44- 



Mifcellama Curiofa. 



to be formed which, for Diftin&ions Sake} 

 is called the Plain of Projection ^ and the Pole 

 oppofite to the Eye, the remoter Pole. 



2. That the Pole, when proje&ed, falls in 

 the Center of the Plain of Projection. 



3. That Jtt great Circles interfering eacho- 

 ther in the Eye-Point, will, when projected, 

 become right Lines, interfering each other in 

 the Center or Pole of Projedion, inafmuch as 

 they all lye in the fame Plain with the Eye. 



4. That the Poles of every fuch Circle will 

 be found in the Circumference of the Plain of 

 Projedion, at 90 Degrees diftance from the 

 Circles Interfedion. 



5. That the Lines flowing from the Eye, to 

 any other Circle whatfoever, form a Conical 

 Superficies. 



And in order to enquire into their Nature 

 and Properties when projeded, it is neceffary 

 to premife the two following Lemma's. 



If an upright Cone be cut with a Plain, pa- 

 rallel to the Bafe, the Section made in the Super- 

 ficies of the Cone will be the Circumference of 

 a Circle, whofe Center will be found in the 

 . right Line, conneding the Vertex of the Cone, 

 and Center of its Bafe. 



Whence, and from the general Definition, it 

 follows. 



Cml 1. That all fmall Circles parallel to the 

 Plain of Projedion, will become Circles in the 



Projedion. 



noiTjtfjoin to 



2. That 



