"To induce Circulation and Warmth--8. Rub the limbs upwards, with firm grasping pressure and with energy, using handkerchiefs, etc. by this measure the blood is propelled along the veins towards the heart. 9. Let the limbs be thus dried and warmed, and then clothed, the bystanders supplying coats, waistcoats, etc. 10.. Avoid the continuous warm-bath, and the position on or inclined to the back."
Litter for the Wounded.--If a man be wounded or sick, and has to be carried upon the shoulders of others, make a little for him in the Indian fashion; that is to say, cut two stout poles, each 8 feet long, to make its two sides, and three other cross-bars of 2 1/2 feet each, to be lashed to them. Then supporting this ladder-shaped framework over the sick man as he lies in his blanket, knot the blanket up well to it, and so carry him off palanquin-fashion. One cross-bar will be just behind his head, another in front of his feet; the middle one will cross his stomach, and keep him from falling out; and there will remain two short handles for the carriers to lay hold of. The American Indians carry their wounded companions by this contrivance after a fight, and during a hurried retreat, for wonderful distances. A king of waggon-roof top can easily be made to it, with bent boughs and one spare blanket. (See Palanquin.)
[Black and white sketch of two "Indians" carrying litter].
SURVEYING INSTRUMENTS.
In previous editions I reprinted here, with a few trifling alterations, part of a paper that I originally communicated to the Royal Geographical Society, and which will be found at the end of their volume for 1854. In addition to it, communications are published there from Lieutenant Raper, Admiral FitzRoy, Admiral Smyth, Admiral Beechey, and Colonel Sykes; the whole of which was collected under the t.i.tle of "Hints to Travellers;"
they were printed in a separate form and widely circulated. When the edition was exhausted, a fresh Committee was appointed by the Council of the Royal Geographical society, consisting of Admiral sir George Back, Admiral R. Collinson, and myself, to revise the pamphlet thoroughly. This process was again gone through in 1871, and now the pamphlet is so much amended and enlarged that I should do no good by making extracts. It is much better that intending travellers should apply for this third edition of the "Hints to Travellers" at the society"s rooms, 1, Savile Row: for it gives a great deal of information upon instruments that they would find of real value. Its price is 1s.
Porters for delicate Instruments.--Entrust surveying instruments and fragile articles to come respectable old savage, whose infirmities compel him to walk steadily. He will be delighted at the prospect of picking up a living by such easy service.
Measuring low angles by reflexion.--an ordinary artificial horizon is useless for very low angles. They can be measured to within two or three minutes, by means of a vertical point of reference obtained in the following manner:--Tie two pieces of thread, crossing each other at two feet above the ground, put the vessel of mercury underneath it, and look down upon the mercury. When the eye is so placed, that the crossed threads exactly cover their reflexion, the line of sight is truly vertical; and, if the distant object be brought down to them by the s.e.xtant, the angle read off will be 90 degrees + alt.i.tude. Captain George"s arrangement of gla.s.s floating on mercury (made by Cary, Fleet Street, London), allows of very low angles being observed, but the use of this instrument requires considerable caution as to the purity of the mercury and the cleanliness of the gla.s.s.
Subst.i.tute for gla.s.s roof to Horizon.--For want of a gla.s.s roof to place over the mercury a piece of gauze stretched over the vessel will answer very tolerably for the purpose of keeping off the wind. The diameter of the pupil of the eye is so large, compared to the thickness of the threads of the gauze, that the latter offer little impediment to a clear view of the image.
Silvering Gla.s.ses for s.e.xtants.--"Before taking leave of this subject it may not be unimportant to describe the operation of silvering the gla.s.ses of s.e.xtants, as those employed on surveying duties very frequently have to perform the operation.
"The requisites are clean tinfoil and mercury (a hare"s foot is handy)--lay the tinfoil, which should exceed the surface of the gla.s.s by a quarter of an inch on each side, on a smooth surface (the back of a book), rub it out smooth with the finger, add a bubble of mercury, about the size of a small shot, which rub gently over the tinfoil until it spreads itself and shows a silvered surface, gently add sufficient mercury to cover the leaf so that its surface is fluid. Prepare a slip of paper the size of the tinfoil. Take the gla.s.s in the left hand, previously well cleaned, and the paper in the right. Brush the surface of the mercury gently to free it from dross. Lay the paper on the mercury, and the gla.s.s on it. Pressing gently on the gla.s.s, withdraw the paper.
turn the gla.s.s on its face, and leave it on an inclined plane to allow the mercury to flow off, which is accelerated by laying a strip of tinfoil as a conductor to its lower edge. The edges may, after twelve hours" rest, be removed. In twenty-four hours give it a coat of varnish, made from spirits of wine and red sealing-wax. It may be as well to practise on small bits of common gla.s.s, which will soon prove the degree of perfection which the operator has attained." (Admiral Sir E. Belcher.)
MEMORANDA AND LOG-BOOKS.
Best form for Memoranda.--I have remarked that almost every traveller who is distinguished for the copiousness and accuracy of his journals, has written them in a remarkably small but distinct handwriting. Hard pencil-marks (HHH pencils) on common paper, or on metallic paper are very durable. Dr. Barth wrote his numerous observations entirely in Indian-ink. He kept a tiny saucer in his pocket, rubbed with the ink; when he wanted to use it, he rubbed it up with his wetted finger-tip, or resupplied it with fresh ink, and filled his pen and wrote. Captain Burton wrote very much in the dark, when lying awake at night; he used a board with prominent lines of wood, such as is adopted by the blind. It is very important that what is written should be intelligible to a stranger after a long lapse of time. A traveller may die, and his uncompleted work perish with him; or he may return, and years will pa.s.s by, and suddenly some observations he had made will be called in question.
Professor J. Forbes says:--"The practice which I have long adopted is this:--to carry a memorandum-book with Harwood"s prepared paper" (in this point of detail I do not concur; see next paragraph) "and metallic pencil, in which notes and observations and slight sketches of every description, are made on the spot, and in the exact order in which they occur. These notes are almost ineffaceable, and are preserved for reference. They are then extended, as far as possible, every evening with pen and ink, in a suitable book, in the form of a journal; from which, finally, they may be extracted and modified for any ultimate purpose. The speedy extension of memoranda has several great advantages: it secures a deliberate revision of observations, whether of instruments or of nature, whilst further explanation may be sought, and very often whilst ambiguities or contradictions admit of removal by a fresh appeal to facts. By this precaution, too, the risk of losing all the fruits of some weeks of labour, by the loss of a pocket-book, may be avoided."
It has occurred to me, frequently, to be consulted about the best was of keeping MSS. Captain Blakiston, who surveyed the northern part of the Rocky Mountains, and subsequently received the medal of the Royal Geographical Society, for his exploration and admirable map of the Yang-tse-Kiang, in China, paid great attention to the subject: he was fully in possession of all I had to say on the matter; and I gladly quote the method he adopted in North America, with slight modifications, according to the results of his experience, and with a few trivial additions of my own. For the purposes of memoranda and mapping data, he uses three sets of books, which can be ordered at any lithographer"s:--
No. 1. pocket Memorandum Book, measuring three inches and a half by five, made of strong paper. (Captain Blakston did not use, and I should not advise travellers to use, "prepared" paper, for it soon becomes rotten, and the leaves fall out; besides that, wet makes the paper soppy.) The books are paged with bold numbers printed in the corners; two faint red lines are ruled down the middle of each page, half an inch apart, to enable the book to be used as a field-surveyor"s book when required. In this pocket=book, every single thing that is recorded at all, is originally recorded with a hard HHH pencil. Everything is written consecutively, without confusion or attempt to save s.p.a.ce. There may easily be 150 pages in each of these books; and a sufficient number should be procured to admit of having at least one per month. Do not stint yourself in these.
No. 2. Log-Book.--This is an orderly way of collecting such parts of the surveying material as has been scattered over each day in your note-book.
It is to be neatly written out, and will become the standard of future reference. By using a printed form, the labour of drawing up the log on the one hand, and that of consulting it on the other, will be vastly diminished. I give Captain Blakiston"s form, in pages 28, 29, and I would urge intending travellers not to depart from it without very valid reasons, for it is the result of considerable care and experience. The size in which the form is printed here is not quite accurate, because the pages of this book are not large enough to admit of it, but the proportion is kept. The actual size is intended to be five and a half inches high and nine inches wide, so that it should open freely along one of the narrow sides of the page, in the way that all memoranda books ought to open. Four pages go to a day; of these the pages 1 and 2 are alone represented in this book, pages 3 and 4 being intended to be left blank.
[P 28 and p 29 show samples of the log book pages being described].
The bold figures 17 and 18 in the right-hand corners of the form I give, show how the pages should be numbered. The lines in p. 18 should be faint blue.
No. 3. Calculation Book.--This should be of the same size and shape as the Log Book, and should contain outline forms for calculations. The labour and confusion saved by using these, and the accuracy of work that they ensure, are truly remarkable. The instruments used, the observations made, and especially the tables employed, are so exceedingly diverse, that I fear it would be to little purpose if I were to give special examples: each traveller must suit himself. I will, therefore, simply make a few general remarks on this subject, in the following paragraph.
Number of Observations requiring record.--A traveller does excellently, who takes lat.i.tudes by meridian alt.i.tudes, once in the twenty-four hours; a careful series of lunars once a fortnight, on an average; compa.s.s variations as often; and an occulation now and then. He will want, occasionally, a time observation by which to set his watch (I am supposing he uses no chronometer). He ought therefore to provide himself with outline forms for calculating these observations, even if he finds himself obliged to have them printed or lithographed on purpose; and in preparing them, he should bear the following well-known maxims in mind:--
Let all careful observations be in doubles. If they be for lat.i.tudes, observe a star N. and a star S.; the errors of your instruments will then affect the results in opposite directions, and the mean of the results will destroy the error. So, if for time, observe in doubles, viz., a star E. and a star W. Also, if for lunars, let your sets be in doubles--one set of distances to a star E. of moon, and one to a star W. of moon.
Whenever you begin on lunars, give three hours at least to them, and bring away a reliable series; you will be thus possessed of a certainty to work upon, instead of the miserably unsatisfactory results obtained from a single set of lunars taken here and another set there, scattered all over the country, and impossible to correlate. A series should consist of six sets, each set including three simple distances. Three of these sets should be to a star or stars E. of moon, and three to a star or stars W. of moon. Lunars not taken on the E. and W. plan are almost worthless, no matter how numerous they may be, for the s.e.xtant, etc., might be inaccurate to any amount, and yet no error be manifest in their results. But the E. and W. plan exposes errors mercilessly, and also eliminates them. One of the best authorities on the requirements of s.e.xtant observations in rude land travel, the Astronomer Royal of Cape Town, says to this effect:--"Do not observe the alt.i.tude of the star in taking lunars, but compute it. The labour requisite for that observation is better bestowed in taking a large number of distances." So much delicacy of hand and of eyesight is requisite in taking lunars that shall give results reliable to seven or eight miles, and so small an exertion or flurry spoils that delicacy, that economy of labour and fidget is a matter to be carefully studied.
These things being premised, it will be readily understood that outline forms sufficient for an entire series of lunars will extend over many pages--they will, in fact, require eighteen pages. There are four sets of observations for time:--one E. and one W., both at beginning and close of the whole; one for lat.i.tudes N. and S.; six for six sets of lunars, as described above; six for the corresponding alt.i.tudes of the stars, which have to be computed; and, finally, one page for taking means, and recording the observations for adjustment, etc. Each double observation for lat.i.tude would take one page; each single time observation one page; and each single compa.s.s variation one page. An occulation would require three pages in all; one of which would be for time. At this rate, and taking the observations mentioned above, a book of 500 pages would last half a year. Of course where the means of transport is limited, travellers must content themselves with less. Thus Captain Speke, who started on his great journey amply equipped with log-books and calculation-books, such as I have described, found them too great an inc.u.mbrance, and was compelled to abandon them. The result was, that though he brought back a very large number of laborious observations, there was a want of method in them, which made a considerable part of his work of little or no use, while the rest required very careful treatment, in order to give results commensurate with their high intrinsic value.
MEASUREMENTS.
Distance.--To measure the Length of a Journey by Time.--The pace of a caravan across average country is 2 1/2 statute, or 2 geographical, miles per hour, as measured with compa.s.ses from point to point, and not following the sinuosities of each day"s course; but in making this estimate, every minute lost in stoppages by the way is supposed to be subtracted from the whole time spent on the road. A careful traveller will be surprised at the accuracy of the geographical results, obtainable by noting the time he has employed in actual travel. Experience shows that 10 English miles per day, measured along the road--or, what is much the same thing, 7 geographical miles, measured with a pair of compa.s.ses from point to point--is, taking one day with another, and including all stoppages of every kind, whatever be their cause,--very fast travelling for a caravan. In estimating the probable duration of a journey in an unknown country, or in arranging an outfit for an exploring expedition, not more than half that speed should be reckoned upon. Indeed, it would be creditable to an explorer to have conducted the same caravan for a distance of 1000 geographical miles, across a rude country, in six months. These data have, of course, no reference to a journey which may be accomplished by a single great effort, nor to one where the watering-places and pasturages are well known; but apply to an exploration of considerable length, in which a traveller must feel his way, and where he must use great caution not to exhaust his cattle, lest some unexpected call for exertion should arise, which they might prove unequal to meet. Persons who have never travelled--and very many of those who have, from neglecting to a.n.a.lyse their own performances--entertain very erroneous views on these matters.
Rate of Movement to measure.--a. When the length of pace etc., is known before beginning, to observe.--A man or a horse walking at the rate of one mile per hour, takes 10 paces in some ascertainable number of seconds, dependent upon the length of his step. If the length of his step be 30 inches, he will occupy 17 seconds in making 10 paces. Conversely, if the same person counts his paces for 17 seconds, and finds that he has taken 10 in that time, he will know that he is walking at the rate of exactly 1 mile per hour. If he had taken 40 paces in the same period, he would know that his rate had been 4 miles per hour; if 35 paces, that it had been 3.5, or 3 1/2 miles per hour. Thus it will be easily intelligible, that if a man knows the number of seconds appropriate to the length of his pace, he can learn the rate at which he is walking, by counting his paces during that number of seconds and by dividing the number of his paces so obtained, by 10. In short the number of his paces during the period in question, gives his rate per hour, in miles and decimals of a mile, to one place of decimals. I am indebted to Mr.
Archibald Smith for this very ingenious notion, which I have worked into the following Tables. In Table I., I give the appropriate number of seconds corresponding to paces of various lengths. I find, however, that the pace of neither man nor horse is constant in length during all rates of walking; consequently, where precision is sought, it is better to use this Table on a method of approximation. That is to say, the traveller should find his approximate rate by using the number of seconds appropriate to his estimated speed. Then, knowing the length of pace due to that approximate rate, he will proceed afresh by adopting a revised number of seconds, and will obtain a result much nearer to the truth than the first. Table I. could of course be employed for finding the rate of a carriage, when the circ.u.mference of one of its wheels was known; but it is troublesome to make such a measurement. I therefore have calculated Table II., in terms of the radius of the wheel. The formulae by which the two Tables have been calculated are, m=l x 0.5682 for Table I., and m=r x 3.570 for Table II., where m is the appropriate number of seconds; l is the length of the pace, or circ.u.mference of the wheel; and r is the radius of the wheel.
The Tables will be found on the next page.
[Tables I and II appear on p 34].
b. When the length of Pace is unknown till after observation.--In this case, the following plan gives the rate of travel per hour, with the smallest amount of arithmetic.
For statute miles per hour--Observe the number of paces (n) taken in 5.7 seconds: let i be the number of inches (to be subsequently determined at leisure) in a single pace; then ni/100 is the rate per hour.
For geographical miles per hour--The number of seconds to be employed is 5. This formula is therefore very simple, and it is a useful one. (A statute mile is 1760 yards, and a geographical mile is 2025 yards.)
For finding the rate in statute miles per hour in a carriage--Observe the number of revolutions (n) made by the wheel in 18 seconds: let d be the number of inches in the diameter of the wheel; then n d/200 is the rate per hour.
The above method is convenient for measuring the rate at which an animal gallops. After counting its paces it may be through a telescope, during the prescribed number of seconds, you walk to the track, and measure the length of its pace. If you have no measuring tape, stride in yards alongside its track, to find the number of yards that are covered by 36 of its paces. This is, of course, identical with the number of inches in one of its paces.
Convenient Equivalents.--The rate of 1 mile per hour, is the equivalent to each of the rates in the following list:--
Yards. Feet. Inches.
29.333, or 88.000, or 1056.000, in one minute or 0.488, or 1.466, or 17.600, in one second
Measurement of Length.--Actual measurement with the rudest makeshift, is far preferable to an una.s.sisted guess, especially to an unpractised eye.
Natural Units of Length.--A man should ascertain his height; height of his eye above ground; ditto, when kneeling: his fathom; his cubit; his average pace; the span, from ball of thumb to tip of one of his fingers; the length of the foot; the width of two, three, or four fingers; and the distance between his eyes. In all probability, some one of these is an even and a useful number of feet or inches, which he will always be able to recollect, and refer to as a unit of measurement. The distance between the eyes is instantly determined, and, I believe, never varies, while measurements of stature, and certainly those of girth of limb, become very different when a man is exhausted by long travel and bad diet. It is therefore particularly useful for measuring small objects. To find it, hold a stick at arm"s-length, at right angles to the line of sight; then, looking past its end to a distant object, shut first one eye and then the other, until you have satisfied yourself of the exact point on the stick that covers the distant object as seen by the one eye, when the end of the stick exactly covers the same object, as seen by the other eye. A stone"s throw is a good standard of reference for greater distances.
Cricketers estimate distance by the length between wickets. Pacing yards should be practised. It is well to dot or burn with the lens of your opera-gla.s.s a scale of inches on the gun-stock and pocket-knife.
Velocity of Sound.--Sound flies at 380 yards or about 1000 feet in a second, speaking in round numbers: it is easy to measure rough distances by the flash of a gun and its report; for even a storm of wind only makes 4 per cent. difference, one way or the other, in the velocity of sound.
Measurement of Angles.--Rude Measurements.--I find that a capital subst.i.tute for a very rude s.e.xtant is afforded by the outstretched hand and arm. The span between the middle finger and the thumb subtends an angle of about 15 degrees, and that between the forefinger and the thumb an angle of 11 1/4 degrees, or one point of the compa.s.s. Just as a person may learn to walk yards accurately, so may he learn to span out these angular distances accurately; and the horizon, however broken it may be, is always before his eyes to check him. Thus, if he begins from a tree, or even from a book on his shelves and spans all round until he comes to the tree or book again, he should make twenty-four of the larger spans and thirty-two of the lesser ones. These two angles of 15 degrees and 11 1/4 degrees are particularly important. The sun travels through 15 degrees in each hour; and therefore, by "spanning" along its course, as estimated, from the place where it would stand at noon (aided in this by the compa.s.s), the hour before or after noon, and, similarly after sunrise or before sunset, can be instantly reckoned. Again, the angles 30 degrees, 45 degrees, 60 degrees, and 90 degrees, all of them simple multiples of 15 degrees, are by far the most useful ones in taking rough measurements of heights and distances, because of the simple relations between the sides of right-angled triangles, one of whose other angles are 30 degrees, 45 degrees, or 60 degrees; and also because 60 degrees is the value of an angle of an equilateral triangle. As regards 11 1/4 degrees, or one point of the compa.s.s, it is perfectly out of the question to trust to bearings taken by the unaided eye, or to steer a steady course by simply watching a star or landmark, when this happens to be much to the right or the left of it. Now, nothing is easier than to span out the bearing from time to time.
Right-angles to lay out.--A triangle whose sides are as 3, 4, and 5, must be a right-angled one, since 5 x 5 = 3 x 3 + 4 x 4; therefore we can find a right-angle very simply by means of a measuring-tape. We take a length of twelve feet, yards, fathoms, or whatever it may be, and peg its two ends, side by side, to the ground. Peg No. 2 is driven in at the third division, and peg No. 3 is held at the seventh division of the cord, which is stretched out till it becomes taut; then the peg is driven in.
These three pegs will form the corners of a right-angled triangle; peg No. 2 being situated at the right-angle.
Proximate Arcs.-- 1 degree subtends, at a distance of 1 statute mile, 90 feet.
1" subtends, at a distance of 1 statute mile, 18 inches.
1" subtends at a distance of 100 yards, 1 inch.
1" of lat.i.tude on the earth"s surface is 100 feet.
30" is subtended by the diameter of either the sun or the moon.