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LAYING OUT THE SUNDIAL HOUR LINES - Page 21

The Construction To find the Meridian Line, and its Angle with the Horizon Fig. r Draw the perpendicular line AB, and at any convenient point such as F, erect FH perpendicular to AB. Make FH any convenient distance or equal to the height of a perpendicular style. At H draw HG, making the angle FHG equal to the reclination of the sundial (if the sundial inclines, leans toward you, the line HG is drawn downwards). Then draw HP so that angle FHP is equal to the complement of the reclination. Draw GK perpendicular to AB and G; make GD equal to GH; then draw DK, making an angle with AB equal to the declination of the sundial. (If the sundial declines to the west, this angle is set off to the left of AB; if the sundial declines east, the angle is set off to the right of AB). Draw PY through K. This will be the meridian or 12 line of the sundial. TZ is drawn, through P perpendicular to AB. Then, the angle TPK is the angle the meridian makes with the horizon. To Find the Center of the Sundial Fig. z From F draw FL perpendicular to PY and cutting PY at M. Make FO equal to FM; and make ML equal to OH. Then draw LC, which makes an angle with KL equal to the latitude of the place. The intersection of CL with PY at C is the center of the sundial. To Find the Substyle Line Fig. z A line drawn from C to F will be the substyle line. To Find the Height of the Style Fig. z Through F draw XX perpendicular to the substyle CF. Make FS equal to FH; then draw CS. The line CS will be the style and the angle SCF is equal to the height of the style. The line XX cuts PY at N. To Find the Hour Lines Fig. 2 In the figure, the points C, S, F, N, and the line XX correspond to the same points in Figure I. in Figure 2, draw a line from F to CS, which will be perpendicular to CS at W. Extend CF and make FV equal to M. Connect V and N. With V as a center describe the arc QQ and beginning at the point where the line VN cuts the arc QQ, divide this arc into equal spaces of 15° each. Draw lines through these di-visions until they intersect the line XX. Then, lines drawn from C through the intersections on XX will be the required hour lines. Figure 3 shows the way in which the hours should be numbered on a sundial in lat. 3503o'N, reel. 350 and decl. 3o°W. Hour Limitations The length of time the sun will shine on reclining-declining sundials, depends upon the amount of their reclination and declination. See hour limitations for declining sundials. Setting the Sundial The reclination and declination of the plane upon which the sundial is to be placed having been carefully found, the sundial should be securely attached.

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