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DECLINATION LINES OF SUNDIALS - Page 5

If the distances Co, Cd, Ce, are plotted on the corresponding hour lines from C' to o', d', e' and to d", e", a curved line drawn through those points will represent the path of the shadow of the nodus when the sun has a north declination of 23°27'. Similarly, the line K"b'K' (Fig. I), representing the path of the shadow cast by the nodus when the sun has a declination of 23027'S., may also be plotted by taking off the distances from C (Fig. 2) to the various points where the lines Co, Cd, Ce ... cross the line PS. A line drawn from C9 perpendicular to PC and cutting the line PS at K, will give the location of the point where that line of declination intersects the 6 o'clock line, as at K' and K". It is, however, not necessary to ex-tend this line beyond the horizontal line. All other lines of declination will fall between the lines K"b'K' and h"o'h' (Fig. i) ; and they may be plotted as shown above by inserting the desired lines in Figure 2, making angles with PE equal to the declination, on either side of that line, as the declination is north or south. The method of plotting the lines of declination on the horizontal sundial is exactly the same as that used for the south vertical sundial Plate XII. Plate XIII shows the position of the lines on an horizontal sundial in 4o°N latitude. It is evident that the horizontal line cannot be placed on this sundial, since its plane lies parallel to the plane of the horizon.

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