The Art of Travel Part 25

To direct the flash of the Mirror.--There are makes.h.i.+ft ways of directing the flash of the mirror; as, by observing its play on an object some paces off, nearly in line with the station it is wished to communicate with. In doing this, two cautions are requisite: first, the distance of the object must be so large compared to the diameter of the mirror that the play of the flash shall appear truly circular and exactly like a faint sun (see preceding paragraph): secondly, be careful to bring the eye to the very edge of the mirror; there should be as little "dispart" as possible, as artillerymen would say. Unless these cautions be attended to very strictly, the flash will never be seen at the distant station.

[Sketch of arrangement as described below].

An object, in reality of a white colour but apparently dark, owing to its being shaded, shows the play of a mirror's flash better than any other.

The play of a flash, sent through an open window, on the walls of a room, can be seen at upwards of 100 yards. It is a good object by which to adjust my hand heliostat, which I describe below. Two bits of paper and a couple of sticks, arranged as in the drawing, serve pretty well to direct a flash. Sight the distant object through the holes in the two bits of paper, A and B, at the ends of the horizontal stick; and when you are satisfied that the stick is properly adjusted and quite steady, take your mirror and throw the shadow of A upon B, and further endeavour to throw the white speck in the shadow of A, corresponding to its pin-hole in it, through the centre of the hole in B. Every now and then lay the mirror aside, and bend down to see that A B continues to be properly adjusted.

Hand Heliostat.--Some years ago, I took great pains to contrive a convenient pocket instrument, by which a traveller should be able to signal with the sun, and direct his flash with certainty, in whatever direction he desired. I did so in the belief that a signalling power of extraordinary intensity could thus be made use of; and, I am glad to say, I succeeded in my attempt. I at last obtained a pretty pocket instrument, the design of which I placed in the hands of Messrs. Troughton and Simms; and upon the earlier models of which I read a paper before the British a.s.sociation in 1858. I called it a "hand heliostat." I always carry one when I travel, for it is a continual source of amus.e.m.e.nt. The instrument is shown in fig. 1 (p. 280), and its principle is ill.u.s.trated by fig. 2.

The scale is about 2/3.

E is the eye of the signaller; M the mirror; and L, S, fig. 2, a tube containing at one end, L, a lens, and at the other, S, a screen of white porcelain or unpolished ivory, placed at the exact solar focus of L: a shade, K, with two holes in it, is placed before L. Let R, r, be portions of a large pencil of parallel rays, proceeding from any one point on the sun's surface, and reflected from the mirror, as R' r' (fig. 2). R'

impinges upon the lens, L, through one of the holes in K, and R' goes free toward some distant point, O. Those that impinge on the lens will be brought to a focus on S, where a bright speck of light might be seen.

This speck radiates light in all direction; some of the rays, proceeding from it, impinge on the lens at the other hole in the shade K, as shown in fig. 2, and are reduced by its agency to parallelism with r' and R', that is, with the rays that originally left the mirror: consequently E, looking partly at the edge of the lens, and partly into s.p.a.ce, sees a bright speck of light in the former, coincident with the point O in the latter.

[Fig 1 and Fig 2, as described in the text].

What is true for one point in the sun's disc, is true for every point in it. Accordingly, the signaller sees an image of the sun, and not a mere speck of light, in the lens; and the part of the landscape which that image appears to overlay, is precisely that part of it over which the flash from his mirror extends; or, in other words, it is that from any point of which a distant spectator may see some part or other of the sun's disc reflected in the mirror. There is no difficulty in signalling when the sun is far behind the back, if the eye-tubes are made to pull out to a total length of five inches, otherwise the shadow of the head interferes. For want of s.p.a.ce, the drawing represents the tubes as only partly drawn out. The instrument is perfectly easy to manage, and letters can be signalled by flashes. Its power is perfectly marvellous. On a day so hazy that colours on the largest scale--such as green fields and white houses--are barely distinguishable at seven miles' distance, a looking-gla.s.s no larger than the finger-nail transmits its signals clearly visible to the naked eye.

I have made a makes.h.i.+ft arrangement on the principle of my heliostat, using the object gla.s.s of an opera-gla.s.s for the lens, and an ordinary looking-gla.s.s: the great size and short focus of the object gla.s.s is a great convenience when using a mirror with a wide frame.

Professor W. H. Miller, the Foreign Secretary of the Royal Society, has since invented a yet more compact method of directing the flash, which he has described in the Proceedings of the Royal Society for 1865. It consists of a plate of silvered gla.s.s, one of whose rectangular corners is accurately ground and polished. On looking into the corner when the gla.s.s is properly held an image of the sun is seen, which overlays the actual flash. Beautifully simple as this instrument is, I do not like it so much as my own, for the very fact of its requiring no "setting" is its drawback. With mine, when the image of the sun is lost it is immediately found again by simply rotating the instrument on its axis; but with Professor Miller's the image must be felt for wholly anew.

Fire Signals.--Fire-beacons, hanging up a lantern, or setting fire to an old nest high up in a tree, serve as night-signals; but they are never to be depended on without previous concert, as bushes and undulations of the ground will often hide them entirely. The sparks from a well-struck flint and steel can be seen for much more than a mile.

Smoke Signals.--The smoke of fires is seen very far by day; and green wood and rotten wood make the most smoke. It is best to make two fires 100 yards apart, lest your signalling should be mistaken for an ordinary fire in the bush. These double fires are a very common signal to vessels in the offing, on the African coast.

Other Signals.--By Sight.--A common signal for a distant scout is, that he should ride or walk round and round in a circle from right to left, or else in one from left to right.

Mr. Parkyns, speaking of Abyssinia, describes the habits of a caste of robbers in the following words:--"At other times they will lie concealed near a road, with scouts in every direction on the look-out; yet no one venturing to speak, but only making known by signs what he may have to communicate to his companions or leader. Thus he will point to his ear and foot on hearing footsteps, to his eyes on seeing persons approach, or to his tongue if voices be audible; and will also indicate on his fingers the numbers of those coming, describing also many particulars as to how many porters, beasts of burden or for riding, there may be with the party."

A kite has been suggested as a day signal; and also a kite with some kind of squib, let off by a slow-light and attached to its tail, as one by night. (Colonel Jackson.)

Sound.--Whistling through the fingers can be heard at considerable distances: the accomplishment should be learnt. Cooing in the Australian fas.h.i.+on, or jvdling in that of the Swiss, are both of them heard a long way. The united holloa of many voices, is heard much further than separate cries. The cracking of a whip has a very penetrating sound.

Smells.--An abominable smell arrests the attention at night.

Letters carried by Animals.--In short reconnoitring expeditions made by a small detachment from a party, the cattle or dogs are often wild, and run home to their comrades on the first opportunity; in the event of not being able to watch them, owing to accident or other cause, advantage may be taken of their restlessness, by tying a note to one of their necks, and letting them go and serve as postmen, or rather as carrier-pigeons.

BEARINGS BY COMPa.s.s, SUN, ETC.

Pocket Compa.s.s.--A pocket compa.s.s should not be too small; if one of the little toy compa.s.ses be carried in the pocket, it should be as a reserve, and not for regular use. A toy compa.s.s 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 ident.i.ty 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 compa.s.s, 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.

Compa.s.s for use at night.--The great majority of compa.s.ses 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 compa.s.s card is painted black, the northern being left white. With a very faint light, this difference can be appreciated. In compa.s.ses 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 compa.s.s or a watch at night is increased by looking nearly at it through a magnifying-gla.s.s.

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 compa.s.s by a burning gla.s.s, or other subst.i.tute for it. (See "Burning Gla.s.s.")

True and Magnetic Bearings.--The confusion between true and magnetic bearings is a continual trouble, even to the most experienced travellers.

Sir Thomas Mitch.e.l.l's exploring party very nearly sustained a loss by mistaking the one for the other. I recommend that the points of the compa.s.s, 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-compa.s.s 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 compa.s.s (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 compa.s.s-needle is often found to be disturbed, and sometimes apparently bewitched, when laid upon hill-tops; even when they consist of bare ma.s.ses 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 compa.s.s observations on hill-tops, if unchecked by a s.e.xtant 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 alt.i.tudes. 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 compa.s.s. The diagram is calculated for the lat.i.tude 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 alt.i.tudes; 2ndly, the path of sun, stars, etc., for each 10th degree of declination; 3rdly, the hour angles, all projected down upon--4thly--the level compa.s.s card.

Thus, six circles are drawn round the centre of the compa.s.s card at equal distances apart, each ring between them representing a s.p.a.ce of 15 degrees in alt.i.tude.

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 compa.s.s. 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 alt.i.tude of the sun. The point in the diagram where the alt.i.tude so obtained crosses the pencil mark, corresponds to the position of the sun.

The hour is then read off; and the compa.s.s 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 alt.i.tude 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 compa.s.ses 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 compa.s.s 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 pus.h.i.+ng 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 pa.s.sing 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.

MARKS FOR THE WAY-SIDE.