DOI Page / Citation link:
https://doi.org/10.11588/diglit.19949#0049
CIRCULAR OBJECTS.
45
Let a o b be the vertical diameter of the wheel;—then
according to the preceding rules, draw the right lines
c a d,f o e, and, i b g. Draw d e g parallel to a b, and
at a distance from it equal to the apparent width of half
the diameter (which in this position will appear some-
what less than the real semi-diameter); draw cfi parallel
to a b but still less distant from the centre o than d g is,
because o g is more remote.
Produce o b to x, making b x equal to o b. Draw o i,
o g ; then lines drawn, from x to e and/, will cut o g and
o i in two points, through which the curve must be
described, and touching the straight lines at the points
e b, and/. The wheel being an overshot wheel, the lower
portion is not visible. Should, however, the entire wheel
be seen, the lower points for the curve will be on the
diagonals immediately beneath the others, as shown in
the figure.
The student may have recourse to similar means for
drawing the circular arches of a stone bridge. It seldom,
however, happens that a bridge of this kind is a desirable
object in a landscape, unless perhaps in the distance,
or in the middle distance, of the picture. Arches, how-
ever, are frequently found in association with the most
romantic features of nature; such, for instance, as that
near Aberyswith, called the Devil's Bridge, and many
others.
45
Let a o b be the vertical diameter of the wheel;—then
according to the preceding rules, draw the right lines
c a d,f o e, and, i b g. Draw d e g parallel to a b, and
at a distance from it equal to the apparent width of half
the diameter (which in this position will appear some-
what less than the real semi-diameter); draw cfi parallel
to a b but still less distant from the centre o than d g is,
because o g is more remote.
Produce o b to x, making b x equal to o b. Draw o i,
o g ; then lines drawn, from x to e and/, will cut o g and
o i in two points, through which the curve must be
described, and touching the straight lines at the points
e b, and/. The wheel being an overshot wheel, the lower
portion is not visible. Should, however, the entire wheel
be seen, the lower points for the curve will be on the
diagonals immediately beneath the others, as shown in
the figure.
The student may have recourse to similar means for
drawing the circular arches of a stone bridge. It seldom,
however, happens that a bridge of this kind is a desirable
object in a landscape, unless perhaps in the distance,
or in the middle distance, of the picture. Arches, how-
ever, are frequently found in association with the most
romantic features of nature; such, for instance, as that
near Aberyswith, called the Devil's Bridge, and many
others.