Chapter XXVII: Part II: Construction (4)

A lamp is fastened to each corner of the frame on top, as shown in Fig. 4, with a piece of wire wrapped once around the screw ferrule and the extending ends held with staples. The wire used should be heavily insulated or, if it is of iron, a rubber tube slipped over it. A piece of tin, or bright metal, is placed beneath each globe for a reflector.

A glass plate was used to cover the box, and a lawn spray of the fountain type was placed on the glass. The globes, as they light beneath the spray, illuminate the top and the light follows the streams of water so that they appear like streams of light. Each light is turned on in succession as the frame revolves within the box, and by using globes of different colors, an exceedingly beautiful effect is obtained. If the bared ends of the wires are twisted together between the globes, these will all glow at once.

A Mystery Coin Box

The effect of this trick is as follows: A small metal box, just large enough to hold a half dollar and about 1/2 in. high, with a cover that fits snugly over the top, is passed out to be examined, and when handed back to the performer he places it on the finger ends of his left hand, and a half dollar is dropped into it and the cover put on. The box is then shaken to prove that the coin is still there. The performer then taps the box with his fingers and picks it up with the other hand and the coin will appear to have fallen through the bottom. Both the coin and box are then handed out for examination.

This seemingly impossible effect is made when the performer places the cover on the box. The box is resting on the fingers of the left hand and the cover is held between the thumb and forefinger of the right hand, but just before placing the cover on, the box is turned over with the right thumb, and the cover is placed on the bottom instead of the top.

The trick can be done within a foot of the spectators without their seeing the deception. It is a good plan to hide the box with the right hand when placing the cover, although this is not necessary.

How to Make a Small Series Motor

The motor here described has been constructed and found to give very good results. It is simple to build and the materials required can be easily obtained. The armature core and field, or frame, are made of laminated iron, instead of being cast as is often done by the manufacturers, which is a decided advantage, as certain losses are thereby reduced, and its operation will be improved by this type of construction especially if used on an alternating-current circuit.

The machine will be divided into three main parts, the construction of each of which will be taken up in turn and the method of procedure discussed in detail. These parts are the completed armature, the field and bearings, and the brushes together with suitable terminals and connections.

The armature core is constructed from a number of pieces, having dimensions that correspond to those given in A, Fig. 1. These pieces are cut from thin annealed sheet iron, in sufficient number to make a pile, 3/4 in. high, when placed on top of each other and firmly clamped. It would, no doubt, be best to first lay out one of these pieces very carefully and then cut it out and mark out the other pieces with the first one as a pattern, being careful to file off all the rough edges on each piece.

Now obtain a piece of 1/4-in. iron or brass rod, 3-1/4 in. long, that is to serve as a shaft upon which to mount the armature and commutator. This rod is threaded for a distance of 7/8 in. on one end and 1-7/8 in. on the other. Procure five brass nuts, 1/8 in. thickness, to fit the threads on the rod. If possible have the ends of the rod centered before the threads are cut, for reasons to be given later. Place one of the nuts on that end of the shaft that is threaded for 7/8 in., and in such a position that its inner surface is 3/4 in. from the end of the rod. Solder this nut to the rod when it is in the proper place and remove all extra solder. Drill a 1/4-in. hole in each of the armature stampings and place them on the shaft, clamping them together with three small clamps, one on each extension or pole. Then place a second nut on the shaft and draw it up tight against the last stamping placed in position, and solder it to the shaft. Next wind two or three layers of good strong tape around each of the rectangular portions of the armature and then remove the clamps. Make sure that all the edges of the different laminations are perfectly even before applying the tape.

The shaft is then placed between two centers to determine whether the core is approximately balanced and runs true. If the armature core is unbalanced or not true, the trouble should be corrected before proceeding with the remainder of the armature construction. The armature winding is not to be put on the core until the commutator has been constructed and mounted on the shaft.

The commutator consists of three pieces of thin sheet brass similar to that shown at B, Fig. 1, mounted on the surface of a cylinder of insulating material, 3/8 in. long and 7/8 in. in diameter. A 1/4-in. hole is drilled lengthwise through the cylinder of insulating material. Bend the pieces of brass around the outside of the cylinder, and turn all the lugs, except the center one, marked C, over at right angles and put a small nail or screw through the holes in the ends of the lugs into the cylinder. These pieces of brass are equally spaced around the cylinder so that all the lugs, not turned down, project in the same direction. Now place a nut on the end of the shaft that extends the greatest distance through the armature, so that its outside surface is 1/2 in. from the surface of the end of the armature core next to it, and solder the nut to the shaft. Place the commutator on the shaft so that the projections on the pieces of brass are toward the armature core and the spaces between the ends of the pieces occupy the position relative to the cores, shown at A, Fig. 2. Another nut is then placed on the shaft and drawn up tight against the cylinder. The proper spacing of the various parts on the shaft of the machine is shown at D, Fig. 1. Another small nut is placed on the end of the shaft, away from the commutator, so that its outside surface is 1/2 in. from the surface of the end of the armature core.

The threads on that part of the shaft extending beyond the last nut on each end are now filed off, which can be easily done by placing the shaft between the centers of a lathe and revolving it quite rapidly, the file being applied to the parts that are to be cut down.

Obtain a small quantity of No. 22 gauge single-cotton-covered copper wire and wind four layers on each of the three legs, or poles, of the armature core, insulating the layers from each other and the entire winding from the core by means of paper and shellac. The three coils are wound in the same direction about their respective cores and each winding is started at the center of the armature with 2 or 3 in. of wire extending out toward the commutator. The outside end of each winding will terminate at the end of the coil toward the center of the armature, if an even number of layers is wound on, and is securely fastened by means of two or three turns of heavy thread. The inside end of one coil is then connected to the outside end of the next one, and so on. These connections can be easily made, and at the same time the proper connections made to the commutator, by cutting the inside end of one coil and the outside end of the next so that they will reach the lug on the nearest segment of the commutator, with about 1/4 in. to spare, then removing the insulation from each for about 1/8 in. and soldering them both to the same lug. The arrangement of the winding is shown at A, Fig. 2. Connect all of the coils and segments in this manner, and the armature of the motor is complete.

The field or frame of the machine is made from a number of laminations whose dimensions correspond to those given in B, Fig. 2. As many laminations are used in the construction of the frame as the number of pieces in the armature, if iron of the same thickness is used. Four of the laminations have extensions at their lower corners to correspond to the parts shown by the dotted lines in B, Fig. 2. Place all of these laminations in a pile and clamp them rigidly together, then drill the four holes, indicated by the letters C, D, E and F, with a 3/16-in. drill. Two of the pieces with the extensions on them are placed in the bottom of the pile and the other two on top.

Place a 3/16-in. bolt through each of the lower holes and draw up the nuts on them tight. Procure two pieces of 3/16-in. rod, 1-1/2 in. long, and thread each end for a distance of 1/2 in. Get 8 nuts for these rods, about 1/8 in. thick and 5/8 in. across the face, if possible. Both sides of these nuts are filed down flat. Put the threaded rods through the two upper holes in the field frame and place a nut on each end and draw them tight, leaving an equal length of rod protruding from each side.

Obtain two pieces of 1/8-in. brass, 5/8 in. wide, one 4-3/4 in. long and the other 5-3/4 in. long. Bend these pieces into the forms shown at A, Fig. 3. Drill a 3/16-in. hole in each end of both pieces so that they may be mounted upon the ends of the rods protruding from the field frame. The exact center of the space the armature is to occupy is then marked on each of these pieces, and a hole is drilled in each, having the same diameter as the ends of the armature shaft.

The extensions on the outside laminations are bent over at right angles to the main portion of the frame, thus forming a base upon which the motor may rest. Holes may be drilled in the extensions after they are bent over to be used in mounting the frame upon a wooden base.

Procure about 1/2 lb. of No. 18 gauge single-cotton-covered copper wire and wind it on the lower center portion of the frame until the depth of the winding is about 1/2 in. Be careful to insulate the winding well and, to insure mechanical protection, place a layer of adhesive tape outside. About 4 or 5 in. of wire is allowed at each end for making connections. It is best to have these ends terminate on the commutator side of the frame.

The brushes for the machine are made from some thin sheet copper or brass, and are shaped and dimensioned approximately as shown at B, Fig. 3. Two pieces of hard rubber, or fiber, 1/2 in. square and 7/8 in. long, serve as mountings for the brushes. These pieces of insulation are mounted in the corners of the armature support, at the commutator end, by means of two small screws in each. Mount the brushes on these pieces so that their free ends bear on the commutator exactly opposite each other. One brush is mounted on the upper end of its support and the other brush on the lower end of its support. This is shown at C, Fig. 3. Two small binding posts are mounted at the same time as the brushes, and are electrically connected to the brushes, thus affording an easy means of making a connection to the armature. The brushes are so mounted as to bear firmly upon the commutator.

To operate the motor, connect the armature and field windings in series, and the combination to a source of electromotive force of several volts. If it is desired to reverse the direction of rotation, reverse the connections of either the armature or field windings, but not both. The motor may be mounted on a neat wooden base and the connections all brought down to a reversing switch, which may also be mounted on the same base as the motor. The speed can be varied by changing the impressed voltage, or by connecting a variable resistance in the armature circuit, such as a wire rheostat.

A small pulley may be made and attached to the armature shaft so that the motor may be used in driving various kinds of toys.

Cooler for Milk and Butter

An earthen jar or crock, with a cover, set in a box containing moist sand will keep butter and milk in hot weather better than a refrigerator. The sand must be kept moist at all times.--Edwin J. Bachman, Jr., Fullerton, Pa.

Rubber Bumper on a Water Faucet

Sometimes a dish is broken by striking it on the faucet. This is easily remedied by cutting a rubber washer from a rubber-boot heel with a sharp chisel and a hammer. The washer is pushed into place on the end of the faucet, and the dishes may strike the rubber without being broken.--Contributed by Harriette I. Lockwood, Philadelphia, Pa.

Boring a Clean-Edged Hole

When boring a hole in wood, withdraw the bit as soon as the worm shows, then start the worm in the hole on the opposite side and finish boring the hole. It will then have clean edges on both sides of the wood. Often the bit pushes splinters of wood ahead of it, when passing through, but by using the method described this is avoided.

Drilling Thin Metal

In drilling very thin stock the drill, if not properly ground, will tear the metal and leave a ragged edge. To cut a hole through neatly the drill should be ground as illustrated. The center A should extend about 1/64 in. beyond the points B. The point A locates the center and the sharp points B cut out the disk of metal. Holes have been neatly and quickly made with this drill grinding in metal measuring .002 in. thickness.--Contributed by Joseph J. Kolar, Maywood, Ill.

* * * * *

A pencil may be kept from falling out of the pocket
by wrapping a couple of turns of tape around it or by
wrapping it with a small rubber band.

Flexible-Cord Adjuster for an Electrical Flatiron

When using an electrical flatiron the flexible cord frequently gets under the iron, causing much trouble for the user, and mussing up the clothing. The cord can be kept out of the way by fastening a pulley to the ironing board and attaching a coil spring to the electric cord between the pulley and the electric-fixture socket. A coil spring that will draw out about 3 ft. should be used.--Contributed by Herbert Blandford, Elmira, N. Y.

A Wood Clothes Peg

If clothes that are slightly damp are hung on a nail or metal peg, a rust stain that is almost impossible to remove will be the result. To prevent this, drive a nail with the head removed into the wall or cleat, and place a wood peg over it. The peg may be turned up or whittled out with a pocket knife and the hole bored with a hand drill.--Contributed by Wm. A. Robinson, Waynesboro, Pa.

To Make Scratch Pads of Old Labels

Labels and blank paper of uniform size, that would otherwise be cast aside, can be turned into handy scratch pads by placing them between blocks of wood, secured by a wood clamp, and applying paste on two edges, then pressing a strip of paper on the pasted portions. The edges to be pasted should project a trifle beyond the edges of the blocks.

How to Make an Electric Heater

The electric heater described in this article is very simple to construct, its operation exceedingly satisfactory, and the necessary material easily procured at a small cost at most electrical-supply stores. The few tools needed are usually found about every home, and the heater may be constructed by any ingenious person.

Procure 6 porcelain tubes, 20 in. long and approximately 13/16 in. in diameter. On each of these tubes wind 25 ft. of bare No. 26 gauge "Climax" resistance wire. The various turns should be uniformly distributed along the tubes and not allowed to come into contact with each other, which can be prevented by placing a thin, narrow coat of plaster of Paris along the side of each of the tubes immediately after the winding has been put on. Several inches of free wire should be allowed at each end, for making connections, and the first and last turns on each tube should be securely fastened to the tube by several turns of binding wire. It would be best not to extend the winding nearer the ends of the tubes than 3/4 in.

Cut from some heavy tin, or other thin sheet metal, two disks, 6 in. in diameter, and punch six 5/16-in. holes in each of the disks at equal distances and within 3/4 in. of the outer edge. Punch two 1/8-in. holes in one of these disks, to be used in mounting a porcelain socket, and also one 1/2-in. hole through which the wires may be led to the socket, as shown in Fig. 1. In the other disk punch four 1/8-in. holes, for mounting two porcelain single-pole snap switches, and two 1/2-in. holes, for leading the wires through to the switches, as shown in Fig. 2.

Cut off six lengths of 5/16-in. iron rod, 22 in. long, and thread both ends of each piece for a length of 1-1/4 in. Fasten the porcelain tubes between the metal disks, by placing one of the rods through each of the tubes and allowing the ends to extend through the 5/16-in. holes in the outer edge of the disks. A nut should be placed on each end of all the rods and drawn up so that the length of rod protruding at each end is the same. Obtain two single-pole snap switches and a porcelain socket, and mount them on the ends by means of some small stove bolts.

The windings on the porcelain tubes should be connected as follows: Let the windings be designated by the letters A, B, C, D, E, and F, and their position be that indicated in Figs. 1 and 2. The primes indicate the ends of the windings at the socket end, and the letters without the primes indicate the ends of the windings at the switch end of the heater. The ends A and D should be connected directly together. The ends B and C to the clips of the right-band snap switch, and E and F, to the clips of the left-hand snap switch. The ends F, A, and B should be connected to one terminal of the socket, and C, D, and E to the other terminal of the socket. Electrical connection is made to the winding by means of a plug and piece of lamp cord. It is obvious that the windings A and D will be connected as soon as the plug is screwed into the socket, if the circuit is closed at all other points, and the windings B and C, and E and F are controlled by the right and left-hand snap switches, respectively. Make sure all the connections are properly insulated, and that there is little chance of a short circuit occurring.

After the socket and snap switches have been connected to the windings, two more thin disks, the same diameter as the first, may be fitted over the ends and held in place by two units on the end of each rod, a nut being placed on each side of the disks. A better way of mounting these disks would be by small machine screws that enter threaded holes in the ends of the rods. These last disks are not absolutely necessary, but they will add some to the appearance of the completed heater. Four small ears, about 5/8 in. square, should be cut on the outer edge of the outside or inside disks and bent over at right angles to the main portion, to be used in mounting the outside case of the heater.

Cut from a sheet of 1/8-in. asbestos a piece just long enough to fit between the inside disks and wide enough to cover the three lower windings C, D, and E. The object of this piece of asbestos is to protect the surface upon which the heater will stand from excessive heat, since it is to rest in a horizontal position.

Obtain a piece of perforated, thin sheet metal, 19-1/2 in. wide and long enough to reach from one outside disk to the other. Bend this into a cylinder and fasten it to the lugs on the disks by means of small screws or bolts.

The legs may be made of 1/8-in. strap iron, 5/8 in. wide, bent into the form shown in Fig. 3. These pieces may be attached to the perforated cylinder, before it is mounted on the heater proper, by means of several small bolts. The piece of asbestos should be wired to the cylinder after the heater is all assembled, so that it will always remain in the lower part of the cylinder and serve the purpose for which it is intended.

The heater, as described above, is constructed for a 110-volt circuit, which is the voltage commonly used in electric lighting. The total consumption of the heater will be approximately 600 watts, each part consuming about 1/3 of the total, or 200 watts. If it is desired to wind the heater for a 220-volt circuit, 25 ft. of No. 29 gauge "Climax" resistance wire should be used on each tube.

A Molding-Sawing Block Used on a Bench

Having occasion to saw some short pieces of molding, I experienced considerable trouble in holding them without a vise until I made a block, as shown in the sketch. This answered the purpose as well as a vise. The block is not fastened in any manner, but is simply pushed against the edge of the bench or table and held with the hand. It should be about 9 in. wide and 1 ft. long, with strips 2 in. thick at each edge.--Contributed by W. F. Brodnax, Jr., Bethlehem, Pa.

Pipe Caps Used as Castings for Engine Pistons

Desiring to make a small piston for a model engine and not caring to make a pattern and send it away to have a casting made, I thought of using ordinary pipe caps, these being both inexpensive and of a quality adapted to machining.

The cylinder bore was 1-1/2 in. in diameter, so I secured a standard pipe cap for 1-1/4-in. pipe which gave an outside diameter of about 1-5/8 in. The cap, not having sufficient depth for holding in a chuck, was screwed on a short piece of pipe and then trued in the lathe chuck. The outside surface was turned to a diameter of 1-1/2 in., then removed from the pipe, reversed and chucked again, and the threads bored out to reduce the walls to 1/8 in. This made an excellent piston for a single-acting engine.--Contributed by Harry F. Lowe, Washington, D. C.

An Electric Horn

A simple electric horn for use on a bicycle, automobile, or for other purposes, can be constructed as shown in Fig. 1. The size will of course depend somewhat on the use for which it is intended, but one with the diaphragm 1-3/4 in. in diameter and the horn 5 in. long and 4 in. in diameter, at the large end, will be sufficient for most purposes. This will make the instrument 7-1/2 or 8 in. in over-all length.

The horn proper, A, Fig. 1, is constructed first. This can be formed from sheet brass. To lay out the metal to the desired size draw a cross section, as ABCD, Fig. 2, then project the lines AC and BD until they meet at E. Strike two arcs of circles on the brass sheet, using EC as radius for the inner one and EA for the outer. Measure off FG and HJ equal to 3-1/4 times DC and AB, respectively, and cut out FGJH. Roll and lap 1/4 in. at the edges and solder the joint neatly.

After smoothing the edges on the ends, solder a very thin disk of ferrotype metal, B, Fig. 1, to the small end of the horn. This is used for the diaphragm. Cut out a ring, C, from 1/4-in. hard fiber and bevel it on the inside edge to fit the horn. Also make a disk of fiber, D, having the same outside diameter as the ring C. These parts form the ends for a brass cylinder E, which is made in two parts or halves joined on the lines shown in Fig. 3. Fasten one of the halves, F, Fig. 3, to the fiber ring C and disk D, Fig. 1, with small screws, the other half to be put in place after the instrument is completed and adjusted.

A small support, G, is cut from fiber and fastened in as shown. A pair of magnets of about 50 ohms are mounted on this support. The parts from an old bell or buzzer may be used, which consist of a soft-iron armature, H, Fig. 1, having a strap of spring brass, J, attached by soldering and pivoted at K, with an adjusting screw, L, to set the tension. Another U-shaped spring-brass strip, M, constitutes the current breaker, which has an adjusting screw, N. The points of contact on the current breaker should be tipped with platinum. A piece of brass wire, O, is soldered to the diaphragm disk B and the soft-iron armature H, to connect them solidly. The tone of the horn can be adjusted with the screws L and N. The faster the armature vibrates, the higher the tone, and vice versa. The connections are the same as for an electric bell.--Contributed by James P. Lewis, Golden, Colo.

Combination Meat Saw and Knife

A very handy combination knife and meat saw can be made of an old discarded saw blade. The blade is cut on a line parallel with the toothed edge, allowing enough material to make a good-sized blade, then the straight part is ground to a knife edge and a wood handle attached at one end. The handle is made in halves, placed one on each side of the blade, and riveted together, then the projecting metal is ground off to the shape of the handle.--Contributed by A. C. Westby, Porter, Minn.

Clamp Used as a Vise

A carpenter's wood clamp fastened to the edge of a bench, as shown in the sketch, makes a good substitute for a vise for many kinds of light work. If the clamp is located over or in front of the bench post, holes must be bored in the latter to admit the ends of the clamp screws. A hole is bored through the shoulder screw and a handle attached as shown.--Contributed by H. W. J. Langletz, Harrisburg, Pa.

Wire Expansion Meter

When there is a current of electricity in an electrical conductor a certain amount of heat is generated due to the opposition or resistance of the conductor to the free passage of the electricity through it. The heat thus generated causes a change in the temperature of the conductor and as a result there will be a change in its length, it contracting with a decrease in temperature and expanding with an increase in temperature. The temperature of the conductor will change when the current in it changes, and hence its length will change, and it will reach a constant temperature or a constant length when the current in it is constant in value and the rate at which it is giving off heat is exactly equal to the rate at which heat is being generated in it.

The fact that there is an actual change in the length of the conductor due to a change in current in it constitutes the fundamental principle of the following simple instrument.

The parts needed in its construction are as follows: An old safety-razor blade; one 8-in. hatpin; two medium-size nails; a short piece of German-silver wire; a small piece of sealing wax; a 1/2-in. board for the base, approximately 3-1/2 in. by 10 in., and a small piece of thin sheet brass. Remove the head from the hatpin and fasten the blunt end in the center of the safety-razor blade A with a piece of sealing wax so that the pin B is perpendicular to the blade as shown. Now drive the two nails into the board C, so that they are about 1/4 in. from the edges and 1-1/2 in. from the end. Fasten the piece of German-silver wire D to these nails as shown. The size of this wire will depend upon the value of the current to be measured. Make a small hook, E, from a short piece of rather stiff wire and fasten it to the hatpin about 1 in. from the razor blade. The length of this hook should be such that the pointed end of the hatpin will be at the top of the scale F when there is no current in the wire, D. The scale F is made by bending the piece of sheet brass so as to form a right angle and fastening it to the base. A piece of thin cardboard can be mounted upon the surface of the vertical portion of the piece of brass and a suitable scale inked upon it. The instrument is now complete with the exception of two binding posts, not shown in the sketch, that may be mounted at convenient points on the base and connected to the ends of the German-silver wire, thus serving as terminals for the instrument.

The completed instrument can be calibrated by connecting it in series with another instrument whose calibration is known and marking the position of the pointer on the scale for different values of current.

How to Make a Fire and Burglar Alarm

A very serviceable fire and burglar alarm may be installed by anyone who can work with carpenters' tools and who has an elementary knowledge of electricity. Fire and burglar alarms are divided into two general types, called "open circuit" and "closed circuit," respectively.

In the open-circuit type of alarm all the windows, doors, and places to be protected are equipped with electrical alarm springs which are in circuit with an ordinary vibrating bell and battery, and these alarm springs are all normally open. When a window or door is disturbed or moved more than a predetermined amount, the bell circuit is closed and the alarm sounded. The arrangement of such an alarm is shown in Fig. 1. A switch, A, is placed in circuit so that the alarm may be disconnected during the day and the opening and closing of doors and windows will not operate the bell. It is best not to place a switch in the fire-alarm circuit as this circuit should be in an operating condition at all times.

The alarm switch controlled by the window consists of a narrow metal plate, B, and a spring, C, mounted in a recess cut in the side of the window frame. The spring C is bent into such a form that its upper end is forced into contact with the plate B, when the window is raised past the outwardly projecting part of the spring C, and the bell circuit is thus closed. The position of the alarm switch can be adjusted so that the window may be opened a sufficient distance to permit the necessary ventilation but not allow a burglar to enter.

The alarm switch controlled by the door is arranged in a different manner. In this case the free end of the spring D is held away from contact with the spring E by the edge of the door, which forces the spring D back into the recess cut in the door jamb. When the door is opened the spring E is permitted to move out and come into contact with the spring or plate E, and the alarm circuit is thus closed. The form of the spring D can be so adjusted that the door may be opened some distance, but not enough to allow a person to enter, before the alarm is sounded.

An alarm switch, identical with that just described for the door, should be mounted in the upper part of the window frame to take care of the upper sash. This alarm switch may be located low enough to permit the window to be lowered for the purpose of ventilation without sounding the alarm.

The wires for these various alarm switches should be run as near completely concealed as possible to prevent them being tampered with by curious parties, who may unintentionally break one of the conductors and thus make some part of the system inoperative. It might be best to test the system occasionally, to make sure all switches are in operating condition.

The fire-alarm switch consists of two springs that are held from contact with each other by means of a thin cord. This switch is placed in the location to be protected, or wherever a fire is most likely to break out, such as over the furnace, in the coal bin, etc. When the cord is destroyed the springs make contact and the alarm is sounded. A metal having a very low melting temperature may be used instead of the cord, and the alarm will be sounded when the temperature exceeds a certain amount and the actual occurrence of a fire thus prevented. In some cases, the fire-alarm switch may be completely destroyed and the alarm circuit will then be opened and the bell will cease ringing. To prevent this trouble a small electric drop may be placed in the circuit, the arrangement being similar to that shown in Fig. 2. When the shutter of the drop falls, due to the closing of the alarm circuit, there is a second circuit closed, and this second circuit remains closed until the shutter is restored to its vertical or normal position, or the switch, A, is thrown to the open point. The addition of the drop in the burglar-alarm circuit may prove to be an advantage, as a burglar cannot stop the alarm, after he has once closed any of the alarm switches and operated the drop, by simply restoring the window or door to its original position.

In the closed-circuit type, the alarm switches are all normally closed and the alarm is sounded by opening the circuit at some point. The arrangement of such an alarm is shown in Fig. 3. The alarm switches are all connected in series in this case and in circuit with a closed-circuit battery and relay or drop. The drop or relay controls a local circuit composed of an open-circuit battery and an ordinary vibrating bell.

The operation of a drop on a closed circuit is a little different from its operation on a normally open circuit. The drop for the closed circuit must be so constructed that its latch holds the shutter in a vertical position when there is a current in the drop winding, but allows it to fall as soon as the drop circuit is opened.

An ordinary telegraph relay may be used in connection with the closed-circuit alarm. The connections to the relay are such that the bell circuit is normally open and remains so until the armature of the relay is released, which does not occur until the circuit of which its winding is a part is opened at one of the alarm springs. A special switch, A, and resistance, B, are shown connected in circuit in Fig. 3, the object of which is as follows: When it is desired to disconnect the alarm springs or make them inoperative they must be replaced by another circuit which will permit a sufficient current to pass through the relay winding at all times, to prevent its armature from being released and sounding the alarm. The switch A is so constructed that either the alarm switches or the resistance B is in series with the battery and relay winding at all times, there being no open-circuit position for the switch.

The fire-alarm switch for this type of signal may be made from a narrow piece of tin foil, or some metal having a low melting temperature, mounted between two insulated clips that are connected in the alarm circuit.

Strips of gold or silver foil may be placed on windows and connected in the alarm circuit, which will give a protection from theft by breaking the glass.

Two or three gravity cells will serve very nicely for the closed-circuit battery, while several dry cells will do for the open-circuit or bell battery.

All types of alarm switches can be purchased at any up-to-date electrical supply house, but their construction and operation is so simple that they may be easily made by almost anyone. A detailed description of the construction of the various parts of the above circuits will not be given here, but such details can be safely left to the ingenuity of the person installing the system.

It is easily seen from the above description that a burglar who might discover that a house was wired for alarm would be greatly perplexed to know what to do, for the very thing that would prevent one kind of alarm from ringing would cause the other to ring.

Removing a Rear Bicycle Sprocket

If a bicycle rider desires to remove the rear sprocket for changing the gear, or for any other reason, and there is no large pipe wrench at hand, a piece of tube or pipe, as shown in the sketch, can be used as a lever. Fasten one end of the chain in one end of the pipe with a wedge and place the other end of the pipe on a sprocket. The chain is then placed over the sprockets and a leverage equal to any pipe wrench is secured.--Contributed by Jno. V. Loeffler, Evansville, Ind.

Hand Propeller-Wheel Attachment for a Rowboat

The rear fork of an old bicycle frame, with the crank hanger attached, and the rear hub constitute the main parts of the propelling device. One of the cranks is cut from the hanger and a bracket attached to the frame, as shown, for making it fast to the stern of the boat. Two propeller blades are bolted to the rear hub. A rudder is fastened to the rear tube of the frame with hooks and eyes so that it can be turned with a handle at the top, or with ropes run to a wheel. The illustration shows the connection of the device to a boat.--Contributed by Berge Lion, Fresno, Cal.

An Attached Back for a Photographic Printing Frame

In using the ordinary photographic printing frame with a spring-pressure back, the back must be entirely removed from the frame to put in the paper, and as this operation is carried on in a dim light, the back is often mislaid, causing no little inconvenience and delay. To do away with this annoyance, I placed at one end of the frame, as shown in the sketch, a second hinge made of cloth or any pliable material. When the pressure springs are released, the back swings down on this auxiliary hinge, and after changing the papers, it is instantly closed by a slight movement of the hand, making it very rapid and easy to use.--Contributed by Thos. L. Parker, Wibaux, Mont.

Repairing a Worn Stop Cock

The plug of a worn stop cock, or one that has been reground, of the type shown in the illustration will project beyond the bottom so that the ring, or washer, and screw will not draw it tightly into place.

To remedy this trouble, file off a portion of the plug on the line AA and also file off a sufficient amount of the screw on the line BB. When the plug is replaced and the washer and screw drawn up, the stop cock will be as good as a new one.--Contributed by James M. Kane, Doylestown, Pa.

Tool Holders Made of Brass Clips

Hangers to grip tool handles can be easily formed of sheet metal in any desired material. The clips are shaped as shown at A in the sketch. Any number of the clips may be fastened with screws to a wood crosspiece or a wall in such a manner as to make openings into which the handles of the tools are pressed. Before fastening the clips they should be spaced for the widths of the handles.--Contributed by F. H. Tillotson, Sycamore, Ill.

Removing Perspiration Stains from Delicate Cloth

Lay the stain in the cloth over some blotting paper, and sponge the cloth with a grain-alcohol and ether solution, which should be made by mixing equal portions of each. The sponging should be quite vigorous and kept up until the cloth is dry, then the spot should be touched lightly with ammonia water, which can be purchased at any drug store. This will leave a slight blur, which can be removed by rubbing with French chalk on the wrong side. The chalk is cheap and can be procured with the ammonia water. Do not forget the blotting paper, as it keeps the solution from forming a ring around the spot.

Buttonhole Cutter

If the buttonhole scissors are mislaid or there are none at hand, the holes may be cut in the manner shown in the sketch. Place a piece of wood, having a width equal to the length of the buttonhole, on the table and lay the cloth over it in the line where the holes are required, then draw a sharp knife across the cloth on the wood where the holes are marked. This will cut the cloth neatly and accurately.--Contributed by A. S. Thomas, Gordon, Can.

Filing Small Rods in a Lathe

Reducing the diameter of a small rod by filing while it is turning in a lathe is a difficult thing to do, as the pressure of the file on one side bends the rod. The filing may be easily accomplished by using two files, as shown in the sketch. In this manner almost any amount of pressure can be applied by squeezing the files together without danger of bending the rod.--Contributed by J.F. Tholl, Detroit, Mich.

* * * * *

Young sleepwalkers may be cured if watched and given
a good switching until they are wide awake.

A D'Arsonval Galvanometer

A galvanometer in which the moving part of the instrument is a permanent magnet controlled by the action of the earth's magnetic field and the magnetic effect of a current in a coil of wire, that usually surrounds the magnet, has the great disadvantage of having its indications changed, although the current itself may remain constant, due to a change in the strength of the magnetic field in which the instrument operates. The operation of instruments of the above type is satisfactory only in localities where there is a practically constant magnetic field for them to operate in, which it is almost impossible to have, due to the presence of permanent and electric magnets and magnetic materials such as iron and steel.

An instrument constructed as follows will not have the above disadvantage and its operation will be a great deal more satisfactory, as its indications will be practically independent of outside disturbances. In this instrument, the moving part is the coil carrying the current, and it moves in a permanent magnetic field so strong that other disturbing magnetic effects can be neglected. The coil is hung by means of a fine wire and the twist in this wire is the only force acting to bring the coil back to its zero position, after it has been deflected, and maintain it there.

The construction of the magnet and containing case for the instrument will be taken up first. Obtain a piece of Norway iron, 1/2 in. square and about 9 in. long. Bend this piece into the form shown in Fig. 1, and file off the inner edges until they are parallel and about 7/8 in. apart. Drill four 1/8-in. holes in the ends of this piece, two in each end, as indicated. This piece of iron is first tempered and then magnetized by placing it in contact with a powerful electromagnet. Cut a second piece from some soft iron with dimensions corresponding to those given in Fig. 2. Drill two 1/8-in. holes, A and B, in this piece as shown in the sketch. This second piece is mounted between the poles of the magnet, as follows: Cut from some 1/32-in. sheet brass a piece similar to the one shown in Fig. 3. Drill the holes indicated and thread those designated by A, B, C, D, E, and F to take a 1/8-in. machine screw. Bend the upper end of the piece over at the point indicated by the dotted line until it is perpendicular to the lower part. The center of the hole in the projecting part K, when it is bent over, should be about 1/4 in. from the outer surface of the main part of the piece. The small piece of iron is then fastened to the piece of brass with two round-headed screws that pass through the two holes in it and into the holes A and B in the brass piece. The magnet is mounted, also with small brass screws, so that the main part of the magnet and the piece of brass extend in opposite directions, as shown in Fig. 1. The assembled parts are then mounted on a wooden board, whose dimensions are given in Fig. 1, with three brass screws that pass through the holes G, H, and J, as shown.

The moving coil of the galvanometer is constructed as follows: Cut from some 1/8-in. pine a piece 1-1/8 in. long and 5/8 in. wide. Cut two other pieces whose dimensions, except their thickness, are 1/4 in. larger than the first piece. Then fasten these two pieces to the sides of the first, with three or four small screws through each of them, thus forming a small spool. Saw about 16 slots with a very fine saw in the edges of the projecting pieces and a short way into the edge of the center piece. Wind on this spool about 300 turns of No. 38 gauge silk-covered copper wire. Start with the terminal of the wire in the center of one end of the spool, with a few inches of free wire for making connections, and end up with the terminal in the center of the opposite end of the spool. A small thread is then passed through the slots under the coil and tied, thus serving to hold the various turns of wire together when the coil is removed from the form. The coil should be given a coat of shellac as soon as it is removed from the form.

Two pieces must now be attached to the top and bottom of the coil to be used in making electrical connections and suspending the coil. Cut from some very thin sheet brass two pieces whose dimensions correspond to those given in Figs. 4 and 5. Drill a small hole in the center of each of these pieces. Bend the lower part of each piece over at the dotted lines L until it is perpendicular to the main portion of the piece. The bent-over portions of these two pieces are then fastened to the ends of the coil with some fine thread, making sure that they are in the center of the ends before they are fastened. The terminals of the coil are now soldered to these pieces. It would be best to place a sheet or two of thin paper between the brass pieces and the coil, to prevent any part of the coil, except the ends, from coming into contact with the brass pieces. Obtain a small piece of thin mirror and mount it with some glue, as shown by the dotted lines in Fig. 4.

The upper support for the suspension is shown in Fig. 6 and consists of a 1/8-in. threaded screw, A, that passes through the hole in the part K, Fig. 3, and is provided with two lock nuts, B. The lower end of this screw should be slotted a short distance, and a small screw put through it, perpendicular to the slot, so that a wire can be easily clamped in the slot by turning up the screw. Next, take a piece of 1/32-in. brass, as shown in Fig. 7, and bend it at the dotted line A until it forms a right angle. The hole B should be threaded to take a 1/8-in. screw. The holes C and D are for mounting the piece on the back of the instrument. Slot the end of a 1/8-in. screw, about 1/2 in. long, and put a screw through the end as for the upper support for the suspension. This piece is mounted below the position the coil is to occupy, as shown by M, Fig. 1.

A case should be made for the galvanometer whose inside dimensions correspond to those of the piece N, Fig. 1, and whose depth is about 3/4 in. more than the thickness of that piece. Four pieces of wood can be fastened in the corners that will allow the case to slip just far enough on the piece N to make the edge of the case and the back surface of the piece N flush. Cut an opening in the front of this case, about 2 in. long and 1 in. wide, in such a place that the center of the opening is about level with the ends of the magnet. Fasten, back of this opening, a piece of thin glass with four small screws whose heads rest upon the edge of the glass. The interior of this case and all the parts should be given a coat of lampblack mixed with a little vinegar. Two small binding posts, O and P, are mounted on the upper end of the piece N and connected to the upper and lower supports for the suspension of the coil.

This galvanometer will work best, of course, when it is in an exactly vertical position and the following simple device, when attached to it, will allow it to assume this position independent of the level of the surface its base may rest upon. Cut from some 1-1/8-in. brass two pieces, 1/2 in. wide and 2-1/2 in. long. Drill a 1/8-in. hole in the center of each end of them, 1/4 in. from the end, and a 1/4-in. hole through the center of each. Bend these pieces to a 3/4-in. radius. Cut from some 1/2-in. hard wood a block, 1-1/4 in. square. Fasten the two pieces of brass to the wooden block with 1/8-in. screws, as shown in Fig. 8. One of these pieces is fastened to the upper end of the piece N, Fig. 1, so that the galvanometer will hang vertically. The other piece is fastened to a bracket from which the galvanometer is suspended. A suitable bracket for this purpose can be easily made. When the galvanometer is hung in this way, two binding posts are mounted on the bracket, and connected to the two on the galvanometer. In this way the galvanometer will not be disturbed when making connections.

The suspension is made as follows: Take a piece of small copper wire and roll it out flat. Solder one end of a piece of this wire in the hole in the piece of brass, with the mirror mounted on it. Fasten a piece of the same wire to the lower brass piece, attached to the coil. The upper piece of wire is then clamped in the end of the screw A, Fig. 6, so that the coil hangs perfectly free about the iron core. The lower piece of wire is bent around a small rod several times and its end fastened in the slot in the lower screw.

The deflection of the instrument is read by causing a beam of light from a lamp or candle to be reflected from the mirror to a scale located in front of the instrument. If the light from the lamp is allowed to shine through a small slit in a piece of dark paper, there will be a streak of light reflected upon the scale, instead of a spot.