Frontis planiciem, refilirent unde repulfi ,
1770
Tranfque duarum aliam r e d i, illxfique mearent
Frontem egreffuri , parvoque immittere poifcnt
Sic fefe tu bu lo , rerumque inferre figuras.
Sed quia cryjlalli fpeculo eft frons bina cavato ,
Bis revom it radios: non omnes ergo , necelfc e f t ,
1775
Contendant unum in pundtum, & licet utraque flexu
D iv e rfo cu rvare tu r, non talibus aufis
ProfedUim e ft, eadem loca adirent ut radiorum
P ro jed tx fpecies : totus vitarier error
Non poterat c e rte , non tali vincicr a r te .
1780
iEquatas porro triquetri diftendere frontes
Uflis erat v i t r i , & confternerc, perque polire ;
Quod quam difficile eft factu, durumque , profedto
Tcntantes novere, opera qui fcilicet iita
Saepius effufos fruftra indoluere labores.
1785
Proterea per^ to t trajectus luminis atque
T e n -
L I B E R O C T A V U S .
acp
o p p o fit a m re d to p r if m a t is a n g u
lo , q u x o b liq u it a s c u m fit m a
jo r r e q u ifit a p r o ra d io r u m refle
x io n e
in t o t u m , n u llu s
cx iis
xadiis p r o d i b a t c v it r o , fed o m n e s
ic f lc d t c b a n c u r ad fe c u n d a m fu p e r-
ficieni p r i o r i p e r p e n d ic u la r c m jp e r
ejuam t i a n f m i t c c b a n t u r fin e fen fi-
bili r e fr a d t io n e , ta n q u a m fi refle
xi fu ifle n e a b u n ic a lu p c r fic ie re
fle c te n te p la n a .
V itr a q u i d e m a d h ib e b a n t u r o b
d iffic u lt a t e m ita p o lie n d i m e ta l
la , u t fa t is m a g n a m ra d io ru m
p a rte m r c f l c d l c r e n t : v e r u m illud
ib i a c c i d i t i n c o m m o d u m , q u o d
id f p c c u l u m h a b e t b in a s fu p e r-
ficics re fle d te n te s , q u a r u m u tra-
ique f u a m e ffic it im a g in e m in fu o
f o c o , n c c v e r o ii fo c i a ccu ra te
c o e u n t , e t i a m fi b i n x fuperfieies
h a b e a n t c u r v a t u r a m e a n d e m .
Ha
b e tu r q u i d e m d iffe re n tia e x ig u a
c u r v a t u r a r u m , q u x in d ica t f o
c o ru m c o in c id e n t ia m fa lte m p r o
radiis , q u i in c id a n t p a ra lle li in te r
f c , & p r o x i m i a x i $ fed eft a d m o
dum d iffic ile ita fo r m a r e illas b i
nas f u p e r f i e i e s ,
uc
n o n h a b e a n t,
nifi illud ita e x i g u u m d i f e r i m e n .
D e in d e h a b e n t u r
te
a l i a i n c o m
m o d a plura : n a m i lla i m a g o v i
v i d i o r , q u x r e f l e f t i t u r a f e c u n
da fu p crficic , fit n o n p e r f o l a m
re flex io n em , fe d p e r i p f a m i n t e r
p o lita m b in is r e f r a d t i o n i b u s , a l
te ram in in p r c ftu > a l t e r a m
in.
e g r e f l u : in iis j a m h a b e t u r a l i
q u is e rro r d i v e r f x r e f r a n g i b i l i t a
tis : p r x t c r c a illa r a t i o f p h x r i c L
t a t u m , q u x in d a t a v i t r i c r a f l i -
t u d in e c o n ju n g it b i n a s i m a g i n e s ,
illa ipfa n ec c o r r i g i t
e r r o r e s fi-
g u r x f p h x r i c x , n c c e r r o r e s d i
v e r f x r c fr a n g ib ilic a tis . E a o m n i *
in c o m m o d a , e r r o r e s o m n e s , r a
tio n e m c o r r ig e n d i u n u m q u e m v i s
c x iis ,
te
q u a n t i t a t e m e o r u m ,
q u i rem an e n t ip fo c o r r e d l o , p e r -
lc c u tu s e g o fq m i n t e g r a d i f f e r -
t a t i o n c , q u x e ft p o f t r e m a i n t e t
q u in q u e Viennae i m p r e f l a s , q u a
ru m
te
fu p e riu s i n je d l a e f t m e n
tio . H x c
q u id e m
p e r t i n e n t a d
fp c c u lu m c a v u m ; in p r i f m a t c v e
ro o ccu rrit in g e n s f a n c d if f ic u lt a s
p o lien d i tres f u p e r f ie ie s p l a n a s ,
c u m
accuratum
p l a n u m a d m o d u m
