Chap. I of Gardening. 



There are feveral Inftruments made ufe of fof' tradng 

 upon the Ground but the moft ordinary are the Grapho- 

 metre, or Semi-circle, and the Square^ or perfed Circle. 



The Semi-circle is ufually made of Brafs, and fliouid 

 have from fix to twelve or fifteen Inches Diameter : The 

 larger it is, the better for Ufe. The Semi^circle is divided 

 into 1 80 Degrees, which is half the complete Circle into 3 60 

 and go Degrees, which is the quarter of the Circle, ferves 

 to form a Right Angle, and raife a Square. There are two 

 Rulers or Indexes, one immoveable, which ferves as a Bafe i 

 and the other moveable, v/hich the French call xhtAlhidadCy 

 which turning about upon a Center-Pin in the Middle, ferves 

 to take the Openings of Angles. Thefe two Rulers are ter- 

 minated by Sights (landing up at Right Angles, which di- 

 red and guide the Vifual Ray. The Middle of this Inftru- 

 ment is generally furniilied with the Sea Compafs, for lay- 

 ing down the Points thereof upon a Plan. The Semi-circle 

 i^ mounted upon a Knee-joint, or Ball, for the Conveniency 

 of turning it every way, having a Screw to it, which makes 

 die Joint go ftiffer, or flacker, at Pleafure. 'Tis fet upon 

 the Ground by means of three Legs or Staves tipt with Iron, . 

 which are put into as many Sockets beloW the Ball, and 

 thruft into the Ground, as Occafion requires* See the Fi- . 

 gure. 



The lejfer Sort of 

 Semi-circles are fixed 

 upon a Bail with no 

 more than one Soc- 

 ket^and confequently 

 require but. one Leg, 

 which is placed ex- 

 actly upon any Point 

 affign'd intheGround. 

 But the greater Semi- 

 circles that ftand up- 

 on three Legs, as it 

 would be difficult to 

 fet them precifely over a given Point, have a Plummet which 

 han^s down, and lliews when the Center is juft over the ^ 

 Place in C^ieftion. 



M The 



