1 6 Geometrical InflrtiBions 



Before we proceed to fhew tlie laying out Polygonal V'c 

 gurcs or Figures of five, fix, feven, or eight Sides, &C' 

 it will be neceflary vvre Ihould lay down the Methods of 

 flriking out circular or crooked Figures, which are, genei:- 

 alJy fpeaking, the Balis of all Polygonal Superficies. 



PROPOSITION V. 



To find the Center of a Circle, the Center of which is losi^, or 

 any itker Way required. 



Place at Difcretion the three Points ABC upon the 

 Out-Line of the Circumfer.eiice, and from the Points A B; 

 make the Se6i:ions E and F ; draw the right Lines E F, 

 from the Points R C ; make the Sections G H ; then draw 

 the right Line G H, from the Interfeflion and Center T, 

 and from the Interval I A, and from this Center in the 

 Middle of F 1 G, you may ftrike your Circle. Hd, Fig. 

 I . and 2. 



TraBice on the Ground. Fig. G, 



This is the fame as on the Pa^er, as does plainly appear 



from Fig. 5. ..;f;^;>^..:T,.o.'::'Mi':-:A 



PROPOSITION' VI. 

 To jtrike A Circle on Ptipcr. 



Keep the Foot of your Compaifcs in A, and trace the o- 

 ther Point round, it will make the Circle B C D E. Fig. 

 '^ 



TraEltce on the Gronnd. Fig. 6. 



The fame is perform'd by a Line, as was before taught 

 of the CompafTes. f^id. Fig. 6. 



PROPOSITION VII. 

 A Spiral Liney tho" it is not properly a Superficies, yet, fis it 



m^ikes by its Volnta Jor^iething like it, I teach the Method 



of Tfiaki'ig it in this Place, 



Suppofe you would divide the Line L into eight Parts, 

 divide it firft into two Parts B I ; after that into four Parts 

 of each Side B C, E G, I ; divide alfo B C into two, e- 

 qually in A, and from the Point A, draw the Semi-circles 

 B C, D E, FG, H I ; and from the Point B, draw C 

 D, E F, G H, I L, and that dial] be the Spiral Line re- 

 quir'd.. Vid. 4. and 7. 



On the Ground, Fig. 7. 

 The Pra£]^ice is the fame. 



