Gravesande, Willem Jacob 's
,
An essay on perspective
Text
Text Image
Image
XML
Thumbnail overview
Document information
None
Concordance
Notes
Handwritten
Figures
Content
Thumbnails
Table of handwritten notes
<
1 - 3
[out of range]
>
<
1 - 3
[out of range]
>
page
|<
<
(79)
of 237
>
>|
<
echo
version
="
1.0RC
">
<
text
xml:lang
="
en
"
type
="
free
">
<
div
xml:id
="
echoid-div285
"
type
="
section
"
level
="
1
"
n
="
151
">
<
p
>
<
s
xml:id
="
echoid-s1854
"
xml:space
="
preserve
">
<
pb
o
="
79
"
file
="
0141
"
n
="
163
"
rhead
="
on PERSPECTIVE.
"/>
dicular is on one Side or other of the perſpective
<
lb
/>
Plane with reſpect to the Eye. </
s
>
<
s
xml:id
="
echoid-s1855
"
xml:space
="
preserve
">And the Line
<
lb
/>
paſſing through the Extremities of the ſaid Pa-
<
lb
/>
rallels, will determine the Repreſentation ſought,
<
lb
/>
by its interſecting the Line T a, as is evident by
<
lb
/>
what is demonſtrated.</
s
>
<
s
xml:id
="
echoid-s1856
"
xml:space
="
preserve
"/>
</
p
>
</
div
>
<
div
xml:id
="
echoid-div286
"
type
="
section
"
level
="
1
"
n
="
152
">
<
head
xml:id
="
echoid-head158
"
xml:space
="
preserve
">
<
emph
style
="
sc
">Method</
emph
>
III.</
head
>
<
p
style
="
it
">
<
s
xml:id
="
echoid-s1857
"
xml:space
="
preserve
">97. </
s
>
<
s
xml:id
="
echoid-s1858
"
xml:space
="
preserve
">To find the Repreſentation of ſeveral Perpen-
<
lb
/>
diculars equal in Length to ſome one, whoſe Per-
<
lb
/>
ſpective is already drawn.</
s
>
<
s
xml:id
="
echoid-s1859
"
xml:space
="
preserve
"/>
</
p
>
<
p
>
<
s
xml:id
="
echoid-s1860
"
xml:space
="
preserve
">Let H I, be the Perſpective of a Perpendicular
<
lb
/>
<
note
position
="
right
"
xlink:label
="
note-0141-01
"
xlink:href
="
note-0141-01a
"
xml:space
="
preserve
">Fig. 52.</
note
>
to the Geometrical or Perſpective Plane. </
s
>
<
s
xml:id
="
echoid-s1861
"
xml:space
="
preserve
">Now
<
lb
/>
about the accidental Point T, as a Center, and
<
lb
/>
with the Radius T H, deſcribe the circular Arc
<
lb
/>
H G, whoſe Chord let be equal to H I, and draw
<
lb
/>
the indefinite Line TGC, and let a and b, re-
<
lb
/>
preſent the Feet of the Perpendiculars, whoſe
<
lb
/>
Repreſentations are requir’d.</
s
>
<
s
xml:id
="
echoid-s1862
"
xml:space
="
preserve
"/>
</
p
>
</
div
>
<
div
xml:id
="
echoid-div288
"
type
="
section
"
level
="
1
"
n
="
153
">
<
head
xml:id
="
echoid-head159
"
xml:space
="
preserve
">
<
emph
style
="
sc
">Operation</
emph
>
.</
head
>
<
p
>
<
s
xml:id
="
echoid-s1863
"
xml:space
="
preserve
">Deſcribe about the Center T, the Arcs b F E,
<
lb
/>
and a DC, paſſing through the Points a and b, and
<
lb
/>
draw the Lines T b and T a; </
s
>
<
s
xml:id
="
echoid-s1864
"
xml:space
="
preserve
">in each of which
<
lb
/>
aſſume b L equal to E F, and a X equal to C D;
<
lb
/>
</
s
>
<
s
xml:id
="
echoid-s1865
"
xml:space
="
preserve
">and the ſought Repreſentations will be had.</
s
>
<
s
xml:id
="
echoid-s1866
"
xml:space
="
preserve
"/>
</
p
>
</
div
>
<
div
xml:id
="
echoid-div289
"
type
="
section
"
level
="
1
"
n
="
154
">
<
head
xml:id
="
echoid-head160
"
xml:space
="
preserve
">
<
emph
style
="
sc
">Demonstration</
emph
>
.</
head
>
<
p
>
<
s
xml:id
="
echoid-s1867
"
xml:space
="
preserve
">If H I, and a X repreſent Perpendiculars of
<
lb
/>
the ſame Length, it follows from the Demon-
<
lb
/>
ſtration of the precedent Method, that I H is to
<
lb
/>
H T, and a X to a T as the Difference of the
<
lb
/>
ſaid Perpendiculars, and Height of the Eye, </
s
>
</
p
>
</
div
>
</
text
>
</
echo
>