Abstract
THIS is an account of a device intended to replace the dial or circles in magnetic compasses and surveying instruments, with numerous illustrations of its application for the purposes of engineers, surveyors, naval and military officers and travellers. Half of the circle is divided into octants, and the graduation of each octant is effected by dividing its tangent, which is equal to the radius, into 100 equal parts and then drawing lines from these divisions to the centre of the circle. The divisions on the octant thus always subtend equal spaces on an offset laid out at right angles to the quadrantal radius. The spaces on the octant divided in this manner correspond to a hundredth part of the radius, and the angles being read in percentage divisions, trigonometrical formulæ are replaced by simple arithmetic. A considerable simplification of several practical problems is suggested by the examples given, but the advantages of the method can scarcely be judged without actual experience. It is stated, however, that many distinguished engineers and surveyors have expressed complimentary opinions as to its merits. Messrs. T. Cooke and Sons are the manufacturers of the new circle, which can be adapted to old or new instruments.
Fergusson's Surveying Circle and Percentage Tables.
By J. C. Fergusson Pp. 84. (Published by the Author, 1901.)
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Fergusson's Surveying Circle and Percentage Tables . Nature 64, 278 (1901). https://doi.org/10.1038/064278a0
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DOI: https://doi.org/10.1038/064278a0