142 



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. 





V 



u-z" 



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. 



A 



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. 



m—s^ep 



"-fiubber 



To open c/rcu/T-- 



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. 



