CONSTRUCTION.
The mercury tube should be made first. Take a piece of glass tubing 20 inches long, and bend it at a point 9 inches from one end after heating in a spirit flame. The legs should be kept as parallel as possible. Lay the tube, while the heated part is still pliant, on a flat surface, the bend projecting over the edge, So that the two legs shall be in line. When the glass has cooled, bend over two inches of the longer leg to an angle of about 45 degrees.
A standard for the tube is now made out of one-inch wood. Hollow out a bed in which the tube shall lie and be completely protected. To the right of the tube the standard is notched to take a small bottle. The notch should be slightly narrower than the diameter of the bottle, and have its sides hollowed out to fit.
Halfway up the tube draw a zero mark across the standards, and above this a scale of inches in fractions on both sides. Each inch represents 1 lb. pressure.
The cork of the bottle must be pierced with a red-hot wire for two glass tubes, one of which is bent over for the blowing tube. Both tubes should be pointed at the bottle end so that they may enter the cork easily. Make the top of the cork air tight with sealing-wax. The purpose of the bottle is to catch any mercury that might be sucked out of the tube; one does not wish mercurial poisoning to result from the experiments. Also it prevents any saliva entering the mercury tube.
When the latter has been secured to the standard by a couple of slips of tin nailed to the front, connect it up with the bottle, and fill it up to the zero mark with mercury poured in through a small paper funnel.
The open end of the tube should be provided with an inch of tubing. Clips placed on this and on the rubber connection between tube and bottle will prevent the escape of mercury should the apparatus be upset when not in use.
The average blowing pressure of which the lungs are capable is about 1-1/2 lbs. per square inch; inspiration pressure without mouth suction about 1 lb. per square inch; suction pressure 2-1/2 to 3 lbs. per square inch.
Caution.—Don’t ask people with weak lungs to try experiments with the apparatus described in this chapter.
XXXI.
HOME-MADE HARMONOGRAPHS.
Have you ever heard of the harmonograph? If not, or if at the most you have very hazy ideas as to what it is, let me explain. It is an instrument for recording on paper, or on some other suitable surface, the figures described by two or more pendulums acting in concert.
The simplest form of harmonograph is shown in Fig. 168. Two pendulums are so suspended on points that their respective directions of movement are at right angles to one another—that is, pendulum A can swing only north and south, as it were, and pendulum B only east and west. On the top of B is a platform to carry a card, and on the upper end of A a lever is pivoted so as to be able to swing only vertically upwards and downwards. At its end this lever carries a pen, which when at rest lies on the centre of the card platform.
[Illustration: FIG. 168.—Simple Rectilinear Harmonograph.]
The bob, or weight, of a pendulum can be clamped at any point on its rod, so that the rate or “period” of swing may be adjusted or altered. The nearer the weight is brought to the point of suspension, the oftener will the pendulum swing to and fro in a given time—usually taken as one minute. From this it is obvious that the rates of swing of the two pendulums can be adjusted relatively to one another. If they are exactly equal, they are said to be in unison, and under these conditions the instrument would trace figures varying in outline between the extremes of a straight line on the one hand and a circle on the other. A straight line would result if both pendulums were released at the same time, a circle,[1] if one were released when the other had half finished a swing, and the intermediate ellipses would be produced by various alterations of “phase,” or time of the commencement of the swing of one pendulum relatively to the commencement of the swing of the other.
[Footnote 1: It should be pointed out here that the presence of friction reduces the “amplitude,” or distance through which a pendulum moves, at every swing; so that a true circle cannot be produced by free swinging pendulums, but only a spiral with coils very close together.]
But the interest of the harmonograph centres round the fact that the periods of the pendulums can be tuned to one another. Thus, if A be set to swing twice while B swings three times, an entirely new series of figures results; and the variety is further increased by altering the respective amplitudes of swing and phase of the pendulums.
We have now gone far enough to be able to point out why the harmonograph is so called. In the case just mentioned the period rates of A and B are as 2: 3. Now, if the note C on the piano be struck the strings give a certain note, because they vibrate a certain number of times per second. Strike the G next above the C, and you get a note resulting from strings vibrating half as many times again per second as did the C strings—that is, the relative rates of vibration of notes C and G are the same as those of pendulums A and B—namely, as 2 is to 3. Hence the “harmony” of the pendulums when so adjusted is known as a “major fifth,” the musical chord produced by striking C and G simultaneously.
In like manner if A swings four times to B’s five times, you get a “major third;” if five times to B’s six times, a “minor third;” and if once to B’s three times, a “perfect twelfth;” if thrice to B’s five times, a “major sixth;” if once to B’s twice, an “octave;” and so on.
So far we have considered the figures obtained by two pendulums swinging in straight lines only. They are beautiful and of infinite variety, and one advantage attaching to this form of harmonograph is, that the same figure can be reproduced exactly an indefinite number of times by releasing the pendulums from the same points.
[Illustration: FIG. 169.—Goold’s Twin Elliptic Pendulum Hamonograph.]
But a fresh field is opened if for the one-direction suspension of pendulum B we substitute a gimbal, or universal joint, permitting movement in all directions, so that the pendulum is able to describe a more or less circular path. The figures obtained by this simple modification are the results of compounded rectilinear and circular movements.
[Illustration: FIG. 170.—Benham’s miniature Twin Elliptic Pendulum
Harmonograph.]
The reader will probably now see even fresh possibilities if both pendulums are given universal movement. This can be effected with the independent pendulums; but a more convenient method of obtaining equivalent results is presented in the Twin Elliptic Pendulum invented by Mr. Joseph Goold, and shown in Fig. 169. It consists of—(1) a long pendulum, free to swing in all directions, suspended from the ceiling or some other suitable point. The card on which the figure is to be traced, and the weights, are placed on a platform at the bottom of this pendulum. (2) A second and shorter free pendulum, known as the “deflector,” hung from the bottom of the first.
This form of harmonograph gives figures of infinite variety and of extreme beauty and complexity. Its chief drawback is its length and weight, which render it more or less of a fixture.
Fortunately, Mr. C. E. Benham of Colchester has devised a Miniature Twin Elliptic Pendulum which possesses the advantages of the Goold, but can be transported easily and set up anywhere. This apparatus is sketched in Fig. 170. The main or platform pendulum resembles in this case that of the Rectilinear Harmonograph, the card platform being above the point of suspension.
Value of the Harmonograph.—A small portable harmonograph will be found to be a good means of entertaining friends at home or elsewhere. The gradual growth of the figure, as the card moves to and fro under the pen, will arouse the interest of the least scientifically inclined person; in fact, the trouble is rather to persuade spectators that they have had enough than to attract their attention. The cards on which designs have been drawn are in great request, so that the pleasure of the entertainment does not end with the mere exhibition. An album filled with picked designs, showing different harmonies and executed in inks of various colours, is a formidable rival to the choicest results of the amateur photographer’s skill.
Practical Instructions for making Harmonographs.
Pendulums.—For the Rectilinear type of harmonograph wooden rods 5/8 to 3/4 inch in diameter will be found very suitable. They cost about 2d. each. Be careful to select straight specimens. The upper pendulum of the Miniature Twin Elliptic type should be of stouter stuff, say a broomstick; that of the Goold apparatus stouter still.
All pendulums on which weights are slid up and down should be graduated in inches and fractions, reckoning from the point of suspension as zero. The graduation makes it easy to re-establish any harmony after the weights have been shifted.
Suspensions.—For a harmonograph to give satisfaction it is necessary that very little friction should be set up at the point of suspension, so that the pendulums may lose amplitude of swing very slowly.
One-way suspensions are easily made. Two types, the point and knife-edge respectively, are shown in Fig. 168 and the top part of Fig. 172. The point suspension is most suitable for small rods and moderate weights; the knife-edge for large rods and heavy weights which would tend to crush a fine point.
[Illustration: FIG. 171.—Gimbal giving universal movement: point suspension.]
Points should rest in cup-shaped depressions in a metal plate; knife-edges in V-shaped grooves in a metal ring.
[Illustration: FIG. 172.—Knife-edge universal-motion gimbal.]
Screws turned or filed to a sharp end make convenient points, as they can be quickly adjusted so that a line joining the points lies exactly at right angles to the pendulum. The cups to take the points should not be drilled until the points have been thus adjusted. Make a punch mark on the bedplate, and using this as centre for one of the points, describe an arc of a circle with the other. This will give the exact centre for the other cup. It is evident that if points and cup centres do not coincide exactly there must be a certain amount of jamming and consequent friction.
In making a knife-edge, such as that shown in Fig. 172, put the finishing touches on with a flat file drawn lengthwise to ensure the edge being rectilinear. For the same reason the V slots in the ring support should be worked out together. If they are formed separately, the chances are against their being in line with one another.
Gimbals, or universal joints, giving motion in all directions, require the employment of a ring which supports one pair of edges or points (Fig. 172), and is itself supported on another pair of edges or points set at right angles to the first. The cups or nicks in the ring should come halfway through, so that all four points of suspension shall be in the same plane. If they are not, the pendulum will not have the same swing-period in all directions. If a gimbal does not work with equal freedom in all ways, there will be a tendency for the pendulum to lose motion in the direction in which most friction occurs.
By wedging up the ring of a gimbal the motion of the pendulum is changed from universal to rectilinear. If you are making a harmonograph of the type shown in Fig. 168, use a gimbal for the platform pendulum, and design it so that the upper suspension gives a motion at right angles to the pen pendulum. The use of two little wedges will then convert the apparatus in a moment from semirectilinear to purely rectilinear.
Weights.—The provision of weights which can be slipped up and down a rod may present some difficulty. Of iron and lead, lead is the more convenient material, as occupying less space, weight for weight, and being more easily cast or shaped. I have found thin sheet roofing lead, running 2 lbs. to the square foot, very suitable for making weights, by rolling a carefully squared strip of the material round the rod on which it will have to move, or round a piece of brass tubing which fits the rod. When the weight has been rolled, drill four holes in it, on opposite sides near the ends, to take nails, shortened so that they just penetrate all the laps but do not enter the central circular space. These will prevent the laps sliding over one another endways. A few turns of wire round the weight over the heads makes everything snug.
Just one caution here. The outside lap of lead should finish at the point on the circumference where the first lap began, for the weight to be approximately symmetrical about the centre.
An alternative method is to melt up scrap lead and cast weights in tins or flowerpots sunk in sand, using an accurately centred stick as the core. This stick should be very slightly larger than the pendulum rod, to allow for the charring away of the outside by the molten metal. (Caution.—The mould must be quite dry.)
Failing lead, tin canisters filled with metal scrap may be made to serve. It will in this case be necessary to bore the lid and bottom centrally and solder in a tube fitting the rod, and to make an opening through which the weighting material can be inserted.
Adjustment of Weights.—As lead is too soft a metal to give a satisfactory purchase to a screw—a thread cut in it soon wears out—it is better to support a leaden weight from underneath by means of a brass collar and screw. A collar is easily made out of a bit of tubing thickened at the point where the screw will pass by soldering on a suitably shaped piece of metal. Drill through the reinforcement and tubing and tap to suit the screw used, which may well be a camera tail screw, with a large flat head.
I experienced some trouble from the crushing of wooden rods by a screw, but got over it as follows. The tubing selected for the collar was large enough to allow a piece of slightly smaller tubing to be introduced between it and the rod. This inner piece was slit from one end almost to the other, on opposite sides, and soldered at one end to the outer tube, a line joining the slots being at right angles to the axis of the screw. The pressure of the screw point was thus distributed over a sufficient area of the wood to prevent indentation. (See Fig. 173.)
[Illustration: FIG. 173.]
[Illustration: FIG. 174.—Pivot for pen lever.]
Pen Levers.—The pen lever, of whatever kind it be, must work on its pivots with very little friction, and be capable of fine adjustment as regards balance. For the Rectilinear Harmonograph the form of lever pivot shown in Fig. 174 is very suitable. The spindle is a wire nail or piece of knitting needle sharpened at both ends; the bearings, two screws filed flat at the ends and notched with a drill.
The brass standard should be drilled and tapped to fit the screws fairly tight, so that when once adjusted they may not slacken off. If the lever is made of wood, the tail may be provided with a number of metal pegs on which to place the weights; if of wire, the tail should be threaded so that a brass weight and lock screw may be moved along it to any desired position. It is very important that the pressure of the pen on the card should be reduced to a minimum by proper balancing, as the friction generated by a “heavy” pen slows the pendulum very quickly; and that the centre of gravity should be below the point of suspension, to put the pen in stable equilibrium. The lever shown in Fig. 169 is suitable for the Twin Elliptic Pendulum.
In this case the lever is not moved about as a whole. Mr. C. E. Benham advocates the use of wood covered with velvet to rest the lever points on.
For keeping the pen, when not in use, off the platform, a small weight attached to the lever by a thread is convenient. When the pen is working, the weight is raised to slacken the thread.
[Illustration: FIG. 175.—End of pen lever.]
Attaching Pen to Lever.—In the case of wooden levers, it is sufficient to slit the end centrally for a few inches after drilling a hole rather smaller than the pen, at a point which lies over the centre of the card platform, and quite squarely to the lever in all directions, so that the pen point may rest squarely on the card. (Fig. 175.)
Another method is to attach to the end of the lever a vertical half-tube of tin, against which the pen is pressed by small rubber bands; but even more convenient is a small spring clip shaped as in Fig. 176.
[Illustration: FIG. 176.—Clip to hold glass pen.]
The card platform should be perfectly flat. This is essential for the production of good diagrams. If wood is used, it is advisable to glue two thin pieces together under pressure, with the grain of one running at right angles to the other, to prevent warping.
Another important point is to have the card platform square to the rod. If a piece of tubing fitting the rod is turned up true in the lathe and soldered to a disc screwed to the underside of the table, perpendicularity will be assured, and incidentally the table is rendered detachable.
To hold the card in place on the table, slit a spring of an old photographic printing frame down the middle, and screw the two halves, convex side upwards, by one end near two opposite corners of the platform. (See Fig. 170.) If cards of the same size are always used, the table should be marked to assist adjustment.
Making Pens.—The most satisfactory form of pen is undoubtedly a piece of glass tubing drawn out to a point, which is ground down quite smooth. The making of such pens is rather a tedious business, but if care be taken of the pen when made it will last an indefinite time.
Tubing 3/16 or 1/8 inch in external diameter is suitable. Break it up (by nicking with a file) into 9-inch lengths. Take a piece and hold its centre in the flame of a small spirit lamp, and revolve it till it softens. Then draw the glass out in as straight a line as possible, so that the points may be central. If the drawing is done too fast, the points will be much too long to be of any use: half an inch of taper is quite enough.
Assuming that a point of satisfactory shape has been attained—and one must expect some failures before this happens—the pen may be placed in the pen lever and ground down on a perfectly clean wet hone laid on the card platform, which should be given a circular movement. Weight the lever so as to put a fair pressure on the point.
The point should be examined from time to time under a strong magnifying-glass, and tested by blowing through it into a glass of water. For very liquid ink the hole should be as small as you can possibly get it; thick inks, such as Indian, require coarser pens.
The sharp edge is taken off and the width of the point reduced by drawing the pen at an angle along the stone, revolving it all the time. The nearer to the hole you can wear the glass away the finer will be the line made by the pen.
Another method is as follows:—Seal the point by holding it a moment in the flame. A tiny bulb forms on the end, and this has to be ground away till the central hole is reached. This is ascertained by the water test, or by holding the pen point upwards, so that light is reflected from the tip, and examining it under the magnifier. Then grind the edge off, as in the first case.
Care of Pens.—The ink should be well strained, to remove the smallest particles of “suspended matter,” and be kept corked. Fill the pen by suction. On no account allow the ink to dry in the pen. Squirt any ink out of it when it is done with, and place it point downwards in a vessel of water, which should have a soft rubber pad at the bottom, and be kept covered to exclude dust. Or the pen may be cleaned out with water and slipped into a holder made by rolling up a piece of corrugated packing-paper. If the point gets stopped up, stand the pen in nitric or sulphuric acid, which will probably dissolve the obstruction; and afterwards wash it out.
Inks.—I have found Stephens’s coloured inks very satisfactory, and can recommend them.
Paper and Cards.—The paper or cards used to draw the figures on should not have a coated surface, as the coating tends to clog the pen. The cheapest suitable material is hot pressed paper, a few penny-worths of which will suffice for many designs. Plain white cards with a good surface can be bought for from 8s. to 10s. per thousand.
Lantern Slides.—Moisten one side of a clean lantern slide plate with paraffin and hold it over a candle flame till it is a dead black all over. Very fine tracings can be obtained on the smoked surface if a fine steel point is substituted for the glass pen. The design should be protected by a cover-glass attached to it by a binding strip round the edges.
Details of Harmonographs.
The reader may be interested in details of the apparatus shown in Figs. 168 and 170, made by the writer.
The Rectilinear Harmonograph, shown in Fig. 168, has pendulums of 5/8-inch wood, 40 inches long, suspended 30 inches from the lower ends, and set 10 inches apart, centre to centre. The suspensions are of the point type. The weights scale 5 lbs. each. The platform pendulum is provided with a second weight, which can be affixed above the suspension to slow that pendulum for 2:3, 4:5, 7:8, and higher harmonies.
The baseboard is plain, and when the apparatus is in action its ends are supported on boxes or books laid on two tables, or on other convenient supports. The whole apparatus can be taken to pieces very quickly for transport. The total cost of materials used did not exceed 3s. 6d.
The Twin Elliptic Pendulum of Fig. 170 is supported on a tripod base made of three pieces of 1-1/2 x 1-1/2 inch wood, 40 inches long, with ends cut off to an angle of 72 degrees to give a convenient straddle, screwed at the top to an oak head 3/4 inch thick, and braced a foot below the top by horizontal crossbars 2 inches wide and 1/2 inch thick. For transport this stand can be replaced by a flat baseboard similar to that of the Rectilinear Harmonograph described in the last paragraph.
The main pendulum is a straight ash rod, 33 inches long and 1-1/4 inches in diameter, suspended 13-1/2 inches from its upper end. Two weights of 4-1/2 lbs. each, made of rolled sheet lead, are provided for this pendulum. According to the nature of the harmony, one only, or both together below the suspension, or one above and one below, are used.
The weight of the lower pendulum, or deflector, is supported on a disc, resting on a pin passing through the bottom of a piece of brass tubing, which is provided with an eye at its upper end. This eye is connected by a hook with several strands of silk thread, which are attached to the upper pendulum by part of a cycle tyre valve. The stem part of the valve was cut off from the nut, and driven into a suitably sized hole in the end of the main pendulum. The screw collar for holding the valve in place had a little brass disc soldered to the outside, and this disc was bored centrally for the threads to pass through. The edges of the hole had been rounded off carefully to prevent fraying of the threads. (Fig. 177.) The over-all length of the pendulum, reckoning from the point of suspension, is 20 inches. The weights of the lower pendulum are several in number, ranging from l lb. to 3 lbs.
[Illustration: FIG. 177.—Suspension for lower weight of Twin Elliptic
Harmonograph.]
Working the Harmonograph.—A preliminary remark is needed here. Harmonies are, as we have seen, a question of ratio of swing periods. The larger the number of swings made by the more quickly moving pendulum relatively to that of the slower pendulum in a given time, the higher or sharper is the harmony said to be. Thus, 1:3 is a higher harmony than 1:2, and 2:3 is lower or flatter than 3:8.
The tuning of a harmonograph with independent pendulums is a simple matter. It is merely necessary to move weights up or down until the respective numbers of swings per minute bear to one another the ratio required. This type of harmonograph, if made of convenient size, has its limitations, as it is difficult to get as high a harmonic as 1:2, or the octave with it, owing to the fact that one pendulum must in this case be very much shorter than the other, and therefore is very sensitive to the effects of friction.
[Illustration: FIG. 176a.—Hamonograms illustrating the ratio 1:3. The two on the left are made by the pendulums of a twin elliptical harmonograph when working concurrently; the three on the right by the pendulums when working antagonistically.]
[Illustration: FIG. 177a.—Harmonograms of 3:4 ratio (antagonistically).
(Reproduced with kind permission of Mr. C. E. Benham.)]
The action of the Twin Elliptic Pendulum is more complicated than that of the Rectilinear, as the harmony ratio is not between the swings of deflector and upper pendulum, but rather between the swings of the deflector and that of the system as a whole. Consequently “tuning” is a matter, not of timing, but of experiment.
Assuming that the length of the deflector is kept constant—and in practice this is found to be convenient—the ratios can be altered by altering the weights of one or both pendulums and by adjustment of the upper weight.
For the upper harmonies, 1:4 down to 3:8, the two pendulums may be almost equally weighted, the top one somewhat more heavily than the other. The upper weight is brought down the rod as the ratio is lowered.
To continue the harmonies beyond, say, 2:5, it is necessary to load the upper pendulum more heavily, and to lighten the lower one so that the proportionate weights are 5 or 6:1. Starting again with the upper weight high on the rod, several more harmonies may be established, perhaps down to 4:7. Then a third alteration of the weights is needed, the lower being reduced to about one-twentieth of the upper, and the upper weight is once more gradually brought down the rod.
Exact figures are not given, as much depends on the proportions of the apparatus, and the experimenter must find out for himself the exact position of the main weight which gives any desired harmonic. A few general remarks on the action and working of the Twin Elliptic will, however, be useful.
1. Every ratio has two forms.
(a) If the pendulums are working against each other— antagonistically—there will be loops or points on the outside of the figure equal in number to the sum of the figures in the ratio.
(b) If the pendulums are working with each other—concurrently—the loops form inside the figure, and are equal in number to the difference between the figures of the ratio. To take the 1:3 ratio as an example. If the tracing has 3+1=4 loops on the outside, it is a specimen of antagonistic rotation. If, on the other hand, there are 3-1=2 loops on the inside, it is a case of concurrent rotation. (Fig. 176, A.)
2. Figures with a ratio of which the sum of the numbers composing it is an even number (examples, 1:3, 3:5, 3:7) are symmetrical, one half of the figure reproducing the other. If the sum is Uneven, as in 1:2, 2:3, 2:7, the figure is unsymmetrical. (Fig. 177, A.)
3. The ratio 1:3 is the easiest to begin upon, so the experimenter’s first efforts may be directed to it. He should watch the growth of the figure closely, and note whether the repeat line is made in front of or behind the previous line of the same loop. In the first case the figure is too flat, and the weight of the upper pendulum must be raised; in the second case the weight must be lowered. Immediately an exact harmonic is found, the position of the weight should be recorded.
Interesting effects are obtained by removing the lower pendulum and allowing the apparatus to describe two elliptical figures successively, one on the top of the other, on the same card. The crossing of the lines gives a “watered silk” appearance to the design, which, if the pen is a very fine one and the lines very close together, is in many cases very beautiful.
Readers who wish for further information on this fascinating subject are recommended to purchase “Harmonic Vibrations,” published by Messrs. Newton and Co., 72 Wigmore Street, London, W. This book, to which I am much indebted, contains, besides much practical instruction, a number of charming reproductions of harmonograms.
Before closing this chapter I should like to acknowledge the kind assistance given me by Mr. C. E. Benham, who has made a long and careful study of the harmonograph.
XXXII.
A SELF-SUPPLYING MATCHBOX.
This useful little article can be constructed in a couple of hours by a handy person. In general idea it consists of a diamond-shaped box to hold vestas, working up and down diagonally on a vertical member (A in Fig. 179 (1)), which passes through slits at the top and bottom, and runs in grooves cut in the sides of the box. The top of A is grooved to allow a match to rest on it. When the box is drawn up to the full extent allowed by a transverse pin in the slot shown in Fig. 179 (2), the groove is at the lowest point of the box, and is covered by the matches. When the box is lowered, A catches a vesta and takes it up through the top, as seen in Fig. 178, for removal by the fingers.
The only materials required are a cigar-box, some pins, and a supply of glue. The box should be carefully taken to pieces, and the parts soaked in hot water till freed of all paper, and then allowed to dry under pressure, small slips of wood being interposed across the grain to keep them separate and permit the passage of air.
[Illustration: FIG. 178.—Self-supplying matchbox, with match in position for removal by fingers.]
When the wood is dry, cut out with a fret saw two pieces shaped like Fig. 179 (3), to form the ends of the box. Allow a little surplus, so that the edges may be finished off neatly with chisel and plane. The two ends should match exactly, or there will be trouble at a later stage.
Now cut, down the centre of each a groove for one edge of A to run in. By preference it should be square; but if you do not possess the necessary chisel, a V groove made with a knife will suffice—and, of course, in this case the edges of A will have to be bevelled to fit.
[Illustration: FIG. 179.—Details of self suplying matchbox.]
The four sides of the box, BB and CC, are next cut out. Their sectional shape is shown in Fig. 179 (1). They should be rather longer than the length of the ordinary vesta, and all of exactly the same length, and rectangular. A very small hack saw (costing about 1s.) with fine teeth is the best possible tool for close cutting, and a small 1 shilling iron plane is invaluable for truing and bevelling the edges.
The glue pot, which we will assume to be ready for use, is now needed to attach the fixed B (the other B is hinged to form a lid for filling the box through) and CC to the ends. This operation must be carried out accurately, so that the slots may not be blocked.
While the glue is setting, cut out A, allowing an extra 1/16 inch of width for fitting. The slot down the centre is best made with a fret saw, and should be smoothed internally by drawing a strip of fine glass paper to and fro through it. The length of the slot is of great importance. It must reach to just that distance from the top edge which brings that edge flush with the bottom of the box when the box is raised; and in the other direction must permit the box to settle on to its foot, so that the match lifted shall project above the box.
Work the edges of A down carefully (double-bevelling them if the notches are V-shaped) till A will run easily, but not loosely, in the box. Then cut out two slips, DD, and bevel them at the top to an angle of 45 degrees. Put A in place and glue them on, taking care that the glue does not hold them fast to A.
Pierce a small hole through DD, in line with the slot, and insert a pin.
Draw the box fully up, and see if the top of A sinks to the proper place.
If it projects a little, lengthen the slot a trifle.
Cut out the supports EE, finish them neatly, and glue them to A. Make sure that the pin lets the box touch them.
Fix on the lid B with two pins for pivots, and fit a little catch made of brass wire. To give extra security, drive ordinary pins, cut off to 5/8 inch, through the sides into fixed B, CC, and DD, and through EE into A. This is an easy enough business if pilot holes are made with a very fine awl or a tiny drill, and a small, light hammer is used. It now remains only to go over the whole box with glass paper or emery cloth, and to glue a diamond of coarse glass paper to one end for striking the matches on.
Note that the lid must not be opened when the box is down, as it would be wrenched off its pivots.
XXXIII.
A WOODEN WORKBOX.
The box illustrated by Fig. 181 was copied from an article of Norwegian manufacture. Its construction is an extremely simple matter, provided that one can get a piece of easily bent wood (birch, for instance), not exceeding 3/16 inch in thickness, for the sides.
[Illustration: FIG. 180.—Showing how to draw an ellipse.]
[Illustration: FIG. 181.—Norwegian workbox.]
The bottom of the box is made of 5/16 or 3/8 inch wood, cut to an oval or elliptical shape. To mark out an ellipse about 8 inches long and 5-1/2 inches wide—this will be a. convenient size—stick two pins into the board 5-1/8 inches apart, pass a loop of thread 14 inches in circumference round these, and run the point of a pencil round the pins in the path which it has to take when confined by the slack of the loop (Fig. 180). Fret-saw along the line.
The wood strip for the side is 4-1/2 inches deep, and 1-1/2 inches longer than the circumference of the bottom. The ends are thinned off somewhat, as shown in Fig. 181, to prevent the lap having a clumsy appearance, and the surface is smoothed all over with sandpaper. Bore a number of small nail holes 3/16 inch from one edge, and then steam the wood over a big saucepan or other suitable vessel until it is quite lissom.
When attaching the side piece to the bottom, begin at the middle, and work first towards what will be the inside end of the lap, and then towards the outside end. Nails are driven in through the holes already drilled. When nailing is finished, clip the top of the overlap with a hand-vice or screw spanner, to prevent the tops of the ends sliding over one another, and bore a line of holes l/4 inch apart, and at the same distance from the outer end. Fine copper wire drawn to and fro through alternate holes from one end of the row to the other and back again, will secure the joint.
The lid overlaps the side 1/4 inch in all directions and has a square notch cut in it at one end to pass under the piece A, and at the other a deeper, circular-ended nick to enable it to pass over the key B when that is turned into the position shown in the illustration. A is cut out of 1/4-inch wood; B, in one piece, out of 1/2-inch. Their length under the heads exceeds the inside depth of the box by the thickness of the lid.
A is affixed rigidly to the side by small screws or wire, while B must be attached in a manner, which will allow the head to rotate. Cut two nicks round the shank, and two horizontal slots at the same height through the end of the box. A couple of brass rings must then be procured of such a size that, when flattened into a somewhat oval shape, they will project beyond the slots sufficiently to allow a piece of wire to pass through them and prevent their being drawn back again.
Quarter-inch wood will do for the lid. A handle is made out of a couple of inches of small cane bent into a semicircle, let through the lid at each end, glued, and cut off flush.
The exterior may be decorated by a design in poker-work, or be stained and varnished. This is left to the maker’s discretion.
XXXIV.
WRESTLING PUPPETS.
[Illustration: FIG. 182.—Peg marked for cutting and drilling.]
The expenditure of a halfpenny, and a quarter of an hour’s use of a pocket knife, bradawl, and pliers, will produce a toy which is warranted to amuse grown-ups as well as children. Wrestlers made out of clothes pegs may be bought for a copper or two in the street, and are hardly a novelty; yet a few notes on home production will not be a waste of space, as making is cheaper, and much more interesting, than buying.
The clothes pegs used must be of the shape shown in Fig. 182, with a round top. They cost one penny per dozen.
Drill holes through body and legs as indicated in Fig. 182. Cut the legs from the “trunk,” and whittle them to the shape of Fig. 183. The arms, made out of any thin wood, are 2-1/4 inches long between centres of end holes.
To get the best results the two arms and the four legs should be paired off to exactly the same length.
[Illustration: FIG. 183.—Clothes-peg wrestlers.]
The neatest method of attaching the parts is to use small brass tacks, which must, of course, be of somewhat larger diameter than the holes in the body. Holes in arms and legs are a loose fit, so that the wrestlers may be very loose-jointed, and the tacks must not be driven in far enough to cause any friction.
Instead of tacks one may use wire passed through the parts and secured by a bend or loop at each end. Wire has the disadvantage of entangling the thread which works the figures.
When assembling is finished, bore holes in the centres of the arm pieces, pass a piece of wire through, and twist it into a neat loop at each end. To one loop tie 2 feet of strong thread (carpet thread is best), and to the free end of the thread a large nail or hook. The other loop has 6 feet or so of thread tied to it, to be worked by the hand. If the thread is stained black, it will be practically invisible by artificial light.
The nail or hook is stuck under the edge of the carpet, or into some crack or cranny which affords a good hold, and the wrestlers are worked by motions of the hand. The funniest antics are produced by very slight jerks.
If the arms are set too close together the heads may stick between them, in which case one must either flatten off the sides of the heads or insert fresh arm wires of greater length. If a head persists in jamming against the thread wire or getting under it and staying there, cut 1/2 inch off a pin and stick it into the front of the crown, so that the head is arrested by the wire when the wrestler bends forward.
[Illustration: FIG. 184.—Large wrestlers made of stout wood.]
Large Wrestlers.—A more elaborate and realistic pair is shown in Fig. 184. The originals of the sketch are 8 inches high. Half-inch deal was used for the bodies, 3/8-inch for the legs and arms. The painting-in of hair, features, tights, and shoes adds considerably to the effect. The heads and limbs are mere profiles, but anyone with a turn for carving might spend a little time in rounding off and adding details which will make the puppets appear more lifelike.
XXXV.
DOUBLE BELLOWS.
The small-sized bellows which have become popular in sitting-rooms are usually more ornamental than efficient, and make one think regretfully of the old-fashioned article of ample capacity which is seldom seen nowadays.
Fig. 185 illustrates a method of coupling up two small bellows in such a manner as to provide an almost continuous blast, besides doubling the amount of air sent through the fire in a given time, at the coat of but little extra exertion. A piece of wood half an inch thick is screwed across one bellows just behind the valve hole. The two bellows are then laid valve facing valve, and are attached to one another by a strip of tin passed round the wood just behind the nozzles and by tying the two fixed handles together.
[Illustration: FIG. 185.—Double-acting bellows. Two methods of coupling shown.]
Make a rectangle of stout wire somewhat wider than the handles and long enough to reach from the outer face of one moving handle to that of the other, when one bellows is quite closed and the other full open. The ends of the wire should be soldered together, and the ends of the link held up to the handles by a couple of staples.
An alternative method is to use a piece of wood with a screw driven into it at right angles near each end through the staples on the handles (Fig. 185, a). In place of the staples you may use screw-in eyes fitting the screws.
XXXVI.
A HOME-MADE PANTOGRAPH.
The pantograph is a simple apparatus for copying drawings, maps, designs, etc., on a reduced or enlarged scale, or to the same size as the original.
[Illustration: FIG. 186.—Details of simple pantograph.]
A sketch of a pantograph is given in Fig. 186. Four rods are jointed together to form a parallelogram, the sides of which can be lengthened or shortened to suit the scale of reproduction. One is attached by a fixed pivot at a to the board on which the drawing is done. At b and e are removable pivots, used for adjusting the rods; at c is a pivot which projects an inch or so below the rods. The pointer is inserted at d for enlargement, or at f for reduction, the pencil being in the unoccupied hole at d or f.
If a same-sized copy is desired, the fixed pivot is transferred to d, and the pencil and pointer placed at a and f respectively.
Construction of an Enlarging and Reducing Pantograph.—Cut out of 1/8-inch oak, walnut, or beech four rods 5/8 inch wide and 19 inches long. Smooth them well all over, and make marks near the ends of each, exactly 18 inches apart. The graduation of the rods for the adjustment pivot holes is carried out in accordance with the measurements given in Fig. 187. It is advisable to mark out and bore each rod separately if you do not possess a machine which will drill holes quite perpendicularly; if you do, all four rods can be drilled at one operation.
In Fig. 187 the lower row of numerals indicates the number of times (in diameters) the original is enlarged when all four holes similarly figured are used; the upper row, the size of the copy as compared with the original in case of reduction.
If proportions other than those given are required, a very little calculation will locate the necessary holes.
Pivots.—All the pivots must fit their holes accurately, as any looseness at the joints detracts from the truth of reproduction. For pivots band b and e may use brass screws and small pieces of hard wood as nuts to hold them in position. The nuts should screw on rather stiffly, and not be forced hard against the rods, as free motion with little friction at all joints is essential for good work.
[Illustration: FIG. 187.—Diagram showing how to mark off pantograph rods. The dotted lines above rod give distances of holes from ends.]
The fixed pivot at a may be merely the shank of a wire nail of the proper size driven into the board, a cork collar being slipped over it to keep the rod the proper distance from the board. For c use a screw to the head of which has been soldered half an inch of a round-headed brass nail, which will move easily over the paper. At d is needed a hollow pivot, fashioned out of a quarter of an inch of pencil-point protector or some other thin tube, burred over slightly at the ends so as not to fall out. The end of B at f has a slotted hole to grip the pencil or pointer, as the case may be.
A Same-size Pantograph.—For making a same-size copy, tracing may be preferred to the use of a pantograph; but if a pantograph is adopted, a special apparatus may be constructed for the purpose. The arrangement is exactly the same as that already described, excepting that the only holes needed are those at a, c, d, f, at the middle points of the four rods, the parallelogram formed by the rods being equal-sided. The fixed pivot is situated at d, and pencil and pointer holes are made at a and f.
Using the Pantograph.—When adjusting the instrument for reduction or enlargement, make sure that the adjustment pivots are in the holes corresponding with the scale. The fixed pivot, pointer, and pencil must be rigid, and, with pivot c, be of such a length that the pantograph as a whole moves parallel to the paper. A little sliding weight to place on the rod near the pencil will be found useful for keeping the pencil point in constant contact with the paper.
If the apparatus works stiffly, ease the holes a trifle and lead-pencil the wood at all points where two surfaces rub. It is absolutely impossible to make a good reproduction with a stiff, jerky pantograph.
To decide the positions of original and the paper for the copy, get the pointer centred on the original and adjust the paper till its centre is under the pencil.
XXXVII.
A SILHOUETTE DRAWING MACHINE.
With this very simple apparatus you will be able to give good entertainment to such of your friends as may wish to have black paper records of their faces in profile.
The machine is merely a long rod, with a sliding pencil attached to one end and a metal pointer stuck into the other, supported near the pencil end on a pivot which permits free movement in all directions.
For heads and busts only, the rod and pointer combined need not be more than 4 feet 6 inches long. The rod is a 1/2-inch blind rod, the pointer a stout knitting-needle driven axially into one end of the rod. This pointer, being of small diameter, follows the minor curves and angles of the features much more closely than would be possible with the rod.
The support is a piece of wood, 1-1/2 inches square and 12 to 15 inches long, screwed on to a large foot, which should be fairly heavy, as any tilting or slipping will, of course, spoil the silhouette. The universal joint for the rod is made by soldering a small U-shaped piece of metal to the end of a short metal bar. The ends of the U are drilled for a pin passing through the rod; and a hole is sunk into the top of the support to take the bar. The fit should be close, to prevent the pivot rocking about, and the hole in the support deep enough to bring the bottom of the stirrup down against the wood.
If a series of holes half an inch apart is drilled, through the rod, the nearest 9 inches from the pencil end, the size of the silhouette proportionately to the original can be varied by moving the pin from one hole to another.
[Illustration: FIG. 188.—Silhouettograph in use.]
[Illustration: FIG. 188a.—Group of silhouettes drawn with the machine described.]
The pencil holder is 4 inches of tubing, in which the pencil can slide easily without shaking. If necessary, the size of the pencil should be reduced by rubbing with glass paper. Bind the holder tightly to the end of the rod away from the pointer, so that one extremity just overhangs the rod. A piece of thin elastic is tied to the unsharpened end of the pencil and to the pencil tube, the adjustment allowing the pencil to project an inch when the elastic is taut but not stretched.
A fairly soft pencil and a thick, smooth paper or card give the best results. Paper should be backed by something hard to prevent the pencil digging in. Attach the paper to a firm vertical surface, such as the side of a box, a drawing board, a wall, etc.
Using the Machine.—The rod support, paper, and sitter should be arranged so that the rod is level at the height of the sitter’s nose and the pencil on the centre of the paper. Bring the support near enough to the paper to drive the pencil back into the tube until the point projects only half an inch.
A thread attached to the pencil will enable you to keep the pencil off the paper until you wish to begin drawing the profile.
Begin with the pointer pressing against the sitter’s chest, and bring it over the face and down the back of the head and neck. Do not press it into the hair, but carry it along what you consider to be the outline; though it must be in actual contact with the features and clothes. It is hardly necessary to mention that the sitter must keep perfectly still if the silhouette is to be at all accurate.
The tracing is cut round with fine-pointed scissors, and the paper blacked and stuck on a piece of white card. Some trouble is saved by using paper white on one aide and black on the other. If duplicates are needed, two or more pieces of paper should be stuck together by the corners and to the paper on which the silhouette is drawn, and all be cut through at one operation.
With a little practice the actual tracing of the outline occupies but a few seconds. Things are expedited if an assistant adjusts the paper and pencil.
XXXVII.
A SIGNALLING LAMP.
Visual signalling is effected at night in the Morse code by means of a lamp fitted with an easily-moved shutter, which passes or cuts off the light at the will of the operator. Readers who know the Morse code might well go to the trouble of constructing in duplicate the simple apparatus to be described, as the possession of an outfit will enable them to extend their signalling capabilities.
The stand for the lamp is admirably supplied by the ordinary camera tripod.
For the illuminant we may select any good acetylene cycle lamp.
For this a holder is made of 1/2-inch wood, according to the sketch shown in Fig. 189. The width of all the four parts should be about 2 inches greater than the front glass of the lamp. B and C should be sufficiently far apart to allow the lamp to rest on the rim above the carbide chamber; and the front, A, should be at least an inch higher than the top of the lamp glass.
[Illustration: FIG. 189.—Signalling lamp with quick-moving shutter.]
The hole cut in B must be so situated as to bring the front of the lamp close to the front of the holder, so that the greatest possible amount of light may be utilized. The hole in A should be rather larger than the lamp front, and, of course, be accurately centred. Mark these two holes off carefully, and cut out with a pad saw or fret saw.
A socket must be attached to the centre of the underside of the base to take the camera screw; or, if such a socket is not easily obtainable, a hole should be drilled in the base to take an ordinary wood screw of good size, the surplus of which is cut off so as not to interfere with the lamp.
The Shutter.—The woodwork is so simple that nothing further need be said about it. The more difficult part of the business is the making of the shutter, which must be so constructed that it can be opened and closed rapidly by motions similar to those used in working the telegraph key described in a preceding chapter. Speed of working is obtained by dividing the shutter into two or three parts, each revolving on its own spindle, but all connected so as to act in perfect unison. The thinnest sheet brass or iron obtainable should be used, so that the tension of the spring used to close the shutter need not be great. Our illustration shows a two-part shutter, each half an inch wider than the hole in the front, and jointly a similar amount deeper. The upper half overlaps the lower, outside, by a quarter of an inch.
The spindles are two straight pieces of brass wire, revolving in sockets which are most easily made of notched pieces of wood (as shown in Fig. 189), with removable caps of strip tin. The lower spindle should be an inch longer than the width of the front, to allow for a cranked end, to which the closing spring will be attached.
Having cut out the halves of the shutter, solder the spindle wires to one edge of each on what will be the back side. The wires must be so arranged as to allow a quarter of an inch to project beyond the left edge of the front, as the opening mechanism is situated on this side as the most convenient for the operator.
Take a couple of metal discs, an inch or so in diameter, and bore a hole in each near the circumference to fit the ends of the pivots fairly tight. Three-eighths of an inch from this—centre to centre—bore and tap a hole for a small screw. The tapping should be done with a taper tap and carried just so far that the screw turns stiffly without danger of being broken off by the screw-driver.
Next find the correct positions of the parts of the shutter and the spindle sockets on the front of the holder, and mark them off carefully. Screw the wooden parts of the sockets to the front. Four little “distance pieces” should now be cut out of small tubing, or made by twisting tin round the spindle, to place on the spindles between shutter and sockets, so that the shutters cannot shift sideways.
The right-hand end of the lower spindle must be bent over (after slipping on the distance piece) to form a 1/2-inch crank making an angle of 45 degrees with the line of the front, in an upward direction, as it will be depressed by the opening of the shutter. Flatten out the end with a hammer, and drill a small hole near the tip.
The shutters can now be placed in position, and the caps of the sockets be screwed on. The next thing to make is the connecting rod to join the cranks at the left side of the front. For this purpose we may use a piece of fairly stiff strip metal—brass by preference—5 or 6 inches long. Half an inch from one end make a mark with the centre punch; then measure off exactly the distance between the shutter spindles, and make a second punch mark. Drill holes at the marks large enough, for the disc screws to pass through easily, but not loosely.
Attach the rod to the discs by the screws, and slip the discs on to the ends of the shutter spindles. (The free end of the rod should be upwards.) Press the shutters against the front so that they cannot open, adjust the discs at an angle of 45 degrees to the front in an upward direction, and solder them firmly to the spindles.
The upper end of the connecting rod should be turned over to form a finger rest, or be sharpened off to take a knob. The last operation is the fitting of the spring to close the shutter. A spiral spring attached at one end of the crank on the lower spindle and at the other to a nail projecting from the side of the front is the most convenient arrangement. If you have not got a spiral spring, you can easily make a. fairly efficient substitute out of hard brass wire wound a few times round a large wire nail.
An alternative method of springing is to add an arm, a, to the connecting rod, as shown by dotted lines in Fig. 189, and to use the projection for engaging a spring, made by winding hard brass wire a few times round a nail. A screw passed through the coil holds it to the front.
The tension of the spring must be just sufficient to close the shutter smartly and prevent it rebounding far enough to pass any light.
XXXIX.
A MINIATURE GASWORKS.
The most primitive method of making coal gas on a small scale is to fill a tin—which must have folded, not soldered, joints—with small coal, punch a hole in the bottom, and place it lid downwards in the fire. Gas soon begins to issue, but, owing to the quantity of moisture and impurities present, it will not ignite until some minutes have elapsed. The flame, when it does make its appearance, is very smoky and gives little light, because, in addition to the coal gas of commerce, there are present ammonia gas, sulphuretted hydrogen, carbonic acid, tar vapour, etc., which prevent brightness of flame.
[Illustration: FIG. 190.—General view of gas-making apparatus.]
A miniature gasworks, if it is to be worthy of its name, must obviously endeavour to separate the troublesome components from the useful gas. The doing of this involves several processes, all simple enough in principle, and requiring but simple apparatus for demonstration on a small scale. To take them in order the processes are—
(l) The formation of gas in a retort;
(2) The condensation of the tar;
(3) The condensation of steam;
(4) The removal of the ammonia gas;
(5) The removal of the sulphuretted hydrogen and carbonic acid.
The last two processes are, in a real gasworks, usually separated, but for simplicity’s sake we will combine them. Finally, the storage of the gas has to be provided for.
The Retort.—To get very good results, the retort should be of cast iron, and have a removable air-tight cover; but, to keep down expense, we will use an ordinary 2-pound self-opening coffee tin. A short piece of brass pipe is soldered into the lid near one edge to carry off the gas as it is generated. To get a fairly gas-tight joint, red-leaded asbestos string should be rammed tightly between the lid and the tin. The tin may be laid on an open fire on the slant, the lid end uppermost, and the pipe at the top, where the gas will collect; or, if you wish to make things more realistic, you may easily construct an oven with sides and back of fire-brick, and front of sheet iron, through the hole in which the tin is pushed horizontally, so that only half an inch projects. This is a. suitable arrangement for out of doors.
[Illustration: FIG. 191.—Vertical section of condenser.]
The Hydraulic Main.—This is represented in Fig. 190 by a double-necked bottle, B, standing in a bowl of cold water. The pipe from the retort passes through the cork in one neck and dips half an inch below the surface of the water inside. The gas, on meeting the water, is cooled, and some of the steam in it is condensed, also most of the tar present, which floats on the top of the water. From the bottle the gas passes on to the Condensers, where the process of cooling is completed gradually. The condenser (Fig. 191) is so designed as to cause the gas to pass through several pipes in succession. The base consists of a tin box, 6 inches long, 4 wide, and 1-3/4 deep. This is divided longitudinally down the centre by a 1-1/2-inch partition, soldered to the bottom and sides; and the two divisions are again subdivided, as shown in Fig. 192, by shorter cross partitions.
[Illustration: FIG. 192.—Plan of condenser.]
For the condensing pipes, “compo” tubing of 1/2-inch outside diameter is convenient. The amount required will, of course, depend on the number of pipes used and the length of the individual pipes. The design shows 6 pipes, each 3 feet long, bent to a semicircular curve (Fig. 191) at the middle to form very long, narrow horse-shoes. The pipes are supported at the curve by the crossbar, S (Fig. 191), of a frame, and their ends enter short pieces of brass tubing soldered into holes in the bottom of the tin box. Rubber bands make the joints air-tight.
[Illustration: FIG. 193.—Vertical section of purifier.]
The base is stood bottom upwards in a larger tin containing an inch and a half of water. The water acts as a seal, preventing the passage of the gas from one compartment to another through the pipes which it traverses, in the order indicated by the arrows and numbers in Fig. 192, to reach the outlet. On its way the gas is deprived of any water and of any traces of tar. The condensed water and tar fall from the open ends of the pipes into the base.
The Purifier is made of a large tin with overlapping lid. Near the bottom is soldered on an inlet pipe; just below the lid an outlet pipe. Cut out two discs of perforated zinc or sheet tin to fit inside the tin easily, but not loosely. (If tin is used, make a number of small holes in it.) The lower of the discs (Fig. 193, Bl) has three wire legs, AA, soldered to it, to support the upper disc, B. Three short supports keep it clear of the bottom.
The tin must be charged with a mixture of two parts green sulphate of iron and one part lime. The lime should be slaked a short time before use. The sulphate, lime, and sufficient water to moisten the whole are ground into a pulp and left to dry. The dry mixture, which has a reddish-yellow colour, is broken up fine. Put tray B1 into place and spread half the chemical over it; then lay B on the top and cover it with the remainder. The lid joint is sealed by a broad rubber band.
While passing through the tin, the ammonia, sulphuretted hydrogen and carbonic acid gases all combine with the chemical, and fairly pure gas issues from the outlet.
The Gasholder.—As the gasometer is an important feature of a gasworks, our small plant should contain its counterpart, as it serves to regulate the pressure of the gas, and, therefore, the steadiness of the flame, as well as affording storage room.
As a gasometer, one may use a container made on the principle of the lung-testing apparatus described on p. 361; or the gasholder of a lantern acetylene apparatus, which must, of course, be suitably counterweighted.
Working the Plant.—When starting up the plant, leave the burner open until inflammable gas issues, so that the air present in the various chambers may be displaced.
[Transcribers note: Premature lighting of the burner may cause the flame to propagate into the system and explode. I speak from experience.]