^&^: 



PRACTICAL DIAGRAMS. 



line e /, taking o as the center, fig. 12. To set off a walk 

 perpendicular to the corner of a wall. — Carry out the lines 

 a and h 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 bisect each other, draw 

 a line to the corner of the wall, which line will be the center 

 of the walk, fig. 13. 



The annexed diagram, fig. 14, illustrates an instrument 

 very useful in laying out mathematical figures. It consists 

 of an upright pole two 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, eight, 

 ten, or more feet in length, marked in feet 

 and inches. Upon this rod there is a mova- 

 ble iron slide, with an iron sharp-pointed 

 stud. The two-feet pole being placed in the 

 center, or point from which the figure is to 

 be described, the slide is moved along the 

 rod to the proper distance, 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 

 to be formed. 



Another useful instrument is a pair of wooden compasses shod with iron, the legs 

 of which are five 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 perforated at 

 every three inches, and furnished with a screw-pin to keep the legs of the instrument 

 distended to the extent required. The quadrant rod is placed exactly in the middle 

 of the leg of the instrument, so that when the leg is moved, for example, three inches 

 on the quadrant, it gives six inches at the points of the compasses ; if moved one 

 foot on the quadrant, it gives two feet, and so on, being always double the former 

 ext(int. 



The following figs., 15 to 29, which sometimes occur in flower-gardens, are given, 

 with their centers marked to facilitate their being laid down on the ground. They 

 are from a German work entitled HmidhihliothecJc far Gartner, by Ligiler of Berlin. 



