442 SUPPLEMENT. 



To maK.e a horizontal dial, by the cylinder, for any 

 latitude to which its axis is elevated ; draw out the axis 

 and cut the cylinder quite through, as at e hfg, parallel 

 to the horizontal board H, and take off the top part 

 e A Dfe; and the section e h fge will be of an ellip- 

 tical form, as in jf'Vg. 3. Then, from the points of this 

 section (on the remaining part e B Cf) where the pa- 

 rallel lines on the outside of the cylinder meet it, draw 

 right-lines to the center of the section ; and they will be 

 the true hour-lines for a horizontal dial, as q b c d e in 

 Fig. 3. which may be included in a circle drawn on that 

 section. Then, put the wire into its place again, and it 

 will be a stile for casting a shadow on the time of the 

 day, on that dial. So, E (Fig. 3.) is the stile of the' 

 horizontal dial, parallel to the axis of the cylinder. 



To make a vertical south dial by the cylinder, draw 

 out the axis, and cut the cylinder perpendicularly to the 

 horizontal board H, as at giCkg, beginning at the 

 hour line (BgeA) of XII. and making the section at 

 right angles to the line S H N on the horizontal board. 

 Then, take off the upper part g A D C, and the face of 

 the section thereon will be elliptical, as shewn in Fig. 4. 

 From the points in the edge of this section, where the 

 parallel hour-lines on the round surface of the cylinder 

 meet it, draw right-lines to the center of the section ; 

 and they will be the true hour-lines on a vertical direct 

 south dial, for the latitude to which the cylinder was 

 elevated : and will appear as in Fig. 4. on which the 

 vertical dial may be made of a circular shape, or of a 

 square shape as represented in the figure. And /'will 

 be its stile parallel to the axis of the cylinder. 



And thus, by cutting the cylinder any way, so that its 

 section may either incline, or decline, or recline, by any 

 given number of degrees ; and from those points in the 

 edge of the section where the outside parallel hour-lines 

 meet it. draw right lines to the center of the section 



