1000000031

AB,

and f. iI

~or.,lld

upon ,he grea, mirrou r

are

thence reflelted conv.!rg;ng to

it:S

focus, whcrc lhcyform

.he: lower extn.mity A- of the iot"crtcd

j m a~c

1K,

(imilar

to ,he upper ."'I'emi,y

of ,he obj .:c'l

.10;

anJ ll:encc

paffing

che

fm~1I

mirrour

and

(;:)Jillg

upon

,hq are ,hence rcR:tted in ,he eonverging (I.,e

hO;

and going on through lhe ho le

of lhe grcal mirrou!'.

they

would mcc.t fomewhere abollt

fj,

aud form there

lhe

upper extremi:-y

of che ereél

ima(!c

ah.

fimila~

lhe

upper c""emi,y

of ,he objea

AH:

bu, by r alling

through lhe convex

glafs

in lheir way. theV meet and

~rors

faoner, as al

where

thal point of the creét ¡mage

i, formed .- T be like being underfiood of

, 11

,hofe rays

which .Bow from the intermediate points of lhe objrét

b: twcen

and

and enter lhe tube

T r ¡

al!

lile

iotcr–

medi,de poines

lhe

¡mage between

and

will be fo rm o

.ed; and the rays Piilling on

Crom

the ímage, through the

eye-glaCs S, and throu:h a fmall hole

in the end

the

'Jeff.:r tube

11,

they enter the eye

(which rees the image

meons of ,he eye_glafs) un¿er ,he I. rge angle

Cid,

and m.gnifi ed in leng!h under , hat angle from

' o

In ,he bd l reRcaing ,elefcop", ,he foeus of ,he fm.1I

mirrour is never coincident Wilh tne focus

111

of ,he great

one, \Vhere ,he 6rfl image

i, formed, bu,

Iinle be–

yond i, (wi ' h "rpea

,he eye) as at

n :

, he eonfequenee

of which

lS,

d Ial lhe

rays

of lhe

pcnciJs

will not

paral.

lel

after

relleélion

froOl

[he fmall mir rour, bUI

converge

torr.eet in poines

about

q,e,r;

where

they

would

{olm

a larger up'¡gh, image ,han

a6,

if ,he -gI, C,

\Vas no' in

Iheir way

and

this ¡maae might be viewed

me:ms of

a fingl. eye·gl. fs proFerly plaeed be,ween ,he image and

Ihe eye; bu[ ,hen ,he fie ld of view \VouJd be lefs, and

conf'quentl y no' fo pl..Cao'; fo r wbieh reafoD, ,he

gl af,

is fiiJl retained, 'o enlorge ,be fcope or area of

, he field.

T o find ,he magnifying power of ,hi, !elefcope, mul_

tiply ,be foca l J ifi ance of ,he grea, mirrour by ,he difi. nee

the fmall

mirroll r

from the image oe

lhe cye, and

multiply ,he foe.1 difiance

,h. fm.U mirrour by ,he

focal dirlo nce of ,he cye'glafs; ,hen, divide ,he produ'"

of ,be forme r muh iplieatio n by ,he proJ ua of ,be Jaller,

aod

(he quotient will

eXFrers

lhe ma:!nifying power.

W e

0131J

here fe' clown ,he dimenfions of one of MI'.

Shorl"

"fleé,in:; ,elefcope., as deferib, d in D r.

Smilh's

optics.

The focal di(hnee of ,he great mirrour 9 .6 ioches, i..

bread,h 2.3, ,he focal diflanee of [he Cmall mirrour 1.5,

i.. breod ,h 0 .6; ,he brc.d,h of , he boj. in ,he gre.. mir–

lour

o ,) ;

,he

difbmce bCl ween tbe fmaJJ mirrour

and

lhe

next

eye~glafs

14 ,2;

the ddh.oce

ltlW~en

rhe

t \VD

eye·

gl. Oc. 2.4; ,he focal dillance'Of ,he eye·elaf. n<x, ,he

melal. 3.8 ; aod ,I.e focal diOance of ,h.e eye-glaf. nex [

,he eye

l.'.

One

great

vanlage

the

re'fI~éljng

tc1crcope ¡s, rhat

will ,dmi, of an eye-glaf. of a mu<h ilionor focal di–

(lance than a rdral'bng

tdercope

will ;

and,

confcC)uent.

Jy.

will n·.agnify fo mucl¡ lhe

mc.le:

for lhc

rays

are

not coloured

rcfletlion from a

Cúr..Cíl\'e

mirranr,

br ground

ro:\

tr ile figure,

they are by

p~fJjng

lh rough

Convex

ghlrs,

I~t

ir b-::

cround

evn

tru~.

Thc adj ufling

Cert W

011

,ho

O"I(,:I, .uf

,h"

gre.~

'ube

fil$ ' hi' !elefeofes ,0 . 11 fon s cf eyes, bybringing ,he fm;tU

mirrour either ncarer

the eye, er nmoving ir f:l.rther;

which

me¡¡os,

the

rays are

made

div~rgc!

a Jiulc fJ r

fhon-fightc!d eyes,

or tO

converge

for thofe of a

long

f'ight.

T he nearer ao objea is

the

lele(cope,

th't

17I0fl

its

peneil. of " y,

\Viii

diverge before ,hcy fall upon ,he

great

mirrouT

and tl!ererore

they

will

be lhe Jem,ge r

meeting in

poinls

afeer refleétion ; ro thó\t

tbe.firU

image

will

formed at .. gre.,er dillanee froOl ,h; Jarge

mirrour, when the objcél:

oear the td cfcope,

than

when it is

very

remote. But as th is image muH be

formed

fa rther

from the

frnall

mirrou r than its

pririci~

pal focu s

chis

mirrour

mua be

always {ee

grealer'

ddhnce from lhe

large

one, in viewi ng oea r objeéts, lhan

in viewiog

remote

ones. And this is done

turning

the

fcrew

0 0

the omGde of Ihe lubc, unli1

the

{mall

m1r.

rour be fo adjufled, ,ha' ,he objea

(01'

ra,her its image)

' ppears perfea.

In looking ,hrollgh any telefeope ,owards an objec!}•.

never

fee lhe

oujeét

¡tCelf, but only that image of it

which is forrned oexc the eye in lhe lelefcope.

For

if a

mao holus his finger

a Hick.

belween

his

uare

eye and

.n objea, i,

\Viii

hide pa" (if no' ,he ", hole) of ,be'

objca

from his

vicw.

BUl if he des a fl ick acrafs

,he mou ,h of a ,d . Ceope before th. objea-glaf. , i, will

bide

pa" of ,he imaei nary objea he faw ,hrouj¡h ,he

telefcope

before, unJeCs

covers the who]c mouth of the,

,ube: for, all ,he err. a ",ill be, ' o make ,he objett ap–

pcar dimmcr, becaure it interccpts part

eh«! rays . .

Where~s,

if he

p~ltS

ooly a piece of

wire

acrors the in.

fide of lhe tub, uetwcen the eye.

glafs

and his ere, ir wili

hide par! of ,be objeél whieh he ,hink. he fees: whieh

proves,

th3t he {ces not lhe re.d

objt~q ,

bu(

íoS

image:.

1 'his is

al(o

cOIlr.rmeu

means of lhe fmall mirrour

L,_

in the

reReéling

tdefcape. which is made of opl ke

metaJ~

aDd flands direaly be,ween ,he 'ye and ,ho objea ' 9_

wards hích

the

tel(fcope

turnlo ;

and

wiIJ

lude lLe

whole objea from Ihe eye "

if ,he

' \va

¡¡I./fes

aod .

S are taken out of ,he ,ube.

O; Ihe

MULT'PL Y' NG GLA,..

T H

muhiply: ng

.gl~fs

i, mado by grindiog down ,he

round Gde

hi/¡

(No. 27 ) of. con\'e" gl. r•

•

, B,

imo.fe

–

.....1 Ra, Curfa« . , as

hh, bid, d/¡.

An ohjeél

l'Iill not

'ppear magnifi eJ when feen tI\l ough ,his gl. fs by tbe

eye al

bUl it wi lI

appcar

mult iplico

Il1to

as nliol ny dif.

{~rt:nr a~j e{ls

as rhe glafs contains

planc

fu rf"ces. Fur.

Gnee rays will Oow from ,he obj , a

' o al l

pH"

of ,he

(;1

a!"s ,

anei c:ach pl;me furface wlll n:fraél lhc(e

la)

lhe

~ye.

the (ame objeét wil1 appear

the eyt: in the di.

rcélion of rhe r ys which

t llter

it through each fu rface.

Thus, a

ray ,gill,

falllng

perpend:cnlad )'

on lhe miJ¿Je

furface,

will go lhrough lhe

glars

fhe

eye

\~'I:J!OU l

fl.f_

fering

aoy

rt:frall:ion; and will

lhereCore

(b~\\,

lhe ohju!t

in its true place at

whiln

a rí\y

Buwing [rem the

f.me

objoa , and f.lling obliquely on ,he pl;,ne (urfoce

v:ill be refraéled in lhe

d,rct.'llún

br ,

b)' paffiñg

tillO·

the ,glafs

and

upon

Jeaving

it,

wi lJ go on to rhe

c-) ('

rhe di rt!aion

~H ;

which will

caure

lhe

(,lIa(

at-j~ét

C to

lIrpc~r

alfo

E, in the

dirct.'liul1

the

ray

J/~,

fI (.Ju.

cc:d::1 tL\! ¡:r,ht Ene

l /rll .

Andtht:

r~ y

((f,

fiu\',:1

::. f¡ ol\l

' 1!c