HIS ASTRONOMICAL STUDIES: SUN- WATCH, 



105 



rectified, to show the hour of the day, the time of the sun's 

 rising and setting, the sun's declination and the days on 

 which the sun enters the signs of the Zodiac. Ferguson 

 thus describes it : 



" The lines a d, a b, and b c of the gnomon, or stile, 

 must be cut quite through the card ; and as the end a b 

 of the gnomon is raised occasionally above the plane of 

 the dial, it turns upon the uncut line c d as on a hinge. 

 The line dotted A B, must be slit quite through the card, 

 and the thread must be put through the slit to keep it from 

 being easily drawn out." 



In Duncan's dial, the slit was also cut through the 



