722 



PRACTICAL DIAGRAMS. 



Pie. 1024. 



be drawn, it will be perpendicular to 

 c d. By the same rule the centre of a 

 walk will be found perpendicular to the 

 line ef, taking o as the centre, fig. 1023. 



To set olf a walk perpendicular to the 

 corner of a wall : Carry out the lines a 

 and b straight 

 with the face of 

 the wall, and of 

 equal lengths ; 

 from the two 

 ends of these 

 lines, with equal 

 radii, describe 

 two arcs; from 

 where they bi- 

 sect each other, 

 draw a line to 

 the corner of the wall, which line will be 

 the centre of the walk, fig. 1024. 



The annexed diagram, fig. 1025, illus- 

 trates an instrument very useful in laying 



out mathematical figures. It consists of 

 an upright pole 2 feet in length, shod 



with iron, upon which revolves a metallic 

 tube with a projecting shoulder, to which 

 is attached, by a screw, a wooden rod 

 8, 10, or more feet in length, marked in 

 feet and inches. Upon this rod there is 

 a movable iron slide with an iron sharp- 

 pointed stud. The 2-feet pole being 

 placed in the centre, or point from which 

 the figure is to be described, the slide is 

 moved along the rod to the proper dis- 

 tance, and fixed there by means of a 

 screw. An iron handle, turned up at the 

 end of the rod, about 18 inches in length, 

 is taken hold of, and, as it is moved 

 round, the iron stud in the horizontal rod 

 describes the figure intended. 



Another useful instrument is a pair of 

 wooden compasses shod with iron, the 

 legs of which are 5 feet in length. To 

 one leg a quadrant bar of iron is attached, 

 and made to pass through the other leg. 

 This quadrant-shaped iron rod is perfo- 

 rated at every 3 inches, and furnished 

 with a screw-pin to keep the legs of the 

 instrument distended to the extent re- 

 quired. The quadrant rod is placed ex- 

 actly in the middle of the leg of the 

 instrument, so that when the leg is 

 moved, for example, 3 inches on the 

 quadrant, it gives 6 inches at the points 

 of the compasses ; if moved 1 foot on the 

 quadrant, it gives 2 feet, and so on, 

 being always double the former extent. 



The following figs. 1026 to 1040, which 

 sometimes occur in flower-gardens, are 

 given, with their centres marked to faci- 

 litate their being laid down on the 



Figs. 1026. 



1027. 



1028. 



1029. 











< J 





Figs. 1030. 



1031. 



1032. 



