To Assemble the Box,
first nail sides A to the edges of back B (Fig. 580), then to the edges of front B. Notice that the back piece comes even with the tops of the sides, and that the front piece comes even with the bottoms-of the sides. With pieces A and B nailed together, fasten ends C between them. These pieces will hold the mirrors in position.
The opening in the back of the periscope box is the one that you look into, the one in the front is turned toward the object you wish to view. As the upper mirror will be exposed it must be protected from snowballs by a piece of screen wire tacked over the opening (F, Fig. 574). A frame of narrow wooden strips (Fig. 575) tacked over the edges of the wire will hold the wire in place.
Handles nailed to the lower portion of the box (G, Fig. 576) will complete the periscope.
Paint the Periscope Box white so that it will be invisible from a distance, against the snow background.