The story of a house . a right angle with the first base line; sincetwo diameters, cutting a circle divided into 360 degrees atright angles, give 90 degrees for each quarter of the the aid of this instrument, having previously indicatedon the plan of the building it is intended to erect theangles which form certain lines between them, from a cer-tain point, you can transfer these angles to the ground. Suppose you want to plant a semicircular portico. Hav-ing found the centre, and traced the semicircle on theground, you can, by placing the graphometer on that centre, 94 THE STORY OF
The story of a house . a right angle with the first base line; sincetwo diameters, cutting a circle divided into 360 degrees atright angles, give 90 degrees for each quarter of the the aid of this instrument, having previously indicatedon the plan of the building it is intended to erect theangles which form certain lines between them, from a cer-tain point, you can transfer these angles to the ground. Suppose you want to plant a semicircular portico. Hav-ing found the centre, and traced the semicircle on theground, you can, by placing the graphometer on that centre, 94 THE STORY OF A HOUSE. determine the lines which will regularly cut the circumfer-ence, and would indicate, for instance, the axis of the col-umns of pillars. (Fig. 20.) As you have from the point Ato the point B 180 degrees, you will divide these 180 de-grees into as many parts as you wish on the circle of thegraphometer, and the centre of the glass will give you, at along distance, the same divisions on the semicircular In the same way that the graphometer serves for plant-ing a building, it serves to take the bearings of a that the base E F is of a known length, which hasbeen measured; placing your instrument at E, you sightwith a glass a point c, whether it be a tree, a steeple, or apicket; you have then the number of degrees, on the circle,which the. angle C E F includes. You carry this angleupon your plan ; then, carrying the instrument to the pointE, you sight from thence the same point G; you obtain thesame angle C E F, which, carried upon the plan, gives youexactly-the position of the point C, and the unknown dis- PLANTING THE HOUSE. 95 tance between E and C, between F and C; then one orother of these lengths serves you as a base in their turn,and operating from the point C or F, in sighting a fourthpoint D, you ascertain the lengths 0 D and F D. Thusyou can operate all over a section of country; it is calledf triangulation, the first operation in making a
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectarchitecturedomestic
