74 TIIK WORLD. 



I, &c., thus indicated on the paper, and the centre of the circle A, 

 draw the hour-lines A F, A G, A H, &c., extending, however, 

 only to the circumference of the circle, and we have a dial ready 

 for use, after adding the figures. Of course the little chicle must 

 be so adjusted that when the line is passed by some one of its 

 graduations, it will reach the horizontal plane at a point in the 

 meridian line A C. Instead of a wire for the gnomon, we may 

 use an inclined plane, so that our dial will now be not unlike this 



-'. : " - '' - 



figure. In order to use it, we must next determine the north and 

 south line, or a meridian line, and place the lino on our dial which 

 marks XII, to correspond therewith. This may be ascertained 

 by means of a surveyor's compass, provided the variation of the 

 needle from true north is known ; or, at the time of the solstices, 

 mid-summer or mid-winter, when the sun's declination is 

 changing very slowly, a number of circles may be traced upon a 

 horizontal plane, having a 'common centre, over which centre a 

 plumb-line must be suspended, having two or three knots tied in 

 it. Upon marking where the shadow of these knots falls, suc- 

 cessively, on the circles, in the forenoon and afternoon, and then 

 bisecting the space so measured on each circle, and drawing a 

 line through the centre and these points of bisection, a pretty 

 exact meridian line may be laid down. The use of several circles, 

 is simply to ensure greater accuracy in the result. We will now 

 suppose the dial constructed, and located in a window facing to 

 the south. We may here observe, that there will be no use in 

 graduating the dial all the way round, as that portion only can be 

 used over which the shadow passes during the day, say from 5 

 o'clock to 5 o'clock, on each side, viz : from V, on the western 

 side, through VI, VII, VIII, IX, X.-XI, to XII, and from XII, to 

 V, on the eastern side. When the sun rises before 6 o'clock, say 



