Pocket Compass.--A pocket compass should not be too small; if one of the
little toy compasses be carried in the pocket, it should be as a reserve,
and not for regular use. A toy compass will of course tell N. from
N.N.E., and the like; and that may be very useful information, but the
traveller will find that he constantly needs more precise directions. He
doubts the identity of some hill or the destination of some path, and
finds on referring to his map, that the difference of bearing upon which
he must base his conclusion, is small: he therefore requires a good sized
compass, to determine the bearing with certainty. One from 1 1/2 to 2
inches in diameter is practically the best. It should have plenty of
depth, so that the card may traverse freely, even when the instrument is
inclined: it should be light in weight, that it may not be easily jarred
by a blow; the catch that relieves the card, when the instrument is
closed, should be self-acting and should act well: lastly the movements
of the needle should be quick; one that makes slow oscillations should be
peremptorily refused, whatever its other merits may be: the graduation of
the degrees on the card should be from 0 degrees to 360 degrees, North
being 0 degrees and East 90 degrees. I wish some optician would make
aluminum cards. The material can be procured as foil, like tinfoil. It
can then be stamped and embossed, in which case it retains its shape
perfectly, but I cannot satisfy myself as to a good pattern, nor do I see
how to make the North and South halves of the disc sufficiently different
in appearance.
Compass for use at night.--The great majority of compasses are well-nigh
useless in the dark, that is, when it is most important to be able to
consult them. They are rarely so constructed, that the difference between
the north and south sides is visible by moonlight or by the light of a
cigar or piece of tinder. The more modern contrivances are very
effective; in these the southern half of the compass card is painted
black, the northern being left white. With a very faint light, this
difference can be appreciated. In compasses consisting simply of a
needle, the north end of the needle should have a conspicuous arrow-head.
It is extraordinary how much the power of seeing a compass or a watch at
night is increased by looking nearly at it through a magnifying-glass.
Thus, young people who can focus their vision through a wide range may be
observed poring with their eyes close to their books when the light
wanes. So again, at night-time, a placard, even in large type, is
illegible at a short distance, but easily read on approaching it. It
seems, in order that a faint image on the retina should be appreciated by
the nerves of sight, that image must have considerable extent.
Moonlight or the light of a cigar may be condensed on the compass by a
burning glass, or other substitute for it. (See "Burning Glass.")
True and Magnetic Bearings.--The confusion between true and magnetic
bearings is a continual trouble, even to the most experienced travellers.
Sir Thomas Mitchell's exploring party very nearly sustained a loss by
mistaking the one for the other. I recommend that the points of the
compass, viz. North, N.N.E., etc., should be solely used for the
traveller for his true bearings; and the degrees, as 25 degrees (or N. 25
degrees E.), for his magnetic. There would then be no reason why the two
nomenclatures should interfere with one another, for a traveller's
recollection of the lay of a country depends entirely upon true
bearings--or sunrise, sunset, and the stars--and is expressed by North,
N.N.E., etc.; but his surveying data which find no place in his memory,
but are simply consigned to his note-book, are necessarily registered in
degrees. To give every facility for carrying out this principle, a round
of paper should be pasted in the middle of the traveller's pocket-compass
card, just large enough to hide the ordinary rhumbs, but leaving
uncovered the degrees round its rim. On this disk of paper the points of
the compass (true bearings) should be marked so as to be as exact as
possible for the country about to be visited.
Errors in Magnetic Bearings.--The compass-needle is often found to be
disturbed, and sometimes apparently bewitched, when laid upon hill-tops;
even when they consist of bare masses of granite. The disturbance is
easily accounted for by the hornblende in the granite, or by other
iron-bearing rocks. Explorers naturally select hills as their points of
triangulation; but compass observations on hill-tops, if unchecked by a
sextant observation of the sun's bearings, are never so reliable as those
taken on a plain.
[Sketch of card as described on following pages].
Bearings by Sun and Stars.--It requires very great practice to steer well
by stars, for, on an average, they change their bearings even faster than
they change their altitudes. In tropical countries, the zodiacal stars -
as Orion and Antares--give excellent east and west points. The Great
Bear is useful when the North Pole cannot be seen, for you may calculate
by the eye whereabout it would be in the heavens when the "pointers" were
vertical, or due north; and the Southern Cross is available in precisely
the same way. The true North Pole is about 1 1/2 degree or 3 diameters of
the full moon, apart from the Pole star; and its place is on a line
between the Pole Star and the Great Bear. An almanac, calculated to show
the bearing, and the times of moonrise and moonset, for the country to be
travelled over, as well as those of sunrise and sunset, would be a very
great convenience; it would be worth while for a traveller accustomed to
such calculations to make one for himself.
Diagram.--The diagram (preceding page) is intended to be traced in lines
of different colours, when it will be found to be far less confused than
at present.
Its object is to enable a traveller to use the sun, both as a rude watch
and as a compass. The diagram is calculated for the latitude of London,
but will do with more or less accuracy for the whole of England. A
traveller going to other countries may easily draw up one for himself,
and on a larger scale if he prefers it, by using the Azimuth tables and
the Horary tables of Lynn.
The diagram represents, 1st, circles of equal altitudes; 2ndly, the path
of sun, stars, etc., for each 10th degree of declination; 3rdly, the hour
angles, all projected down upon--4thly--the level compass card.
Thus, six circles are drawn round the centre of the compass card at equal
distances apart, each ring between them representing a space of 15
degrees in altitude.
The following angles were then calculated for each 10th degree of
declination in turns, viz.:--The height of the sun, etc., when above the
horizon at each point of the compass. 2ndly, the bearing of the sun at
each consecutive hour. These points were dotted out; and, by joining the
several sets of them, the drawing was made.
The broken lines which diverge in curves from P are hour lines; those
which surround P in more or less complete ovals, are the paths of the sun
and stars, for each 10th degree of declination; the prominent line
running from E. round to W. being its path when on the Equator.
The diagram, when it is traced out for use, should have the names of the
months written in coloured ink on either side of the south line at places
corresponding to the declination of the sun during those months: viz.:--
January S. 23 degrees to S. 17 degrees
February S. 17 " S. 8
March S. 7 " N. 4
April N. 5 " N. 15
May N. 15 " N. 22
June N. 22 " N. 23
July N. 23 " N. 18
August N. 18 " N. 8
September N. 8 " S. 3
October S. 3 " S. 14
November S. 15 " S. 22
December S. 22 " S. 23
To use the card.--Draw a broad pencil line, which may afterwards be
rubbed out, corresponding to the date of travel, and there will be no
further confusion.
Then, to know what o'clock it is, "span out" (see "Spanning") roughly the
altitude of the sun. The point in the diagram where the altitude so
obtained crosses the pencil mark, corresponds to the position of the sun.
The hour is then read off; and the compass bearings on the diagram are
adjusted by holding it level, and turning it round until a line, drawn
from its centre through the point in question, points towards the sun. As
to the moon or a star, if its declination be unknown, but its bearing and
altitude being given, its declination and path may be found, and
therefore the time since its rising or before its setting; a most useful
piece of information to a traveller. Watches break, and compasses cannot
be used on horseback without stopping, and therefore a diagram of this
description, of which any number of copies can be traced out, may be of
use for rough purposes.
Other Signs of Direction.--Bearings by the Growth of Trees.--In exposed
situations and near the sea, the growth of trees is rarely symmetrical;
they betray by their bent heads and stunted branches the direction of the
prevalent influences most adverse to their growth. This direction is
constant over wide districts in a flat country, but cannot be equally
relied upon in a hilly one, where the mountains and valleys affect the
conditions of shade and shelter, and deflect the course of the wind.
Moss grows best where there is continuous damp, therefore it prefers that
side of a tree which affords the most suitable combination of exposure to
damp winds and shelter from the sun. When the winds do not differ
materially in dampness, the north side of the forest trees are the most
thickly covered with moss.
Bearings by the shape of Ant-hills.--That most accurate observer, Pierre
Huber, writes as follows concerning the nests of the yellow ants, which
are abundantly to be found in the Swiss Alps and in some other
mountainous countries. It must be recollected, in reading his statement,
that the chief occupation of ants is to move their eggs and larvae from
one part of the nest to another, to ensure them a warm and equable
temperature; therefore, it is reasonable to expect that the nests of ants
should be built on a uniform principle as regards their shape and aspect.
Huber says "they serve as a compass to mountaineers when they are
surrounded by thick mists, or have lost their way during the night; they
do so in the following manner:--The ant-hills (of the yellow ants),
which are by far more numerous and more high in the mountains than
anywhere else, are longer than they are broad, and are of a similar
pattern in other respects. Their direction is invariably from east to
west. Their highest point and their steepest side are turned towards the
point of sunrise in the winter-time (au levant d'hiver), and they descend
with a gradual slope in the opposite direction. I have verified these
experiences of the shepherds upon thousands of ant-hills, and have found
a very small number of exceptions; these occurred only in the case where
the ant-hills had been disturbed by men or animals. The ant-hills do not
maintain the constancy of their form in the lowlands, where they are more
exposed to such accidents."
Ripple-marks on Snow or Sand.--The Siberians travel guided by the ripples
in the snow, which run in a pretty fixed direction, owing to the
prevalence of a particular wind. The ripples in a desert of sand are
equally good as guides; or the wind itself, if it happens to be blowing,
especially to a person pushing through a tangled belt of forest. Before
leaving a well-known track, and striking out at night into the broad open
plain, notice well which way the wind blows as regards the course you are
about to pursue.
Flight of Birds.--I have read somewhere that in the old days coasting
sailors occasionally took pigeons with them, and when they had lost their
bearings they let one fly, which it did at once to the land.
To follow a Track at Night.--Where the track is well marked, showers of
sparks, ably struck with a flint and steel, are sufficient to show it,
without taking the pains of making a flame.
Smell of an Old Track.--The earth of an old and well-trodden road has a
perceptible smell, from the dung and trampling of animals passing over
it, especially near to encampments. It is usual at night, when a guide
doubts whether or no he is in the track, to take up handfuls of dirt and
smell it. It is notorious that cattle can smell out a road.