thread running to each corner and a nail for ballast tied where the four threads are knotted together, can be sent up by this messenger, released, and allowed to float down from a great height. Paper gliders sent up this way will do many "stunts" before they reach ground. Fold a flimsy paper napkin in such a way as to hold a bunch of confetti with a pin thru only three or four thicknesses of the napkin. This can be tied to the keel and the pin withdrawn by the release and fall of a nail, and, behold, a shower of confetti! Be sure the falling nail will do no injury where it strikes.

A light, frail model like this will require considerable time and patience to make and adjust so that it will work. Make the hull and posts from a stick about 13" long. Bore the 3/16" holes for the mast and keel, the former a little to the left (port, a sailor would say) of the center and 2-1/2" from the bow, the latter in the center 2" from the stern. Make the wheels of the ends of spools by sawing them off just where the straight portion begins, and glueing them together on a hard dowel. Very accurately find their centers and drill holes for 1" brads which form their axles. Drive these into the post so that the wheels run very freely. Do not nail the posts to the hull till the wire parts have been put in place. Make three staples of pins and drive them in the bottom of the hull so that a fine wire will just slide thru them easily.

Three are used so that the wire will always be held straight. Next make the two eyes which hold the kite-string under the wheels. Coiled around once and a half, the coils must be separated enough to allow the string to slip between. The safety of the model, swinging violently high in the air, depends upon these eyes. They can be driven thru small, tight holes and bent on the under side to make them secure. They must be just high enough to allow the string to run free. The forward one is elongated because the kite-string slants upward so much. Bend the 4" wire trigger three times around a brad driven in a piece of wood for convenience. To handle wire readily for such work as this, two pliers will be found useful. Saw a notch in the bow just wide enough for this coil. Now glue and nail the posts in position.

[Ill.u.s.tration: KITE-STRING SAILBOAT

PLATE 16]

Make the mast, all the spars, in fact, smaller at the outer end. Rig it completely before gluing the mast in place. Be sure that the booms will swing _over_ the forward wheel, so as not to interfere with its easy running. The sails should be of light cloth. The booms and the gaffs (see Plate 30 for names of parts) must swing freely on the mast, so as to fold together when the trigger is released. For the main-sheets, use thread tied with a long loop to slip over the fine wire part of the trigger. A cork 1-1/4" in diameter, slit to the center, can be put on the kite-string far enough from the kite to be safe from any entangling.

On the keel, fasten ballast enough (about 1 oz.) to make the sailboat ride upright.

THE HYGROSCOPE OR WEATHER COTTAGE--PLATE 17.

This model serves to indicate the humidity (dampness) of the air. It consists of the house, turntable, and figures, the turntable being suspended on a violin string. The violin string absorbs moisture from the air and untwists, thus causing the man to come out; when the air become dry the string twists tighter, thus causing the woman to come out. The model should be placed out doors but not exposed to rain or sun.

The arches of the doorways may be made with a big bit (1-3/8") or a scroll saw. If a bit is used, bore a hole for the spur first, lest it split the board. While boring hold the board vertically in the vise. The portion cut off between the doorways can be sawed with the tip of the back-saw if the board is laid flat on the bench-hook. The slanting lines at the top, also, can be sawed while held down on the bench-hook. After the front, back and sides are made, nail the back to the sides, but screw the front. When this is done, put the house in the vise in an upright position and plane the tops of the sides slanting. Notice that one roof is wider than the other. Nail the narrower one first, with the grain running from front to back. Do not drive nails into the front but nail it securely at the back and side. Letting the plane rest on the other side of the house, plane the upper edge of this roof slanting, so that the other roof will fit. Nail this in place; set all nails; and plane the upper edge of this roof slanting, letting the plane rest on the first roof. Two brads may now be driven near the center of the ridge-pole to hold the roofs together. After making the floor, place the house in position on it (1/4" from back, 1/2" from ends) and draw a line around the house. Remove the house; drive three brads straight down thru the floor; pull them out and start them from the under side in the same holes; then put the house in place again and drive the brads home. Put in more brads to hold the house securely.

To make the chimney, saw a notch 3/16" deep in the end of a 3/4" square stick. If it fits on the roof, bore a 5/16" hole thru its center, and saw the chimney off 3/4" long. Glue it 3/8" from the front end of the roof. When dry, bore the hole thru the roof. The chimney top with the dowel attached to it below is made to revolve so that the Hygroscope may be adjusted. To make the chimney top, bore a 1/4" hole into the end of a 1/2" dowel; then saw it off 1/2" and glue in the upper dowel. Make the turntable somewhat round at each end. In the center of it, glue and nail the lower dowel. Next, paint the house if desired. The violin string is glued and wedged into holes in the upper and lower dowels so that the turntable will swing 3/16" above the floor.

The man and woman may be made of cardboard, wood, clay, chalk or plaster of Paris; or they can be bought at a toy store. Painted in bright colors and sh.e.l.lacked, or varnished, they look well. They can be made to balance on the turntable by adding a piece of lead. Of course, neither they nor the turntable should touch any part of the house as they swing around.

[Ill.u.s.tration: HYGROSCOPE

OR

WEATHER COTTAGE

PLATE 17]

ELECTROPHORUS--PLATE 18.

The electrophorus consists of two parts, a pan filled with a resinous mixture, and a cover which has been completely covered with tinfoil.

Under favorable conditions, a spark of electricity 1/2" long can be obtained from this electrophorus. The favorable conditions are these: The air should be dry; both parts of the electrophorus should be warm, dry, and clean; and the tinfoil and rosin should be perfectly flat, so as to come in close contact with each other.

Make the pan and its sides as shown in Plate 18. Glue and nail the sides in place and round their upper edges well with sandpaper. To make the resinous mixture, melt a half teacup of rosin with two teaspoons of turpentine and about the same of paraffin in a rather deep dish, and pour the mixture into the pan. As all these materials are inflammable, perhaps the safest place to melt them is in the oven. After the pan is cold, test the surface of the rosin to see that it is flat every way. If it is not flat, sandpaper the high parts slowly with coa.r.s.e sandpaper.

When making the cover, observe the directions on page 20, then round the edge to a good half-circle. Test the cover also to see that it is flat, especially on its under side, for to get good sparks, the tinfoil and rosin must come just as close together as possible. Cut two circles of tinfoil 4-1/2" in diameter. Smooth them carefully on a piece of paper, spread glue thinly on the cover, lay the tinfoil on the glue, and smooth it with the fingers. Press the edges as smooth as possible because electricity escapes easily from sharp corners. Cover the larger open s.p.a.ces with bits of tinfoil. Hard rubber (ebonite), being a non-conductor of electricity, makes the best handle. A piece of an old rubber comb or a fountain pen can be used for this purpose.

To get a spark of electricity, rub the rosin with soft leather, fur, or woolen; place the cover on it; touch the top of the cover with the finger (to remove the negative electricity); lift the cover by the top of the handle; bring the edge of the cover near a finger, or other conductor, and a spark will fly off with a snap. It is a miniature flash of lightning. Some books on electricity describe many other experiments which can be tried.

[Ill.u.s.tration: ELECTROPHORUS

PLATE 18]

WATERWHEEL--PLATE 19.

This waterwheel is designed to be placed in a flowing stream. A longer trough might well lead the water into this one so as to get greater speed.

Make the trough first, being careful to make a good fit where the sides nail to the bottom. Nail the top 5" from the end where the wheel is placed. The upper corners of the axle blocks are to be cut off 1". The center of the 5/16" hole for the axle is 7/8" from the lower edge. When nailing the axle blocks in place, put a dowel or lead pencil thru the holes to help in nailing the blocks exactly opposite each other.

After sawing a board for the wheel 4-1/4" square, draw the diagonals and diameters (cornerwise and crosswise, that means) to divide it into eight parts. Draw a 4" circle for the wheel and a 3-1/4" circle to mark the depth of the notches for the paddles. Shape the wheel. (See page 20 for directions.) Test it with the trysquare to keep the edge square with the flat surface. Bore a 1/4" hole in the center with the greatest care, or the wheel will wobble sidewise. The notches are cut with the back-saw alone. One-eighth of an inch to one side of the eight lines across the circle, saw straight down to the inner circle. Be careful to hold the saw square with the wheel. After this saw cut is made, measure the width of the notch by holding the edge of a paddle so as just to cover the saw cut, and, with a knife point make a dot at the other side of the paddle.

Holding the trysquare against one side of the wheel and the inner edge of its blade over the dot, score a knife line across the edge of the wheel. Then saw straight down again _inside_ this knife line. Saw cornerwise a few times and the wood will be removed sufficiently. The notches may better be too small than too large, for the paddles can be planed thinner to fit. Clean the wheel with the plane before nailing the paddles. All these paddles except one can be nailed with the wheel held in a corner of the vise. To nail that one, put a thin board upright in the vise and rest the wheel on its top. All nails should be started in the paddles, not in the wheel.

[Ill.u.s.tration: WATERWHEEL

PLATE 19]

Make the axle of hard wood. Push it thru the axle blocks and wheel, and lock it to the wheel with a brad, Plate 19. The axle is made long so that a pulley (spool) can be put on and a belt (string) run from this to other pulleys. A leather washer outside each axle block keeps the wheel in the center. If the work has been carefully done, the paddles will not strike; if they do strike, they must be pared off.

WATER MOTOR--PLATE 20.

This motor is a waterwheel designed for an ordinary hose faucet. Under a stream of water no bigger than a large needle, it will fairly buzz. If the wheel does not run exactly true on the axle, the motor will need legs screwed on the outside of the box.

Make the wheel of soft wood just as true as possible. (See page 20.) For the axle a small bra.s.s rod or a large knitting needle may be used. In the center of the wheel, drill a hole smaller than the axle so as to make a tight fit. Be very careful to bore this hole straight. Force the axle thru the wheel, and if the wheel wobbles only slightly drive wooden wedges beside the axle to force it square with the wheel. If it wobbles too much, plug the hole and try boring again. Resting the axle on the jaws of the vise, revolve the wheel rapidly to see where it is out of true, and patiently pare it down. The flat side of the wheel which wobbles only a little can be planed off. The strip of screen wire netting should now be tacked on the wheel. It is long enough to go twice around the wheel, and should be tacked on with a dozen small tacks.

For suggestions about the pulley see page 56.

Prepare a block of soft wood for the coupling. From its bottom, gage a line marking the height of the dovetails in which the blocks C and D fit 3/8" on each side. Saw these dovetails 3/16" deep, and pare them slanting with a chisel. In the center of the top, bore a 1" hole, 3/4"

deep; continue the hole thru the block with a 1/2" bit. Bore holes 3/8"

from the top, 1/2" from the ends for the two 1-1/2" screws which are shown in the small drawing, Plate 20. Gage and saw out the left-hand half of the block (as shown in the plate) as deep as the 1" hole. The purpose of this is to permit a squeezing fit on the threads of the faucet. When first trying it on the faucet, squeeze it hard with a hand-screw to jamb the threads into the wood; after that, the screws can be put in and the coupling attached at pleasure. A 1/4" hole is bored in the 1/2" dowel, which serves as a nozzle, until the spur just shows.

Without allowing the bit to bore any farther, turn it around enough so that the spur will wear the wood and thus make a tapering hole as shown in the sectional drawings.

Prepare the sides, ends, and top of the box, the three blocks, the key wedge, and the two stops. The wedge should be 1/16" wider at one end than the other and should fit the dovetail. Block C should fit the other. In the top piece, bore a 3/4" hole in the middle 1-1/4" from the end. This hole is larger than the nozzle to allow for adjustments. All these parts must now be thoroly soaked with paraffin. Melt the paraffin, apply it with a brush to all surfaces, and drive it in with heat. During the process, the nozzle can be made fast in the coupling, using plenty of paraffin to make it water tight. See that the tiny outlet occupies the best position for directing the water onto the wheel. After the nozzle is cold again, the outlet should be carefully worked out again with the warm point of a big hat-pin or wire, filed to a good point.

Put the parts together as follows: Nail one side (the right in the plate) to the ends; screw the other side to ends; nail top to ends and first side only; nail block B to A; then A to the top. Unscrew the side and bore holes in the center of the sides for the axle. Make them fit nicely, then soak them with paraffin. Put the wheel, the side, the pulley, and the stops in place. Put the coupling in such position that the nozzle comes over the rim of the wheel and nail block C. After putting two or three soft leather washers in the coupling screw it to the faucet, lock it to the motor, and the motor is ready.

Better bearings for the axle can be made of two pieces of solder screwed to the inside of the sides. If these are made, the holes in the sides should be large enough not to touch the axle. The wheel and pulley can be locked to a bra.s.s axle by boring a hole thru the axle with a drill made of a needle. (See Drills, page 11.)

[Ill.u.s.tration: WATER MOTOR

PLATE 20]