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Sundial Hour Lines Lay out

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Declination Lines of Sundials

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Interesting Sundials of the World

LAYING OUT THE SUNDIAL HOUR LINES - Page 13

The construction of each type is similar and only one need be described here. The example shows the construction of the hour lines for a south sundial declining 28'W, in latitude 40°3o'N. The plane of this sundial is perpendicular to the plane of the horizon, but it does not face any of the cardinal points. Unlike the preceding sundials, two things must be known before the hour lines can be constructed: first, the latitude of the place; and second, the declination of the sundial or the declination of the plane upon which the sundial is to be placed. (The declination of the plane may be found by one of the methods described in Section V). The GNOMON is perpendicular to the face of the sundial. The STYLE points to the celestial pole. The SUBSTYLE is to be determined (The substyle is not the 12 o'clock line, in this type of sundial). The HEIGHT OF THE STYLE is to be determined. The Construction Note: For clarity, the construction diagram has been divided into two parts. In practice, Fig. 1 would be incorporated in Fig. 2. To Find the Substyle Line Fig. r Draw the horizontal line ABC. From B let fall a perpendicular line BD, which will be the meridian or 12 o'clock line. Draw the line BE so that the angle DBE is equal to the complement of the latitude,, which in this case is 49°30' (90° 40°30'=49°30').

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