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Sundial Hour Lines Lay out

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LAYING OUT THE SUNDIAL HOUR LINES - Page 10

At B, on AC, draw DE so that the angle EBC is equal to the latitude of the place, in this case 52°30'. DE.will also be the substyle line, and the 6 a.m. line. Make BD equal to the desired height of the style in inches. Through D, draw the line KL perpendicular to DE. With B as a center, and the radius BD, describe the arc GDH. Beginning with the point D, divide this arc into equal parts of 15° each, on each side of the line DE. From B draw lines through the points found on the arc until they cut the line KL. Through the points thus found on KL draw lines parallel to DE, which will be the required hour lines. FIGURE 2 shows the hour lines transferred to the sundial plate, and the way in which they should be numbered. The west sundial is also shown. Note the position of the lines on each face The gnomon generally used on this type of sundial. Hour Limitations The east sundial will show only the hours from 'sunrise to noon; the west sundial, the hours from noon to sunset. These sundials will not show the noon hour, because they lie in the plane of the meridian. The sun's rays at that time are parallel to the face of the sundial; consequently the shadow cast by the gnomon will be infinite in length, and the edge of the shadow cannot be seen. Setting the Sundial The plane of each sundial must be perfectly vertical, and lie in the plane of the meridian.

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