Page:Popular Science Monthly Volume 88.djvu/170

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The runner irons are not perfectly flat on the bearing edge, but have about %" rocker curve. Fig. 5 shows how the runners are pivoted on the riding bolt. The top of the rudder post is square. Drill a sm^ll hole at top of the rudder

���Fig. 4. Construction of the runners

post for a cotter pin so that the tiller will not slip off while sailing. A good rudder post can be made from an old bicycle fork. Put an iron plate and washers under the boat so the rudder will turn easily.

For the runner plank use a 2" x 8" plank 8' long. The side braces are 2" x 4" and the bowsprit is a 2" x 6" re- enforced by a 1" board on each side, Fig. 2. The cockpit is 5' long and for the flooring use 1" matched boards. Give all woodwork a few coats of paint.

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��Fig. 5. Method of piv- oting the runners on the riding bolt

��How to Draw an Ellipse

DRAW the major and minor axes. With a radius equal to one-half of the major axis from the extremity the minor axis describe an arc cutting the major axis. At the two points where the major axis is cut, place tacks or pins. Then place the pencil on the end of either axis and pass a thread around the point of it and the two tacks. Draw the thread tight and tie it. Describe the eclipse. If it is desired to use ink a pen is substituted for the pencil.

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��Popular Science Monthly

A Doorstep Burglar Alarm

N alarm ringing arrangement which will announce the intrusion of un- desirable visitors can be installed on a door step, and be completely concealed. One of the steps is removed and re- placed with a hinge at the back. Be- neath the step a spring contact is placed and connected with batteries and a bell. A rubber cushion is tacked along the edge of the board upon which the step rests. The weight of the body on the step will press the contacts to- gether, closing the circuit. The resilien- cy of the rubber cushion will press the step back in place when the weight is re- moved.

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To c/ojed c/rcu/f-^:^^'- -^-vr=-

��The contaqt is made and the alarm

bell rung by the pressure of any

weight, even that of a child

A Simple Laboratory Burner

AG O O D burner for the laboratory which can be eas- ily constructed is shown in the sketch, which is self-explanatory. The standard was made from %'' pipe fittings, and the valve was obtained from an old kitchen gas range.

Waterproofing Shoes

THE soles of shoes or boots may be made waterproof, and also made to wear much longer, by giving them three coats of varnish, allowing each coat to soak into the leather well before applying another.

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