The Discovery of the Source of the Nile by John Hanning Speke
page 44 of 672 (06%)
page 44 of 672 (06%)
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My first occupation was to map the country. This is done by timing the rate of march with a watch, taking compass-bearings along the road, or on any conspicuous marks--as, for instance, hills off it --and by noting the watershed--in short, all topographical objects. On arrival in camp every day came the ascertaining, by boiling a thermometer, of the altitude of the station above the sea-level; of the latitude of the station by the meridian altitude of the star taken with a sextant; and of the compass variation by azimuth. Occasionally there was the fixing of certain crucial stations, at intervals of sixty miles or so, by lunar observations, or distances of the moon either from the sun or from certain given stars, for determining the longitude, by which the original-timed course can be drawn out with certainty on the map by proportion. Should a date be lost, you can always discover it by taking a lunar distance and comparing it with the Nautical Almanac, by noting the time when a star passes the meridian if your watch is right, or by observing the phases of the moon, or her rising or setting, as compared with the Nautical Almanac. The rest of my work, besides sketching and keeping a diary, which was the most troublesome of all, consisted in making geological and zoological collections. With Captain Grant rested the botanical collections and thermometrical registers. He also boiled one of the thermometers, kept the rain-gauge, and undertook the photography; but after a time I sent the instruments back, considering this work too severe for the climate, and he tried instead sketching with watercolours-- the results of which form the chief part of the illustrations in this book. The rest of our day went in breakfasting after the march was over--a pipe, to prepare us for |
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