( ) 
The firft Sedion contains an Explanation of the funda- 
mental Principle of this Art, widi the Definitions of the 
Terms, and four Theorems. The undamental Principle 
of this Art, is, th c the Reprefentation of any Point is a 
Point on the Picture where it is cut by a Line drawn 
from the original Point really placed where it ought to 
feem to be, to the place of the Spcdarors Eye : and con- 
fequently, the Representation of any Line is thc:!ntcrfe- 
dion of the Pidure with a Surface radde by drawing 
Lines from the place of the ipedator s Eye, to the feverai 
Points of the original Line to be reprefenced, really placed 
where it ought to feem to be. For tbefe Tines which 
come from the feverai Points of the original Objedro be 
placed in its proper Situation, to the Spfcdators Eye, are 
a-s To many vifuai Rays which make due Objed tbnfible. 
-When a Right Line is continued in infinitum, the Vi- 
fualRay becomes at lad parallel to ir, and an Objed of 
any given bignels, if-it goes (fill further and further off 
on thatLine, will at 1 aft item rovanilhV and at that time 
the place of its Reprefentation on the Pidure is the Point 
where the Ray parallel to the original Line cuts the Pi- 
dure. 1 For thisreafon our Author has thougnt it proper 
t6 dalE that Point rhe JJtyifjhfr-g -Point of fuch . an original 
Line (and confequently'of all' others^ parallel to it (Def.y.) 
And for the fame Reafcon he calls that Line on the 
Pidure a Fanijhing Line ( ,)efi b ) which is produced by 
the fnterfedion of the Pidure with a lane palling thro’ 
the Spedatpr’s Eye parallel to an original Tiaoe. There 
are ten Definitions in all, but thele are the principal. 
And in our Author s Method thefe Vanifhing Points and 
Vanifhing Lines are of great uie for the Reprefentarioo of 
any Line paffing through its vanilhing Point. (Prop, i.) 
Having found theRdprelentation of one Poinr itt any Line, 
by any Method whacfoever. he finds the Reprefentation of 
the whole Line by its vanifhing Point, which he fhews an 
eafy 
