the relative position of some of the
fixed stars to his course while sailing out to sea, he could form a
rough idea of the proper course to steer in order to return to the port
whence he had started.
The compass, then, shows the sailor the course he has been going, and
the _log_ (of which more presently) enables him to ascertain the rate at
which he has proceeded; while his chronometers, or time-keepers, tell
him the _time_ during which the course and rate of sailing have been
kept up. And many a long cruise on the unknown deep has been
successfully accomplished in days of old by bold seamen, with this
method of dead-reckoning; and many a mariner at the present day depends
almost entirely on it, while _all_ are, during thick, stormy weather,
dependent on it for days and sometimes weeks together.
The _log_, to which we have referred, is the instrument by which is
determined the rate at which a ship is progressing. It is a very simple
contrivance: a triangular piece of wood about the size of a large
saucer, with a piece of stout cord fastened to each corner, the ends of
the cords being tied together, so that when held up, the "log," as it is
called, resembles one of a pair of scales. One of the cords, however,
is only temporarily attached to its corner by means of a peg, which when
violently pulled comes out. One edge of the triangle is loaded with
lead. The whole machine is fastened to the "log-line,"--a stout cord
many fathoms long, which is wound on a large reel.
"Heaving the log," as we have said, takes place every hour. One sailor
stands by with a sand-glass which runs exactly half a minute. Another
holds the wooden reel; and a third heaves the log overboard, and "pays
out" line as fast as he can make the reel spin. The instant it is
thrown the first sailor turns the sand-glass. The log, being loaded on
one side, floats perpendicularly in the water, remaining stationary of
course; while the man who hove it watches sundry knots on the line as
they pass over the stern of the ship, each knot representing a mile of
rate of speed in the hour. As the last grain of sand drops to the
bottom of the glass the first sailor gives a sharp signal, and the
second clutches and checks the line, examines the knot nearest his hand,
and thus knows at once how many knots or miles the ship is sailing at
that time. The sudden stoppage of the line jerks the peg, before
referred to, out of the log, thereby allowing the other two fixed cords
to drag it flat and unresisting over the surface of the sea, when the
line is reeled up and put by. The flight of another hour calls for a
repetition of the heaving of the log.
As scientific knowledge advanced, instruments of peculiar and more
complicated form were devised to enable navigators to ascertain more
correctly their position on the surface of the sea; but they did not,
and never will, supersede the method by dead-reckoning--for this reason,
that the latter can be practised at all times, while the former are
useless unless the sun, moon, or stars be visible, which in some
latitudes they are not for many days and weeks, when clouds and fogs
shroud the bright sky from view.
The _Quadrant_ is the chief of those instruments. It is represented on
next page. To give a succinct account of this would take up more space
than we can spare. It may suffice the general reader to say that by
observing the exact position of the sun at noon, or of the moon or a
star, in relation to the horizon, the precise _latitude_ of a ship--that
is, her distance north or south of the equator--is ascertained. The
method of "taking an observation" is complicated, and difficult to
explain and understand. We refer those who are curious on the point to
treatises on navigation.
_Chronometers_ are exceedingly delicate and perfect time-keepers, or
watches, which are very carefully set at the commencement of a voyage.
Thus the _time_ at the _meridian_ whence a vessel starts is kept up
during the voyage. By means of an observation of the sun with the
quadrant, or sextant (a somewhat similar instrument), the true time at
any particular point in the voyage may be ascertained. A _difference_
is found to exist between the time at the spot where the observation is
taken, and the time of the chronometer. A calculation founded on this
difference gives the ship's _longitude_--that is, her distance east or
west of the meridian that passes through Greenwich. That meridian is an
imaginary line drawn round the world longitudinally, and passing through
the north and south poles, as the equator is a line passing round it
latitudinally.
When a ship's latitude and longitude have been ascertained, and a line
drawn through the first parallel to the equator, and another line
through the second parallel to the first meridian, the point where these
two lines intersect is the _exact_ position of the ship upon the sea.
The size and form of ships having gradually improved, the compass and
other scientific appliances having been discovered, cannon also and
gunpowder having been invented, seamen became more courageous and
venturesome; and at last the Portuguese nation began that career of
maritime enterprise which won for it the admiration of the world.
About the beginning of the fourteenth century (1330), the Canary
Islands, lying off the west coast of Africa, were re-discovered by the
accident of a French ship being blown off the coast in a storm, and
finding shelter amongst them. This group had been known to the ancients
under the name of the Fortunate Islands, but had been forgotten for more
than a thousand years. During the course of the century the Spaniards
plucked up courage to make discoveries and settlements upon them,
although by so doing they were compelled to undergo that much-dreaded
ordeal--sailing _out of sight_ of their once fondly "hugged" land!
In the beginning of the next century arose a prince, Don Henry, son of
John the First of Portugal, whose anxiety to promote discovery, and to
find a passage by sea round the coast of Africa to India, induced him to
send out many expeditions, all of which accomplished something, and many
of which added very extensively to the geographical knowledge of the
world at that time. Navigators, sent out by him from time to time,
discovered the Madeira Islands; sailed along the western coast of Africa
a considerable distance; ascertained the presence of gold-dust among the
savages on the Gulf of Guinea; discovered the Azores, besides numerous
other islands and lands; crossed the equator, and approached to within
about eighteen hundred miles of the south-most cape of Africa.
The discovery of gold-dust stirred up the energies of the Portuguese in
a remarkable degree, and caused them cheerfully to undertake ventures
which, without that inducement, they would probably never have
undertaken at all. Moreover, they had now learned to quail less at the
idea of losing sight of land; and towards the end of the fifteenth
century (1486), Bartholomew Diaz, an officer of the household of John
the Second, achieved the grand object which had long been ardently
desired by the Portuguese--he doubled the great southern cape of Africa,
which King John named the "Cape of Good Hope," although Diaz had named
it the "Cape of Tempests." The circumstance is thus alluded to by a
poet of that period--
"At Lisboa's court they told their dread escape,
And from her raging tempests named the Cape.
`Thou southmost point,' the joyful king exclaimed,
`_Cape of Good Hope_ be thou for ever named!'"