344 FERGUSON'S LECTURES. 



meridian at right angles with the six o'clock line g h, 

 and setting one foot of your compasses in the intersec- 

 tion a, as a center, describe the quadrant ge with any 

 convenient radius or opening of the compasses : then, 

 setting one foot in the intersection I, as a center, with 

 the same radius describe the quadrant fh, and divide 

 each quadrant into 90 equal parts or degrees, as in the 

 figure. 



Because the hour-lines are less distant from each 

 other about noon, than in any other part of the dial, it 

 is best to have the centers of these quadrants at a little 

 distance from the center of the dial-plane, on the side 

 opposite to XII, in order to enlarge the hour-distances 

 thereabout under the same angles on the plane. Thus, 

 the center of the plane is at C, but the centers of the 

 quadrants at a and 6. 1 * 



Lay a ruler over the point b (and keeping it there for 

 the center of all the afternoon hours in the quadrant f A) 

 draw the hour-line of I, through llf degrees in the 

 quadrant ; the hour-line of II, through 24i degrees ; of 

 III, through 38^ degrees ; IV, through 53,, and V 

 through 71-h : and because the sun rises about four in 

 the morning, on the longest days at London, continue 

 the hour-lines of IV and V, in the afternoon, through 

 the center b to the opposite side of the dial. This 

 done, lay the ruler to the center a, of the quadrant eg, 

 and through the like divisions or degrees of that quad- 

 rant, viz. 113, 245, SSij, 53*, and 71^, draw the forenoon 



Note 106. Enlarging the distance of the hour-lines, were they laid 

 down correctly, could never be an advantage, but would render the 

 dial erroneous. The center of the dial, which corresponds to the center 

 of the globe, is situated at the intersection of the stile with the plant- of 

 the dial. But, since it is necessary to have the gnomon of some physical 

 thickness, the edges of the gnftmon become in fact the stile, and the 

 shadow is cast by different edges in the morning and afternoon. The 

 center of the dial therefore, which is the intersection of the stile, or 

 edge, casting the shadow with the plane of the dial, is alternately repre- 

 sented by a and 6. 



