Improved Instrument for Graphically Solving Spherical Triangles on a Plane Surface.

摘要

12,714. Edmonds, H. H. June 20. Bearings, instruments for determining.-By means of a plane surface and a movable radius bar, both provided with a number of scales of natural trigonometrical functions, various problems in plane and spherical trigonometry may be solved, the application to nautical astronomy being particularly described. The surface A is of metal or celluloid and of rectangular form with a square marked upon it and divided up by lines H, J, which start from natural cosine graduations along the base C and left side D, the vertical lines being produced to meet the upper edge E, an arc G is struck with radius equal to the side of the square and centre at the lower left corner, and is graduated in time and arc. Other scales are :-Squares of numbers Q, cotangents E, tangents F, cosines and tangents upon the sliding piece K and sines N beneath it, a parallel fixed scale of tangents, and a uniform scale P of which the unit is conveniently 0À3056 inch to suit the ex-meridian problem. The radius R is of celluloid or other transparent material graduated upon its lower surface, and readings are taken along the median line. It has two centres S, T of motion and graduation, one or the other of which is placed over the peg M ; it has also two handles V, and bears scales of sines, cosines, and versines. The accessories include a marker U for the radius, and three transparent plates X, Y, Z, of use respectively as an -intersection marker, a means for carrying on graduations from an edge, and a proportionalpart instrument. Examples are given of the application to the following problems, namely, azimuth at rising or greatest elongation, altitude azimuth, time azimuth, exmeridian, hour-angle at rising,' and hour-angle from altitude.