Figure 1. 



(Note. — The line A. B. may just as appropriately be drawn below the circle, or cutting through it. 

 It is here made tangential merely to simplify the measurements to which reference is made.) 



A SIMPLE METHOD OF CONSTRUCTING A 

 HORIZONTAL SUN-DIAL. 



Bv CH.\RLES E. BEXH.VM. 



reful 



into 



equal 



Strike out a circle on a piece of paper. The size 

 is not important, but as some guide it may be 

 mentioned that it will be found that the height of 

 the gnomon of the dial will be a little less than the 

 radius of this circle. 



Divide the circle very 

 parts, and at right 

 angles to one of these 

 radii draw a horizontal 

 line (AB, Figure 1) 

 tangential to the cir- 

 cumference. Cut the 

 paper along this line, 

 and produce the 11 

 nearest radii to the 

 cut edge as show n. 



On a larger piece 



Figure 2. 



of paper draw two lines at right angles in the form 

 of a T, and to the top line of this T apply the 

 cut edge, so that its central line touches the centre 

 of the top of the T- Mark off on the top line of 

 the T all the points where the produced radii meet 

 the cut edge. 



Draw two lines meeting at an angle equal to the 

 latitude of the place for which the dial is to be 

 constructed, and form a right-angled triangle 

 (ABC, Figure 2) with this angle for its acute 

 angle C, and with the length of the side AB 

 exactly one radius of your circle. Mark a point 

 on the upright line of the T exactly the length 

 of BC from the top. Rule lines through all 

 the points on the top line of the T to this point 

 on the other line, and produce them on through the 



point. TliL-se will be the hour lines of the dial plate 

 and must be numbered — 12 for the central one, 

 with 11, 10, 9, and so on, in order on the left, and 

 1. 2, 3, and so on, in order on the right. A line 

 parallel with the top of the T will form the hour 

 line for the two sixes. Of course it is not necessary 

 to number the hours further than S in the evening 

 or before 4 in the morniu! 



required the original circle mus 



If half hours are 

 be divided into 48 

 instead of 24 : if quarters, 96 parts. 



The gnomon must be a triangle of metal corres- 

 ponding with the triangle of Figure 2, the base being 

 BC. the point B at the head of the T and the point 

 C where the hour lines intersect. 



This simple method of dialling will incidentally 

 suggest the curious form necessary for a dial at the 

 latitude of the equator — degrees. 



In this case, the angle at C being degrees, the 

 line AC, instead of sloping downwards, would have 

 to be parallel with the dial face, so that a rectangle 

 would take the place of the triangle for the gnomon. 

 The hour lines, having no point to converge to, 

 would also run parallel w ith the top of the gnomon, 

 and the dial would take the form show n in Figure 3. 



Figure .;. 



Form of Horizontal Dial adapted to the latitude of 

 the Equator. 



117 



