I Dc Orbita Caffsniarta. t)r Gregory. 
El X quo Cdeberriraus Hof». Ci»gini'^ ift JraSafy de Ori- 
^ gine Progrejjii Aflrononti£^ Curvam quandam pro 
Planetje Orbita Aftronorois pfopoTuit, & do ipfius Curvae 
mtara, & de Gravitatis lege ad earn percurrendam re- 
quifita , varie mukuroque ab pud^tis difputatum eft. 
Mihi etiam de eadem deriub cdgitatiti cum diverfse ejus 
fpecics, turn & hamm propri^fatesi *^}JiqU3S nqndurn fet'is 
perfpefe ocGUrrebantii fj^s Iqfif j^vjHter.^onjtj^erey & 
publice coniraunicare volcp, quibuj hvijofmodi contem- 
plationes non injacund^e yidebuntur. 
Satis notum eft iftius Orbjr^ banc cfle naturam. Si a 
datisduobus punftfef ,& 6j?l <JW curvae ptjpftun? H 
ducantur ttOix F H, C H 5 reft^gulqin Tub F I^, G H 
aequale eft datO' / 
fpatio; Redta F G D n 
hinc inde produfta 
denec curvse oc- 
currat 5 oftendit 
Vertices A &B5 &i^ 
A B eft Axis prin- 
cipalis 5 mediumque 
inter vertices pun- 
&\xm C eft figura^ 
Centrum 5 & DE, 
per Cad A BTjOrmalis, Axis minor 5 punftaque F & G Foci. 
In hac figura fi axis minor excedat diftantiam foco- 
rum, Curva figuram terminsns eft ubique verfus centrum 
cava, qualis vulgo habetur. Si, manente axe principal!, 
diftantja focorum minuatur, augebitur axis mipor^vqui la- 
raen minor manet axe EllipGs eodem axe principali, iif- 
demque focis defcript^e s donee tandem, coeuntibos fo- 
cis^ ille evadat sequalis ax! majori, & figura i^hmt in 
Circulum. Si vero, e contra, diftantia focorum aogea- 
tur j minuetur axis minor, fietqiic cequalis dict^ diftantia, 
cum hxc eft ad axem principalem ficut unita^^ ad medium 
proportionalem inter unitatem ^ tcrnariuia Si 
