1000000031

t he o"

i.ea

.nd C"1Iing.obliqucly on the pllOe Curface

dk,

",,11 be refr. {ted

(b~;

palling through tho glaCs and

lca'ving

to~ ihe cy~

which wili c<lufe the

f.me

obje~

appear at

io the direélion

Hím.-If

the gl.f. be turoed round the lioe

glH,

as an axis, the

objeol C..will keep its place, becauCe the Curface

bid

is oot

Temoved'; b"t al1 the other objeéls \Vil1 Ceem to go round

r..

b:cauCe the oblique plane., 00 which the rays

ah td

fall, will go rouod by the turoiog of the glafs.

Oí/he

CAMERA OBSCURA.

T~.E

camera o¡¡Cura

i. made by a convex-glaf,

CD,

(No. 28.) plaeed in a hole of a

wiodo~-fl\ulter.

Tboo!

if the room be darkeoed fo, as no IIght eao eQter¡but

what comes through the glafs, the piélures of all the 'ob–

j eas (as fields, trees, buildings, men, eattle, &e.) on tne

Qudide,

will

be (hewn

an iovcrted order.

a white

p'per pl."ed at

io the foeu. of Ihe glaC,; aod will

afford a mufr

~eautiful

ánd perfeél pieee of perCpeaive or

'Jaodfc"ape of whatever is before tbe glaf" efpeeially if

.lhe fun fhio., upon the objeas.

If the eo"vex ¡¡lafs

be plaeed ir... tube io the lide

.of a fquare box, within whieh is the planc mirrour

Er,

rec1irling baekwards in ao angle of

degrec. from the

perpendicular

Jq,

the pencils of rays 1l0wiog froro the

outward opjeas, and pafliog.throogh the

coov~x

¡¡Ia(s tO

..he plane mir.r4ur;·

i.ll

!I¡e' reReéled upward. from it, aod

",ect io points; as

1·

and

(at the (ame difrahee tbat

,hey would have met at

aod

c:.

if the nlirrour had

not been in tne way,) aod will form the afórefaid images

'on ao oiled paper /tretehe,! horizontally in the d;-reaion

J[(;

on whieh pap"', the out-line, of the image. may

pe e."ly drawo witb

blaek·lead peneil; aod then eo–

l'ied 00 a cleao fheer, aod coloured by art, as the objea.

th~mfelves

aro by nature.-':Io tpis machine, it i, ufual

to place aplane glafs, uDpolifhed, in rbe horizontal

Ii_

.luatíon

I K,

which glafs

reccíves

the

images of

the

out:'

,ward objeéls; and their outlines ruay be traced upoo it

.bya bbck-Iead penéil.

N. B.

The lube in

whi~h .

the convex glars

fixed, mull be made

t O

draw out, . or pufh jn, fo as to

~dju/l

the di/lanee of tbat

gl.fs

from the plane mirrour,

jo proponian to the diftaoce pf"lhe

oUlward

objeéls;

whích rhe operatar dac" unlil he fces their images di.

llinaly pointed on the horizontal glafs at

IK.

The forming a horizontal image, as

IK,

ofao uprighl

objel'f

A.'D,

depends upoo the angles of ineideote ohbe

.ray' upon Ihe plane mirrour

EF,

being equal to their ao–

&1..

of refleaion from it. For, if a perpeodicular be

fuppofed to be drawo to Ih.e furfaee' of Iheplaoe mirrour

where the ray

AoCe

fall, upon it, thal ray will be

refleaed upward, iD an equal angle with t he 'other lide of

..he perpendie.lar, in lhc line

edI.

Agaio, if a perpen–

dicular be drawn to the mirrour from the poiol

¡;

where

.lhe ray

A b!

fall. upon il, Ihat .ay will be relleéled in an e–

qual angle from the other lide of the perpendicular, in

·the

lineíhI.

And if a perpendicular be drawn from tbe

:point

where the

/leg

falls upon the mirro"r, that

fray

will be refleéled io an equal angle from the other fide

-9f the r erpeodieular, io the line

gi l.

So that alJ Ihe

..:ays

<he peoeil

ahe,

Jlowing from tbe upper extrcmi·

ty ortl,e objoa

AB,

.nd polling through lhe

con~cx

glaf.

cn,

the plano mirrour

E F,

wilJ be relleéled from ,he

min our,

and

meee at

where they will form the: ex.

tremity

of the im. !:"

1K,

fi,milar to the extremity

Ihe objeél

AB.

The like is 10 be .nd..llood of the

peneil

qrl ,

Howing fro,!, the lower eXlremity of the ob_

jeél

AB,

a~d

'meeting

(after reBeélion frcm the

plane mirrour)'the rays form the extremity

of the i–

mage, fimilar to tlie ."tremit y

of the objeél: and

of a1l rhe pencils rhat flow from rhe

iDtermediate

points

of tbe

o~jea

lO the mirrour, through the coovex gl.f••

0(.

It'e

OPERA·GLAS5,

a coovex glars, of a fhort focal di(lance, be plaeed

near rhe plaoe miCfour in lhe cnd of a (bort lube, and a

coooex glaCs he plaeed iD a .hole iD the lide of the

tube, fo a. the image may be formed betweeo !he

lafr . menlioned conyex glafs .od the plaoe mirrour;

the image being viewed through Ihis glaf., will .ppear

magoi6ed -In chis manner, the

D,tra~gIQ.ifu

are con·

/lruaed; with whieh a gentlemao may look at any la–

dy al a di!laoee iD <he compaDy, aod the lady' koow

Dotbiog of it.

Oí Ihe

Commoo .LooK'NG-GLASS.

'TffE image of aoy objeél tha! i. plaeed before •

pI.ne

mirrour appears aS big to Ihe eye .s the ohjeél itfelE.;

and i. ereél, di/linél, aDd feemiogly as far behiDa the

mirrour, as che objeét

before

ic: and that parc of the

mirrour, whieh reHeéls rbe i",age of Ihe objeél to the eye

(the eye being fuppoCed equ.lIy di/lan! from the

gl.Cs

with

,he objeél) is jufr half as loog aod half as brpad as the

objeél itfelf. L el

(No

29,)'

be an objeél plaeed

before the reHeéling

furf.ce

ghi

of Ihe plaio mirrour

CD;

antl ley/the eye he at

L el

be a ray of lighl

How–

iog from Ibe 10p

of lhe objeél aod falling upon the

mirrour at

aqd,

he a perpeodleular lO, Ihe fur–

face of the mirrour at

the ráy

will he ,eHetled from

the mirreur to the

eye at

making an

aogle

'tllho

e–

qual lO Ihe aogle

Ahm :

then will Ihe top of the image

appear to the eye, in the direélioo of tbe refleéled ray

produeed to

where the right line

ApE,

from the

top of the objeél, .euts Ihe right line

ohE.

Let

.Dí.

ray of lighl proeeediog from the foo! of rhe ob–

jeét at

the mirrour

at ;;

and

perpendicular

to che mirrour from

the

poiot

where the

ray

falls

upon il: tbis ray will be r<lleéled in the linc!

io,

making

aogle

nio,

eqúal

Jbe angle

Bil/,

with (hat per–

pendicular) and Il1tering 'che eye at

then wiU the

foot

of the image arpear in the diretlion of the

relleaed ray

,í,

prouueed lo

\Vhere the right line

CUts

the refleéled ray produced io

AII the o–

ther ray! that flow from the intermediate: points of

the objea

AB,

and fall upon the ' mirrour hetw«n

and

wilJ

be refleéled to the eye

and aB the in–

termediate poin!; o("lhe image

El"

will

appear.to

the eye

in.the direélion or there relleéled rays produeed . But

al1 lhe rays thac 1l0w from the .objel!, and fall upon thc

mirrour above

will be refldl:ed back above the eye at

.; and all the

r.ys

that flow from the objeél, and f,1I

upon Ihe mirrour beJow

wül

he reflcéled baek bdolV

the