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Reserves are allowed to be made for all necessary public roads and other internal communications, either by land or water; also for the sites of towns, villages, school-houses, churches, and other purposes of public utility and convenience.
When the division between Provinces or Counties, or other lines of territorial demarcation, is represented, either altogether or in part, by a meridian line; or a line having any fixed angle with the meridian; or by a portion of the arc of a parallel (as is the case in many of the Australian provinces); it is of course necessary to be able to determine and mark upon the ground with accuracy such meridian or parallel, directions for which are given in the last chapter on Practical Astronomy. Most useful practical information upon this subject will also be found in the narrative of the survey, and marking of the boundary between the British possessions in North America and the United States of America, in 1842, published by Major Robinson, Royal Engineers, in the second and third volumes of the "Corps Papers.'
Operations of this nature, if conducted with the very great care and precision that were bestowed upon the boundary alluded to, involve the perfect knowledge of the manner of using and adjusting the transit, and altitude and azimuth instruments; and also the management of chronometers. The boundary line between South Australia and what now constitutes the province of Victoria, (the 141st degree of east longitude) was however determined (and since marked on the ground for a considerable distance,) under the New South Wales Government, by one of their surveyors *, with only a sextant, a pocket chronometer, and a small 3-inch theodolite; but though the work was performed with the greatest care and attention, and with probably as great a degree of accuracy as could be obtained with these imperfect instruments; the result can of course only be looked upon as an approximation far too vague for the determination of a division of importance. The North American boundary, on the other hand, may perhaps have been defined with more precision than was absolutely necessary in a line of demarcation running for its whole length through a wild uncleared country.
.* Mr. Tyers.
Having now gone through the method of dividing the land into minute sections for occupation, and its further division for territorial purposes; this chapter will conclude with a short reference to the objects to be held in view in conducting exploring expeditions beyond the bounds of the settled districts, for the purpose of adding to the geographical knowledge of the country and developing its resources; which objects are very similar in character to those described in page 3, when treating of the preliminary operations of a survey in a newly-formed colony.
The nature of the country to be traversed will, as far as this is known, indicate the method of travelling that must of necessity be adopted. Extensive inland water communication, as in the Canadas, points to the canoe as the readiest mode of transport; comparatively open and generally grassy land, as in Australia and Southern Africa, requires the use of horses and oxen; whilst in many other countries the thick underwood can, in parts, be traversed only on foot; and barren deserts by the aid of camels. These different modes of locomotion evidently all require different preliminary arrangements. The objects in view, however, are much the same in all cases*; viz. a knowledge of the climate, soil, native population, geological formation, botanical character, of the country, and its resources of all kinds; as well as the delineation (as perfect as the time and means that are available will admit) of the natural features of the ground.
All points known as portions of the settled country being soon left behind, the explorer has to trust to his own judgment as to the best directions in which to conduct his party; to his own energy in overcoming the natural obstacles that he will be certain to encounter; and his own practical skill in fixing at proper intervals his different positions by means of astronomical observations, and mastering rapidly the general massive features of the ground for the purpose of making a rough sketch of the country passed over, showing more particularly the directions of the principal ranges of hills, and of rivers, and watercourses.
In a large party these labours may often be subdivided ad
Expeditions for one single definite object, such as tracing the sources of a river, &c., are not intended to be here referred to.
vantageously; but the leader must remember that the entire responsibility still rests with him; and if he does not actually participate in every portion of the work, he must nevertheless exert a general influence over the whole.
As regards the fixing, with as much accuracy as may be attainable, the various positions of encampments, the directions and sources of rivers, and all marked prominent features; much assistance is to be obtained by carrying on, as far as it can be done, a species of rough triangulation (with a sextant or other portable instrument), from the extreme trigonometrical stations, or any prominent landmarks the positions of which are known and represented on the plans. This may however very soon become impracticable from the nature of the country or other causes, and the traveller then finds himself much in the same predicament as at sea, having little beyond his dead reckoning to trust to for the delineation on paper of his day's work. In this position he must look to the heavens for his guide; and hence the necessity for his becoming himself, or having with him, a good and rapid observer.
At sea, the latitude is always obtained at noon by a meridian altitude of the sun* (when visible); "sights," as they term observations of single altitude for time, having been taken three or four hours before. The latitude obtained at noon is then reduced by dead reckoning to what it would have been at the time and place of the morning observation, (using the traverse table;) and with this deduced latitude the hour angle is computed +, and the equation of time, plus or minus, applied for the mean local time; which, when compared with the Greenwich time, shown by the chronometer, (allowing for its rate and error), gives the longitude east or west of Greenwich at the time of the morning observation.
By applying, by dead reckoning, the change in longitude between that time and noon, the longitude of the ship at noon is obtained,— the latitude has already been found by direct observation, and the two determinations afford the means of recording upon the chart the position of the ship at noon on that day.
Somewhat similar to the above proceeding must be that of the
* For the method of calculating the latitude from a meridian altitude, see chapter xi. See chapter xi.
explorer in a wild unknown tract of country. He would not probably find it convenient always to obtain his latitude at noon; but he can generally do so, and more correctly, at night*, by the meridian altitude of one or more of the stars of the first or second magnitude, whose right ascension and declination are given in the Nautical Almanac. His local time can, immediately before or after, be ascertained by a single altitude of any other star out of the meridian (the nearer to the prime vertical the better); and if he carries a pocket chronometer upon which any dependance can be placed, he has thus the means, by comparison with his local time, of obtaining his approximate longitude, and of laying down his position upon paper.
In travelling, the rate of the chronometer will probably be found to vary; but as frequent halts of two or three days are likely to occur, these opportunities should never be lost of ascertaining the change of rate. The longitude should also be obtained occasionally by lunar observations on both sides of the meridian; or by some of the other methods given in the last chapter.
The results deduced from such observations must not be relied upon within ten or twelve miles, but a careful observer should rarely exceed these limits; and his latitude ought always to be within half a mile, or under the most unfavourable circumstances, one mile, of the truth.
With these all-important data, enabling him to fix with approximate accuracy point after point† in his onward course, the explorer can have no difficulty in interpolating by angles, taken with a sextant or with an azimuth compass, all strongly-marked prominent features, or in laying down his route upon paper correctly enough for the purposes of identifying particular spots, and giving a faithful general representation of the features of the ground he has travelled over. The value of this sketch will be much enhanced by its having recorded on it, as nearly as they can be ascertained by the mountain barometer or aneroid‡, or by the temperature at * See chapter xi. on Practical Astronomy.
The distances between positions, the latitudes and longitudes of which have been determined, can be easily calculated in the manner described in the next chapter; by which means they can be laid down with more accuracy, if the extent of ground travelled over is not very great.
See chapter xi.
which water is found to boil*, the altitudes of the most important positions, as the summits of hills, the levels of plains, and sources of springs and rivers.
Daily meteorological observations, even of the most simple character; such as merely recording the readings of the thermometer and barometer at stated times, will also prove of essential service as illustrative of the climate; and these will be of additional value if accompanied by a record of the quantity of rain fallen on different days, should any portion of the party be stationary for sufficient length of time at any one spot, to make these observations. If not provided with a rain gauge of a better description, a tin pipe with a large funnel, the area of the top of which bears a certain proportion to that of the tube, will answer perfectly to measure the quantity of water fallen. A light graduated wooden rod is fixed in a cork float, and indicates, above the level of the top of the funnel, the number of inches ;—the graduations of the rod of course being proportioned to the ratio between the areas of the surface of the funnel and that of the tube. Thus, if the proportion is 10 to 1, the measuring rod will be lifted 10 inches for every inch of rain.
* See page 111.