4^0 DE TELESCOPIIS 



ita vt fit 



^-l + ^^^zi^^-^et^zr^ fiiic xizi 



tum vero ponatur 



P = -|-,-q=-l- et R = -.J- 



atqiic ob miiltiplicatinncm dntam — w, debcbit effc 

 P QR zr — w, ficqiie liitcraruni P, Q^ ct K vna de- 

 bet effe negatiua ; practtrca ponatur 



^ = Bbi y — Cc 



hincque porro 



^ = -^ et e =: -1:^ 



1 -t- B 1 -f- C 



ita vt fit 



^ n: 23 i ; r r= (T t' et j- rr i 

 ex his autem littcris viciflim erit 



L _« . ^. — Ba. J . — BCas 



'^ F 1 ^ — Fq'> — P Q.R 



vnde interualla lentium crunt 



I-lIir:aCi-^)i Ii - III = - ^^ ( i - ^) ; 



lIl-IV-|l?(i--k). 



§. T4. Quod fi iam femidiamctri aperturarum 

 ternarum lentium ftatuantur : 



m q i n:' r et ti" / erit 

 femidiameter campi adpareiuis cp n — ^-^ — • •, 



tum vcro erit 



