October, 19 lo 



AMERICAN HOMES AND GARDENS 



395 



The Handicraftsman 



Conducted by 

 A. Russell Bond 



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Sun Dials Made at Home 



By A. J. Squires 



NE might imagine that a sun dial could be 

 laid out without resorting to mathematics 

 or mathematical formulce by merely erect- 

 ing a post at the center of the dial face and 

 putting a mark at the end of the shadow 

 cast by the post at each hour during the 

 day, as indicated by a good timepiece. Un- 

 fortunately, the problem is not quite as simple as this. 



Everyone knows that the sun rises higher in the sky in 

 summer than in winter. Hence, it will not do to use 

 the end of the shadow to mark the hours, for winter 

 shadows are longer than those of summer, and the late 

 afternoon shadows summer or winter are too long for any 

 dial face. For this reason, the edge rather than the end 

 of the shadow is used to point out the hour, and in order 

 to hav^e this shadow correct for any season of the year, it 

 is necessary (in the Northern Hemisphere) that the post 

 point north and lie parallel with the axis of the earth. The 

 proper inclination for any locality may be found by con- 

 sulting a good atlas and taking the latitude of the place as 



the inclination of the post. For instance, the latitude of 

 New York is about 40 degrees 45 minutes. The post or 

 gnomon, as it is called, would then have to be inclined to 

 the face of the dial at an angle of 40 degrees 45 minutes. 

 The form of the gnomon may be varied to suit one's 

 taste, so long as the shadow casting edge, that is, the 

 upper edge in a horizontal dial, is maintained at an angle 

 equal to the latitude of the place. An observer sighting 

 along this edge at night would find his gaze directed ex- 

 actly at the celestial pole of the heavens, or almost exactly 

 at the North Star. 



With the gnomon set at the right angle and pointing due 

 north, our problem is not yet solved, because we have to 

 bear in mind that there are three different kinds of time. 

 The sun dial gives us only solar time, and 12 o'clock solar 

 time occurs at the moment that the sun crosses the meridian, 

 which is a plane passing due north and south through the 

 position of the observer. Unfortunately, the sun is rather 

 irregular in its apparent motion, arriving at the meridian 

 earlier at some times of the year than at others. The 



'Vine-covered mound as a sun dial pedestal 



Gothic pedestal for a sun dial 



