[ 946 ] 
tranfponendo r.AD xKL — / . K D x A L = AD 
x KD x LE x (— £■ + kl)* 
Ponatur jam L A = A, LK=K, radius fphaerse 
DL — a, adeoque A D = A -f- G et D K = k — a . 
His in noviflima aequatione fcriptis, erit r K x A -f- a 
— ;'AxK^« = A + tf xK — axLEx (^ + £), 
__ i A d 
unde tranfponendo et dividendo, K = - — — — - * 
r , — r . A — r a 
A -f- <i X K — a X L E 
X 
(s + e)- 
i — r . A — r a 
Jam ft radius incidens A G fuerit axi A D vi- 
ciniflimus, evanefcet L E, adeoque et terminus 
a -j- a x iv ‘j x L h x f ]_ Quare in hoc calu 
id eft, diftantia foci geometric! 
K = 
r . A — r a 
i A a 
r. A 
r a 
ipfi A conjugati a vertice L, erit = 
i Aa 
unde 
* — r . A — r a 
aberratio radii refradti G K ab hoc foco erit 
A + a X K — a X L E 
x (iq iV fumendo a foco 
i — r . A — r a ' ^ ^ ' 
contra diredionem curfus radiorum. Quoniam vero 
aberratio ilia femper eft valde parva, erit 
valor prope verus diftantiae L K live K, adeoque in 
expreflione aberrationis fine fenfibili errore pro K 
ufurpari poteft. Sit itaque diftantia L B foci geomc- 
j A ci 
trici B a vertice fuperficiei L, ftve == — : = B, 
i — y , A 
r a 
critque 
