. Calcutta journal of natural history, and miscellany of the arts and sciences in India. Natural history. Self-Calculating Sextant. bl'S the limb (as in other instruments), the measure of an angle ; —on the line of cotangents, the relative proportion of two sides of a right-angled triangle. This last is a piece of in- formation which no other instrument gives direct. This additional information gives a command over the quantities concerned much greater than otherwise could be had. Availing ourselves of the lineal scale^ our first aim will be to reduce the problem to a case of right-angled tria
. Calcutta journal of natural history, and miscellany of the arts and sciences in India. Natural history. Self-Calculating Sextant. bl'S the limb (as in other instruments), the measure of an angle ; —on the line of cotangents, the relative proportion of two sides of a right-angled triangle. This last is a piece of in- formation which no other instrument gives direct. This additional information gives a command over the quantities concerned much greater than otherwise could be had. Availing ourselves of the lineal scale^ our first aim will be to reduce the problem to a case of right-angled triangles. In all that respects heights and distances on the vertical or horizontal planes, this may, in general, be done with the ut- most ease. On the vertical plane, every altitude may be viewed as a perpendicular to the horizontal line passing through the eye of the observer, and since the instrument affords the means of ascertaining that line, and also the proportion which the height bears to the distance, it is evident that we are put in possession of considerable information on the subject. If we wish farther to know the actual measurement of parts, set the instrument a division backward or forward on the line of cotangents, and advance or retreat. By measuring the intervening space you may then proceed with facility and cer- Let BC be a mountain whose height and distance are un- known; occupying the station A, apply the instrument ver- tically to your eye, and having ascertained the horizontal line AB, look steadily along it by direct vision, and move the index Ac until you see the top of the object C by reflex vision 3 Y. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original McClelland, John, d. 1883. Calcutta, Bishop's College Press
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Keywords: ., booka, bookcentury1800, bookdecade1840, booksubjectnaturalhistory
