opticks book(10)

 [ 8 ]

a lot of when the celebrity manner, if ACBD (in

Fig. three ] reprefent a Glafs ſpherically gibbous on each each (uſually referred to as a Lens, ſuch as could be a could be a, or Spectacle glaſs, or AN Object glaſs of a Teleſcope) and or not it's needed to understand however lightweight falling upon it from any lucid purpose Q

ſhall be refracted, let Q M repreſent a Ray

falling upon any purpose M of its firſt ſpherical

Surface ACB, and by building a Perpendicular

to the Glaſs at the purpose M, notice the firſt re-

fracted Ray M N by the Proportion of the

Sines seventeen to eleven.

Let that Ray in going out of the Glaſs be incident upon N, and so notice

the ſecond refracted Ray weight unit by the Proporti-

on of the Sines eleven to seventeen.

And when the ſame manner might the Refraction be found once the

Lens is gibbous on one ſide and Plane or Con-

cave on the opposite, or bowl-shaped on each each.

A X. VI.

Homogeneal Rays that ensue feveral

Points of any Object, and fall sheer or almoſt sheer on any reflective or refract- ing Plane or ſpherical Surface, ſhall afterward diverge from ſo several alternative Points, or be Parallel to ſo several alternative Lines, or converge to ſo several alternative Points, either accurately or with none with none.

and therefore the and therefore the can happen, if the

Rays be mirrored or refracted ſucceſſively by 2 or 3 or additional Plane or Spherical Surfaces.

the purpose from that Rays diverge or to

which they converge could also be referred to as their Focus.

and therefore the focus of the incident Rays being gi-

ven, that of the mirrored or refracted ones might

be

[ 10 ]

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.

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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