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Besides the Refractions hitherto described, there is a refraction of
another kind made in glass Island-glass, chor pellucid stone
found in Island, in the form of an easily p
to any of its not fusible or not ththe thIt has six plane
sides bounded thare
52′, & degr 8′ eat[It has eight solid angles two of This ch
another are thth
obtuse & two acute ones.]th
on has been
Hugenius in he Treatise De la Lumiere
ABFEHDCG represent the a piece of this glasse, [ABFE bounded with six parallelogram sides
its parallelogram base whose opposi obtuse angles at B & E
are 101 52 each & acute ones at A & F are 78
each & let ABCD, BCGF, GFEH & AEH be it four AB
[ABFE, BCD, CBFG, GFEH, HEAD & DCGH,] each of whose obtuse ch
angles all other angles each And let willthe
each of them thpl of those obtuse angles Bisect with the line
bisect the solid obtusethbisect
line CHthe angle one of the obtuse angles e
parallelogram BCKL & let this parallelogram be called the principal section
of this
If a beam of light fall perpendicularly upon any surface of this glass, this beam sh
that ch
glass eordina rules of Opticks & the other beam shall
start e
arrives
it shall
the e
oblique always ch
be refracted e
of refraction
This th
Bartholine book Treatise of light
written
a pth
sides
101° 52′ & their acute ones 68° 8′. And let three
of this obtuse angles lye about the solid angle
C & other three about the opposite solid angle
E the other six solid angles being composed of
And let the two biggest solid angles
principal solid angles. And che
first surface of the glass AB at e
ST shall divide it self into two beams TV & TX some of the rays in the beam ST
being refracted ac according to the known laws of Opticks & going in the beam TV
to the place V in the second && being there the sine of the refracti
on of these rays being to the sine of their incidence as 3 to 5. And the rest of the
rays in the beam ST being refracted according to another law & going in the
to another place X chIn ech
found.
Find the line N ch
between the two refracting surfaces as the sine of 6° 40′ is to e
the point V draw the lin upon the further surface of the glass draw he line VK
equal to the line N & parallel to the lines che
further surface chopposite
have to point X to ch
Ph. 4che
shall be again refracted
the beam ch
shall be again refracted
shall emerge out of the second surface in lines parallel to the first
incident beam ST.
Ph. 4 If two t
all the surfaces of the latter be parallel to all the corresponding surfaces of
the fchregularly regularly ech
usual manner in the first surface will be e
all the following surfaces. And
light by means of chregularly & the
after e
difference was in the rays before their first refraction f latter refractions
effect upon them in all the refractions.
Ph.
yet if their planes of perpendicular refraction be parallel to one another
the rays chregularly eregularly ech
the unusual manner in the first surface shall be e
suall manner in all the following surfaces.
Ph. 6. But if the planes of perpendicular refraction of the second glass be per at right angles the
first glass: the rays ch
through the first glass will all of them be refracted after the unusual manner
in passing through the second glass & the rays che
unusual manner in passing through the first
refracted after the unusual manner in passing through the second glass.
And therefore there are not two sorts of rays ch
after the usual manner & the other constantly tbut one & the same way is refracted sometimes regu in the usual & sometimes
in the unsual manner according to the position chhath
glass. Let every ray be conceived to be distinguished into four quadrants by two planes crossing one another perpendicularly to eee[ch] ch
not incline it to
And let the planes cheplane
parallel to the lines chplane surface parallelogram surface
of perpendicular refraction. For if an
upon any surface of this glass it shall divide at the point of incidech& as is represented in the annexed scheme where repre
sentsray perpendicularly ray perpendicularly e
face, e
the refracted divaricating from ethe angle in an angle usua
usual rules of Opticks, the other shall start aside & diaricate from the per
pendicular ray making with it an angle of 6° 40′, & e
perpendicular refraction & bending from the perpendicular towards the
sides of the glass ch
two begger solid angles. Let ST represent the beam incident
cularly on the surface ACTV TX the two be this beam at the point
of incidence T shall become divided into ch
shall go perpendicularly into edecline from e
perpendicularit & declining [who
whose in the pl whichethe
perpendicular refraction] &
refraction VTX towards thch
refracting plane surface AB the one of the solid angle C ch
one of the two biggest solid angles. let the two rays TV & TX fall upon
the further side of the glass EF at e
VX [& this line VX will be to e
the planes AB & EF as the tangent of 6 40 to e
the lines ch
Now let ST represent any e
first surface of the glass AB & let the point of incidence be T & this
beam shall ech
TV shal be refracted after the usual manner, the sine of incidence being
to the sine of refraction as five to three, & the Let this beame fall upon the further surface of the glass EF upon at the point V. & Draw the line
VX equal & parallel to eche
line VX lies from V & joyning TX this line TX shall be the other beam
of light carried by the unusual refraction from T to V.
When these two beams &c