EXVERIMENTA ET EXFLICATIONES. 19$ 



axem fecant , et proinde ad conftituendum focum extra 

 vitnim inutiles fiint. Hmc vt determinetur in re&a AG 

 locus , extra quem nulli radii amplius ad focum extra 

 vitrum conftituendum concurrunt , fiat FGzro , vnde @li- 

 eitur j— - Wua a V rr) ; ex qua formula facilis conftriwftio ip<- 

 fius y deducitur , fub qno FG euanefcit \ nam centro C, 

 radio CG , defcribatur femicirculus TXG , in hunc ex 

 pundto G applicetur re&a GXrz: radio conuexkatis vitri 

 CM , eritque ducta per pundum X re&a XZ parallela 

 axi TH , is ipfe radius, qui in pundum G refleetetur. 



Corollarlum 2» 



Quoniam finus PDM generaliter eft — =i-- , inuenie- 

 tur finus YGZ fubftituecdo pro y valorem modo inuen- 

 tum ipfius GY , qui finus adeoque erit m-^l- . Vt ve- 

 ro radii reflexo-refradti cadaut extra fhpeniciem planam, 

 angulus PDM inaior effe debet angulo YGZ, quare 

 ^~P- > r -^r- , aut zay—^ay^r*— 2.0*1* , aut denique 



* a £r r i>j , hoc eft GY^>y \ vnde patet , omnes radi- 

 os in liiperficiem AY circumcirca incidentes non concur- 

 reie ad focum extra punclum G conftituendum ; confe- 

 quenter fpatium latitudinis AY annulare in plana fuperfi- 

 cie vitri obtegi poffe plano radiis imperuio , manente ni- 

 hilo minus foco in F inuariato. 



Corollarium 3. 



Du&o radio CA, erit AG~ V(rr— ad) , quare AYz= 

 V(/" 2 — a*)— GY • itaque vt fpatium hoc AY , ad focura 

 producendum inutile , euanefcat , debet effe V(rr—aa)zz 



Bb GY 3 



