To the under side of the 8-ft. plank bolt a piece of timber 2 by 4 by 22 in. in front of the rudder block, and to this cross piece and the 6-ft. plank nail 8-in. boards to make the platform.

The spar should be 9 ft. long and 2-1/2 in. in diameter at the base, tapering to 1-1/2 in. at the top.  This fits in the square hole, Fig. 1.  The horn should be 5-1/2 ft. long, 2 by 3 in. at the butt and 1 in. at the end.

Figure 4 gives the shape and dimensions of the mainsail which can be made of muslin.  Run the seam on a machine, put a stout cord in the hem and make loops at the corners.

Figure 6 shows the way of rigging the gaff to the spar.  Figure 7 shows the method of crotching the main boom and Fig. 8 a reef point knot, which may come in handy in heavy winds.

Make your runners as long as possible, and if a blacksmith will make an iron or steel runner for you, so much the better will be your boat.

** Electric Rat Exterminator [358]

Some time ago we were troubled by numerous large rats around the shop, particularly in a storehouse about 100 ft. distant, where they often did considerable damage.  One of the boys thought he would try a plan of electrical extermination, and in order to carry out his plan he picked up an old zinc floor plate that had been used under a stove and mounted a wooden disk 6 in. in diameter in the center.  On this disk he placed a small tin pan about 6 in. in diameter, being careful that none of the fastening nails made an electrical connection between the zinc plate and the tin pan.

This apparatus was placed on the floor of the warehouse where it was plainly visible from a window in the shop where we worked and a wire was run from the pan and another from the zinc plate through the intervening yard and into the shop.  A good sized induction coil was through connected with these wires and about six dry batteries were used to run the induction coil whenever a push button was manipulated.

It is quite evident that when a rat put its two fore feet on the edge of the pan in order to eat the mush which it contained, that an electrical connection would be made through the body of the rat, and when we pushed the button up in the shop the rat would be thrown

[Illustration:  Electric Rat Trap]

2 or 3 ft. in the air and let out a terrific squeak.  The arrangement proved quite too effective, for after a week the rats all departed and the boys all regretted that their fun was at an end.  —­Contributed by John D. Adams, Phoenix, Ariz.

** How to Make a Simple Fire Alarm [359]

A fire alarm which is both inexpensive and simple in construction is shown in the illustration.  Its parts are as follows: 

A, small piece of wood; B, block of wood nailed to A; S S. two pieces of sheet brass about 1/4 in. wide, bent into a hook at each end; P, P, binding-posts fastening the springs S S, to block B, so that they come in contact at C. W is a piece of wax crayon just long enough to break the contact at C when inserted as shown in the illustration.