66 Infinmental InfiruSkions. 



of equal Parts, fucK as we have detoibM ^ 

 and next thetn a Surveying Scale, fuch an one 

 as is alfo defcrib'd. 1 he Edge of this Inftru- 

 ment is to go thro' the Centers before fpoken 

 of, or any afiign'd Center on the Table. 



The life of the Plain Table. 



The Figure that is moil ufually produced, 

 on taking a Survey, is an irregular Polygon, 

 having no Side parallel to its Oppofite, nor 

 any Side or Angle, correfponding with any o- 

 ther Side or Angle, and is cail'd a Trapezium. 



Fig. 5. Let the irregular Polygon or Tra- 

 pezium A B C D, be a Field to be furvey'd. 



Place your Table horizontally, (or paral- 

 lel with the Earth) in any Part of the 

 Fcild, as at E^ fo that (landing there, you 

 can fee to each Angle A B C D^ having a 

 Sheet of clean Paper on your Table, and affii- 

 ming any Point thereon, imagine it E, in.E 

 £x a Pin, and placing the Edge of the Index 

 clofe thereto, dired your Sights to Angle A, 

 and then draw the occult Line E A^ do fo 

 by the other Angles, and draw E B, EC, and 

 E D. This being done, let two Perfons fet 

 out with the Chain from E towards A, the 

 Foremoft provided with fix, or more,fharpen'd 

 Sticks or Irons of a Foot long each, and let 

 them meafure E A thus. Caufe the foremoft 

 Perfon to go one Extent of the Chain 3 fuppofe 



to 



