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Sundial Hour Lines Lay out

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LAYING OUT THE SUNDIAL HOUR LINES - Page 14

With B as a center and any convenient radius, draw the arc AC, which cuts the line BE at F. From F draw a line perpendicular to BD at G. From B draw BH, making the angle HBD equal to the declination of the sundial, which in this case is 28°. Make BK equal to GF, and from K draw KL perpendicular to BD. Then on GF make GN equal to KL. Draw a line from B through N, cutting the arc AC at M. This line is the substyle line upon. which the gnomon must be erected, perpendicular to the face of the sundial. It will be noticed that the substyle line must fall among the afternoon hours if the sundial declines west; among the morning hours if the sundial declines east. To Find the Height of the Style Fig. r With N as a center and the radius BL, describe an arc cutting the arc AC at R. Draw a line from B through the point R. The line BR is the style, and the angle RBM is the height of the style. (The style must make an angle with the face of the sundial equal to the angle RBM). To Find the Hour Lines Fig. 2 In this figure the lines BD and BM have been reproduced from figure I. In Fig. I the line MP is perpendicular to BR. In Figure 2 the line MB has been produced so that MN is equal to MP (Fig. I). With N as a center and any convenient radius, describe the arc VW; and at M draw the line PR perpendicular to BM, cutting BD at 12. Now draw N 12, cutting VW at T. Beginning at T divide the arc VW into equal spaces of 15° each.

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