106 JOHN DUNCAN, WEAVER AND BOTANIST. 



wooden board on which the card was fastened, and the 

 cord inserted was fastened to a white mother-of-pearl 

 button at the under side which moved along the slit as 

 required. 



" On the other end of this thread is a small plummet, 

 and on the middle of it a small bead for showing the hour 

 of the day. 



" To rectify tJie dial Set the cross line on the slider 

 to the day of the month, and stretch the thread from thence 

 over the angular point XII, where the curve lines meet ; 

 then shift the bead on the thread to that point. 



" To find tJie hour of the day w/ien the sun shines. Raise 

 the gnomon, and hold the edge of the dial next the gnomon 

 toward the sun, so as the upper edge of the shadow may 

 just cover the shadow line ; and the bead then playing 

 freely on the face of the dial (by the weight of the plum- 

 met) will show the time of the day among the hour lines, 

 as it is before or after noon. 



" To find the time of sun-rising and sun-setting. Move 

 the thread among the hour lines, till it either covers some 

 one of them, or lies parallel betwixt any two ; and then it 

 will cut the time of sun-rising among the forenoon hour 

 lines, and of sun-setting among the afternoon hour lines, for 

 the day of the year indicated by the cross line on the 

 slider." 



Ferguson's dial also showed the sun's declination, but 

 Duncan had not copied that part on his drawing, as not 

 being of practical value for his purpose. It answered only 

 for places in the latitude of London, and required to be 

 rectified for other latitudes, which Duncan did for Aberdeen. 

 This dial he used during the greater part of his life, and he 



