Chapter XXVI: Part II: Construction (3)

The support for the heating coil is made of a piece of 5/16-in. asbestos wood or transite. Cut it to fit into the recessed bottom of the mug, then with a chisel remove the material in the top to form a depression 1/16 in. deep to receive the coil with its top flush. The leads of the coil are run through the disk. The surface of the coil is then plastered evenly with retort cement. The legs are fastened to a second piece of insulating material with round-head brass machine screws, 1/2 in. long, with nuts. The heads of these screws are shown in Fig. 6, the nuts being above the brass and between the two insulating pieces.

The ends of the heating ribbon are brought through the lower insulating disk and attached to binding posts as shown. The leads may be covered with tape to prevent any short circuit.

The mug uses 3-1/2 amperes at 110 volts, either direct or alternating current, and it will cost about 3 cents an hour to operate it. Care should be taken to use a separable attachment for connecting, as an ordinary lamp socket may be burned out by turning off the current, it being adapted only to a small capacity.

In assembling the parts, several pieces of mica should be placed between the coil and the metal of the mug to insulate the coil from the mug.

A Handbag Lock

The pickpocket finds it easy to unsnap a handbag and remove some of the contents, especially in crowded places. To make it less easy for the pickpocket, I fixed my mother's handbag as shown in the sketch. I used a chain which had served its day holding a small coin purse--any small chain will do--by passing it through the links that hold the handle and winding it once or twice around the snap fasteners to hold them securely closed.

The chain may be either shortened enough to make it convenient to hold with the handle of the handbag, or may be left long and used over the shoulder under the coat, thus making it possible to have both hands free for shopping while the handbag hangs by the side. This leaves a person free from the worry of taking care that the bag is not laid down somewhere and lost. The bag may be easily opened by unwinding the chain after loosening it by raising the bag slightly.--Contributed by Wm. Waterhouse, Aurora, Ill.

An Emery-Cloth Holder

Emery cloth in sheets is very easily spoiled around a workbench. Oil or other fluids used on work are apt to drop on it and when wet for a short time the abrasive is useless. The illustration shows a tin holder, A, that can be placed on the under side of the bench where space is not required for drawer room.

The portion cut out of the bottom of the holder B is to enable the workman to easily grasp the sheets of emery cloth. As the holder is on the under side of the bench, there is little danger of any liquid or other substance spoiling the sheets. The sheets are also within easy reach.--Contributed by F. W. Bently, Huron, S. D.

The Operation of the Compass

After trying to tell a few small boys what a compass is, they wanted a practical illustration--something they could see. Not having a compass or knowing where to locate one handily, I used a piece of cork with needles and a needle for a pivot and found it very satisfactory. The method used is shown in the sketch.

It is best not to magnetize both needles unless care is exercised in maintaining pole relationship, or they will oppose each other and not point to the north. The extreme ends or the heads of the needles must be opposites, the head of one negative and the head of the other positive.

If a good compass is brought carelessly in contact with a magnet, the poles may become reversed and the north end will no longer point to the north but to the south until the current has been reversed again by bringing the opposite pole of the magnet in contact with the compass.--Contributed by W. H. Albright, Bellevue, O.

Thawing Out Frozen Pipes

When the water pipes connecting a range boiler become frozen, get a plumber and avoid an explosion of the water back. If, however, the frozen pipe is a cold-water pipe in no way connected with the hot-water boiler, it can be thawed out as follows:

Procure some grain alcohol--not denatured or wood alcohol--and after turning the spigot upward or upside down, as shown, open it and pour in the alcohol. When the water begins to flow turn it to its proper position.--Contributed by James M. Kane, Doylestown, Pa.

A Wire Clothespin

The pin is made of galvanized wire, A, 8 or 10 in. long, wound spirally, B, on a round surface, such as a broom handle, to make the holding part. The ends are fastened together as shown. The space between the spiral turns makes the cloth-holding part.--Contributed by Wesley H. Freeman, Palestine, Tex.

Vent for Pouring Heavy Liquids

A tube placed in a jug or bottle as shown in the sketch will assist greatly in removing molasses or heavy liquids. The tube can be placed in the receptacle without getting the liquid inside by holding a finger over the outer end. The air can easily enter without disturbing the flow of the liquid.--Contributed by Homer Payear, Owensboro, Ky.

A Hat Hanger

Procure a piece of 1/8-in. wire, about 3 ft. long, bend it into the shape shown in the sketch, and sharpen the projecting end. Drive this into the wall above a coat hanger. This provides a better hat hanger than the ordinary hook.--Contributed by John D. Watt, Roxbury, Mass.

Repairing a Broken Tenon on a Chair Post

Instead of cutting off the four posts to make new tenons where one tenon was broken I used a metal piece made from a short length of bicycle tubing, as shown. The tube was slotted two ways to make four parts which were turned out and flattened. The remaining end of the tube was slipped over the broken post and the four parts were fastened with screws to the under side of the chair seat.--Contributed by Chas. H. Roberts, Calumet, Mich.

Substitute for an Iron-Holder Knob

The wood knob on the holder for my irons became charred from the heat and finally broke away from the pin. The pin would get so hot in continued use that it could not be moved without burning my fingers. I remedied the difficulty by attaching a short string to the handle and the pin. A pull on the string with the forefinger readily released the iron. I have found this better than the knob, as it is handier to use.--Contributed by Mrs. H. C. Dixon, Johnstown, Pa.

An Egg-Frying Pan

The frying of eggs in an ordinary frying pan is accompanied with some difficulty in removing them when they are cooked without breaking the yolk. Then, sometimes, the pan is too hot and the egg sticks to the pan and the top remains uncooked. A much better way is to shape a piece of sheet metal or tin as shown in the sketch to place the egg in and use it in the ordinary pan. It will not burn the egg, and the egg can be lifted out of the pan and easily slipped on a plate or toast when it is cooked.--Contributed by W. A. Jaquythe, San Diego, Cal.

A Sander Mandrel for the Lathe

A cylindrical sander for use in the lathe can be easily made of two pieces of wood, turned to a diameter that will take the stock size of sandpaper, and clamped together with pinch dogs at the ends. One edge of the sandpaper is clamped between the pieces and then it is wrapped around the wood, the opposite edge being glued to the starting edge, as shown at A. The dimensions given are for a 9 by 12-in. sheet of sandpaper. The sander is easily placed in the lathe centers when needed, and the sandpaper may be replaced at any time.--Contributed by James T. Gaffney, Chicago.

How to Construct a Simple Galvanometer

A galvanometer is an instrument used to detect the presence of an electrical current in a circuit or to measure the value of the current in amperes. The operation of practically all galvanometers is based upon the same principle, and they differ chiefly in mechanical construction and the relative arrangement of their different parts.

A very simple galvanometer, that will give quite satisfactory results, under favorable conditions, may be constructed as follows: Turn from a piece of hard wood a ring having dimensions corresponding to those given in the cross section, Fig. 1. Fill the groove in this ring to within 1/8 in. of the top with No. 18 gauge double-cotton-covered copper wire, insulating the different layers from each other by means of a layer of good bond paper. The winding may be started by drilling a small hole through the side of the groove, as close to the bottom as possible, and allowing about 6 in. of the wire to protrude through it. The outside end may be terminated in a similar manner, and the two ends should be on the same side of the ring, or as near each other as possible. A protecting covering of bookbinder's paper is placed over the winding and the completed ring given a coat of shellac. The electric current to be detected or measured is to pass around the winding of this coil and produce an effect upon a compass needle mounted in its center. In order that the current may produce a maximum effect upon the needle, the coil should be mounted in a vertical position.

The base upon which the ring is to be mounted may be cut from some 1/2-in. hard wood. It should be circular in form and about 5 in. in diameter, and have its upper edge rounded off and shellacked to improve its appearance. The ring is mounted in a vertical position on this base, which may be done as follows: Cut a flat surface on each of the flanges of the ring so that it will stand in a vertical position and the terminals of the winding will be as near as possible to the surface upon which the ring rests. Then form a stirrup from some thin sheet brass, similar to that shown in Fig. 2, so that it will fit tightly over the ring and its outwardly projecting ends will rest upon the base of the instrument. Small wood screws are used in fastening the stirrup to the base. The fastening may be made more secure by cutting a groove across the inside of the ring for the stirrup to fit in, Fig. 3, thus preventing the possibility of the ring moving through the stirrup. Two holes should be drilled in the base for the terminals of the winding to pass through, and it would be best to cut two grooves in the side of the ring for these wires so as to prevent their coming into contact with the metal stirrup. Two back-connected binding posts, A and B, Fig. 3, are mounted on the base and the ends of the winding attached to them. The wires should be placed in grooves cut in the under side of the base, and the screws used in fastening the binding posts should be countersunk.

A short compass needle is then mounted on a suitable supporting pivot in the center of the coil. This compass needle will always come to rest in an approximate north and south position when it is acted upon by the earth's magnetic field alone. If now the plane of the coil be placed in such a position that it is parallel to the direction of the compass needle (no current in the coil), the magnetic field that will be produced when a current is sent through the winding will be perpendicular to the magnetic field of the earth and there will be a force, due to this particular current, tending to turn the compass needle around perpendicularly to its original position. There will be a deflection of the needle for all values of current in the coil, and this deflection will vary in value as the current in the coil varies. The mere fact that the compass needle is deflected due to a current in the coil gives a means of detecting a current in any circuit of which the coil is a part, and the degree of this deflection affords a means of measuring the current, the value of the different deflections in terms of the current in the coil having been experimentally determined by sending a known current through the coil and noting the positions of the compass needle for each value of current used.

In order to determine the deflection of the needle, a scale, C, Fig. 3, must be mounted directly under the compass needle and a pointer, D, attached to the compass needle so that any movement of the needle results in an equal angular displacement of the pointer. The compass needle, E, should be short and quite heavy, say, 5/8 in. in length, 1/16 in. in thickness and 1/4 in. in width at its center, and tapering to a point at its ends. It should be made of a good grade of steel, tempered and then magnetized by means of a powerful electromagnet. The reason for making the compass needle short is that it will then operate in practically a uniform magnetic field, which exists only at the center of the coil. On account of the needle being so short and in view of the fact that it comes to rest parallel to the coil for its zero position, it is best to use a pointer attached to the needle to determine its deflection, as this pointer can be made much longer than the needle, and any movement of the needle may be more easily detected, as the end of the pointer moves through a much larger distance than the end of the needle, and since it may be attached to the needle, at right angles to the needle's axis, the end of the pointer will be off to one side of the coil and its movement may be easily observed. The pointer should be made of some nonmagnetic material, such as aluminum or brass, and it should be as long as it may be conveniently made. A suitable box with a glass cover may be provided in which the needle, pointer and scale may be housed. The construction of this box will be left entirely to the ingenuity of the one making the instrument.

In order to use this instrument as an ammeter, it will be necessary to calibrate it, which consists in determining the position of the pointer for various values of current through the coil. It will be necessary to obtain the use of a direct-current ammeter for this purpose. The winding of the galvanometer, ammeter, battery and a variable resistance of some kind should all be connected in series as shown in the diagram, Fig. 4. Allow the compass needle to come to rest under the influence of the earth's magnetic field and then turn the coil into such a position that it is as nearly parallel with the needle as possible. This corresponds to the zero position, and the instrument must always be in this position when it is used. The position of the ends of the pointer is now marked on the scale for different values of current, first with the current in one direction and then in the opposite direction. The deflection of the needle will, of course, reverse when the current is reversed.

The effect produced by any current upon the compass needle can be changed by changing the number of turns in the coil. In measuring a large current, a few turns of large wire would be required, and in measuring a small current, a large number of turns of small wire could be used. In other words, the size of the wire will depend upon the current it is to carry and the number of turns in the coil will depend upon the magnetic effect the current is to produce, which is proportional to the product of the number of turns and the current, called the ampere-turns.

Experiments with Camphor

Place a few scrapings from gum camphor in a tumbler of water and watch the phenomenon. The scrapings will go through all kinds of rapid motions as if they were alive. A drop of turpentine, or any oil, will stop their maneuvers. This experiment will show how quickly oil spreads over the surface of water.

Boiling Cracked Eggs

Eggs with the shells cracked can be boiled in the ordinary manner without danger of the white boiling out, if they are first wrapped in tissue paper. As soon as the paper becomes wet it will cling so tightly to the shell that the cracks are effectively closed.

A Trousers Hanger

A very serviceable hanger can be easily made of two clothespins of the clip type and about 2 ft. of large wire.

The wire should be bent into the shape shown at A with a loop about 1 in. in diameter as a hanger. The ends of the wire are slipped under the hooks on the sides of the clothespins, which are fastened to the trousers as shown in B.--Contributed by Olaf Tronnes, Evanston, Ill.

Removing Tight-Fitting Can Covers

Tight-fitting covers on lard and similar pails can be readily removed by tying a stout cord loosely below the cover, then placing an ordinary nail under the cord and twisting it. This will tighten the cord around the can evenly, which will loosen the cover.

A Skimming Spoon

A handy skimming spoon can be made very quickly of an ordinary spoon of any size desired. Slits are sawn across the bowl in the manner shown, using a hacksaw. The illustration is self-explanatory.--Contributed by G. H. Holter, Jasper, Minn.

How to Make Falling Blocks

Procure a thin board large enough to cut six blocks, 2 in. wide and 3 in. long; also 2 yd. of cotton tape, 1/4 in. wide, and some very small tacks. Cut the board into pieces of the size mentioned, and number two of them on both surfaces, 1, 2, 3, and 4. Cut off three pieces of tape, 4-3/4 in. long, and on the side of block 1 tack one piece of tape in the center at one end, and the other two pieces at each edge on the opposite end, all being on one side of the block as shown. Take the other block and lay the side numbered 4 up, then draw the two strips of tape on the edges of block 1 under it and back to the end of the surface on block 4, and tack them on this surface at the edges as shown. The center tape is passed under block 4 and turned over the opposite end and tacked. This is clearly shown in the sketch. Thus the second block will hang from either end of block 1 by simply folding them together and separating the ends.

Mark the sides of the third block 5 and 6, and place it with the two others so that the sides numbered 2, 3, and 5 will be up. Cut off three more pieces of tape, 4-3/4 in. long, and tack them on as shown, being careful not to tack through any of the first three pieces. Put on the fourth block in the same manner as the third block was attached to the second, and so on, until all the blocks are attached.

Take hold of the first block on the edges and tip it as shown by the arrow. The second block will then fall as shown by the second arrow, and the third block falls away in the same manner, and so on, down to the end.--Contributed by Wayne Nutting, Minneapolis, Minn.

Writing Name Reversed on Paper Placed on Forehead

The following is an entertaining experiment in a party of young people. One of those present is asked if he can write his name, and will, of course, answer "yes." He is then subjected to the following test: He is asked to sit down in a chair, a paper, folded several times, is placed on his forehead, a lead pencil is handed him and he is asked to write his name on the paper. As little time as possible to reflect should be left him; if he hesitates, he should be told to just go ahead, and in most cases it will be found that he starts writing his name at the left temple and, to the amusement of the others present, writes it in the way of many left-handed persons, that is, so that it is legible only when held in front of a mirror, unless one is practiced in reading reversed writing.

Use for an Old Table

An old table of the extension type, that may have a post broken, can be used against the wall in a kitchen as a work table. If there is a damaged part, that side is removed by sawing the crosspieces of the table in two and attaching it to the wall against the leaf which is turned in a reverse position.--Contributed by A. S. Thomas, Gordon, Can.

How to Make a Small Rheostat

In operating small motors there is as a rule no means provided for regulating their speed, and this often is quite a disadvantage, especially in the case of toy motors such as used on miniature electric locomotives. The speed, of course, can be regulated by changing the number of cells of battery by means of a special switch, but then all the cells are not used the same amount and some of them may be completely exhausted before the others show any appreciable depreciation. If a small transformer is used with a number of taps taken off the secondary winding, the voltage impressed upon the motor, and consequently the speed, can be changed by varying the amount of the secondary winding across which the motor is connected.

But in both these cases there is no means of varying the speed gradually. This can, however, be accomplished by means of a small rheostat placed in series with the motor. The rheostat acts in an electrical circuit in just the same way a valve does in a hydraulic circuit. It consists of a resistance, which can be easily varied in value, placed in the circuit connecting the motor with the source of electrical energy. A diagram of the rheostat is shown in Fig. 1, in which A represents the armature of the motor; B, the field; C, the rheostat, and D, the source of electrical energy. When the handle E is in such a position that the maximum amount of resistance is in circuit there will be a minimum current through the field and armature of the motor, and its speed will be a minimum. As the resistance of the rheostat is decreased, the current increases and the motor speeds up, reaching a maximum value when the resistance of the rheostat has been reduced to zero value. Such a rheostat may be used in combination with a special switch F., as shown in. Fig. 2. The switch gives a means of varying the voltage and the rheostat takes care of the desired changes in speed occurring between those produced by the variations in voltage.

A very simple and inexpensive rheostat may be constructed as follows: Procure a piece of thin fiber, about 1/16 in. thick, 1/2 in. wide and approximately 10 in. long. Wind on this piece of fiber, after the edges have all been smoothed down, a piece of No. 22 gauge cotton-covered resistance wire, starting about 1/4 in. from one end and winding the various turns fairly close together to within 1/4 in. of the other end. The ends of the wire may be secured by passing them through several small holes drilled in the piece of fiber, and should protrude 3 or 4 in. for connecting to binding posts that will be mounted upon the base of the rheostat.

Now form this piece of fiber into a complete ring by bending it around some round object, the flat side being toward the object. Determine as accurately as possible the diameter of the ring thus formed and also its thickness. Obtain a piece of well seasoned hard wood, 1/2 in. thick and 4-1/2 in. square. Round off the corners and upper edges of this block and mark out on it two circles whose diameters correspond to the inside and outside diameters of the fiber ring. The centers of these circles should be in the center of the block. Carefully saw out the two circles so that the space between the inside and outside portions will just accommodate the fiber ring. Obtain a second piece of hard wood, 1/4 in. thick and 4-3/4 in. square, round off its corners and upper edges and mount the other pieces upon it by means of several small wood screws, which should pass up from the under side and be well countersunk. Place the fiber ring in the groove, but, before doing so, drill a hole in the base proper for one end of the wire to pass through. Two small back-connected binding posts should be mounted in the corners. One of these should be connected to the end of the winding and the other to a small bolt in the center of the base that serves to hold the handle or movable arm of the rheostat in place. These connecting leads should all be placed in grooves cut in the under side of the base.

The movable arm of the rheostat may be made from a piece of 1/16-in. sheet brass, and should have the following approximate dimensions: length, 2 in.; breadth 1/2 in. at one end, and 1/4 in. at the other. Obtain a 1/8-in. brass bolt, about 1 in. long, also several washers. Drill a hole in the larger end of the piece of brass to accommodate the bolt and also in the center of the wooden base. Countersink the hole in the base on the under side with a 1/2-in. bit to a depth of 1/4 in. On the under side of the piece of brass, and near its narrow end, solder a piece of thin spring brass so that its free end will rest upon the upper edge of the fiber ring. A small handle may be mounted upon the upper side of the movable arm. Now mount the arm on the base by means of the bolt, placing several washers between it and the upper surface of the base, so that its outer end will be raised above the edge of the fiber ring. Solder a short piece of thin brass to the nut that is to be placed on the lower end of the bolt, and cut a recess in the countersunk portion of the hole in the base to accommodate it. When the bolt has been screwed down sufficiently tight a locknut may be put on, or the first nut soldered to the end of the bolt. If possible, it would be best to use a spring washer, or two, between the arm and base.

The insulation should now be removed from the wire on the upper edge of the fiber ring with a piece of fine sandpaper, so that the spring on the under side of the movable arm may make contact with the winding. The rheostat is now complete with the exception of a coat of shellac. A cross-sectional view of the completed rheostat is shown in Fig. 3.

Folding Arms for Clothesline Posts

The inconvenience of using a number of clothesline posts and the limited space available resulted in the making of a clothesline post as shown in the sketch. The entire line is supported on two posts, which should be about 6 in. square and are set in concrete. The upper ends of the posts are equipped with two arms, hinged to the sides of the posts in such a manner that the inside ends of the arms will meet on top of the post when they are in a horizontal position. Each arm is provided with three wood pins, equally spaced for the line. The arms are supported in a horizontal position by two bars of metal at the center, as shown. Holes are bored into the sides of the posts to receive the pins when the arms are at rest.

A small box is fastened to one post, to provide a place for the clothesline and the clothespins. The line, when put up, gives space for an entire washing without the use of a prop, as the line can be drawn taut enough to hold the garments.--Contributed by Olaf Tronnes, Evanston, Ill.

A Folding Bookrack

Having need of a bookrack which I could pack away in my trunk and still have room for my clothes, I made one as follows: I procured a piece of pine, 5/8 in. thick, 6 in. wide and 18 in. long, and laid out the plan on one side. Holes were drilled in the edges, 3/4 in. from the ends, to receive 1-1/2-in. round-head brass screws. The design for the ends was sawn out with a scroll saw and the edges smoothed up with fine sandpaper, whereupon the surfaces were stained and given a coat of wax. The screws were put in place to make the ends turn on them as on a bearing. In use the ends were turned up.--Contributed by Spencer Hall, Baltimore, Maryland.

A Simple Balance

Having use for a balance in a laboratory and being unable to procure any scales at the time, I hastily rigged up a device that served the purpose as well, as the work did not require very great precision. An elastic band and a short piece of string was procured and the band cut open. The string was then fastened around the beaker as shown, and the whole suspended from a shelf.

Into the beaker was then poured 100 cubic centimeters of water and the stretch of the elastic band noted by the displacement of a knot in the string in respect to the scale on a graduate, placed beside the beaker. The length of the elastic was then changed until the knot was exactly opposite the 100-division mark on the graduate scale. Then, since the elongation of the elastic band follows Hook's law, the extension of the band to the amount of one scale division means an added weight of one gram in the beaker.--Contributed by L. Horle, Newark, New Jersey.

An Ink Eraser

A good knife eraser for ink can be made from a discarded or broken ruling pen. One of the parts, or nibs, is cut off close to the handle and the remaining one sharpened on both edges at the point. This instrument is better than a knife or the regular scratcher, because the cutting edge will shave the surface of the paper or tracing cloth and not roughen or cut it. Erasing done with this knife will readily take ink without further preparation of the surface.--Contributed by Warren E. Crane, Cleveland, O.

Gate Fasteners

Buttons on gates or small doors are apt to become loose and then drop down, thereby allowing the gate or door to become unfastened. The ordinary button is shown at A where it is loose and turned by its own weight. If the button is cut as shown at B, it will remain fastened, even if it is loose on the screw or nail.--Contributed by A. S. Thomas, Amherstburg, Ont.

A Compensating Siphon

The homemade siphon shown in the sketch consists of two rubber corks and a glass tube with a rubber hose connected to it. The cork A is used as a bearing and support on the edge of the tank. The position of the cork B on the tube determines the distance that the mouth of the tube will be under the surface of the liquid, also to some extent the sensitiveness of the apparatus. However, the principle of the device is the buoyant effect of the water and the lever action of the rubber tube which is attached.

The one that I made had a tube 14 in. long, and the cork B was 1-3/4 in. in diameter, 1 in. thick, and weighed about 1/10 of a pound. The practical application of this siphon will be found in sieve tests where it is necessary to collect the residue on the bottom of the tank while drawing off the liquid at the surface, also in oil-storage tanks where it is not wished to disturb the dirt or other residue which collects on the bottom of the tank.--Contributed by James Hemphill, Jr., Duquesne, Pennsylvania.

A Polarity Indicator

Lines in a cable or the ends of connections at a distance from the battery must be tested to determine the polarity. Where a large amount of this work is to be done, as in automobile and motorboat repairing, it is necessary to have an indicator to save time. A cheap indicator for this purpose can be made of a 6-in. test tube having its ends sealed and inclosing a saturated solution of ammonium chloride (sal ammoniac) and water. The sealed ends are made by inserting a piece of wire through a cork and, after forcing this tightly into the end of the test tube, covering it with sealing wax.

To use, connect the terminals to the battery lines, and the end of the wire in the solution giving off bubbles is the negative wire.--Contributed by H. S. Parker, Brooklyn, N. Y.

Small Steam-Engine Cylinders Made from Seamless Brass Tubing

In making a small steam engine it was desired to use seamless brass tubing for the cylinders. To have them exactly alike a piece of tubing of the right size and of sufficient length for both cylinders was fitted on a wood mandrel, A, and the ends trued up in a lathe. As these cylinders were to fit into holes bored in a steel bedplate, it was necessary to have a flange at one end. A groove was turned in the tubing B in the center, and as a final operation a parting tool was used on the line CD. This resulted in a pair of cylinders flanged to fit the bedplate.--Contributed by Harry F. Lowe, Washington, D. C.

A Pocket Direct-Current Voltmeter

The assembled drawings of a very simple voltmeter are shown in Fig. 1, and its operation is as follows: The moving portion consists of a pointer, or needle, A; a small permanent magnet, or armature, B, and a counterweight, C, mounted upon a small steel shaft, D. The ends of this steel shaft are pointed and rest in bearings provided in the U-shaped piece of brass E, which is rigidly fastened to the fiber base F, by means of two screws. The permanent magnet B, carried on the shaft D, is at all times under the magnetic influence of the permanent horseshoe magnet, G, which is fastened, by means of thin brass straps, H H, and small screws, to the base F, so that the ends of the armature B are directly above the poles of the horseshoe magnet. The armature B will assume the position shown in the sketch when it is acted upon by the permanent magnet G alone and the moving system is perfectly balanced. A solenoid, J, is mounted in the position shown. When there is a current in its winding its soft-iron core will become magnetized and the magnetic pole produced at the lower end will produce a magnetic force upon the armature B, with the result that the armature will be rotated either in a clockwise or counter-clockwise direction, depending upon its polarity and the polarity of the end of the core adjacent to it. Thus, if the left end of the armature has north polarity, the right end south polarity, and the lower end of the core is magnetized to a south polarity the armature will be rotated clockwise, for the left end, or north pole, will be attracted by the lower end of the iron core, which is a south pole, and the right end will be repelled. This is in accordance with one of the fundamental laws of magnetism which states that magnetic poles of unlike polarity attract each other and those of like polarity repel each other. The amount the armature B is rotated will depend upon the relative effects of the pole of the solenoid and the permanent magnet G. The strength of the pole of the solenoid will depend upon the current in its winding and the number of times the current passes around the core, or the number of turns in the winding. In other words, the strength of the pole of the solenoid varies as the product of the current and the number of turns, which is called the ampere-turns. The same magnetic effect can be produced by a large current passing through a few turns or a small current passing through a relatively large number of turns. This simple relation of current and turns gives a means of adjusting the current capacity of the instrument so that a full-scale deflection of the needle will correspond to any desired maximum current. The instrument may be used as either a voltmeter or as an ammeter, and its operation will be identical in each case. The resistance of the voltmeter, however, will be many times the resistance of the ammeter, as it will be connected directly across the line, while the ammeter will always be in series in the circuit in which it is desired to measure the current. The following description and suggestion as to how to proceed in the construction of this instrument may be useful to those who undertake to build one. All the minor details and some of the dimensions will be omitted in the description, but these can be easily supplied.

Procure a piece of hard rubber or fiber, about 1/4 in. in thickness and of sufficient size to cut from it a disk, 2-1/2 in. in diameter. Make a small horseshoe magnet from a piece of the very best steel obtainable, and magnetize it to as high a strength as possible. This magnet is made of a piece of steel, 1/8 in. thick, about 3/8 in. in breadth, and of such length that the overall lengthwise dimension of the completed magnet will be about 1-7/8 in. and the distance between the inside edges of the ends a little greater than 1/2 in. Fasten the completed magnet to the base F by means of two or three straps, made from some thin brass, and small machine or wood screws.

Then cut from some 1/16-in. sheet brass a piece having the general appearance and dimensions shown at A, Fig. 2. Bend the ends of this piece over at right angles to the center portion along the dotted lines. Drill the hole at the upper end and thread it for a 1/16-in. machine screw. By means of a pointed drill, make a small recess at the lower end directly opposite the first hole. This small recess is to form the lower bearing for the shaft supporting the moving system, while a small recess cut centrally in the end of a screw, mounted in the upper hole, will form the upper bearing. The screw placed in the upper hole need be only about 3/16 in. long. The holes in the two wings are for mounting this piece upon the fiber base, as shown in Fig. 1.

The shaft for supporting the moving system is made of a piece of a hatpin. It is about 13/16 in. long and its ends are pointed so that they will turn freely in the bearings provided for them.

The armature is cut from a piece of 1/16-in. sheet steel. It is made about 3/4 in. long, 5/16 in. wide at the center, tapering to 1/8 in. at the ends. A hole is drilled in its center so that it may be forced onto the shaft. It is mounted so that its lower surface comes about 1/4 in. from the lower end of the shaft.

Then cut from some very thin brass a piece, that is to form the needle, 1/4 in. wide at one end and tapered to a point at the other, the total length being about 3 in. Drill a hole in the large end of this piece, the same size as the shaft and 1/2 in. from the end. This piece is not fastened to the shaft until some of the other parts are completed.

The spool upon which the winding is to be placed is made as follows: Procure a piece of very soft wrought iron, 1-1/4 in. long and 1/4 in. in diameter, to form the core. The ends of the spool are made of thin brass and are dimensioned as shown in Fig. 2, at B and C. The piece shown at B is to form the lower end of the spool, and is bent at right angles along the dotted line. The two holes at the lower edge are for attaching the end of the spool to the fiber base. The piece shown at C forms the upper end of the spool and at the same time a back upon which the scale of the instrument is mounted. The holes in the lower edge are threaded for small machine screws, as it will be necessary to fasten this piece to the base by means of screws that pass through the base from the under side, as shown in Fig. 1. Bend the upper and lower portion of the piece over at right angles to the center portion along the dotted lines. Make sure that the large hole in the center of each end piece is of such size that it will fit very tight on the end of the wrought-iron core. Force the end pieces onto the ends of the core a short distance, say, 1/16 in., and hammer down the edges of the core so that the end pieces cannot be easily removed. In fastening the ends to the core be sure that the parts that are to rest upon the base are parallel with each other and extend in opposite directions; also that the ends are at right angles to the core. Then insulate the inner portions of the completed spool with several thicknesses of onion-skin paper, or any good-quality, thin writing paper, and shellac. The winding will be described later.

Mount the spool and support for the bearings upon the base so that they occupy the positions, relative to each other, indicated in Fig. 1. A paper scale is then mounted upon the brass base provided for it by means of some thin shellac. The upper and lower lines for the scale can now be drawn upon the paper, using the center of the screw at the lower end of the needle as a center. These lines are best placed about 1/8 in. apart and not nearer the edge of the base than 1/4 inches.

The needle is bent over at right angles 5/16 in. from the center of the shaft. Another right-angle bend in the needle is then made so that the pointed end will be about 1/16 in. above the surface of the scale when the large end of the needle is fastened to the shaft 3/8 in. from the upper end of the latter. Turn the needle on the shaft so that the pointer is at the left end of the scale when the moving system is at rest. The shaft must be exactly vertical when this adjustment is made. Cut the end of the needle down until its end is midway between the two scale lines. Solder the needle to the shaft, and then place a sufficient quantity of solder on the broad end to balance the system perfectly and allow it to come to rest in any position when the armature B is not influenced by any magnetic field.

A containing case for the instrument may be made as follows: Make a cylinder from some thin sheet brass, having exactly the same inside diameter as the base, and a height a little greater than the vertical distance from the lower surface of the base to the upper surface of the needle. Also a disk from some thin sheet brass, having a diameter 1/8 in. greater than the outside diameter of the cylinder. Round off the edges of this disk and cut a curved slot in it directly over the scale, about 3/8 in. wide and of the same length and form as the scale. Solder the disk to one end of the cylinder, placing the solder all on the inside. To prevent moisture from entering the case, fasten a piece of thin glass on the under side of the slot in the disk by means of some shellac and several pieces of brass soldered to the disk and bent down onto the glass. The case can now be fastened to the base by means of several screws, passing through its lower end into the edge of the base. Two small binding posts are mounted on the outside of the case, about 90 deg. apart and well insulated from each other and from the case, to serve as terminals for the instrument.

The instrument is now complete with the exception of the winding. Since this is to be a voltmeter and it is always desirable that a voltmeter take as small a current as possible, the winding must consist of a relatively large number of turns of small wire, each turn carrying a small current. The difference in the construction of different instruments necessitates that their winding contain a different number of turns in order that a given voltage may produce a full-scale deflection. A little experimenting with different windings is the easiest means of determining the proper size of wire and number of turns to meet individual requirements. After adjusting the winding so that the maximum voltage it is desired to measure produces a full-scale deflection, the scale is calibrated by marking the positions of the needle in accordance with those of the needle of a standard instrument connected in parallel with it. In marking the scale of an ammeter, connect the instruments in series. Remember that if the instrument is to be used as an ammeter, it must have as low a resistance as possible and that to prevent undue heating, the wire must have ample cross section.

If difficulty is experienced due to the continuous vibration of the needle, although the current be practically constant, this trouble can be greatly reduced by mounting a paper wind vane on the moving system, which will tend to dampen its movement.

Falling Leaves in a Nature Scene

Use an ordinary pasteboard box, a shoe box or larger, and cut out one end. Fasten the box to the ceiling by means of pasteboard strips. One end of these strips is pasted on the bottom of the box and the other ends tacked to the ceiling. Fit a piece of board, 1/2 in. thick, into the open end of the box so that it will slide easily back and forth on the inside. Place this slide in the back of the box, attach a string to it and run this through double tacks placed in the ceiling and to the side wings.

Have the box almost full of autumn leaves, and when the slide is pulled slowly by the operator, they will be pushed, one or two at a time, out of the open end, and will drift down to the stage as naturally as if falling from trees, making quite a realistic scene.--Contributed by Miss S. E. Jocelyn, New Haven, Conn.

Home or Traveling Utility Bed Pocket

The pocket is made of cretonne with wire hooks attached on the upper edge. The compartments are arranged as needs may require. It can be hooked on the head, foot or side rail of the bed or used, as shown, in a sleeping car. It provides a place to keep the slippers, gown and other necessities, and can be rolled up and put in a bag.--Contributed by Harriette I. Lockwood, Philadelphia, Pa.

A Paper Perforator

In an emergency an ordinary hacksaw blade may be made to serve very acceptably as a paper perforator. The toothed edge is applied to the paper and the reverse edge tapped with a mallet or hammer. A considerable number of sheets may be perforated at one time, depending of course on the thickness and softness of the paper.

Turning Brass Rings

Occasionally an amateur has need of brass rings of round cross section, and if their construction is not understood, the task is a difficult one. If a piece of brass tubing, an old bushing or a cored piece is at hand, a part of the work is already done. If not, a piece of stock with large enough outside diameter should be chucked in the lathe and drilled out with the right size of drill. A tin or pasteboard template should be prepared the size of the ring section--a half circle is best, and it is easiest made by drilling a hole in the tin and cutting it in two. An inside boring tool and a turning tool are necessary. It is preferable to shape the inside first, cutting it out roughly and checking up with the template. The amount of inside cutting is shown in the drawing. A hard scraper and emery cloth may be used for smoothing and polishing.

Turn and polish the outside and finally turn as far down on the inner quarter as can be done without cutting off the finish, then polish and cut it off. It only requires a little filing to smooth up the rim of rough metal left.

An Electric Fountain By Walter P. Butler

To make the grounds as attractive as possible for a lawn party given one night, I constructed an electric fountain which at first appeared to be an expensive proposition, but when completed the desired effect was produced without any expense whatever, as I had the things used in its construction on hand.

A light frame, 9 in. square, was made, of 3/4-in. material, as shown in Fig. 1, and a grooved pulley was attached exactly in the center on the under side of the crosspiece. A turned stick, A, 2 in. in diameter and 2-1/2 in. long, was fastened to the face of the pulley so that it turned true as the pulley and frame revolved. A hole was then bored centrally through the three parts, the frame crosspiece, the pulley, and the turned stick, of a size to fit a spindle about 3/8 in. in diameter.

A box was procured, large enough for the frame to turn in freely, and a block of wood was fastened centrally in its bottom, which had a 3/8-in. pin set in a hole bored in the center. The pin may be of hard wood, but it is better to use metal. A bolt, or piece of rod, will answer the purpose of a pin very well.

A small battery motor--I had one on hand and did not need to purchase one--was fastened to one side of the box so that its pulley was in line with the pulley on the lower surface of the frame. The batteries to run the motor were placed in the corner of the box, where the revolving frame would not touch them. The motor may be of larger current capacity, however, and run direct on the current used for the lamps.

About 1/2 in. from the lower end of the turned piece A, a brass strip was fastened around it. This work should be neatly done, and the joint soldered and smoothed, so that the outer surface will not catch on the brush used to make the contact. This ring can be better made by cutting the width from a piece of brass tubing of a size to fit on the turned stick A. About 1-1/2 in. from the lower end four segments of a circle were fastened so as to make a space of about 1/4 in. between their ends. This construction is clearly shown in Fig. 2. A cross section, showing the wire connections from the brass ring and segments to the lamps and where they lead out on top, is shown at B. The contact brushes consist of brass strips fastened with bolts to an upright, C, made of wood and attached to one edge of the block in the bottom of the box. Two nuts are used on each bolt, between which are fastened the lead wires from a source of current.

The wiring diagram is shown in Fig. 3. The wire D from the ring is run to the brass base of each lamp, of which there are four. The wires E, from each segment, are connected with solder to each screw ferrule of the lamps, and the ends are left bare and open, as shown, between the lamps.