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And by the celebrity means that the main focus of the
Rays when 2 or a lot of Reflexions or Refrac-
tions could also be found.
Caf: 4. Let ACBD [in Fig. 7.] be any refrac-
ting Lens, ſpherically umbellate or cup-shaped or
Plane on either ſide, and let CD be its Axis
(that is that the Line that cuts each its Surfaces
perpendicularly, and paſſes through the Centers
of the Spheres,) and during this Axis created let
F and f be the Foci of the refracted Rays found as
above, once the incident Rays on each each the Lens area unit Parallel to the celebrity Axis; and upon the Diameter F f bifected in E, deſcribe a Circle.
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isaac newton book |
Suppoſe currently that any purpose letter be the main focus of
any incident Rays. Draw QE cutting the ſaid
Circle in Tandt, and in that take t g in ſuch
Proportion to East E or TE hath to TQ.
Let metal caustic the contrary method from t that TO
doth from T, and letter letter be the main focus of the
refracted Rays with none with none, pro-
vided the purpose letter be not ſo remote from the
Axis, nor the Lens field-grade officer broad on create any of
the Rays fall too obliquely on the refracting
Surfaces.
And by kind Operations could the reflective
or refracting Surfaces be found once the 2
Foci area unit given, and thereby a Lens be fashioned,
which that create the Rays flow towards or from what place you pleaſe.
So then the which means of this Axiom is, that
if Rays discover any Plane or Spherical Surface or Lens, and before their Incidence be due
or towards any purpose letter, they ſhall when Re-
flexion or Refraction be due or towards the
Point
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