the bottom view of the piece (position
3) becomes the top view in the drawing. A second disadvantage is that if
we desire to put in dotted lines, to show how one view is derived from
the other, and denote corresponding parts, then these dotted lines must
be drawn across the face of the drawing, making it less distinct; thus
the dotted lines connecting stem E in position 1 to E in position 3,
pass across the faces of both A and B of position 1.

[Illustration: Fig. 145.]

[Illustration: Fig. 146.]

In a large drawing, or one composed of many members or parts, it would,
therefore, be out of the question to mark in the dotted lines. A
further disadvantage in a large drawing is that it is necessary to go
from one side of the drawing to the other to see the construction of the
same part.

[Illustration: Fig. 147.]

To obviate these difficulties, a modern method is to suppose the piece,
instead of rolling upon the paper, to be lifted from it, turned around
to present the required view, and then moved upwards on the paper for a
top view, sideways for a side view, and below for a bottom view. Thus
the three views of the piece in Figure 145 would be as in Figure 146,
where position 2 is obtained by supposing the piece to be lifted from
position 1, the bottom face turned uppermost, and the piece moved down
the paper to position 2, which is a bottom view of the piece, and the
bottom view in the drawing. Similarly, if the piece be lifted from
position 1, and the top face in that figure is turned uppermost, and the
piece is then slid upwards on the paper, view 3 is obtained, being a top
view of the piece as it lies in position 1, and the top view in the
drawing. Now suppose we require to find the shape of member B, then in
Figure 145 we require to look at the top of position 1, and then down
below to position 2.

[Illustration: Fig. 148.]

But in Figure 146 we have the side view and end view both together,
while the dotted lines do not require to cross the face of the side
view. Now suppose we take a similar piece, and suppose its end faces,
as F, G, to have holes in them, which require to be shown in both views,
and under the one system the drawing would, if the dotted lines were
drawn across, appear as in Figure 147, whereas under the other system
the drawing would appear as in Figure 148. And it follows that in cases
where it is necessary to draw dotted lines from one view to the other,
it is best to adopt the new syste