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XXIII.—Hints To Travellers;
1. Report of Sub-Committee of the Royal Geographical Society, consisting of Capt. R. FitzRoy; R.N., and Henry Raper, Esq., R.N.; also 2. Papers by Rear-Admiral W. H. Smyth; 3. Rear-Admiral F. W. Beechey; 4. Lieut.-Col. W. H. Syhes; 5. Francis Galton, Esq., $fc.
[applications are frequently made to the Council of the Royal Geographical Society by travellers about to set out for imperfectly known countries for instructions by which they may make their labours useful to geography. When a traveller addresses a specific question relating to a local matter, or some particular point of equipment as regards instruments of observation, it will generally be easy to refer him to some member of the Society whose experience may enable him to afford a satisfactory answer; but when he puts his question in a general form, it is extremely difficult for the Council to return a suitable reply.
It seems a natural solution of the difficulty that the Council should themselves draw up .a body of instructions to meet such occasions. But some insuperable objections very speedily suggest themselves. A complete system of instructions adapted to general application would embrace every point which could present itself to the notice of the accomplished traveller, and such a work would be an encyclopaedia. On the other hand, a few general remarks of an elementary nature would be superfluous to an individual of moderate attainments, while it could not possibly impart the necessary qualifications to one who had no other knowledge or experience of the subject. Again, the nature of the observations which a traveller may make must depend on the character and quality of the instruments he carries—that is, on the quantity of baggage which it may be convenient or safe to carry with him, and therefore on his personal resources. It is evidently as impossible to treat all such particulars to any useful purpose, as it would be to prescribe the equipment suited to the various unexplored regions of the world. But this is not all; differences prevail amongst experienced travellers themselves, not merely as to details of observations, the degree of accuracy which it is advisable to aim at, and other matters, but as to whether particular instruments should be carried or not.
On these grounds the Committee do not think it advisable to undertake the formal publication of instructions for travellers; nevertheless, as many valuable suggestions have been made by scientific men on the occasion of these applications, which they are desirous should be made accessible to travellers in quest of information on particular points, they have recommended the publication of certain papers which follow, with the names of the authors.]
Hints to Travellers.
With respect to such applications for instructions, it may be advisable to reply in the first instance with reference to special enterprises, and afterwards to compile more extended and detailed information for the use of travellers generally—if, indeed, so wide and comprehensive a range should be deemed within the province of the Royal Geographical Society.
Some inquiries refer more particularly to the case of "a traveller who proposes to visit really wild countries," and "to lay down a useful map of his journey.'
It is understood that he has already travelled, and has given proofs of his acquaintance with the use of several necessary instruments. Were not this the case, we fear that the fullest instructions would hardly suffice to give any traveller possession of such practical skill as should be acquired experimentally.
We think that the following list of instruments will be found sufficient for the traveller's purposes, and not too cumbersome or difficult to carry :—
A sextant, horizon, pocket-sextant, Kater's compass, Rochon's micrometer, and a sympiesometer, two pocket-chronometers, two thermometers, two portable barometers, two aneroids, and two boiling thermometers. It would be very desirable to carry a second sextant or circle, an additional horizon, and another prismatic compass, in case of accidents. Writing and drawing materials, stationery, scales, tapes, and register-books, should be carried in convenient cases—water-tight, if possible. With these, or even a part of these materials, a complete map may be laid down.
We consider the sextant (or circle) and horizon to be an efficient and reliable observatory for travellers, when accompanied by two or three chronometers. With such simple means there is far less risk of error than in using instruments of higher pretensions and more complicated structure.*
To lay down a useful map is an easier task than usually supposed, if correct principles be adopted and carefully followed in practice. A field-book (angle or bearing-book) should be always at hand, in which every particular relating to the direction travelled (or course), the distances, times, angles, bearings, and observations, should be noted on the spot and as they occur, as far as may be practicable: the less left to memory the better. Descriptions should be written with the objects in view. Times of occurrences, changes of course, and other data, should be noted as often as possible; but that which is subsequently found invaluable when laying down the work permanently, is a collection of sketches of the country passed over, in plan, with a partial mixture of profile views, on which the angles observed or lines of bearing are traced by hand, with their corresponding figures written along them or across the angles, thus :—
By noting the angles and bearings on the plan, as well as in regular columns, in the field (or bearing, or angle) book, and inserting as many profile views, half-plan half-profile sketches, and horizontal plans, in the book as time will allow, an immense
* Kaper's Navigation is a storehouse of information, not only on the practical use of instruments, but on the various methods of computing or reducing the observations by easy compendious calculations (suitable for the traveller on a journey, or the seaman in a gale); as well as by the longer and exactly accurate com
Eutatious. Neither seaman nor traveller ought to leave England without the iteat edition of this valuable work.—R. F.
amount of perplexity will be prevented, and increase of accuracy will be ensured.
Such plans as these are so many sketch maps made on the spot, from which accurate compilations may afterwards be made with comparative ease. In laying down or connecting points trigonometrically between the stations that are determined astronomically, true bearings and angles by reflecting instruments should be preferred to any use of the compass, which, however valuable as an auxiliary to fill in minor details, is not to be relied on in all places, and is apt to get out of order in consequence of its centre wearing by friction, as well as from other causes not always self-evident.
By fixing principal points astronomically, using trigonometrical connection between them, and filling in minor details by angles, bearings, and eye-sketches, it is surprising how much work may be done in a short time by a practised traveller.
For latitudes, besides the ordinary meridian or circum-meridional observations, single, double, or equal altitudes will be useful, the Time being always obtained as accurately as may be.
Cross-altitudes* of stars are excellent, and easily obtained in tropical climates, where the sun is usually too high at noon for convenient observation in the artificial horizon.
Observations of the moon are not to be relied on to such accuracy as those of stars or the sun, on account of her parallax and irregularities. This applies still more to determinations of longitude by the right ascension or declination of the moon, in which a very small error of observation, or tabular position, will affect the result excessively.
For longitudes we think there is no method available for travellers in a wild country so sure and easy as cross-lunars.f A few good sets of cross-lunars taken in one night by the same observer, with the same instrument, will give the longitude within three miles of the truth. This is stated confidently as the result of experience. The altitudes must be calculated, for which the time must, of course, be known nearly. Differences of time by chronometers suffice for intermediate distances, and are, within such limits, most satisfactory. But in a country where there are good marks well defined, accurate meridian distances may be obtained by good differences of latitude and true bearings between points connected trigonometrically.
When equal altitudes are not obtained for time (with a view to ascertaining the error and rate of chronometers, or difference of longitude), absolute (single or independent) altitudes may
* By cross-altitudes we mean observations of stars on opposite sides of the zenith, and nearly equidistant from it.
t Observations of the moon's distance from stars, nearly equidistant, east and west.—R. F.
be observed; and it should be remembered that those taken before noon should be compared with other forenoon sights, and those taken afternoon with other afternoon sights, in deducing the difference of time between places from their results.
For base lines, the more rapid methods of attainment are alone suitable to the present object. No measure is more accurate and speedy than that obtained by meridian altitudes of the same heavenly body (sun or star, not the moon) at different stations, by the same observer, with the same instruments. If the stations are in the true meridian, or nearly so, their difference of latitude is their distance, near enough for our traveller's purpose; and if they are otherwise situated, their true bearing, obtained by an azimuthal observation of the sun or a star, and their difference of latitude, give the true meridian distance or difference of longitude between them, as well as their direct distance, the required base line.
If for particular purposes, such as a local plan, a short base line be required, an accurately measured board or pole, and a Rochort micrometer, or a sextant, will suffice. A short base may be measured first, two poles erected, and then a longer space ascertained by angular measurement. Field-work should be laid down on a moderately large scale, from a quarter of an inch to an inch, and for particular plans even several inches to a mile.
Magnetic observations, geological researches, mineralogy, zoology, botany, and ethnology, require the assistance of competent authorities on those subjects.
Your Sub-Commfttee will now add a few brief remarks on the instruments they have recommended.
Beautiful as instruments of a higher class than sextants and reflecting circles seem to be in theory, and are, when fixed securely and properly, in practice;—the great difficulty of finding a secure foundation for them to stand on, of adjusting them accurately (under the ordinary circumstances of a traveller), and of maintaining their exact adjustment while the observer is moving round them on, perhaps, unsound ground, are reasons which have induced us to think it unadvisable to recommend them to hurried travellers, who are not such adepts in their use as practised astronomers, and who might easily overlook an error of adjustment that would vitiate a whole set of observations.
Unless the results that are carefully recorded be those of observations made on correct principles, with instruments sufficiently accurate, practically as well as theoretically, all the time and. pains they have cost are thrown away; and these consequences have been witnessed too frequently where transit, or azimuth and altitude, or other instruments on stands were employed.^
It should be borne in mind that travellers cannot attempt to