1000000031

~"tjon

p"rl',,~h·.

nlay be \lndernood by ruppofing the

'pantagon

AB[)~¡:

( l'late

CKLIII.

fig.

l .)

\Vere to be re

:prereotec! by tlio rule. of pedpe,'!iv<. oa the traofporent

.plane VP plared p« pendieularly on th.· borizootal plane

·HR ;

dottcd lioes are im.gioed to paC. Crom tb. eye C

••<h point of the pent_gon,

CA,

€B,

CO.

&c.

whicl, are fuppo(cd in their

patr.~e

through .he pl.o. PV.o

:Je¡vc thcir traces ..or vdligia in the points

(J.b,d.

&.c.

oi1lhc:

plon., aod

lhere~y

t0cldioeate lhe peol. gon

aM,{;

whieh,

·a.

it flrike, lhe eye I>y .he Carne rayo lha< lhe original penta–

:flon AB D EF do.,. will be a true perCpeltive repre Cento–

ció" of

it.

The bufineCs of

perrpel!i~e.

lherefore, j, to lay down

'&c3mcl1;cal

rul~,

ror finding the

poi

a,b,d,~J,

upon the

pl.ne

; aod heoee alfo we Ha"e a moehanieal mechad of

odelioeating any objel1 v"y

oceurAl.ly

•

Pe. fpeltive i, , i.her employed In reprefeoiiog the iehno,

'graphii:S or grounq plot. of objeéls; or the Ceenographi...

or rrprrCentatio". of lhe

o~j<éh

themfelves.

befMe ,'. e

gi~e.

any ex.mple. of ei ther. it will be pro,

p'::r to ( y.plain fome tcchanical

lunn

ln regard to perfpec.

....e

in geoera l : aod firJl. lh. horizoot.1 lioe i. ,h., fup_

paCed " 0 be (lrawo parallel la .he horizoo through the eye

ó;f

lhe fpcflator; or rathcr

is a line which

fepar~tcs

the

'-h e.v", from the eirth. 30d which limits lhe fight. Thu••

A,B.

(i6id.

fig.

2.)

ac< two pillan bdow lhe horizontal

lioe CD.

reafoo the lioe i. c1e<ated above them; in

:tig.

3. •

hey are faid to be equal wi. h ·i., .nd in fig.

raired ahove

it.

Thu~.

according to the difierent points in

vie·... lhe "bjeéts will be ei.her higher or lower Ihan .he ho–

rizootal

li~e.

The poiot of fight A

(ibid.

fig .

)

is lhat

'Which makcs the centrical

ray

on the horizontal

Jlne

ob:

e>r, it

t~e

point where all the ' other vifual

ray~

'\Jnite.

Th~

poio" of dUlaoee. C.C. are poio" (el off in

.he horizon...1 lioe

equal diflaoees on eaeh fide of lhe

'P0int of fighl A; and iD the fame figure SS rcpreCen..

..he bare lioe. or fundamen.a l lioe: EE i. the abridgment

:of .he {qu... :' of "'hieh

.0,0.

are the fiae.; F.F. ihe d.a_

-g00,1 lioe.; whieh go la lhe pointo of diChnee C .C. Ac–

cidental poiots are lhoCe where lhe objeéts eoel :' lhefe may

l1e can nrgligendy; b.caufe ncilher drawn to .he POiOI or

6ghl, nOr tO lhofe of di llanee, b'ut meetiog eaeh other io the

h.oriz"ntal~line.

For example, rwo pieces of lquare timo

. ber

aod H

(i.id

6g. 6 .) make the poio.. r,I.I.l on

•he horizootal 1I0e : but)to OOl

the poiol o'f fi ghl K.·oor

to, the poin" of dillanc< .C.C ;

t~eCe

afeidental points ferve

Jikewife forcafemenu, daors. windows, tables, chairs,

&c.

'The point of direfl. "iew, or of the

fronl,l

is when we have

the objeél direélly

b~forc

us ; iD whieh caCe.

fhe\V. only

tbe fo«fide; aod. if below lhe harizan. a linle of the tOp ;

but nOlhiog of lhe fides. uolef. lhe

obje~

he pnlygooous.

Thu•• he plan ASCD .

(ihid.

Sg. 7.) is all in frolll. aod

if it were raiCed we fhould oot Cee aoy lhiog of the fideo

or CD, bu. 'ooly .he ·{roo. AD: the reaCoo is. thal the

poio. of vie.... E beiog direltly oppofite thereto, eaufe. a di–

m:nution on cach fide;

'which

however is oo)y to

l1nder·

/lood where ao e1eva.ioo i. the objelt; fot if il be a .pldo.

it Chew. the whole,

ABCO.

The poiot of oblique view. i. when we Cee

.0·

objel!·. –

(¡de of u'. and as

were

2f1ant,

or with the corntr of Ihe

.eye

Ihe

eye. howeV'er. being all the while oppofitc to

lile:

10ial of fighl; in which eafe, w. fce lhe objc{l laterally.

~Dd

'ii ¡refeoll lO us

wo fideo or fac....

F..

ror inn.nee, if the point of fight be

iI'

{ibM.

6g.

8.)

.he obje{l

G l-flK

wdl "ppear "h"'3rt, . od Ih"", tlVO

C.e..

aod

CH.

io \Vhieh

e.Ce

it will be a fide pOiOI.

We Ih,lI no",

s.ve

fome exo mple••. (,y whi .h il \Villa?:

.pear, that the "'hole pr.

{l.ee

of perfpeltive i. boilt upoo .he

{ounda"on olreacly

.I..

d down, Thu•• to ¡¡od the ptrCpee,

tive

appearar.ee

01 • triaogle ABC

(ii id.

lig.

9.)

betwecn

the eye . nd .he trioogle dra\V .he Jioe O E, ",h,eh i. eaUetl

the fundamental Jine

{rom

dr¡w

reprerenting

the

pcrp'eodielllor diClaoce of the eye above the fuodameotall[oe.

be il wha. il

w.lI

; .od .hrough

V dr-a."

at righ.

a o~l

.. to

V . HK

parallel too

V E:

lheo wdl d.e plaoe

PHKE

re:

.preCem lhe traoCrareOl plaoe 00 whieh .he perCpe{live re–

prert otation is to be

rndde.

N ext

ñild the perfpfftive

poio" of ,he aogle. of lhe tri,nnl•• lel Call perpeodieulara

B 3.

from the aogles lO lhe fundamental OE :

fel off lhefe perpendieulars upon the fuad.mental oppofilf

lo the poinl 01 d.clancc

C; froOl

l . 2.

<Iraw lioes la the princrpal poiot

and Crom lbe poiots

B....

d C . on lhe ¡uodamentallioe, draw the righl lines

"RK. CX.

tO the poinl of di.Oaoee

whieh i. {o caUed.

becaaCe the Cpeélator ougl\l ·to bo fa far removed from the

fi gure or

p.i~tiog.

as it is diOanl from lhe priocipal poiot

,The points

ti,

!J,

and ' . where tbe vifualliocs V

V 3

ioterCelt the lioes of difl.aee

AK. BK.-

CK. will be the

aogular poio" Df the aagle

tbe true reprefeotatioD of

AHC .

drl1'UJ a

jqUQ"

pa.""unl

p,rjptflio,.

See 6g.

lO,

aod

t . of Pla.e CXLIII.

SuppoC~

your picee of pa,e",.ot to·eo061l or 64 pie.eto

o{ matble.

e.eh

a foot Cquare.

Y.ur

6r11 buGod. i•• '0

draw ao iehoographie.1 phn or ground·plot of it. whicb i.

.hus per{ormed. H.vioe toade ao exaél Cquare of the

r.z~

you ioteod your plon, divide lhe baCe and horizoo iOlo eight

t-quaJ'parts; and {rom

é,rery'divdjon

in the baCe to

oppo.

lite'point in the horizon, rule perpendicular )

lo.es

: 1hco di.

vide the fides iOlo .he

C.me

oumber, ruliDg patallel liod a–

eroCe from poiot to póiot:

wil! yoúr pavemeo. be

di,id.~

inlo 64 fquare' feet; beeáufe the eight feet io leng.h. mulo

liplied by the Came io bread.h. give the number of Cqua,e feet

or piee.. of marble eootained in the "hale: theo rule-dia–

gonals (rom corner to

c0r:,ner¡

aod

thU3

will

Jour ,rouod.

plotappear as io fig .

10.

Now• •0.I.y this in. perfpeltive. draw another fquare to

your io,eoded fize, .od divide, lbe baCe lioe AS ' iOlO eight

equal p.m. as befare; theo fix your point of Gghl C in

.he middle of the bonzon DE. aod from lbe fame poiol rule

Iines '0 evrry divifioo io ,he baCe AS; after whieh, rule

diagonal lioe. {rom O la B , aDd from E la A. aoC",erable

to ,hoCe io the grouod ·plot. aod your Cquare will be reduccd

to lhe triaogle ABC; .heo from lbe poiot F. where lhe

di.gooal OH ioterCeéls the line AC.

.he oppofi« inter–

feétioo

where .he di.gooal EA erotres .he liDe

cn.

rule

a parallel lioe. \Vhieh i, .he

abrid~meDt

of .be fquare.

Theo ,hrough lhe poin.. where lhe diagonaJo <:rofs .he.

ren Of the liDes whien go' from lhe bafe la ,he poiot

figh••

rule parallel Iioca. and yóur fquare pavemeDt will be laid i.

perfpe61i.e. as io 6g.

11.

r o

tlimini/"

[quau

v¡"uud

hy ID'

tingle

O. Seo' Flat•

CXLIJI.

fig.••

lIavioJ: defcribcd tbe plaDCABeD. d,aw a IiDe to toueh