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Declination Lines of Sundials

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DECLINATION LINES OF SUNDIALS - Page 10

The application of this method to the various types of sundials is the same as that shown in the following example, where the path of the shadow cast by the nodus is plotted on a horizontal sundial in latitude 400, when the sun has a declination of 20°N. From the tables mentioned above, take out the values for the altitude (angular distance above the horizon) of the sun, for each hour of the day, thus: the line F'k' represents the substyle line on the sundial. The foot of the perpendicular style is noted at F', and the nodus at N. NF is the height of the perpendicular style. Draw lines from N to the line F'k', making angles with F'k' equal to the altitudes shown in the table above. Thus, angle F'a'N 700 ; angle F'b'N = 66°14 ;.. . Then, lay off from F (the foot of the perpendicular style) the distances Fa, Fb, Fc, . equal to F'a', F'b', F'c',.. respectively. With center at F and radii Fb, Fc, Fd,... describe arcs cutting the corresponding hour lines (radius Fb cuts the hour lines i and I1; Fc, 2 and To; and so on). Through the points thus found on the hour lines, draw a curved line, which will be the desired line of declination. All other lines of declination may be plotted in the same manner.

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