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obf^rve one of the Images, viz. the Fixt H D to be congruent 
to the fubjacent line B whil'ft the otherj namely the Mo- 
vcab^i^E I 3 tendeth towards But^if afterwards the Eye 
bepofit^dinO, the fame Objed, I mean the line B will 
not only be reprefented double by the images K and L 
G5 but alfo the Movable Image G L be congruent tothe in- 
feriourline B Q while the Fixed F K is not foj but tends 
towards N. 
After the Author hath given us thefe Experiments^he urn 
dertaketh to determine the ^antity of the Refractions io this 
Double-refrading Body; and haveing firft given th^ Demons 
^r^^/<?/? of the Method of Meafuring the Refraftion ofGlafi^ 
(omitted by Des-Cartes m his D!Optricl{Sy) he finds, after fe- 
vera! TryalSj the Angle bf Fnclination to the Angle of Re- 
fradlion in this ///^W-Chryftal to be as 5 to 
But this Ingenious Perfon doth not (top here, but proceeds 
to demonjlrate all the recited Experiments, obferving firft^ 
that the Teachers of the Corpufcularian Hypothefis, which in- 
cludeth that of F/g«re/ and Pores y could not wifh for a fitter 
Body, than this^ to alTert their Dodrine ^ in regard that it 
appears, firft^that this Double-refradting Body hath its Pores 
according to the D^S;;^y of the fideSj and parallel therereto 5 
fince it m^iy be obfcrv'd, that, according to this difpofition 
of the fides^ it is brokenj and the parts fever'd fi'om one ano- 
ther ^ and that one of the Images, namely the MIoveabkjpaf- 
feth through them. Next, befides thefe Poresj lying accor- 
ding to the Parallelifme of the fides, it hath^others^ fuch as 
Glafs, Water, and right Chryftals have^ through which the 
Fixt Image is tranfmitted» 
But palling by thefe, our Author affbmeth tvjo Hypotkefes^ 
asneceffary tohis defign, not fo much found out by Ratioci- 
nation^ as by the above related Experiments* The one is^ 
that there are fome Lines, by which the Rays pafs through 
the tranfparent Bod y un- refraded ^ which Lines though they 
have been held to be Perpendicular in Diaphanous Bodies 
hitherto known, yet this Author requireth not, that they 
fhould be always fuppofed fuchj fince they may perhaps ia 
M pi fome 
