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Figure 6.25 Figure 6.26

Parallel-line
Rectangular Prism. In order to find the development of the rectangular prism in Fig. 6.27, the
back face, B’-C’-C-B, is supposed to be placed in contact with some plane, then the prism turned on
the edge C’-C until the side C’-D’-D-C is in contact with the same plane, and this process continued
until all four faces have been placed on the same plane. Rectangles B’-C’-D’-A’ and B-C-D-A are
for the top and bottom respectively. The development then is the exact size and shape of a covering
for the prism. If a rectangular hole is cut through the prism, the openings in the front and back faces
will be shown in the development in the centers of the two broad faces.
The development of a right prism, then, consists of as many rectangles joined together as the
prism has sides, these rectangles being the exact size of the faces of the prism, and in addition two
polygons the exact size of the bases. It will be found helpful in developing a solid to number or
letter all of the corners on the projections, then designate each face when developed in the same
way as in the figure.

Figure 6.27 Development of Rectangular Prism.

Circular Cylinder. If a circular cylinder is to be developed, or rolled upon a plane, the
elements, being parallel, will appear as parallel lines, and the base line being perpendicular to the
elements, will appear as a straight line of length equal to the circumference of the base. The base of
the cylinder in Fig. 6.28 is divided into twelve equal parts, I, II, III, etc., and commencing at point I
on the development, the twelve equal spaces are laid off along the straight line, giving the total
width.

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