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 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 59 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.
The SCIENTIFIC AMERICAN BOY OR The Camp at Willow Clump Island
By A. RUSSELL BOND
NEW YORK
MUNN & CO., Publishers
1906
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