[Illustration: Fig. 56 Brass Fastener.]

[Illustration: Fig. 57. The Mouthpiece.]

Another device we made in preparation for the expedition was a megaphone.
A sheet of light cardboard 30 inches square was procured. At the center of
one edge a pin was stuck into the cardboard, then a piece of stout thread
was looped over the pin and the two ends were knotted together just 5
inches from the pin. Another knot was a also made 29 inches from the pin.
Now, with a pencil hooked into the loop, and resting first against the
inner knot and then against the outer one, two arcs were drawn on the
paper, one of 5-inch radius and the other of 29-inch radius. A line was
now drawn from the pin to the point where the longer arc met the right
hand edge of the paper, and a dotted line was drawn from the pin to a
point 1-1/2 inches from the edge at the other end of the arc. From a point
1 inch to the left of the pin we then drew a line to the left end of the
arc. With a scissors we cut the cardboard along the arcs and straight
lines, all but the dotted line, leaving a piece of the shape shown in Fig.
55. This piece was rolled into a cone with the right edge lapped over the
left edge and lying against the dotted line. In this position it was held
by means of several brass fasteners of the kind shown in Fig. 56.

A mouthpiece was formed out of a block of wood in which a large hole had
been drilled. The block was then cut away until the walls were quite thin.
The hole was reamed out at the top, as shown in Fig. 57, and the outer
surface was tapered so that the small end of the megaphone would fit
snugly on it.

We planned to reach our camping grounds by way of the canal, and had